Large discrepancy between observed and modeled wintertime tropospheric NO<sub>2</sub> variabilities due to COVID-19 controls in China
Jiaqi Chen, Zhe Jiang, Rui Li, Chenggong Liao, Kazuyuki Miyazaki, Dylan B. A. Jones
Abstract
Abstract Recent studies demonstrated the difficulties to explain observed tropospheric nitrogen dioxide (NO 2 ) variabilities over the United States and Europe, but thorough analysis for the impacts on tropospheric NO 2 in China is still lacking. Here we provide a comparative analysis for the observed and modeled (Goddard Earth Observing System-Chem) tropospheric NO 2 in early 2020 in China. Both ozone monitoring instrument and surface NO 2 measurements show marked decreases in NO 2 abundances due to the 2019 novel coronavirus (COVID-19) controls. However, we find a large discrepancy between observed and modeled NO 2 changes over highly polluted provinces: the observed reductions in tropospheric NO 2 columns are about 40% lower than those in surface NO 2 concentrations. By contrast, the modeled reductions in tropospheric NO 2 columns are about two times higher than those in surface NO 2 concentrations. This discrepancy could be driven by the combined effects from uncertainties in simulations and observations, associated with possible inaccurate simulations of lower tropospheric NO 2 , larger uncertainties in the modeled interannual variabilities of NO 2 columns, as well as insufficient consideration of aerosol effects and a priori NO 2 variability in satellite retrievals. In addition, our analysis suggests a small influence from free tropospheric NO 2 backgrounds in E. China in winter. This work demonstrates the challenge to interpret wintertime tropospheric NO 2 changes in China, highlighting the importance of integrating surface NO 2 observations to provide better analysis for NO 2 variabilities.