Spatial variability in global atmospheric CO during Covid-19 lockdown: Implication of air quality policies

The COVID-19 lockdown (LD) presented a unique opportunity for examining shifts in regional and global air quality. The alterations in atmospheric carbon monoxide (CO) during LD necessitate thorough analysis, given that CO is a significant air pollutant impacting human health, ecosystems, and climate. Our examination reveals a 5-10% decrease in the CO column during LD (April-May 2020) compared to the pre-lockdown (PreLD, March 2020) periods in regions with elevated anthropogenic activity, such as East China (EC), Indo-Gangetic Plain (IGP), North America, parts of Europe, and Russia. However, this reduction was absent in regions prone to frequent and intense wildfires and agricultural waste burning (AWB). There is substantial heterogeneity in CO column distributions, ranging from regional to city scales, during the LD period. To identify the sources of CO emissions during LD, we analyzed the ratios of nitrogen dioxide (NO2), sulfur dioxide (SO2) to CO for major cities worldwide. This analysis facilitated the identification of contributions from various sources, including vehicles, industries, and biomass burning during LD. Comparisons between CO levels during LD and PreLD periods indicate a significant reduction in global tropospheric CO but no noteworthy change in the stratosphere. Notably, CO emissions decreased during LD in hotspot regions but rebounded after the lifting of LD restrictions. This study underscores the importance of policy decisions and their implementation on both global and regional scales to enhance air quality, safeguarding public health and the environment.