Thirteen years of observations on biomass burning organic tracers over Chichijima Island in the western North Pacific : An outflow region of Asian aerosols

摘要

East Asia is the world's greatest source region for the emission of anthropogenic aerosols and their precursors due to the rapid industrialization and intensive biomass burning (BB) activities. BB emits specific organic tracers such as levoglucosan, mannosan, and galactosan, which are produced by pyrolysis of cellulose and hemicellulose and then transported downwind to the western North Pacific by westerly winds. Here we present long-term observations of BB tracers over the remote Chichijima Island in the western North Pacific (WNP) from 2001 to 2013. Elevated concentrations of BB tracers by an order of magnitude were found in midautumn to midspring with winter maxima, which are strongly involved with the atmospheric transport by westerly winds from the Asian continent to the WNP, as supported by backward trajectory analyses. Throughout the observations, we found an increase in the averaged concentrations of BB tracers from 2006 to 2013, which is mainly caused by enhanced BB events in Asian urban and rural areas, as supported by enhanced fire/hot spots in East Asia via satellite images. We also found that the period of the high concentrations was prolonged from 2006 to 2013. Comparison between monthly averaged concentrations of BB tracers and backward air mass trajectories clearly demonstrates that the winter/spring maxima over Chichijima are involved with the seasonal shifting of atmospheric circulation followed by downwind transport of BB aerosols to the WNP. High abundances of BB tracers over the WNP indicate that BB-laden air masses can be transported to remote marine environments.