Sources Levels Chemistry and Fates

At the beginning of this book, we presented some discussion of health-based air quality standards. In the final chapter, which follows this one, the scientific bases of control measures for various pollutants are discussed. In between, the complex chemistry that occurs in both polluted and remote atmospheres, and that converts the primary pollutants into a host of secondary species, has been detailed. To provide further perspective on airborne gases and particles and human exposure levels, we briefly treat indoor air pollution in this chapter. As we shall see, for many species it is simply a question of emissions leading to elevated levels indoors. However, there is some chemistry that occurs in indoor atmospheres as well, and it is of interest to compare this to that occurring outdoors.

From the point of view of health impacts, it is the combination (not necessarily linear) of concentrations and duration of exposure to a pollutant or combination of pollutants that is important. In this regard, it is noteworthy that most individuals spend the majority of their time indoors, even in relatively moderate climates. For example, in California, people spend 87% of their time indoors on average, 7% in enclosed transit systems, and only 6% outdoors (Jenkins et al., 1992). Similarly, Quackenboss et al. (1986) report that only 15% of the average day in Portage, Wisconsin, was spent outdoors in summer and less than 5% in winter. As a result, elevated concentrations of air pollutants indoors can have a significant impact on human health and can lead to enhanced chemical sensitivities (Hile-man, 1991) as well as other health impacts such as cancer. Establishing the contribution of indoor air pollution to carcinogenicity and assessing the relative risks (e.g., Tancrede et al., 1987) are complex and difficult. An interesting approach suggested recently is pet epidemiology, discussed in detail by Bukowski and Wartenberg (1997).

The term "indoors" is used in the literature to refer to a variety of environments, including homes, work places, and buildings used as offices or for recreational activities. In addition, a number of studies have been carried out to measure various compounds inside vehicles during commutes. As we shall see, and consistent with expectations, levels measured indoors are characteristic both of the particular sources present and, to a significant extent, of the outdoor concentrations of the species. We shall not, in general, distinguish in this chapter between the various types of indoor environments but rather focus on the sources of various compounds and their indoor chemistry.

Table 15.1 summarizes the major species of concern for indoor air pollution and some of their sources (Su, f996). We focus in this chapter primarily on those species common to indoor and outdoor air environments, including oxides of nitrogen, volatile organic compounds (VOC), CO, ozone, the OH radical, S02, and particles. In addition, a brief discussion of radon is included since this has been one of the major foci of concern in the past with respect to indoor air pollution.

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