On the Relevancy of Observed Ozone Increase during COVID-19 Lockdown to Summertime Ozone and PM_2.5 Control Policies in China

Abstract

In February 2020, China’s strict lockdown policies led to significant reductions in anthropogenic nitrogen oxides (NO x ) emissions, and notable increases in surface ozone (O 3 ) followed in many urban areas, raising concerns about potential rises in summertime O 3 due to NO x emission controls. On the basis of O 3 isopleths from a series of air quality simulations under different levels of NO x and volatile organic compound (VOC) emission reductions, we found that such concerns are not necessary. As NO x emissions have been reduced in recent years for particulate matter control, future NO x reductions are generally favorable for summertime maximum daily average 8-h (MDA8) O 3 reductions. Decreases in summertime O 3 due to NO x reductions will also lead to lower atmospheric oxidation capacity, characterized by decreased OH and NO 3 concentrations, resulting in further reduction of secondary inorganic aerosols (nitrate, sulfate, and ammonium ion, NSA) formation. VOC emission reductions help to further reduce MDA8 O 3 and are needed to control HCHO and primary air toxics simultaneously, but they are ineffective in reducing NSA. This study indicates that a nationwide NO x emission reduction policy has great potential in controlling O 3 and PM 2.5 simultaneously. However, its effectiveness could be greatly reduced when applied on a limited spatial scale.

Tropospheric NO2 and O3 Response to COVID‐19 Lockdown Restrictions at the National and Urban Scales in Germany

“…Notably, we found an increase (4%) in meteorology accounted for mean in‐situ concentrations in spring (March 21 and May 31, 2020) and a slight decrease (3%) in meteorology accounted for mean in‐situ concentrations in early summer (June, 2020) compared to the same period in 2019. This implies that the degree of saturation of ozone production is weakening from winter to summer (consistent with weekend effects and Jin et al., 2017 ; Kang et al., 2021 ). During the lockdown period, the daily maximum 8‐h mean concentration in metropolitan areas also exceeded the EU target value (120 g/ ) (2 days in Munich, Berlin, Cologne, Stuttgart metropolitan areas).…”

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

“…Obviously, the nocturnal NO 3 concentrations in both Beijing and Shijiazhuang significantly increased during the lockdown period when compared with the normal period. This can be explained by the reduction of NO and the increase of O 3 on a regional scale ( Kang et al, 2021 ). In addition, the mean concentration of SOA increased as a function of NO 3 radical concentration when SOA concentrations were higher than 20 μg m −3 , usually occurred in the lockdown period (Fig.…”

“…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.…”

Tropospheric NO_2 and O_3 response to COVID-19 lockdown restrictions at the national and urban scales in Germany

“…There also is a shift between concentrations in early summer (June, 2020) compared to the same period in 2019. This implies that the degree of NO X E saturation of ozone production is weakening from winter to summer (consistent with weekend effects and Jin et al, 2017;Kang et al, 2021). During the lockdown period, the daily maximum 8-h mean 3 O E concentration in metropolitan areas also exceeded the EU target value ) (2 days in Munich, Berlin, Cologne, Stuttgart metropolitan areas).…”