O Cd

FIGURE 15.8 Median ratios of indoor-to-outdoor concentrations of CO and some other air pollutants measured in restaurants in Korea where either gas alone (□) or gas with charcoal (■) was used for cooking (adapted from Baek et al., 1997).

Toluene

FIGURE 15.8 Median ratios of indoor-to-outdoor concentrations of CO and some other air pollutants measured in restaurants in Korea where either gas alone (□) or gas with charcoal (■) was used for cooking (adapted from Baek et al., 1997).

charcoal. The use of charcoal increases this ratio to more than four; in one such restaurant, an indoor concentration of 90 ppm CO was measured.

In buildings where motor vehicle exhaust can be entrained from outdoors or attached parking garages, elevated indoor CO levels may also result (e.g., Hodgson et al., 1991).

On the other hand, in homes and offices where there was no direct indoor source of CO, the indoor-to-outdoor ratio was about one, and sometimes less. For example, in Riyadh, Saudi Arabia, CO concentrations were measured indoors and outdoors; the indoor-to-outdoor ratio varied from 0 to 2, but was typically below one (Rowe et al., 1989).

There have been a number of measurements of CO in the "indoor environment" of automobiles. Given that cars are major CO sources in urban areas, one might expect higher concentrations of CO during commutes and this is indeed the case. Typical CO concentrations of ~9-56 ppm have been measured inside automobiles during commutes in major urban areas (Flachsbart et al., 1987; Koushki et al., 1992; Ott et al., 1994; Dor et al., 1995; Fernandez-Bremauntz and Ash-more, 1995). This can be compared to peak outdoor levels of ~ 10 ppm in highly polluted urban areas (see Chapter 11.A.4c). Thus, a significant enhancement of CO inside automobiles during commutes is common. For example, Chan et al. (1991b) report a ratio of the in-vehicle CO concentration to that outdoors of ~4.5 in Raleigh, North Carolina.

As is the case for CO, S02 levels indoors and outdoors tend to be similar if there are no combustion sources indoors. For example, Hisham and Grosjean (1991b) report that the ratio of indoor-to-outdoor S02 concentrations averaged 0.89 for three museums in southern California, with a range from 0.36 to 1.92. On the other hand, quite high S02 concentrations can result when there are indoor combustion sources. For example, in China, where unvented stoves using coal are used extensively for cooking and heating, average S02 levels indoors are typically 250 ¡xg m~3 (96 ppb) during the summer and 750 ¡xg m~3 (287 ppb) during the winter, compared to average annual outdoor concentrations of 72-94 /igm"3 (28-36 ppb) (Florig, 1997; Ando et al., 1996).

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