Hemp Growing

The observed marijuana-oropharyngeal cancer associationwas then divided by the bias factor to estimate an adjusted OR which accounted for confounding by HPV. The studies included in this analysis primarily collected information on marijuana use using interviewer or self-administered questionnaires. Therefore, differential misclassification of the reporting of marijuana use between cancer cases and controls is a possibility. To estimate the potential effect of reporting bias, simple probabilistic sensitivity analyses were conducted based on methods previously described . Sensitivity and specificity estimates used in this analysis were deriv.The rising incidence of oropharyngeal and oral tongue cancers over the last twenty years has paralleled trends of increasing use of marijuana among individuals born after 1950 . Therefore, we initially hypothesized that marijuana use could, in part, have contributed to the rising incidence of these cancers. Using pooled data from 9 case-control studies that contributed to the INHANCE consortium, we found evidence of a possible positive association of marijuana use with oropharyngeal cancer and a negative association with oral tongue cancer.. Our findings of a positive association of marijuana use and oropharyngeal cancer while in agreement with two prior studies contrasts with findings from five studies that showed no association . The possibility of a true association of marijuana use with oropharyngeal cancer risk was supported in the present study by the consistency of the observed associations with multiple measures of marijuana use including ever use, duration and frequency of use and was unaffected across strata of smoking and drinking. However,microgreens shelving the inconsistent association across studies in this pooled analysis combined with an attenuation in the association after adjustment for smoking and drinking make the effect of residual and unmeasured confounding highly plausible.

Differential exposure to HPV infection among marijuana smokers as compared to nonsmokers could be one source of potential confounding to explain the association of marijuana use with oropharyngeal cancer, as marijuana users engage more frequently in risky sexual behaviors leading to higher rates of sexually transmitted infections . We had serologic information on HPV 16 from four studies. Unfortunately, the association of marijuana use and oropharyngeal cancer among these four studies was not representative of all the studies included in the pooled analysis, although stratified analyses among these four studies by HPV 16 L1 serostatus revealed a modest positive association of ever and long duration marijuana use oropharyngeal cancer among seropositive individuals. Therefore, we attempted to estimate the potential confounding effect of HPV on this association using plausible estimates of the association of HPV infection on oropharyngeal cancer risk as well as differences in oral HPV prevalence by marijuana usage. This approach revealed a substantial and nearly complete attenuation of the association of marijuana use with oropharyngeal cancer risk. Lastly, the association of marijuana use appeared to be specific for those oropharyngeal cancers most likely to be HPV-associated: non-smoker/nondrinkers, and those with tonsil or base of tongue sites. These data suggest that the positive association of marijuana use and oropharyngeal cancer may be dependent on exposure to HPV. In lieu of more definitive information on tumor HPV infection status among cases and oral HPV infection status among cases and controls, the role of marijuana use as a potential risk factor in oropharyngeal cancer cannot be determined. We observed that marijuana use was strongly inversely associated with oral tongue cancer specifically, which is similar to what has been reported previously among oral cavity cancers in general . This association remained robust across all marijuana use metrics, was strengthened after adjustment for tobacco and alcohol use, and was consistent across the five studies that had sufficient numbers of cases. Given that a very small fraction of oral cavity cancers are attributed to HPV , it is not surprising that marijuana use remained strongly inversely associated with oral tongue cancer even after adjustment for HPV . Lastly, the inverse association appeared to be strongest amongst individuals <50 years of age, which are the same individuals that have the greatest observed per year increases in oral tongue cancer incidence . Therefore, this association may reflect a true inverse association of marijuana use on oral tongue cancer.

The major bio-active cannabinoid compound found in marijuana smoke, Δ – tetrahydrocannabinol -THC, has been shown to have both pro- and anti-carcinogenic capabilities. This cannabinoid functions primarily through engagement of specific cell surface receptors CB1, expressed on a range of cell types and CB2 present primarily on a variety of immune cells, particularly those found in the human tonsil . Engagement of these receptors on immune cells has been shown to suppress pro-inflammatory cytokine production and enhance anti-inflammatory cytokine production leading to reduced host immune responses to infectious agents as well as suppression of anti-tumor immunity . Conversely, Δ -THC has also been shown in epithelial cell lines to have distinct antitumor effects through arrest of uncontrolled cell growth, enhancement of apoptosis, and down regulation of angiogenesis and cellular migration . As a result, this cannabinoid has been investigated as a potential therapeutic agent in the treatment of glioma, breast and prostate cancers . Interestingly, the anti-tumor effect of this cannabinoid is mediated through the same CB1 and CB2 receptors. The effects of tetrahydrocannabinol -THC and other cannabinoids on modulating tumorigenesis may be cell and tissue specific based on receptor expression profiles. This may help explain the differing associations of marijuana smoke with oropharyngeal and oral tongue cancers. Lastly, the presence of other carcinogenic compounds present in marijuana smoke may also play a role in driving the association. Differences in the measurement of marijuana use, study sample recruitment, and measurement of demographic and other risk factors for Head and Neck Squamous Cell Carcinoma across the studies included in this analysis may have contributed to the heterogeneity observed across study sites. However, this heterogeneity was observed only for oropharyngeal cancer and not oral tongue cancer. Nevertheless, we included in our logistic regression models a random-effects term for each study to account for the heterogeneity of the association of marijuana use with oropharyngeal cancer outcomes. Furthermore, we acknowledge the possibility that misclassification in the measurement of marijuana use between cases and controls may explain some of these findings. Misclassification of marijuana exposure due to the use of self-administered or interviewer administered questionnaires has been suggested previously to be significant source of error in the observed association with head and neck cancers .

Sensitivity analyses that modeled the effects of differential and non-differential misclassification of marijuana exposure demonstrated that correction for misclassification did alter the strength of the association with each cancer outcome . Therefore,greenhouse tables it cannot be ruled out that either differential or non-differential misreporting of marijuana exposure may explain the observed associations of marijuana use with oropharynx and oral tongue cancers. This pooled analysis of nine case-control studies conducted in the US and Latin America is the largest to date to investigate the relationship of marijuana use specifically with cancers of the oropharynx and oral tongue. The differing associations of marijuana use on oropharyngeal and oral tongue cancers observed in this study provides some epidemiologic support for the biological effect of cannabinoids as both a pro- and anti-carcinogenic agent. However, given the strong association of HPV on orpoharyngeal cancer not measured in this study, the modest attenuated effect of marijuana on these caners may well be explained by confounding by HPV. Additional studies focusing on cannabinoid receptor expression profiles and downstream effector functions across cell types involved in tumorigenesis of these cancers may yield important etiologic information as to the role of marijuana on head and neck cancer risk. Depressive disorders have been associated with morphological brain abnormalities, although the majority of studies have been conducted in adults. Reduced hippo campal volumes have been found among depressed adults , although this may be associated with age of onset and one found no hippo campal differences . White matter abnormalities have also been associated with increased depressive symptoms and suicidality in adult populations . Due to adolescent neuromaturation, which includes pruning of gray matter and proliferation of white matter, these adult results cannot be generalized to depressed adolescents . Three studies including depressed children and adolescents found no significant differences in hippocampal volumes , although one did report larger amygdala-hippocampus ratios and another reported reduced amygdale volumes .Further, one study found that depressed adolescents had smaller overall and frontal white matter volumes compared to healthy controls . To make matters more complicated, marijuana use is highly prevalent among adolescents; nearly half of high school seniors have tried it during their lifetime . Further, marijuana use appears moderately associated with an increased risk of depressive symptoms in both adults and adolescents . While some longitudinal studies found no or weak links between marijuana use and depression , recent studies have shown that heavy marijuana use during adolescence is associated with later risk for depressive symptoms . There are several possible explanations for the link between major depressive disorders and chronic marijuana use. The endogenous cannabinoid system is widely distributed throughout the central nervous system, including the prefrontal and hippocampal regions , as well as white matter areas . Although animal studies have suggested cellular effects, especially in hippocampal regions , and despite developmental changes to the endogenous cannabinoid system during adolescence , no studies to date have examined structural brain changes associated with marijuana use among human adolescents. Adult animal models suggest that damage to the cannabinoid system, specifically to the CB1 receptors, results in depressive-like symptoms in mice .

Adult human studies utilizing magnetic resonance imaging have yielded conflicting results, with two studies finding gray and white matter abnormalities among young adult marijuana polydrug users and one study found no differences . Wilson and colleagues , found that adult participants who had used marijuana before age 17 had smaller gray matter and larger white matter volumes compared to later-onset users. In sum, because marijuana may disrupt adolescent neurodevelopment , including the developing endogenous cannibinoid system , previous findings among depressed adolescents without comorbid substance use cannot necessarily be generalized to the rather sizeable population of marijuana users . Therefore, the goals of the present study were to examine: 1) the relationship between white matter and hippocampal volumes and depressive symptoms and 2) whether marijuana use moderates the relationship between brain structure and depressive symptoms in a sample of thirty-two adolescents. Adolescents were recruited from high schools, universities, and through ads. All youth were between 16 to 18 years old, fluent in English, and had a parent/guardian available to consent and provide history. Other comprehensive exclusionary criteria included: psychotropic medication use; history of DSM-IV Axis I disorder ; LOC >2 minutes; serious medical illness; learning disability/mental retardation; significant maternal drinking or drug use during pregnancy; complicated birth ; parental history of bipolar I or psychotic disorders; left handedness; vision or hearing problem; and MRI contraindications. Finally, any youth with data suggestive of substance use in the 28 days prior to the session were excluded from analyses. All participants and, if under age 18, their parent/guardian, underwent written informed consent and, for minors, assent in accordance with the UCSD IRB. Of those eligible, data were collected from sixteen marijuana using and sixteen drug-free adolescents . MJ-users took marijuana at least 60 times in their lifetime, did not meet criteria for Heavy Drinker status , and did not use substances other than marijuana, alcohol, or nicotine > 25 times in their lifetime. Controls never met criteria for Heavy Drinker, had < 5 experiences with marijuana, and never used any other drug besides nicotine. Trained laboratory assistants administered the youth screening interviews to assess the aforementioned inclusion and exclusion criteria. Parents or guardians of youth were then contacted. Parents and youth were informed that they would not receive information regarding each other’s responses or test results. If still eligible, potential youth and parent/guardians were administered a detailed interview assessing demographic and psychosocial functioning, Axis I psychiatric disorders, and drug use history. To improve open disclosure, different lab assistants interviewed the parent and youth. If eligible, they were scheduled to begin the monitored abstinence protocol.

Given the importance of this issue for drug policy, research on the mechanisms through which medical marijuana laws promote the initiation of marijuana use by young adults should be prioritized. This study was subject to several limitations. We were unable to rule out the possibility that, over longer windows of time, state medical marijuana laws will exert impacts on marijuana consumption and initiation by younger people dwelling in these states. We tested models using variables representing the length of time that each state’s medical marijuana law had been in place but found no statistically significant effects. We also could not examine whether legalization of marijuana for medical purposes has different effects as compared with recreational legalization; the NSDUH data did not extend into the years after recreational policies were established. The NSDUH data collection takes place at various points through the calendar year, and the date of any given participant interview may or may not have matched up with enactment of new medical marijuana legislation in their state; however local variation in availability of marijuana would make even a stricter date-based classification subject to the same potential mismatch on the individual level. Under reporting of drug consumption and initiation is also likely because of social acceptability concerns and survey respondents’ fears of disclosure . The NSDUH used computer-assisted interviewing to increase the validity of self-reports consistently throughout the 10-year observation period. As young people’s views about marijuana grow more permissive over time , survey respondents could become more willing to report that they have tried marijuana thus introducing bias into this analysis. Our multivariate models controlled for time trends to address this problem. Finally, our analyses could not capture sub-state variation in the implementation of medical marijuana laws .Adolescence requires some risk-taking as independence from the family is taking form, but for some teens,rolling grow table risk taking may lead to unhealthy or unsafe decisions. Risky behaviors such as unprotected sex, reckless driving, and substance use are associated with lasting negative outcomes .

