四川盆地多层逆温特征及其对大气污染的影响

Characteristics of multi-layer inversions in Sichuan Basin and their influences on air pollution.

利用2015~2018年探空观测资料以及国家生态环境部发布的环境空气质量监测数据,对四川盆地多层逆温这一特殊的､尚未见详细报道的逆温结构进行了研究,并评估不同逆温类型及垂直结构对大气污染的影响.结果表明:四川盆地多层逆温实际上是一种并不少见的现象,年平均出现频率为20.1%.冬季最为频发,成都冬季高达51.6%.以边界层逆温叠加对流层低层逆温(LTI)的配置为主要特征.依据其垂直结构,划分为四种配置类型,即贴地逆温(SI)叠加脱地逆温(EI)､SI+LTI､EI+LTI､SI+EI+LTI,分别对应第Ⅰ､Ⅱ､Ⅲ､Ⅳ类多层逆温.其中以第Ⅱ､Ⅲ类多层逆温为主.逆温的叠加作用对大气污染的影响更大,多层逆温(特别是第Ⅱ､Ⅳ类多层逆温)尤其加大了中度及重度污染出现的可能性.第Ⅰ､Ⅳ类多层逆温对污染物扩散的抑制作用最为明显,其次是第Ⅱ类多层逆温和仅SI(即只出现SI).第Ⅱ类多层逆温在污染最重的冬季出现频率高､强且厚,叠加抑制作用明显,应是重点关注对象.

The radiosonde data and the ambient air quality data,released by Ministry of Ecology and Environment of the People’s Republic of China,in the Sichuan Basin from 2015 to 2018 were used in this study.The aim was to document the special multi-layer inversion structure in the Sichuan Basin,which has not been reported in detail,as well as to evaluate the effects of different inversion types and vertical structures on air pollution.The result showed that the multi-layer inversion in the Sichuan Basin was actually a common phenomenon,with an average annual frequency of 20.1%.It occurred most frequently in winter and the wintertime frequency in Chengdu reaches 51.6%.The multi-layer inversions were mainly characterized by the boundary layer inversion overlaid with the lower troposphere inversion(LTI).They are divided into four types according to the vertical structure.That is,the surface-based inversion(SI)overlaid with the elevated inversion(EI),SI+LTI,EI+LTI,and SI+EI+LTI,correspond to typeⅠ,Ⅱ,Ⅲ,andⅣmulti-layer inversions,respectively.Most were typeⅡandⅢ.The superimposing effect of the inversions had more serious impact on air pollution than non-multi-layer inversions.The multi-layer inversions,especially typeⅡandⅣ,made more important contribution to increasing the possibility of moderate and heavy pollution.Among the four types,typeⅠandⅣmulti-layer inversions had the most obvious inhibitory effect on diffusion of air pollutants,with typeⅡmulti-layer inversion and only-SI followed.In winter,the most polluted season of a year,the typeⅡmulti-layer inversions were frequent,deep,and strong,and had an obvious superimposing effect on air pollution.Thus,it should be the focus of attention.