heavily polluted environments (Table 2–5). In small interior compartments, such as automobiles, occupants who smoke tobacco have generated nicotine concentrations of 1,010 µg/m³ (Badre et al., 1978).

Freshly generated tobacco smoke contains nitric oxide, but not nitrogen dioxide. On release into the environment, nitric oxide is gradually oxidized to nitrogen dioxide. The estimated half-life of nitric oxide is 10–20 minutes, depending on the degree of air dilution. Table 2–6 shows concentrations of nitric oxide and nitrogen dioxide in smoke-polluted environments and indicates means ranging from 9 to 195 ppb for nitric oxide and 21 to 76 ppb for nitrogen dioxide. Generally, the nitrogen oxide values reported in Table 2–6 are significantly in excess of those observed for outdoor atmospheres. However, some severe air pollution episodes in industrial areas have reportedly caused levels of 100 ppb, which persisted over several hours or even for several days (Goldsmith and Friberg, 1977). As a constituent of the respiratory environment, nitrogen dioxide conceivably contributes to endogenous nitrosation, which leads to the presence of nitrosamines in exposed subjects. Whereas it has been clearly demonstrated that inhaled cigarette smoke increases the endogenous formation of N-nitrosamines (Hoffmann and Brunnemann, 1983; Ladd et al., 1984; Lu et al., 1986; Tsuda et al., 1986), the endogenous formation of N-nitrosamines in nonsmokers exposed to ETS has so far not been demonstrated (Brunnemann et al., 1984).

Tables 2–7 and 2–8 show concentrations of acrolein and acetone in ETS. These volatile carbonyl compounds are known to affect mucociliary function and thus inhibit the clearance of smoke particles from the lung (Wynder and Hoffmann, 1967).

Table 2–9 shows concentrations of some additional toxic agents in ETS. Benzene, N-nitrosodimethylamine, N-nitrosodiethylamine, and the polynuclear aromatic hydrocarbons, represented by benzo[a]pyrene, are of concern, because they are known carcinogens (Vainio et al., 1985).

The radioactive isotopes of lead (Pb-210), bismuth (Bi-210), and polonium (Po-210), known as long-lived radon daughters in the decay chain of uranium via radium and radon (Radford and