With regard to substance use, the annual Monitoring the Future study reported that marijuana is the most commonly used illicit drug in the United States, with 7% of 12th graders reporting daily use . Individuals who engage in regular substance use may have a higher propensity to take unsafe risks despite the possible negative consequences . Without testing adolescents prior to initiation of substance use, it is difficult to determine whether elevated levels of risk-taking predated substance use. However, risk-taking performances of adolescents with and without histories of regular marijuana use can help us to understand what leads some individuals to substance-related problems. The Balloon Analogue Risk Task offers a behavioral assessment of risk-taking. In adult samples, riskier BART performance has been associated with higher levels of alcohol use as well as substance use, gambling, unsafe sex, and stealing , and it has successfully differentiated MDMA 3,4-methylenedioxymethamphetamine; “ecstasy”) users from controls . Riskier BART performance was also associated with greater alcohol, cigarette, and poly drug use in a community sample of young adults . Among adolescents, riskier BART performance was related to greater self-reported substance use and safety risk behaviors . Adolescent patients with conduct disorder and co-morbid substance abuse/dependence have also shown greater risk-taking with the BART compared to healthy controls . Some studies have examined marijuana users specifically. For example, adolescent marijuana users demonstrated impulsive decision-making with the Information Sampling Test ; however, users had a median of less than 24 h of abstinence. Using the BART, Schuster et al. found that riskier BART performance was correlated with higher levels of risky sexual behavior among young adult marijuana users; however, participants may have used marijuana the day prior to testing and were not compared to non-users. Gonzalez et al. found no differences on the BART in a sample of young adult marijuana users versus non-using controls; however, Gonzales et al. allowed for recent marijuana use , with a median of three days since past use. Because previous studies of young marijuana users allowed for recent use, the effects of residual marijuana levels may have affected task performance. In the current study, we examined risk-taking via the BART in late adolescent marijuana users with at least two weeks of abstinence from marijuana, in comparison to non-using controls.

This approach considers how marijuana users function relative to their non-using peers and reduces possible residual effects from recent substance use. We hypothesized that participants reporting greater substance use would demonstrate riskier BART performance. Further, previous studies have not yet examined the relationship of risk-taking to executive functioning in adolescent marijuana users. Executive function is a complex collection of abilities primarily modulated by the prefrontal cortex. Several studies have found altered prefrontal cortex processing and executive dysfunction in marijuana users . Completing the BART has also been linked to increased prefrontal cortex activation in healthy controls , and a recent meta-analysis of neuroimaging studies suggested that individuals with substance use disorders may have altered risk processing compared to healthy controls, primarily in ventromedial prefrontal cortex, orbitofrontal cortex, striatum, and other areas involved in risk and decision-making . Given the involvement of the prefrontal cortex in both risk-taking and executive functioning, we examined whether elevated risk-taking, as measured by the BART, was associated with poorer executive functioning, as measured by traditional neuropsychological tests. We hypothesized that a riskier approach to the BART would be associated with poorer performance on executive function tests.Participants were part of a longitudinal study of marijuana’s effects on neurocognition during adolescence and young adulthood, with assessments at intake and at 18- and 36-month follow-ups . Adolescents were recruited from local high schools. Teens and their parents/guardians were screened for demographics, psychosocial functioning, and family history of Diagnostic and Statistical Manual for Mental Disorders, 4th Ed. , 2000) substance use and other Axis I disorders. Confidentiality was ensured within legal limits to encourage full disclosure. Prior to participation, written informed assent and consent were obtained in accordance with the University of California, San Diego Human Research Protections Program. At study intake, exclusionary criteria included history of psychiatric disorder other than substance use disorder, serious medical problem or head trauma, premature birth, prenatal drug or alcohol exposure, and substance use during monitored abstinence.

Intake classification criteria for the marijuana-user group included >60 lifetime marijuana experiences; past month marijuana use; <100 lifetime uses of drugs other than marijuana, alcohol, or nicotine; and not meeting Cahalan criteria for heavy drinking status . To produce an adequate sample size, controls were included if they had <5 lifetime experiences with marijuana , no previous use of any other drug except nicotine or alcohol, and did not meet criteria for heavy drinking status. The current data were collected at the 18-month follow-up, when participants were aged 17–20 years. A total of 48 marijuana users and 52 controls completed the BART task at the 18-month follow-up; however, 24 marijuana users and 18 controls were excluded from analyses based on the following abstinence requirements: at least two weeks since last use of marijuana, other drugs, or alcohol binge ; and at least three days since last use of any alcohol or psychiatric medications . Beyond the abstinence requirements, follow-up controls were further excluded for meeting abuse or dependence criteria for alcohol or any other substance . One participant in the baseline marijuana group had no marijuana uses in the previous 18 months and was also excluded, and one additional control was excluded due to meeting DSM-IV criteria for current post-traumatic stress disorder. Following these exclusions, the resulting sample of 58 demographically matched adolescents and young adults included 24 marijuana users and 34 non-using controls. At the 18-month follow-up, marijuana users were about seven months older , and as expected, reported higher levels of marijuana, alcohol,indoor plant table and other drug use than controls. marijuana users had 200+ lifetime marijuana use episodes and <130 lifetime experiences with other drugs. In addition, 10 marijuana users met DSM-IV criteria for marijuana abuse and seven for marijuana dependence , 10 met criteria for alcohol abuse, and two met criteria for other drug abuse. At the 18-month follow-up, the 34 controls had ≤15 lifetime experiences with marijuana, minimal to no previous other drug use except nicotine or alcohol .A structured clinical interview measured psychosocial functioning, health history, and family history of psychiatric and substance use disorders . Probable DSM-IV Axis I disorders were determined by the computerized Diagnostic Interview Schedule for Children Predictive Scales . Adult participants living independently completed corresponding modules of the computerized Diagnostic Interview Schedule .Parent interview. A parent/guardian was interviewed on child development and behavior, and youth/family medical and psychiatric history . Parents/guardians corroborated youth diagnostic reports with the parent version of the Diagnostic Interview Schedule for Children Predictive Scales. If participant self-report and parent collateral data were discrepant, additional information was reviewed from the file, and data were coded to reflect the presence of the symptom, to reduce participant and researcher bias. Substance use. Participants were administered the Customary Drinking and Drug Use Record to evaluate their lifetime, past three-month, and past 18-month use of nicotine, alcohol, marijuana, stimulants , hallucinogens, inhalants, opiates , dissociatives , sedatives , and abuse of over-the-counter or prescription medications.

Teens were also assessed for alcohol and drug withdrawal symptoms, related life problems, and DSM-IV abuse and dependence criteria . The Timeline Follow back facilitated recall of substance use over the past 28 days through a calendar layout. BART. The BART is a computer-based risk-taking assessment . Participants used the space bar to pump 30 simulated balloons one at a time to achieve the highest possible score. Balloons pop at an unpredictable rate , and a noise follows each response . The points earned for a balloon are lost if it pops, but temporary points can be saved by choosing “Save Points.” Participants weigh the increasing risk of popping each balloon against the potential gain of continuing to pump the balloon . The primary outcome measures were the mean number of pumps for balloons that did not pop and the total number of popped balloons during the session. High values on either variable suggest greater risk taking. The number of points earned on any balloon and the total points saved are not revealed to the participant – only whether they had earned a small, medium, big, or bonus prize depending on the amount of points saved. They were shown the possible candy rewards prior to starting the task and received the reward immediately upon completion of the task. Participants had no practice trials to assess risk, and each participant completed the same task . This measure has good test-retest reliability . Mood and personality. Mood and personality were measured to help characterize the sample and examine whether elevations in depressive, anxiety, or internalizing/externalizing symptoms were related to BART performance. Mood and anxiety were assessed using the Beck Depression Inventory and the Spielberger State-Trait Anxiety Inventory . We used the Child Behavior Checklist Youth Self-Report and Adult Self-Report to measure internalizing and externalizing behaviors. Neuropsychological testing. General intellectual ability was assessed by the Vocabulary and Block Design subtests of the Wechsler Abbreviated Scale of Intelligence . Measures of executive function included the Digit Span task from the Wechsler Adult Intelligence Scale-Third Edition ; and the Trail Making, Towers, and Verbal Fluency tests from the DelisKaplan Executive Functioning System .Participants were abstinent from marijuana, other drugs, and alcohol binge for at least two weeks prior to the assessment, verified with biweekly breathalyzer tests and urine screens including at the neuropsychological testing session. The urine screen tested for major substances including amphetamines, barbiturates, benzodiazepines, cocaine metabolites, marijuana metabolites, and opiates.All participants completed questionnaires and the neuropsychological battery. Teens and their parents/guardians received monetary compensation upon study completion.We used Fisher’s Exact Tests to compare categorical variables between groups and analysis of variance to examine group differences on continuous variables. Some alcohol and drug use variables did not meet requirements for parametric analysis; therefore we used the Mann-Whitney procedure to compare these characteristics between groups. Because marijuana users were slightly older than controls, age was controlled in analyses of test performance using univariate analysis of covariance .

To a first approximation, the rate at which soiling occurs via partitioning is independent of surface orientation. Vertical surfaces soil at rates similar to horizontal surfaces. The surface accumulation resulting from partitioning is commonly referred to as a “film.” We estimate that a pollutant film of 5 to 10 monolayers is thick enough to alter the interface with which airborne organic compounds interact. For a film composed of primarily indoor SVOCs, this is equivalent to a thickness on the order of 10 nm or less. Rates at which films accumulate on initially clean impermeable indoor surfaces have been measured in different indoor environments and are summarized in Table 2 of Weschler and Nazaroff. Film growth rates in the range 0.1-0.2 nm/d have been reported. At such rates, films with thicknesses of 5-10 nm would accumulate on indoor surfaces in 1-3 months. In a composite sample of five homes in urban Toronto, a film thickness of 5 nm was measured 3-5 months after window cleaning.Toward the higher end of organic soiling conditions, Wu et al. exposed aluminum, polished glass and ground glass disks for 2-3 weeks in a kitchen where cooking occurred daily. Prior to exposure, the clean surfaces exhibited significantly different sorptive partitioning of DEHP. The 2-3 weeks of exposure was sufficient for the disks to acquire an organic film that resulted in similar sorptive partitioning of DEHP across diverse substrate materials. Taken together, these measurements suggest that within a period of a few months, impermeable indoor surfaces are covered by a film, acquired via partitioning, that is thick enough to alter the chemical surface that it presents to indoor air. We note that the deposition velocities for lower molecular weight organic acids are comparable to those for SVOCs. However, the indoor gas-phase concentrations of species such as formic and acetic acid are orders of magnitude larger than those of indoor SVOCs. Hence,vertical rack the flux of lower molecular weight organic acids to an aqueous surface is potentially orders of magnitude larger than the flux of SVOCs to an incipient surface film.

While the rate at which SVOC partitioning contributes to surface soiling is independent of the surface’s orientation, the rate at which particles deposit on a surface varies substantially with orientation. Because particles settle under gravity’s influence, upward facing horizontal surfaces soil much faster than vertical or downward-facing surfaces. Based simply on geometry, upward horizontal surfaces account for roughly 20% of exposed indoor surfaces. Table 3 in Weschler and Nazaroff presents estimated rates for particle accumulation on vertical and upward-facing horizontal surfaces. The rate at which vertical surfaces soil via particle deposition is predicted to be much slower than the rate at which they soil via partitioning. Even in the case of upward-facing horizontal surfaces, soiling by fine particle deposition is relatively slow. Since water soluble salts and associated water comprise larger mass fractions of fine particles than of coarse particles, this is an important consideration.In summary, on impermeable indoor surfaces, semivolatile organic compounds accumulate much faster than particle-associated water-soluble salts. Only in the instance of an upward facing horizontal surfaces does particle deposition become important, and, in this case, gravitational settling of coarse particles dominates the deposition process. Upward-facing horizontal surfaces can accumulate particles to a level of 1 µg/cm2 on a time scale as short as a few days, whereas surfaces of all orientation can have a 1 µg/cm2 accumulation of SVOCs in a few months. As expected from theoretical considerations, the specific SVOCs that comprise indoor organic films are similar to those found in indoor airborne particles. In a recent intensive field study conducted in a test house, the HOMEChem project, such similarity was observed experimentally: “the signal intensities of the mass spectra for the indoor aerosol filter and surface extracts have high overlap, with a dot product of 0.98.” While we know something about the formation and composition of films on impermeable indoor surfaces, we have little information about the soiling of semipermeable or porous surfaces such as paint films, vinyl flooring, brick, concrete, carpets and upholstery. Among other factors, morphology, as well as orientation, are expected to influence the soiling of such materials.

