Trend analysis of ground level ozone in the greater Vancouver/Fraser Valley area of British Columbia

A multiple linear regression model incorporating meteorological parameters, annual cycles and random error due to serial correlation was used to investigate the annual and summer season ozone trends between 1985 and 2000 at five stations in the Greater Vancouver/Fraser Valley area of southern British Columbia. Results indicate that although average daily maximum ozone concentrations were relatively low compared to many urban areas of Canada, maximum levels, which typically occur during the summer, were similar to those measured in large urban centers in the Great Lakes-St. Lawrence corridor of southeastern Canada. Ozone levels were found to occasionally exceed the National Ambient Air Quality Objective of 82 ppb, although these occurrences were relatively infrequent. The annual cycle of ozone was typical of areas influenced by both background and locally produced ozone, as indicated by the spring peak followed by elevated maxima occurring during summer months. General Least Squares analysis performed on the meteorologically adjusted data found decreasing trends for summer ozone at all stations. Decreasing trends were also found for annual ozone for stations in the eastern portion of the study area, which are more strongly affected by locally produced ozone. These trends were consistent with local declines in ozone precursors and are in agreement with reported declines in summer ozone in urban areas of United States and Europe. In contrast, increasing trends were found for annual ozone at stations in the western portion of the study area, which, due to their geographical location, are less affected by locally produced ozone. There is some indication that increasing trends at sites in the western portion of the study area may be reflective of a hemispheric increase in background ozone levels. The results of this study suggest that ozone trends in the Greater Vancouver/Fraser Valley area are in line with broad changes in ozone occurring in North America and Europe.