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Transboundary Secondary Organic Aerosol in the Urban Air of Fukuoka, Japan

To understand the influence of transboundary secondary organic aerosol (SOA) in the urban air of Fukuoka, we conducted simultaneous field studies in December 2010 and March 2012 on Fukue Island and in the city of Fukuoka, representing a rural and an urban sites of western Japan. During the studies, organic aerosol in PM1.0 was analyzed by aerosol mass spectrometers. Independently, airborne total suspended particulate matter (TSP) was collected on filters, and low-volatile water soluble organic carbon (LV-WSOC) extracted from the TSP samples was analyzed by an elemental analyzer coupled with a high precision isotope ratio mass spectrometer for its concentration and stable carbon isotope ratio (d13C). Plots of LV-WSOC concentrations versus m/z 44 concentrations for the study in December 2010 showed high correlations (r2 > 0.85), but different slopes between the two sites (0.58 microg microgC-1 at Fukuoka and 0.22 microg microgC-1 at Fukue), indicating additional contribution of m/z 44 from local sources. Because of this complex composition, evaluation of transboundary SOA was unsuccessful in this case study. In contrast, comparison of LV-WSOC concentrations with the m/z 44 concentrations during the study in March 2012 showed high correlations (r2 > 0.91) with similar slopes (0.3 microg microgC-1) at both sites, indicating predominance of transboundary LV-WSOC. Furthermore, the plot of d13C of LV-WSOC as a function of m/z 44 fraction showed a systematic increasing trend, indicating SOA. These findings suggest that the observed LV-WSOC and m/z 44 in the Fukuoka air were predominated by transboundary SOA in this case study.