长江三角洲冬季一次低能见度过程的地区差异和气象条件

采用NCEP再分析资料、MICAPS地面、高空气象资料以及国家环保部空气质量监测资料,对2014年2月20~22日长江三角洲地区一次低能见度过程地区差异和气象条件进行了分析.天气形势分析表明,长三角地面处在高压的控制下,地面风速较小,使污染物积累,有利于低能见度(雾-霾)的形成和维持.根据不同区域的雾、霾分布和日变化特征,将长江三角洲地区分为3个子区域:Ⅰ区为江苏大部(雾霾混合型),Ⅱ区为上海及其周边(霾类型),Ⅲ区为浙江大部(雾类型),该区域白天能见度较高,夜间能见度较低的特征是由湿度因子造成的.影响Ⅰ区能见度变化的主要原因是:热力原因:大气对流层低层的层结稳定;湿度原因为:空气较湿润,气溶胶粒子吸湿性增长;动力原因主要是垂直方向和水平方向的大气扩散能力弱;污染因子对能见度变化的影响较小.影响Ⅱ区能见度变化的主要原因是PM2.5浓度高导致的污染,热力因子、湿度因子和动力因子对能见度的变化影响很小.影响Ⅲ区能见度变化的热力原因是:大气对流层低层层结稳定、近地面存在逆温;湿度原因是因为:空气较湿润,气溶胶粒子吸湿性增长;动力原因是因为边界层高度较低导致的垂直扩散能力较差.各个区域的气象因子解释方差的计算结果表明:Ⅰ区湿度因子和动力因子对能见度的影响更大,Ⅲ区.湿度因子对能见度的影响更大.

Regional differences and meteorological conditions of a low visibility procedure over the Yangtze River Delta Region in winter.

The regional difference and meteorological condition over the Yangtze River Delta (YRD) region during a low visibility episode (from 20 February to 22 February 2014) was investigated by using NCEP reanalysis data, MICAPS meteorological data and air quality data from the Ministry of Environmental Protection. Weather situation shows that the surface of the YRD region was under the control of high pressure, surface wind speed was low, which was favorable for the accumulation of pollutants as well as the formation and maintain of low visibility process (fog or haze). The YRD region was divided into 3sub-regions according to the temporal and spatial distributions of fog and haze. Region I covered the most part of Jiangsu province, which was affected by both fog and haze; region II included Shanghai and its surrounding, which was affected by haze; region III covered the most part of Zhejiang province, which was affected by fog. Factors that influence visibility in region I included that stabilized stratification in the lower tropospheric (thermodynamic factors), aerosol hygroscopic growth under high relative humidity conditions (humidity factor), and weak vertical and horizontal diffusion (dynamic factors). However, pollution factors had little effect on visibility in region I. High mass concentration of PM2.5 was the most important factor that influence visibility in region II. Thermodynamic factors, humidity factor, and dynamic factors had little effects on visibility. Thermodynamic factors, which influences visibility in region III, was represented by stabilized stratification in the lower tropospheric layer and temperature inversion in the surface layer. Humidity factor in region III was represented by aerosol hygroscopic growth under high relative humidity condition. Dynamic factors in region III was characterized by low boundary layer height and weakvertical diffusion speed. The explained variance of meteorological factors in each region showed that humidity factor and dynamic factors were more important in region I while humidity factor was the most important in region III..