Graduation Year


Document Type

Campus Only Senior Thesis

Degree Name

Bachelor of Arts



Reader 1

Kathleen Purvis-Roberts

Reader 2

Franck Fu

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© 2021 Caroline N Wofford


The COVID-19 pandemic and related restrictions led to dramatic behavioral change, including substantial reductions in mobility as citizens were urged to stay at home. It has been widely anecdotally noted that air quality improved visibly in many cities during the duration of the stay-at-home orders, which is credited to the precipitous drop in vehicle travel. To assess the validity of these observations, nitrogen dioxide (NO2), ground-level ozone (O3), and fine particulate matter (PM2.5) data were analyzed for 11 urban areas of the US for the years 2017-2020, using daily data from EPA’s AirNow database. Locations were selected based on a minimum population of 1 million, and locations that maximize geographic distribution in the continental US. There are three periods of the study: ‘pre- pandemic’ (January 1st – start of stay-at-home orders), ‘stay-at-home’ (duration of stay-at- home order), and ‘reopening’ (end of stay-at-home order – June 30th), which are specific to each location, to establish changes in observable air pollutants relative to the same dates in years prior to 2020. It was found that NO2 was the only pollutant that decreased significantly in a majority of cases; PM2.5 and O3 had varied trends, which were mostly insignificant compared to prior years. General trends of NO2 and O3 confirm NOx based O3 formation regimes in the troposphere. Vehicle travel data, in the form of vehicle miles traveled (VMT) on a county-level was obtained for 2020 from Streetlight Data LLC. These data were compared across the same periods to 2020 NO2 data, to assess whether changes in VMT align with changes in measurable NO2. It was found that VMT decreased in 2020 during stay-at-home relative to pre-pandemic period in most counties, as well as reopening to a lesser degree, however due to the lack of VMT data predating 2020, no reliable conclusions were drawn from this analysis, though, it is likely the drop in VMT explains the significant changes in NO2 from prior years, at least in part. Lastly, COVID-19 cases and deaths were compared with overall AQI for each county, to assess whether any correlation exists between air quality and likelihood of COVID-19 fatality. Without other controls, COVID-19 death rate had no correlation with AQI.

This thesis is restricted to the Claremont Colleges current faculty, students, and staff.