Ground-level ozone causes significant health impacts, including increased mortality and respiratory distress. The target level for this category in the 2008 EPI is an ozone exposure limit of 85 parts per billion (ppb). This is based on the established United States EPA standard (EPA 2007).
Ideally, people should not be exposed to any ozone concentration above the target level selected. Therefore, we calculated the indicator by multiplying the level of exposure that exceeded the target in any one hour by the population exposed (all values for the year 2000). Countries exceeding the target level received raw data values above zero. Since zero represented the target, a positive score in the raw data translated into a lower category score. Scores vary, however, based on the percent of population affected by exposure.
