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.