Characteristics And Sources Of Water-soluble Organic Carbon Pollution In PM_2.5 In Dongting Lake Area

Water-soluble organic carbon（WSOC）is an important component of fine particulate matter,and has an important impact on climate change,ecological environment and human health.Therefore,studying the pollution characteristics,distribution and source analysis of WSOC is of great significance for understanding the regional air pollution status and its prevention and control.The study was collected PM_2.5 samples in Dongting Lake area from September 2017 to August 2018,mainly analyzed the pollution characteristics of PM_2.5 and WSOC in Dongting Lake during the sampling period,and compared WSOC with Changsha.Furthermore,We explored the transmission paths and potential source contributions of WSOC using HYSPLIT and PSCF models,and then analyzed the source of WSOC using PCA and PMF models.The result showed that:（1）The annual average mass concentrations of PM_2.5 and WSOC in the Dongting Lake area were 43.41μg/m³ and 4.33μg/m³,respectively.The proportion of WSOC/PM_2.5was 11.66%.The WSOC concentration was high in autumn and winter and low in spring and summer.Compared with Changsha urban area,the concentrations of PM_2.5 and WSOC in Dongting Lake were relatively low.WSOC in both places was highest in winter and lowest in summer.The proportion of WSOC in PM_2.5 in Changsha was 14.16%.（2）WSOC had good correlation with NO₃^-and SO₄^2-in autumn,and WSOC had significant positive correlations with K⁺,Na⁺,Ca²⁺and Mg²⁺in spring and autumn.In winter,WSOC was significantly positively correlated with Na⁺and Mg²⁺,but weakly correlated with NH₄⁺,NO₃^-,SO₄^2-,and K⁺.In summer,WSOC was significantly correlated with Ca²⁺and Mg²⁺,indicating that industrial sources and dust sources might be one of the sources of WSOC.（3）The concentrations of WSOC in the polluted period(PM_2.5>75μg/m³)of Dongting Lake area was higher than in the clean period(PM_2.5<75μg/m³),and the WSOC/PM_2.5 ratios were 6.91%and 12.26%in the polluted period and the clean period,respectively.PM_2.5 had a good correlation with WSOC during the pollution period,and there was a significant positive correlation between WSOC and SO₂ and NO₂.It is possible that WSOC was affected by industrial sources and motor vehicle exhaust.（4）The cluster analysis results of the backward trajectory showed that the air mass trajectories in the Dongting Lake area were divided into four categories,mainly from the northeast and the south.In both spring and summer,Dongting Lake area was affected by air masses from the southern region.Potential source contribution analysis showed that Dongting Lake was mainly affected by pollution from surrounding cities;the potential WSOC source area in winter was wider than that in autumn,and the potential source area of WSOC in spring and summer were mainly distributed in the south and east of the sampling point,respectively.（5）PCA analysis results showed that WSOC mainly came from secondary sources and industrial sources in autumn.In winter,WSOC was greatly contributed by biomass burning.In spring,WSOC mainly came from dust sources and biomass burning sources.In summer,WSOC was also affected by industrial sources.Based on the source analysis of the PMF model,the Dongting Lake WSOC is affected by industrial sources,secondary sources,dust sources,motor vehicle sources and biomass combustion sources.