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.