“…The use of the NWP system for data assimilation allows the use of the existing infra-structure for satellite data handling and the MACC system is able to assimilate more than one data set from a large array of satellite instruments (GOME, MIPAS, MLS, OMI, SBUV, SCIAMACHY, MOPITT, IASI, TANSO, AIRS) for O 3 , CO, NO 2 , SO 2 , HCHO, CH 4 , CO 2 and AOD. In the USA, CDA is conducted in WRF-Chem using both 3DVAR (Pagowski et al, 2010;Liu et al, 2011;Schwartz et al, 2012;Saide et al, 2012Saide et al, , 2013 and EnKF (Pagowski and Grell, 2012); there is an on-going project to assimilate surface PM 2.5 data as well as AOD using a hybrid approach that employs both EnKF and 3DVAR. Furthermore, the adjoint of WRF-Chem is currently under development with the objective of performing sensitivity analysis with a variational method in the near future and possibly CDA with inverse modelling of parameter fields later.…”