Abstract |
Statistical analyses of the human health effects of airborne pollutants based on aggregate population time-series data have often relied on ambient concentrations of pollutants measured at one or more central sites in a given metropolitan area. In the particular case of ground-level ozone pollution, central-site monitoring has been justified as a regional measure of exposure partly on grounds that correlations between concentrations at neighboring sites measured over time are usually high. In analyses where multiple monitoring sites provide ambient ozone concentrations, a summary measure such as an average has thus often been regarded as adequately characterizing the exposure distribution. Indeed, a number of studies have referred to multiple-site averaging as the method for measuring ozone exposure. This report revisits the practice of multiple-site averaging. The results are drawn from an analysis examining simultaneous mapping of population density and ambient ozone concentrations on the scale of a single metropolitan area. Because of the ready availability of data associated with a related research effort, the city selected for this analysis was Phoenix, AZ. |