基于CE-318观测的甘肃省气溶胶光学特性分析

Optical Characterization of Aerosols in Gansu Province Based on CE-318 Observations

对于大气气溶胶地基观测资料的定量分析是了解气溶胶光学特性和大气污染特征的基本途径,可为探讨污染治理方向提供一定的依据。近年来,利用地基观测资料分析甘肃省不同区域气溶胶光学特性的研究较少。为了解甘肃省不同下垫面的大气气溶胶光学特性,本文基于2018年4月至2020年9月CE-318型太阳光度计观测资料,通过ASTPwin软件反演获得了甘肃省四个站点的气溶胶光学厚度AOD,计算了Angstrom波长指数α,分析了甘肃省不同区域不同季节AOD和α的分布和变化特征以及气溶胶光学厚度和波长指数的关系。结果表明:(1)观测时段内,所有站点各波段AOD的变化趋于一致,且AOD值随波长增大而减小。兰州和皋兰山AOD值冬季最高,春、秋季次之,夏季最低,兰州冬、春季AOD值分别比年均值超出14.98%和4.68%,皋兰山冬季AOD值比年均值超出3.88%。敦煌和民勤AOD值均为春季最高,比各自的年均值高出24.49%和26.30%。敦煌AOD季节分布为:春季>夏季>冬季>秋季,而民勤则表现为从春到冬季逐渐减小的趋势。(2)兰州和皋兰山春夏季主控粒子为粗模态,秋冬季则为细颗粒物主导。敦煌和民勤大气气溶胶常年由粗模态粒子主控。2019年冬季,兰州市区AOD值比其城郊的皋兰山高出68.0%;敦煌和民勤2019年春季沙尘气溶胶污染较为严重,敦煌AOD值比民勤超出42.42%。(3)四个站点AOD和α的频率分布均呈单峰曲线,不同季节AOD高频次分布范围存在差异性,但都处于1.0以下。α的高频次范围分布较为复杂,兰州春季、皋兰山春夏季、敦煌四季、民勤春夏秋季,α分布区间均小于1.0,而兰州夏秋冬季、皋兰山秋冬季、民勤冬季α主要分布于1.1以上。(4)不同季节AOD和α的关系存在差异,表现为不同季节,大气出现严重或者局部污染时,气溶胶的主控粒子粒径大小不同。春季大气出现局部或者严重污染、夏季大气局部污染时,四个站点气溶胶主要是大粒径粒子,其中沙尘气溶胶的贡献较大。夏季大气处于严重污染时,皋兰山气溶胶主要是细模态粒子,兰州、敦煌、民勤气溶胶依然由粗模态主控,但是兰州小粒径粒子导致的污染比重高于其余两站,其中85%以上属于城市工业-气溶胶污染。秋季大气处于严重污染状况时,兰州和皋兰山均由细模态粒子主导,其中城市工业-气溶胶占比明显增加,而敦煌和民勤依然由粗模态粒子主导,其中沙尘气溶胶占比偏重。冬季大气严重污染时,兰州依然由细模态粒子主导,而其他三站由粗模态粒子占据主导地位,冬季大气局部污染时,敦煌和民勤粗模态粒子与细模态粒子同时出现,皋兰山以细模态粒子为主。分析可知,总体上甘肃偏北地区气溶胶污染以沙尘气溶胶为主,而偏南地区气溶胶污染表现为粗模态与细模态粒子交替出现,这为下一步结合卫星遥感资料研究甘肃不同区域的气溶胶特性及大气污染特征提供了一些参考。

The quantitative analysis of ground-based observations of atmospheric aerosols is a basic way to understand the optical properties of aerosols and the characteristics of atmospheric pollution,which can provide a certain basis for exploring the direction of pollution control.In recent years,there are few studies on the analysis of aerosol optical properties in different regions of Gansu Province using ground-based observations.In order to understand the atmospheric aerosol optical characteristics of different land surfaces in Gansu Province,we obtained the aerosol optical depth(AOD)of four stations in Gansu Province through ASTPwin software based on CE-318 solar photometer observations from April 2018 to September 2020 and calculated the Angstrom wavelength indexα.The distribution and variation characteristics of AOD andαin different regions of Gansu Province in different seasons and the relationship between aerosol optical depth and wavelength index were analyzed.The results show that:(1)the changes of AOD in each wavelength band tend to be consistent in all stations during the observation period,and the AOD value decreases with increasing wavelength.The AOD values of Lanzhou and Gaolan Mountain were the highest in winter,followed by spring and autumn,and the lowest in summer.The winter and spring AOD values of Lanzhou exceeded the annual average by 14.98%and 4.68%,respectively,and the winter AOD value of Gaolan Mountain exceeded the annual average by 3.88%.Dunhuang and Minqin both had the highest AOD values in spring,which were 24.49%and 26.30%higher than their respective annual averages.The seasonal distribution of AOD in Dunhuang was:spring>summer>winter>autumn,while Minqin showed a trend of gradually smaller values from spring to winter.(2)The dominant particles in Lanzhou and Gaolan Mountain are coarse modal in spring and summer,while fine particles dominate in autumn and winter.Dunhuang and Minqin atmospheric aerosols are dominated by coarse modal particles all year round.In the winter of 2019,the AOD value of Lanzhou was 68.0%higher than that of Gaolan Mountain;Dunhuang and Minqin had more serious sand and dust aerosol pollution in spring 2019,and the AOD value of Dunhuang exceeded that of Minqin by 42.42%.(3)The frequency distribution of AOD andαat all sites showed a single-peaked curve,with variability in the range of high-frequency distribution of AOD in different seasons,but they were all below 1.0.The distribution of high-frequency range ofαwas more complex,with the range ofαdistribution less than 1.0 in spring in Lanzhou,spring and summer in Gaolan Mountain,four seasons in Dunhuang,and spring,summer and autumn in Minqin,whileαin summer,autumn and winter in Lanzhou,autumn and winter in Gaolan Mountain,and winter in Minqin was mainly distributed at 1.1 or above.(4)The relationship between AOD andαdiffers in different seasons,which shows that the size of the dominant particles of aerosol differs in different seasons when the atmosphere is seriously or locally polluted.In spring when the atmosphere is in local or serious pollution and in summer when the atmosphere is in local pollution,the aerosols at the four stations are mainly large particle size,with the contribution of sand and dust aerosols being larger.In summer when the atmosphere is in serious pollution,Gaolan Mountain aerosol is mainly fine mode particles,Lanzhou,Dunhuang and Minqin aerosol is still controlled by coarse mode,but the proportion of pollution caused by small particle size in Lanzhou is higher than the remaining two stations,of which more than 85%belongs to urban industrial-aerosol pollution.In autumn,when the atmosphere is in serious pollution,Lanzhou and Gaolan Mountain are both dominated by fine modal particles,of which urban industrial-aerosols account for a significant increase,while Dunhuang and Minqin are still dominated by coarse modal particles,of which dust aerosols account for a large proportion.In winter,Lanzhou is still dominated by fine modal particles,while the other three stations are dominated by coarse modal particles.In winter,Dunhuang and Minqin are dominated by coarse and fine modal particles,while Gaolan Mountain is dominated by fine modal particles when the atmosphere is locally polluted.The analysis shows that,in general,aerosol pollution in the northern part of Gansu is dominated by sand and dust aerosols,while aerosol pollution in the southern part of Gansu shows alternating coarse-mode and fine-mode particles,which provides some references for the next study of aerosol properties and atmospheric pollution characteristics in different regions of Gansu by combining satellite remote sensing data.