Abstract
The Lower Fraser Valley of British Columbia is currently experiencing rapid population growth and episodically suffers elevated oxidant concentrations, the frequency of which is linked to meteorological conditions on the synoptic scale. This study is a first step toward developing and validating a methodology for “declimatizing” air quality data so that postulated effects of changing emissions patterns can be addressed. Principal component analysis of gridded fields at three atmospheric levels (sea level–reduced surface pressure, 850-mb height, and 500-mb height) yields four principal components (or modes of the atmospheric circulation) that account for over 83% of geophysical dataset variance. Daily component scores from these components are used as independent parameters in a region equation of the daily maximum ozone concentrations at a site (Rocky Point Park) in Vancouver over five summers (1984–88, inclusive). The coefficients in this equation are used to construct another algorithm that is used to predict maximum daily ozone concentrations at this site during the summers of 1989–92 on the basis of synoptic-scale meteorology. The algorithm correctly predicts the low frequency of ozone episodes in the July 1989–July 1992 period but cannot account for the reduction in daily maximum ozone concentrations on nonexceedance days at Rocky Point Park over this period. The implications of these findings are that during the summers of 1989–92 meteorological conditions on the synoptic scale were not conducive to the occurrence of ozone exceedances but that the reduction in average daily maximum ozone concentrations cannot be accounted for on the basis of synoptic-scale meteorological variability as parameterized by the component scores.
