Pollution Characteristics And Source Analysis Of PM_2.5-bound Typical Organic Compounds In Zhengzhou High-tech Zone

Organic aerosols are an important part of atmospheric PM2.5.Organic aerosols play a very important role in the formation of haze,and have significant effects on air quality and human health.The air pollution in Zhengzhou is serious.The study of the pollution characteristics and sources of organic components in Zhengzhou,could provide effective scientific basis for the government to formulate air pollution control measures.In this study,PM2.5 samples were collected in the typical months of different seasons in Zhengzhou High-tech zone from 2019 to 2020.The concentrations and seasonal variation of PM2.5,organic carbon(OC),elemental carbon(EC),8 dicarboxylic acids,33 n-alkanes,and 3 anhydrosugars were analyzed.The effects of biomass burning on atmospheric fine particles were studied using levoglucosan as biomass combustion tracer.The positive matrix factorization(PMF)model was used to identify the emission sources of typical organic compounds qualitatively,and the backward trajectory model was used to analyze the regional transport pathways.The results showed that the annual average mass concentration of PM2.5 during the sampling period was 67.0μg·m-3,which was 1.9 times of the Chinese grade Ⅱannual limits,and showed a seasonal trend of winter>autumn>spring>summer.The annual mean concentrations of OC and EC were 9.4 μg·m-3 and 1.5 μg·m-3,accounting for 15.3%and 2.4%of PM2.5,respectively.By using OC/EC ratio,it is found that the carbonaceous aerosol in Zhengzhou is mainly affected by motor vehicle emissions and coal combustion.According to the calculation,the annual average concentration of SOC was 3.4 μg·m-3,accounting for 37.1%of OC.The total annual average concentration of the tested organic compounds was 812.4 ng·m-3,among which the most abundant classes of compounds were anhydrosugars,followed by dicarboxylic acids and n-alkanes.During the sampling period,the annual average concentration of dicarboxylic acid was 263.8 ng·m-3,and the seasonal variation was in the order of summer>spring>autumn>winter.The characteristic ratios showed that the dicarboxylic acids are affected by vehicle emission and secondary photochemical conversion,and the contribution of anthropogenic sources is more significant than that of biological sources.The results of correlation analysis showed that the dicarboxylic acids were from similar sources.The annual average concentration of n-alkanes was 201.4 ng·m-3 and showed a seasonal trend of winter>autumn>spring>summer.The carbon number maxima,carbon preference index,and plant wax contribution of n-alkanes indicated that emissions from anthropogenic and biological sources.The annual average concentration of anhydrosugars was 347.1 ng·m-3 and showed a seasonal trend of winter>autumn>spring>summer.Levoglucosan was the most abundant of the three anhydrosugars.Correlation analysis showed that the three anhydrosugars were homologous and came from biomass combustion sources.According to the characteristic molecular ratios and the local forestry and crop production,the main types of biomass combustion are crop residues and softwood in Zhengzhou.Levoglucosan was regarded as the biomass combustion tracer to estimate the contributions of biomass combustion to PM2.5 and OC in the study area,reporting 10.2%and 32.6%of total respectively.In spring and winter,levoglucosan showed strong correlations with dicarboxylic acids,indicating that biomass combustion may be an important source of dicarboxylic acid in spring and winter in Zhengzhou.The correlation between levoglucosan and n-alkanes indicated that biomass combustion was an important source of n-alkanes in this study area.PMF results showed that secondary photochemical oxidation(30.2%)and coal burning(20.0%)were the major sources of atmospheric organic aerosols in Zhengzhou,followed by biomass burning(18.8%),motor vehicle emissions(16.1%),and higher plant emissions(14.9%).The backward trajectory analysis results showed that the air mass trajectory is mainly affected by long-distance transport from northwest and northeast in spring and autumn,and the air mass trajectory is mainly from east and southwest in summer,and the air mass trajectory is mainly affected by long-distance transport from the northwest in winter.