The chemicals that comprise surface films evolve. They might initially be dominated by SVOCs; however, over time, they acquire particles and the water-soluble salts associated with these particles. The initial SVOCs in the film oxidize, which should tend to increase the oxygen to carbon ratio. This process may make the surface film more hygroscopic. The acquisition of inorganic salts and increases in the O/C ratio should lead to increased water content of surface films, especially during periods with higher indoor humidity, and the viscosity of the film may decrease as a consequence. Such changes could influence heterogeneous acid/base reactions, making them more likely in aged films under high RH conditions. Oxidation of surface films may also lead to phase separations that might further influence acid/base reactions. Evidence from nicotine The pH of skin’s surface typically is in the range 4.5-6.The pKa of monoprotonated nicotine is 8.0.Hence, at skin’s pH, one would anticipate that most would be ionized . Based on measurements from excised pig skin, ionized nicotine passes through skin about fifty times slower than neutral nicotine. If there is a homogeneous film on the surface of skin that is a mix of water, salt and skin lipids with pH of 4.5-6, then the capacity of this film for acquiring a combination of ionized nicotine and neutral nicotine would be very large. Since only the much less abundant neutral fraction is rapidly absorbed by the skin, transport from air through skin to blood should be relatively slow. However, actual measurements of the dermal uptake of nicotine from the gas phase indicate a fast transport rate.A possible explanation is that skin surface lipids and aqueous salt solutions coexist on the skin isolated from one another rather than being homogeneously mixed.As a crude analogy, they may exist more in the fashion of oil and vinegar rather than as mayonnaise. According to this conceptualization, nicotine that partitions from the gas-phase into islands of skin lipids would remain neutral, subsequently passing through the stratum corneum and viable epidermis to the dermal capillaries. Something similar may occur on impervious indoor surfaces; there may exist regions with aqueous surface films isolated from regions with organic rich films. Within porous surfaces, there may exist pockets of aqueous solutions and pockets of hydrophobic organics. If such is the case, then organic acids and bases could partition to both aqueous and organic substrates, and the relative amounts in each phase could influence the resultant surface chemistry.

Different methods have been used to characterize surface acidity.The more common methods have been reviewed by Sun and Berg. These include colloid titration, indicator dye adsorption, X-ray photo electron spectroscopy, and calorimetry. Most metal surfaces acquire a charge and, consequently,microgreen flood table an electrical double layer at an aqueous interface. The isoelectric point is defined as the pH value at which the potential of the double layer at the interface is zero. The isoelectric point is frequently used to characterize the acidity of solid surfaces. The IEP is measured by electrokinetic titration, which is a type of colloid titration. Another approach that has been used to evaluate the acidity and basicity of metal oxides is microcalorimetry. Using NH3 and CO2 as probe molecules, Auroux and Gervasini determined the number and character of basic and acidic sites on twenty metal oxides. Some metal oxides are basic , some are acidic , and some are amphoteric , reacting with both acidic and basic gases. Recently, Rindelaub et al. have made direct measurements of pH in individual particles using a Raman micro-spectrometer coupled with a confocal optical microscope. Wei et al. have applied a related method using 2D and 3D confocal Raman microscopy to determine the pH of suspended aerosol droplets smaller than 50 µm diameter. Such methods might be adapted to probe surface acidity. The acid-base properties of glass have received considerable attention. 500 Silicon dioxide, forming the chemical framework of glass, is acidic in a Lewis-acid sense . Glass is relatively inert to acids, but is attacked by bases, especially when an aqueous layer in contact with glass has pH > 9. The acid base properties of a polymer can often be described as those of its repeating unit. A substantial proportion of the SVOCs found in surface films are organic acids. Some of these can have human origins. Liu et al. measured the major organic constituents in films on impermeable indoor surfaces from five sites in greater Toronto.Monocarboxylic acids with 11-31 carbons accounted for between 76% and 81% by mass of the total organic fraction. Together, monocarboxylic acids, dicarboxylic acids with 6-14 carbon atoms, nine aromatic polycarboxylic acids, and five terpenoid acids accounted for 81- 95% by mass of the total organic fraction, which included n-alkanes, PAHs, PCBs, and pesticides. These study results demonstrate an acidic character for organic surface films. Surfaces that are basic and porous can be large sinks for acidic gases.

Concrete, especially if it is improperly cured, and brick are examples of surfaces with basic properties. In China it is common to whitewash walls in apartments and other buildings. , prior to the introduction of modern paints and sealants. Among some enthusiasts in the US and Europe, whitewashed wood walls, brick walls and furniture are making a comeback . Whitewash is made by mixing hydrated lime with water, producing a white sealant. A whitewashed/limed wall is chemically basic and would have a high capacity for sorptive uptake of gas-phase acids. To what extent is the pH of a surface determined by the surface itself versus gases dissolved in water associated with the surface? In the case of a hydrophobic surface, the amount of sorbed water is small and the nature of the surface itself should determine its acidity. In contrast, the acidity of a hydrophilic surface may be largely influenced by gases that have dissolved in the water associated with the material. Such may be the case for cotton fabrics or untreated nylon carpeting.Some surfaces attract water ; others repel water . Surfaces are somewhat arbitrarily categorized as hydrophilic or hydrophobic based on the contact angle between a water droplet and the surface. If the contact angle is < 90° , the surface is considered hydrophilic . Common hydrophilic surfaces indoors include nylon, glass, stainless steel, gypsum in wallboard, and cotton fabrics. Hydrophobic examples include untarnished silver, chromium, candle wax, and polypropylene. Surfaces that are extremely hydrophobic, such as Teflon or those treated with perfluorocarbon stain repellants, repel water and other highly polar compounds. Ionization of an acidic or basic species is limited on a hydrophobic surface with very little water available, and so, acid-base chemistry would be deterred on such a surface. The degree of hydrophilicity also influences processes such as the disproportionation of NO2 onto indoor surfaces to form HONO and HNO3. An example of the latter process has been reported for a series of experiments in which NO2 was injected into a 2.5-m3 chamber and the airborne concentrations of both NO2 and HONO monitored. The chamber surfaces were either all Teflon or all vinyl wallpaper ; in a subset of experiments, the floor of the Teflon or vinyl chamber was covered with a hydrophilic synthetic carpet. The measured NO2 surface removal rate was more than an order of magnitude larger with carpet on the floor of the chamber than when all the surfaces were Teflon or vinyl . Additionally, the peak gas-phase concentration of HONO, generated from the NO2 injection, was larger with carpet in the chamber than when all the surfaces were Teflonor vinyl . These results were likely due to a combination of increased surface area and the larger moisture content of the carpet compared to either Teflon or vinyl. When the chamber surfaces were vinyl wallpaper and the RH was either 50% or 70% RH, HONO decayed significantly more slowly than the air-exchange rate indicating prolonged release of HONO from the surface. However, when the chamber surfaces were Teflon, HONO decayed significantly slower than the air-exchange rate only at 70% RH; it decayed at a rate similar to the air exchange rate at 50% RH.

Given the presence of amines in outdoor air that ventilates buildings, amines are also common constituents of indoor air, including airborne particles, and in indoor surface films. Indoor sources of amines, in addition to outdoor-to-indoor transport, include smoking; cooking; anticorrosive agents used in humidification or HVAC units; textiles and textile carpet tiles; and the decomposition of casein-containing building materials. Amines, amino acids, and urea are also known constituents of human skin.These compounds are used as active agents in personal care products, including skin moisturizers. Schmeltz and Hoffmann reviewed amines and amino acids identified in tobacco smoke.Their tabulations included 36 aliphatic amines with one to eight carbons, 40 aromatic amines including many aniline related species, and 16 amino acids. The 16 amino acids are noteworthy, given their relatively low volatility. α-Alanine is the most abundant amino acid. Grimmer et al. measured aromatic amines in mainstream and sidestream cigarette smoke.The identified amines included 2-aminobiphenyl, 1-aminonaphthalene, 2- aminonaphthalene, 4-aminobiphenyl, 2-aminofluorene, 1-aminoanthracene, 9- aminophenanthrene, 2-aminoanthracene, 3-aminofluoranthene, 1-aminopyrene. Per cigarette, sidestream smoke contained about ten times the summed mass of amines as in mainstream smoke. Dolara and co-workers, 406 using a sensitive mass spectrometry method, also measured amines from mainstream and sidestream cigarette smoke. The summed mass of aniline, 2- toluidine, 3-toluidine, 4-toluidine, 2-ethylaniline, 3-ethylaniline, 4-ethylaniline, 2,3- dimethylaniline, 2,4-dimethylaniline, 2,5-dimethylaniline, 2,6-dimethylaniline, 1- naphthylamine, 2-naphthylamine, 2-methyl-1-naphthylamine, 2-aminobiphenyl,3- aminobiphenyl and 4-aminobiphenyl in mainstream smoke was 0.2-1.3 µg/cigarette,indoor garden table while in sidestream smoke the summed mass was 20-30 µg/cigarette. They also measured these and other aromatic amines in homes with and without smoking .

Amines are anticipated to be emitted during the cooking of proteinaceous foods, especially meat. However, neither Rogge et al. nor Schauer et al. mention simple amines in their detailed studies of organic emissions from meat cooking. Certain heterocyclic aromatic amines are known carcinogens, and, consequently, several studies address their occurrence in cooked food products, especially meat, fish, and poultry. However, we have found no studies that have examined the emission of heterocyclic aromatic amines into air during cooking. Chiang et al. targeted aromatic amines in cooking oil fumes.They found that fumes from heated sunflower oil, vegetable oil and refined lard contained 2-naphthylamine and 4-aminobiphenyl.Amines are used as corrosion inhibitors in systems designed to humidify indoor air. Given their volatility, they can be present in the air of rooms that are humidified by such systems. They can also partition to indoor surfaces in the humidified rooms. Early indoor measurements were made by NIOSH investigators responding to employee complaints at a Cornell University museum in Ithaca, NY. At this site, diethylaminoethanol , also known as diethylethanolamine, was used as a corrosion inhibitor at the time of the investigation. Among 14 samples collected by Fannick et al., DEAE was detected in two, at concentrations of 40 and 50 µg/m3 . The investigators proposed that some of the complaints resulted from contact with surfaces onto which DEAE had sorbed. Volent and Baer review the Cornell museum case and other cases in which DEAE has been identified in the air of museums with humidification systems.They state that DEAE can react with acidic pollutants in museum environments to form hygroscopic salts that can accelerate metal corrosion. Edgerton et al. used a trace atmospheric gas analyzer to make continuous measurements of DEAE and cyclohexylamine in a typical steam-humidified room at the Battelle facility in Columbus, OH.At 42% RH, the concentration of DEAE and cyclohexylamine were 0.6 ppb and 0.7 ppb , respectively. At 61% RH, the concentrations were 2.4 ppb for DEAEand 0.8 ppb for cyclohexylamine.

During humidification, sorption to room surfaces was found to be a major sink for these amines, with reported rates of transfer to surfaces as follows: at 42% RH, 12 µg/s for DEAE and 8 µg/s for cyclohexylamine; at 61% RH, 14 µg/s for DEAE and 11 µg/s for cyclohexylamine. Given the volume of the room and an estimated surface area , the corresponding average deposition velocity for these amines to room surfaces would be ~ 16 m/h, a value that exceeds the likely mass-transport limit. When the humidification system was off, the amines decayed more slowly than would be the case for removal by air exchange, indicating that the amines were desorbing from room surfaces. Although numerous studies have examined the emission of amines from indoor sources, only a few have measured amines in indoor air. The Dolara group measured aromatic amines in outdoor and indoor air at offices and residences in the greater Florence region of Italy.Aniline and 2-toluidine were above the detection limit in all samples. Aniline ranged from 15 ng/m3 in outdoor air to 190 ng/m3 in a hairdresser’s shop with smokers, while 2-toluidine ranged from 2.5 ng/m3 in outdoor air to 17 ng/m3 in a recreation room with smokers. The concentrations of these species were elevated in the office of a nonsmoker adjacent to offices with smokers . Other amines whose average concentrations exceeded 2 ng/m3 in smoking environments included 3- and 4-toluidine and 2,3- 2,4- and 2,5-dimethylaniline. The Dolara group made more extensive measurements of aromatic amine concentrations in indoor and outdoor air in nine homes and 22 non-domestic buildings in Florence, Italy. Five of the homes were occupied by nonsmokers and four by smokers; the non-domestic sampling included both smoking and nonsmoking environments. Researchers focused on ten aromatic amines that they had measured in their earlier study: aniline, the three toluidine isomers , four dimethylaniline isomers , 2-naphtylamine and 4- aminobiphenyl. Excluding aniline, the summed indoor concentrations of nine of these amines were 5-11 ng/m3 in homes with nonsmokers and 15-34 ng/m3 in homes with smokers.

