This feature likely reduces the influence of amine chemistry indoors. For example, trimethylamine, methylamine, triethylamine, diethylamine, ethylamine, and ethanolamine each react with nitric acid to form aminium nitrate particles, and the dissociation constants of diethyl- and triethylammonium nitrate were found to be similar to that of ammonium nitrate. Since the indoor concentration of NH3 tends to be about four orders of magnitude larger than that of these amines, reactions between nitric acid and either diethyl- or triethylamine are of negligible importance indoors. Similarly, although Murphy et al.found that 100 ppb of methylamine displaced NH3 from ammonium sulfate in a low humidity chamber, such displacement is anticipated to be of negligible significance indoors where methylamine is present at ppt levels. Ge et al.have estimated solid/gas equilibrium dissociation constants for aminium chlorides and aminium nitrates at various temperatures. Of the various amines in these tables, only ethanol amine, diethanolamine and triethanolamine have dissociation constants small enough – five to six orders of magnitude smaller than those for ammonium chloride or ammonium nitrate – to suggest that they can compete with ammonia for either HCl or HNO3 in typical indoor environments. In the few surveys of amines in indoor environments, the dominant compound is aniline. This finding is consistent with the known indoor sources of amines,greenhouse grow tables most of which have higher emission rates of aniline compared to other amines. Aniline’s concentration in occupied environments is typically three orders of magnitude smaller than ammonia’s, and aniline is much less basic than ammonia .
Aniline has a larger Henry’s law constant, KH = 530 M/atm, than ammonia, KH = 59 M/atm. However, the difference is not large enough to compensate for the differences in basicity and gas-phase concentration. Hence, aniline is likely to have much less of an impact on indoor acid-base chemistry than ammonia. Given the basicity of amines, their presence in indoor aerosols or aqueous surface films will be influenced by acidic or other basic species in these aerosols or films. Ge et al. examined partitioning of amines into aqueous aerosols. The extent of this process depends on the pH of the liquid water present in the aerosol. Partitioning increases as the aerosol acidity increases. They conclude that “For several common amines the tendency to partition to the particle phase is similar to or greater than that of ammonia.”Conversely, increasing basicity decreases partitioning of amines into aerosols or films or onto indoor surfaces. Ongwandee et al. varied the concentration of NH3 as they measured trimethylamine on the surface of zirconium silicate beads. At 20% RH, 10 ppm of NH3 decreased the TMA partition coefficient by 10% compared to its value in the absence of NH3. At 50% RH, NH3 decreased the partition coefficient by about 50%. In a subsequent study, Ongwandee and Morrison found that NH3 at 4 and 40 ppm decreased the capacity of carpet and the painted gypsum board for TMA.Given that NH3 levels indoors are typically two to three orders of magnitude smaller than the levels employed in these experiments, one anticipates a relatively small impact of NH3 on TMA sorption to materials in ordinary indoor environments. Destaillats et al. used attenuated total reflection-FTIR spectroscopy to investigate the rate at which pyridine desorbed from cellulose and gypsum surfaces.
Their results indicated that there were at least two sorptive states for pyridine – a chemisorbed state and a physisorbed state – and that there was spectroscopic evidence for acid-base interactions between pyridine and these surrogates for common indoor surfaces. Amino acids possess both a basic N-atom and an acidic O-atom. In the pH range between approximately 2 and 9, the N-atom in a “human” amino acid is protonated with the H-atom from its carboxyl group; the N-atom bears a positive charge while the O-atom bears a negative charge, as illustrated in Figure 18. The resulting entity is called a zwitterion. In the region around pH 2, the zwitterion is in equilibrium with a meaningful fraction of its conjugate acid, which bears a net +1 charge. In this region the amino acid functions as an acidic buffer. In the region around pH 9, the zwitterion is in equilibrium with a meaningful fraction of its conjugate base, which bears a net -1 charge. In this region, the amino acid functions as a basic buffer. Hence, human amino acids serve as “backstops” for pH in aqueous solutions, buffering against pH changes in the region of roughly pH 1 to pH 3 as well as in the region of roughly pH 8 to pH 10. When water containing such species evaporates, low volatility imidazoles and other nitrogen containing oligomers may form. The only meaningful source of indoor nicotine is tobacco. Nicotine levels are highest in environments where smoking or vaping occurs. Nicotine can also be brought into nonsmoking, nonvaping environments sorbed to clothing or other materials. Because nicotine sorbs reversibly to surfaces, it is persistent indoors.
