Preprints
https://doi.org/10.5194/acp-2022-557
https://doi.org/10.5194/acp-2022-557
 
20 Sep 2022
20 Sep 2022
Status: this preprint is currently under review for the journal ACP.

Composited analyses of the chemical and physical characteristics of co-polluted days by ozone and PM2.5 over 2013–2020 in the Beijing–Tianjin–Hebei region

Huibin Dai, Hong Liao, Ke Li, Xu Yue, Yang Yang, Jia Zhu, Jianbing Jin, and Baojie Li Huibin Dai et al.
  • Jiangsu Key Laboratory of Atmospheric Environment Monitoring and Pollution Control, Jiangsu Collaborative Innovation Center of Atmospheric Environment and Equipment Technology, School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China

Abstract. The co-polluted days by ozone (O3) and PM2.5 (particulate matter with an aerodynamic equivalent diameter of 2.5 μm or less) (O3&PM2.5PD) were frequently observed in the Beijing–Tianjin–Hebei (BTH) region in warm seasons (April–October) of 2013–2020. We applied the 3-D global chemical transport model (GEOS-Chem) to investigate the chemical and physical characteristics of O3&PM2.5PD by composited analyses of such days that were captured by both the observations and the model. Model results showed that, when O3&PM2.5PD occurred, the concentrations of hydroxyl radical and total oxidant, sulfur oxidation ratio, and nitrogen oxidation ratio were all high, and the concentrations of sulfate at the surface were the highest among all aerosol species. We also found unique features in vertical distributions of aerosols during O3&PM2.5PD; concentrations of PM2.5 decreased with altitude near the surface but remained stable at 975–819 hPa. Process analyses showed that secondary aerosols (nitrate, ammonium and sulfate) had strong chemical productions at 913–819 hPa, which were then transported downward, resulting in the quite uniform vertical profiles at 975–819 hPa in O3&PM2.5PD. The weather patterns for O3&PM2.5PD were characterized by a high pressure ridge of the Western Pacific Subtropical High at 850 hPa. The strong southerlies at 850 hPa brought moist air from the south, resulting in a high RH and hence the strong chemical productions around this layer in O3&PM2.5PD. The physical and chemical characteristics of O3&PM2.5PD are quite different from those of polluted days by either O3 alone or PM2.5 alone, which have important implications for air quality management.

Huibin Dai et al.

Status: open (until 01 Nov 2022)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Huibin Dai et al.

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Short summary
We apply the 3-D global chemical transport model (GEOS-Chem) to simulate O3&PM2.5PD in BTH in years of 2013–2020, and investigate the chemical and physical characteristics of O3&PM2.5PD by composited analyses of such days that are captured by both the observations and the model. We report for the first time the unique features in vertical distributions of aerosols during O3&PM2.5PD and the physical and chemical characteristics of O3&PM2.5PD.
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