COVID-19-Induced Lockdowns Indicate the Short-Term Control Effect of Air Pollutant Emission in 174 Cities in China

Abstract

The contradiction between the regional imbalance and an one-size-fits-all policy is one of the biggest challenges in current air pollution control in China. With the recent implementation of first-level public health emergency response (FLPHER) in response to the COVID-19 pandemic in China (a total of 77 041 confirmed cases by February 22, 2020), human activities were extremely decreased nationwide and almost all economic activities were suspended. Here, we show that this scenario represents an unprecedented “base period” to probe the short-term emission control effect of air pollution at a city level. We quantify the FLPHER-induced changes of NO2, SO2, PM2.5, and PM10 levels in 174 cities in China. A machine learning prediction model for air pollution is established by coupling a generalized additive model, random effects meta-analysis, and weather research and forecasting model with chemistry analysis. The short-term control effect under the current energy structure in each city is estimated by comparing the predicted and observed results during the FLPHER period. We found that the short-term emission control effect ranges within 53.0%–98.3% for all cities, and southern cities show a significantly stronger effect than northern cities (P < 0.01). Compared with megacities, small–medium cities show a similar control effect on NO2 and SO2 but a larger effect on PM2.5 and PM10.

Evolution of organic carbon during COVID-19 lockdown period: Possible contribution of nocturnal chemistry

“…For example, the fraction of OA in PM 2.5 was 28.9% in Shijiazhuang and 34.6% in Beijing, respectively, during the lockdown period. In previous work, attention was mainly paid to the formation of secondary inorganic aerosol during the COVID-19 lockdown ( Chen et al, 2020a ; Lu et al, 2021 ), while less attention was paid to organic aerosol formation. In the following sections, we will focus on the evolution of OA component.…”

“…The outbreak of the COVID-19 was followed by a strict nationwide lockdown in China, which has restricted anthropogenic activities such as transportation, commerce, and industry to prevent the spread of COVID-19 on a national scale. As a consequence, the emissions of primary air pollutants from anthropogenic sources were significantly reduced ( Chen et al, 2020a ; Le et al, 2020 ; Liu et al, 2020b ; Lu et al, 2021 ; Ma et al, 2021 ). This was also observed as the spread of the COVID-19 pandemic worldwide ( Baldasano, 2020 ; Kanniah et al, 2020 ; Lee et al, 2020 ; Otmani et al, 2020 ; Zhang et al, 2021a ; Zoran et al, 2020 ).…”

“…OC can be directly emitted from various sources, such as traffic exhaust, biomass combustion, and plant respiration, and secondarily formed through photochemical or heterogeneous reactions in the atmosphere ( Bae et al, 2004 ; Turpin and Huntzicker, 1995 ). Many previous works have discussed the concentration changes of air pollutants, such as O 3 ( Kang et al, 2021 ; Lu et al, 2021 ), NO 2 and HONO ( Liu et al, 2020b ), PM 2.5 ( Chen et al, 2020a ; Zheng et al, 2020 ), heavy metal elements ( Cui et al, 2020 ), light absorption components in PM 2.5 ( Chen et al, 2020b ), the source changes from biomass burning ( Metya et al, 2020 ), and secondary formation ( Huang et al, 2021 ; Sun et al, 2020b ) during the lockdown period. However, there were few studies focusing on OC and the possible formation mechanism of SOC during the COVID-19 pandemic in the NCP region.…”

Decomposing PM2.5 air pollution rebounds in Northern China before COVID-19

“…However, PM 2.5 concentrations declined remarkably in the 2019 HS due to the impact of COVID-19 lockdown (Supplementary Table S1 ) (Huang et al 2021 ), resulting in a smaller rebound in northern cities during 2017–2019 HS (Supplementary Table S2 ). Given that lockdown only had a short-term impact on PM 2.5 trends (Lu et al 2021 ), we excluded its impacts by removing data in February and March 2020 (post-Feb 2020) from the baseline results. As such, PM 2.5 rebound continued into the 2019 HS, with the PM 2.5 concentrations further increased by 4.79 µg/m 3 (8.1%).…”

Association of population migration with air quality: Role of city attributes in China during COVID-19 pandemic (2019–2021)

“…Transportation is the primary source of NO 2 in China. Megacities and large cities serve as transportation hubs and industry centers more than medium and small cities ( Krecl et al, 2020 ; Lu et al, 2021 ). Daily commuting, which causes more air pollutants, was much greater than in smaller cities because of the separation of work and residence.…”