Variations and Sources of Organic Aerosol in Winter Beijing under Markedly Reduced Anthropogenic Activities During COVID-2019

Abstract

The COVID-19 outbreak provides a “controlled experiment” to investigate the response of aerosol pollution to the reduction of anthropogenic activities. Here we explore the chemical characteristics, variations, and emission sources of organic aerosol (OA) based on the observation of air pollutants and combination of aerosol mass spectrometer (AMS) and positive matrix factorization (PMF) analysis in Beijing in early 2020. By eliminating the impacts of atmospheric boundary layer and the Spring Festival, we found that the lockdown effectively reduced cooking-related OA (COA) but influenced fossil fuel combustion OA (FFOA) very little. In contrast, both secondary OA (SOA) and O3 formation was enhanced significantly after lockdown: less-oxidized oxygenated OA (LO-OOA, 37% in OA) was probably an aged product from fossil fuel and biomass burning emission with aqueous chemistry being an important formation pathway, while more-oxidized oxygenated OA (MO-OOA, 41% in OA) was affected by regional transport of air pollutants and related with both aqueous and photochemical processes. Combining FFOA and LO-OOA, more than 50% of OA pollution was attributed to combustion activities during the whole observation period. Our findings highlight that fossil fuel/biomass combustion are still the largest sources of OA pollution, and only controlling traffic and cooking emissions cannot efficiently eliminate the heavy air pollution in winter Beijing.

Drivers of High Concentrations of Secondary Organic Aerosols in Northern China during the COVID-19 Lockdowns

“…The changes of major SOA pathways, A-SOA, I/S/xL-SOA, and aq-SOA, all present similar spatial patterns. Therefore, our model shows that the observed SOA concentration increase revealed by previous studies , mainly happened in the northern region that includes Beijing.…”

“…The enhanced concentrations indicate an unfavorable meteorological condition during the lockdown as compared to that before the lockdown. Such unfavorable condition is reflected by higher RH, higher temperature, and weaker dispersion, as is discussed in detail by Hu et al However, the meteorological impact on SOA is much greater than that on POA. Specifically, the SOA concentration was enhanced for 119% by meteorology, while POA was only enhanced for 30%.…”

“…Note that such a brute-force method might result in a larger COA concentration (approximately 5% larger based on our previous assessment) due to nonlinearity. As for SOA, to make it comparable with the PMF analysis of Hu et al, we also separate the modeled SOA into LO-OOA and MO-OOA based on the O/C. The observed O/C of LO-OOA and MO-OOA are 0.67 and 1.09, respectively.…”

Multiyear emissions of carbonaceous aerosols from cooking, fireworks, sacrificial incense, joss paper burning, and barbecue as well as their key driving forces in China

“…Recently, due to the strengthened control of combustion-related sources, the important role of cooking emissions with respect to affecting air quality has gradually become visible in densely populated downtown areas. Cooking-related organic aerosol (COA) contributed 15 %-34 % of total OC emissions and 6 %-9 % of total PM 2.5 emissions in a downtown site in Shanghai (Huang et al, 2021) and 31 % of the total organic aerosol in Beijing in winter (Hu et al, 2021). Existing studies on the FMSs have mainly been based on ambient air monitoring datasets at certain sites or during certain periods (See and Balasubramanian, 2011;Wu et al, 2015;Shen et al, 2017;Lao et al, 2018;Tanda et al, 2019;Yao et al, 2019;Hu et al, 2021;Huang et al, 2021).…”

“…Cooking-related organic aerosol (COA) contributed 15 %-34 % of total OC emissions and 6 %-9 % of total PM 2.5 emissions in a downtown site in Shanghai (Huang et al, 2021) and 31 % of the total organic aerosol in Beijing in winter (Hu et al, 2021). Existing studies on the FMSs have mainly been based on ambient air monitoring datasets at certain sites or during certain periods (See and Balasubramanian, 2011;Wu et al, 2015;Shen et al, 2017;Lao et al, 2018;Tanda et al, 2019;Yao et al, 2019;Hu et al, 2021;Huang et al, 2021). However, to date, no studies have been able to pro-vide their quantitative contributions on a large scale due to the scarcity of emission inventory information, which has limited the identification of their contributions in various regions or during certain periods.…”