Discerning changes in primary and secondary pollutants due to COVID-19 amid natural variability and exceptional events by using routine monitoring network data

Abstract:

The COVID-19 pandemic caused major disruptions to our society and way of life. It also affords the opportunity to study the air-quality impacts of reduced emissions due to decreased traffic and other activities. Here we examine atmospheric data from a network of monitoring sites in some of the most populated urban areas of the U.S. to determine the changes in the primary pollutants: carbon monoxide (CO) and nitrogen dioxide (NO₂) as well as the secondary products: ozone (O₃) and particulates (PM_2.5).

We find significant variability in the impact of the reduction in emissions for different regions. Attributing atmospheric changes to lowered emissions from COVID-19 is complex because year to year meteorological variability that affects pollutant concentrations can be of a similar magnitude as those anticipated from emissions reductions in 2020. Exceptional events such as stratospheric intrusions, Saharan dust events, and fires all occurred in 2020, potentially skewing observed concentrations during periods with concurrent emissions reductions. This analysis will explore the attribution of specific observed variations in pollutant concentrations to meteorology, exceptional events and emissions reductions.