北京及周边地区夏季PM2.5中含碳组分污染特征与来源解析

为研究《打赢蓝天保卫战三年行动计划》等政策实施后北京及其周边区域夏季环境PM_2.5含碳组分特征及来源,2019年7月分别在北京城区与河北郊区的2个站点同步连续采集大气PM_2.5样品,利用热光碳分析仪分别测定了有机碳(OC)和元素碳(EC)及其组分的质量浓度;通过最小OC/EC比值法、最小相关系数法估算了二次有机碳(SOC)浓度;利用主成分分析、后向轨迹分析等方法探究了含碳气溶胶的来源。结果表明:夏季北京城区PM_2.5中ρ(OC)和ρ(EC)平均分别为(6.34±0.64),(1.96±0.29)μg/m3,分别占ρ(PM_2.5)的18.65%和5.78%;河北郊区PM_2.5中ρ(OC)与ρ(EC)平均分别为(6.29±0.79),(3.54±0.63)μg/m3,分别占ρ(PM_2.5)的17.69%和9.53%。2种方法估算出北京城区的ρ(SOC)分别为(3.35±0.59),3.98μg/m3,分别占ρ(OC)的(51.77±6.97)%和68.48%;河北郊区的ρ(SOC)分别为(3.28±0.69),4.17μg/m3,分别占ρ(OC)的(62.42±9.62)%和68.32%。此外,夏季北京城区与河北郊区均存在较为严重的二次污染;北京城区含碳组分主要污染源是混合机动车排放、道路扬尘及燃烧源;而工业燃煤排放、机动车尾气及扬尘是河北郊区含碳组分的主要污染源。后向轨迹分析发现,夏季气团轨迹主要来自东南、西南及偏南方向,且对北京城区与河北郊区2个区域PM_2.5中碳组分的影响较大。

POLLUTION CHARACTERIZATION AND SOURCE ANALYSIS OF CARBON COMPONENTS OF PM2.5 IN BEIJING AND SURROUNDING AREAS IN SUMMER

In order to study the characteristics and sources of carbon components in PM_2.5 in Beijing and its surrounding areas in summer after the implementation of the Three-year Plan on Defending the Blue Sky and other policies, samples were collected at sites in Beijing urban area and Hebei suburban area in July 2019. The organic carbon(OC), elemental carbon(EC) and their components concentrations were determined using a thermo-optical carbon analyzer. The concentrations of secondary organic carbon(SOC) were also estimated by the OC/EC minimum ratio method and the minimum R squared method. The sources of carbon aerosols were analyzed by principal component analysis and back-trajectory analysis. The results showed that the average concentrations of OC and EC in PM_2.5 were(6.34±0.64) μg/m3 and(1.96±0.29) μg/m3 in Beijing urban area, accounting for 18.65% and 5.78% of PM_2.5, respectively. The average concentrations of OC and EC were(6.29±0.79) μg/m3 and(3.54±0.63) μg/m3 in Hebei suburban area, accounting for 17.69% and 9.53% of PM_2.5, respectively. The values of SOC in Beijing urban area were(3.35±0.59) μg/m3 and 3.98 μg/m3, respectively, accounting for(51.77±6.97)% and 68.48% of total OC concentration. The values of SOC in Hebei suburban area were(3.28±0.69) μg/m3 and 4.17 μg/m3, respectively, accounting for(62.42±9.62)% and 68.32% of total OC concentration. There was severe secondary pollution in Beijing urban area and Hebei suburban area in summer. Mixed vehicle emissions, road dust and combustion sources were the primary pollution sources of carbon aerosols in Beijing urban area. Industrial coal emission, vehicle exhaust and dust were the main pollution sources of carbon aerosols in Hebei suburban area. Back-trajectory analysis showed that the air mass trajectories in summer mainly came from southeast, southwest and south direction, which had a significant impact on carbon components of PM_2.5 in the urban area of Beijing and the suburban area of Hebei.