Résumé
In this study, ozone and particulate matter variations from four monitoring stations in the Southwest Ohio region were analyzed at different stages of the COVID-19 pandemic in 2020, and compared with those in 2019. These stations include a U.S. EPA NCore site (Taft), an urban-suburban site (Sycamore), an industrial source site (Yankee) and a residential site near the source (Amanda). The air quality time series were broken down to the lockdown period (March 23–May 31) and the re-opening periods from June to December, 2020. Publicly available monitoring data on PM2.5, ozone and PM10 were used for analysis. PM2.5 reductions were non-uniform with strong seasonal variations. PM2.5 reductions were 4.04%, 15.6%, 11.63% at Sycamore, Taft and Yankee sites respectively during the lockdown, but increased 11.23% at Amanda. Reductions at Taft may be related to traffic restrictions while those at Yankee may be due to both reduced industrial production and source control measures. Ozone reductions were 7.94% and 6.50% at Sycamore and Taft sites during the lockdown with Sycamore having higher ozone concentrations pre, during and post lockdown. Ozone formation is NOx-limited in Southwest Ohio region and the variations are uniform. Lower temperatures during the lockdown and fall of 2020 can also be a contributing factor. The Air Quality Index (AQI) of combined ozone and PM2.5 improved during the pandemic year. Consistent with a few other studies, COVID-19 restrictions did not bring uniform air pollutant reductions to the Southwest Ohio region.