As noted, the pH of sorbing surfaces can influence the capacity for nicotine and other chemically basic reduced-nitrogen constituents of third hand smoke . Spectroscopic measurements indicate that sorbed nicotine and amines are present on surfaces primarily as the monoprotonated species rather than the neutral species, consistent with their basicity. The amount of nicotine on a surface is relevant to health concerns, because, among other reasons, sorbed nicotine can subsequently react with indoor nitrous acid to generate carcinogenic nitrosoamines that would otherwise not be present. It can also react with ozone, with a half-life of ~ 6 days at 40 ppb O3, to generate various oxidation products including formaldehyde, N-methylformamide, nicotinaldehyde, cotinine, myosmine, and nicotyrine. Given that pH plays a significant role in nicotine’s sorption to surfaces, a related issue for future study is how the reactivity of non-ionized nicotine compares to that of monoprotonated nicotine.Despite their importance, indoor surfaces and interfaces are poorly defined, especially porous materials such as wood, gypsum board, paint films, vinyl, and carpets. While there is a large body of literature addressing chemistry and catalysis on ideal surfaces, there is a dearth of such information for real-world surfaces. Hence, the information summarized in this section is not as strongly grounded in physical science as that in the previous sections of this review. Despite this limitation, we aim to provide the reader with a clear sense of what is currently known and call out areas that warrant further investigation.Indoor surfaces influence the concentrations, dynamic behaviors, and fates of indoor acids and bases. Gas-phase acids and bases partition to surfaces; acidic and basic constituents of airborne particles deposit on surfaces; acid-base chemistry occurs on surfaces. When we speak of surfaces, we are referring to the exposed surfaces of building materials,hydroponic stands coatings and furnishings, as well as surfaces within these materials that are accessible to indoor air via relatively rapid mass transport.

We include the air-surface interface of bulk water and organic films. Indoor surfaces should be understood to have a third dimension, i.e. a thickness that is generally much smaller than the areal dimensions but may be much larger than molecular scale. Scientifically, the extent of surface thicknesses that can interact meaningfully with indoor air composition remains not well resolved. It certainly varies with material properties, such as porosity, permeability, and viscosity. The thickness also varies with the time scales of concern, as the time needed for diffusive transport through a thin layer of a homogeneous substance scales with the inverse square of the layer’s thickness. Near one end of the range of possibilities, an organic film on an impermeable indoor surface with a thicknessof ~50 nm would likely be fully accessible to interact with gaseous species without meaningful transport restrictions. A permeable and porous paint layer of 50-100 µm thickness might also be substantially accessible. On the other hand, the materials that comprise gypsum wallboard, with typical overall thickness of 13 mm, might not be fully accessible to interact with gaseous species indoors because of lengthy transport times, even though the material is porous and somewhat permeable. For low-porosity and highly impermeable materials, such as tile and glass, the scale of interaction of gaseous species with indoor surfaces may only extend through a few molecules thickness into the surface because of the slow molecular diffusivity into such solids. In a typical room, indoor surfaces comprise floor, walls, ceiling and furnishings. Through air exchange with hidden spaces, other materials such as wood framing and insulation may also influence indoor air pollutant dynamic behavior. The surface in contact with room air may differ from the underlying material that constitutes the bulk of the floor, walls or ceiling. Wood floors are frequently varnished; concrete floors are often covered by tiles or synthetic flooring , and synthetic floors may be polished, waxed or coated with a polymer. Some floors are partially or completely covered with carpeting. Walls are commonly painted or papered. In China, walls are often “limed,” i.e. coated with layers of aqueous Ca2. External walls have windows, which may have adjustable coverings, such as blinds, shades or drapery. Ceilings may be painted or may be finished with ceiling tiles.

Occupants also contribute to indoor surfaces with their clothing, skin, and hair.An important feature of indoor environments is the high ratio of surface area to volume of air in contact with those surfaces. Surface-to-volume ratios are orders of magnitude larger indoors than outdoors. Hence, processes that are impacted by surfaces are of much greater consequence indoors than outdoors. Two moderate-scale studies plus several smaller ones have reported surveyed surface-to-volume ratios. Hodgson et al. measured S/V in 33 rooms in nine residences in San Francisco, CA. All objects with a surface area > 300 cm2 were included in these surveys. Surface areas were based on shape and dimensions, but did not attempt to adjust for fleeciness, roughness or porosity. The average ± standard deviation S/V values for all rooms was 3.6 ± 1.0 m2 m-3 . Bathrooms averaged 4.9 ± 0.3 m2 m-3 ; bedrooms/offices averaged 3.7 ± 0.9 m2 m-3; and common rooms averaged 2.8 ± 0.3 m2 m-3 . More recently, Manuja et al. measured S/V ratios in ten bedrooms, nine kitchens and three offices in Blacksburg, VA. Including contents, the average ± standard deviation S/V values for all rooms was 3.2 ± 1.2 m2 m-3; offices averaged 3.6 ± 0.4 m2 m-3 ; bedrooms 3.0 ± 0.4 m2 m-3; and kitchens 3.2 ± 1.8 m2 m-3. These two studies considered only macroscopic surface area. Neither attempted to account for the additional area associated with rough or porous surfaces . Microscopic surface area is anticipated to be much larger than these reported S/V values. As one illustration of the scale of effect that might be expected, Morrison and Nazaroff reported that the microscopic surface area of carpet samples exceeded the floor area covered by factors of 30 and 33 for two commercial loop carpets and by factors of 46 and 66 for two residential, cut-pile carpets.483The surface area of indoor airborne particles contributes negligibly to total indoor surface area. Consider a 30 m3 room with a total superficial surface area of 95 m2. An extensive dataset for outdoor air pollution collected in the Ruhr Valley, Germany,grow table found a median PM10 concentration of 20 µg/m3 and a median lung-deposited particle surface area concentration of 36 µm2 /cm3 . 484 Using this surface area concentration as a magnitude estimate for indoor environments, the corresponding total particle-associated surface area in the 30 m3 room would be ~10-3 m2, or about 5 orders of magnitude smaller than the superficial area associated with the fixed interior surfaces.

