南京北郊秋冬季相对湿度及气溶胶理化特性对大气能见度的影响

Effects of Relative Humidity and Aerosol Physicochemical Properties on Atmospheric Visibility in Northern Suburb of Nanjing

为了解南京北郊秋冬季相对湿度与气溶胶理化特性对大气能见度的影响,利用2012年秋冬季气象要素资料、颗粒物浓度及其主要成分和气溶胶粒子谱分布等观测数据,分析了南京北郊大气能见度与气象要素、颗粒物污染之间的关系.结果表明,南京北郊秋冬季节平均大气能见度仅为4.76 km.颗粒物浓度与能见度存在一定的负相关关系,尤其细粒子对能见度的影响更为显著.随细粒子质量浓度和相对湿度(RH)的增大,低能见度出现的频率呈现上升趋势.能见度从5~10 km衰减到<5km时,PM10和PM2.1质量浓度分别增加了7.56%和37.64%;其中SO2-4和NO-3质量浓度均有显著增加.气溶胶粒子数浓度对能见度的影响与相对湿度有关,粒径0.5~2μm的气溶胶数浓度随RH增加增长缓慢,而2~10μm范围内的粒子数浓度随RH增加而减小;结合气溶胶表面积浓度与能见度进行相关性分析,表明0.5~2μm的细粒子及相对湿度是导致南京北郊秋冬季大气能见度下降的主要因素.

To understand the effects of relative humidity( RH) and aerosol physicochemical properties on the atmospheric visibility in autumn and winter in northern suburb of Nanjing,the relationships between meteorological elements,particulate matter and visibility were analyzed with the data of meteorological elements,aerosol particle spectra,particulate matter concentration and chemical composition. The average visibility was 4. 76 km in autumn and winter in northern suburb of Nanjing. There was a certain negative correlation between the particulate matter concentration and the visibility,especially the influence of fine particles on the visibility was more remarkable. The occurrence frequencies of low visibilities showed an increasing trend with the increasing concentration of fine particles and RH. When the visibility decreased from 5-10 km to < 5 km,the mass concentrations of PM10 and PM2. 5increased by7. 56% and 37. 64%,respectively. Meanwhile,the mass concentrations of SO2-4and NO-3increased significantly. Effects of aerosol particle number concentration on the visibility were related with RH. Aerosol number concentration with diameters ranging from 0. 5 μm to 2 μm increased slowly with the increase of RH,while those ranging from 2 μm to 10 μm decreased. The correlation analysis between the aerosol surface area concentration and the visibility showed that RH and fine particles between 0. 5 μm and 2 μm were the main factors which caused the decrease of atmospheric visibility in autumn and winter in northern suburb of Nanjing.