Top-down estimate of NOx and NMVOC emissions over the CONUS for the summers of 2019-2021: assessing the benefits of improved satellite remote-sensing observations

This study gives a demonstration of the benefits of using novel high spatiotemporal retrieval products from newer satellites for top-down emission estimates of nitrogen oxides (NO_x) and non-methane volatile organic compounds (NMVOCs) over the contiguous United States (CONUS) for the summers of 2019-2021. We conducted inverse modeling using tropospheric nitrogen dioxide (NO₂) and formaldehyde (HCHO) column retrieval products from the Ozone Monitoring Instrument (OMI) and TROPOspheric Monitoring Instrument (TROPOMI) in conjunction with the Weather Research Forecast and Community Multiscale Air Quality Modeling system (WRF-CMAQ). In order to provide a better representation of background chemical composition and avoid misalignment of emission adjustment, we applied monthly scaling factors for ozone (O₃) and carbon monoxide (CO) boundary concentrations in addition to the inclusion of lightning and aviation NO_x emissions. As a result, we will present the differences and improvements in model performance when using newer and higher spatial resolution TROPOMI-retrieved information compared to OMI when model results are evaluated with various ground measurements. This improvement stems from advanced spatiotemporal resolution and greatly reduced error/uncertainty of recent satellite retrievals compared to spaceborne sensors launched in the past. In addition, we will discuss the trends of satellite-constrained NO_x and NMVOCs posterior emissions, affected by emission reduction during the COVID-19 pandemic and its recovery.