Using satellite observations for air quality assessment with an inverse model system

The EURAD-IM chemistry transport model and its 4d-var inverse model extension is applied to one summer and one winter episode, in order to identify the benefit of tropospheric NO2 column retrievals for estimating near-surface nitrogen dioxide concentrations. Initial values and emission rates are jointly optimised by assimilating tropospheric NO2 data from the OMI, while European ground based observations are used for impact evaluation. Results show a moderate improvement of surface level nitrogen dioxide estimates during the summer episode, successfully sustained after the assimilation period through emission adjustments. In the winter case, the OMI data is of limited value due to lower boundary layer heights and thus smaller impact on emission rates.