Tracer-based investigation of organic aerosols in marine atmospheres from marginal seas of China to the northwest Pacific Ocean

Abstract

We investigated the geographic distributions of organic tracers in total suspended particles over the marginal seas of China, including the Yellow and Bohai seas (YBS) and the South China Sea (SCS), and the northwest Pacific Ocean (NWPO) in spring, when Asian outflows strongly affect downwind marine atmospheres. The comparison of levoglucosan observed in this study with values from the literature showed that the concentrations of biomass burning aerosols over the NWPO increased largely in 2014. However more observations, in addition to our snapshot measurement, are need to confirm whether the large increase has occurred continuously over the last few decades. The increase led to a mean observed levoglucosan value (8.2±14 ng m−3) over the NWPO that was close to that over the SCS (9.6±8.6 ng m−3) and almost half of that over the YBS (21±11 ng m−3). Small geographic differences in monoterpene-derived and sesquiterpene-derived secondary organic tracer concentrations were obtained among the three atmospheres, although the causes may differ. By contrast, a large difference in isoprene-derived secondary organic tracer concentrations was observed among the three atmospheres, with the sum of tracer concentrations over the SCS (45±54 ng m−3) being several times and approximately 1 order of magnitude greater than that over the YBS (15±16 ng m−3) and the NWPO (2.3±1.6 ng m−3), respectively. The geographic distribution of aromatic-derived secondary organic tracers was similar to that of isoprene-derived secondary organic tracers, with a slightly narrower difference: 1.8±1.7, 1.1±1.4 and 0.3±0.5 ng m−3 over the SCS, the YBS and the NWPO, respectively. We discuss the causes of the distinctive geographic distributions of these tracers and present the tracer-based estimation of organic carbon.