Isoprene And Monoterpene Secondary Organic Aerosol In Marine Boundary Layer:Distribution,characteristic And Potential Influencing Factors

Biogenic secondary organic aerosol(BSOA)is an important component of atmospheric aerosols.Isoprene and monoterpenes are the most important BSOA precursors and can undergo rapid atmospheric oxidation and heterogeneous reactions to generate secondary organic aerosol(SOA).Isoprene and monoterpenes are mainly emitted by higher plants,or by phytoplankton in the ocean.Emissions of isoprene and monoterpenes by phytoplankton,although small,may generate significant amounts of BSOA,which have impact on atmospheric environment of marine boundary layer.However,the concentration,global distribution characteristics and sources of BSOA in marine boundary layer have not been sufficiently studied,especially in the polar regions.In this paper,we collect total suspended particulate samples along the cruises during the 30th Chinese Antarctic Research Expedition and the 6th Chinese Arctic Research Expedition.The study area covers seas from the Arctic to the Antarctica,including the Southern Ocean,the Indian Ocean,seas along Australia coast,seas among Southeast Asia,the Yellow Sea,the Sea of Japan,the Sea of Okhotsk,the Bering Sea and the Arctic Ocean.Isoprene and monoterpene secondary organic aerosol(SOA)tracers were analyzed by GC-MS,their concentration and distribution characteristics were obtained,and the potential influencing factors were preliminarily revealed by combining ion composition analysis,carbon speciation analysis of aerosol,meteorological parameters,surface seawater parameters and air backward trajectories.The concentration of isoprene SOA tracers ranged from 0 to 127 ng/m3,with a mean concentration of 6.4 ng/m3.Concentration of monoterpene SOA tracers ranged from 0 to 91 ng/m3,with a mean concentration of 3.8 ng/m3.Isoprene SOA tracers and monoterpene SOA tracers were detected in aerosol samples in marine boundary layer of different sea areas,and the estimated concentrations of isoprene SOA were higher than those of monoterpene SOA in most sea areas.The spatial distribution of SOA concentration varied greatly,with higher concentration near the continent.The concentration of isoprene SOA tracers and monoterpene SOA tracers had obvious latitudinal distribution characteristics in the northern hemisphere,and reached the highest level in the middle latitude.In the circumpolar Antarctic region,isoprene and monoterpene SOA concentrations were low but fluctuating.Isoprene and monoterpene SOA contributed approximately 7%to organic aerosol in aerosol samples during two cruises.Base on model calculations,the interfacial photochemistry at the ocean surface contributed greatly to isoprene SOA in part of polar regions,accounting for about 8%in the Southern Ocean and about 4%in the Arctic Ocean.Biomass burning affected isoprene and monoterpene SOA in many regions and can be transported over long range to the Arctic and Antarctic regions.