Ozone Changes Over the United States Due to COVID-19

The COVID-19 pandemic has caused significant changes in emissions of both nitrogen oxides (NOx) and volatile organic compounds (VOCs) over U.S. cities, which are precursors of tropospheric ozone formation. We investigate the ozone changes over the continental US due to the emission reductions, and non-linear chemistry during summertime ozone season. A Fuel-based Inventory of Vehicle Emissions and Volatile Chemical Products (FIVE-VCP) inventory was developed specifically and constrained with TROPOspheric Monitoring Instrument (TROPOMI) TROPOMI satellite data. We conduct simulations during summer in 2020 using the Weather Research and Forecasting with Chemistry (WRF-Chem) model and compare with simulations from a base case run in 2018. Model simulations in 2020 are conducted using both a business-as-usual and COVID perturbed emission cases, to assess the role of meteorology in interpreting satellite observations versus past years. Ratios of formaldehyde to nitrogen dioxide from TROPOMI is used to assess NO_x sensitivity for ozone formation, along with ground-based monitoring data. Our preliminary analysis suggests that ozone has likely decreased in most cities due to perturbations in anthropogenic emissions. Considering that NO_x emissions of transportation have decreased by 30-50%, the decreasing ratios of ozone are relatively lower due to co-reduction of VOCs and non-linear chemistry. Our analyses for COVID-19 provide insights on future ozone control pathways, including those related to the transportation sector.