Two surveys of indoor surface materials important for moisture uptake and humidity buffering were mentioned in §2.4.In addition to surface-to-volume ratios, Hodgson et al. and Manuja et al. catalogued the different materials that constituted the surfaces in their surveyed environments. These material descriptions were used by Hodgson et al.: metal, glass, ceramic/porcelain/tile, finished wood, unfinished wood, painted wood, PVC, other plastic, painted/papered plaster and wallboard, thin fabrics, upholstery/carpet, and paper. Finished/painted surfaces accounted for a substantial fraction of total surface area in all room types: finished wood with median contributions of 0.54 m2 m-3 in common areas, 0.73 m2 m-3 in bedroom/offices, and 0.26 m2 m-3 in bathrooms; painted wood with median contributions of 0.38 m2 m-3 in common areas, 0.34 m2 m-3 in bedroom/offices, and 0.44 m2 m-3 in bathrooms; painted/papered plaster and wallboard accounted for a substantial fraction of total surface area in all room types, with median contributions of 1 m2 m-3 in common areas, 1.2 m2 m-3 in bedroom/offices, and 1.6 m2 m-3 in bathrooms. Impermeable surfaces were extensive in bathrooms, with median S/V for metal, glass, ceramic, porcelain and tile summing to 1.3 m2 m-3 . Such impermeable surfaces were less abundant in common areas and bedrooms with median S/V values of 0.16 m2 m-3 . In all room types, vinyl and other plastic surfaces had median S/V values of 0.38-0.98 m2 m-3 , whereas textiles and fibrous materials had median S/V values of 0.45-0.55 m2 m-3 . Manuja et al. used somewhat different material categories: cardboard, concrete, fabric/fiber, glass, metal, paint, paper, plastic, wood , or other. The dominant material was paint covered surfaces , chiefly walls and ceilings, followed by stained wood . Fabric/fiber surfaces were abundant in bedrooms; plastic and metal surfaces were abundant in offices and kitchens. Glass surfaces comprised a small proportion of total surface area. Exposed concrete contributed slightly to indoor surfaces in kitchens and was barely present in bedrooms and offices. It is noteworthy that together painted surfaces and stained/finished-wood surfaces accounted for almost two-thirds of the surfaces in the rooms evaluated in these two studies. The substrates beneath the paint are often gypsum wallboard or pressed wood composites . In these cases, both the paint and the substrate are somewhat permeable, suggesting that painted surfaces and stained wood could serve as substantial sinks for gas-phase species that interact strongly with their chemical constituents. As summarized in §2, at 50% RH the moisture content of painted gypsum board is 0.5-1.1%, while that of wood is notably higher, at 8- 10%. The abundance of such permeable surfaces with significant moisture content may help explain the large indoor reservoirs that are seen for nitrous, formic and acetic acid, as discussed below. Human occupants can contribute meaningfully to the total surface area of the rooms they occupy, and acid-base chemistry can occur on exposed skin, hair and clothing.

A typical adult has a total body surface area of approximately 2 m2 . If two adults occupy a 30-m3 room with an S/V of 3.5 m2 m-3 , the human surfaces contribute about 4 m2 to the total surface area. Skin and hair are covered by surface lipids, about 25% of which are organic acids. Human skin has a pH in the range of 4.5 to 6. Bodies are most commonly clothed; certain fabrics in clothing can have substantial moisture content at typical indoor humidity. For example, at 50% RH, the equilibrium moisture contents of nylon, cotton and wool are approximately 3%, 5%, and 10%, respectively . As discussed in §2, water sorbs to indoor surfaces. When impermeable surfaces have water coverage larger than about five equivalent monolayers, the nature of the surface interacting with room air is closer to that of water than that of the underlying substrate. Given the importance of surface interactions influencing indoor air constituents, including gaseous acids and bases, the limited available evidence from surveys of indoor surface materials is striking. Surveys similar to those undertaken by Hodgson et al.23 and Manuja et al. are needed in homes, schools and offices in other US cities and in other countries. It would be especially valuable to have results from such surveys conducted in different cultures with large populations and high population densities, such as China and India.All surfaces become soiled. Three processes are primarily responsible for soiling: contact transfer by occupants , partitioning of semivolatile species from the gas phase, and particle deposition. Whereas partitioning and particle deposition impact all exposed surfaces, contact transfer only influences surfaces that are commonly touched by occupants . As a consequence of contact, chemicals are transferred from a surface to occupants, and also from occupants to surfaces. Fingerprints are a prime example of skin oils left behind on a surface that has been touched. Indeed, Zhou et al. relied on human touch to transfer skin oils to glass capillaries prior to investigating their oxidation by ozone. Experimental measurements have provided information about film growth and particle deposition on impermeable surfaces. Based on results from such studies, coupled with modeling, we can estimate approximately how long a surface must be exposed to indoor air before soiling has substantially altered the nature of its surface. Evidence is emerging that soiling imposes a degree of commonality among indoor surfaces that can be quite different from one another when clean.Absorption of semi-volatile organics to an impermeable surface requires a few layers of organic species on the surface to kick-start the partitioning process. How this might occur has been considered by Eichler et al., but a full description of the processes that initiate absorptive partitioning on indoor surfaces remains to be elucidated.

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.

In the case of acetic acid, for example, the peroccupant emissions rate in the classroom was about 0.3 mg/h. That value, if applied to the two occupants of the house studied by Liu et al., would account for less than 10% of the inferred total emissions rate of 12 mg/h and 20 mg/h . Similarly, the per-person emission rate from the classroom study for formic acid, 0.05 mg/h, suggests that occupant associated emissions are only a small portion of the total indoor generation rates of 2.3 mg/h and 4 mg/h determined in the study house. An interesting and important lesson can be extracted from the data in Table 16, when considered in the context of how physiological response varies across compounds in a homologous series. Cometto-Muñiz et al. measured the odor thresholds for five carboxylic acids. The results spanned 5 orders of magnitude from formic acid to octanoic acid . The reported average concentrations of formic acid and octanoic acid in Table 16 differ by about two orders of magnitude. Here is a key point: focusing on the most abundant organic compounds, which naturally emerges from chemical analyses, can readily mask the prevalence of compounds that are more important with regard to human physiological response. In this particular instance, the measured average concentration of formic acid is a few orders of magnitude below its odor threshold. However, the much smaller measured concentration of octanoic acid exceeds its odor threshold by an order of magnitude. Several studies have assessed carboxylic acid emissions from woods, emphasizing acetic acid as a prominent species. For example, Risholm-Sundman et al. reported that “some hardwoods give a high emission of acetic acid.” The highest reported emissions of acetic acid in their study were from cherry and oak. Manninen et al. found that the temperature history of the wood mattered, writing “in the emissions of heat-treated wood,trim bin tray the most abundant individual compounds, 2- furancarboxaldehyde, acetic acid and 2-propanone, made up about 60% of the total VOC emission. … None of these compounds was found in the VOC emission from air-dried wood.”

