Impacts of TROPOMI-Derived NOXEmissions on NO2and O3Simulations in the NCP during COVID-19

Abstract

NO2and O3simulations have great uncertainties during the COVID-19 epidemic, but their biases and spatial distributions can be improved with NO2assimilations. This study adopted two top-down NOXinversions and estimated their impacts on NO2and O3simulation for three periods: the normal operation period (P1), the epidemic lockdown period following the Spring Festival (P2), and back to work period (P3) in the North China Plain (NCP). Two TROPOspheric Monitoring Instrument (TROPOMI) NO2retrievals came from the Royal Netherlands Meteorological Institute (KNMI) and the University of Science and Technology of China (USTC), respectively. Compared to the prior NOXemissions, the two TROPOMI posteriors greatly reduced the biases between simulations with in situ measurements (NO2MREs: prior 85%, KNMI -27%, USTC -15%; O3MREs: Prior -39%, KNMI 18%, USTC 11%). The NOXbudgets from the USTC posterior were 17-31% higher than those from the KNMI one. Consequently, surface NO2levels constrained by USTC-TROPOMI were 9-20% higher than those by the KNMI one, and O3is 6-12% lower. Moreover, USTC posterior simulations showed more significant changes in adjacent periods (surface NO2: P2 vs P1, -46%, P3 vs P2, +25%; surface O3: P2 vs P1, +75%, P3 vs P2, +18%) than the KNMI one. For the transport flux in Beijing (BJ), the O3flux differed by 5-6% between the two posteriori simulations, but the difference of NO2flux between P2 and P3 was significant, where the USTC posterior NO2flux was 1.5-2 times higher than the KNMI one. Overall, our results highlight the discrepancies in NO2and O3simulations constrained by two TROPOMI products and demonstrate that the USTC posterior has lower bias in the NCP during COVD-19.