Ozone at South Fayette, Pennsylvania: A Case Study of Stratospheric Ozone and Air Pollution

Tropospheric ozone is one of the criteria pollutants monitored by the Environmental Protection Agency. In the Greater Pittsburgh Metropolis, air quality is often impacted by ozone. While the photochemical reactions of emissions are the major cause of ozone, regions close to sea level may experience a rare stratospheric intrusion of ozone. These intrusions bring ozone from the stratosphere to the free troposphere through tropopause folding and entrainment into the boundary layer to the surface. This case study examined a three-day event (30 April 2020 – 03 May 2020) at South Fayette, Allegheny County, Pennsylvania of fluctuating ozone with a higher-than-average day on 03 May 2020. The Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2) tool was used to identify incidences of high potential vorticity and its evolution through the Eastern United States to observe a possible case of stratospheric intrusion. Total column of ozone from the MERRA-2 and data from Environmental Protection Agency ground monitoring sites were compared. Although the study is inconclusive, access to vertical data could give evidence to the possible stratospheric intrusion.