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Explanation of Ozone Maps

The ozone air pollution maps shown on this website are the result of obtaining the most recent, or real-time, measurements of ground-level ozone in the Tucson metropolitan area. Several ozone monitors, described as a monitoring network, are situated within the Tucson metropolitan area and continuously provide measurements of hourly-averaged ground-level ozone. These hourly-averaged ozone measurements are then promptly transferred to a central computer where the data are used to generate ground-level ozone maps.

Each monitor in Tucson's ozone monitoring network is only truly representing its local vicinity. However, the measurements obtained from each location can be representative of more than a single geographic location found in a metropolitan area over the same time period (e.g. 10-11 a.m.). For example, a monitor located some distance from air pollution sources (e.g. busy roadways, built-up urban areas, industrial sectors) is likely to represent ozone concentrations that would be observed in other (unmeasured) locations also some distance from air pollution sources. Similarly, a monitor located nearby busy urban areas with elevated traffic emissions is likely to represent ozone concentrations that would be observed at other busy urban areas. Thus, it is feasible to take measurements from a monitor and use these measurements to estimate ozone at another location, given that both locations are similar with respect to geographic air pollution factors such as proximity to air pollution sources, prevailing wind direction and topography. Therefore, in making these maps the geography of the Tucson metropolitan area is used to generate estimates of ground-level ozone concentrations nearby and some distance from actual monitor locations.

Since the geography of Tucson can be used to create estimates of ozone concentrations at locations where measurements are not regularly taken, a model was developed to relate real-time ozone measurements to the local geography of the monitors in Tucson's network. The model was developed with a statistical tool called regression, and allows the prediction of ozone concentrations by knowing the local geography of locations where ozone measurements are not taken. Several years (1995-1998) of hourly-averaged ozone data were used to 'train' the model, developing statistical relationships between local geography and measured ozone concentrations. Once the model is adequately trained, it is able to provide a continuous surface (i.e. a map) of estimates of ground-level ozone across the Tucson metropolitan area, given that the important geographic factors are available for each and all locations where estimates are to be made.

With real-time ozone data available from several monitors, the statistical model is capable of generating real-time ozone maps for the Tucson metropolitan area. The ozone pollution maps on this web page are the result of the availability of real-time data, as well as a model that is capable of utilizing this data. Without these two ingredients, Tucson's ozone data would not be available in a mapped format or as current, updated ozone pollution information.

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