Evaluation of Sulfur Dioxide (SO2) Simulations with the GEOS-5/ GOCART Model during the Frostburg/DISCOVER-AQ Field Campaigns

Sulfur dioxide (SO2) is a major atmospheric pollutant, with a strong anthropogenic component mostly produced by the combustion of fossil fuel and other industrial activities. As a precursor of sulfate aerosols that affect climate, air quality and human health, this gas needs to be monitored on a global scale. Global climate and chemistry models including aerosol processes along with their radiative effects are important tools for climate and air quality research. Validation of these models against in-situ and satellite measurements are essential to ascertain the credibility of these models and to guide model improvements. In this study the Goddard Chemistry, Aerosol, Radiation, and Transport (GOCART) module running on-line inside the Goddard Earth Observing System version 5 (GEOS-5) model is used to simulate aerosol and SO2 concentrations. The global GEOS-5 system runs at a nominal 25 km horizontal resolution with 72 vertical levels; a comprehensive atmospheric data assimilation system is used to constrain the meteorological state of the model. Data taken over Maryland in the UM's Frostburg (November 2010) and NASA DISCOVER-AQ (July 2011) field campaigns are used to evaluate the GEOS-5 SO2 concentrations. In this presentation we show comparisons of simulated and measured SO2 concentration, using airborne and ground-based data sets, as well as data from the space-based OMI instrument. Preliminary data analysis indicated the model's overestimation of SO2 concentration at the surface, leading to a close examination of mixing processes in the model and the specification of SO2 anthropogenic emission rates. As a result of this analysis, we have implemented a revision of anthropogenic emission inventories in GEOS-5, and updated the vertical placement of SO2 sources. In this presentation we show how these revisions improve the model agreement with observations not only locally but also in regions outside the area of these field campaigns. In particular, we use the ground-based measurements from the Environmental Protection Agency (EPA) for the year 2010 to evaluate the revised model simulations over North America.