presents:\camx/training1198.ppt Introduction to CAMx Presented by Chris Emery ENVIRON International Corporation June 2003 ( i, j) T , p , q , K v (i, j) ( i, j) ( i, j-1 ) (i-1 , j) u , K x u , K x v , K y v , K y 0 200 400 600 800 1000 0 20 40 60 80 100 0 40 80 120 160 200 240 Maxim um O zone (ppb) Initial VO C (ppbC) Initial NO x (ppb)
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Presents:\camx/training1198.ppt Introduction to CAMx Presented by Chris Emery ENVIRON International Corporation June 2003.
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• Decoupled Direct Method (DDM) of sensitivity analysis
• Process Analysis tools (IPR, IRR, CPA)
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Description of CAMxTechnical Approach
Overview– Solves continuity equation for each species
– Time splitting operation• Each process solved individually each time step, each
grid
– Master time step:• Maintains stable solution of transport on master grid
• Multiple nested grid steps per master step
• Multiple chemistry steps per master step
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Description of CAMxTechnical Approach
Transport– Advection and diffusion solvers are mass conservative– 3-D advection is mass consistent
• Linked via divergent atmospheric incompressible continuity equation
– Order of east-west and north-south advection alternates each master step
– Two options for horizontal advection solver:• Bott (1989): area-preserving flux-form solver• Colella and Woodward (1984): piecewise-parabolic
method
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Description of CAMxTechnical Approach
– Vertical transport solved with implicit scheme• Resolved vertical velocity
• Mass exchange across variable vertical layer structure
– Vertical diffusion solved with implicit scheme• Dry deposition rates used as surface boundary condition
– Horizontal diffusion solved with explicit scheme• 2-D simultaneous
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Description of CAMxTechnical Approach
• Pollutant removal– Dry deposition
• First order removal rate based on deposition velocity (Weseley, 1989)
• Dependent upon: season, land cover, solar flux, surface stability, surface wetness, gas solubility and diffusivity, aerosol size
– Wet scavenging• First order removal rate based on scavenging coefficient• Gas rates depend upon solubility and diffusivity• Aerosol rates depend upon size• Separate in-cloud and below-cloud rates (Seinfeld and
Pandis, 1998)
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Description of CAMxTechnical Approach
• Photochemistry– CBM-IV (Gery et al., 1989)
• 3 variations available
– SAPRC99 (Carter, 2000)• Chemically up-to-date
• Tested extensively against environmental chamber data
• Uses a different approach for VOC lumping
– All mechanisms are balanced for nitrogen conservation
– Photolysis rates derived from TUV preprocessor• Can be affected by cloud optical depth
presents:\camx/traininggenerictrng1198.ppt
Description of CAMxTechnical Approach
• Gas-phase chemistry solvers– Most “expensive” component of simulation
– CAMx CMC solver• Increases efficiency and flexibility
• Adaptive hybrid approach:– Radicals (fastest reactions) – in steady state
– Fast state species – second-order Runge-Kutta
– Slow state species – solved explicitly
• “Adaptive” = number of fast species can change according to chemical regime
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Description of CAMxTechnical Approach
– Implicit-Explicit Hybrid solver (Sun et al, 1994)• Accuracy comparable to reference methods (LSODE)
• Additional biogenic olefin (terpenes)• Condensible organic gas species• Chlorine and HCl chemistry• Homogeneous SO2 to sulfate• Photochemical production of nitric acid
– Aerosol mechanism calculates:• Aqueous SO2 to sulfate (CMAQ/RADM-AQ)• Condensible organic gasses to organic aerosols (SOAP)• NO3/SO4/NH3/Na/Cl equilibrium (ISORROPIA)• Size spectrum is static, user-defined
presents:\camx/traininggenerictrng1198.ppt
Description of CAMxTechnical Approach
– Aerosol species treated:• Sulfate
• Nitrate
• Ammonium
• Sodium
• Chloride
• Secondary Organics
• Primary Organics
• Elemental Carbon
• Primary Fine (+dust)
• Primary Coarse (+dust)
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Description of CAMxTechnical Approach
• Plume-in-Grid (PiG)– Resolves chemistry/dispersion of large NOx plumes– Tracks plume segments (puffs) in Lagrangian frame
• Each puff moved independently by local winds• Puff growth (diffusion) determined by local diffusion
PiG restart (Fortran binary)– All relevant PiG information for model restart
• Diagnostic files (text)– Repeat run control parameters and I/O file names
– Diagnostic messages and warning/error messages
– CPU timing
– Mass budgets
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Description of CAMxModel Output
Probing Tool files– Master and fine grid instantaneous tracer files (UAM
Fortran binary)
– Master and fine grid average tracer and PA rates files (UAM Fortran binary)
– OSAT and DDM receptor file (text)• Tracer/sensitivity concentrations at discrete receptors
– IPR and IRR rates files (Fortran binary)• Time-varying rate information for user-selected cells
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Description of CAMxComputer Requirements
