You are here:
A COMPARISON OF AEROSOL OPTICAL DEPTH SIMULATED USING CMAQ WITH SATELLITE ESTIMATES
Citation:
ROY, B., R. MATHUR, J. SZYKMAN, A. GILLILAND, AND C. KITTAKA. A COMPARISON OF AEROSOL OPTICAL DEPTH SIMULATED USING CMAQ WITH SATELLITE ESTIMATES. Presented at Air and Waste Management Association 98th Annual Conference, Minneapolis, MN, June 21 - 24, 2005.
Impact/Purpose:
The objective of this task is to thoroughly characterize the performance of the emissions, meteorological and chemical/transport modeling components of the Models-3 system, with an emphasis on the chemical/transport model, CMAQ. Emissions-based models are composed of highly complex scientific hypotheses concerning natural processes that can be evaluated through comparison with observations, but not truly validated. Static and Dynamic Operational, Diagnostic, and ultimately Probablistic evaluation methods are needed to both establish credibility and build confidence within the client and scientific community in the simulations results for policy and scientific applications. The characterization of the performance of Models-3/CMAQ is also a tool for the model developers to identify aspects of the modeling system that require further improvement.
Description:
Satellite data provide new opportunities to study the regional distribution of particulate matter. The aerosol optical depth (AOD) - a derived estimate from the satellite measured irradiance, can be compared against model derived estimate to provide an evaluation of the columnar aerosol distributions simulated by the air quality forecast models. In this study, we inter-compare the modeled AOD data computed using three different methods. The first two are empirical approaches whereas the third method uses a parametric approximation to Mie extinction. The first method is based on using relative humidity bulk factor dependent scattering coefficients for the various anthropogenic aerosol constituents. The second method assumes that one-half of the organic mass is soluble and involves a reconstructed particle scattering and absorption scheme that utilize the modeled relative humidity to ascertain hygroscopic growth factor. The third method used a modified Mie scattering algorithm and the modeled number and size distributions for computing AOD's in the period July 14-August 17, 2004. Cloud-free National Aeronautics and Space Administration (NASA)/Moderate Resolution Imaging Spectroradiometer (MODIS) level-2 granular AOD swath product (with a 10 km resolution at nadir) is re-gridded to the CMAQ computational grid to aid in statistical comparison between the modeled and satellite data. Results for May and August, 2001 are obtained using MM5-CMAQ concentration data and using the first two methods. These AOD's are directly compared with the satellite estimates. Using Eta-CMAQ simulated concentration data for the period July-August 2004 and following the second and third methods AOD at 550 nm are inter-compared and also in context of two wildland fire events.