compound class specific AMS 14C analysis

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Compound class specific radiocarbon analysis (CCSRA) was performed for polycyclic aromatic chydrocarbons (PAHs) associated with airborne particulate matter (APM) with diameter <10μm (PM_<10>) and <1.1μm (PM_<1.1>) collected from a residential area of suburban Tokyo, Japan and seasonal and particle-size radiocarbon variations were investigated. Total PAHs concentrations (sum of 38 compounds with 3-6 aromatic rings) ranged 0.94-3.25 ng/m^3 for PM_<10> and 0.69-2.68 ng/m^3 for PM_<1.1> samples. Source diagnostic isomer pair ratios indicated mixed contributions from petroleum combustion and from biomass and coal combustion to the PAHs in APM. The Δ^<14>C-PAHs in APM ranging from -787 to -514‰ indicated dominance of fossil fuel combustion. The Δ^<14>C of 5-6 rings (HMW) PAHs were higher than the 3-4 rings (LMW) species in both PM_<10> and PM_<1.1> samples. The Δ^<14>C of HMW-PAHs indicated greater biomass-burning contributions in summer than in winter and no apparent particle-size variation. Conversely, the Δ^<14>C of LMW species showed a greater contribution from fossil sources in summer and in larger particles (PM_<10>). This finding could be tentatively attributed to the recondensation of fossil-PAHs vaporized from petroleum sources. A ^<14>C isotopic mass balance approach estimated that biomass burning contributes 17 to 45% of the PAH burden in suburban Tokyo, and that the increase in the biomass-PAH accounts for approximately 27% and 22% of winter-time elevation of LMW- and HMW-PAHs, respectively. These are far exceeding what is expected from the emission statistics for CO_2 and combusted materials in Japan and emphasizing the importance of biomass-burning as a source of PAHs ; which, in turn, demonstrates the utility and the significance of field-based source assessment by using CCSRA for an effective regulation of atmospheric pollution by PAHs.