Gibson and Watt272 stated that, “acetic acid is known to emit from all natural woods with hardwoods, e.g. oak, being thought to emit the highest concentrations of acetic acid …”. They found that emissions were sensitive to temperature, being much higher at 45 °C than at 20 °C, and also to humidity, with lower emissions for drier conditions. Carboxylic acids can be generated through the oxidative decomposition of higher molecular weight fatty acids. Linoleic acid is a prominent ingredient of linoleum, a common flooring material. Jensen et al. modeled the concentrations of propanoic acid utilizing emission measurements from a linoleum flooring sample. They predicted an indoor concentration of 56 µg/m3 one month after installation, only 2´ below the odor threshold. Other processes in atmospheric oxidative chemistry also can generate formic and acetic acids. For example, summed over the global atmosphere, the dominant sources of formic and acetic acids are believed to be “photochemical oxidation of biogenic organic compounds, in particular isoprene.” Zhang et al. conducted experiments in a Teflon test chamber designed to explore the production of formic and acetic acid from oxidative chemistry. In that work, ozonation of limonene using indoor-relevant concentrations was found to generate acetic acid. Formic acid was produced in each of the three systems tested: ozonation of styrene, of limonene, and of 4- vinylcyclohexene, respectively. Destaillats et al. quantified formic and acetic acid levels in chamber studies of the ozonation of three household consumer products: a pine-oil based cleaner, an orange-oil based degreaser, and a plug-in air freshener. Median reported concentrations in 11 experiments were 14 ppb for formic acid and 22 ppb for acetic acid.Interior paints can be a source of carboxylic acid emissions. Reiss et al. studied ozone reactions with latex paints. They did not find formic and acetic acid to be generated by ozone reactions. However, they did report that both compounds off-gassed from the latex paints themselves. They also found that the rates of emissions of these compounds were higher at higher relative humidity.

Investigating finishing materials that might be used for preserving cultural artifacts, Schieweck and Bock reported that “low-VOC” and “zero-VOC” paints “released heightened acetic acid levels and are therefore not favored for the use in sensitive environments.” Incomplete combustion and/or high-temperature volatilization from fuels can be another source of carboxylic acids. For example, Kuo et al. determined an emissions factor for acetic acid from incense use to be 840 ± 520 µg per g of incense burned, based on experiments with four popular brands. Christian et al. measured emission factors of formic acid and acetic acid from biomass combustion. Considering open wood cooking fires, they reported 0.25 ± 0.12 g of formic acid to be emitted per kg of wood burned. The corresponding emission factor for acetic acid was 1.8 ± 1.3 g/kg. Let’s next consider the phase state of formic and acetic acid. In the presence of condensed water, there are three potentially important states: gaseous, aqueous and undissociated, and aqueous in the form of the conjugate base . As we have already described, the partitioning among these three states depends on two key properties of the volatile acid: Henry’s law constant and the acid-dissociation constant . Influential features of the indoor environment include the relative abundance of condensedphase water and the pH of that water. Factors influencing the pH of indoor condensed water include the abundances of all of the indoor air acids and bases plus the properties of any material substrate in contact with the water. The presence of any gas-phase carboxylic acid would tend to acidify condensed water. For the present analysis, let’s assume that the condensed-water pH is externally regulated, independent of the influence of carboxylic acids. That could apply, for example, in the limit of a small abundance of the carboxylic acids. As described in §2.1, liquid water abundance can be quantified as a volume fraction, with dimensions liters of water per m3 of air. We use the symbol L* to signify an equivalent volume fraction that is chemically equilibrated with indoor air. We restrict analysis here to fixed common indoor conditions of pressure and temperature . In §3, we presented equations describing equilibrium quantitative partitioning of a monoprotic acid considering the three phase states.

Equation describes the fraction of the total abundance that is in the gas phase. Figure 11 displays the results for formic acid and acetic acid ,pollen trim tray showing gas fraction in relation to the liquid water volume fraction for four different values of pH .The thermodynamic properties used in these calculations are reported in Table 14. These plots show that the overall behavior of formic and acetic acids is qualitatively similar with regard to phase partitioning between air and water. Even a small amount of condensed water can be a major sink for these carboxylic acids if the water is maintained by external factors to have a high pH . Conversely, at a low pH , most of these carboxylic acids will remain gaseous provided that the equilibrated liquid water abundance remains small . In the event that the condensed water is relatively abundant , there is the opportunity for substantial partitioning to water, even for acidic pH conditions.Because of the material damage risks posed, many studies of carboxylic acids have been conducted in museums and archives. The nature of the specific risks from formic and acetic acid in damaging cultural artifacts is well described by Brimblecombe and Grossi, including“Byne’s disease,” which refers to efflorescence of calcareous materials owing to their dissolution upon exposure to organic acids. Prosek et al. provide a useful introductory overview of corrosion risks associated with volatile carboxylic acids and also describe the development of a direct monitor “to assess small changes in air corrosivity in real time.” Graedel described the corrosive nature of organic acid vapors for lead, indicating that “acetic acid [is] five to ten times as aggressive as formic acid.” In an interesting application of corrosion concerns, Niklasson et al. reported that “high concentrations of acetic and formic acid vapours are present in the wind system of the corroded [church pipe] organs. … The main source of acetic acid is the wood from which the wind system is built. In contrast, formic acid is generated in the church environment outside the wind system.” Reinforcing the idea of wood as an important emission source, Kontozova-Deutsch et al. measured levels up to 450 µg/m3 of formic acid and up to 1050 µg/m3 of acetic acid in enclosed showcases at the Metropolitan Museum of Art in New York. Much lower levels were found in the galleries. Concern about material degradation risks posed by organic acids has spurred efforts in the development of novel control technologies. For example, Dedecker et al. have developed a metal-organic framework for removing “low concentrations of acetic acid from indoor air at museums.” Among the challenges in sorbent performance that MOF technology has the potential to overcome is poor selectivity for polar compounds compared to the much more abundant water vapor.Hodgson et al. assessed the performance of an air cleaner utilizing ultraviolet photochemical oxidation .

