Global tropospheric ozone responses to reduced NO _x emissions linked to the COVID-19 worldwide lockdowns

Abstract

Efforts to stem the transmission of coronavirus disease 2019 (COVID-19) led to rapid, global ancillary reductions in air pollutant emissions. Here, we quantify the impact on tropospheric ozone using a multiconstituent chemical data assimilation system. Anthropogenic NOx emissions dropped by at least 15% globally and 18 to 25% regionally in April and May 2020, which decreased free tropospheric ozone by up to 5 parts per billion, consistent with independent satellite observations. The global total tropospheric ozone burden declined by 6TgO3 (∼2%) in May and June 2020, largely due to emission reductions in Asia and the Americas that were amplified by regionally high ozone production efficiencies (up to 4 TgO3/TgN). Our results show that COVID-19 mitigation left a global atmospheric imprint that altered atmospheric oxidative capacity and climate radiative forcing, providing a test of the efficacy of NOx emissions controls for co-benefiting air quality and climate.

Ozone Anomalies in the Free Troposphere During the COVID‐19 Pandemic

“…While these changes have some effect, they do not fundamentally alter our conclusions. Overall, our different tested scenarios, together with similar ozone reductions obtained in other simulations (Mertens et al, 2021;Miyazaki et al, 2021;Weber et al, 2020) indicate that the uncertainty of the calculated ozone anomaly in the free troposphere is of the order of 1-2 ppbv (2%-4%), and is associated with the adopted model formulation as well as the assumed magnitude of the emission reductions. As more accurate information on actual emission reductions is becomes available, future simulations should reduce the current uncertainties.…”

Societal shifts due to COVID-19 reveal large-scale complexities and feedbacks between atmospheric chemistry and climate change

“…Reductions in NO x emissions were apparent in both in situ ( 5 ) and satellite ( 6 ) observations of NO 2 concentrations due to the short atmospheric lifetime of NO x ( <1 d). Estimates of NO x emissions reductions from assimilating satellite data in global models ( 7 ), combining global chemical models with machine learning trained on surface measurements ( 8 ), or activity data (including electricity use, traffic/mobility data, flight data, etc.) ( 9 – 11 ) find regional reductions of 10 to 40% during the strictest lockdown periods.…”

“…Generally, methods assimilating satellite data report smaller reductions (10 to 20%) than studies based on activity data (25 to 40%). Estimates of the reduction in global NO x emissions in the first half of 2020 range from 5% ( 8 ) to 13% ( 7 ).…”

COVID-19 lockdown closures of emissions sources in India: Lessons for air quality and climate policy

“…This can aid the development of future policy actions aimed at securing multiple benefits to air quality and climate. Recent studies have modelled emissions during the lockdown ( Beig et al, 2021 ; Forster et al, 2020 ; Le Quéré et al, 2020 ; Liu et al, 2020 ; Misra et al, 2021 ; Miyazaki et al, 2021 ; Sarfraz et al, 2021 ; Xing et al, 2020 ; Zhang et al, 2021 ; Zheng et al, 2020 ) exploring a variety of aspects such as global temperature response ( Forster et al, 2020 ), impact of emission changes on ambient O 3 and PM 2.5 concentrations ( Miyazaki et al, 2021 ; Xing et al, 2020 ; Zhang et al, 2021 ), sectoral impacts on urban air pollution ( Beig et al, 2021 ; Misra et al, 2021 ) and possible future emissions recovery pathways post lockdown ( Forster et al, 2020 ; Le Quéré et al, 2020 ). These studies model single pollutants such as CO 2 ( Le Quéré et al, 2020 ; Liu et al, 2020 ; Sarfraz et al, 2021 ; Zheng et al, 2020 ), CO ( Beig et al, 2021 ) and NOx ( Misra et al, 2021 ; Miyazaki et al, 2021 ) or O 3 and PM 2.5 ( Zhang et al, 2021 ) to examine changes in air quality.…”