Weakened Aerosol-PBL Interaction During COVID-19 Lockdown in Northern China

Zilin Wang; Xin Huang; Ke Ding; Chuanhua Ren; Lu Cao; Derong Zhou; Jian Gao; Aijun Ding

doi:10.1029/2020GL090542

Weakened Aerosol-PBL Interaction During COVID-19 Lockdown in Northern China

Geophys Res Lett. 2021 Feb 16;48(3):e2020GL090542. doi: 10.1029/2020GL090542. Epub 2021 Feb 2.

Authors

Zilin Wang^{1

2}, Xin Huang^{1

2}, Ke Ding^{1

2}, Chuanhua Ren^{1

2}, Lu Cao³, Derong Zhou^{1

2}, Jian Gao⁴, Aijun Ding^{1

2}

Affiliations

¹ School of Atmospheric Sciences Nanjing University Nanjing China.
² Collaborative Innovation Center of Climate Change Nanjing Jiangsu Province China.
³ Meteorological Observatory of Jiangsu Province Nanjing China.
⁴ Chinese Research Academy of Environmental Science Beijing China.

Abstract

Anthropogenic emissions were greatly constrained during COVID-19 lockdown in China. Nevertheless, observations still showed high loadings of fine particles (PM_2.5) over northern China with secondary aerosols increasing by 15 μg/m³ yet a ∼10% drop in light-absorbing black carbon (BC). Such a chemical transition in aerosol composition tended to make the atmosphere more scattering, indicated by satellite-retrieved aerosol absorption optical depth falling by 60%. Comparison between weather forecast and radiosonde observations illustrated that, without upper-level heating induced by BC, the stabilized stratification diminished, which was conducive for planetary boundary layer (PBL) mixing and thus near-surface pollution dispersion. Furthermore, coupled dynamic-chemistry simulations estimated that emission reduction during the lockdown weakened aerosol-PBL interaction and thus a reduction of 25 μg/m³ (∼50%) in PM_2.5 enhancement. Based on the unique natural experiment, this work observationally confirmed and numerically quantified the importance of BC-induced meteorological feedback, further highlighting the priority of BC control in haze mitigation.

Keywords: COVID‐19 emission reduction; aerosol chemical composition; aerosol optical properties; aerosol–PBL interaction; boundary layer development; haze pollution.