Kalman filter inversions on NOx and VOCs emissions in China using TROPOMI satellite observations

Kalman filter inversions with multipollutant may improve the accuracy of inversion results and model performance. A joint inversion of VOCs and NOx emissions was conducted using the HCHO and NO2 column data from the TROPOspheric Monitoring Instrument and the simulated sensitivities of VOCs and NOx from an air quality model from June to September 2019. The results showed that joint inversion results typically outperformed that of separate inversion in reducing model bias and error and regional variations of emission estimates under satellite data constraints. The inversed NOx emissions over China decreased from a priori by approximately 30 %, and the inversed VOCs emissions over China increased from a priori by around 50 %. Joint inversion results aligned more closely with satellite-observed NO2 and HCHO columns, capturing the unique belt-like distribution of HCHO and stabilizing maximum NO2 column at approximately 15 molec/cm². The accuracy of simulated ground-level ozone concentrations was enhanced by the joint inversion, with the mean bias decreased by 11.6 μg/m³ overall. Meanwhile, ozone sensitivities prevalently shifted towards NOx-limited conditions during summer after the joint inversion.