HEALTH EFFECTS OF OZONE A Critical Review

Health and pollution control professionals and the general public need to develop a more complete understanding of the health effects of ozone (O3) because: 1) we have been unable to significantly reduce ambient O3 levels using current strategies and controls; 2) in areas occupied by more than half of the U.S. population, current peak ambient O3 concentrations are sufficient to elicit measurable transient changes in lung function, respiratory symptoms, and airway inflammation in healthy people engaged in normal outdoor exercise and recreational activities; 3) the effects of O3 on transient functional changes are sometimes greatly potentiated by the presence of other environmental variables; and 4) cumulative structural damage occurs in rats and monkeys exposed repetitively to O3 at levels within currently occurring ambient peaks, and initial evidence from dosimetry models and interspecies comparisons indicate that humans are likely to be more sensitive to O3 than rats. The extent and significance of these effects, and the multibillion dollar costs of ambient O3 controls need to be considered in any future revisions of ambient standards and the Clean Air Act. The transient effects of O3 are more closely related to cumulative daily exposure than to one hour peak concentrations, and future revisions of the ambient standard for O3 should take this into account. The effects of long-term chronic exposure to O3 remain poorly defined, but recent epidemiologic and animal inhalation studies suggest that current ambient levels are sufficient to cause premature aging of the lungs. More research is needed to determine the need for a standard with a seasonal or annual average concentration limit.