鄂中东部两次秸秆焚烧引发的严重灰霾天气分析

Comprehensive Analysis of Two Heavy Haze Events Induced by Straw Burning in Central-Eastern Hubei

利用气象卫星监测、微波辐射计、常规气象观测、NCEP再分析资料及环境监测等资料，采用气流后向轨迹模拟，对2012年6月11日和6月15日发生在鄂中东部的两次灰霾天气，从特征和成因进行了综合分析。结果表明，这两日的污染物指数（API）分别达到233 μg/m3和139 μg/m3，11日PM2.5最高值达141 μg/m3 ；两日的能见度均在2 km以下，11日平均能见度仅565 m，最低能见度246 m。这两次灰霾天气与北方冬小麦主产区大范围秸秆集中焚烧，造成大量污染物排放有密切关系。在115°E，39°～32°N存在大范围逆温层，垂直高度950~850 hPa 厚度为一致的东北气流，使得排放的污染物在“逆温层盖”的阻挡下不能向高空扩散，而随东北气流向鄂中东部输送。同时鄂中东部近地面静风、地面“均压场”、逆温、近地层弱垂直速度、正涡度和负散度等物理量条件，及适宜的湿度条件等因素，导致污染物不能及时扩散或沉降，为灰霾在本地形成和维持提供了有利的气象条件，加剧了灰霾的严重性。

By means of the relative humidity data from meteorological satellite, microwave radiometer, and regular meteorological observations, as well as NCEP reanalysis data and environmental monitoring data, through air flow backward trajectory simulation, the characteristics and causes of two haze weather events in 11 and 15 June 2012 over the eastern Hubei are analyzed. The results show that the pollution indexes （API） are 233 μg/m3 and 139 μg/m3, respectively, with the highest PM2.5 being 141 μg/m3 in 11 June; the visibility in the two days is below 2000 m, with the average visibility being only 565 m in 11 June and the minimum visibility 246 m. The two heavy haze events are closely related to the concentrated straw burning over the region, where is one of the main winter wheat producing areas in China. There existed a large range of temperature inversion layer around 115°E, 39° to 32°N; the vertical height of 950 to 850 hPa thickness was consistent with the northeast flow, so that the pollutant cannot diffuse into the air and transmit to the eastern Hubei with Northeast flow. At the same time, because of calm wind, uniform pressure field, temperature inversion, weak vertical shear, positive vorticity, negative divergence, and suitable humidity conditions, pollutants cannot be timely diffused or subsided, which is favorable for haze formation and aggravation.