title: Mass extinction efficiency and extinction hygroscopicity of ambient PM2.5in urban China.
abstract: The ambient PM2.5pollution problem in China has drawn substantial international attentions. The mass extinction efficiency (MEE) and hygroscopicity factor (f(RH)) of PM2.5can be readily applied to study the impacts on atmospheric visibility and climate. The few previous investigations in China only reported results from pilot studies and are lack of spatial representativeness. In this study, hourly average ambient PM2.5mass concentration, relative humidity, and atmospheric visibility data from China national air quality and meteorological monitoring networks were retrieved and analyzed. It includes 24 major Chinese cities from nine city-clusters with the period of October 2013 to September 2014. Annual average extinction coefficient in urban China was 759.3±258.3Mm-1, mainly caused by dry PM2.5(305.8.2±131.0Mm-1) and its hygroscopicity (414.6±188.1Mm-1). High extinction coefficient values were resulted from both high ambient PM2.5concentration (68.5±21.7µg/m3) and high relative humidity (69.7±8.6%). The PM2.5mass extinction efficiency varied from 2.87 to 6.64m2/g with an average of 4.40±0.84m2/g. The average extinction hygroscopic factor f(RH=80%) was 2.63±0.45. The levels of PM2.5mass extinction efficiency and hygroscopic factor in China were in comparable range with those found in developed countries in spite of the significant diversities among all 24 cities. Our findings help to establish quantitative relationship between ambient extinction coefficient (visual range) and PM2.5& relative humidity. It will reduce the uncertainty of extinction coefficient estimation of ambient PM2.5in urban China which is essential for the research of haze pollution and climate radiative forcing.
authors.affiliation: School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
authors.forename: Zhen
authors.initials: Z
authors.lastname: Cheng
authors.affiliation: National Meteorological Center of China, Beijing 100081, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Ma
authors.affiliation: School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
authors.forename: Yujie
authors.initials: Y
authors.lastname: He
authors.affiliation: School of Environment, and State Key Joint Laboratory of Environment Simulation and Pollution Control, Tsinghua University, Beijing 100084, China. Electronic address: jiangjk@tsinghua.edu.cn.
authors.forename: Jingkun
authors.initials: J
authors.lastname: Jiang
authors.affiliation: Division of Atmospheric Sciences, Desert Research Institute, 2215 Raggio Parkway, Reno, NV 89512, USA.
authors.forename: Xiaoliang
authors.initials: X
authors.lastname: Wang
authors.affiliation: GAGO Inc., Milpitas, CA 95035 USA. Electronic address: yungang.carl.wang@gmail.com.
authors.forename: Yungang
authors.initials: Y
authors.lastname: Wang
authors.affiliation: National Meteorological Center of China, Beijing 100081, China.
authors.forename: Li
authors.initials: L
authors.lastname: Sheng
authors.affiliation: National Meteorological Center of China, Beijing 100081, China.
authors.forename: Jiangkai
authors.initials: J
authors.lastname: Hu
authors.affiliation: School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai 200240, China.
authors.forename: Naiqiang
authors.initials: N
authors.lastname: Yan
mesh_terms: D000393:Air Pollutants / Q000032:analysis*; D001272:Atmosphere; D002681:China; D002947:Cities; D004784:Environmental Monitoring; D006813:Humidity; D010316:Particle Size; D052638:Particulate Matter / Q000032:analysis*; D017155:Wettability
chemical_list: D000393:Air Pollutants; D052638:Particulate Matter
keywords: China; Extinction coefficient; Hygroscopic factor; Mass extinction efficiency; Particulate matter; Visibility