合肥秋季气溶胶光学特性及来源分析

气溶胶通过吸收和散射效应与太阳辐射相互作用，对地球辐射收支和气候造成扰乱，对云凝结核形成和云的光学性质造成间接影响。利用黑碳仪和积分浊度计于2019年11月5日至12月10日在合肥市分别开展了气溶胶吸收系数(σ_ap)、散射系数(σ_sp)的外场观测，结合气象数据，分析了气溶胶吸收系数(σ_ap)、散射系数(σ_sp)的日变化特征及风依赖性。结果表明，合肥市秋季PM_2.5，σ_sp和σ_ap均值分别为(43±25) μg·m-3，(238.70±161.52) Mm-1，(32.04±17.01) Mm-1。研究期间σ_sp，σ_ap的时间变化趋势与PM_2.5较为一致。PM_2.5，σ_sp和σ_ap均具有显著的双峰日变化特征，分别在早8点至10点和晚20点至21点出现峰值，主要与交通排放和气象条件有关。合肥市气溶胶光学性质的风依赖性主要体现在PM_2.5，σ_ap与σ_sp的高值大多处在弱风(风速<3 m·s-1)的区域，低温高湿小风的天气条件有利于污染物的积累和形成，但较高的风速也易输送周边的污染物，σ_sp和σ_ap部分高值主要受西北风向的污染气团影响。同时，基于HYSPLIT后向轨迹模型，通过聚类分析不同输送途径的空间特征，并利用潜在源贡献法(PSCF)和浓度权重轨迹法(CWT)，探讨了研究期内合肥σ_sp的潜在源区分布及其贡献特性。结果发现污染气团主要来源于合肥的西北方向，占比最高的气团1和3来自于内蒙古自治区和新疆维吾尔自治区，而对散射系数贡献较大的气团2来自于陕西省宝鸡市，气团6源于内蒙古，途径山西省、山东省、江苏省，从安徽省的东南方向到达合肥，携带较多的污染物。PSCF较大值(>0.5)主要分布在合肥的西北方向和西南方向。合肥冬季CWT高值主要分布在河南省东北部、山东省西南部、安徽省北部地区。尤其是山东济宁市、河南商丘市的污染物远距离传输是影响合肥地区秋季空气质量的重要源区。

Characteristics of Aerosol Optical Properties and Their Potential Source in Hefei in Autumn

Aerosols directly disturbs the earth’s radiation budget and climate by absorbing and scattering solar radiation, indirectly affecting the formation of cloud condensation nuclei, and further changing the optical properties. A field study was carried out using an aethelometer and nephelometer from 5 November to 10 December 2019 in Hefei. Based on the meteorological data, diurnal variation and wind dependence of the optical properties of aerosols were analyzed. The average PM_2.5, aerosol scattering coefficient (σ_sp), absorption coefficient (σ_ap) in autumn in Hefei were (43±25) μg·m-3, (238.70±161.52) Mm-1, and (32.04±17.01) Mm-1, respectively, and the trend of time variation of σ_sp and σ_ap was consistent with PM_2.5. The contents of PM_2.5, σ_sp, and σ_ap have significant double-peak daily variation characteristics, peaking at 8:00-10:00 and 20:00-21:00, which was mainly related to traffic emissions and meteorological conditions.The wind dependence of aerosol optical properties in Hefei mainly reflects that the weather conditions of low temperature, high humidity and low wind are conducive to the accumulation and formation of pollutants, but the higher wind speed is also easy to transport pollutants around. The σ_ap and σ_sp were mainly affected by the pollution air mass in the northwest wind direction. Based on the HYSPLIT backward trajectory model, the spatial characteristics of different transport pathways were analyzed by cluster analysis, and the potential source contribution method (PSCF) and concentration weight trajectory method (CWT) were used to investigate the potential source area distribution of Hefei. The results showed that the polluted air masses mainly originated from the northwest of Hefei. The highest proportion of air masses 1 and 3 were from Inner Mongolia Autonomous Region and Xinjiang Uygur Autonomous Region. Air mass 2, which contributes more to the scattering coefficient, comes from Baoji City, Shaanxi Province, and air mass 6, which originates from Inner Mongolia, passes through Shanxi, Shandong and Jiangsu Provinces, and arrives at Hefei from the southeast of Anhui Province, carrying more pollutants. PSCF larger value was mainly distributed in the northwest and southwest of Hefei. The high CWT values in autumn in Hefei were mainly distributed in northeast Henan Province, southwest Shandong Province and North Anhui Province. In particular, Jining city in Shandong Province and Shangqiu city in Henan Province are the potential sources of air quality in Hefei.