Characteristics Of Water-soluble Organic Carbon In Atmospheric Particulate Matter In The Yellow River Delta

Water-soluble organic carbon(WSOC),accounting for about 20%-80%organic carbon(OC),is an important component of carbonaceous aerosols.WSOC exerts a certain influence on radiative forcing.Because WSOC can absorb sunlight near the ultraviolet band.and it can also affect cloud formation process via changing the physical properties of aerosols such as surface tension and hygroscopicity.In the condition of excluding the effects of biomass burning,WSOC could also be used as a tracer to estimate the concentration of secondary organic aerosol(SOA)in the field observations.Therefore,it is very important to systematically investigate the characteristics of WSOC for both regional climate change and the study of SOA.The Yellow River Delta(YRD)is located in the North China Plain.With the rapid development of economy,the air quality in the YRD has deteriorated sharply in recent years.The development of oil exploitation in Dongying City,where the YRD is located,has resulted in a large amount of volatile organic compounds(VOCs)emissions.In addition,the YRD is close to the Bohai Sea,and the relative humidity of the area is relatively high,which is conducive to the formation of WSOC in particulate phase.Therefore,observation experiments were conductedatin the Yellow River Delta Nature Reservein in winter and summer of 2017.Carbonaceous matters,water-soluble ions and WSOC were analyzed,and the seasonal variation characteristics of WSOC,including sources,properties of secondary formation,light absorption and regional transportation were investigated using some source apportionment model,airtrajectory model etc,.In addition,the characteristics of WSOC in the YRD were also compared with those in Jinan to identify the differences of WSOC between the regional background site and the urban site.The results showed that WSOC was the main component of OC in the YRD,accounting for 70%of OC.The average concentration of WSOC in summer(4.62 ±2.90 μg/m3)was higher than that in winter(3.23 ± 1.75 μgg/m3),Regional transportation might be one of the factors that caused the seasonal variation of WSOC.Dongying and some inland cities in central and southern Shandong Province,such as Weifang,Zibo,Jinan and Linyi,were indentified as the main sources of WSOC.In addition,the Beijing-Tianjin-Hebei region and the eastern coastal areas of Jiangsu Province also transported significant amount of WSOC to the sampling site in winter and summer,respectively.The mass absorption efficiency of WSOC was 1.32 m2/g in winter and 0.38 m2/g in summer,suggesting the light absorption ability of WSOC in winter was much stronger,There were five main sources of WSOC:sulfate-based source,nitrate-based source,mixed secondary formation,mixed primary source and biomass burning.Secondary formation,the dominant source,contributed 59.5%and 76.0%to WSOC in winter and summer,respectively.High aerosol liquid water(ALW)and particle acidity were found to enhance the secondary formation of WSOC.In winter,the concentration of WSOC at the background site of the YRD was lower than that in Jinan,but the ratio of WSOC/OC there was slightly higher.The mass absorption efficiency of WSOC in the YRD was higher,indicating the light absorption ability of WSOC in the YRD was stronger than that in Jinan.The sources of WSOC in Jinan were similar to that in the YRD.However,the main source of WSOCin the YRD was secondary formation(59.5%),while the main source of WSOC in Jinan was primary emission(60.3%).This study provides basic scientific data to the scientific researchers so that they could systematically understand the pollution of fine particles in the YRD,especially the pollution characteristics of WSOC.Moreover,it could also provide a scientific theoretical basis to the prevention and control of fine particle pollution in this region.