Quantifying changes in carbon monoxide (CO) vehicle emissions in New York City during the COVID-19 shutdown

During the COVID-19 pandemic in 2020, New York State ordered the closure of all non-essential commercial activities. This shutdown lead to a peak of 80% reduction in on-road transportation and improving air quality across New York City. Carbon monoxide (CO) is a pollutant released in incomplete combustion processes related to vehicles, heating, etc. The COVID-19 citywide shutdown was a natural experiment in the improvement in air quality possible from the electrification of the vehicle fleet in New York City. The shutdown allows us to evaluate the accuracy of the other sector emissions in the inventories.

We measured CO concentrations at a site in West Harlem Jan - June 2019 and 2020 allowing us to observe the impact of the COVID shutdowns. We interpret our observations using an atmospheric transport model and two CO emission inventories: Emissions Database for Global Atmospheric Research (EDGAR) Fuel-based Inventory of Motor-Vehicle Emissions (FIVE). In order to compare the calculated boundary layer enhancement of CO with the observations, a background is estimated using wind direction and a series of EPA CO monitoring sites surrounding NYC. The background concentrations indicate the preexisting pollution in the air before entering the city, allowing us to more accurately find the CO change caused by NYC changes as opposed to changes in surrounding regions.

We observed a 40% reduction in afternoon CO concentrations over March 2020 before and during the shutdown. We identified a seasonal cycle for the background with reduced CO concentrations into the summer. We find that the FIVE inventory has higher road emissions, particularly on weekdays, as predicted compared to the EDGAR inventory The FIVE estimates better match the pre-COVID CO observations, suggesting an underestimate of EDGAR vehicle emissions. While during the COVID shutdown, EDGAR total emissions match the observations quite well, again indicating an underestimate in CO on-road emissions.