Particle-Associated. PAHs in Ambient Air

Similarly, Greenberg (1989) determined the concentrations of six selected PAHs at three urban sites in 

New Jersey over two summer periods and one winter period and ratioed them to the stable PAH benzo[h]fluoranthene, BbF (Class V, Table 10.30). The [BaP]/[BbF] ratios were 0.61 in the summer of 1982 compared to 0.92 in the winter of 1983 for [CPP]/[BbF] they were 0.17 during the summer compared to 0.57 in the winter. In contrast, winter to summer ratios for the carcinogenic Class V PAHs benzo[/c]fluoranthene and indeno[l,2,3-c 7]pyrene (Table 10.30) are equal and close to unity, indicative of the low reactivity predicted by Nielsen (1984, 1988). 

Masclet and co-workers (1986) have also developed a relative PAH decay index. They used it, for example, to identify various major sources of urban pollution and developed a model for PAH concentrations at receptor sites. An interesting and relevant area that is beyond the scope of this chapter is the use of PAHs as organic tracers and incorporating their relative decay rates (reactivities) into such receptor-source, chemical mass balance models. Use of relative rates can significantly improve such model performances (e.g., see Daisey et al., 1986 Masclet et al., 1986 Pistikopoulos et al., 1990a, 1990b Lee et al., 1993 Li and Kamens, 

---

In their thoughtful 1983 review, Nielsen and coworkers noted that particles of diesel soot or wood smoke can absorb significant amounts of water. Thus, they suggested that the most plausible mechanism(s) for nitration (and possibly other electrophilic reactions) of particle-associated PAHs in ambient air may involve reactions both in a liquid film and on solid surfaces and that fundamental laboratory studies of the rates, products, and mechanisms of PAHs in polar solvents would be atmospherically relevant for reactions in the liquid films. Based on this, they proposed a classification scheme for the reactivities of key PAHs in electrophilic reactions, which was subsequently described in detail (Nielsen, 1984). 

---