Assimilated inversion of NOx emissions over east Asia using OMI NO2 column measurements

Assimilated inversion on a daily basis using OMI tropospheric NO 2 columns is developed and applied in a regional chemical transport model (REAM) to constrain fossil fuel (FF) NO x emissions over east Asia in 2007. The iterative nature of the assimilated inversion improves upon the widely used monthly‐mean inversion by accounting for the chemical feedbacks of changed NO x emissions and reducing the dependence of the a priori emissions. The assimilated a posteriori emissions from FF combustion over east Asia are 9.5 Tg N/yr comparable to 10.9 Tg N/yr of the a priori. Significant changes in the spatial distribution of FF NO x emissions are found in the assimilated inversion from the a priori or monthly‐mean inversion. The assimilated inversion shows that the a priori FF NO x emission inventory tends to overestimate the emissions over the economically developed areas and underestimate over the underdeveloped areas in East China, which may reflect in part FF NO x emission reductions resulting from the urban‐centric air quality controls in China.