EVALUATION OF CALGRID USING 2 DIFFERENT OZONE EPISODES AND COMPARISONTO UAM RESULTS

Air quality models serve as the foundation for policy decisions regard ing programs designed to improve air quality. The California Air Resou rces Board Airshed Model (CALGRID) is one of the latest photochemical air quality models developed for assessing ozone control strategies. C ALGRID was modified to include the latest CBIV chemical mechanism in p lace of the original SAPRC mechanism. After modification, a detailed e valuation of CALGRID was carried out using two different ozone episode s. The first evaluation used data obtained during the Southern Califor nia Air Quality Study (SCAQS). The second evaluation used data obtaine d for the September, 1984 SCCCAMP episodes in the South Central Coast Air Basin (SCCAB). Model results were compared against observations of O3, NO, NO2, and different organic compounds. For the SCCAB episode, the results were also compared with those obtained from the Urban Airs hed Model (UAM). Similar to other studies, the ozone predictions from the SCAQS application were biased low, as were various ROG components. The reason for this can be linked to the under-representation of ROG and CO in the emissions inventory. For the SCCAB episode, both the UAM and CALGRID models significantly underestimated NO and NO2 concentrat ions. The two models slightly underestimated ozone concentrations abov e approximately 9 pphm on the third and last day of the simulation. Se nsitivity experiments were performed for both the studies. It was foun d that both CALGRID and UAM are strongly sensitive to the boundary con ditions and moderately sensitive to the emissions for the episodes mod eled.