They reported a strong caution: “formaldehyde, acetaldehyde, acetone, formic acid and acetic acid were produced … due to incomplete mineralization of common VOCs.” Truffier-Boutry et al. assessed photocatalytic paints and found “that the degradation of the organic matrix [of the paint itself] leads to the release of organic compounds into the air….” This evidence supports a finding that partial oxidation of organic molecules can generate formic acid and acetic acid at levels of potential concern for indoor environmental quality. In contrast to formic and acetic acid, which have been extensively studied indoors, there is little published work reporting on the higher molecular weight carboxylic acids in indoor environments. However, absence of evidence isn’t the same as evidence of absence. The limited available information does point toward the potential for these compounds to be of interest indoors, as highlighted by the following observations. Liu et al.69 characterized the organic matter found in films extracted from interior surfaces of the windows of various building types, including a residence, a restaurant, and an office. They found that monocarboxylic acids dominated among polar compounds, with C11-C31 monoacid densities in the range 6.5-100 µg m-2. Fang et al.309 reported on chemical characterization of dust extracts collected from homes, a gymnastics studio, and office environments. In the portion of dust extracts most associated with agonism of human peroxisome proliferator-activated nuclear receptor gamma, “fatty acids … including oleic acid, stearic acid, palmitic acid and myristic acid, were the primary chemicals identified.” Higher molecular weight n-alkanoic carboxylic acids, especially palmitic and stearic acids, have been identified as important markers of the impact of cooking emissions on urban air quality. For example, in an atmospheric monitoring study in the Los Angeles area, carboxylic acids were quantifiable contributors to fine particulate matter. In that study, monthly average values of palmitic acid in atmospheric fine PM were in the range 0.10-0.25 µg/m3. In a study of atmospheric fine particulate matter in Beijing, averaged airborne concentrations were reported for lauric , myristic , palmitic , and stearic acid . Several studies have reported quantitative emission factors for particle-phase carboxylic acids from commercial or institutional-scale cooking activities, including western-style meat cooking, stir-frying and deep-frying vegetables with seed oils, and various Chinese styles of cooking. Palmitic and stearic acids are prominently featured among the emitted chemicals in all of these studies. Candle burning has also been characterized as a source of particle-phase carboxylic acid emissions. 316 Emissions from paraffin candle wax were predominantly palmitic and stearic acid, as a “result of unburned wax volatilization.”For beeswax candles, the most prominent emissions of particle phase n-alkanoic carboxylic acids were palmitic and lignoceric acid . A few studies have reported on the indoor carboxylic acid abundance in “quasi-ultrafine” and fine particulate matter. Arhami et al. studied the abundance and sources of organic compounds in quasi-UF PM in four retirement homes in the Los Angeles basin. They found that the “n-alkanoic acids were likely to be influenced by indoor sources.” They also reported that, for outdoor air, “hexadecanoic, octadecanoic, and phthalic acids were the most dominant measured acids in quasi-UF PM.”

In the presence of liquid water, each molecule of SO2 that is converted to sulfuric acid can liberate up to two aqueous H+ ions along with the sulfate ion . When considered per atom of sulfur, the net effect of the oxidation reaction occurring in the presence of liquid water is to change the most preferred state from gaseous to aqueous , with the associated liberation of H+ ions. Guo et al. studied the pH of fine-mode particulate matter in the southeastern United States. They found mean pH at four study sites to be in the range 1.1-1.3 in summer and at two study sites to be 1.8 and 2.2 in winter. The authors noted that “in the southeastern USA, inorganic ions [in fine-mode aerosol] are currently dominated by sulfate and ammonium.”Figure 7 illustrates the influence that the oxidation of S to S could have on pH of condensed-phase water indoors. For example, with 1 ppb of SO2 in an indoor environment , water would have an equilibrium pH of 5.37. Given an assumed liquid water content of 1 L per 400 m3 of interior volume , converting half of that SO2 to sulfuric acid that is fully transferred to the water would lower the pH to 4.77. Complete oxidation would further reduce the pH to 4.49. Previous discussion has summarized some of the evidence indicating that sulfur oxidation reactions may occur on certain indoor surfaces. Conversely, there is not strong evidence to suggest that significant gasphase oxidation of S to S occurs indoors. In indoor air, whereas SO2 would primarily exist as a gas, indoor sulfate is predominantly in airborne particles. Like SO2, evidence supports a view that, in most circumstances, the principal source of indoor sulfate is supply from outdoor air via ventilation. Table 9 provides a summary of measurement results from one major field campaign investigating indoor and outdoor sulfate levels in residences. In that study, the use of unvented kerosene space heaters was associated with an indoor sulfate concentration several times higher than in homes without unvented kerosene heaters.In a source-apportionment study for fine particles and associated elements in residences in New York state, Koutrakis et al.reported that, “for homes with kerosene heaters, approximately 40-50% of the sulfur was found to be contributed by kerosene burning.” Ruiz et al.also reported substantially elevated indoor concentrations of fine-particle sulfate and SO2 in homes in Santiago, Chile that had kerosene heaters.

In another study,commercial greenhouse supplies “increased indoor concentrations of sulfates were found to be associated with smoking and also with gas stoves.”The associated sulfate increase was 0.046 µg/m3 per cigarette for smoking in a fully air-conditioned house and 1.1 µg/m3 from use of a gas stove. In the case of smoking, the surprising origin of sulfur was inferred to be the matches used to light cigarettes, rather than the cigarettes themselves. For gas cooking, a likely source is sulfur-containing odorants, such as methyl mercaptan , added to the fuel for safety.Wallace and Williams reported measurements of fine-particle sulfur for 36 households in Research Triangle Park, NC. They monitored each home for seven consecutive days in each of four seasons, relying on 24-h average sample results. They concluded that “sulfur has few indoor sources” in the houses they studied. The average indoor to outdoor fine-particle sulfate ratios per household varied across the range 0.26 to 0.87 . With summer AC use, mean I/O ratio was 0.50 as compared with 0.62-0.63 for the other three seasons. Based on the reported means for 36 houses , the mean fine-particle sulfate levels were 3.4 µg/m3 indoors and 6.2 µg/m3 outdoors, with a corresponding average I/O ratio of 0.56.184 Besides ventilation, the major removal process for SO2 from indoor air is deposition onto interior surfaces, as parameterized using the deposition velocity and with its influence quantified by equation . The possibility that SO2 is also removed incidentally by aqueous scrubbing when air conditioning causes water condensation was discussed. For fine-particle sulfate, in addition to ventilation, there would generally be two important mechanisms to consider for removal from indoor air. These are deposition to indoor surfaces and active removal by particle filtration in the mechanical ventilation or central air handling system. Less common, but worth noting, would be removal by means of a portable recirculating air filter.The deposition of fine-particle sulfate to indoor surfaces has two important distinctions from the case of gaseous SO2. First, fine-mode particles can be assumed to adhere without limit to indoor surfaces that they contact. As a result, the rate of uptake of sulfate particles is purely mass-transport limited, whereas for SO2, both mass transport and surface chemistry could influence the overall rate. Second, fine mode particles are transported by diffusive processes much more slowly than are gas molecules. Consequently, the mass-transport limited deposition velocity of SO2 to indoor surfaces would be much larger than the deposition velocity of fine-mode particle sulfate. Overall empirical evidence suggests a somewhat larger deposition velocity for SO2 compared to fine particle sulfate, with the former increasing with increasing RH.