In the non-domestic buildings, summed indoor concentrations of these nine amines were < 20 ng/m3 in environments without smokers and tended to be higher with smoking. Aniline concentrations were commonly larger than the sum of the other nine amines and did not correlate with the concentrations of these other amines. Several of the non-domestic settings had aniline levels > 400 ng/m3 , including a hospital ward and a hospital waiting room. It was apparent that there were indoor aniline sources other than tobacco smoke. Zhu and Aikawa targeted nicotine and seven monoaromatic amines, including aniline, in measurements made in 69 residences in two regions of Canada. Smoking occurred in seven of these homes. Of the targeted compounds, only nicotine and aniline were routinely measured at levels above their detection limits. N-Methylaniline was detected in one home at 23 ng/m3 and was otherwise below its detection limit of 6 ng/m3 . N,N-Dimethylaniline, 2-ethylaniline, and 2- chloroaniline had detection limits of 9-10 ng/m3, while 4-ethylaniline and 2,4-dichloroaniline had detection limits of 20 ng/m3 . None of these amines were detected in any of the homes. Aniline was detected in 26 of the 69 homes, including five of the seven homes with smoking, at concentrations above the detection limit of 7 ng/m3. The highest aniline concentration in a home without smoking was 35 ng/m3 , while the highest level in a home with smoking was 58 ng/m3 . Among the homes in which aniline was successfully measured, without smoking, the mean concentrations in outdoor and indoor air were equal at 11 ng/m3 . The mean aniline concentration was higher in homes with smoking, 34 ng/m3 . In one of the homes, shoe polishing was demonstrated to contribute to indoor aniline concentrations. Akyüz developed an analytical method for measuring amines in air samples and demonstrated the method’s applicability for indoor and outdoor sampling during summer and winter months at six locations in Turkey.The indoor sites included both smoking and nonsmoking areas. In smoking environments,grow rack piperazine was measured at mean concentrations of 8 ng/m3 in summer and 22 ng/m3 in winter. In nonsmoking settings, average concentrations were 5 ng/m3 in summer and 10 ng/m3 in winter. Corresponding averages for aniline were 6 ng/m3 and 21 ng/m3 in smoking environments versus 1 ng/m3 and 4 ng/m3 in nonsmoking environments. Summed across 33 reported species , the mean concentrations for summer sampling were 42 ng/m3 in smoking environments, 20 ng/m3 in nonsmoking environments, and 13 ng/m3 outdoors.

For winter sampling, analogous results were 117 ng/m3 for smoking environments, 47 ng/m3 for nonsmoking environments, and 35 ng/m3 outdoors. Based on this small set of studies, we conclude that amines are commonly much more abundant in smoking than nonsmoking locations. In smoking environments, aniline, methylaniline isomers, butylamine, and piperazine dominate, while in the nonsmoking environments, aniline and the alkylamines dominate. Aniline is typically the most abundant amine indoors. The other amines are substantially less abundant. Amines and amino acids that have been measured or are anticipated to occur indoors are listed with some of their key properties in Tables 25 and 26, respectively.Given the reported presence of amino acids in outdoor airborne particles collected at both marine and land-based locations, 385 coupled with outdoor-to-indoor transport of such particles, one can anticipate that amino acids are present in particles indoors. Amino acids are present in sweat;  in corneocytes; in skin surface films; and in natural moisturizing factor , which plays an important role keeping the stratum corneum hydrated. Hence, we expect these amino acids to be transferred to surfaces that humans contact, and to surfaces soiled with their squames . However, we found no peer-reviewed publications that report measurements of amino acids in either indoor airborne particles or indoor surface films.Dunstan et al. have reported amino acid levels in sweat collected from male athletes exercising at 32-34 °C. When the subjects began sweating, the net concentration of amino acids in their sweat was almost 10 mM. After 35-40 minutes of exercise, the net concentration in sweat had declined to match the net concentration of amino acids in plasma . That is, the sweat was no longer leaching amino acids from the stratum corneum. This abundance is presumably the lower bound for net amino acid concentration in sweat . In post-exercise sweat, the most abundant amino acids were histidine , serine , ornithine , glycine , and alanine ; total amino acid abundance was 8 mM. How significant are amino acids in sweat for potential accumulation on indoor surfaces? If an occupant transfers 10 ml of sweat to indoor surfaces , then ´ 10-4 moles of total amino acids would also be transferred. If the average molecular weight of the transferred amino acids is 100 g/mol, this equates to 3-10 mg of amino acids being transferred to indoor surfaces — equivalent to the whole-body emissions of ammonia over a period of 1-2 h approximately 5-10 h. The mass of amino acids transferred to clothing is expected to be substantially larger. Amines are the most abundant organic bases in outdoor air. Through acid-base reactions with sulfuric acid, they play key roles in atmospheric nucleation and particle formation. More generally, they can neutralize strong acids in outdoor air. For example, Shen et al. found that amines, emitted during the burning of coal in the Yangtze River Delta region of China, react with nitric and sulfuric acid to form aminium salts . Aminium nitrates were more abundant than aminium sulfates, with average concentrations of methylaminium, dimethylaminium and ethylaminium salts in aerosol particles of 6 ± 3 ng m−3 , 8 ± 5 ng m−3 , and 20 ± 17 ng m−3 , respectively. However, ammonium nitrate and ammonium sulfate tended to be 1000 to 10,000 times more abundant than these aminium salts, indicating the much more important role of ammonia as an atmospheric base. Reviews from the Wexler group discuss amine acid-base chemistry, and much of their discussion is applicable to indoor environments.Ge et al. specifically addresses chemical properties of amines, including Henry’s law constants, acid dissociation constants, vapor pressures, activity coefficients, solubilities, and solid/gas dissociation constants of their aminium salts. Amines contribute to new particle formation, including sulfuric acid nucleation.Reactions with strong acids such as HNO3, HCl and H2SO4 form aminium salts. Reactions with dicarboxylic acids form amides. Amines can also partition from the gas-phase to airborne particles. To have an impact on particle formation in outdoor or indoor environments, an amine must compete with ammonia for strong acids. Typically, outdoor ammonia concentrations are three orders of magnitude larger than outdoor amine concentrations, and indoor ammonia concentrations are even larger than those outdoors.

Mean outdoor values for palmitic and stearic acids were each in the approximate range 40-80 ng/m3. The mean I/O ratio for palmitic acid was 2.1 during cooler weather and 5.8 for warmer periods. The mean I/O ratio for stearic acid was 1.8 during cooler weather and 24 for warmer periods. Hasheminassab et al. subsequently reported on fine PM organic chemical composition for three of these study sites. They determined that “organic acids inside the retirement communities were dominated by indoor sources .” Total fine particle organic acid concentrations were in the approximate range 0.2-1.7 µg/m3 . Speciated concentrations were not reported. Human skin lipids contain a noteworthy abundance of n-alkanoic carboxylic acids, spanning a broad range of carbon numbers. Among the most prominent of these compounds are palmitic acid , myristic acid and stearic acid . Weitkamp et al. analyzed the fatty acids extracted from the hair of barber shop sweepings and detected the presence of nalkanoic carboxylic acids with carbon numbers ranging from 7 to 22 ; palmitic and stearic acids were especially abundant. Through the routine shedding of particles from the human envelope, one can anticipate that occupants are primary sources of these carboxylic acids in occupied spaces. The presence in indoor dust of squalene, a major skin lipid, reinforces the idea that occupants constitute emission sources of skin lipids to indoor environments. Daher et al. reported on the chemical characterization of both fine and coarse particles “inside the refectory of Santa Maria Delle Grazie Church, home of Leonardo Da Vinci’s ‘Last Supper.’” This highly controlled environment was well protected from the influence of outdoor air pollution. The investigators found, however, that “fatty acids … had high indoor-to-outdoor concentration ratios … showing a good correlation with indoor [fine-particle organic carbon mass concentrations],weed trimming tray implying a common indoor source.” In their supporting information, the authors report monthly concentrations of indoor n-alkanoic carboxylic acids from C14 through C29.

Averaged across all months, the three most abundant species were myristic , palmitic and stearic acids, with respective mean concentrations of 31, 27, 9.6 ng/m3 , which sum to 80% of the total for all n-alkanoic acids . Daher et al. noted that “potential indoor sources include skin emissions from visitors….” Kristensen et al.15 reported on time resolved measurements of gaseous and submicron particle-phase semivolatile organic compounds from a weeks-long sampling campaign in a normally occupied single-family home in northern California. That study identified cooking as an important source of indoor SVOCs, especially in the particle phase. The authors reported that, “the most abundant compounds related to cooking events include straight-chained saturated and unsaturated fatty acids .”Given this perspective, it should not be surprising that Liu et al.69 found dicarboxylic acids to be prominent organic components accumulated in indoor window films. Specifically, dicarboxylic acids with carbon numbers in the range 6 to 14 were the second or third most abundant class for most samples, behind monocarboxylic acids and comparable to n-alkanes . Among the dicarboxylic acids, azelaic acid, a product of ozone reacting with oleic acid, was generally the most abundant. Surface densities were highly variable across samples, with the highest reported value for azelaic acid being 7.3 µg m-2 on the indoor surface of an urban laboratory site in Toronto. Liu et al. inferred from their data that, “the greater accumulation of dicarboxylic acids in indoor rather than outdoor window films suggests indoor sources such as cooking.” With the high propensity to be in the condensed phase, it is worthwhile to consider whether dicarboxylic acids could materially influence the pH of indoor aqueous surface films. Consider the example of a surface film density of azelaic acid being 7.3 µg m-2. Assume that this abundance represents the sum of undissociated azelaic acid plus the two conjugate bases. Consider the influence on pH of surface water of this abundance of azelaic acid in isolation.

We do not have data on the abundance of water in the surface films studied by Liu et al. For exploration, consider three possibilities, corresponding to surface water thicknesses of 1 nm, 3 nm, and 10 nm. Also, assume that the surface water behaves thermodynamically like bulk water. Finally, neglect any substrate effects on aqueous film chemistry. This set of assumptions along with the reported pKa values in Table 17 allow for calculation of the equilibrium pH in the surface water. The results, in relation to the water film thickness, are pH = 3.0 for 1 nm, pH = 3.2 for 3 nm, and pH = 3.5 for 10 nm. Evidently, with such a highly favored aqueous phase, even the relatively weak azelaic acid can be sufficiently abundant to strongly acidify thin water films on indoor surfaces.In their classroom monitoring study, Liu et al.13 reported measurement results for 14 “diacid/hydroxycarbonyl acid ” compounds in the gas phase. Oxalic and malonic acid were reported as non-detectable indoors, even though there were substantial concentrations in outdoor air . The three most abundant diacids in indoor air reported in this study were succinic acid , glutaric acid , and adipic acid . The study by Liu et al.13 represents the most extensive and detailed set of gas-phase indoor organic acid data reported to date. Their supplemental information reports time average indoor and/or outdoor concentrations for 155 species. Table 18 reproduces the indoor and outdoor concentrations for the 18 species for which the time-averaged indoor concentration exceeded 10 ppt. Half of these species were reported as “not detected” in outdoor air. Among the remaining nine, the ratio of average indoor to average outdoor concentrations ranged from 4 to 25 , with a median ratio of 8. The consistently high I/O ratios reflects the importance of indoor emission sources for this group of abundant species. Wisthaler and Weschler326 have shown that these oxoacids are major secondary products of ozone/squalene chemistry, noting that squalene is a primary component of human skin lipids.In an extensive monitoring campaign undertaken in an ordinarily occupied single-family residence, Liu et al. reported on the gas-phase concentrations of a few other organic acids in addition to several n-alkanoic carboxylic acids. With tentative species identification, they reported that the time-average indoor concentration of acrylic acid was ppt during summer monitoring and 312 ppt during winter.

