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Grid Resolution Sensitivity in Air Quality Modeling: VISTAS Phase Analysis

This study examines the impact of grid resolution on air quality model performance using VISTAS Phase I data for Southeast US domains. Results indicate mixed effects on model accuracy with finer grids showing advantages but also highlighting limitations in resolving point sources. The analysis suggests that changes in precipitation and transport patterns significantly influence local air quality. The study concludes that a combination of 36 km and 12 km grids will be used for VISTAS Phase II annual modeling.

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Grid Resolution Sensitivity in Air Quality Modeling: VISTAS Phase Analysis

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  1. VISTAS Grid Resolution Sensitivity Ralph Morris, Bonyoung Koo and Steven Lau ENVIRON International CorporationGail Tonnesen, Zion Wang, Chao-Jung ChienUniversity of California at RiversideT.W. Tesche and Dennis McNallyAlpine GeophysicsNational RPO Modeling Meeting Denver, Colorado May 24-25, 2004

  2. Grid Resolution Sensitivity • Three VISTAS Phase I Episodes • January 2002 • July 1999 • July 2001 • MM5 PX_ACM(2) • 36 km national RPO grid and 12 km Southeast US VISTAS Grid • Examine Model Performance in VISTAS Southeast US Domain

  3. VISTAS Phase I 36/12 km Domains

  4. SO4 IMPROVE36 kmvs. 12 km January 2002 – SO4 July 1999 – SO4

  5. WSO4 NADP36 kmvs. 12 km January 2002 – WSO4 July 1999 – WSO4

  6. July 200136 kmvs.12 km July 2001 – SO4 IMPROVE July 2001 – WSO4 NADP

  7. IMPROVE SO4 Fractional Bias and ErrorCMAQ 36 km and 12 km & CB4 and SAPRC99

  8. IMPROVE NO3 Fractional Bias and ErrorCMAQ 36 km and 12 km & CB4 and SAPRC99

  9. IMPROVE OC Fractional Bias and ErrorCMAQ 36 km and 12 km & CB4 and SAPRC99

  10. Ozone Performance July 1999 EpisodeCMAQ and CAMx at 36 km and 12 km (CB4) CMAQ ozone performance degradation to under-estimation with finer grid CAMx ozone performance similar at 36 km and 12 km

  11. CAMx 36/12/4 km Performance for MRPO June 18 – August 13, 2001 Episode Mean Normalized Bias Degradation in most gas-phase species with higher resolution Aerosol species stay same or improve

  12. CAMx 36/12/4 km Performance for MRPO June 18 – August 13, 2001 Episode Mean Normalized Gross Error

  13. Conclusions: Grid Resolution Sensitivity • Effects of grid resolution on model performance is mixed • Changes in precipitation patterns and magnitudes can have large effect locally • Changes in transport patterns also can have big local effect (e.g., Jim Boylan’s analysis of sulfate clouds) • 12 km grid technically superior for grid modeling than 36 km, but still does not resolve point sources and urban areas very well • 12 km takes more CPU time than 36 km • VISTAS Phase II annual modeling will use both 36 and 12 km grids

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