Dependent upon size of CAMx application– Standard model vs. large Probing Tool configuration– Number of nested grids needed and number of cells per
grid– Chemistry mechanism
• SAPRC99 slower than CBM-IV• PM chemistry slows model significantly
– Chemistry solver• IEH slower than CMC
– Plan according to episode length and desired throughput for desired number of simulations
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Description of CAMxComputer Requirements
Example: CAMx application on 1 Ghz Pentium III PCCBM-IV Mech 3 (no aerosols), CMC solver
Application Memory
Disk Usage
Execution Time
1 grid OTAG domain (64 x 63 x 5) No OSAT
49 Mb
90 Mb/episode day
5 min/episode day
2 grids OTAG domain (64 x 63 x 5) and (137 x 110 x 7) No OSAT
115 Mb
200 Mb/episode day
40 min/episode day
2 grids OTAG Domain (64 x 63 x 5) and (137 x 110 x 7) 17 OSAT source regions 4 OSAT source groups Total OSAT tracers = 280
387 Mb
500 Mb/episode day
5 hours/episode day
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Description of CAMxComputer Requirements
Recommended hardware – Linux workstation– Minimum 256 Mb memory– Fastest affordable PC chipset available– Minimum 10 Gb available disk space– Graphics monitor and associated drivers
• Recommended software– Portland Group F77/F90 compiler for Linux– PAVE, Vis5d, Surfer (or some other graphics viewer)– Ancillary support software for pre- and post-processing
• SAS (for EMS-95), ArcInfo or other GIS systems• MM5, RAMS, NCAR Graphics (for meteorological
preprocessing)
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Description of CAMxComparison to Other Grid Models
Practicality/Regulatory Acceptability Comp Requirements low medium medium high high medium Documentation good fair fair poor fair fair Ease of Use fair fair fair poor poor fair Availability publicly available restricted restricted restricted publicly available publicly available Peer Review yes yes yes no yes yes Regulatory Use yes yes yes yes yes yes
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Application of CAMx
• CAMx Setup• Base Case Development• Performance Evaluation• Future Base Case• Emission Control Scenario Evaluation
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Application of CAMxCAMx Setup – Domain Definition
• Coverage– Geographical/political issues– Influence of boundary conditions– Need for fine resolution in key areas– Depth– Resource/time constraints
• Resolution– Master grid: met model, coordinate projection, layer
structure– Nested Grids: where, how many, vertical nesting
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Application of CAMxCAMx Setup -- Domain Definition
OSAT and DDM source/receptor areas– Source mapping assigns each grid cell to a source area
• Can specify one source area (entire domain)• Can specify multiple source areas on master or nested
grids– Receptor locations:
• Optional user-specified receptor locations• Can select: point, single cell, cell average, or wall of
cells
• Landuse– Depends upon available geographic databases– Often developed from emission surrogates
– Aerosol chemistry• Define species, representative sizes, density
– Dry deposition• Define Henry’s law solubility, diffusivity, reactivity
– Wet deposition• Define Henry’s law solubility
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Application of CAMxCAMx Setup – Chemistry Definition
Contents of chemistry parameters file– Mechanism (choose from 1 through 5 or inert)– Photolysis reaction parameters and options– Gas phase species list
– Scaling of emissions and/or emission components (mobile vs. biogenic vs. area, etc.)
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Application of CAMxFuture Base Case
• Application to attainment demonstrations and/or control strategy evaluation
• Base-year emissions must be adjusted for conditions expected in a future year– Growth due to new sources and increased activity
– Controls expected as mandated by existing regulations
• Model runs use future base emissions to predict future air quality
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Application of CAMxFuture Emissions Control Scenarios
• If attainment is not predicted for the future base case, then additional controls must be considered– “Attainment” of air quality standards must be
demonstrated according to EPA guidelines
• A variety of control scenarios are developed and their effectiveness explored
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Application of CAMxFuture Emissions Control Scenarios
• An emissions control scenario is a collection of generic or specific control measures on individual sources or groups of source– Sources are often grouped by type or location– Examples of typical control measures are:
• Reduction of Vehicle Miles Traveled• Low NOx burners on power plant or industrial boilers• Lower auto tail pipe standards (LEV, ULEV, ZEV)• Fugitive VOC detection and control programs• Consumer product reformulation• Gasoline reformulation• Vapor recovery at fueling stations
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Application of CAMxFuture Emissions Control Scenarios
• Since the number of combinations of feasible control measures is almost endless,– A means of narrowing the list to a manageable number
of scenarios is needed
– Prior experience and economic feasibility usually enter into the selection process
– CAMx source apportionment is also an aide in identifying the most effective control scenarios