2013年1月河北省中南部严重污染的气象条件及成因分析

年1月河北省中南部出现了长时间、大范围的雾霾天气,大气污染严重. 利用河北省AQI(逐日空气质量指数)、气象常规观测数据及NCEP(美国国家环境预报中心)1°×1°格距再分析资料,对此次严重污染事件的气象条件、大气环境背景和形成机制进行了研究. 结果表明:①2013年1月河北省中南部地面气象要素表现异常,与历史同期相比,平均气温低1~2℃、相对湿度高15%以上、日照时数少40%以上、降水日数多但量级小. 地面风力较小且多风向、风速的辐合线,地面散度场上河北省中南部为明显的辐合区,致使水汽和污染物汇聚不易扩散,导致雾霾天气异常偏多,大气污染严重. ②边界层高湿区中丰富的水汽与污染物互为载体,强逆温层结、大气低层的干暖盖、边界层下沉运动等均使水汽和污染物存留在近地层且不易向高空扩散；同时,稳定的大气环流形势为雾霾天气和严重污染提供了有利的大气环境场. ③河北省中南部特殊的地理条件也是雾霾和污染持续的一个重要原因. 低空稳定的偏西气流越过太行山后在山麓东侧下沉,在华北平原地区易形成地面辐合线,从而加剧了近地层水汽和污染物的汇聚. 

Analysis on the Meteorological Condition and Formation Mechanism of Serious Pollution in South Hebei Province in January 2013

There were some fog hazy days accompanied by serious long-term air pollution in the southern Hebei Province during January, 2013. The weather conditions, atmospheric environmental background and mechanism of formation for heavy air pollution were analyzed based on daily data, including air quality index (AQI), routine weather observation and spatial grid 1°×1° reanalysis of NCEP. The results showed that the weather factors were abnormal in January, 2013, by showing low air temperature at 1-2℃, relative humidity higher 15%, short sunshine hours less 40% than under normal condition, and more rainy days with little amount. The hazy days often occurs in the middle and south part of Hebei Province, since the water and air pollutants easily meet when surface wind speed was weak and both wind speed and direction focused on the ground. Abundant moisture and pollutants with high humidity of boundary layer could carry each other. In addition, strong temperature inversion layer, dry warm cover in the lower atmosphere, and sinking motion in the boundary layer prevent water and pollutants diffuse to the upper air. The stable atmospheric circulation feature provided favorable environmental field for hazy weather and heavy air pollution. The special geographical condition in the south Hebei Province was an important factor for the fog haze and pollution lasting. Stable west wind in low level sunk to the east of foothills of the Mountain Taihang after across the mountain, and easily formed convergence lines in the plain areas, and further aggravated the gathering of water and pollutants in the ground layer.