Analogously, glycolic acid was reported at 32 ppt for summer and 36 ppt for winter. Methanesulfonic acid was found to be present at an average abundance of 35 ppt in the summer and 115 ppt in the winter. In each case, the I/O ratio was well above 1.0, implicating indoor sources as important contributors to indoor concentrations. That study also reported an observation regarding a dicarboxylic acid: “Spikes of C2H3O4 + were observed during some occasions of sautéing in the summer.”The estimated average oxalic acid concentration in the summer season in the single-family residence was 16 ppt; in the winter, the average level was not stated, indicating that it was below the 10 ppt reporting threshold.In a follow-up investigation in Portugal, Alves et al. sampled PM10 inside and outside of a primary school classroom in the Aveiro city center during the winter and spring of 2011. They conducted detailed chemical analyses of composited samples, including measurements of diacids, cannabis grow setup ketoacids and aromatic acids. Table 20 records the reported indoor and outdoor concentrations for eight acidic species whose individual concentrations exceeded 10 ng/m3 . A striking feature is the extraordinarily high indoor concentration of malic acid. Alves et al. remarked that, “the fact that this acid is found in many sour or tart-tasting foods can eventually justify its detection at such high levels in indoor particles. The most common use of malic acid is in candy and potato chips.”Dehydroabietic acid and abietic acid are also known as “resin acids,” as they occur in tree resins. Resin acids occur in certain soaps. They are prominently emitted organic compounds from biomass burning. Noonan and coworkers have reported on indoor concentrations of abietic acid and dehydroabietic acid in PM2.5 samples collected in homes that used wood stoves for heat. The studies were conducted in association with a remediation program to improve the impact of wood stove use on ambient PM2.5 levels. Sampling in 16 homes, Ward and Noonan  reported average ± standard deviation indoor concentrations before the remediation to be 80 ± 61 ng/m3 for dehydroabietic acid and 3.7 ± 5.7 ng/m3 for abietic acid. Corresponding results for 21 homes as reported by Noonan et al. were 102 ± 73 ng/m3 for dehydroabietic acid and 8.8 ± 20 ng/m3 for abietic acid. The higher concentrations after remediation were attributed by the study authors to the more effective heating of fuel prior to its combustion in the higher efficiency stoves, leading to enhanced release into indoor air of these semivolatile wood constituents. Many studies have reported outdoor concentrations in the gas and/or particle phase for dicarboxylic and other organic acids reflecting urban and regional air quality concerns.

In summarizing selected results here, we focus on sampling conducted in urban and suburban environments, rather than in the more remote portions of the atmosphere, because of the implicit connection of urban studies to larger numbers of indoor environments and therefore greater relative significance for indoor air quality concerns, including human exposure. An early report by Kawamura and Kaplan characterized outdoor dicarboxylic acids in gas plus particle phases in the Los Angeles area from sampling during summer and autumn of 1984. They concluded that “oxalic acid is the dominant species.” Considering the sum of C2-C6 plus C9 , the total average concentration ± standard deviation for 12 atmospheric samples was 8.3 ± 4.5 nmol/m3 . The three most prominent species were oxalic acid , succinic acid and adipic acid . An early study in Tokyo sampled at intervals between late spring and autumn 1989. In that study, dicarboxylic and ketocarboxylic acids were assessed for the particle-phase only, with no particle size cutoff. The total average mass concentration of n-alkanoic dicarboxylic acids spanning C2 to C10 was 440 ng/m3 with the three most prominent species being oxalic acid , malonic acid and succinic acid .Among the total of 24 reported acids, only two other species had reported average concentrations above 30 ng/m3 : pyruvic acid and glyoxylic acid . Altogether, diacid concentrations averaged 540 ng/m3 and ketoacids 98 ng/m3 .Rogge et al. conducted detailed organic chemical composition analysis for fine particles collected outdoors at uniform intervals for year 1982 at four sites in the Los Angeles area. The average concentration of total aliphatic dicarboxylic acids was 239 ng/m3 . The four most abundant species were succinic acid , malonic acid , azelaic acid , and glutaric acid . These four species contributed 70% of the total mass concentration reported for aliphatic dicarboxylic acids. Oxalic acid was not reported. Khwaja collected and analyzed seven atmospheric samples collected over two days during October 1991 in a semiurban area of New York state. They reported concentrations of oxocarboxylic, ketocarboxylic, and dicarboxylic acids in the particle phase. Average ± standard deviation levels were 231 ± 118 ng/m3 for oxalic acid, 119 ± 44 ng/m3 for succinic acid, 84 ± 20 ng/m3 for malonic acid, 59 ± 21 ng/m3 for pyruvic acid, and 44 ± 16 ng/m3 for glyoxalic acid. Several recent studies have reported particle-associated organic acids sampled from outdoor air in and near Beijing, China. 336-339 Results from one illustrative study are highlighted in Table 21, which reports a subset of species for which the annual average ambient concentration of the analyte in PM2.5 was above 10 ng/m3 . Several dicarboxylic acids are featured, with oxalic acid being the most abundant. Seasonally, the average ± standard deviation for total dicarboxylic acid concentrations varied from a low of 366 ± 261 ng/m3 in autumn to a high of 763 ± 701 ng/m3 in winter. Among the other prominent organic acids quantified in PM2.5 in Beijing are phthalic acid and terephthalic acid, whose structures and thermodynamic properties are illustrated in Figure 16 and its caption.Cooking is a major air pollutant emission source. Even though most cooking occurs indoors, because of the much greater overall research emphasis on outdoor air pollution, most studies on emissions of organic acids from cooking activities have focused on larger-scale cooking operations, e.g. as practiced in restaurants or in the food-preparation industry, rather than from residential cooking. Abdullahi et al. have reviewed emissions from cooking of particulate matter and associated chemical components.

The lower average values for HONO in AC homes may partially reflect HONO loss to the air conditioner condensate. Dividing these same 58 homes between those with gas stoves and those without, average HONO concentrations were 0.8 ± 0.8 ppb in non-gas-stove homes and 4.0 ± 2.8 ppb in gasstove homes . During winter months, Leaderer et al. measured average HONO concentrations to be 6.8 ± 6.1 ppb in kerosene-heater homes and 3.5 ± 3.6 ppb in nonkerosene heater homes .For the homes without kerosene heaters, average wintertime HONO concentrations were 2.4 ± 3.1 ppb in non-gas-stove homes and 5.5 ± 3.8 ppb in gas-stove homes . All of this evidence points to unvented combustion as contributing to measurable increases in indoor HONO levels.In 99 homes in Upland, CA, and San Bernardino County, Lee et al.measured average HONO concentrations of 4.6 ± 4.3 ppb, considerably higher than the outdoor levels of 0.9 ± 2.3 ppb. Homes with gas ranges had higher indoor NO2 and HONO concentrations than those without. Indoor concentrations of HONO were positively correlated with NO2, with HONO levels occurring at approximately 17% of the NO2 levels. HONO concentrations were inversely correlated with O3 concentrations. A similar inverse correlation between HONO and O3 was reported by Weschler et al.based on spot measurements made in a Burbank telecommunications office. In both studies, the authors suggest that this observation may be a result of ozone-initiated oxidation of nitrite ions in aqueous surface films; the concentration of nitrite ions in indoor aqueous solutions is linked to gas-phase HONO concentrations . Semi-continuous measurements of HONO concentrations were made in an unoccupied school classroom in France,planting racks using wet chemical sampling and subsequent quantification with high performance liquid chromatography. Five experiments were conducted with controlled injections of NO2 under different lighting and relative humidity conditions.

With average indoor NO2 levels in the range 28-46 ppb and indoor RH levels in the range 30-60%, average indoor HONO levels were 5.1-6.2 ppb. Mendez et al. developed a description for HONO formation that assumes NO2 is first sorbed to surface sites, which are limited in number, and that NO2 then reacts with water to produce HONO and HNO3. Key parameters were fitted based on measurements in one experiment, and, with these fitted parameters, the model reasonably predicted the measured HONO concentrations in the other four experiments. As part of a study in a Syracuse home, Zhou et al. made time-resolved measurements of HONO concentrations during baseline conditions and cooking events. Mean ± standard deviation HONO concentrations were 4.3 ± 2.2 ppb during baseline conditions, rising to 19.5 ± 10.5 ppb during cooking . A short-term peak concentration of 50 ppb was measured. To our knowledge, this is the first study to report indoor baseline HONO concentrations larger than indoor baseline NO2 concentrations . Collins et al. measured time-resolved HONO levels inside and outside a Toronto home in November using a high-resolution time-of-flight chemical ionization mass spectrometer with acetate as the reagent ion. They found that, while indoor NO2 levels varied over a large range depending on outdoor levels, indoor HONO concentrations varied over a relatively narrow range and did not correlate with NO2 concentrations. Perturbation experiments were conducted in the kitchen using a burner on a gas stove and opening/closing windows and a door. During these perturbations, NO2 emitted by the gas burner only weakly affected HONO levels. Flushing the kitchen via open windows and a door reduced HONO levels during the high ventilation period, but when windows and door were closed, HONO returned to a gas-phase concentration close to its pre-airing value. The temporal responses of HONO were similar to those of small carboxylic acids in these airing experiments.

The authors concluded that gas-phase HONO was in equilibrium with, and strongly controlled by, surface sources. This inference was further supported by nitrite levels measured on various impermeable vertical surfaces in the kitchen and the upstairs of the home. Nitrite levels averaged approximately 1012 molecules cm-2 ; the authors cautioned that this value should be considered a lower limit. HONO measurements that were made during venting experiments as part of the HOMEChem campaign in Austin TX158 substantiate the Toronto home findings by Collins et al.When the Austin test house was vented, gas-phase HONO concentrations decreased from ~ 4 ppb to about 1 ppb. When windows were then closed, the HONO concentration returned to a level close to that measured before venting. See §4.6 for further discussion. It is interesting to compare the influence of HONO to that of HNO3 on the pH of aqueous surface films or bulk water. To begin, consider that the equilibrium pH of water exposed to 800 ppm of CO2 and 20 ppb of NH3 is 7.12. Adding 5 ppb of gaseous HONO to this mix would decrease the equilibrium pH to 6.53, whereas adding 0.1 ppb of HNO3 would decrease the equilibrium pH to 3.48. So, although measured indoor concentrations of HONO tend to be 10- 100´ larger than those of HNO3, the expected influence of HONO on pH is considerably weaker, based on analyses for equilibrium conditions. Taken together, these studies illustrate a strong direct contribution from indoor combustion to indoor HONO concentrations, a contribution from the partial transformation of NO2 to HONO on indoor surfaces, the potential for ozone to decrease indoor HONO levels via oxidation of nitrite ions in aqueous solution, and the ability of indoor basic surfaces to serve as large reservoirs for nitrous acid. More measurements of nitrite ions on indoor surfaces, as well as of the time-dependent pH of aqueous films on different indoor surfaces, would improve our understanding of the reported and inferred dynamics of this inorganic acid.During a study conducted in a 79-m3 stainless steel climate chamber, Brauer et al. examined the impact of human occupants on indoor HONO concentrations.

