2014年2月下旬京津冀持续重污染过程的静稳天气及传输条件分析

利用常规气象观测资料、空气质量监测资料、再分析资料和数值模式资料，分析了2014年2月20-26日京津冀地区持续重污染天气过程的环流背景、气象要素特征、静稳天气条件和传输条件.结果表明：2月20-26日，亚洲东部受弱高压脊控制，京津冀及周边地区位于地面高压后部，等压线较为稀疏，气压梯度小，造成地面风速较小；与此同时，混合层高度低，通风系数小和逆温存在，构成重污染天气出现和维持的气象条件，均不利于大气中污染物和水汽的垂直和水平扩散.静稳天气指数对于重污染天气有一定的指示意义，高静稳天气指数通常对应高PM_2.5浓度，且二者变化趋势一致性高；2月20-26日静稳天气指数总体上大于2014年1-3月其他几次污染过程，且在高位长时间维持，造成此次污染过程更严重.此外，传输条件也是京津冀重污染天气的主要成因：地面高压西侧的偏南或偏东气流有助于污染物和水汽向京津冀地区输送和聚集，使能见度进一步降低、污染物浓度进一步升高.

Analysis of the stagnant meteorological situation and the transmission condition of continuous heavy pollution course from February 20 to 26, 2014 in Beijing-Tianjin-Hebei

In this paper, the atmospheric circulation background, influence system and characteristics of meteorological factors during the continuous heavy pollution period from February 20 to 26, 2014 in Beijing-Tianjin-Hebei were analyzed using the data of meteorological observation, air quality monitoring, reanalysis and numerical model result, the stagnant meteorological situation and air pollution transmission conditions were studied. The results showed that the eastern Asia was controlled by a weak ridge of high pressure, the rear of the surface high pressure was located in Beijing-Tianjin-Hebei and its surroundings, while the isobars were relatively sparse and the pressure gradient was small, which resulted in a lower wind speed on ground during February 20 to 26. Meanwhile, the low mixing layer height, small ventilation coefficient and temperature inversion promoted the formation and maintainance of the heavy pollution by weaken the atmospheric pollutant diffusion on vertical and horizontal directions. Directive significance of the stagnant weather index on heavy pollution event was significant because the high stagnant weather index always corresponded to the high concentration of PM_2.5 and their trends varied consistently. The stagnant weather index from February 20 to 26 was higher than other air pollution periods during January to March in 2014 and keep at a high level for a long time, resulting in such more serious pollution. Furthermore, the transmission conditions were also the major causes of the air pollution in Beijing-Tianjin-Hebei. The southerly or easterly airstream from west of the high pressure on ground was conducive to the transport or aggregate of vapor and pollutants to Beijing-Tianjin-Hebei, which lead to the further low visibility and high pollutants concentrations.