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

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 (NO_X) 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 NO_X 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 NO_X 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 NO_X 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).