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

ABSTRACT

In this study, TROPOspheric Monitoring Instrument (TROPOMI) observations were resampled to obtain 0.01° × 0.01° 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 ~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.