Gas/particle partitioning of PCDD/Fs, PCBs, PCNs and PAHs

In a study to establish the baseline contamination of the environment prior to the start-up of a new municipal incinerator, air samples were collected continuously over a period of one year at eight locations in southern Bavaria. The air samples were analysed in six week intervals for the particle bound and gaseous concentrations of polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), biphenyls (PCBs) and naphthalenes (PCNs) as well as polycyclic aromatic hydrocarbons (PAHs). The logarithms of the particle/gas partition coefficients (Kp) were closely correlated with the inverse mean ambient temperature (r2 > 0.9 in most cases). When log Kp at 25°C was plotted vs. the logarithm of the compoundsʹ subcooled liquid vapour pressure (PL), the investigated compounds separated out into two groups. Within each of the two groups a linear correlation between Kp and PL was observed, but for the PAHs and PCNs the particle bound fractions were always considerably higher than for the PCDD/Fs and PCBs with comparable PL. These differences indicate that PL is not a good parameter for describing the interchemical variability in gas/particle partitioning. Log Kp was also plotted against the logarithm of the octanol/air partition coefficient (KOA), and in this case the different chemical groups did not separate out on the plot. This suggests that KOA may be a better descriptor of partitioning behaviour for these substances. However, the r2 for the log Kp vs. log KOA plot was identical to that for the log Kp vs. log PL plot (0.77), and hence no conclusions could be drawn about the relative utility of the two properties. Future improvements in the KOA data base may help to resolve this issue.