GATOR-GCMM - 2. A study of daytime and nighttime ozone layers aloft, ozonein national parks, and weather during the SARMAP field campaign

The GATORG-GCMM global- through urban-scale nested air pollution/weather fo recast model was applied to study ozone layers aloft, ozone in national par ks, and weather during the August 3-6, 1990, SARMAP field campaign in north ern and central California. Predictions of meteorological variables and mix ing ratios of 20 gases were compared with observations. With nesting, the n ormalized gross error in predicted near-surface Kelvin temperatures was 1.0 2% and that in near-surface ozone above 50 ppbv was 22.5%. Statistics from outer nested domains indicated that the coarser the grid spacing, the great er the underprediction of ozone. In the absence of nesting, statistics dete riorated but not a lot. The model simulated observed nighttime ozone layers aloft and daytime ozone mixed layers in the San Joaquin Valley and San Fra ncisco Bay Area. It also simulated observed daytime and nighttime ozone lay ers aloft over the San Francisco Bay near Hayward. The formation mechanism of these layers is discussed. The model was used to estimate that about 47- 57% of peak daytime ozone in Sequoia and Yosemite National Parks during SAR MAP was produced By anthropogenic gases, 13-3% was produced by biogenic hyd rocarbons, and the rest (about 40%) was background.