Impact/Purpose:

The objectives of this task are to develop, improve, and evaluate EPA's Community Multiscale Air Quality (CMAQ) model, as an air quality management and NAAQS implementation tool. 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.

The model will be tested and evaluated to thoroughly characterize the performance of the emissions, meteorological and chemical/transport modeling components of the CMAQ 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. Both operational and diagnostic evaluations, together with sensitivity analyses are needed to both establish credibility and build confidence within the client and scientific community in the simulation 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:

This task provides a credible state of the art air quality model and guidance for use in implementation of National Ambient Air Quality Standards for ozone and PM. This research effort is to develop and improve the Community Multiscale Air Quality (CMAQ) modeling system, a multiscale and multi-pollutant chemistry-transport model (CTM). Specific research components include: meteorological modeling, land-surface and PBL modeling, emissions modeling, gas phase mechanisms and solvers, cloud dynamics and aqueous chemistry, photolysis rates and radiative transfer model improvements, aerosol representations for grid models, transport and diffusion, plume-in-grid approach, CMAQ code integration and efficiencies.

Evaluation of the CMAQ modeling system is also conducted in this task - with an emphasis on photochemical oxidants (especially ozone) and fine particulate matter. Two different types of evaluations will be performed. The first is a performance evaluation, which utilizes data from routine, nationwide monitoring networks (i.e. CASTNet, IMPROVE, STN, AIRS) to determine if pollutant concentrations of regulatory interest are adequately being simulated (is the model providing the right answer). The second type is a diagnostic evaluation, which uses intensive, regional field studies (i.e. BRACE, Supersites) to examine the ability of the model to accurately simulate all of the physical and chemical processes that lead to the simulated concentration (is the model providing the right answer for right reason). In addition to direct evaluations, model sensitivity analyses will also be conducted to characterize model response to uncertainties. Other model evaluation techniques will be applied, including space-time analysis.

Record Details:

Record Type:PROJECT

Start Date:10/01/2004

Projected Completion Date:09/01/2005

OMB Category:Other

Record ID: 113783

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Project Information:

Progress :A series of CMAQ modeling system releases has been accomplished under this Task and its predecessor Task. The most recent public release of the CMAQ model ? September 2004, included a computationally efficient aerosol coagulation routine, improved the efficiency of the secondary organic aerosol (SOA) solver, added the EBI_SAPRC99 chemistry solver (highly efficient solver specific to the SAPRC99 chemical mechanism), added the generalized Rosenbrock chemical solver, corrected an error in the PPM advection scheme, added the capability for aerosols in the plume-in-grid (PinG) module, and incorporated input/output optimizations suggested by Sandia National Lab. The most recent model release can simulate ozone and PM over the continental U.S. for a full year run in less than a week on an 8-processor Linux cluster of workstations. An interim CMAQ model release ? April 2004, was made available to OAQPS for use in 8-hr ozone and annual average PM2.5 NAAQS implementation assessments. This version has science enhancements guided by the results of the CMAQ model evaluation studies conducted over the past several years for ozone and PM2.5. In addition, code modifications guided by collaboration with Sandia Labs provided significant run time speed-ups, enabling annual simulations to execute in days rather than weeks. The CMAQ model release of September 2003 including a modified treatment of secondary organic aerosol formation, modification to the heterogeneous N2O5 reaction probability, the addition of a fast, accurate Euler Backward Iterative gas-phase chemistry solver for the CB4 mechanism family, an improved synchronization time step algorithm that implements layer-dependent horizontal advection time-stepping, and various other enhancements and bug fixes, including molar mixing ratio units for aerosols in the vertical diffusion process instead of mass density concentrations. The CMAQ model release of June 2002 included a new aerosol model (AERO3; updates to SOA and thermodynamics), new chemical mechanism (SAPRC-99) and a new efficient numerical solver for chemistry for all mechanisms, use of Fortran-90 dynamic allocation and windowing.

Recently, the 2003 release of CMAQ was thoroughly evaluated over two simulation periods (4 January - 19 February 2002 and 15 June - 16 July, 1999) against observational data from five different networks: CASTNet, AIRS, IMPROVE, STN and SEARCH. Results indicate continued good performance for ozone, sulfate, ammonium, organic fine particles and improvement in the simulation of nitrate aerosol. A series of CMAQ evaluations have been performed in recent years comparing a variety of modeling configurations, domains and resolutions against various observational data sets. Initially, a series of simulations was performed for the eastern U.S. with nested grid resolutions of 36, 12, and 4-km cell size, for the period of July 2-19, 1995 and at 36-km resolution for June 1995. Results of comparisons with AIRS, PAMS and NARSTO-NE data showed the CMAQ to be performing at least comparably well to other contemporary ozone models. A briefing on the results was given to the OAQPS director and his staff in July 2000. The July 1995 CMAQ simulations were also used for initial comparisons of visibility data as well as IMPROVE data in the eastern U.S. Preliminary results with the visibility data indicate that the model was performing acceptably well. Preliminary comparisons with speciated fine particle IMPROVE data for June 1995 indicate the model was also performing well for sulfate, but not well for organic fine particulates. Another, longer series of air quality simulations were also performed for the eastern U.S. with grid resolution of 36-km cell size, for the months of January, March, April, May, June, July, August, and October 1990. Inverse modeling for ammonia was conducted for these months which showed ammonia emissions should have a very strong seasonality. Results

Relevance :EPA and the states are responsible for implementing the National Ambient Air Quality Standards for ozone and PM. New standards for 8-hr average ozone and annual average PM2.5 concentrations are in the process of initial implementation. State Implementation Plans (SIPs) will be due to EPA in the 2007-2008 timeframe. Air quality simulation models, such as Models-3/CMAQ, are required components of the SIP analyses. The research performed in this task is designed to provide the necessary simulation capabilities for the Models-3/CMAQ air quality model, and to keep the science in the model at the state-of-the-art. This model, used for research and regulatory applications by the EPA, states, and others must have current up-to-date science for the highest level of credibility for the regulatory decision-making process. Confidence in the use of this modeling system by the user community is largely built through evaluation exercises such as those conducted in this task. Model evaluation therefore is a key component in the research conducted with the CMAQ and related models and a key component supporting Annual Performance Goals associated with developing modeling tools for Goal 1 objectives. Annual CMAQ modeling system releases are made directly to EPA?s client office (OAQPS) as well as to the general public through the Community Modeling and Analysis System center.

Clients :Tyler Fox, Norm Possiel-OAR/OAQPS

Project IDs:

ID Code :20461

Project type :OMIS