Countries around the world are expending significant resources to improve air quality, in part, to improve the health of their citizens. Are they improving public health? We consider these issues by tracking the risk of death associated with outdoor air pollution over both space and time in 24 Canadian cities from 1984 to 2000. We propose a multi-year estimator that uses current plus several previous years of data to estimate current year risk. The estimator is derived from sequential time series analyses using moving time windows. The annual average daily concentrations of ozone appeared to be increasing over the 17 year period while those of NO2 are decreasing. Despite decreasing concentrations, public health risks related to NO2 appear to be increasing. Further investigations are necessary to understand why the concentrations and adverse effects of NO2 show opposite time trends.