New Features of the 2003 Release of the CMAQ Model

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New Features of the 2003 Release of the CMAQ Model

• Jonathan Pleim1, Gerald Gipson2, Shawn Roselle1,
  and Jeffrey Young1
• 1 ASMD, ARL, NOAA, RTP, NC
• 2 AMD, NERL, USEPA, RTP, NC

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Whats new in CMAQ 2003

• Updates to science
• Updates to Nitrate aerosol and Nitric acid
• Updates to Secondary Organic Aerosols
• Efficiency improvements
• Faster chemistry solver
• Modified model time stepping
• Other updates and corrections
• Air Quality Forecasting

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Nitrate

• Previous release (2002) shows large
  overprediction of Nitrate aerosol and Nitric acid

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Nitrate related changes

• Dry Deposition (winter)
• Added explicit resistance to snow and ice with
  dependence on temperature (melting)
• Modified cuticle resistance for NH3 as function
  of relative humidity
• Added wet ground similarly to wet canopy
• Revised model produces much greater Vd for NH3
  thus reducing ammonium nitrate aerosol
  concentrations
• Heterogeneous and Gas-Phase Reactions
• Gas-phase nitric acid also greatly overpredicted
• Identified key pathway N2O5 H2O --gt 2HNO3
• Revised the heterogeneous reaction rate
• Turned off gas phase reaction

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Heterogeneous N2O5 Reaction

• 2002 release
• Reaction probability ? 0.1 recommended by
  Dentener and Crutzen (JGR 1993)
• Makes a lot of HNO3 at night
• Recent studies show wide range of ? values
• Dependence on humidity, temperature, chemical
  composition - sulfate, nitrate, and organic
  content
• Updated version
• Reaction probability ? 0.002 - 0.02 depending
  on NO3/(SO4NO3) according to Riemer et al. (JGR
  2003) based on lab measurements of Mentel et al
  (PCCP 1999)

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2003 release vs 2002 release
Aerosol Nitrate
Gas Phase Nitric Acid
January 4 20, 2002
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CMAQ02 vs CMAQ03 - Nitrate
Nitrate Aerosol CMAQ03
Nitrate Aerosol CMAQ02
Nitrate Aerosol diff
Total Nitrate diff
Average concentrations January 4 20, 2002
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Secondary Organic Aerosols

• Corrections to Gas-Particle partitioning to allow
  reversibility
• Lowers SOA concentrations by 60-70
• SOA precursor factors for SAPRC99
• 57 of ALK5 (longer chain alkanes)
• 93 of ARO1 (less reactive aromatics)
• Eliminated SOA from olefins
• SOA production in CB4 unchanged
• No production from alkanes or olefins
• 100 of aromatics

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Organic Carbon Aerosol
June 15 29, 1999
Jan. 4 - 20, 2002
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CMAQ02 vs CMAQ03 - SOA
Total SOA CMAQ03
Total SOA CMAQ02
Total SOA Ratio 03/02
Total SOA diff
Average concentrations June 15 29, 1999
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Changes for improved efficiency

• Euler Backward Iterative (EBI) solver
• EBI uses analytical solution for two chemical
  groups rather than numerical solution used in
  MEBI
• EBI about twice as fast as MEBI
• Currently for CB4 only
• Eliminated transport for radical species
• Layer dependent advection time steps
• Synchronization time step set by Courant
  condition in lower layers (up to sigma0.7)
• Multiple advection steps allowed in upper layers
• Maximum sync time step changed to 12 min and
  minimum to 1 min for improved accuracy

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Other Updates

• Cloud processes and aqueous chemistry
• Updated equilibrium constants
• Corrected vertical diffusion of aerosols (density
  -gt mixing ratio)
• Reordered operators
• Vertical diffusion with emissions
• Advection (x,y,z)
• Horizontal diffusion
• Clouds
• Gas chem
• Aerosols

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Updates to other system components

• Latest MCIP - version 2.2
• Major corrections to layer interpolation of winds
  and vertical velocity (v2.1)
• Updated dry deposition for both M3dry and RADMdry
• Emission modeling (Georges Presentation)

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AQF System

• NWS Eta model forecasts
• Interpolated to 22 layer CMAQ grid
• Hourly output with additional variables
• AQF version of CMAQ
• Optimized for massive parallel system
• New version of MCIP called Premaq
• Testing this past summer (2003)
• 48 hr forecasts starting at 12z
• 30 hr forecasts starting at 6z
• 6 hourly cycling

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AQF Ozone Aug 14, 2003
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Future Work

• EBI for SAPRC99
• New mass conservation technique
• New PBL models
• CB4-2002
• New advection schemes
• WRF connections
• Source apportionment for primary aerosols
• Coarse aerosol improvements
• Sectional aerosol models
• Continued performance improvements

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Further information

• EPAs CMAQ website
• www.epa.gov/asmdnerl/models3/cmaq.html
• Click on Model changes for more detailed
  description of changes for the 2003 release
• Click on Announcements and then on Performance
  Evaluation for the August 2003 Release of CMAQ
  for a powerpoint presentation

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Related ASMD Presentations

• Brian Eder Evaluation results
• 2003 release of CMAQ
• AQF CMAQ
• George Pouliot latest developments in emission
  modeling
• Jason Ching Air toxic modeling
• Shaocai Yu
• Diagnostic analysis of CMAQ SOA
• Poster Primary and secondary SOA
• Poster Thermodynamic aerosol models
• Jeff Arnold CMAQ Sensitivity to vertical mixing
• Jeff Young Parallel CMAQ

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AQF Ozone Aug 15, 2003