On variational data assimilation for estimating the model initial conditions and emission fluxes for short-term forecasting of SOx concentrations

► Two chemical data assimilation strategies are compared in modelling experiments. ► 3D-VAR and 4D-VAR assimilation of in-situ measurements. ► The most consistent improvements are obtained using emission rate adjustment with the 4D-VAR method. ► Emission adjustment with daily resolution too coarse in some cases.