Camx

Model name

CAMx

 

Full model name

Comprehensive Air Quality Model with Extensions

 

URL

www.camx.com

 

Remarks

CAMx is programmed in F90, and can be run in parallel mode using OMP and MPI. ENVIRON has also developed several tools to prepare CAMx input data and process output fields. A test case is available at the CAMx web site that provides all input and output for a 2-day U.S. example episode.

 

Intended field of application

Urban to continental scale photochemical air pollution, including gas, aerosol, mercury, and toxics species. Regulatory, research, and assessment applications

 

Model type and dimension

“One-atmosphere” three-dimensional Eulerian (gridded) tropospheric photochemical dispersion model, 1 km to 1000 km spatial scales, hourly to annual time scales

 

Model description summary

The Comprehensive Air quality Model with extensions (CAMx) is a publicly available Eulerian computer modeling system for the integrated assessment of photochemical and particulate air pollution over many scales ranging from urban to super-regional. Most notable features:

- two-way nested grid structure and flexi-nesting

- three gas-phase chemical mechanism options (CB-IV, CB05, and SAPRC99)

- three gas-phase solver options (IEH, EBI or LSODE)

- Treatment of particulate matter, inorganic (ISORROPIA) and organic (SOAP)

- Mercury and toxics chemistry

- Plume-in-Grid module

- Horizontal Advection Solver options (Bott or PPM)

- Dry and wet deposition

- advanced photolysis model

- detailed cloud impact on photolysis rates and aqueous chemistry

- parallel processing on shared-memory systems (OMP) or distributed memory systems (MPI)

- Ozone and Particulate Source Apportionment Technology

- Decoupled Direct Method

- Process Analysis

 

Model limitations/approximations

Eulerian (gridded) framework, tropospheric chemistry, applicable scales range from urban (1 km) to continental (3000 km).

 

Resolution

Temporal resolution

Typical output frequency is 1 hour, but this can be chosen by the user. Model time steps range from <1 min for high-resolution grids (~1 km) to 15 min for coarse-resolution grids (30-50 km).

 

Horizontal resolution

CAMx is a variable-nested grid model. Resolution can range from a recommended minimum of ~1 km to 30-50 km, depending upon the application. Multiple nested grids are used where high-resolution is needed.

 

Vertical resolution

Typical vertical domain depth is chosen to simulate the lower troposphere (i.e., the planetary boundary layer, or ~3000 m). CAMx can be used to simulate transport throughout the entire troposphere. Suggested maximum domain depth is ~10-15 km. The user may resolve this depth with any arbitrary number of model layers. Typically, 10-30 layers are used, with higher resolution near the ground. Often the model layer structure is defined by the meteorological model used to provide environmental inputs to CAMx.

 

Schemes

Advection & Convection

Horizontal advection is choice of PPM (Colella and Woodward, 1984; Odman and Ingram, 1993) or Bott (1989). Equations expressed in flux form

 

Turbulence

Eulerian continuity equation is closed by K-theory. Horizontal diffusion based on Smagorinsky (1963) wind deformation approach. Vertical diffusion coefficients are diagnosed externally and supplied via input file.

 

Deposition

DRY Physical model: separate resistance models for gases and aerosols (Wesely, 1989; Slinn and Slinn, 1980; Kumar et al., 1996). Numerical model: deposition velocity as surface boundary condition for vertical diffusion. WET Physical model: separate scavenging models for gases and aerosols based on equations in Seinfeld and Pandis (1998). Numerical model: uptake as a function of rainfall rate, cloud water content, gas solubility and diffusivity, PM size.

 

Chemistry

Gas phase: Carbon Bond 2005 (CB05; Yarwood et al., 2005), Carbon Bond 4 (CB4; Gery et al., 1989) or SAPRC99 (Carter, 2000) mechanisms. Three solvers are available: EBI (Hertel et al., 1993), IEH (Sun et al., 1994), or LSODE (Hindmarsh, 1983). Particulate Matter: * RADM aqueous chemistry scheme (Chang et al., 1987) * ISORROPIA gas/aerosol partitioning scheme (Nenes et al, 1999) * SOAP scheme for SOA formation (Strader et al., 1999) * both Coarse/Fine scheme and Multi sectional approach Mercury: multiphase chemistry of Hg(0), Hg(II) and Particulate Hg Toxics: Flexible user-defined toxic species and chemical mechanims reactions and rates provided to the CAMx “RTRAC” extension; solution can be analytical or numerical (LSODE).

