Review of the Governing Equations, Computational Algorithms, and Other Components of the Models-3 Community Multiscale Air Quality (CMAQ) Modeling System

Abstract

This article describes the governing equations, computational algorithms, and other components entering into the Community Multiscale Air Quality (CMAQ) modeling system. This system has been designed to approach air quality as a whole by including state-of-the-science capabilities for modeling multiple air quality issues, including tropospheric ozone, fine particles, acid deposition, and visibility degradation. CMAQ was also designed to have multiscale capabilities so that separate models were not needed for urban and regional scale air quality modeling. By making CMAQ a modeling system that addresses multiple pollutants and different spatial scales, it has a “one-atmosphere” perspective that combines the efforts of the scientific community. To implement multiscale capabilities in CMAQ, several issues (such as scalable atmospheric dynamics and generalized coordinates), which depend on the desired model resolution, are addressed. A set of governing equations for compressible nonhydrostatic atmospheres is available to better resolve atmospheric dynamics at smaller scales. Because CMAQ is designed to handle scale-dependent meteorological formulations and a large amount of flexibility, its governing equations are expressed in a generalized coordinate system. This approach ensures consistency between CMAQ and the meteorological modeling system. The generalized coordinate system determines the necessary grid and coordinate transformations, and it can accommodate various vertical coordinates and map projections. The CMAQ modeling system simulates various chemical and physical processes that are thought to be important for understanding atmospheric trace gas transformations and distributions. The modeling system contains three types of modeling components (Models-3): a meteorological modeling system for the description of atmospheric states and motions, emission models for man-made and natural emissions that are injected into the atmosphere, and a chemistry-transport modeling system for simulation of the chemical transformation and fate. The chemical transport model includes the following process modules: horizontal advection, vertical advection, mass conservation adjustments for advection processes, horizontal diffusion, vertical diffusion, gas-phase chemical reactions and solvers, photolytic rate computation, aqueous-phase reactions and cloud mixing, aerosol dynamics, size distributions and chemistry, plume chemistry effects, and gas and aerosol deposition velocity estimation. This paper describes the Models-3 CMAQ system, its governing equations, important science algorithms, and a few application examples. This review article cites 114 references.

Air quality simulations for London using a coupled regional-to-local modelling system

“…Global and regional models use gridded emissions data to calculate transport and chemistry over global or regional modelling domains, such as EMEP MSC-W (EMEP, Simpson et al, 2012) used in this study, CAMx (Ramboll Environment and Health, 2016), CMAQ (Byun and Schere, 2006) and WRF-Chem (Grell et al, 2005). Models on a smaller scale apply detailed transport and fast chemistry processes to individual sources, such as ADMS-Urban (Owen et al, 2000) also used in this study, the US EPA model AER-MOD (Cimorelli et al, 2004) and CAR-FMI (Kukkonen et al, 2001).…”

Implementation of a module for risk of ozone impacts assessment to vegetation in the Integrated Assessment Modelling system for the Iberian Peninsula. Evaluation for wheat and Holm oak

“…The air quality modelling system relies on the Community Multiscale Air Quality (CMAQ) model (Byun and Ching, 1999;Byun and Schere, 2006), a state-of-the-art Eulerian chemistry transport model based on the one-atmosphere paradigm, widely used worldwide to investigate tropospheric ozone (e.g., Brankov et al, 2003;Xu et al, 2008;Shi et al, 2009). Emissions are taken from an emission model based on the Sparse Matrix Operator Kernel Emissions (SMOKE) modelling system (UNC Carolina Environmental Program, 2005) as described in Borge et al (2008a).…”

Urban Emissions and Regional Air Quality in India

“…Model simulations are conducted for four seasonally representative months-January, April, July, and October-representing winter, premonsoon, monsoon, and post-monsoon fall respectively. The CMAQ model includes processes related to surface and upper level emissions, photolysis, gaseous and particulate chemistry, deposition, and dispersion across grid cells and 36 vertical layers in the troposphere up to about 150hPa [Byun and Schere, 2006]. Model specifications include the chemistry bond 05 (CB05) chemical mechanism [Yarwood et al, 2005], the AERO 6 aerosol mechanism, and the inclusion of windblown dust [Dong et al, 2015;Tong et al, 2015].…”