Classification of ozone and weather patterns associated with high ozone concentrations in the san francisco and monterey bay areas

Ozone concentrations exceeded the federal ozone standard on eight days between 1987 and 1992 at an elevation of 335 m in Pinnacles National Monument, the only site to do so in the Monterey Bay Unified Air Pollution Control District (bordering the San Francisco Bay Area to the south) from 1987 through 1989. There are no nearby sources of ozone precursors. Cluster and empirical orthogonal function (EOF) analysis were used to define the spatial patterns of daily ozone maxima associated with Pinnacles violations. Meteorological data were also categorized to determine the combination of conditions that were unique to the Pinnacles violation days. It was concluded from the analyses that the ozone violations at the Pinnacles site represent conditions within or just below the subsidence inversion that is associated with the semipermanent high-pressure system off the west coast. It appears that the ozone is preserved for a considerable period of time in the stable inversion and has traveled long distances. Neither the mechanism by which the ozone is originally trapped, nor the original sources of its precursors are clear from this analysis.