FIGURE 15.12 Ratio of indoor-to-outdoor concentrations of formic and acetic acids and some carbonyl compounds in some homes: unshaded, data from Reiss et al, 1995a, for summer data; shaded, data from Zhang et al., 1994a.
p-dichlorobenzene is observed when mothballs containing this compound are in use (e.g., Tichenor et al., 1990; Chang and Krebs, 1992).
Elevated concentrations of the n-C13 to n-Cl8 alka-nes and branched-chain and cyclic analogs were measured in a building having a history of air quality complaints; the source was found to be volatilization from hydraulic fluids used in the building elevators (Weschler et al., 1990).
Enhanced levels of chlorinated compounds have been observed indoors due to human activity as well. For example, increased levels of perchloroethylene have been observed from unvented dry-cleaning units (e.g., Moschandreas and O'Dea, 1995) and volatilization of chlorinated organics such as chloroform from treated tap water can occur (e.g., McKone, f 987). Other sources include the use of household products. For example, chloroform emissions have been observed from washing machines when bleach containing hypochlorite was used (Shepherd et al., 1996). ft is interesting that emissions of organics associated with the use of washing machines are decreased when the machine is operated with clothes inside (Howard and Corsi, 1998).
Of course, activities such as smoking result in enhanced levels not only of nicotine (e.g., Thompson et al., f989) but also of a variety of other gases associated with cigarette smoke (e.g., California Environmental Protection Agency, 1997; Nelson et al., 1998). For example, using 3-ethenylpyridine as a marker for cigarette smoke, Heavner et al. (f 992) estimated that 0.2-39% of the benzene and 2-49% of the styrene measured in the homes of smokers were from cigarette smoke.
Humans emit a variety of VOCs such as pentane and isoprene (e.g., Gelmont et al., 1981; Mendis et al., 1994; Phillips et al., 1994; Jones et al., 1995; Foster et al., 1996). In addition, emissions from personal care products have been observed. Decamethylcyclopen-tasiloxane (D5), a cyclic dimethylsiloxane with five Si-O units in the ring, and the smaller D4 analog, octameth-ylcyclotetrasiloxane, are used in such products as underarm deodorant and antiperspirants at concentrations up to 40-60% by weight (Shields and Weschler, 1992; Shields et al., 1996). Increased concentrations of D5 have been measured in offices and are correlated to human activity, as expected if personal care products were the major source (Shields and Weschler, 1992). In some cases, increased concentrations attributable to emissions from silicone-based caulking materials were also observed (Shields et al., 1996).
The use of pesticides indoors can lead to very large concentrations not only of the pesticide but of the additional VOCs used as a matrix for the pesticide, which represent most (>95%) of the mass of the material as purchased. For example, Bukowski and
Meyer (1995) predict that VOC concentrations immediately after the application of a fogger could reach levels of more than 300 mg m 3!
However, lower levels of pesticides themselves are common after use inside homes. For example, Lewis et al. (1988) reported the presence of 24 pesticides in homes, ranging in concentration from 0.002 to f5 /jlg m~3 (the latter for chlorpyrifos), while outdoor levels measured simultaneously were much lower, from <0.001 to 0.4 /xg m~3. The compounds present indoors at the highest concentrations were those used recently at the home. Similarly, Whitmore et al. (1994) reported 22 pesticides in homes in Jacksonville, Florida, and Springfield, Massachusetts, at indoor levels up to 0.5 ¡xg nT3 indoors, but only 0.04 ¡xg nT3 outdoors. The pesticides not only were present as gases but also adsorbed to dust particles in the home, particularly for the less volatile compounds. Indeed, higher concentrations of some pesticides have been found in dust than in air (e.g., Roinestad et al., 1993).
There are a few data that suggest that pesticides can undergo reactions indoors. For example, Wallace et al. (1996) observed that the aldrin levels inside a home decreased with time, whereas those of dieldrin did not. Dieldrin had been applied with aldrin but is also an oxidation product of aldrin. One of the reasons for the lack of change in dieldrin may be that it was being formed as the aldrin decayed; however, this could not be differentiated from the effects of a lower vapor pressure of dieldrin, which could lead to lower overall removal rates. In the same study, pentachloroanisole was also measured inside the home and attributed to formation by degradation of pentachlorophenol, which is used as a wood preservative and termiticide.
Not surprisingly, some indoor organics are readily taken up on building surfaces, such as carpets and wallboard, and are subsequently released into the room. For example, Chang et al. (1998) showed that some of the alcohols found in indoor air environments are taken up by carpets and gypsum board and could be desorbed back into the gas phase later. However, revolatilization was observed to be slow, and Chang and co-workers estimated that it would take more than a year to remove the adsorbed organics. Similarly, Van Loy et al. (1998) showed that nicotine from environmental tobacco smoke can be readily adsorbed and then desorbed and that surfaces can hold significant amounts of nicotine. As a result of this reversible adsorption-desorption process, measurable levels of organics can be maintained indoors after the initial exposure by slow degassing from surfaces.
Not surprisingly, the concentrations of VOCs from automobile exhaust are higher in the "indoor environment" of automobiles during commutes. For example,
Duffy and Nelson (1997) report during commutes in Sydney, Australia, that the benzene concentrations inside vehicles were 10-25 times those in ambient air and that the concentrations of f ,3-butadiene were more than 55-115 times greater. The source appeared to be primarily from the exhausts of surrounding vehicles. Similar enhancements of benzene and other VOCs such as toluene, ethylbenzene, and the xylenes in automobiles and buses have been reported in many countries, including Korea (Jo and Choi, 1996), Taiwan (Chan et al., 1993), and the United States (e.g., Chan et al., 1991a,b; Lawryk and Weisel, 1996).
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