The impact of COVID-19 lockdown on atmospheric CO2 in Xi'an, China

Abstract

Lockdown measures to control the spread of the novel coronavirus disease (COVID-19) sharply limited energy consumption and carbon emissions. The lockdown effect on carbon emissions has been studied by many researchers using statistical approaches. However, the lockdown effect on atmospheric carbon dioxide (CO2) on an urban scale remains unclear. Here we present CO2 concentration and carbon isotopic (δ13C) measurements to assess the impact of COVID-19 control measures on atmospheric CO2 in Xi'an, China. We find that CO2 concentrations during the lockdown period were 7.5% lower than during the normal period (prior to the Spring Festival, Jan 25 to Feb 4, 2020). The observed CO2excess (total CO2 minus background CO2) during the lockdown period was 52.3% lower than that during the normal period, and 35.7% lower than the estimated CO2excess with the effect of weather removed. A Keeling plot shows that in contrast CO2 concentrations and δ13C were weakly correlated (R2 = 0.18) during the lockdown period, reflecting a change in CO2 sources imposed by the curtailment of traffic and industrial emissions. Our study also show that the sharp reduction in atmospheric CO2 during lockdown were short-lived, and returned to normal levels within months after lockdown measures were lifted.