At a high air-exchange rate , four human occupants had only a small effect on HONO concentrations resulting from the addition of NO2 to the chamber. However, at a much lower air-exchange rate , the measured indoor HONO concentration with occupants was reduced to 40% of its value without humans in the chamber . When the subjects left the chamber, HONO levels returned to levels previously observed for the empty chamber.Direct removal by breathing could not account for the observed HONO removal rate. Reaction of HONO with NH3 emitted by the occupants also did not explain the observed reduction of indoor HONO levels. Brauer et al. speculated that “the effect of increased surface area is a plausible explanation for our observations.”One can estimate the potential magnitude of HONO removal by exposed skin, hair and clothing of the four subjects in the chamber. Assume that the deposition velocity for HONO to human surfaces is similar to that measured for ozone and assume a body surface area of 1.8 m2 for each human in the chamber. Then four humans would remove HONO at a rate equivalent to ventilating with clean air at 58 m3 /h or 0.73 h-1 in the 79 m3 chamber. Such a removal by human occupants is predicted to yield a reduction of approximately 60% in HONO concentration at a chamber air exchange rate of 0.5 h-1 , which is consistent in scale with the reduction shown in Figure 4 of Brauer et al.Conversely, the effect of removal on human surfaces would only be expected to reduce the indoor concentrations of HONO by about 5% for the high air-exchange rate condition of 12 h-1. If HONO loss does occur on the occupant envelope,sub irrigation cannabis important questions remain to be answered. Is this phenomenon transient, terminating when equilibrium partitioning is achieved? Or is HONO being irreversibly sorbed by skin and clothing? Based on 48-h measurements of O3 and NO2 in a Southern California museum gallery, coupled with their model of indoor chemistry, Nazaroff and Cass200 predicted that O3/NO2 chemistry would generate NO3 and N2O5 at substantial net rates. Weschler et al.suggested that under certain circumstances, O3/NO2 chemistry would generate indoor nitrate radical concentrations comparable to outdoor nighttime levels and that subsequent chemistry could be a substantial source of indoor nitric acid. Using a detailed chemical model, Sarwar et al. estimated an indoor nitrate radical concentration of 0.15 ppt for “base case” indoor conditions. Using a detailed model of gas-phase indoor chemistry, Carslaw predicted low NO3 concentrations under indoor conditions that included elevated concentrations of terpenes and unsaturated alkenes, which rapidly consume nitrate radicals. Carslaw noted that an anticipated consequence is formation of RO2·radicals, and subsequent production of organic acids. Nøjgaard made the first time-integrated measurements of the sum ‘NO3 + N2O5’ based on concentrations of an oxidation product of the NO3/cyclohexene reaction. Eleven separate measurements were made in an unoccupied 60 m3 conference room in Copenhagen, DK, during August. There were no indoor sources of O3 or NO2; these species originated outdoors.

The sum ‘NO3 + N2O5’ ranged from 1 to 58 ppt, and was influenced by the fraction of time mechanical ventilation occurred, levels of O3 and NO2, lighting and time of day. For the four samples collected during daylight hours, the sum of NO3 + N2O5 ranged from 3 to 10 ppt or approximately 0.6 to 1.4 ppt of NO3 given the measured cooccurring NO2 concentrations. These measured values are larger than Carslaw’s modeled estimates of NO3 levels under typical indoor conditions. Nøjgaard speculated that this discrepancy might be due to actual NO concentrations being lower than those used in the model and concluded by calling for time-resolved measurements of indoor NO3, such as could be achieved using cavity ring down spectroscopy. Arata et al. made the first real-time indoor NO3 measurements in the kitchen of a single family home during simulated-use conditions. Experiments included cooking with a butane stove in the presence of deliberately released ozone. At an enhanced O3 level of 40 ppb, researchers ignited the stove, operated it for about five minutes to boil water, and turned it off. After O3 had titrated the NO in the kitchen air, the N2O5 level began to increase, reaching a value of 190 ppt, while the NO3 concentrations leveled off at about 3 ppt. Based on simultaneous measurements of NO2, O3 and NO3, they estimated total nitrate radical reactivity with volatile organic compounds to be 0.8 s-1 . Using a box-model they calculated a peak NO3 production rate of 7 ppb h-1 . The model’s output indicated that reaction of N2O5 with indoor surfaces, producing nitric acid, accounted for 20% of NO3 loss during the period of peak NO3 production. More generally, these studies indicate that, under conditions with elevated indoor levels of O3, combustion events can result in meaningful levels of nitric acid, organonitrates and various oxidized VOC – even when measured residual NO3 concentrations are relatively low.Isocyanic acid is moderately acidic and moderately soluble . It has been recognized as a gas-phase acid in the outdoor atmosphere since 2008. More recently, experiments have demonstrated that gas-phase oxidation of nicotine by hydroxyl radicals generates HNCO. Measurements using an acetate CIMS in a chamber and in a Toronto home have explored indoor sources of HNCO. 238 The chamber studies indicated a molar ratio of HNCO/CO in side stream cigarette smoke of 2.7 × 10-3 . In a home, the background HNCO concentration was 0.15 ppb, about twice the outdoor level. A single cigarette’s side stream smoke increased the HNCO concentration to about 1.5 ppb. In chamber experiments, there was evidence for photochemical production of HNCO from cigarette smoke, doubling the concentration in about 30 minutes at an OH concentration of 1.1 × 107 molecules/cm3. However, in the home there was no evidence of photochemistry influencing the HNCO concentration. Simultaneous, time-resolved measurements of HNCO and CO indicated that partitioning to indoor surfaces was a significant sink for indoor HNCO. Isocycanic acid reacts with ammonia to form urea. Among halogenated acids, chlorine-containing species are the most noteworthy. In the atmosphere, hydrochloric acid is a prominent atmospheric inorganic strong acid. Important sources of atmospheric HCl are the combustion of fuels and wastes that contain chlorine, which include coal, bio-fuels, and plastics. Hydrochloric acid is also generated from acid-displacement reactions in which other atmospheric strong acids, such as HNO3, react with sea-salt aerosol, with the net effect represented by HNO3 + NaCl ® HCl + NaNO3. In a global emission inventory of HCl, combustion and sea-salt dechlorination were the largest sources.

Although most of the experiments measured whole-body emission rates, a subset of experiments measured dermal and breath emissions separately. Over the range of conditions studied, the measured NH3 emission rates ranged from 0.4 to 5.4 mg h-1 person-1 . These values are much lower than the per person NH3 emission rates reported almost 30 years earlier in Table 4 of Lee and Longhurst.Based on current literature, we judge that the NH3 emission rate of a typical adult is dominated by emissions from skin, is influenced by temperature, sweating, fraction of exposed skin, and is commonly in the range of 0.3 to 5 mg NH3 h-1 person-1 = 2 to 36 g NH3-N y-1 person-1. Humans also contribute to indoor NH3 levels via their skin squames . In mechanically ventilated buildings, squames can accumulate in HVAC systems. Ng et al.report the generation of NH3 and volatile fatty acids via bacteria acting on skin squames in air cooling units. Temperature was seen to have a pronounced effect on NH3 generation. Insufficient information was reported to quantitatively estimate an emission rate from this source under typical building conditions. Concrete treated with urea-based antifreeze during mixing can be a substantial source of ammonia. Bai et al. measured NH3 emissions to vary with air-exchange rate in the range 1-6 mg m-2 h-1 for samples prepared with about 1 kg of urea per 300 kg of concrete. The investigators estimated that, at typical ventilation rates, it would take more than ten years to exhaust the ammonia emanating from their concrete samples. They also made measurements in five undecorated apartments in a building that had been built four years earlier with concrete containing urea. The mean NH3 concentrations in the bedrooms and living rooms were approximately 5000 ppb when windows and outside doors were closed and were slightly above 1000 ppb when the apartments were ventilated.

Lindgren116 measured ammonia levels between 3000 and 6000 ppb in a newly built Beijing office,growers equipment reporting that additives in the concrete were the likely cause of the high values. Jang et al. examined how the organic content of the aggregate affected NH3 emissions from different cement mortars. The NH3 emitted from the aggregate increased with the mass fraction of organic matter in the aggregate. Due to the potential for NH3 emissions from concrete, Chinese buildings are often tested for ammonia. While it is well known that environmental tobacco smoke contains elevated levels of NH3, direct measurements of the influence of smoking on indoor NH3 levels are scarce. Risner and Conner100 report a mean ammonia concentration of 107 µg/m3 in a 28 m3 room in which four cigarettes had been smoked. No information was reported on occupancy or air-exchange rate. In addition to NH3 generated by the combustion of tobacco, NH3 in ETS can also be a consequence of the deliberate addition of ammonia-forming compounds to cigarettes. Ammonia increases the fraction of nicotine that is present in ETS as the free base in contrast to the protonated form. The free-base nicotine is more readily absorbed by the smoker. Pankow et al. have investigated the partitioning of nicotine between particles and the gas phase in ETS and mainstream smoke. See also §3.10.Indoor ammonia concentrations tend to be much larger than outdoor concentrations. Ampollini et al. have assembled an extensive summary of indoor ammonia measurements reported in the peer-reviewed literature. Table 6 summarizes indoor and outdoor ammonia concentrations measured in representative studies. Ammonia measurements indoors first appeared in the literature in the late 1980s and early 1990s. Sisovic et al. measured indoor NH3 levels multiple times in six offices spanning five buildings in Zagreb, Yugoslavia, during summer and winter. The mean summer concentration was 74 µg/m3 ; the mean winter concentration was 67 µg/m3 . This outcome suggests substantially higher indoor NH3 emission rates in summer, since air-exchange rates were presumably lower in winter.

Li and Harrison119 measured indoor and outdoor NH3 levels at University of Essex buildings. They found that indoor levels were 3.5 to 21 times the corresponding outdoor levels; indoor levels ranged from 7 to 48 µg/m3 with a mean value of 20 µg/m3 . Atkins and Lee120 made repeated measurements in 10 British homes. The mean NH3 concentrations in kitchens, living rooms and bedrooms were 39, 37, and 32 µg NH3-N/m3, respectively . During winter months, Tidy and Cape121 measured NH3 concentrations in houses and public buildings in Edinburgh. In private living rooms, NH3 levels ranged from 7 to 63 ppb with higher values where smoking occurred. A similar range of values was found in public buildings. More recently , researchers in Finland have measured NH3 concentrations in newly constructed apartments and residences , as well as office buildings with indoor air problems . In Prague, NH3 measurements were made at the historic National Library, which is naturally ventilated. During warmer months the monthly mean NH3 concentrations were somewhat larger than those measured during cooler months of December-March . Researchers from Kumamoto University, using a novel automated flow-based ammonia gas analyzer, measured a mean NH3 concentration of 28 ppb in their university laboratory. The values reported in Table 6 are for occupied environments. Investigators from Lawrence Berkeley National Laboratory measured NH3 concentrations in an unoccupied home in Clovis, CA. During the months of October, December and January, the mean levels were 21, 17 and 15 ppb, respectively. These indoor values were only slightly larger than co-occurring outdoor values. In more comprehensive multi-pollutant studies, Brauer et al., Liang and Waldman and Suh et al. measured indoor NH3 and examined its relationship to aerosol strong acidity. Brauer et al., sampling in Boston homes, found that NH3 concentrations were higher indoors than outdoors, with mean indoor NH3 concentrations of 8 ppb in summer and 19 ppb in winter . In three New Jersey facilities, Liang and Waldman also found NH3 concentrations to be higher indoors than outdoors. In a daycare facility the mean NH3 concentration was 61 ppb; in a nursing home, 56 ppb; and in a home for the elderly 31 ppb and 29 ppb .

For 24 homes in Uniontown, PA, Suh et al. reported a geometric mean indoor NH3 concentration of 22 ppb , much higher than the outdoor level of 0.3 ppb.In a study of 47 homes in State College, PA, Suh et al. obtained similar results: geometric mean = 20 ppb; GSD = 2.2.As expected, indoor NH3 concentrations tended to be higher in residences with lower air-exchange rates, albeit with considerable scatter. In Connecticut and Virginia, Leaderer et al. measured NH3 levels, in addition to other inorganic species, in 58 homes in the summer and 223 homes in the winter. During the summer, mean NH3 levels were 32 ppb in air-conditioned homes and 28 ppb in homes without AC. During the winter, mean NH3 levels were 44 ppb in homes with kerosene heaters and 38 ppb in homes without. In 10 Albuquerque homes, known to have elevated levels of nitrogen dioxide, mean NH3 concentrations were 20 ppb.Recently, Ampollini et al. reported time-resolved NH3 concentrations, measured with a cavity ring-down spectrometer in a test house in Austin, Texas, during the HOMEChem campaign.During unoccupied periods, the mean NH3 concentration was 32 ppb, increasing when indoor temperature increased. During high-occupancy events, the mean concentration was 52 ppb. Levels rose to an average of 62 ppb while cooking a turkey, and 73 ppb while cleaning with an ammonia-based product.When the air conditioning cooling coil cycled on, the NH3 concentration dropped,plant benches qualitatively consistent with expectations for two influencing factors: dissolution of NH3 in water on coils and lower emission rates at lower temperatures. A half hour of venting with outdoor air substantially reduced the indoor NH3 concentration, but it returned to its prior concentration in less than an hour after the venting ended. The return to concentrations before venting was confirmed during five separate venting periods on a day dedicated to such experiments. These results suggest the presence of a large reservoir of sorbed and/or dissolved NH3 associated with exposed indoor surfaces in the test house. It is instructive to compare the values in Table 6 for indoor NH3 concentrations with calculated estimates based on whole-body emission rates. Assuming no loss of indoor NH3 other than by ventilation and using Li et al.’s average whole-body emission rate at moderate temperatures of approximately 1 mg h-1 person-1 in a residence ventilated at 5 L s-1 person-1 , the calculated NH3 concentration would be about 80 ppb. This is higher than all of the reported mean indoor concentrations in Table 6, suggesting that loss of NH3 from indoor air by processes other than ventilation is an important fate.

