石家庄市秋季典型天气背景下重污染特征分析

Pollution characteristic under typical weather background in autumn over Shijiazhuang

利用石家庄市气象观测资料和环境监测资料,重点分析了2013年石家庄市两次重污染天气过程前期PM10及PM2.5污染物浓度快速升高的天气背景、气象要素、边界层特征和污染物输送后向轨迹,并利用20 m、86 m和200 m环境梯度观测资料探讨了PM2.5浓度随高度的变化。结果表明:当高空环流较平直,低空850 h Pa为弱偏南风,地面处于入海变性高压后部和暖低压底部时,形成东南高、西北低的气压场,在此种天气类型(暖低压型)影响下,石家庄市夜间逆温层厚,风速小,不利于污染物扩散,造成污染物在本地累积。白天主导风向为南至东南风,中午前后风速较大(≥2 m·s-1),湿度小(平均相对湿度<55%),周边污染物在地面及低空偏南风的作用下向石家庄市输送明显,污染物浓度随风速增大振荡上升,霾加重。太行山地形对污染物汇聚起重要作用,本地污染和周边污染叠加,导致石家庄市污染物浓度升高较快,AQI在24 h内上升幅度可达100以上,导致重度或严重污染发生。梯度观测表明,在重污染期间石家庄市污染层较厚,上层(200 m)PM2.5浓度高于下层(20 m),在暖低压天气背景下此现象更明显,说明上层PM2.5污染不仅来源于本地污染,外来输送也起一定作用。

PM10 and PM2.5 concentrations rose rapidly before two heavy air pollution events in 2013 in Shijiazhuang, so corresponding weather situation, meteorological elements, boundary layer characteristics and pollutant transport backward trajectory were analyzed based on the meteorological data and environmental monitoring data. At the same time, vertical variation of PM2.5 concentration was discussed combining environmental gradient dam at 20 m,86 m and 200 m. The results indicate that when upper air circulation is flat and south wind is weak at 850 hPa as well as the surface is located in the back of seaside denaturalization high-pressure and the bottom of warm low-pressure, surface pressure field is high in southeast and low in northwest. This weather situation is defined as warm low pattern. Under this situation,inversion layer is thick in night in Shijiazhuang, and wind speed is small, which is not favorable to diffusion of the pollutants. Thus, it leads to pollutants accumulation in the local area. On the other hand, the dominant wind direction is south to southeast in daytime; wind speed is large （ ≥2 m·. s^-1） ;relative humidity is small （average relative humidity 〈 55 % ） around noon. The surrounding pollutants are transferred obviously to Shijiazhuang with the ground and low-level south wind. The concentrations of pollutants shake up with increase of wind speed and haze aggravates. Terrain of Taihang mountain also plays an important role for pollutants gathering. The local and surrounding pollutants together result in rapid rise of pollutants concentrations. Even increasing amplitude of AQI reaches 100 within 24 hours, and then the heavy or serious pollution occurs. Gradient observations show that the pollution layer is thick and PM2.5 concentration is larger at upper layer （200 m） than at surface layer （20 m） during the heavy pollution period. It is distinct under the warm low pattern condition. Therefore, it suggests that upper PM2.5 not only comes from local emission, but also from surrounding transport.