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 US EPA NCore site (Taft), an urbansuburban site (Sycamore), an industrial source site (Yankee) and a residential site near the source (Amanda). The air quality data were broken down to the lockdown period (March 23 to 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 A C C E P T E D M A N U S C R I P T2 production and source control measures. Ozone reductions were 7.94% and 6.50% at Sycamore 26 and Taft sites during the lockdown with Sycamore having higher ozone concentrations pre, 27 during and post lockdown. Ozone formation is NOx-limited in Southwest Ohio region and the 28 variations are uniform. Lower temperatures during the lockdown and fall of 2020 can also be a 29 contributing factor. The Air Quality Index (AQI) of combined ozone and PM2.5 improved during 30 the pandemic year. Consistent with a few other studies, COVID-19 restrictions did not bring 31 uniform pollutant reductions to the Southwest Ohio region.

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 US EPA NCore site (Taft), an urbansuburban site (Sycamore), an industrial source site (Yankee) and a residential site near the source (Amanda). The air quality data were broken down to the lockdown period (March 23 to 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 A C C E P T E D M A N U S C R I P T2 production and source control measures. Ozone reductions were 7.94% and 6.50% at Sycamore 26 and Taft sites during the lockdown with Sycamore having higher ozone concentrations pre, 27 during and post lockdown. Ozone formation is NOx-limited in Southwest Ohio region and the 28 variations are uniform. Lower temperatures during the lockdown and fall of 2020 can also be a 29 contributing factor. The Air Quality Index (AQI) of combined ozone and PM2.5 improved during 30 the pandemic year. Consistent with a few other studies, COVID-19 restrictions did not bring 31 uniform pollutant reductions to the Southwest Ohio region.