Nicotine that has sorbed to indoor surfaces during smoking can also be released back to indoor air after smoking is terminated. The proportion of US adults who smoke decreased from 43% in 1965 to 21% in 2005. Cigarette smoking has continued to decline slowly, with a reported prevalence among adults of 14% in 2017. Random samples, taken between 1990 and 2014, of almost 15,000 individuals living in 13 European countries indicated that smoking bans have significantly reduced exposures to tobacco smoke both at work and, to a lesser extent, at home. Today, smoking is banned in many public spaces, schools and offices. Even among those who smoke, the fraction who smoke indoors has decreased. Hence, tobacco smoking as a source of indoor nicotine has decreased substantially during the past decades in the US, in Europe, and in some other regions. However, this strong decline has not prevailed in the developing world, although restrictions on indoor smoking in public spaces are increasing. Meanwhile, electronic cigarette use is rising. In 2016, the usage rates of e-cigarettes among US residents ranged from 2.4% in Washington, DC, to 6.7% in Oklahoma. 447 Some vaping occurs indoors and could affect the abundance of nicotine in indoor environments.Typical indoor nicotine levels in homes with moderate to heavy smoking are in the range 0.05- 0.5 ppb. Even with such relatively low concentrations, nicotine could have a large effect on the pH of aqueous solutions, especially if they are otherwise acidic. For example, comparing water in equilibrium with 800 ppm CO2 to water in equilibrium with 800 ppm CO2 and 0.5 ppb nicotine, the pH would increase from 5.46 to 7.57. If the mixture also contains 20 ppb of NH3, the pH would be 7.12 without nicotine and 7.60 with nicotine. Quantitatively, 0.045 ppb of nicotine neutralizes the influence of 1000 ppm CO2. Molecule for molecule, nicotine is roughly 300 times as effective as NH3 in this regard.Nicotine’s basicity can strongly influence the amount of total nicotine in the aqueous phase of airborne particles and in liquid water in a room, including on indoor surfaces. Because the pKa of monoprotonated nicotine is 8.0, at pH levels above 9 there is little change in the ratio of gasphase nicotine to total nicotine in the aqueous film at either value of L*. Conversely, below a pH of 7, this ratio decreases in a manner that is linear on the logarithmic scales of the plots. In other words, for each unit decrease in pH,cannabis growing system the proportion of nicotine that is gaseous at equilibrium decreases by a factor of 10. At pH 5, 1.2% of nicotine is gaseous at L* = 1 ´ 10-5 L/m3 and only 0.0012% is gaseous at L* = 1 ´ 10-2 L/m3 . It is apparent from Figure 20 that when nicotine is equilibrated with even a relatively small volume of water with pH < 6, the fraction of nicotine in the gas phase is low. For gas-phase nicotine equilibrated with water at an abundance of L* = 1 ´ 10-2 L/m3 , even at the unusually high pH of 12, the amount of nicotine in liquid water would be 80´ as large as the amount in the gas phase.
However, the time required for gas phase nicotine to equilibrate with liquid water increases as water’s mass per unit area increases. For thick reservoirs of liquid water indoors, there may not be sufficient time to achieve equilibrium.The partitioning of nicotine to airborne particles is influenced by the pH of the particle phase in a fashion similar to that for aqueous surface films; however, there are less likely to be kinetic constraints on achieving equilibrium. Pankow449 presented an excellent tutorial on the partitioning of nicotine to the PM phase of ETS, the “effective pH” of the PM phase, and impact of the effective pH on partitioning to PM. Figure 21 illustrates partitioning of nicotine to the particle phase when the latter is at a lower pH and a higher pH . It is apparent from Figure 21 that the capacity of indoor PM as a partitioning compartment for total nicotine increases as the particle pH decreases. The consequences of such behavior are nicely illustrated in recent papers by DeCarlo et al. and Collins et al.DeCarlo et al. describe the use of aerosol mass spectrometry to measure constituents of PM in a nonsmoking classroom. The investigators identified a reduced nitrogen compound that constituted almost 30% of the PM mass at certain times of the year. Although smoking is forbidden in the classroom, the investigators surmise that nicotine enters the room on clothing and from adjacent spaces, partitions to room surfaces, and later partitions from surfaces through the gas phase to fine particles that originated outdoors. The fine particulate matter is strongly acidic and this acidity greatly increases its capacity for nicotine. This process requires that an aqueous phase be present in the airborne PM. The phenomenon was observed in the summer when absolute humidity in outdoor air is high, but not in the winter, when absolute humidity in ambient air is low. Controlled laboratory experiments reproduced the process transferring nicotine from ETS to glass walls of a vessel and then to PM of outdoor origin when the relative humidity was high enough for water to constitute a meaningful mass fraction of the PM. In complementary experiments, Collins et al. measured uptake of constituents in third-hand smoke, previously sorbed to walls of an experimental chamber, to particles consisting of either ammonium sulfate, ammonium bisulfate, sodium sulfate, squalene, or sucrose. Changes in the composition of the aerosol particles were monitored using an AMS. Signals characteristic of nicotine and other reduced nitrogen compounds are clearly apparent in the AMS spectra of the aged aqueous ammonium sulfate and ammonium bisulfate particles, but less so for the other particles. Furthermore, third-hand smoke constituents partitioned to aqueous ammonium sulfate much faster than they partitioned to solid ammonium sulfate. Three hours after the initial “seed” PM was injected, reduced nitrogen compounds accounted for ~30% of the total organic matter accumulated by aqueous ammonium sulfate and ammonium bisulfate particles, but less than 10% of the organic mass accumulated by aqueous sodium sulfate or solid ammonium sulfate particles. Quoting the authors: “Temporal trend analysis along with the more general comparison with neutral pH seed aerosol suggest that the uptake of CxHyNz compounds responded dynamically to aerosol pH.” This discussion has focused on the partitioning of nicotine to surface water and bulk water, including the aqueous phase of aerosol particles. However, non-ionized nicotine can also partition to organic matter in airborne particles or settled dust and to organic films on indoor surfaces. A question for future exploration is how partitioning to aqueous surface films and condensed water compares to partitioning to indoor organic films.158Leaderer and Hammond made one-week measurements of vapor-phase nicotine and airborne particle mass in 96 homes in New York state. For all homes, nicotine concentrations were in the range 0-10 µg/m3 , with an average gas-phase concentration of 1.1 µg/m3 . For homes with nicotine levels above the detection limit , the average gas-phase concentration was 2.2 µg/m3 . Similar ranges of gas-phase concentrations were reported by Coultas et al., with average indoor nicotine concentrations spanning 0.6 to 6.9 µg/m3 in ten smokers’ homes.