To meet future air quality modeling needs, U.S. EPA has been developing a next generation air quality modeling system, Models-3/Community Multi-scale Air Quality (CMAQ) modeling system. It is a multiple scale and multiple pollutant chemistry-transport model that includes all the critical science processes such as atmospheric transport, deposition, cloud mixing, emissions, gas- and aqueous-phase chemical transformation processes, and aerosol dynamics and chemistry. The CMAQ system can use any quality prognostic meteorological model as its driver. A generalized coordinate approach enables CMAQ to be configured consistently with the driver meteorological model's dynamic assumptions. The Models-3/CMAQ system is expected to be released to the public this summer.
It is well known that urban air quality is strongly influenced by the pollutant influx at boundaries. Therefore, one needs to apply multi-level nesting simulations from regional to urban scale. Also, use of a nonhydrostatic meteorological model is required to simulate dynamics for an urban area with significant topographic features correctly. Many earlier air quality models have relied on simplified assumptions on atmospheric dynamics such as hydrostatic atmosphere, or further, nondivergent atmospheic flows. These models cannot be linked to the nonhydrostatic meteorological model output. There have been a few approaches to retooling existing hydrostatic air quality models for use with nonhydrostatic meteorological models. However, these attempts suffer shortcomings because of the inconsistent descriptions of the atmosphere in the meteorological and air quality models.
If air quality were solved as a part of the meteorology modeling, the problem would have been much less. However, because of the need for re-running air quality models many times to understand the effects of emissions control strategies on the concentration predictions, and the need for characterizing past atmospheric conditions using meteorological observations through assimilation, it becomes very impractical to imbed an operational air quality model as a part of the meteorological modeling system.
In this paper, we will introduce a nesting procedure with CMAQ to
simulate air quality from regional to urban scales while maintaining dynamic consistency with meteorological model simulations. Also, we will compare effects of grid resolution and dynamic assumptions on air quality predictions. This study will demonstrates CMAQ's capability for simulating urban air quality.