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Intercomparison of the community multiscale air quality model and CALGRID using process analysis
Susan M O'Neill1, Brian K Lamb
1Pacific Wildland Fire Sciences Laboratory, USDA Forest Service, 400 N 34th Street, Suite 201, Seattle, Washington 98103, USA. oneill@fs.fed.us
Environmental Science & Technology
|August 30, 2005
Summary
Two advanced air quality models, EPA Models-3/CMAQ and CALGRID/CALMET, showed similar performance for ozone episodes, though they used different chemical mechanisms and meteorological inputs. Process analysis revealed distinct modeling pathways despite comparable outcomes, highlighting the need for field measurements.
Area of Science:
- Environmental Science
- Atmospheric Chemistry
- Computational Modeling
Background:
- Photochemical air quality models are crucial for understanding and predicting ozone pollution.
- Comparing different modeling systems with various chemical mechanisms and meteorological inputs is essential for model improvement.
Purpose of the Study:
- To compare the performance of EPA Models-3/CMAQ and CALGRID/CALMET photochemical air quality models.
- To investigate the impact of different chemical mechanisms (CB-IV, RADM2, SAPRC-97) and meteorological inputs on ozone modeling.
- To analyze the underlying processes contributing to ozone formation and transport in an urban corridor.
Main Methods:
- Application of EPA Models-3/CMAQ and CALGRID/CALMET to an ozone episode in the I-5 urban corridor, Washington and Oregon, July 11-14, 1996.
- Utilized identical modeling domains and emission inventories.
- Employed different chemical mechanisms (CB-IV, RADM2 for CMAQ; SAPRC-97 for CALGRID) and meteorological data from MM5 with observational nudging.
- Evaluated model performance using statistical measures and conducted process analysis.
Main Results:
- Both modeling systems demonstrated similar overall performance, performing well in the Portland area and downwind of Seattle but less effectively north of Seattle.
- Improving meteorological inputs for CALGRID/CALMET enhanced its performance.
- Process analysis indicated that CMAQ exhibited faster and more variable transport rates, leading to different ozone plume placements compared to CALGRID.
- CALGRID with SAPRC-97 showed a more pronounced diurnal ozone production/loss cycle than CMAQ with RADM2 or CB-IV.
Conclusions:
- Advanced photochemical models can yield similar results through different mechanisms, underscoring the complexity of ozone modeling.
- Meteorological data quality significantly influences model performance.
- Further field measurements are necessary to validate the specific chemical and physical processes simulated by these models.