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USING CMAQ-AIM TO EVALUATE THE GAS-PARTICLE PARTITIONING TREATMENT IN CMAQ
Citation:
Nolte, C, P. Bhave, R L. Dennis, K. M. Zhang, AND A. S. Wexler. USING CMAQ-AIM TO EVALUATE THE GAS-PARTICLE PARTITIONING TREATMENT IN CMAQ. Presented at 2004 Models-3 Conference, Chapel Hill, NC, October 18 - 20, 2004.
Impact/Purpose:
The objectives of this task are to continuously develop and improve EPA's mesoscale (regional through urban scale) air quality simulation models, such as the Community Multiscale Air Quality (CMAQ) model, as air quality management and NAAQS implementation tools. CMAQ is a multiscale and multi-pollutant chemistry-transport model (CTM) that includes the necessary critical science process modules for atmospheric transport, deposition, cloud mixing, emissions, gas- and aqueous-phase chemical transformation processes, and aerosol dynamics and chemistry. To achieve the advances in CMAQ, research will be conducted to develop and test appropriate chemical and physical mechanisms, improve the accuracy of emissions and dry deposition algorithms, and to develop and improve state-of-the-science meteorology models and contributing process parameterizations.
Description:
The Community Multi-scale Air Quality model (CMAQ) aerosol component utilizes a modal representation, where the size distribution is represented as a sum of three lognormal modes. Though the aerosol treatment in CMAQ is quite advanced compared to other operational air quality models, various members of the CMAQ community have commented that improvements to the aerosol module should be made in order to bring it to the state of the science found in research-grade air quality models. Among the shortcomings noted are that (1) a trimodal representation is insufficient to resolve the aerosol size and composition distribution; (2) interactions of the gas phase with coarse particles, such as sea-salt, are neglected; and (3) the assumption of instantaneous equilibrium between gas-phase species and fine-mode aerosol is inaccurate. In the present study, we seek to understand the effects of the latter two assumptions on predicted fine-particle mass and chemical composition in regional-scale air quality models.
A sectional aerosol module that uses dynamic mass transfer rather than assuming instantaneous equilibrium between the gas and particle phases has been developed and integrated into the Community Multi-scale Air Quality model (CMAQ) (Zhang and Wexler, 2004). The resulting model, CMAQ-AIM, provides a useful platform to gauge the impact of certain assumptions made in the CMAQ aerosol module.
The research presented here was performed under the Memorandum of Understanding between the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) and under agreement number DW13921548. Although it has been reviewed by EPA and NOAA and approved for publication, it does not necessarily reflect their policies or views.