A review of current knowledge concerning PM2.5 chemical composition, aerosol optical properties, and their relationships across China
Jun Tao1, Leiming Zhang2, Junji Cao3, and Renjian Zhang41South China Institute of Environmental Sciences, Ministry of Environmental Protection, Guangzhou, China 2Air Quality Research Division, Science and Technology Branch, Environment and Climate Change Canada, Toronto, Canada 3Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China 4Key Laboratory of Regional Climate-Environment for Temperate East Asia, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing, China
Received: 23 Mar 2017 – Accepted for review: 13 Apr 2017 – Discussion started: 18 Apr 2017
Abstract. To obtain a thorough knowledge of PM2.5 chemical composition and its impact on aerosol optical properties across China, existing field studies conducted after the year of 2000 are reviewed and summarized in terms of geographical, inter-annual, and seasonal distributions. Annual PM2.5 was up to six times of the national air quality standard in some megacities in northern China. Annual PM2.5 was higher in northern than southern cities, and higher in inland than coastal cities. In a few cities with data longer than a decade, PM2.5 showed a slight decrease only in the second half of the past decade, while carbonaceous aerosols decreased, sulfate (SO42−) and ammonium (NH4+) remained at high levels, and nitrate (NO3−) increased. The highest seasonal averages of PM2.5 and its major chemical components were mostly observed in the cold seasons. Annual average contributions of secondary inorganic aerosols to PM2.5 ranged from 25 % to 48 %, and those of carbonaceous aerosols ranged from 23 % to 47 %, both with higher values in southern regions due to the frequent dust events in northern China.
The geographical pattern of scattering coefficient (bsp) was similar to that of PM2.5, and that of aerosol absorption coefficient (bap) was determined by elemental carbon (EC) mass concentration and its coating. bsp in ambient condition of RH = 80 % can be amplified about 1.8 times of that under dry condition. Secondary inorganic aerosols accounted for about 60 % of aerosol extinction coefficient (bext) under ambient conditions in megacities with RH higher than 70 %. The mass scattering efficiency (MSE) of PM2.5 ranged from 3.0 to 5.0 m2 g−1 for aerosols produced from anthropogenic emissions and from 0.7 to 1.0 m2 g−1 for natural dust aerosols. The mass absorption efficiency (MAE) of EC ranged from 6.5 to 12.4 m2 g−1 in urban environments, but the MAE of water-soluble organic carbon (WSOC) was only 0.05 to 0.11 m2 g−1. Historical emission control policies in China and their effectiveness were discussed based on available chemically resolved PM2.5 data, which provides the much-needed knowledge for guiding future studies and emission policy making.
Tao, J., Zhang, L., Cao, J., and Zhang, R.: A review of current knowledge concerning PM2.5 chemical composition, aerosol optical properties, and their relationships across China, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-271, in review, 2017.