Unexpected rise of atmospheric secondary aerosols from biomass burning during the COVID-19 lockdown period in Hangzhou, China

Huifeng Xu; Linghong Chen; Jiansong Chen; Zhier Bao; Chenxi Wang; Xiang Gao; Kefa Cen

doi:10.1016/j.atmosenv.2022.119076

Unexpected rise of atmospheric secondary aerosols from biomass burning during the COVID-19 lockdown period in Hangzhou, China

Atmos Environ (1994). 2022 Jun 1:278:119076. doi: 10.1016/j.atmosenv.2022.119076. Epub 2022 Mar 28.

Authors

Huifeng Xu¹, Linghong Chen¹, Jiansong Chen², Zhier Bao¹, Chenxi Wang¹, Xiang Gao¹, Kefa Cen¹

Affiliations

¹ State Key Laboratory of Clean Energy Utilization, Zhejiang University, Hangzhou, 310027, China.
² Hangzhou Ecological and Environmental Monitoring Center of Zhejiang Province, Hangzhou, 310007, China.

Abstract

After the global outbreak of COVID-19, the Chinese government took many measures to control the spread of the virus. The measures led to a reduction in anthropogenic emissions nationwide. Data from a single particle aerosol mass spectrometer in an eastern Chinese megacity (Hangzhou) before, during, and after the COVID-19 lockdown (5 January to February 29, 2020) was used to understand the effect lockdown had on atmospheric particles. The collected single particle mass spectra were clustered into eight categories. Before the lockdown, the proportions of particles ranked in order of: EC (57.9%) < K-SN (13.6%) < Fe-rich (10.2%) < ECOC (6.7%) < K-Na (6.6%) < OC (3.4%) < K-Pb (1.0%) < K-Al (0.7%). During the lockdown period, the EC and Fe-rich particles decreased by 42.8% and 93.2% compared to before lockdown due to reduced vehicle exhaust and industrial activity. By contrast, the K-SN and K-Na particles containing biomass burning tracers increased by 155.2% and 45.2% during the same time, respectively. During the lockdown, the proportions of particles ranked in order of: K-SN (39.7%) < EC (38.1%) < K-Na (11.0%) < ECOC (7.7%) < OC (1.2%) < K-Pb (0.9%) < Fe-rich (0.8%) < K-Al (0.6%). Back trajectory analysis indicated that both inland (Anhui and Shandong provinces) and marine transported air masses may have contributed to the increase in K-SN and K-Na particles during the lockdown, and that increased number of fugitive combustion points (i.e., household fuel, biomass combustion) was a contributing factor. Therefore, the results imply that regional synergistic control measures on fugitive combustion emissions are needed to ensure good air quality.

Keywords: Biomass burning; COVID-19; Regional atmospheric transport; SPAMS; YRD.