Operational Evaluation and Model Response Comparison of CAMx and CMAQ for Ozone

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Operational Evaluation and Model Response
Comparison of CAMx and CMAQ for Ozone PM2.5

• Kirk Baker, Brian Timin, Sharon Phillips
• U.S. Environmental Protection Agency, Research
  Triangle Park, NC
• Presented at the 2008 CMAS Conference

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Operational Evaluation Response Comparison

• Comprehensive Air Quality Model with Extensions
  (CAMx4) and the Community Multiscale Air Quality
  Model (CMAQ), treat the physical processes and
  chemistry that form ozone and PM2.5
• SIPS are submitted using either model
• Model performance is typically evaluated on an
  operational basis comparing base year
  predictions to observations
• Since the modeled attainment demonstration
  includes modeling the relative change between
  current and future year emissions it is important
  to have confidence that modeling systems will
  predict ozone and PM2.5 concentrations
  consistently when emissions change

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Modeling Background

• CMAQ v4.6 (aero4)
• CAMx v4.5
• CB05 gas phase chemistry
• RADM aqueous phase chemistry
• ISORROPIA inorganic chemistry
• Variations in secondary organic chemistry between
  models
• Base year 2002
• Future year 2020

• 12 km sized grid cells
• 14 vertical layers up to 15 km
• 30 m thick first layer

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Domain Total Emissions (tpd)
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PM2.5 Bias Metric by Quarter for 2002
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Annual PM2.5 Model Response

• Models are used in a relative sense for
  regulatory modeling
• Relative response factor (RRF) estimated
  concentrations in future year / estimated
  concentrations in base (current) year
• RRFs are applied to observed design values to
  estimate future year design values
• RRFbase design value future design value
• RRFs are calculated for each chemical component
  of PM2.5
• RRFs estimated using the MATS software tool

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Annual PM2.5 Future Year Design Values and
Speciated RRFs
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Quarterly Nitrate Concentration (left) and RRFs
(right)
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Relationships between CAMx and CMAQ estimated RRF
and FYDV by specie
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Bias of Daily 8-hr Ozone Maximum
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8-hr O3 Future Year Design Values and RRFs
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8-hr O3 Model Response

• Examined future year design values, RRFs, and
  number of days for RRF calculating by 4 bins of
  model estimate 8-hr ozone
• 85
• 75 to 85
• 65 to 75
• 55 to 65
• Assess how model response changes based on
  predicted concentrations

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8-hr O3 RRFs by Model Prediction Bin (4 bins)
CAMx
CMAQ
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8-hr O3 RRFs by Model Prediction Bin (4 bins)
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8-hr O3 number of days in RRF calc. by Model
Prediction Bin (4 bins)
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8-hr FYDV, RRF, and days used for 85 ppb bin
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Remarks

• CMAQ and CAMx modeling systems consistently
  predict ambient concentrations of 8-hr ozone and
  PM2.5, which is encouraging since they are used
  to support modeled attainment demonstrations for
  NAAQS
• The relative response factors and future year
  design values of 8-hr ozone and annual PM2.5 are
  very similar using both CAMx and CMAQ even though
  there are differences in base year model
  predictions
• Larger 8-hr O3 reductions are seen at higher
  model predicted concentrations
• Using a different modeling system should give
  similar predicted future year design values when
  inputs and key physics options are consistent

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Future Work

• 24-hr PM2.5 model response
• A more thorough dynamic evaluation is needed to
  determine if these modeling systems appropriately
  respond to emissions changes

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END
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PM2.5 Model Performance
CAMx
CMAQ