Deposition to indoor surfaces is supported by observations made after cleaning with an ammonia-based product in the HOME Chem experiments. After reaching its peak concentration, ammonia levels decreased at a rate substantially faster than the air-exchange rate. In summary, in occupied buildings measured indoor NH3 concentrations are typically in the range 15-75 ppb and are much higher than outdoor concentrations. Indoor enhancement is consistent with strong NH3 emissions from occupants. Higher concentrations occur when other sources are present .In bulk condensed water, in aqueous atmospheric aerosols, and in aqueous surface films, NH3 equilibrates with the ammonium ion . Outdoors, as SO2 is oxidized to H2SO4, gasphase ammonia partially neutralizes H2SO4, forming ammonium salts, e.g., 2SO4, HSO4, and 3H2. The dominant ammonium salt depends on the relative amounts of NH3 and H2SO4 and is also influenced by the presence of nitric acid. Ammonium sulfate salts are often the most abundant inorganic constituent of fine-mode particles. In regions with high levels of nitrogen oxides, aerosol ammonium nitrate levels can approach or exceed those of ammonium sulfate salts. Indoors, ammonium is a common counterion for sulfate, nitrate, and chloride salts present in airborne particles and settled dust. Indoor sources of ammonium include outdoor-to-indoor transport of particles and generation indoors by the reaction of ammonia with acidic species . Many of the studies that have measured indoor ammonia concentrations have also measured ammonium concentrations in indoor airborne particles, commonly reporting results in terms of nmol of ammonium per m3 of air. Table 7 summarizes such measurements in selected studies, contrasting indoor and outdoor values. Sinclair et al. measured NH4 + in fine- and coarse-mode indoor and outdoor particles for extended periods at sparsely occupied telephone switching offices in Wichita KS, Lubbock TX, Newark NJ and Neenah WI. Ammonium was present primarily in fine-mode particles. These offices were mechanically ventilated and HVAC systems contained particle filters, which removed some of the particles from the ventilation air. Consequently, the I/O ratios for fine-mode ammonium were low, ranging from 0.065 to 0.20 , depending on the removal efficiency of the filters at a given facility.The low I/O ratios translate to low indoor NH4 + concentrations in fine-mode particles, ranging from mean values of 0.13 µg/m3 in Lubbock to 0.26 µg/m3 in Wichita. Li and Harrison measured much higher ammonium levels in indoor aerosol particles in university buildings,finding a mean value of 2.44 µg/m3 and an average I/O ratio of 0.96. These higher values are reasonable, given that they were measured in a communal kitchen, coffee room, and corridors, whereas the measurements by Sinclair et al. were in offices with filtered ventilation air. Although Li and Harrison found no correlation between indoor and outdoor NH3 levels, they did find significant correlation between indoor and outdoor NH4 + levels, indicating the importance of outdoor-to-indoor transport as a source of indoor particle-phase ammonium.Based on measurements made in five Los Angeles area museums, Ligocki et al. observed that the indoor/outdoor ratios for NH4 + in fine particles was always less than one and tended to be higher in summer compared to winter. A linear regression model indicated significant correlation between indoor and outdoor levels for fine-mode NH4 + . The ion balances for the aerosol samples indicated that ammonium was primarily associated with sulfate in the summer and with nitrate in the winter. In a study of Boston homes, Brauer et al. found that mean ammonium levels were higher in summer than in winter. In both seasons, the I/O ratio was close to unity. In the New Jersey institutional buildings sampled by Liang and Waldman, I/O ratios for fine-particle NH4 + ranged from 0.44 to 1.1, with median indoor concentrations in the range 73-117 nmol/m3 . Suh et al. measured indoor and outdoor levels of fine-particle ammonium in the homes of 24 children in Uniontown, PA.

Novel medications and novel biological targets call for careful assessment of mechanisms beyond the “usual suspects”, such as changes in mean levels of subjective response and alcohol craving. Ultimately, the combination of multiple scientific approaches, including human laboratory, DDAs, neuroimaging, and biomarker assessment, offer complementary and clinically useful findings that can inform the development of ibudilast, and immune treatments for AUD more broadly. The chemical composition of indoor air influences its healthfulness as well as its suitability for preserving cultural artifacts and protecting sensitive electronic equipment. As measurement technologies have improved, our understanding of the complexity of indoor air has grown. A striking feature of the atmosphere in general and of indoor environments in particular is the steep increase in the number of chemical species of potential interest as the minimum quantifiable concentration diminishes. In the atmosphere, the number of chemical species present at a level of 0.1% or higher is only four: N2, O2, Ar, and H2O. Decreasing the minimum level of concern to one part per million adds only a few components, such as CO2 and CH4. However, when the threshold for concern is set at a part per billion or a part per trillion, the number of constituents rises to hundreds or thousands of species. These numerous species exhibit a broad range of chemical properties and pose diverse health-risk and material-damage concerns. Even at relatively low fractional abundance, some chemical components may significantly influence the attributes of indoor air. Thinking about the vast number of molecules in a given macroscopic air volume can help to establish perspective. Consider, for example,marijuana grow system that adults inhale an average of 15 m3 or about 600 moles of air daily. This daily quantity of inhaled air corresponds to almost 4 ´ 1026 molecules.

Even at the small fractional abundance of one part per trillion, the daily number of molecules of a trace species inhaled could be nearly 400 trillion. In part because of the large number of compounds of potential interest, it is scientifically valuable to categorize species according to key properties. One prominent example is the grouping of organic compounds into categories based on volatility, i.e., very volatile organic compounds, volatile organic compounds, and semivolatile organic compounds. 1 Such a grouping allows for more efficient identification and treatment of important physicochemical processes governing the sources, dynamic behavior, and fates of indoor-air constituents than would be possible using a purely chemical-by-chemical approach. This review is concerned with two broad and interrelated categories of chemicals occurring in indoor environments: acids and bases. We are guided principally by the Brønsted-Lowry conceptualization, in which a key feature of an acid is its tendency to donate a proton when in aqueous solution; the key complementary feature of a base is to accept a proton. The review’s scope is specifically restricted to compounds that can be found in indoor air, considering gaseous species and also species primarily associated with airborne particles. The review aims to be thorough but does not aspire to be comprehensive. We do intend to include all major classes of acids and bases that occur indoors with substantial exploration of specific examples within these major classes. The indoor environments of concern are those that are normally occupied and of the types in which people spend much time, including but not limited to residences, schools, and offices. As much as possible, our review approach is strongly grounded in physical science and aims to be incisively critical. We synthesize and report measured concentrations. We are particularly interested in processes that govern such concentrations, including characterizing sources and associated emission rates; factors influencing the dynamic behavior; fates; and consequences.

Depending on the relative abundance of condensed-phase water indoors and key physicochemical properties of the chemical compounds, aqueous-phase processes can strongly influence the airborne concentrations of acids and bases indoors as well as altering the pH of indoor water. Although there is a deep and extensive history of interest in indoor acids and bases, until now there has not been a systematic and thorough review of the state-of-knowledge for these important chemical classes. As early as the 1850s, Max von Pettenkofer used indoor abundance of carbonic acid to determine the level of ventilation required to achieve good indoor air. In the middle of the 20th century, sulfur dioxide emerged as an important urban air pollutant, and studies were undertaken to better understand the extent of protection provided by being indoors. Later, as urban and regional air pollution concerns began to focus on particulate matter, a specific interest emerged in the role of aerosol strong acidity as a potential cause of adverse health effects. Several studies were undertaken in the late 1980s and 1990s to better understand indoor concentrations and associated exposures of acidic aerosols. 5,6 Long-term awareness that acidic pollutants can damage cultural and historic materials has been documented by Baer and Banks. Corrosion of metals in indoor environments in relation to acid gases and other pollutants was already studied in the early 1970s.During the past decade, strong new research interest has emerged concerning indoor acids and bases. One dimension has been some evidence, although not yet conclusive, that exposure to excessive carbon dioxide levels indoors can impair cognitive performance. This concern is but one example of a broad array of issues regarding how occupants influence indoor air quality, including through the acidic and basic species they generate, such as the fatty acids in skin oils. Following parallel advances in outdoor atmospheric chemistry, a new area of focus indoors is the class of compounds that are water soluble organic gases, of which acids are a major subcategory. In addition, instruments that have advanced the study of outdoor atmospheric chemistry are now beginning to be applied indoors.

Advanced technologies, such as high-resolution time-of-flight chemical ionization mass spectrometry , aerosol mass spectrometry , and semivolatile thermal-desorption aerosol gas chromatography are permitting new aspects of indoor air quality to be probed, reflecting their capabilities for sensitive measurement with fast time response combined with strong levels of chemical specificity. Recently published studies with such instruments are providing new insights in many aspects of indoor air quality, including the sources, abundances, and dynamic behaviors of indoor acids and bases. The body of this review is divided into three main sections. The first considers water in indoor environments. An important topic in its own regard, only certain aspects of indoor water have been well-addressed in prior studies. For this review, it is an important subject because of the strong two-way interactions between condensed-phase water and airborne acids and bases: acid and base uptake influence the pH of liquid water, a “master variable” of water chemistry; partitioning into the condensed phase alters the airborne concentrations and fates of airborne acids and bases; and condensed-phase water can serve as a large reservoir for acids and bases,cannabis vertical farming buffering their airborne concentrations. Because of water’s important role influencing indoor acids and bases, we review the state of knowledge across a range of physicochemical forms: water vapor, bulk liquid water, sorbed water, water in surface films, and water in suspended airborne particles. The middle section of the article explicitly addresses indoor acids and bases. Acknowledging the richness of the subject and the diversity of the species involved, the material is presented in ten subsections, respectively addressing carbon dioxide, ammonia, sulfur dioxide and sulfate, nitric and nitrous acid, hydrochloric and hypochlorous acid, carboxylic acids, other organic acids, aerosol strong acidity, amines and amino acids, and nicotine. The final core section of the report is concerned with the roles of indoor surfaces and surface materials influencing the dynamic behavior, fates and consequences of indoor acids and bases. A prominent feature that contrasts indoor air from outdoor air is the high surface-to-volume ratio indoors, amplifying the importance of surface interactions influencing indoor air quality. With respect to indoor acids and bases, this feature is pertinent, extending beyond the roles of surfaces as substrates for aqueous and organic films and sorbents for water. Water is centrally important to the concentrations, fates and consequences of indoor acids and bases. When a molecule of a gaseous acid dissolves into condensed-phase water, it can release a proton, changing the pH of that water. The extent to which the acid or base undergoes a proton-exchange reaction depends on several key factors: the pH of the aqueous phase, which is influenced by the abundance of that particular species; the abundance and strengths of other acids and bases; the amount of condensed-phase water; the presence of other anions and cations ; and the influences of solid substrates in contact with the water.

