| Water-soluble organic carbon(WSOC)is the water-soluble part of organic carbon(OC)in fine particle,accounting for about 10-70%of OC.The hygroscopicity of WSOC not only affects the process of atmospheric cloud formation and then leading to global climate change,but also significantly reduces atmospheric visibility and affects the normal life of human.WSOC has strong absorption capacity in ultraviolet band and near ultraviolet band of visible light,which will have a direct impact on global radiation forcing.In addition,WSOC can also enter the human body through the respiratory system,posing a threat to human health.Therefore,it is of great significance to systematically study on the characteristics of WSOC for regional climate change and human health.Jinan is the capital of Shandong Province and one of the most polluted cities in North China.In recent years,the characteristics of WSOC in PM2.5 have not been systematically investigated,especially the studies on the seasonal characteristics of WSOC.In this research,a comprehensive investigation on PM2.5 had been performed in summer of 2015,autumn and winter of 2016 and spring of 2017,the water-soluble inorganic ions,carbon constituents,WSOC and levoglucosan were analyzed,the source and formation pathways of WSOC,absorption characteristics and regional transmission characteristics among four seasons were investigated.In this research,WSOC was the main component of OC in PM2.5 in Jinan,accounting for 55.77 to 68.77%of OC.WSOC had the highest absorption efficiency(0.76 m2/g)in winter,resulting in a stronger radiation forcing in the atmosphere.The central and western Shandong Province were the major sources of WSOC in the four seasons of Jinan.In addition,the southeastern Shandong Province and the Yellow Sea,eastern Shandong Province,southern Hebei Province and Beij ing-Tianj in-Hebei region,southern Henan Province were also the important sources of WSOC in summer,autumn,winter and spring respectively.The main sources of WSOC identified by source apportionment in Jinan including sulfate-based source,nitrate-based source,biomass burning and mixed primary source.Among them,the sulfate-based source and nitrate-based source were the largest contributions to WSOC in winter,biomass combustion was the main source of WSOC in summer and autumn,and mixed primary source in spring had the most significant influence on WSOC.The atmospheric transmission trajectories in Jinan included small-scale,middle-scale and large-scale transportation.The transmission trajectories in spring were mostly large-scale transportation,while the other three seasons were mainly small-scale transportation.The sulfate-based and nitrate-based sources had the largest contributions to WSOC in small-scale transportation,the mixed primary source was the main contribution to WSOC in large-scale transportation,while biomass burning had different effects on various trajectories in different seasons.There were different characteristics of WSOC among different polluted events.In summer and autumn,WSOC had higher concentrations and mainly came from secondary formation during the high biomass burning periods.WSOC in haze among winter mainly came from the secondary liquid-phase reaction,and the fireworks burning during the Spring Festival could significantly increased the concentration of WSOC.The WSOC in the dust-storm periods of spring mainly came from mixed primary source in large-scale transportation.This research systematically studied characteristics of WSOC in different seasons,transmission,and special pollution events in Jinan.It could provide scientific references for the prevention and control of WSOC and fine particulate matter in different seasons and pollution events in this region. |
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