Formation and Lifetime of Polycyclic Aromatic Compounds During a National-Scale Transient Pollution Episode

Concentrations of selected particle-borne parent, alkylated, oxygenated, and nitrated polycyclic aromatic compounds (PACs) have been monitored before, during, and after a large national-scale wood-burning pollution episode (5 November 1994 and 4-5 November 1995). Toluene-modified supercritical CO 2 was used for the extraction of PACs from the collected particulate matter. Analysis was performed using an on-line multidimensional chromatographic technique using coupled liquid and gas chromatography (LC-GC) with loop interface. Comparison of average urban and wood smoke particulate PAC profiles identified a marked change in the ambient PAC profile for the pollution episode period, caused by the change in emission source from predominantly vehicular to wood smoke. A chemical mass balance model has been used to calculate the relative contributions from general urban and wood smoke PAC sources and from them, an estimation of the atmospheric life-time of the PAC emissions has been made. When monitored with 24 hr resolution in 1994, the concentrations of quinone-PAC oxidation products were found to peak 1 day after the maximum concentrations in the parent PAH were recorded, consistent with photochemically driven reactions with singlet state molecular oxygen. When concentrations were monitored on a more frequent basis in 1995, the concentrations of oxygenated species were seen to begin increasing in concentration before sunrise but still peaking after the maximum concentrations of parent PAH were recorded. The nighttime rise in product PAC suggests dark reactions with ozone or the NO 3 radical also may be occurring.