北京地区秋季雾霾天PM_(2.5)污染与气溶胶光学特征分析

PM_(2.5) Pollution and Aerosol Optical Properties in Fog and Haze Days During Autumn and Winter in Beijing Area

利用北京城区和郊区2011年9月1日～12月7日PM2.5质量浓度、气溶胶散射系数(σsca)和黑碳浓度观测资料,研究了雾霾天气条件下北京地区PM2.5污染与气溶胶光学参数的变化特征,并讨论了气象条件的作用.结果表明,北京地区PM2.5污染和气溶胶光学特性受雾霾天气的影响非常明显.PM2.5浓度、σsca和气溶胶吸收系数(σabs)在雾霾期均明显高于非雾霾期,雾霾期日均PM2.5浓度在城区和郊区分别达到97.6μg·m-3和64.4μg·m-3,为非雾霾期日均浓度的3.3和4.8倍.城区高PM2.5浓度造成雾霾类天气出现频率明显高于郊区.轻雾天城区PM2.5浓度、σsca和σabs明显高于郊区,区域输送的影响相对较弱,轻雾和霾天城郊差异较小,区域性特征明显,而雾天σsca城郊非常接近且在各雾霾类天气中相对最高,气溶胶散射能力最强,区域性特征较为明显.气象条件的不同造成各雾霾过程PM2.5浓度、σsca和σabs的空间分布、PM2.5污染及气溶胶消光强度上呈现不同的特点.边界层以上偏南风将南部地区污染物向北京输送,在整层下沉气流作用下使得边界层内污染物浓度增加,加之边界层高度持续稳定在600 m左右,边界层内风速很低,污染物水平、垂直扩散均很弱,造成局地污染物的累积,形成了PM2.5污染和气溶胶消光强度最强的一次雾霾过程.

A study on the PM2.5 pollution and aerosol optical properties in haze-fog days was carried out from Sep.1st to Dec.7th,2011 in Beijing area by using PM2.5 concentration,aerosol scattering coefficient（σsca） and absorption coefficient（σabs） measured under urban and rural environment.The effect of weather condition on the PM2.5 pollution and aerosol optical properties was discussed as well.The results showed that the PM2.5 concentration,σsca and σabs were evidently higher in haze-fog days than those in non-haze-fog days.The average PM2.5 concentrations in haze-fog days with values of 97.6 μg·m-3 and 64.4 μg·m-3 were as 3.3 and 4.8 times as those in non-haze-fog days at urban and rural stations,respectively.The higher PM2.5 concentration in urban area resulted in the more frequent fog and haze phenomena than that in rural area.The PM2.5 concentration,σsca and σabs were significantly higher in urban area than that in rural area in mist days,while relatively close in mist-haze days.This difference suggested that the effect of regional transport of pollution was relatively evident in mist-haze days but weak in mist day.In fog days the σsca showed no evident difference between urban and rural area,and was the highest in all types of fog and haze weather.The scattering property of aerosol was the strongest in fog days.The different weather conditions resulted in various characteristics of spatial distribution of PM2.5 concentration,σsca and σabs,as well as the strength of PM2.5 pollution and aerosol extinction.The pollutants transported by the strong southwest wind above the boundary layer and subsided in the boundary layer companying with the local accumulation of pollutants due to the weak diffusion resulted in the most serious haze-fog episode with the strongest PM2.5 pollution and aerosol extinction.