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DESCRIPTION OF ATMOSPHERIC TRANSPORT PROCESSES IN EULERIAN AIR QUALITY MODELS
Citation:
Byun, D W. DESCRIPTION OF ATMOSPHERIC TRANSPORT PROCESSES IN EULERIAN AIR QUALITY MODELS. Mesoscale Atmospheric Dispersion: Advances in Air Pollution Series. WIT Press, Boston, MA, , 289-341, (2001).
Impact/Purpose:
The objectives of this task are to continuously develop and improve the Community Multiscale Air Quality (CMAQ) modeling system, which is the science implementation within the Models-3 system framework for air quality simulation. 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. It relies on Models-3 I/O API to support machine independent data access and maintains simple interfaces among science processor modules to provide a high-level of modularity.
Description:
Key differences among many types of air quality models are the way atmospheric advection and turbulent diffusion processes are treated. Gaussian models use analytical solutions of the advection-diffusion equations. Lagrangian models use a hypothetical air parcel concept effectively removing the need for explicit treatment of transport processes. Eulerian models require solution of the advection-diffusion equation using some numerical techniques. Here, modeling techniques for atmospheric transport processes (except for the subgrid scale cloud mixing) in Eulerian air quality models are presented. First, the presentation describes computational coordinates for atmospheric studies, diagnostic and prognostic meteorological modeling techniques, and assumptions on atmospheric dynamics. Then, it emphasizes use of the flux-form formulations that ensure conservation of mass during the transport processes. Instead of dwelling on specific numerical algorithms or comparison among them, it provides general descriptions of numerical techniques for the transport processes used in Eulerian air quality models.