国庆前后北京城区PM_(2.5)组分污染及来源特征分析

Pollution and source characteristics of PM_(2.5) components in Beijing urban area around National Day

为探究北京城区国庆前后及国庆期间PM_(2.5)主要组分的污染及来源特征情况,采集2019年9月27日-10月14日北京市大气PM_(2.5)样本,并测定其中碳质气溶胶(OC、EC)及8种水溶性离子(Na^(+)、NH_(4)^(+)、K^(+)、Mg^(2+)、Ca^(2+)、Cl^(-)、NO_(3)^(-)、SO_(4)^(2-))的质量浓度,并分析PM_(2.5)中各化学组分的浓度变化特征、来源特性及气象要素的影响,并对北京市细颗粒物进行源解析和区域传输分析.结果表明,整个观测期间PM_(2.5)基本呈现"M"型的变化趋势,国庆期间呈现"V"型的变化趋势.国庆期间总碳质气溶胶、水溶性无机离子质量浓度为(14.45±5.87)μg·m^(-3)和(14.97±9.75)μg·m^(-3),占PM_(2.5)质量浓度的59.7%,各组分质量浓度在国庆期间均有所下降,其中NO_(3)^(-)质量浓度下降最为明显,下降率达53.4%.来源分析结果表明,机动车尾气、燃煤和扬尘是大气PM_(2.5)化学组分的主要来源,其中道路扬尘和建筑扬尘是Ca^(2+)、Mg^(2+)和Na^(+)的主要来源,机动车车尾气排放是碳质气溶胶及二次无机离子的最主要来源.车流量的改变和气象因素与国庆前后PM_(2.5)及其组分变化密切相关,PM_(2.5)及各组分质量浓度在车流量高峰的9月30日和10月6、7日达到峰值,而1-5号移动源贡献减弱和气象要素(降水)导致了最低值的出现.较低的风速及来自于东北、西南方向的污染物输送是观测期间PM_(2.5)较高的重要原因.

In order to study the pollution and source characteristics of main components in PM_(2.5) around the National Day in Beijing,the samples of PM_(2.5) were collected from September 27 to October 14,2019 and the mass concentrations of carbon aerosols(OC,EC)and eight water-soluble ions(Na^(+),NH_(4)^(+),K^(+),Mg^(2+),Ca^(2+),Cl^(-),NO_(3)^(-),SO_(4)^(2-))were measured.The concentration variation,source characteristics and meteorological factors of the main chemical component in PM_(2.5)were analyzed.Then the source analysis and regional transport analysis of fine particulate matter in Beijing were carried out.The results are listed as follows:During the whole observation period,PM_(2.5)presents a"M"-shaped change trend basically,and a"V"-shaped change trend during the National Day.The mass concentrations of total carbonaceous aerosols and water-soluble inorganic ions are(14.45±5.87)μg·m^(-3)and(14.97±9.75)μg·m^(-3)μg·m^(-3)respectively,accounting for 59.7%of the PM_(2.5)mass concentration during the National Day.The mass concentration of each component decreased during the National Day,among which the mass concentration of NO_(3)^(-)decreased the most obviously,with a decrease rate of 53.4%.Source analysis results show that vehicle exhaust,coal burning and dust are the main sources of atmospheric PM_(2.5)chemical components.Road dust and building dust are the main sources of Ca^(2+),Mg^(2+)and Na^(+),and vehicle exhaust is the main source of carbon aerosol and secondary inorganic ions.The change of vehicle flow and meteorological factors are closely related to the changes of PM_(2.5)and its components around the National Day.The mass concentration of PM_(2.5)and its components reaches the peak on September 30 and October 6,7 when the traffic peaks,while the contribution of mobile sources weakened and meteorological elements(precipitation)led to the lowest value from October 1 to 5.The lower wind speed and the transportation of pollutants from the northeast and southwest are important reasons for the higher PM_(2.5)during the observation period.