关中地区秋冬季颗粒物二次有机碳的估算

estimation of secondary organic carbon in PM2.5 and PM10 in Guanzhong area in autumn and winter

2017年9月4日~2018年1月19日期间分别在关中地区的5个主要城市西安(XA),渭南(WN),铜川(TCH),宝鸡(BJ),咸阳(XY)设置采样点进行PM2.5,PM10颗粒物手工采样观测,采用热光透射法(TOT)分析碳组分,最小值法估算二次有机碳(SOC)浓度,结果显示PM2.5与PM10中SOC平均浓度分别为(7.44±5.54),(9.62±7.49)μg/m^3,一次有机碳(POC)平均浓度分别为(7.04±2.59),(9.33±4.33)μg/m^3,不同粒径颗粒物中SOC各点位的浓度值分布表现基本相同为XY>XA>WN>BJ>TCH.PM2.5中SOC含量为8.76%,OC占比为48.03%,PM10含量为6.28%,OC占比为48.09%,季节分布均呈现为秋季低冬季高,关中地区SOC污染严重.后向轨迹聚类分析结果显示污染气团传输主要是关中地区局部污染和西北,东北方向传输,其中局部污染轨迹的数量占比较多,浓度较高.低空传输与近地面风向风速及污染物分布存在差异,结合关中地区盆地地形,静风频率高,边界层低等多种因素造成颗粒物中SOC浓度较高,其中BJ点位易受到东北气团的污染物传输累积.

Particulate matters including PM2.5 and PM10 were analyzed using manual determination method in the sampling sites which were situated at five inner cities of Shaan’xi province including Xi’an(XA),Weinan(WN),Tongchuan(TCH),Baoji(BJ),and Xianyang(XY)from September 4th 2017 to January 19th 2018.Carbon components and secondary organic carbon(SOC)were analyzed using thermo-optical transmission(TOT)and minimum value estimation method,respectively.Results showed the average concentrations of SOC and primary organic carbon(POC)were(7.44±5.54)and(7.04±2.59)μg/m^3in the PM2.5;(9.62±7.49)and(9.33±4.33)μg/m^3 in the PM10.The concentration distributions of SOC in five different sampling sites were XY>XA>WN>BJ>TCH.The SOC concentration was respectively 8.76%and 6.28%in PM2.5 and PM10;the OC proportion was respectively 48.03%and 48.09%in PM2.5 and PM10.The seasonal distribution of pollutants was low in the autumn and high in the winter.SOC pollution was serious in the five inner-cities of Shaanxi Province.Results of backward trajectories clustering analysis showed that the transmission of polluted air mass is mainly local pollution,as well as northwest and northeast direction transmission in the inner-city of Shaanxi province area.Among them,the number of local contamination trajectories and the concentration were relatively high.The pollutant distributions were difference in the five cities due to low-altitude transmission,and diverse near-surface wind direction and speed.The higher SOC concentrations in the particulate matters were caused by many factors such as basin topography,high static wind frequency and low boundary layer in these inner cities.The Baoji(BJ)city was vulnerable to transport and accumulate pollutants in the northeast air mass.