Analysis of Historical Ozone Episodes in the SCCCAMP Region and Comparison with SCCCAMP 1985 Field Study Data

Abstract

A comprehensive air quality and meteorological monitoring project entitled the South-Central Coast Cooperative Aerometric Monitoring Program (SCCCAMP 1985) was conducted in the Santa Barbara Channel and adjacent areas from Point Sal to Point Dume during a five-week period in September?October 1985. As part of a larger study to analyze the SCCCAMP 1985 observations and related databases, an analysis has been conducted of a six-year historical ozone and meteorological database. The objectives of the historical data analysis study were to 1) characterize meteorological and ozone concentration patterns during a six-year historical period (1979?1984), 2) identify relationships between meteorological variables and high ozone concentrations in the SCCCAMP region, and 3) compare the meteorological conditions and ozone concentrations observed during the SCCCAMP 1985 study with those during the same periods in the historical database in order to assess the representativeness of the SCCCAMP 1985 study period as a whole and individual high ozone events within the period. The analysis indicated that high ozone concentrations in Santa Barbara County were associated with two conditions occurring simultaneously: 1) subsidence and limited mixing conditions, and 2) moderate easterly or southerly geostrophic flow. Although the actual flow fields and mixing conditions in the region are complex and variable, the 850-mb temperature and surface-pressure parameters were found to be useful, robust indicators of high ozone conditions in Santa Barbara. The seasonal distribution of high ozone events in Santa Barbara County, which peaks in September with a secondary peak in June, was found to be strongly related to the seasonal frequency of occurrence of favorable values of these meteorological variables. In contrast, the peak Ventura County ozone concentrations did not show the same sensitivity to surface pressure parameters, and the seasonal frequency of high ozone events, which peak in July, corresponds closely to that of the 850-mb temperature. The SCCCAMP 1985 period was unusual in terms of its low frequency of occurrence of meteorological conditions associated with high ozone events in the region. As a result the observed average ozone concentrations were below historical values. However, several high ozone events did occur during the SCCCAMP 1985 study. The meteorological conditions during these individual events were found to be consistent with those typical of historical high ozone events.