北京市大兴新城地区疫情前后细颗粒物二次气溶胶变化特征及潜在源分析

Characteristics of secondary aerosol changes in fine particulate matter before and after the outbreak in Daxing Xincheng District,Beijing and potential source analysis

为探究新冠肺炎疫情结束前后北京市大兴新城地区细颗粒物(PM_(2.5))中二次气溶胶的变化特征,观测了2022年11月15日—2023年3月15日的PM_(2.5)、水溶性离子和碳组分样品并对其进行分析.结果表明,观测期间,二次无机气溶胶(Secondary inorganic aerosol,SNA)(SO_(4)^(2-)、NH_(4)^(+)和NO_(3)^(-))和二次有机气溶胶(Secondary organic aerosols,SOA)平均浓度分别为14.38、6.23、3.47和4.64μg·m^(-3),二次气溶胶整体在PM_(2.5)中的占比为64.57%.疫情前后期间硫氧化率(SOR)和氮氧化率(NOR)的平均值均大于0.1,说明本地二次转化程度较高;在二次组分中,NO_(3)^(-)浓度最高,其次是NH_(4)^(+)、SOA和SO_(4)^(2-).通过分析疫情结束前后NH_(4)^(+)的理论值和观测值的相关性发现,大气中的二次无机气溶胶主要以(NH_(4))_(2)SO_(4)和NH_(4)NO_(3)的形式存在.通过阴、阳离子的相关性分析发现,大兴新城地区大气颗粒物PM_(2.5)总体呈碱性,大气环境处于富氨状态.通过分析PM_(2.5)、SNA、SOA与相对湿度(RH)的关系发现,在高湿度的环境下有利于二次气溶胶的产生.通过后向轨迹分析发现,影响大兴新城地区的污染气团中以河北省气流影响为主,SNA的潜在源区分布结果也证实主要受河北省中南部影响.由此可见,京津冀联防联控工作仍是需要长期持续关注的重点.

To investigate the characteristics of secondary aerosols in fine particulate matter(PM_(2.5))in Daxing Xincheng District,Beijing,before and after the epidemic,samples of PM_(2.5),water-soluble ions,and carbon fractions were observed and analyzed from November 15,2022,to March 15,2023.Throughout the observation period,the average concentrations of secondary inorganic aerosols(SNA)(SO_(4)^(2-),NH_(4)^(+)and NO_(3)^(-))and secondary organic aerosols(SOA)were found to be 14.38,6.23,3.47,and 4.64μg·m^(-3),respectively.The overall contribution of secondary aerosols to PM_(2.5)was64.57%.The mean values of the sulfur oxidation rate(SOR)and nitrogen oxidation rate(NOR)during the observation period were 0.521 and 0.219,respectively.This suggests a high level of local secondary transformation.Among the secondary components,the concentration of NO_(3)^(-)was the highest,followed by NH_(4)^(+),SOA,and SO_(4)^(2-).By analyzing the correlation between the theoretical and observed values of NH_(4)^(+)before and after the epidemic,it was found that the main form of secondary inorganic aerosols in the atmosphere was(NH_(4))_(2)SO_(4)and NH_(4)NO_(3).The analysis of the correlation between anions and cations revealed that the atmospheric particulate matter PM_(2.5)in Daxing New Town was generally alkaline,indicating an ammonia-enriched atmospheric environment.Furthermore,the correlation analysis between PM_(2.5),SNA,SOA,and relative humidity(RH)showed that high humidity conditions favored the production of secondary aerosols.Backward trajectory analysis indicated that the influence of airflow from Hebei Province was the primary cause of polluted air masses affecting the Daxing New Town area.The distribution of the potential source area of SNA confirmed that it was predominantly influenced by the middle and southern parts of Hebei Province.These findings highlight the continued importance of joint prevention and control efforts in the Beijing-Tianjin-Hebei region.