Impact of aerosol-boundary layer interactions on PM2.5 pollution during cold air pool events in a semi-arid urban basin

Min Zhang; Pengfei Tian; Yiyang Zhao; Xin Song; Jiening Liang; Jiayun Li; Zhida Zhang; Xu Guan; Xianjie Cao; Yan Ren; Jinsen Shi; Lei Zhang

doi:10.1016/j.scitotenv.2024.171225

Impact of aerosol-boundary layer interactions on PM_2.5 pollution during cold air pool events in a semi-arid urban basin

Sci Total Environ. 2024 Apr 20:922:171225. doi: 10.1016/j.scitotenv.2024.171225. Epub 2024 Feb 24.

Authors

Min Zhang¹, Pengfei Tian², Yiyang Zhao¹, Xin Song¹, Jiening Liang¹, Jiayun Li¹, Zhida Zhang¹, Xu Guan¹, Xianjie Cao¹, Yan Ren³, Jinsen Shi¹, Lei Zhang⁴

Affiliations

¹ Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China.
² Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China. Electronic address: tianpf@lzu.edu.cn.
³ Collaborative Innovation Center for Western Ecological Safety, Lanzhou University, Lanzhou 730000, China.
⁴ Key Laboratory for Semi-Arid Climate Change of the Ministry of Education, College of Atmospheric Sciences, Lanzhou University, Lanzhou 730000, China; Collaborative Innovation Center for Western Ecological Safety, Lanzhou University, Lanzhou 730000, China. Electronic address: zhanglei@lzu.edu.cn.

PMID: 38408654
DOI: 10.1016/j.scitotenv.2024.171225

Abstract

Global emission reductions still must address winter fine particulate matter (PM_2.5) pollution in urban basins with enclosed terrains and frequent cold air pool (CAP) events when the temperatures within the basin are colder than above it. The effects of urban basin aerosol-boundary layer interactions on PM_2.5 pollution during CAP events remain unclear. Intensive boundary layer observations in January 2021 and numerical models were used to investigate this issue in the semi-arid urban Lanzhou Basin of China. The results showed that CAPs formed because of the synoptic weather system that exacerbated the warming over the basin. The CAPs in this experiment were characterized by stronger temperature inversion (TI) layers in the vertical direction and lower relative humidity, lower wind speed, and weaker turbulence at the bottom of the basin compared to other conditions. The strong TI layers below the top of the basin inhibited the vertical dispersion of pollutants in the basin and concentrated the PM_2.5 within a height of 0.3 km from the bottom of the basin. During CAP events, the proportion of elemental carbon in PM_2.5 increased, whereas that of secondary inorganic species decreased. Aerosol absorption increased faster than scattering during CAP events. Therefore, the mean single scattering albedo decreased from 0.85 during non-CAP periods to 0.81 during CAP events. Radiosonde-sounding observations and numerical simulations indicated that aerosols accumulating in the lower basin heated the atmosphere during the daytime and facilitated boundary layer development via the "stove effect" (absorption aerosol heats lower atmosphere to promote boundary layer development). No significant "dome effect" (absorption aerosol heats the upper boundary layer to suppress boundary layer development) occurred during the two CAP events. These findings provide a theoretical basis for scientifically-guided PM_2.5 pollution control in winter in isolated urban basins.

Keywords: Aerosol-boundary layer interaction; Cold air pools; Semi-arid region; Urban basin; Winter PM(2.5) pollution.