Sinclair et al.reported on studies of the concentrations and fates of ionic substances in telephone switching offices in Wichita, KS; Lubbock, TX; Newark, NJ; and Neenah, WI. The fine-mode sulfate deposition velocities at these four sites were in the range 0.004- 0.005 cm/s. Riley et al.modeled the indoor/outdoor relationship for fine particle sulfate for different prototypical building types. For two residential scenarios, the predicted I/O values were 0.44 for a continuously operating central air system and 0.95 with high levels of natural ventilation. For offices, with mechanical ventilation, the predicted ratios were 0.18 with a high efficiency particle filter and 0.72 when particle filtration efficiency was of a lower grade . All of the experimental evidence from field monitoring studies described thus far is based on time-integrated methods, with sampling typically conducted for a 24-h period followed by chemical analysis in the laboratory. The lack of finer-scale time resolution limits the ability to infer potentially important dynamic processes from the experimental evidence. During the past few years, aerosol mass spectrometry has begun to be utilized in studies of indoor environments.In a mixed-use university laboratory space in Philadelphia, PA, the median indoor sulfate mass in submicron particles was measured to be 0.92 µg/m3 , with a corresponding I/O ratio of 61%. In a classroom in the same university, the I/O ratio based on mean concentrations was measured to be 31% for summer and 33% for winter, with corresponding indoor mean concentrations of 0.43 µg/m3 and 0.28 µg/m3, respectively. In these studies, the researchers treat fine particle sulfate as a nonvolatile marker of the influence of outdoor particles on indoor concentrations. They compare the I/O ratio for other chemical components, including ammonium, nitrate, and organic molecules,cannabis dry rack to that of sulfur to make novel inferences about dynamic processes affecting indoor aerosol composition and concentrations.As is apparent from Table 12, indoor air nitric acid concentrations tend to be very low and, depending on the measurement method, are often indistinguishable from zero. Salmon et al. measured HNO3 concentrations at five museums in the Los Angeles area during summer and winter months. Mean seasonal concentrations ranged from < 0.04 to 0.6 ppb . The mean nitric acid concentration measured in two University of Essex buildings was 0.94 µg/m3 ; the corresponding outdoor level was 4.6 µg/m3 . In six Boston homes, the mean summer level was 0.84 ppb contrasted with 0.03 ppb for five homes in winter.

In a New Jersey daycare facility, nursing home, and home for the elderly, mean HNO3 concentrations were in the range of 0.2 to 0.4 ppb.For 229 12-h samples collected In 47 homes in State College PA, the geometric mean indoor HNO3 concentration was 0.2 ppb . Fischer et al.made outdoor and indoor measurements of nitric acid, with 30-minute temporal resolution, at an unoccupied home in Clovis, CA. Although the outdoor levels were as high as 3 ppb, and indoor NH4NO3 dissociation was an additional HNO3 source, the indoor HNO3 levels were normally lower than the uncertainty in the instrument offset . Although concentrations of nitric acid tend to be low indoors, its influence on pH could still be substantial. For example, the equilibrium pH of water exposed to 800 ppm of CO2 is 5.46. Water equilibrated with both 800 ppm CO2 and 0.1 ppb HNO3 would have a pH of 1.83; with 800 ppm CO2 and 0.5 ppb HNO3, equilibrated water would have a pH of 1.48. Ammonia often co-occurs with CO2 indoors. The equilibrium pH of water exposed to 800 ppm of CO2 and 20 ppb of NH3 is 7.12. Maintaining an abundance of 0.1 ppb of gaseous HNO3 added to this mix would decrease the equilibrium pH to 3.48, while sustained exposure to 0.5 ppb of HNO3 would decrease the equilibrium pH to 3.13.However, these properties also mean that the time required for nitric acid to equilibrate with bulk water becomes unrealistically large as the equivalent thickness of surface water increases. Consequently, equilibrium calculations involving gaseous nitric acid indoors should be regarded as suggestive rather than as quantitatively accurate.Gaseous nitric acid can react with gaseous ammonia, contributing ammonium nitrate to airborne particles. To a lesser extent, nitrous acid can be a precursor for nitrite salts in airborne particles. Table 13 summarizes results from selected studies that have measured indoor and outdoor concentrations of nitrate ions in airborne particles.

Only one study has reported measurements of nitrite levels in indoor airborne particles.In that work, average indoor winter concentrations of nitrite were roughly four times larger than summer concentrations . Interestingly, in both winter and summer, the I/O ratios were substantially larger than unity , indicating an indoor source for particulate nitrite in these homes.Several studies that have measured outdoor and indoor NO2 or HNO3 have simultaneously measured the levels of nitrate in outdoor and indoor particles.Indoor levels of particle associated nitrate are typically in the range of 1-10 nmol/m3 . The presence of unvented gas combustion appliances appears to have little influence on the indoor concentration of particulate nitrate.In a daycare facility and a nursing home, indoor particulate nitrate concentrations were higher than co-occurring outdoor levels, but in a home for the elderly, indoor levels were lower than outdoor levels.In their study of 47 homes in State College PA, Suh et al.measured indoor levels of particulate nitrate that were typically higher than co-occurring outdoor levels. They speculated that the reason for the higher levels of nitrate indoors was the HNO3-NH3 reaction. Conversely, dissociation of ammonium nitrate as particles are transported from outdoors to indoors is a recognized occurrence.153 Sinclair et al.found that there was a nitrate artifact with Teflon membrane filters used to sample fine and coarse mode airborne particles and, consequently, they did not report nitrate levels in their studies. This outcome occurred despite washing the filters prior to use. In hindsight, the phenomenon might have been caused by NH3/HNO3/NH4NO3 partitioning between air and filter surfaces. In the 1980s, Pitts et al., using differential optical absorption spectroscopy , identified and measured ppb levels of HONO in a mobile laboratory after injecting NO2 sufficient to establish low ppm levels. In a subsequent study, HONO levels were measured to be as high as ~ 50 ppb in a mobile home during periods when a gas-fired kitchen stove and kerosene- or propane-fueled space heaters were operated.In the early 1990s, Febo and Perrino measured elevated HONO concentrations in a residence in the suburbs of Rome and in automobile cabins. Since then, indoor concentrations of HONO have been measured in numerous studies, although not as many as for NO and NO2. This body of research has been summarized by Gligorovski and by Collins et al.Of note are studies in multiple homes that have been made using integrated measurements, sometimes with passive diffusion samplers for intervals as long as two weeks. For example, in ten Albuquerque, NM homes with gas cooking, Spengler et al. measured average HONO concentrations of 4.7 ± 2.3 ppb.They found a correlation between indoor concentrations of HONO and NO2, with the indoor HONO level between 5% and 15% of indoor NO2. During summer months in homes in Connecticut and Virginia, Leaderer et al. measured average HONO concentrations of 1.6 ± 2.1 ppb in air-conditioned homes and 3.5 ± 2.6 ppb in non-air-conditioned homes .

