Title 1s Ozone Nonattainment Program

Ground level ozone, otherwise known as smog, is considered to be the most widespread urban air pollution problem today. It is a highly reactive form of oxygen (O3) that results from a complex set of photochemical reactions that occur when favorable conditions exist in the ambient air. These conditions are based on factors such as temperature and the presence of ozone precursors such as NOX and VOC.

Ozone nonattainment areas are classified based on the severity of the problem. Each classification triggers various requirements that the area must comply with to have an EPA-approved SIP. Figure 15-1 shows ozone nonattainment areas, by classification, in the United States (note that the EPA lists areas by cities, but they extend to a region around these cities). Because the level of stringency for the most severe areas is significantly greater than that for the less affected areas, the timelines for attainment are adjusted by attainment status level. As shown in Table 151, those areas with the most extensive requirements have longer to meet them, however, they must demonstrate each year that they are making reasonable further progress toward meeting the standards. Similar programs exist for areas that fail to meet the NAAQS for carbon monoxide and particulate matter.

Since the passing of the attainment dates for Marginal and Moderate areas, several dozen nonattainment areas have been redesignated to attainment status or are waiting for final decisions from the EPA regarding redesignation

Fig. 15-1 Ozone Nonattainment Areas in United States by Classification. Source: EPA
Table 15-1 Design Values and Attainment Dates for Ozone Nonattainment Area Classifications


Design Values (ppm*)

# of Areas**

Attainment Date



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