PSAS and 4D-var data assimilation for chemical state analysis by urban and rural observation sites

Advanced data assimilation can be applied to retrieve as much information as possible from photooxidant measurements in the troposphere in order to analyze the chemical state. Traditional assimilation methods have proved to be unsatisfactory due to their inability (i) to account for locally varying chemical scenarios, (ii) to exploit informations inherent in time series evolution, and (iii) to use observations measured at different times. The Physical-space Statistical Analysis System (PSAS) and a space-time data assimilation analysis are proposed aiming at the combination of both the four dimensional variational calculus (4D-var) and inhomogeneous error covariances allowing to focus on regional differences in emission rates an surface conditions. The University of Cologne, Eulerian mesoscale-alpha Chemistry Transport Model EURAD is part of a comprehensive 4D-var chemical data assimilation system which makes best use of available observations to provide skillful analyses. Special emphasis is placed on the locally varying representativeness of individual measurement sites. (C) 2001 Elsevier Science Ltd. All rights reserved