Measurements were made over a two-day period at each home, “during which four 12-h indoor, two 24-h outdoor, and two 12-h personal samples were collected” using the system described in Koutrakis et al.Geometric mean for fine-particle strong acidity were as follows: outdoors = 77 , personal = 43 , and indoor = 14 . The authors reported that, “H+ was neutralized by NH3 present inside homes.”They specifically found that levels were lower in air-conditioned homes than non-air-conditioned homes and that NH3 levels in the air-conditioned homes were “significantly higher than in non-air-conditioned homes.” Importantly, the authors also found that “both outdoor and indoor H+ concentrations were poor estimators of personal exposure.”Sampling in State College was undertaken in the summer of 1991.Measurements during 12-h daytime periods were acquired for 47 children living in nonsmoking households, about half with air-conditioning. For each child and home, indoor samples were collected during five daytime periods. Corresponding outdoor measurements were made at a single site. Geometric mean for fine-particle strong acidity were as follows: outdoors = 72 , personal = 18 , indoor = 9 . The authors used the data to validate a model for estimating personal exposure that was developed from the Uniontown data, concluding that “predicted personal exposures for … H+ were in excellent agreement with measured personal exposures.”Data from the State College study were used again in Suh et al.Whereas the first paper in this pair focused on developing and validating an exposure model, the second paper was more concerned with factors influencing indoor concentrations. In the second paper, cannabis grow facility layout the reported geometric mean of indoor H+ concentrations for daytime samples was 9.7 nmol/m3 . The small discrepancy from reporting in the earlier paper may be related to the number of samples included in the analysis: in 1994 versus in 1993.

In exploring influencing factors, the authors found that, “the accumulation of NH3 indoors was … the primary determinant of indoor H+ … levels.”We identified only one study that reports measurements of indoor aerosol strong acidity outside the United States. Chan et al. used the same sampling system described by Koutrakis et al. to measure indoor and outdoor levels of aerosol strong acidity during winter of 1993 in Taipei. The report indicates, albeit with ambiguity, that indoor monitoring was conducted in children’s homes: “We monitored 2 days a week in four outdoor sites near the residence of 18 asthmatic children.”Across 101 total indoor samples, the mean ± standard deviation H+ concentration was 6.0 ± 13.1 nmol/m3 , as compared to 4.6 ± 11.6 nmol/m3 for the 39 outdoor samples. The indoor/outdoor ratio is summarized to have a geometric mean of 1.24 . Waldman et al. provided a review of the state of knowledge about “human exposures to particle strong acidity” .Their assessment found that, “where appreciable PSA exists, virtually all exposures occur in the warmer months, and the highest PSA levels are specifically associated with summertime, regional stagnation periods.” They went on to state that, “A number of new studies have shown that the effect of the indoors on human exposures to PSA is entirely protective. That is, there are rarely important sources indoors, and most factors affecting the indoor air quality lead to attenuation of PSA levels.”Although reasonable, we would judge that these and other conclusions in the review by Waldman et al. are stated with too much certainty, given the limited empirical foundation on which they are based.In the past quarter century, there has only been one further study132 to have reported broadly on indoor aerosol strong acidity. Measurements were made of fine-particle strong acidity, again using the sampling system described by Koutrakis et al.The study included 281 homes, with 58 sampled during summer and in winter, in each case for a single 24-h period. All homes were nonsmoking. The summary results for fine-particle associated H+ concentrations are reported in Table 24. Comparing the wintertime means, kerosene heater use is seen as a possible contributor to indoor H+ concentrations, although not strongly so. Summertime indoor levels are higher than wintertime indoor levels, probably because of the much higher outdoor concentrations during the summer months.

The air-conditioned homes exhibit moderately lower indoor H+ concentrations than non-air-conditioned homes, a finding consistent with prior studies and with the lower air-exchange rates and higher NH3 levels in the air-conditioned homes in this study. The authors expressed an important caution about the data for homes with kerosene heat: “The present study did not measure the elevated residential H+ concentrations associated with kerosene heater use that were predicted by the chamber studies. A comparison of indoor winter samples using acid-doped Teflon filters and non-doped Teflon filters in kerosene-heater and non-kerosene-heater homes suggested that substantial amounts of collected strong acidity in homes with kerosene heater use may be neutralized on the Teflon filter in the denuder system used to collect particle acid. The mechanism for this possible neutralization is suspected to be denuder breakthrough of ammonia.”They went on to state that “Occupants in homes using kerosene heaters are likely to experience peak exposures to PM2.5 and SO4 2- and possibly H+ in excess of levels typically experienced outdoors during the summer months.”We identified six major papers that have used epidemiological approaches to assess the relationship between particle strong acidity and adverse health effects. Here, we quote key findings from these studies. Worth noting is that only one includes any explicit consideration of indoor environmental conditions as an exposure modifying factor. In all other cases, the exposure indicators are based directly on outdoor monitoring results. Ostro et al. examined potential associations between acidic aerosols and respiratory symptoms among asthmatics in Denver, Colorado. They reported that, “airborne H+ was found to be significantly associated with several indicators of asthma status, including moderate or severe cough and shortness of breath.” As a caution, though, they report several shortcomings associated with their efforts to measure H+ and so relied upon a combination of measured and imputed values. Dockery et al. investigated the relationships among total daily mortality and a suite of air pollution indicators for St. Louis and counties in eastern Tennessee near Kingston and Harriman. They found that total mortality was most strongly associated with the PM10 mass concentrations and concluded that,indoor grow shelves “these data suggest that the acidity of particles is not as important in associations with daily mortality as the mass concentrations of particles.” Thurston et al. investigated associations between air pollution indicators and daily hospital admissions for respiratory causes for Toronto, Ontario, and Buffalo, NY.