The ionized form of the acid or base has negligible vapor pressure, and so will remain in the condensed phase while ionized. However, acid-base reactions are readily reversible, so a change in pH can lead to the reestablishment of the neutral form of the molecule, which may then return to the gas phase. Indoor water occurs in multiple forms; only some of these are well characterized. Gaseous water is abundant and can play a role in gas-phase chemistry; however, in the context of indoor acids and bases, it is more important as a source and sink for indoor water’s condensed phases. As a condensed species, several forms of water are potentially important in acid-base processes: bulk liquid water, sorbed water, aqueous surface films, and particle-phase water. These different forms of condensed-phase water can influence indoor acids and bases in different ways. In this section of the review, we summarize the state of knowledge about indoor water vapor along with each of these main forms of condensed-phase water. Water is an important component of indoor environmental quality for reasons that extend well beyond the concerns of acids and bases. Dampness and moisture are strongly related to adverse respiratory health symptoms and allergies. Influenza transmission may be influenced by humidity.Humidifiers are used to deliberately increase the water vapor content of indoor air; these have the potential to elevate pollutant exposures and health risks. In warm and humid climates, much of the energy for air conditioning is used to dehumidify ventilation air. The nature and abundance of indoor water varies among building types, across climate zones, and seasonally. In this section, we emphasize general principles and broadly relevant empirical evidence. When specificity is warranted, we consider conditions that are common in residences in the United States.This category includes all forms in contact with indoor air in which the water is sufficiently abundant to be visible. It also includes forms of water that are potentially visible, but normally hidden, such as in sink traps and toilet tanks. We know of no quantitative accounting of the abundance of bulk condensed water in residences or other indoor environments. Direct inspection of spaces occupied by the authors, along with some reflection, suggests that quantities of bulk liquid water in residences might commonly be in the range 0.35-35 L. In the event that all such water was fully equilibrated with gaseous acids and bases, and if such an abundance were present in a 350 m3 residence, then the corresponding contribution to the liquid water volume ratio would be in the range L* = 0.001 – 0.1 L m-3 . Although anecdotal and therefore not directly generalizable, it seems worthwhile to make a brief account of the bulk water observed at a moment in time in the home of one of the authors. In the kitchen, there is about 2 L of visible liquid water, divided among 1 L used to soak dried beans for an upcoming meal, 0.2 L in a teakettle, 0.1 L in a drinking glass, and 0.5 L in an automatic coffee maker. There are smaller amounts of water associated with washed breakfast dishes on a drying rack, dish towels, and the wetted surfaces of the kitchen sink. There is also ~0.25 L of water in a P-trap beneath the kitchen sink. If 2 L of water were fully equilibrated with the kitchen volume of about 50 m3, the corresponding contribution to L* would be 0.04 L/m3 . Each of the two bathrooms in this house has a toilet with about 1 L of water in the bowl and 5 L of water in the tank that provides for flushing. Each bathroom has a sink and a shower. Each of these contains a P-trap connected to the drain.

The ELISA was performed using 96-well high binding micro titer plates coated with coating antigen cAg06 , washed with 10mM phosphate buffered saline + 0.05% Tween 20 , blocked with 0.5% bovine serum albumin in PBS. All standards, quality control samples and urine samples were prepared in 10% MeOH in PBS prior to the assay procedure. A 10-point calibration curve was prepared for each assay using a serial 1:5 dilution from the highest standard solution. A blank 0 ng/mL standard in the same 10% MeOH/PBS solution was also prepared. Wells containing instrument blanks received a 50 uL aliquot of PBST, while all remaining wells received a 50 uL aliquot of anti-rabbit 3PBA antibody #294 diluted 1:7000 in PBST. The goat anti-rabbit IgG-horseradish peroxidase conjugate was diluted 1:3000 in PBST. The substrate solution in dimethylsulfoxide per 25 mL of acetate buffer, pH 5.5 was added and color development was stopped after 15 min with 2 M H2SO4. The absorbance was measured using a Vmax micro plate reader in dual wavelength mode at 450 nm – 650 nm. Urinary creatinine concentrations were determined using the methods described in Ahn et al. 2011 .All urine samples, blank samples and QC samples were analyzed in triplicate. The final concentrations were calculated from the means of the triplicate values. If one of the triplicate values fell below the LOD it was not considered in the calculation of the mean concentration. Mean values that fell between the LOD and the LOQ were retained in all further statistical analyses. For each set of extractions,horticulture rack one urine sample was randomly chosen for QC analysis and was spiked to a level of 10 ng/mL 3PBA before extraction in order to verify that there were no matrix effects from the sample extract and to check method accuracy. Five different urine samples were also extracted and analyzed in duplicate at different time points in the analysis to verify the method precision.

For further validation of the ELISA method, and in order to try to quantify any cross reactivity that may have occurred, a set of six urine samples was sent to Emory University in Atlanta, GA where they were analyzed by high performance liquid chromatography-tandem mass spectrometry using a well established method .Summary statistics for both the volume based and creatinine adjusted 3PBA data were calculated. For concentrations below the limit of detection , an imputed value was assigned equal to the LOD divided by the square root of 2 . To determine predictive variables from the questionnaire data to include in a multivariate analysis, linear regression with both the log-transformed creatinine concentration and the variable of interest, referred to as the bivariate comparisons, were performed for each variable with 3PBA concentration. For each type of pesticide application, we created a continuous variable that represented the number of applications per year as well as a categorical variable indicating if that type of pesticide had been applied. Additional variables were also created summing pesticide applications across different application types. Food diaries were translated to English, and individual food items were grouped into ten different food categories: Fruit, Vegetables, Legumes, Meats, Snack/Processed Foods, Dairy, Beverages, Grains, Mixed Foods , and Other. Each category also had subcategories for specific, popular food items. For example, in the Dairy category, subcategories included Milk, Cheese and Other Dairy. Two variables were created for each food category and sub-category. First a categorical variable that indicated if the participant had consumed an item from a given category or sub-category. Second, a continuous variable was created with the number of servings in each category or sub-category. Volume based 3PBA concentrations were log-transformed to better approximate a normal distribution and regressed against the log-transformed creatinine concentrations and the individual questionnaire variable . Two regression analyses were conducted for each variable, one including only data from the mothers and one including only data from the children . There were a number of variables related to individual measures of home disrepair that were significant in the bivariate analysis. Because many of these measures of disrepair were correlated, item analysis was performed to select and evaluate the internal consistency of a set of items for a summative scale score.

The resulting Home Disrepair Score is computed by summing the water damage, leaks, carpet damage, worn spots or holes in the counters and rotten wood indicators and has good internal consistency in our sample . Multivariate regression was then performed to evaluate which questionnaire variables were most predictive of the urinary 3PBA concentrations. Three models were fit, one with the data from both the mothers and the children, one with data only from the children, and one with data only from the mothers. As an alternative, we also ran the models using the metabolite concentrations directly adjusted by the creatinine concentration. All statistical analyses were performed using SAS version 9.2 .The resulting Home Disrepair Score is computed by summing the water damage, leaks, carpet damage, worn spots or holes in the counters and rotten wood indicators and has good internal consistency in our sample . Multivariate regression was then performed to evaluate which questionnaire variables were most predictive of the urinary 3PBA concentrations. Three models were fit, one with the data from both the mothers and the children, one with data only from the children, and one with data only from the mothers. As an alternative, we also ran the models using the metabolite concentrations directly adjusted by the creatinine concentration. All statistical analyses were performed using SAS version 9.2 .Women in this study ranged in age from 23 to 51 years old; they had very low educational levels, with 46% having only a 6th grade education or lower; they were almost all married and lived in homes with 4 or more residents . Pest problems were common with 59% reporting insect problems, 43% using pesticides indoors and 35% applying pesticides outside . A Spearman rank correlation analysis was performed to see if there were associations between the two measures of home disrepair with pesticide application. Multiple significant correlations were observed , suggesting that poor housing conditions do lead to higher rates of pesticide application. For each set of three triplicates, the sample standard deviation of the urinary 3PBA concentration was computed. The average 3PBA concentration was 2.51 with an average standard deviation of 0.42 ng/mL. Less than 10% of the samples had a triplicate that fell below the LOD resulting in that value being dropped from the calculation of the mean.

Recoveries of the fortified urine samples ranged from 67 to 111% with an average of 82 ± 12%. The LOD of this analysis was estimated to be 0.1 ng of 3PBA in 1 mL urine. The limit of quantitation was determined to be 2 ng/mL. The percent difference between concentrations in duplicate aliquots of selective urine samples ranged from 3.6 to 28% with an average of 14%. Six urine samples were also analyzed by HPLC-MS/MS to further validate the ELISA method. The square of the correlation coefficient between the 3PBA concentrations from the two laboratory methods for the six samples tested was R2 = 0.934, and the %D ranged from 7.9 to 30.6% with an average of 25%, with the ELISA resulting in higher concentrations in four of the samples, and lower concentrations in two of the samples. Urinary 3PBA concentrations in our study were detected in 80% of all samples with a range of 0.3–13 ng/mL .However, adjustment for urinary creatinine resulted in a significantly higher concentration of urinary metabolites in children than in mothers . We calculated the correlation of urinary 3PBA concentrations between mothers and children. Urinary 3PBA concentrations from mothers and children in the same household were positively correlated for both volume based and creatinine adjusted concentrations .Variables included in the multivariate analysis were based upon the results of the bivariate analysis. The Home Disrepair Score, derived from the combination of multiple questionnaire items,vertical grow system was significant in the bivariate analysis only for mothers, while the Inside Housing Conditions score, derived from the staff evaluation during the MICASA follow-up interview, was significant only for the children. Because these two scores were designed to measure similar housing characteristics, both scores along with the Outdoor Spray pesticide use variable from the MICASA baseline questionnaire and the log-transformed creatinine concentrations were included in all three multivariate models described below. Multivariate models assessed factors associated with 3BPA concentrations in the combined sample , children only and mothers only . Both the Home Disrepair Score and Outdoor Spray were positive significant predictors of urinary 3PBA levels in the total study population model, which included logtransformed creatinine, the Home Disrepair Score, Outdoor Spray, Inside Housing Conditions and a Mother/Child variable .

The model restricted to children included food diary variables significant in the bivariate model: Apple , Milk , All Meat and Cereal as well as the log-transformed creatinine, the Home Disrepair Score, Outdoor Spray and Inside Housing Conditions. In this model Outdoor Spray and Inside Housing Conditions were marginally significant positive estimators of urinary 3PBA concentration. Cereal Total, while marginally significant, was negatively associated with urinary 3PBA in the children only data. In the mother only model we included the food diary variables Eggs , Beans , Grapes , Chicken , and Cereal as well as log-transformed creatinine, the Home Disrepair Score, Outdoor Spray and Inside Housing Conditions. The Home Disrepair Score , Outdoor Spray , and Cereal Total were all significant positive estimators of urinary 3PBA levels in the mothers. The models with the metabolite concentrations directly adjusted for creatinine resulted in similar associations .We assessed the exposure to pyrethroid pesticides in 105 women and 103 children in a farm worker population by laboratory measurements of the metabolite 3PBA in urine samples and by questionnaire data. This population had a relatively low educational level, with only about half of the adult women participating in our study reporting a 6th grade education or higher, in contrast to the 85% of U.S. adults who have a high school diploma . The results from the ELISA method used to analyze urinary 3PBA concentrations in this study were validated by a more traditional instrumental method at the Emory University in Atlanta, GA. The suitability of this newer analytical technique for use in biological monitoring of 3PBA is further corroborated by Chuang et al. who analyzed over 100 urine samples and showed high correlation between ELISA and GC/MS data, with the square of the linear correlation coefficient R2 = 0.906 and no significant between the two methods of analysis for any given sample . Children had higher concentrations of this metabolite than their mothers. This result is consistent with multiple pesticide exposure studies and most likely has to do with differences in behavior that leads to higher non-dietary ingestion in children . Once pyrethroid pesticides have entered the home, the carpets and cushioned furniture can act as repositories for pesticides . High levels of pesticides in carpet dust is a particular concern for young children who, due to their continual exploration of their environments, spend a large amount of time on the floor and have increased hand to mouth activity, resulting in increased exposure to the pollutants through dermal and non-dietary ingestion routes . The median concentrations in the National Health and Nutrition Examination Survey , a population based sample, collected from 1999 to 2000 were 0.30 and 0.26 ug/g creatinine for children and adults , respectively, and only increased slightly to 0.33 and 0.30 ug/g creatine for children and adults, respectively, in samples collected from 2001 to 2002 . Median urinary 3PBA concentrations of NHANES samples collected from 2007 to 2008 increased a bit more to 0.42 and 0.38 ug/g creatinine for children and adults, respectively . In the Children’s Total Exposure to Persistent Pesticides 2000 to 2001 study, a population based sample of preschool children living in Ohio, the median level was 0.32 ug/g creatinine for children aged 1–5 years . The 2004 Casa y Campo study, a community-based project aiming to reduce pesticide exposure among farm workers and their families in eastern North Carolina, reported median concentrations of 3PBA in children aged 1–6 years of 0.15 ug/g creatinine .