Liquid water can be a component of airborne particles. This feature is understood to be important in several atmospheric processes, including the roles of aerosols influencing climate, the phase partitioning of water-soluble organic compounds, and the formation of secondary organic aerosol. Liquid water in particles is prominent, even in the absence of clouds. “Liquid water is predicted to be the most abundant particle-phase species in the atmosphere, 2-3 times total aerosol dry mass globally.” Notwithstanding its influence on atmospheric physical and chemical processes, and despite its relative abundance compared to dry aerosol constituents, the condensed phase normally represents a small proportion of tropospheric water molecules. At a temperature of 20 °C and relative humidity of 50%, the mass concentration of water vapor is 8.4 g/m3 and. Outside of fog and clouds, the abundance of aerosol liquid water is commonly at least five orders of magnitude smaller, usually below 100 µg/m3 . Meng et al.used thermodynamic modeling combined with extensive year 1987 measurements of aerosol chemical characterization to estimate the liquid water content of PM2.5 and PM10 for three urban sites near Los Angeles, California, considering separately winter and summer seasons. Using sampling durations of 4-7 h, the median aerosol liquid water contents in PM10 were generally in the range 4-17 µg/m3. The 90th percentile values for PM10 by location and season ranged from 42 µg/m3 at Long Beach during summer to 143 µg/m3 at Long Beach during winter. Nguyen et al. applied thermodynamic modeling to estimate the aerosol liquid water from aerosol mass spectrometry data in several field campaigns. Note that the AMS mainly measures sub-micron particles and so would not capture completely the liquid water associated with PM2.5 or PM10. Nguyen et al. report that “campaign average ALW mass amounts are 12, 11, and 3 µg/m3 for urban, urban downwind, and rural sites, respectively.” Parworth et al. reported an average of 19 µg/m3 for the water content associated with PM2.5 for wintertime conditions in Fresno, California.

Diurnal variability produced lower values in the afternoon and higher values during overnight and early morning periods. Indoors,cannabis drying recent studies are starting to provide some information about aerosol liquid water and its potential significance. Water-soluble organic compounds and indoor aqueous chemistry is highlighted in the work of Duncan et al.They made the important observation that “even a 1 nm water film on indoor surfaces, a film consistent with simple water adsorption, will provide more than 1000 times the volume of liquid water as is found in aerosols in outdoor air .” Note that 3 µg/m3 of aerosol water, chemically equilibrated with air, provides a contribution to the liquid water content of only L* = 3 ´ 10-9 L m-3, considerably smaller than the range expected to prevail indoors or than the contributions of the other forms of water that we have highlighted in this review. DeCarlo et al. inferred an important role for aerosol liquid water in their study of third-hand tobacco smoke. They made an interesting and potentially important observation regarding the role of heating, ventilation and air-conditioning systems influencing water in particles: “In the summertime, warm air with varying amounts of water content is brought into the building, mixed with recirculated air, and conditioned to cooler temperatures … for the supply airstream. This process leads to deliquescence and significant uptake of water by aerosol particles, as RH values will increase to above 90% in the supply air …. Even with the subsequent decrease in RH of the rooms, all of the indoor aerosol will maintain the aqueous phase because the indoor RH does not drop low enough to drive off the water. … In the wintertime, the temperature gradient is reversed with colder, drier outdoor air drawn into the HVAC system mixed with recirculating air and heated to temperatures approaching 38 °C …. This process effectively effloresces the aerosol particles, drying them and resulting in the loss of the aqueous phase in the aerosol.” The first quantitative determination of aerosol liquid water indoors was recently reported by Avery et al.Their study site was a university classroom in Philadelphia, PA. They monitored chemical composition of sub-micron particles indoors and outdoors during both winter and summer periods, using aerosol mass spectrometry.

Aerosol liquid water content was then computed using a thermodynamic model. A key finding was much higher abundance of aerosol liquid water outdoors than indoors, during both summer and winter periods. “Aerosol liquid water in winter has an average outdoor and indoor concentration of 2.6 ± 3.6 µg m-3 outdoors and only 0.11 ± 0.06 µg m-3 indoors. In summer, the decrease in concentrations upon transport indoors is much smaller, and similar to aerosol species at 2.7 ± 2.5 µg m-3 outdoors and 0.53 ± 0.24 indoors.” Water is an important constituent in indoor environments for many reasons. Among these are the partitioning and dynamic behavior of acids and bases. As reviewed in this section, water is manifest indoors in several forms: as water vapor, in bulk condensed liquid, sorbed to interior materials, in surface films, and in particulate matter. The abundance of water vapor is large, on the order of grams per m3 , but the direct influence of water vapor on indoor acids and bases is small. Bulk condensed water can be as large in abundance as water vapor. Acids and bases can partition into bulk condensed water from the gas phase and undergo acid-base chemistry therein. The thermodynamics of this system are generally well understood, but much of the bulk water may not become equilibrated owing to mass-transport limitations. Sorbed water can also be abundant indoors at a scale comparable to water vapor. As described by sorption isotherms, the abundance of sorbed water tends to increase monotonically with increasing relative humidity under equilibrium conditions. However, equilibrium may not be consistently attained for water sorption in indoor environments. Furthermore, the properties of acids and bases in water sorbed to common indoor materials are largely not understood. Surface-film water and aerosol water are far less abundant than the other forms of indoor water; but, water in these forms is highly accessible to gaseous species. Hence, some important acid-base processes may be modulated to meaningful extents by water in these less abundant forms. In this major portion of the review, we describe the state of knowledge regarding specific acids and bases indoors, emphasizing species that can be airborne, either as gases or in the particle phase. We organize the material according to species or groups of species that share core chemical characteristics.

We consider in separate subsections inorganic acids and organic acids. Among the inorganic gaseous acids, we discuss carbon dioxide , sulfur oxides , nitrogen oxides , and chlorinated acids . Particle-phase strong acidity is described in §3.8. Among the organic acids, we discuss n-alkanoic monocarboxylic acids , as well as dicarboxylic, n-alkenoic acids, and several other organic acids . The most important airborne basic species is ammonia; it is the subject of §3.2. Amine bases other than ammonia along with amino acids are the subjects of §3.9. Nicotine, an important indoor base resulting from tobacco smoking and vaping, is the topic of §3.10. In reviewing the states-of-knowledge for acids and bases, we summarize information about indoor concentrations along with the sources and sinks that account for their abundance. We devote substantial attention to the key physicochemical properties that influence phase partitioning and fates indoors. We highlight key reasons for concerns about the presence of these species indoors,greenhouse benches including possible effects on human health and well being and also material damage concerns. Two thermodynamic properties consistently influence indoor dynamic behavior of acids : the water-air partitioning coefficient and the propensity to donate a proton in aqueous solution. Another important attribute, especially for organic compounds, is the tendency to partition into condensed-phase weakly polar organic matter. These properties are quantified through the Henry’s law constant, KH, the acidity constant, pKa , and the octanol-air partition coefficient, Koa.Human ammonia emissions occur from breath, skin, flatulence, urine and feces; rates are highly variable among individuals. Over time, microbes transform urea in urine and feces to NH3; hence, diapers and unflushed toilets also are NH3 sources. As reported in Lee and Longhurst, early estimates of human emission rates included 540 g NH3-N y-1 person-1 ; 250 g NH3-N y-1 person-1 ; and 1300 g NH3-N y-1 person-1 .Based on typical NH3 concentrations in blood , “alveolar blood-gas equilibration alone should lead to an NH3 level of 15-40 ppb in exhaled air.”Special experimental techniques are required to disentangle breath emissions from skin emissions. Larson et al. concluded from a series of clever breath sampling experiments that the NH3 concentration in exhaled breath “is determined largely by the last segment of the respiratory tract traversed.” When the last segment traversed was the mouth , the exhaled concentration spanned the range 40-740 ppb with a central tendency of about 240 ppb; when it was the nose , the exhaled concentration was 10-90 ppb with a central tendency of 35 ppb. The higher level in the mouth was partially attributed to bacterial decomposition of urea in saliva. Norwood et al. studied the influence of different oral hygiene regimes on NH3 in exhaled breath.

