一次低能见度事件中大气颗粒物的微物理特征

Microphysic Characteristics of Atmospheric Particles in a Low-Visibility Event

利用合肥地区高时间分辨率观测资料对2013年1月13-15日一次低能见度事件中大气颗粒物变化进行分析,依据能见度、相对湿度和PM2.5浓度将过程划分为轻雾、霾、雾3个阶段,进而研究不同阶段大气颗粒物的微物理特征。结果表明:这次低能见度事件经历了"轻雾—霾—轻雾—雾—轻雾—雾—轻雾"的阶段转换过程。整个过程PM2.5/PM10和PM1/PM2.5与能见度呈负相关关系,雾阶段PM2.5/PM10大,细颗粒物积聚程度较快;而轻雾和霾阶段PM2.5/PM10小且离散程度大,粗颗粒物生成速度较快。不同阶段的颗粒物谱分布存在较大差异,轻雾和霾阶段的细颗粒物数浓度、表面积浓度和体积浓度谱形相似;雾阶段对不同粒径尺度的颗粒物数浓度、表面积浓度和体积浓度均有沉降作用,雾过程持续时间越长,对颗粒物的沉降作用越强。

The characteristics of atmospheric particles in a low-visibility event in Hefei is analyzed using high time resolution observations from 13 to 15 January 2013. Based on the data of visibility, relative humidity, and PM2.5 concentration, the process is divided into three stages：fog, mist, and haze, and thus the microphysical characteristics of atmospheric particles in different stage are studied. The results show that： The low visibility event experienced a conversion process of mist--haze--mist--fog--mist--fog-- mist. PM2.5/PM10 and PM1/PM2 .5 were negatively correlated with the visibility in whole process; PM2.5/ PM10 was large in the fog stage, with fine particles accumulated faster; while PM2.5/PM10 was small at the mist and haze stages, with coarse particles generated faster. There was large difference in the spectral distribution of particles between different stages, and the number concentration, surface concentration, and volume concentration of fine particles had a similar spectral shape at mist and haze stages; the sedimentation effects were found from the number concentration, surface concentration, and volume concentration of particles with different size scales at the fog stage. The longer the fog stage lasted, the stronger the sedimentation effect of atmospheric particles.