Polychlorinated biphenyls pcbs

As is typical for atmospheric samples, about 90 percent of the total PCBs in the atmosphere at the three sampling sites was in the gas phase, with the other ~10 percent sorbed to airborne particles (aerosols). This percentage sorbed to particles is higher during colder sampling periods due to the decrease in vapor pressure of PCB congeners at lower temperatures, increasing sorption onto airborne particles. The percentage is also higher for the higher MW PCBs. For the octa- and nonachloro congeners, for example, perhaps 50 percent of their total atmospheric concentration is in the particle phase during the warmer months, while essentially 100 percent is sorbed to particles in the winter. Thus the gas-phase PCB concentrations are best used to illustrate spatial differences between the three sampling sites. EPCB gaseous concentrations varied from 96 to 3,800 pg m-3 at Liberty Science Center, from 40 to 2,300 pg m-3 at New Brunswick, and from 77 to 1,800 pg m-3 at Sandy Hook. Although the temporal trends of total concentrations were significantly different at the three sites (p < 0.01), PCB congener profiles were similar (r2 > 0.90,p < 0.001), implicating a dominant emission type and/or process. The concentrations were typically highest at the Liberty Science Center and lowest at Sandy Hook. Temporal changes in congener distribution at the suburban site are consistent with the preferential atmospheric removal of 3to5 Cl-substituted biphenyls by hydroxyl radical attack with estimated half-lives of 0.7 to 1.8 years (Brunciak et al., 2001b).

The gaseous EPCB concentrations are driven primarily by temperature and take the same shape as the annual variation in temperature (Fig. 27.4). One way to investigate the effect of temperature on gas-phase chemical concentrations is to plot the natural log of the gas-phase concentration versus the inverse of the temperature (in degrees K), similar to a Clausius-Clapeyron plot. When this is done for the data from the three sites, the R2 values are greater than 0.5, suggesting that temperature

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