Analysis of an Ozone Episode during the San Diego Air Quality Study: The Significance of Transport Aloft

Abstract

San Diego is subject to transport of ozone and precursors from the Los Angeles area, 170 km to the northwest, as well as to high ozone concentrations from local emissions. The San Diego Air Quality Study was conducted during the summer of 1989. Air quality and meteorological data were obtained at the surface and aloft to provide a high quality database for photochemical modeling and control strategy development for both local and transport-influenced ozone episodes. Six high-ozone episodes were potentially suitable for photochemical modeling, including several from 21 to 29 September 1989; maximum 1-h ozone concentrations exceeded the federal ambient standard on six of the nine days and reached 0.17 ppm on two days. From review of preliminary surface and routine meteorological data and surface trajectory analysis, 25?26 September 1989 appeared to be a local episode with high ozone concentrations downwind from local (i.e., San Diego) emissions sources. This paper examines the candidate episode and finds that transport aloft from the Los Angeles area played a key role.