The following supplementary figure is a more detailed version of Figure 3. The difference in parts per billion between observed and ARIMA-forecasted 2020 ambient NO2 levels is plotted by city over time. SDPs are represented by the shape and color of the points. Vertical lines signify the start of the COVID-19 pandemic in the United States on March 9, 2020. Observations above the horizontal line indicate that the observed NO2 level was greater than forecasted and observations below the horizontal line indicate that the observed NO2 level was lower than forecasted.