O3-VOC-NOx sensitivity before and during the COVID-19 pandemic in NYC

Understanding the local and regional sources of anthropogenic emissions relevant to ozone (O₃) formation is a barrier to accurate O₃ model prediction and effective regulatory efforts in the New York City (NYC) metropolitan area. Pollutant emissions are variable year-to-year depending on the effects of regulatory policies, changes in human mobility, and natural variability in meteorology. Detailed emission inventories used in chemical modeling, like the National Emission Inventory (NEI), are compiled every few years, leading to outdated emissions for years beyond the compilation year. The NEI is based on projected trends of emissions and thus cannot account for abrupt economic changes, further compounding errors when used in O₃ model prediction. Using a blend of satellite and ground-based sensors, Tong et al. (2016) calculated adjustment factors for nitrous oxides (NO_x) and applied them to the NEI to model O₃ during the 2008 recession and for a business-as-usual inventory. Here, adjustment factors for different sectors of emission (transportation, energy production, etc.) are modified in the NEI using observed reductions during the pandemic. The updated NEI is ingested into the WRF-Chem model to simulate the impact of COVID-19 economic and social restrictions on surface O₃ concentrations over NYC. The launch of the TROPOspheric Monitoring Instrument in 2017 provides high-resolution column retrievals of NO₂, allowing for comparison with WRF-Chem NO₂ output as verification of model results and for use in adjusting the NEI. Updates to the NEI will change both the local and regional transport of O₃-relevant pollutants, including anthropogenic volatile organic carbon (VOC) species. To account for these changes, tagged tracers in the WRF model are used to track the transport and dispersion of VOC species around NYC before and during pandemic restrictions. It is possible to refine tagged tracers by pollutant type and geographic region, allowing for detailed analysis on source apportionment and the potential health impacts on communities in NYC. Combining these methods allows for a comprehensive view of O₃ chemistry, transport, and the burden on NYC communities before and during the COVID-19 pandemic to help guide future policy on emission control.