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AMS/EPA Workshop on the Evaluation of Regional-Scale Air Quality Modeling Systems: Overview & Next Steps. Tyler Fox, USEPA 6 th Annual CMAS Conference October 1, 2007. Evolving US Air Quality Management System. Source: John Bachmann, EM Magazine, June 2007. Steering Committee Members.
Tyler Fox, USEPA
6th Annual CMAS Conference
October 1, 2007
Potential to Improve Model Performance
Availability of Lab or Field Measurements
Processes Affecting Modeled PM2.5
Source: Prakash Bhave
How do the model predicted concentrations compare to observed concentration data?
What are the overall temporal or spatial prediction errors or biases?
concentration and deposition
Model Inputs: meteorology and emissions
Chemical transformation: gas, aerosol,
and aqueous phases
Transport: advection and diffusion
Removal: dry and wet deposition
Are we getting
the right answers?
Can we capture observed changes in air quality?
Can the model capture changes related to meteorological events or variations?
Can the model capture changes related to emission reductions?
Can we identify needed improvements for modeled processes or inputs?
Are we getting right answers for right (or wrong) reasons?
Are model errors or biases caused by model inputs or by modeled processes?
Can we identify the specific modeled process(es) responsible?
What is our confidence in the model-predicted values?
How do observed concentrations compare within an uncertainty range of model predictions?
What is our confidence in the model predictions?
Morris, R., et al., “Model and Chemistry Inter-comparison: CMAQ with CB4, CB4-2002, SAPRC99”, National RPO Modeling Meeting, Denver, CO, 2005b.
• Based on US (36-km) and VISTAS (12-km) January 2002 modeling, conducted
chemistry mechanisms inter-comparisons for CMAQ with CB4, CB4-2002,and
• The performance of CB4 and CB4-2002 was similar for PM, and superior to SAPRC99 overall (for the Jan02 case).
• The model performance for CMAQ/CB4, US 36-km domain is in the range of:
Sulfate: MFE = 42% ~ 73%, MFB = -21% ~ +14%
Nitrate: MFE = 62% ~ 105%, MFB = -21% ~ +46%
Organic: MFE = 50% ~ 77%, MFB = +3% ~ +59%
EC: MFE = 59% ~ 88%, MFB = +2% ~ +70%
Soil: MFE = 165% ~ 180%, MFB =+164% ~ +180%
PM 2.5: MFE = 48% ~ 88%, MFB = +25% ~ +81%
• Given that the computational cost of SAPRC99 is twice that of CB4, suggested to use 36 and 12 km grids with CB4 chemistry for PM modeling for the time being.
• Noted that both CB4 and SAPRC underpredicted winter O3 significantly.