Enhanced modern carbon and biogenic organic tracers in Northeast Asian aerosols during spring/summer

To better understand the organic aerosol (OA) sources and formation processes in Northeast Asia, we studied atmospheric aerosol (total suspended particulate matter (TSP)) samples collected from Sapporo, northern Japan over 1 year period for the measurement of radiocarbon (C-14) in aerosol total carbon (TC) and water-soluble organic carbon (WSOC). We also measured various organic tracers and carbonaceous components: organic carbon (OC), WSOC, and elemental carbon (EC). We found that the percent modern carbon (pMC) in TC and WSOC increased during spring/summer with maximum (85% and 117%, respectively) in May. The temporal variations of pMC in WSOC and TC showed a good agreement with changes in the contributions of biogenic OA tracers to OC and WSOC. We also found that emissions of pollen in spring and fungal spores fromsoil in summer/autumn as well as secondary OA formation from biogenic VOCs (BVOCs) in summer/autumn are responsible for the enhanced pMC. Although emissions from biomass burning are significant in winter, enhanced fossil fuel combustion lowers the pMC in WSOC and TC. Throughout the year, modern carbon is more enriched in WSOC fraction than in TC, indicating that WSOC is more associated with biological activity. This study warrants a need to reconcile the atmospheric models, considering seasonal differences in BVOC emissions, particularly in temperate regions, in estimating secondary OA budget and its climatic impacts.