AirWare Reference Manual: CAMx

AirWare On-line Reference Manual

Release Level 5.4
Release Date 2008 10

Revision Level 1.0

Last modified on: Monday, 21-Mar-11 12:53 CET

Simulation models: CAMx

The Comprehensive Air quality Model with extensions (CAMx) is an Eulerian photochemical dispersion model that allows for an integrated one-atmosphere assessment of gaseous and particulate air pollution (ozone, PM-2.5, PM-10, air toxics, mercury) over many scales ranging from sub-urban to continental.

See also: CAMx User Guide V5.30, PDF

It is designed to unify all of the technical features required of state-of-the-science air quality models into a single system that is computationally efficient, easy to use, and publicly available. The model code has a highly modular and well documented structure which eases the insertion of new or alternate algorithms and features.

CAMx simulates the emission, dispersion, chemical reaction, and removal of pollutants in the troposphere by solving the pollutant continuity equation for each chemical species (l) on a system of nested three-dimensional grids. The Eulerian continuity equation describes the time dependency of the average species concentration (cl) within each grid cell volume as a sum of all of the physical and chemical processes operating on that volume.

The governing equations are expressed mathematically in terrain-following height (z) coordinates. It considers a horizontal wind vector, net vertical entrainment rate, multiple vertical layers, atmospheric density, and turbulent exchange (or diffusion). The terms on the right-hand side represents horizontal advection, net resolved vertical transport across an arbitrary space- and time-varying height grid, and sub-grid scale turbulent diffusion. Chemistry is treated by simultaneously solving a set of reaction equations defined from specific chemical mechanisms. Pollutant removal includes both dry surface uptake (deposition) and wet scavenging by liquid precipitation (rain).

Data requirements for CAMx are described in:

Basic physical processes

Module	Physical Model	Numerical Method
Horizontal advection/diffusion	Eulerian continuity equation closed by K-theory	Bott or PPM for advection explicit diffusion
Vertical transport/diffusion	Eulerian continuity equation closed by K-theory	Implicit advection and diffusion
Gas-Phase Chemistry	Carbon Bond IV or SAPRC99 mechanisms	ENVIRON CMC solver, IEH solver, or LSODE
Aerosol Chemistry	Dry and aqueous inorganic and organic chemistry/thermo-dynamics; static 2-mode or evolving multi-section size models	RADM-AQ, ISORROPIA, SOAP
Dry deposition	Separate resistance models for gases and aerosols	Deposition velocity as surface boundary condition for vertical diffusion
Wet deposition	Separate scavenging models for gases and aerosols	Uptake as a function of rainfall rate, cloud water content, gas solubility and diffusivity, PM size

Data Requirements

DATA CLASS	DATA TYPES
Meteorology Supplied by a Meteorological Model	3-Dimensional Gridded Fields: Vertical Grid Structure Horizontal Wind Components Temperature Pressure Water Vapor Vertical Diffusivity Clouds/Rainfall
Air Quality Obtained from Measured Ambient Data	Gridded Initial Concentrations Gridded Boundary Concentrations Time/space Constant Top Concentrations
Emissions Supplied by an Emissions Model	Elevated Point Sources Combined Gridded Sources Low-level Point Mobile Area/Non-road Mobile Biogenic
Geographic Developed from Landuse/Landcover Maps, Drought Index Maps, Modeled or Satellite derived Snow Cover	Gridded Surface Characteristics Land Use/Vegetative Cover UV Albedo Snow Cover Land/Water Mask Roughness Length Drought Stress
Photolysis Derived from Satellite Measurements and Radiative Transfer Models	Atmospheric Radiative Properties Gridded Haze Opacity Codes Gridded Ozone Column Codes Photolysis Rates Lookup Table

Model output

CAMx produces gridded time-averaged concentration output files for each time step (usually hourly). The output can contains just surface layer fields or entire three-dimensional fields, both for the master grid, and a all fine grid nests together.