黄河上游段吸收性气溶胶指数(AAI)时空演化特征及潜在源区分析

Temporal and spatial variation and potential source area analysis of AAI in the upper reaches of the Yellow River

为揭示黄河流域上游段吸收性气溶胶指数(Absorbing Aerosol Index,AAI)的时空演化特征、主要影响因子及污染严重的包头市污染物潜在来源.本文利用OMI OMAERUV L2气溶胶数据集,研究了2005—2020年黄河流域上游段的AAI时空分布,利用熵权TOPSIS法分析主要影响因子,同时借助后向轨迹模型(HYSPLIT)对污染严重城市的污染物进行聚类分析,追踪其潜在来源.结果显示:(1)从时间上看,2005—2009年黄河流域上游段AAI呈下降趋势,2009年AAI降到最小值;2009—2016年AAI波动上升,2016年达到最大值,随后由于国家颁布了一系列保护环境的政策使AAI下降.从空间上看,AAI在黄河上游流域的北部即内蒙古的包头、鄂尔多斯偏高,而在流域的南部大概在四川省内较低.(2)小波分析发现,季节变化方面,黄河上游AAI正负位相交替出现,月均值季节变化明显,且呈现冬>春>秋>夏的特征.夏季雨水的冲刷和扩散条件使得AAI全境低值;冬季污染物排放增加,局部为高压控制区,污染物难以扩散,AAI大范围出现高值.(3)熵权TOPSIS法表明,黄河上游流域环境污染较为严重的城市为包头市,因此,本文以包头市作为重污染典型城市,借助后向轨迹法分析其污染物的潜在来源,结果表明,包头市2019年冬季气流轨迹为5类,其中,西北方向为主要传输方向.(4)包头市污染源主要为沙漠源和工业源;吸收性气溶胶以沙尘气溶胶和污染性沙尘气溶胶为主,碳质气溶胶为辅.

In order to reveal the temporal and spatial variation characteristics,main influencing factors and potential sources of pollutants in Baotou City with serious pollution of absorbing aerosol index(AAI)in the upper reaches of the Yellow River Basin.In this paper,the temporal and spatial distribution of AAI in the upper reaches of the Yellow River from 2005 to 2020 is studied by using OMI OMAERUV L2 aerosol data set,the main influencing factors are analyzed by the entropy weight TOPSIS(technique for order preference by similarity to an ideal solution)method,and the pollutants in heavily polluted cities are clustered by backward trajectory model(HYSPLIT)to track their potential sources.The results show that:(1)in terms of time,the AAI index decreased from 2005 to 2009,and the AAI index was the minimum in 2009;The fluctuation increased from 2009 to2016,reaching the maximum in 2016,and then the AAI index decreased due to the implementation of a series of environmental protection policies.Spatially,the aerosol index is higher in Baotou and Ordos,but lower in Sichuan Province.(2)Wavelet analysis shows that in terms of season,AAI in the upper reaches of the Yellow River appears alternately positive and negative,and the monthly mean has obvious seasonal variation,which is winter>spring>autumn>summer.The erosion and diffusion of rainfall in summer make AAI present a low value in the whole region;In winter,the pollutant emission increases,and some parts are high-pressure control areas,so the pollutants are difficult to diffuse,and the AAI is high in a wide range.(3)The entropy weight TOPSIS(technique for order preference by similarity to an ideal solution)method shows that the city with serious pollution in the upper reaches of the Yellow River is Baotou City.Therefore,this paper takes Baotou City as a typical pollution city,and uses the backward trajectory method(HYSPLIT)to analyze the potential sources of pollutants.The results show that the air flow trajectory in winter 2019 in Baotou City is five categories,of which the northwest direction is the main transmission direction.(4)The main pollution sources in Baotou are desert and industrial sources;Absorbent aerosols are mainly dust aerosols and polluting dust aerosols,supplemented by carbonaceous aerosols.