 

Solution technique

Time- and operator-splitting technique for major physical (transport, diffusion, deposition) and chemistry processes Master time step is internally computed in order to ensure stability of the advection scheme. Multiple time steps per transport time step are used for gas chemistry. A 15 minutes time step is defined to couple gas and aerosol chemistry. Coordinate systems: Lat/lon; UTM; Polar stereographic; Lambert Conformal. Arakawa C grid configuration. Vertical level structure supplied via input file. Two-way or one-way nesting allowed.

 

Input

Availability and Validation of Input data

All input data are generated using various external models or pre-processors. CAMx is distributed with a ready-to-run example test dataset (www.camx.com). Validation of model performance against ambient measurement data is left to the user.

 

Emissions

Gridded (low-level) and elevated point sources (plume rise is determined within the model). Official emission inventories usually are the main source of original data. Emissions are usually available on administrative basis and therefore need to be spatially allocated to the CAMx grid. Temporal profiles and VOC/PM speciation factors are needed to produce hourly point-source and gridded fields of CAMx species emissions. This processing can be done using many external emissions processing systems, such as SMOKE, EPS3, and CONCEPT.

 

Meteorology

3-dimensional gridded fields of: horizontal wind components, temperature, pressure, water vapor, vertical diffusivity, clouds, rainfall. Meteorological fields should be generated by self-consistent meteorological models (MM5, WRF, RAMS, etc.). The CAMx web site provides useful interface programs for these models. Each of these programs includes a diagnostic scheme to compute vertical diffusion coefficients.

 

Topography

Gridded layer interface heights. Gridded land use surface cover. Gridded topographic elevation. Gridded surface UV albedo. All fields can be generated using software available at www.camx.com.

 

Initial conditions

Gridded three-dimensional initial conditions are needed for all or a subset of species. Simple time/space-constant inputs can be developed using software available at www.camx.com. Global model output (i.e., MOZART, GOES-CHEM) can be processed using third-party interface programs.

 

Boundary conditions

Gridded two-dimensional time-varying boundary conditions are needed for all or a subset of species. Simple time/space-constant inputs can be developed using software available at www.camx.com. Global model output (i.e., MOZART, GOES-CHEM) can be processed using third-party interface programs.

 

Data assimilation options

None.

 

Other input requirements

User control is defined by a fortran “namelist” control file defining:

- Model clock control

- map projection parameters

- grids definition

- options (scheme, tools, etc...)

- output specifications

- input files - Constant top concentrations for all or a subset of species

- Gridded haze opacity codes

- Gridded ozone column codes

- Photolysis rates lookup table

 

Output quantities

Hourly (or user-defined interval) two- or three-dimensional concentration fields (ppm for gases, ug/m3 for aerosols).

Hourly (or user-defined interval) two-dimensional surface deposition fields (m/s for deposition velocity, mol/ha for gases, g/ha for aerosols).

Diagnostic and mass balance output files.

 

User interface availability

CAMx is most commonly run on Unix/Linux workstations and PCs using shell scripts. Third-party graphics are needed to visualize output fields. CAMx is distributed with tools to prepare data in several widely used formats.

 

Portability and computer requirements

Portability

UNIX and LINUX platforms (DEC, Sun, SGI, HP, IBM, Linux PC, Apple/MAC)

 

CPU time

The time required to run CAMx depends on grid resolution, grid size, duration of the period to simulate, complexity of chemistry, use of “Probing Tool” extensions. The following examples are for a simple single-grid CAMx run employing CB4 gas-phase chemistry only, on a 2.1 GHz Linux PC with 256 MB RAM:

* 97x90x14 grid - 24 min/day

* 97x90x14 grid - 16 min/day (2 CPU)

 

Storage

For a 60x60x11 domain, 20-400 mB /day (only 2D or also 3D fields)

última atualização a 15-04-2014
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