A distilled water rinse or tooth brushing followed by a water rinse had little effect on NH3 levels. In contrast, an acidic oral rinse reduced the concentration in exhaled breath by more than 90% in all volunteers; breath levels returned to 50% of initial value within an hour. The acidic rinse presumably lowers saliva pH, increasing the ratio of NH4 + /NH3 in saliva and thereby decreasing the fraction of NH3 that volatilizes to breath. Using a cavity ring-down spectrometer, Schmidt et al. measured concentrations of NH3 in breath exhaled through the nose and though the mouth of 20 healthy subjects. The values for nose exhalation agree with those reported by Larson et al., while those for mouth exhalation are in better agreement with Norwood et al. Schmidt et al. observed that an acidic mouth rinse reduced the median level for nose- and mouth-breath to 21 ppb. Based on a review of the literature through 2014, Mochalski et al. estimated a breath emission rate of 91 nmol min-1 person-1 , which corresponds to an average breath concentration of approximately 210 ppb at a volumetric breathing rate of 15 m3 /day. Schmidt et al. measured NH3 emissions from skin of 20 subjects. They reported a median NH3 emission rate of 0.3 ng cm-2 min-1 from the forearms of subjects who had washed their skin and tried to minimize sweating prior to measurements. In their review, Mochalski et al. estimated a total human skin emission rate of 514 nmol min-1 person-1 . In subsequent experiments, Furukawa et al. reported a median emission rate of 270 ng cm-2 h-1 from the forearms of five male and five female volunteers. This average value is 15 times larger than that reported by Schmidt et al. The larger emission rates may have been due to the sampling method, which entailed passive samplers that were sealed to the skin; sweating likely occurred during the 1-hour sampling period, enhancing NH3 emission. Furukawa et al. also measured emission rates at 12 other body locations and summed the emissions from different body locations to obtain whole-body emission rate estimates . For males the range of these estimates spanned a factor three ; for females, somewhat lower values spanned a factor of two . The average whole-body skin-emission rate of NH3, likely enhanced by the sampling method, was estimated to be 5.9 ± 3.2 mg h-1, equivalent to 43 ± 23 g NH3-N y-1 person-1 . Recently, human ammonia emissions have been measured under a variety of conditions in carefully controlled chamber experiments. In eighteen experiments, most with two male and two female volunteers, NH3 emissions were quantified at different temperatures, relative humidities, fraction of exposed skin, and absence/presence of ozone. The investigators found a strong positive correlation between NH3 emission rates and temperature. For fully clothed adults and seniors, the calculated emission rate was 0.41 mg h-1 person-1 at 25 °C, 0.77 mg h-1 person-1 at 27 °C, and 1.4 mg h-1 person-1 at 29 °C. Emission rates also increased with an increase in exposed skin. Relative humidity had only a moderate impact on emission rates, while ozone had no detectable influence.

The national outbreak of e-cigarette, or vaping, product use-associated lung injury has been the first vaping related disease to affect thousands of people . At its core, it is a chemical inhalation injury, most likely caused by heating, aerosolization and inhalation of Vitamin E within THC liquids and vape pens. Examination of airways and lungs of those affected has yielded a pattern of epithelial and alveolar damage. Neutrophils and foamy macrophages are often documented, with lipid laden phagosomes when directly tested through appropriate lipid stains; however, lipid laden macrophages are most likely evidence of vaping in general, not specific to EVALI. Although it has been clear for years that users of e-cigarettes and vaping devices were inhaling known toxins such as diacetyl and formaldehyde, this disease entity was the first to demonstrate that inhalation of clouds of chemicals that have never been tested for safety via inhalation methods can lead to significant impacts on public health. EVALI was first recognized in August 2019, with the number of recognized cases rising precipitously until December 2019. The connection with THC was made within several weeks – approximately 82% of those affected had vaped THC – while the identification of Vitamin E acetate as a prime suspect took months, and has not been confirmed as the etiologic agent at this time. Fourteen percent of those affected vaped nicotine containing e-liquids only, but upon review these subjects were older, female and had less leukocytosis, suggesting that they may have been suffering from a different vaping induced lung disease. Overall, EVALI is a disease of the young, with a median age of 24 years. It also predominantly affects males , which may be directly related to epidemiologic patterns of THC vaping. The majority of patients present with respiratory , gastrointestinal and systemic symptoms, and are found to have elevations in erythrocyte sedimentation rate , Creactive protein ,cannabis grow equipment white blood cell counts, and liver function tests. Beyond these factors, bilateral lung infiltrates are the key diagnostic finding on radio graphic imaging. The mortality rate is quite low, at 2.4% , with the highest mortality rate in older e-cigarette users with comorbidities. The median age of deceased EVALI patients was 49.5 years, with a range from 15 up to 75 years.

Of the cases identified up to December, approximately 47% required ICU admission and 22% required intubation. Because only moderate to severe cases were tracked, the reported numbers are likely to severely underestimate those affected. Since Vitamin E acetate within THC e-liquids has been identified as a likely causal agent, and with the intense media coverage of this disease entity, there is hope that the incidence of this particular vaping disease will decrease. However, as vaping increases across society, with millions of users inhaling hundreds of thousands of chemicals including lipophilic agents similar to VEA, it is clear that vaping associated lung diseases are here to stay. Conventional tobacco has been smoked for over 5000 years and is very well known to cause a myriad of long-term health problems, not the least of which is lung disease. Because modern vaping devices have been on the market for less than 16 years, and only widely used for 5, very little is known about how chronic use will affect human health. Murine dataSince they were first introduced in the 1970s more than 30 synthetic pyrethroids have been commercialized . Their rapid control of insects, relatively low toxicity to mammals and rapid degradation in the environment has made pyrethroids a very important class of insecticides, and they are commonly used worldwide. The federally mandated phase-out of residential uses of the organophosphate pesticides chlorpyrifos and diazinon in 2001 has caused further increases in the usage of pyrethroids indoors . This class of insecticides has a remarkably good safety profile, particularly compared to earlier materials that they replaced. There are cautions with regard to human exposure however. Many studies have shown that high levels of exposure to pyrethroids may cause significant toxicity and health effects. Pyrethroids are acute neurotoxins . They have shown immunotoxic effects and negative effects on mammalian reproduction , and they are reported to likely be carcinogenic to humans . Exposure in the general population results from ingestion of foods such as fruits and vegetables onto which the insecticide has been applied; drinking water; and inhalation, dermal contact and non-dietary ingestion resulting from residential indoor application.