The monitoring period focused on summertime months of July and August. Regarding respiratory admissions on the most polluted days, they concluded that “the relative risk estimated from the highest H+ day … was 1.50 ± 0.25 in Toronto and 1.47 ± 0.16 in Buffalo.” Dockery et al. utilized data from the large monitoring effort summarized in Table 22 to investigate air pollution factors that are associated with respiratory symptoms in children across North America. As noted in the introductory section, they found that “Children living in the community with the highest levels of particle strong acidity were significantly more likely … to report at least one episode of bronchitis in the past year compared to children living in the least-polluted community.” The only other association of note was between fine-particle sulfate and bronchitis. Raizenne et al. utilized the same pollutant measurement data to explore the relationship between pulmonary function in children and air pollution. They reported that “a 52 nmol/m3 in annual mean particle strong acidity was associated with a 3.5% … decrement in adjusted FVC [forced vital capacity] and a 3.1% … decrement in adjusted FEV1.0 [forced expiratory volume in 1s].” They concluded that the data “suggest that long-term exposure to ambient particle strong acidity may have a deleterious effect on lung growth, development, and function.” Gwynn et al. used a 2.5-y record of daily measurements of fineparticle H+ and sulfate sampled outdoors in Buffalo, NY, to explore associations with “respiratory, circulatory, and total daily mortality and hospital admissions.” The overall mean H+ concentration in this dataset was 36 nmol/m3 , with an interquartile range of 15-42 nmol/m3 . The authors reported that “H+ and SO4 2- demonstrated the most coherent associations with both respiratory hospital admissions … and respiratory mortality.” They concluded that “the associations demonstrated in this study support the need for further investigations into the potential health effects of acidic aerosols.” Amines can be viewed as ammonia molecules where one or more of the hydrogen atoms have been replaced by an organic group. Here are some examples: monomethyl amine, NH2; dimethyl amine, NH2; and trimethyl amine, N3. Amines can also be formed when a hydrogen on ammonia is replaced by an inorganic group. In this category, as discussed in §3.5.2, are the chloroamines: monochloramine ; dichloamine ; and trichloramine . Amino acids are a subgroup of organic amines in which one of the hydrogens has been replaced by an organic substituent that contains a carboxyl functional group . Amino acids are numerous. Among the species anticipated to be present indoors are those emitted by humans, especially in their sweat. There are 22 “human” amino acids, and these have the general formula H2NCHRCOOH , where the C attached to the N-atom is referred to as the primary carbon, and the R-group is referred to as the “side chain.” The side chain influences the pH and water solubility of an amino acid, 384 making it a weak acid, a weak base, a hydrophile , or a hydrophobe . Amines are common constituents of outdoor air in both gas and particle phases. The occurrence, chemistry, thermodynamic properties, and toxicity of amines in outdoor air have been reviewed in three articles by Wexler and colleagues.The first of these focuses on sources, fluxes and dynamics.

That review includes a table summarizing sources for more than 150 amines identified in the atmosphere and another table that lists concentrations of amines measured in outdoor air at different sampling sites. Yao et al. used a high-resolution time-of-flight chemical ionization mass spectrometer to make continuous measurements of C1-C6 amines in Shanghai during the summer of 2015. The average concentrations for the C1-C6 amines were 16±6, 40±14, 1.1±0.6, 15±8, 3.3±3.7, and 3.5±2.2 ppt, respectively. The C1-, C2-, and C4-amines were the most abundant, with concentrations of C2-amines as high as 130 ppt. These measurements seem to be representative of outdoor aliphatic amines in the continental troposphere: reported concentrations are typically in the range of single digits to tens of ppt. Concentrations of outdoor aliphatic amines tend to be roughly three orders of magnitude smaller than that of outdoor ammonia. Concentration of aromatic amines are more variable and tend to be elevated near industrial sites.Amines are being considered as active reagents with large-scale use in potential carbon capture applications for power plants. Such utilization could result in significant local discharges of amines to the atmosphere. Nielsen et al. have examined the atmospheric chemistry and environmental impact of ethylamine, diethylamine and triethylamine emitted from such carbon capture and storage operations. Amines are found in airborne particles. Although the lower molecular weight amines are highly volatile, their large water solubility means that they often are present in the liquid water associated with particles. For example, measurements in Ontario, Canada found that dimethylamine and the sum of trimethylamine and diethylamine were present in airborne particles at 0.5-4 ng m−3 , while these same amines were present in the gas-phase at levels of 1- 10 ppt. Higher molecular weight amines have low vapor pressures, large octanol-air partition coefficients and strongly partition to airborne particles.These compounds have been identified in atmospheric particles, precipitation, and fog water collected over land and marine surfaces. Ge et al. tabulated 32 amino acids that have been identified in 12 different studies of atmospheric particles, rain water and fog water. Arginine, glutamic acid, glycine, serine and valine were identified in all of the studies; alanine was identified in 11 of the 12 studies. In some cases, the identified species included those present in proteins and peptides, as well as “free” amino acids.