重庆城区能见度特征与颗粒物消光贡献

Study on Visibility Characteristics of Chongqing‘s Urban Area and the Extinction Contribution by Particulate Matter

为了解重庆市城区颗粒物消光对能见度的影响,对近年城区能见度特征进行统计分析,并在城区开展了为期一年典型季节PM_(2.5)的采样与主要化学组分分析,时间为2014年7月-2015年5月期间,利用化学组分消光重建的方式分析主要组分消光贡献,结果表明,重庆城区近年来能见度平均值为6 120 m,月变化趋势为秋冬低夏季高,日变化趋势为早上低下午高;IMPROVE方程式对颗粒物消光的重建方程可以较好地应用在重庆市城区,重建后2014年城区夏季、秋季、冬季和2015年春季消光系数平均值分别为214、247、422、213 Mm^(-1),PM_(2.5)化学组分对消光系数的主要贡献依次为硫酸盐、硝酸盐、OC和EC,不同季节PM_(2.5)化学组分对消光贡献略有不同,夏季主要贡献因子为硫酸盐,占比42%,秋季主要因子为硫酸盐22.7%和硝酸盐24.3%,冬季主要消光因子为OC 32.6%、硫酸盐23.2%,春季主要消光贡献为硫酸盐25.6%、OC 22.0%。

In order to study the extinction effect of particulate matter on the atmospheric visibility,the recent years’visibility characteristics of Chongqing’s urban area was statistically analyzed.PM2.5sampling during the typical season（July 2014-May2015）was carried out and the major chemical compositions were analyzed for all the samples.Furthermore by means of the chemical composition extinction reconstruction the extinction contribution by each of the major compositions was analyzed.Results of the analysis suggested that the annual average atmospheric visibility in Chongqing’s urban area was 6120 meters;as to monthly variation trend,the visibility during spring and summer was better than that of autumn and winter,while the daily variation indicated visibility in the afternoon was higher than that in the morning.The IMPROVE method was proved to be applicable for Chongqing’s urban area,and the mean extinction coefficients of particulate matter which have been reconstructed,in summer,winter,autumn and spring were 214,247,422 and 213 Mm-1,respectively.It was found that sulfates,followed by nitrates,organic carbon（OC）and elemental carbon（EC）were the major chemical compositions of PM2.5that contributed to extinction coefficient,which slightly differed for different seasons;in summer,sulfates were main contributor,which accounted for 42%of the total;main contributors were sulfates and nitrates in autumn,respectively accounting for 22.7%and 24.3%;in winter,OC 32.6%and nitrates 23.2%;and in spring,sulfates and OC contributed most to extinction,accounting for 25.6%and 22.0%,respectively.