北京市冬季PM_(2.5)污染特征与区域传输影响研究

Pollution characteristics and regional migration impact of PM_(2.5) in Beijing in winter season

选取北京师范大学监测点于2015年1月进行PM_(2.5)样品采集,应用离子色谱仪(IC)分析PM_(2.5)中水溶性无机离子质量浓度,采用WRF-CAMx-PSAT模型系统对采样时段PM_(2.5)及典型离子的区域来源进行了模拟。结果表明,采样期间(2015年1月2—20日)与重污染过程(2015年1月13—15日)北京PM_(2.5)质量浓度分别为(105.9±72.6)μg/m^3和(232.2±80.2)μg/m^3,PM_(2.5)中总水溶性无机离子质量浓度分别为(47.4±39.8)μg/m^3和(120.7±23.3)μg/m^3,分别占PM_(2.5)的44.2%和53.9%。SO_4^(2-)、NO_3^-和NH_4^+是水溶性离子的主要组分,非重污染过程和重污染过程这3种水溶性离子质量浓度之和分别占总水溶性离子质量浓度的80.5%和89.3%。模拟结果显示,本地源排放是北京市PM_(2.5)、SO_4^(2-)、NO_3^-、NH_4^+的主要来源,贡献率分别为81.4%、79.5%、58.1%、95.3%,北京周边源排放对PM_(2.5)贡献率较大的有保定、天津、张家口、唐山,这4市占北京周边省市排放源贡献率的72.0%。

The present paper is aimed at providing for a seasonal statistical report on the characteristic features and regional migration impact of PM2.5 pollutants in Beijing in winter season. For the research purpose, we have collected and analyzed the pollution characteristics and regional migration features of PM2.5 and the water-soluble ions in Beijing, by using PM2.5 samples collected in January of 2015 in Beijing Normal University. Ion chromatograph has been used for testing and analyzing the water-soluble ions in PM2.5. And, then, we have established WRF - CAMx modeling system to simulate and investigate PM2.5 pollution situation during the sampling period by using PSAT technology. The results of our investigation and analysis demonstrate that the mass concentration of PM2.5 during the sampling period （Jan. 2 -20, 2015） has been usually worked out at about （105.9 ±72. 6 ） μg/m^3; whereas that during the severe pollution period （Jan. 13-15, 2015） accounts for（232. 2 ±80. 2）μg/m^3. On the other hand, the meteorological conditions that go against the pollutant dispersion such as high humidity, low temperature, and slow wind velocities can all be the significant reasons for heavy air pollution formation. The mass concentrations of the total water-soluble ions in PM2.5 during the sampling period and severe pollution period are mostly of（47.4 ±39. 8 ） μg/m^3 and （ 120. 7 ±23.3 ）μg/m^3, accounting for 44. 2% and 53.9% of the total PM2.5, respectively. And, SO4^2-, NO3^- and NH4^＋ serve as the major components of the water-soluble species, which should account for 80. 5% and 89. 3% of the total water-soluble ions in the non- severe and severe pollution periods, respectively, with NO3^- being the highest concentration both in the non-severe and severe pollution periods. The simulation results indicate that the local emission serves as the major contributor to PM2.5 in Beijing municipality area, at the percentages of 81.4%, 79. 5%, 58. 1% and 95.3% for PM2.5, SO4^2-, NO3^- and NH4^＋, respectively, whereas Baoding, Tianjin, Zhangjiakou and Tangshan have also made remarkable contribution to PM2.5 in Beijing, which account for 72. 0% of the total pollution status-in-situ from the surrounding cities of Beijing. As to the kinds of pollution, nitrate in PM2. 5 is mainly coming from the surrounding areas of Beijing during the severe pollution periods （ 58.3% ） , with ammonium mainly coming from the Beijing local contribution （contribution rate of surrounding areas 〈 5 % ）.