You are here:
A PRELIMINARY EVALUATION OF MODELS-3 CMAQ USING VISIBILITY PARAMETERS
Citation:
Eder, B K., M R. Mebust, F S. Binkowski, AND S J. Roselle. A PRELIMINARY EVALUATION OF MODELS-3 CMAQ USING VISIBILITY PARAMETERS. Presented at International Symposium on the Measurement of Toxic and Related Air Pollutants, Research Triangle Park, NC, September 12-14, 2000.
Impact/Purpose:
The goal 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 validated. Both performance and diagnostic evaluation together with sensitivity analyses are needed to 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:
Ambient air concentrations of fine particulate matter (PM 2.5) continue to be a major concern for the U.S. Environmental Protection Agency. High concentrations of fine particles have been linked to detrimental health effects (including an increase in mortality) and visibility degradation. Accordingly, the Clean Air Act and Amendment of 1990 called for an assessment of current and future regulations designed to protect human health and welfare. The most reliable tools for carrying out such assessments are air quality models like EPA's Community Multiscale Air Quality (CMAQ), which simulates air concentrations and deposition of PM 2.5 (along with other pollutants) and various measures of visibility associated with specified levels of emissions. These simulations can be used by EPA Program Offices and research laboratories to support both regulatory assessment and scientific studies on a myriad of spatial and temporal scales. This paper provides a preliminary evaluation of CMAQ using a visibility parameter called the deciview. The evaluation compares deciview values computed from visibility observations at 174 stations in the eastern half of the U.S. with those simulation by the model for the 5-day period July 11 - 15, 1995. Visibility was selected for this evaluation for two reasons: it can serve as a surrogate for PM 2.5, for which little observational data currently exist; and it has one of the most spatially and temporally comprehensive observational data sets available. The evaluation revealed a reasonable level of representation as CMAQ captured the basic spatial and temporal patterns of visibility degradation including major gradients and maxima/minima. The correlation coefficient between the observed and simulated deciviews for the entire simulation period was 0.56 and ranged from 0.38 on the 11th to 0.70 on the 13th. The model generally under predicted the visibility degradation by 10 deciviews; however, much of this discrepancy can be attributed to artifacts associated with the observed data.