Measuring regional trends in ozone

We model maximum daily ozone concentration at a number of sites in Ontario in terms of weather classes, temperature, season and a moving average error term. In an effort to detect a regional trend in the remaining residuals, we develop a method related to principal components which obtains the linear combination of sites with greatest autocorrelation. We apply this method to data from sites in Southern Ontario and conclude that there was a regional trend in ozone during the period 1980–1992. A similar treatment does not find a general trend in temperature data but does reveal a widening gap in temperature between northern and southern sites.