辽宁省霾天气季节变化特征及其主导因子分析

Seasonal Variation of Haze Weather and Its Dominant Factors in Liaoning Province

利用辽宁省51个地面气象观测站的能见度、均一化相对湿度和天气现象资料,采用最优距离法和固定比例法对能见度资料进行一致性处理,重建了1961—2020年的辽宁省逐日霾资料,并利用该资料对辽宁省年和四季霾日时空变化特征和主导因子进行分析。结果表明,1961—2020年辽宁省平均年霾日呈显著增加趋势[2.1 d·(10 a)^(-1)],但2015年以来霾日显著减少;空间上,年和四季霾日呈现一致的分布特征,均存在1个高值中心(沈阳)和2个副高值中心(北票和锦州),年平均霾日分别为139、52、46 d,辽东和辽西山区为霾日低发区,年平均霾日在20 d以内。风向和风速是霾日形成的重要气象因子,西南偏南风增加带来的暖湿气流对春季、夏季和秋季霾日的形成贡献较大,北风的减少则对冬季霾日的形成贡献较大。霾发生时辽宁省春季、夏季和秋季发生西南偏南风的频率分别由11.4%、12.1%和8.0%增加至15.8%、19.8%和13.5%,冬季则表现为北风发生频率的减少和静风发生频率的增加;霾发生时四季风速均较平均状况偏小,说明小风有利于霾的形成。辽宁省霾长期演变受到污染物排放、风力因子和环境政策等多种因素影响,1980—2003年霾日的不断增加是污染物增多和风速减小共同导致的,2015年以来的霾日减少则可能与大气污染防治引起的PM 2.5减少有关,同时较少的小风日数也为霾日减少提供了有利的气象条件。

Temporal and spatial variations of haze days in four seasons and dominant factors are analyzed based on meteorological data from 51 surface weather stations in Liaoning Province between 1961 and 2020.The results show that the annual haze days averaged in Liaoning Province have a significant increasing trend of 2.1 d per decade from 1961 to 2020 and a decreasing from 2015 to 2020.In terms of spatial distribution,there is a high-value center(Shenyang)and two sub-high-value centers(Jinzhou and Beipiao),where the annual haze days are respectively 139 d,52 d and 46 d.Comparatively,the annual haze days in the mountain areas of western and eastern in Liaoning Province are the least,less than 20 days on average.Wind direction and wind speed are important meteorological factors for the formation of haze.The warm and humid air brought by the increase of south-southwesterly winds has a greater contribution to haze formation in spring,summer and autumn,while the decrease of northerly winds helps the formation of haze days in winter.The frequencies of south-southwest winds in spring,summer and autumn have increased from 11.4%,12.1%and 8.0%to 15.8%,19.8%and 13.5%,respectively.When haze occurs,the wind speeds in all four seasons are lower than the average,indicating that light wind is conducive to the formation of haze.The long-term evolution of haze in Liaoning Province is affected by pollutant emissions,wind factors and environment-manage policies.The growth of haze days from 1980 to 2003 was caused by the increased pollutants and decreased wind speeds.The reduction of haze days since 2015 is very likely related to the reduction of PM 2.5,which is achieved by air pollution control.At the same time,fewer light wind days also provide a favorable meteorological condition for the reduction of haze days.