Assessing NOX emission reduction of Shanghai during city-wide lockdown from TROPOMI high spatial resolution observations

Abstract

In this study, TROPOspheric Monitoring Instrument (TROPOMI) observations were resampled to obtain 0.01° × 0.01° NO2 VCD (vertical column density) of Yangtze River Delta (YRD), China. The adjusted Exponentially-Modified Gaussian (EMG) model was improved to estimate the quantified nitrogen oxides (NOX) emission. The estimation in typical cities under regionally polluted YRD area has a good correlation with Multi-resolution Emission Inventory for China (MEIC) emission with R more than 0.9 but lower results mainly due to the underestimation of NO2 VCD by TROPOMI in polluted areas. On this basis, using the adjusted EMG method, this study quantified NOX emission in Shanghai during 2022 lockdown period as 32.60 mol/s with a decrease of 50–80%, which was mainly contributed by the transportation and industrial sectors. The significant reduction of NOX emission in Shanghai is much higher than that of volatile organic compounds (VOCs), which led to dramatic changes in formaldehyde-to-nitrogen dioxide ratio (HCHO/NO2, FNR). Thus, when enforcing regulation on NOX emission control in the future, coordinately reducing VOCs emission should be implemented to mitigate urban O3 pollution. This work was supported by Sino-German Mobility Program (M-0509) and National Natural Science Foundation of China (grant number 42075097, 22176037, 42375089, 22376030).