In agricultural communities poor housing conditions can make homes more difficult to clean, potentially leading to a larger pest problem and in turn an increased use of pesticides in the indoor environment . Factors related to farm proximity, including drift from agricultural application and take-home contamination from occupational use, may also have a large influence on exposure to pesticides . Because children have an increased risk of exposure to environmental contaminants as compared to adults children living in agricultural communities are especially susceptible to pesticide exposure . A number of major pyrethroids such as permethrin, cypermethrin, deltamethrin, and fenvalerate are metabolized to 3-phenoxybenzoic acid . This urinary metabolite has been commonly used as a generic biomarker for evaluating human exposure to multiple pyrethroid pesticides . Traditionally, instrumental analytical methods are used to determine 3PBA in urine samples. More recently however, a lower-cost bio-analytical approach using an enzyme-linked immunosorbent assay has been developed and shown to be a suitable alternative method for the analysis of 3PBA in urine samples for exposure monitoring . The city of Mendota is located in agriculturally intensive Fresno County, in California’s Central Valley. According to the USDA’s 2007 Census of Agriculture, Fresno County had 6,081 farms, comprising over 1.6 million acres of land. It was ranked one of the top three counties in the U.S. for either total value or total acreage of agricultural products for the following commodities: cotton and cottonseed; vegetables, melons, potatoes, and sweet potatoes; fruits, tree nuts, and berries; grapes; tomatoes; vegetables harvested for sale; and almonds . With almost 29 million pounds of pesticide active ingredients applied in Fresno County, the highest of any county in California, in 2009 it can be assumed that there is a high risk of pesticide exposure to the farm workers, their families and people living in the surrounding areas. This study was conducted to examine the sources of pyrethroid pesticide exposure in the homes of farm worker families living in Mendota, California. We report housing conditions and exposure data collected in 2009 on pyrethroid pesticides measured by questionnaires and urinary concentrations of the metabolite 3PBA among 105 women, 23–51 years of age and 103 children, 2–8 years of age.

The Mexican Immigration to California: Agricultural Safety and Acculturation Study is a prospective cohort sample of 467 hired farm worker family households from Mendota, CA designed to evaluate occupational and environmental exposures of significance for a farm working population. Households were sampled from randomly selected census blocks and, following door-to-door enumeration, those households containing at least one hired farm worker were contacted for recruitment. Eligible participants in the MICASA study included men and women, residing in Mendota, CA, ages 18–55 years, self-identified as Mexican or Central American, with at least one household member who worked in agriculture 45 days or more in the previous year . MICASA recruitment and baseline interviews were conducted between January 2006 and May 2007. A follow-up interview was conducted between February 2009 and June 2010. Recruitment for the home pyrethroid exposure study began in February of 2009 and sample collection took place between June and December of 2009. In total, 843 participants, representing 467 households, completed the MICASA baseline interview. The analysis highlighted in this paper was designed to look at sources of pyrethroid exposure in the homes of the MICASA study population. As children typically have higher levels of exposure to pesticides ,PIPP horticulture we restricted eligibility to those MICASA families with at least one child aged 7 or under at the time of recruitment in order to better understand the sources in this potentially highly exposed population. Among the MICASA households completing baseline interviews, 175 were eligible for participation in the home pyrethroid exposure study. Eligible households were placed in random order for contact. One hundred twenty seven households were contacted for recruitment before reaching our goal of 105 households who agreed to participate and were enrolled in the study. The remaining 22 households either could not be contacted or declined to participate. If a family had multiple eligible children, one child was randomly selected and enrolled. At the time of sample collection, children ranged from 2 to 8 years of age. Written informed consent was obtained from each participant. Each study component was described verbally and in writing to the participant prior to obtaining written informed consent. Spanish was the primary language of the participants, thus the study description and written informed consent were provided in Spanish. All study procedures were approved by the University of California, Davis Institutional Review Board.

Data collected between June and December of 2009 consisted of urine samples, questionnaires and food recall. As collecting 24-hour urine samples can be difficult for participants, a more convenient end of-day single spot void urine sample was collected from each mother and enrolled child.Plastic bonnets, to be placed under the toilet seat , and prelabeled standard plastic urine cups were provided for urine collection. Total volume of void, time of void collection and time of previous void were recorded. Participants were instructed to store their urine sample in the provided coolers with ice packs overnight until study staff retrieved the samples the following day. Urine samples were then refrigerated at the MICASA field office for generally less than one day, delivered on ice to UC Davis where they were stored in a −80°C freezer until sample extraction and analysis. At the time of urine collection, a questionnaire was administered to the mothers. We obtained the frequency of pesticide use in both the hot and cold season of the previous year. Pesticide use encompassed any type of pest control including sprays, foggers, sticky traps, bait traps, gels, and any application by professional exterminators. To assess the presence of insect or rodent problems in the home, we asked if anyone living in the home had seen rodents, rodent feces, live or dead roaches, roach feces or ants inside the home at any time in the last year. The overall condition of the home was assessed by a series of questions looking at the presence of various common household disrepair items with the aim of creating a summed Home Disrepair Score. These individual disrepair items included water damage, mold, plumbing leaks, rotten wood, holes/worn spots in flooring, walls, ceiling and/or counters, peeling paint and home security. On the day of urine collection, a staff member inventoried all pesticide products in the home, including their EPA registration number and active ingredients. Additional sources of data included pesticide use questions assessed at both MICASA baseline and follow-up interviews and asked of husband and wife in each household.Furthermore, at follow-up interview, an evaluation each participant’s home was conducted by trained staff members. Three assessments–Inside Housing Condition, Outside Housing Condition, and Home Cleanliness–were scored on a 4-point scale based on level of disrepair. The Inside Housing Condition included peeling paint, holes/cracks in walls or floors, stains on floors, and presence of rodents and/or insect feces inside the house. The Outside Housing Condition included peeling paint and landscape maintenance. Home Cleanliness assessed the difficulty level of keeping the home clean. The Inside Housing Condition was based only on the portion of the home visible during the interview, and the research staff did not look for the presence of water damage. Participants were asked to complete a 24-hour food diary for the day prior to urine collection. The diary was split into four sections: breakfast, lunch, dinner, and snacks. The participants were instructed to write down everything they ate or drank during the entire 24- hour period, including the number of servings of each item consumed. Due to the low education level of participants, we did not consider it feasible to collect more detailed serving size information. No information was collected on participants’ time activity. Urine samples were prepared and analyzed for 3PBA using a competitive inhibition ELISA adapted from previously reported methods . Briefly, 0.5 mL urine aliquots were treated by acid hydrolysis, followed by solid phase extraction with a mixed-mode column, and finally solvent exchanged into methanol .