Estimating city NOX emissions from TROPOMI high spatial resolution observations - A case study on Yangtze River Delta, China

In this study, TROPOspheric Monitoring Instrument (TROPOMI) observations were resampled to obtain 0.01 degrees x 0.01 degrees NO2 VCD (vertical column density) over Yangtze River Delta (YRD), China. Based on this high spatial resolution satellite observations, NO2 VCDs in megacities cluster of YRD region were examined with a reduction of similar to 35% during COVID-19 lockdown. The adjusted Exponentially-Modified Gaussian (EMG) model was used to estimate the NOX emission in typical cities under regionally polluted YRD region. Taking 100 km of mass integration interval as an example, during 2018-2019, the averaged NOX emission of Shanghai, Hangzhou, Nanjing, and Ningbo is 139.65 mol/s, 84.49 mol/s, 79.87 mol/s and 88.73 mol/s, respectively. This estimation 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. It was also found that the NOX emissions of Ningbo are higher than expected, which is closely related to massive ship emissions. This study indicates that this approach based on adjusted EMG model can enhance the ability to quantify NOX emissions at city level by utilizing the high spatial resolution observations of TROPOMI.

Automated summary

This study used TROPOMI satellite observations to analyze the NO2 vertical column density (VCD) over the Yangtze River Delta in China. The results show a reduction of about 35% in NO2 VCD during the COVID-19 lockdown period. The study also estimated the NOX emissions in typical cities using an adjusted EMG model and compared it with the Multi-resolution Emission Inventory for China. The findings demonstrate that this approach can enhance the quantification of city-level NOX emissions by utilizing high spatial resolution observations from TROPOMI.