Impact of climate change on ozone pollution in the lower Fraser Valley, Canada

Assuming current emissions and background concentrations, we investigate how changes in synoptic meteorology alone affect ozone episodes in the Lower Fraser Valley, Canada, in future climates. We perform synoptic typing of combined sea level pressure and 500 hPa geopotential heights for June to September 1961- 2000 using the National Centers for Environmental Prediction (NCEP) reanalysis data. Five clusters provide a qualitatively good representation of typical synoptic conditions and stratify exceedance days into one cluster with more than half of all exceedances. Independent cluster analyses for climate model output from the Third Generation Coupled Global Climate Model (CGCM3.1 T63) 1961-2000 control runs and 2046-65 Special Report on Emissions Scenarios (SRES) A1B scenario runs give clusters qualitatively similar to those using NCEP data. When CGCM output is mapped to the NCEP clusters, the CGCM control run cluster frequencies are almost identical to NCEP frequencies, while CGCM 2046-65 output shows only small frequency changes. This indicates that, in future climates, the frequency of occurrence of synoptic types conducive to ozone exceedances will not be appreciably different than they are in the present climate. However, the CGCM predicts substantial increases in daily maximum temperatures in the Lower Fraser Valley across all five clusters. An analysis of exceedance probabilities suggests that the predicted temperature increase will more than double the number of exceedance days per year.