Assimilation of Satellite Ozone Measurements during the 1999 Southern Oxidants Study: Impact on Continental US Regional Air Quality Predictions.

R. Bradley Pierce

NASA Langley Research Center


Global and regional air quality (AQ) is linked through complex interactions between highly heterogeneous surface emissions, local radical chemistry, boundary layer exchange processes, enhancements in background levels of O3 and its precursors, and long range transport. Development of a global chemical data assimilation system (DAS) for constraining regional AQ forecasts provides a link between global and regional AQ. In this presentation we discuss results from a prototype global to regional AQ forecast/chemical DAS study conducted during the US 1999 Southern Oxidation Study (SOS) as part of the NASA Earth Science Enterprise Air Quality Applications Program. Two global ozone analyses are considered. The first comes from the NASA GSFC Finite Volume DAS (FvDAS). FvDAS uses the NASA Global Modeling and Assimilation Office (GMAO) chemical DAS with parameterized chemistry to assimilate SBUV ozone measurements. The second comes from the Regional Air Quality Modeling System (RAQMS). RAQMS is a unified (stratospheric and tropospheric), multi-scale (global to regional) air quality modeling/data assimilation system with online chemistry. RAQMS is used to evaluate the feasibility of assimilating trajectory mapped solar occultation profile and total column ozone measurements. Comparisons with independent satellite measurements and insitu measurements show that assimilation of trajectory mapped solar occultation data reduces biases in the lower stratosphere/upper troposphere relative to assimilation of SBUV measurements, and that including online chemistry improves the representation of observed peak amplitudes and diurnal variability at the surface. The impact of global ozone analyses on continental US AQ predictions is evaluated by conducting RAQMS nested simulations with and without assimilated boundary conditions. Prototype studies such as these are designed to help to identify critical components for future air quality forecasting systems. Knowledge gained from such studies should provide valuable guidance for the development of operational chemical DAS through institutions such as the NASA/NESDIS/OAR/NCEP Joint Center for Satellite Data Assimilation (JCSDA).