A comparison of ozone predictions from UAM-IV CB-4 vs. CALGRID CB-4, SAPRC90, and SAPRC93 for the Los Angeles 27--28 August 1987 episode
Two photochemical grid models, UAM-IV and CALGRID, have been used to study the air quality impacts of reformulated gasoline (RFG), 85% methanol (M85), and compressed natural gas (CNG) for light duty vehicle use in Los Angeles. Several chemical mechanisms were incorporated into the models, including variants of the Carbon Bond Mechanism--Version 4 (CB-4) and the Statewide Air Pollution Research Center Mechanism (SAPRC). This paper focuses on the inter-comparison of the model and mechanism results for the base year simulation with RFG fuel use. The UAM-IV was exercised using the 1994 Air Quality Modeling Plan (AQMP) model inputs prepared by the South Coast Air Quality Management District (SCAQMD). The CALGRID model was exercised in a native fixed layer mode with CALMET-generated meteorological inputs based on the same SCAQMD observation base. Comparison of UAM-IV and CALGRID predictions with the CB-4 mechanism shows that CALGRID predicts considerably larger peak ozone concentrations at the edges and outside of the Los Angeles basin. All other inputs being equivalent, the use of higher vertical resolution and CALMET-predicted meteorological inputs produces an ozone concentration field that agrees better with observations, in contrast to the systematic under-prediction of UAM-IV. The original SAPRC90 chemical mechanism produces considerably smaller peak ozone concentrations than does the original CB-4. The differences in peak ozone predictions are similar to those found when the CB-4 mechanism is disaggregated to provide an explicit representation for aldehyde, internal olefins, and higher PAN analogues. The upgrades in rate coefficients and chemical yields associated with the SAPRC93 produced consistently larger peak ozone concentrations than does SAPRC90.
- Research Organization:
- Earth Tech, Inc., Concord, MA (US)
- OSTI ID:
- 20002099
- Report Number(s):
- CONF-990608--
- Country of Publication:
- United States
- Language:
- English
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