Today marks one week since DC Mayor Muriel Bowser announced a formal stay-at-home order for District residents on Monday, March 30, 2020. By that point, many residents had already been working from home since mid-March. Given that we can assume a reduction in travel demand because of these work and travel constraints, I was curious to see if and how the DC region’s air quality might be impacted.

First, a word about air quality. The EPA’s Air Quality Index (AQI) tracks five pollutants as stipulated in the landmark Clean Air Act of 1970, including ground-level ozone, particle pollution (also called particulate matter, or PM), carbon monoxide, sulfur dioxide, and nitrogen dioxide. The AQI also assigns a range that indicates the impact of air quality on health and the color-coded index ranges from maroon (hazardous) to green (good). There are many factors that influence air quality, but it is reasonable to assume that the scale of the reduced automobile travel will have a positive influence on air quality given their ability to pollute.

Using AirNow data from EPA’s website, I generated a table of daily AQI values for 2019. Each day is represented by a colored line:

Then, I generated a second table that includes 2019 and 2020:

At the very least, we can see that we have had more “green” days in DC from between March 16, 2020 (when many businesses began working from home) until last Monday, when the stay-at-home order was put into place in DC, as compared to the same time last year. However, the current data is a very small window from which to draw any meaningful conclusions. It is also difficult to determine how government directives influence personal decision-making. Given that it took until the end of March to get a direct stay-at-home order from the DC government, many individuals were already practicing social distancing, working from home full-time, and generally sheltering in place, which wouldn’t be reflected in any future data sets that measure environmental impacts after a formal stay-at-home order has been given. In the coming weeks and months, enough data might become available to more quantitatively understand how COVID-19 is impacting our environment and transportation network.

EDIT: A new study was released by Harvard today which found that, “A small increase in long-term exposure to PM2.5 leads to a large increase in COVID-19 death rate…The study results underscore the importance of continuing to enforce existing air pollution regulations to protect human health both during and after the COVID-19 crisis.” This happening in light of the Trump Administration’s rollback last week of fuel efficiency standards that will permit increased CO2 emissions.