Characteristics of sub-micron aerosols above the urban canopy in Beijing during warm seasons

Qingqing Wang; Wei Du; Wei Zhou; Yingjie Zhang; Conghui Xie; Jian Zhao; Weiqi Xu; Guiqian Tang; Pingqing Fu; Zifa Wang; Yele Sun; Lin Peng

doi:10.1016/j.scitotenv.2024.171989

Characteristics of sub-micron aerosols above the urban canopy in Beijing during warm seasons

Sci Total Environ. 2024 May 20:926:171989. doi: 10.1016/j.scitotenv.2024.171989. Epub 2024 Mar 26.

Authors

Qingqing Wang¹, Wei Du², Wei Zhou³, Yingjie Zhang⁴, Conghui Xie⁵, Jian Zhao², Weiqi Xu³, Guiqian Tang⁶, Pingqing Fu⁷, Zifa Wang⁸, Yele Sun⁸, Lin Peng⁹

Affiliations

¹ Engineering Research Center of Clean and Low-carbon Technology for Intelligent Transportation, Ministry of Education, School of Environment, Beijing Jiaotong University, Beijing 100044, China; State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China. Electronic address: wangqingqing0119@163.com.
² State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China; Institute for Atmospheric and Earth System Research / Physics, Faculty of Science, University of Helsinki, Finland.
³ State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China; College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China.
⁴ School of Ecology and Nature Conservation, Beijing Forestry University, Beijing 100083, China.
⁵ State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China; Laboratory of Gas Instrument Testing, Center for Environmental Metrology, National Institute of Metrology, Beijing 100029, China.
⁶ State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China.
⁷ Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China.
⁸ State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry, Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing 100029, China; College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China; Center for Excellence in Regional Atmospheric Environment, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China.
⁹ Engineering Research Center of Clean and Low-carbon Technology for Intelligent Transportation, Ministry of Education, School of Environment, Beijing Jiaotong University, Beijing 100044, China. Electronic address: penglin6611@163.com.

PMID: 38547971
DOI: 10.1016/j.scitotenv.2024.171989

Abstract

To understand the characteristics of atmospheric pollution above the urban canopy in warm seasons, the characteristics of sub-micron aerosol (PM₁) was studied based on high-altitude observations at the Beijing 325 m meteorological tower. The PM₁ at 260 m was 34, 29 and 21 μg m^-3 in May 2015, June 2015, and June 2017, respectively, indicating a reduction in PM₁ pollution above the urban canopy. Meanwhile, an overall decrease was also observed in the concentrations of all PM₁ chemical species (excluding Chl and BC) and organic aerosol (OA) factors. Previous instances of heavy haze in Beijing often coincided with high humidity and stagnant weather conditions. However, the heightened pollution episodes in June 2017 were accompanied by high wind speeds and low relative humidity. Compared to May 2015, the contribution of secondary components to PM₁ in June 2017 was more prominent, with the total proportion of SNA (sulfate, nitrate, and ammonium) and more-oxidized oxygenated OA (MO-OOA) to PM₁ increased by approximately 10 %. Secondary species of NH₄NO₃, (NH₄)₂SO₄, and MO-OOA, as well as black carbon, collectively contributed the vast majority of aerosol extinction coefficient (b_ext), with the four species contributing a total of ≥96 % to b_ext at 260 m. Hydrocarbon-like OA, cooking OA, and less-oxidized oxygenated OA have undergone significant reductions, so continued emphasis on controlling local sources to reduce these three aerosol species and addressing regional sources to further mitigate overall aerosol species is imperative. In lower pollution situation, the diurnal variation of PM was smoother, and its pollution sources were more regionally uniform, which might be attributed to the reduced diversity and complexity in the physical and chemical processes in air pollution.

Keywords: Beijing; Light extinction coefficient; Sub-micron aerosols; Urban canopy; Warm season.