Seasonal Characteristics of Biogenic Secondary Organic Aerosols Over Chichijima Island in the Western North Pacific: Impact of Biomass Burning Activity in East Asia

Abstract

AbstractTo better understand the formation processes of biogenic secondary organic aerosols (SOAs) over remote oceanic regions, aerosol samples were collected from 2010 to 2012 at Chichijima Island in the western North Pacific (WNP). The samples were analyzed by gas chromatography‐mass spectrometry for SOA tracers, which are produced by the photochemical oxidation of biogenic volatile organic compounds (BVOCs), including isoprene, monoterpenes, and sesquitepenes. Although no seasonal trend was identified for the isoprene‐derived SOA tracers, we observed higher levels of the monoterpene‐derived and sesquiterpene‐derived SOA tracers in winter/spring and lower levels in summer/autumn. We found a significant correlation (r = 0.87) of β‐caryophyllinic acid with levoglucosan, the latter being a specific tracer of biomass burning (BB). This suggests that the β‐caryophyllene accumulated in higher plants is evaporated by BB followed by atmospheric oxidation during long‐range transport from the Asian continent over the WNP. The biogenic secondary organic carbon concentration estimated using a tracer‐based approach ranged from 0.11 to 174 ngC m−3 (avg. 34.8 ± 38.2 ngC m−3), accounting for 0.02%–32.0% (avg. 6.11% ± 6.42%) of the measured organic carbon. Our results indicate that SOAs are formed by the photooxidation of BVOCs. The backward trajectories of air masses further support their transport from the central Pacific during mid‐spring to mid‐autumn, whereas BB aerosols are transported from the Asian continent during mid‐autumn to mid‐spring over the WNP. Positive matrix factorization analyses of the SOA tracers suggest that organic aerosols of Chichijima are mostly related to BVOC emissions, with BB’s additional contributions especially in winter and spring.