北京市开发区PM1污染特征及影响霾形成的因素

通过采集北京市亦庄经济技术开发区2016年7月和10月、2017年1月和4月4个季节典型代表月大气亚微米颗粒物PM₁样品，分析研究了该开发区PM₁及其水溶性离子组分的季节变化以及不同污染时段的变化特征，揭示了影响二次组分形成和霾污染形成的重要因素.结果表明：研究期间开发区PM₁平均浓度为73.95μg/m³，高于北京市同期估算的PM₁平均水平，为其1.13倍.夏、秋、冬、春4季PM₁平均浓度分别为69.22，63.38，99.50，57.26μg/m³，明显呈现出冬季 > 夏季 > 秋季 > 春季的季节变化特征，各季节霾天PM₁浓度是清洁天的1.78~3.17倍.PM₁中总水溶性离子浓度为37.30μg/m³，占PM₁总质量浓度的50.44%，其中二次组分SO₄^2-、NO₃^-和NH₄⁺（SNA）平均浓度占总水溶性离子浓度的86.98%，是PM₁中水溶性离子的最主要组成部分.PM₁总水溶性离子浓度的季节变化与SNA的变化一致，表现为冬季 > 夏季 > 秋季 > 春季.研究期间硫氧化率（SOR）高于氮氧化率（NOR），且SOR表现为夏 > 秋 > 冬 > 春，而NOR表现为夏 > 秋~春 > 冬，相应霾污染天SOR和NOR均显著高于清洁天，其中夏季霾天SO₂和NO₂的二次转化过程最为显著.SO₂向SO₄^2-的转化主要受相对湿度RH、温度T、NO₂以及NH₃的影响，且液相反应是硫酸盐形成的重要途径.NO₂向NO₃^-的转化受RH、T、O₃以及NH₃的影响较大.鞍型气压场、均压场、逆温层以及南、东南和西南方向为主的近地面偏弱气团传输是影响霾污染形成的重要因素.

Pollution characteristics of PM1 and factors affecting the formation of haze pollution at a developed zone in Beijing

A campaign of sampling atmospheric submicron particulate matter (PM₁) samples at Yizhuang zone in Beijing during July, October 2016 and January, April 2017, was carried out to investigate the characteristics of PM₁ and itswater-solublespecies during four seasons and different haze periods. The important factors affecting the formations of the secondary ions and haze pollution were discussed. The results showed that the average concentration of PM₁ reached 73.95μg/m³ for the entire study at Yizhuang zone, being 1.13times as high as the corresponding average concentration level of PM₁ in Beijing. Average concentrations of PM₁ in summer, autumn, winter and spring were 69.22, 63.38, 99.50 and 57.26μg/m³, respectively, showing the order of winter > summer > autumn > spring; the concentrations of PM₁ during haze days were 1.78~3.17times as high as those in clean days. The total water-soluble ion concentration in PM₁ was 37.30μg/m³, accounting for 50.44% of PM₁; secondary ions SO₄^2-、NO₃^- and NH₄⁺ (SNA) were the most important water soluble ions, which accounted for 86.98% of the total water soluble ions. The seasonal variation of the total water soluble ion concentrations in PM₁ was in accordance with SNA, following the order of winter > summer > autumn > spring. The average sulfur oxidation rate SOR was higher than the mean nitrogen oxidation rate NOR for the entire study, of which SOR presented the order of summer > autumn > winter > spring, and NOR showed the order of summer > autumn~spring > winter, and SORs and NORs in haze days were all significantly higher than those in clean days, especially in summer. The conversion of SO₂ to SO₄^2- was apparently influenced by relative humidity RH, temperature T, NO₂ and NH₃, and aqueous chemical reactions of SO₂ on the surface of PM₁ might be the important pathway of SO₄^2- formations. The conversion of NO₂ to NO₃^- was greatly influenced by RH, T, O₃, and NH₃. The haze pollution formation was mainly influenced by saddle type pressure field, even pressure field, and inversion layer, as well as weak air mass transport from the south, southeast and southwest directions.