5. Boylan, J., VISTAS, “Calculating Statistics: Concentration Related Performance Goals”,
PM Model Performance Workshop, RTP, NC, 2004b.
• Illustrated a set of standard bias and errors calculations commonly used for model
performance statistics and proposed model performance goal.
• Indicated Mean Normalized Bias and Errors (MNBE) are most biased and least useful
among “MNBE”, “NMBE” and “MFBE”. The Mean Fractional Bias and Errors
(MFBE) is least biased and most useful among the three metrics.
• Recommended MFB & MBE and proposed performance goal: MFE<=50% and MFB
<=+-30% for more abundant species (eg., sulfate & PM2.5) and less stringent for less
abundant species (eg., nitrate, OC, EC, soil, etc.). Performance goal is not criteria and
should be prohibit the modeling from being used if it fails to meet the goal.
• Proposed to use “2.5ug/m3" as the “grayline” for 50% MFE & +-30% MFB and
asymmetrically approaching 200% MFE & +-200% MFB to extremely small
6. 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%
PM2.5: 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.
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