沈阳市冬季不同污染程度PM2.5中OC和EC污染特征

于2018年12月~2019年1月对沈阳市PM_2.5进行持续在线浓度监测，使用有机碳/元素碳分析仪对PM_2.5中有机碳（OC）和元素碳（EC）的质量浓度进行分析，研究了不同污染程度下PM_2.5及其碳组分的污染特征和来源.结果表明，沈阳地区冬季碳组分污染较为严重，不同污染程度下的总碳气溶胶（TCA）约占PM_2.5的36.3%~42.8%.中/重度污染天气下PM_2.5、OC和EC的平均质量浓度达到148.6，29.6，6.6μg/m³，是清洁天的3.1~3.3倍.PM_2.5、OC和EC的日变化均表现为早晚高、午后低，任一时刻其浓度均为中/重度污染>轻度污染>清洁天.不同污染程度下的OC/EC值均大于2，其中污染天比值分布在2.1~25.3区间内，表明燃煤和机动车尾气排放是污染天碳质气溶胶的主要来源.二次有机碳（SOC）随污染程度增加表现出升高趋势，清洁天、轻度污染和中/重度污染下其平均浓度依次为2.9，6.5，10.6μg/m³.后向轨迹聚类结果表明，沈阳地区冬季污染天主要受偏北和西北方向气团影响.

Characteristics of organic carbon (OC) and elemental carbon (EC) under different pollution levels of PM2.5 during winter in Shenyang

The organic carbon (OC) and elemental carbon (EC) in PM_2.5 were measured by organic carbon/elemental carbon analyzer from December 2018 to January 2019 in Shenyang. The pollution characteristics of carbon components under different pollution levels were studied. The pollution of carbon component was serious in winter of Shenyang, and the total carbon aerosol (TCA) accounted for 36.3%~42.8% of PM_2.5 at different pollution levels. The average mass concentrations of PM_2.5, OC and EC were 148.6, 29.6 and 6.6μg/m³ in moderate/heavy pollution days respectively, which were 3.1~3.3times of those in clean days. The diurnal variations of PM_2.5, OC and EC showed a high value in the morning and evening and low in the afternoon. At any time, the concentrations of PM_2.5, OC and EC showed as moderate/heavy pollution> light pollution> clean days. The OC/EC ratios under different pollution levels were all higher than 2. The OC/EC ratio of pollution days ranged from 2.1 to 25.3, which indicated that coal combustion and vehicle exhaust emissions were the main sources of OC and EC in pollution days. The secondary organic carbon (SOC) increased with pollution levels, with the concentration of 2.9, 6.5 and 10.6μg/m³ in clean, light pollution and moderate/heavy pollution days, respectively. The backward trajectory simulation showed that the pollution days in winter of Shenyang were mainly affected by air masses from the northward and northwest directions.