Results from controlled laboratory exposures of human volunteers (Hazucha et al., 1992; Adams (2003, 2006) indicate that higher ozone hourly average concentrations elicit a greater effect on hour-by-hour physiologic response (i.e., forced expiratory volume in 1 s [FEV1]) than lower hourly average values, which implies a nonlinear dose-response relationship. The current 8-h average human health ozone standard is not adequate for describing this nonlinear FEV1 hour-by-hour pattern of response. For developing a consistent standard to protect human health, it is important to identify those ambient-type concentration patterns that elicit adverse human health effects (Hazucha and Lefohn, 2007).

The three scientific experiments, whose results were used to develop the 1997 form of the 8-h average 0.08 ppm ozone standard, were based on constant concentration exposures (US EPA, 2006). These types of ozone exposures do not occur under realistic ambient conditions. Multiple-hour constant exposures (i.e., 0.12, 0.10, and 0.08 ppm) occur very infrequently under ambient conditions (Lefohn and Foley, 1993; Rombout et al., 1986; Plopper et al., 2000; US EPA, 2006). For additional information on variable concentration exposures that occur under ambient conditions, please click here.

Because of the problems associated with the "piston effect", it is highly possible that the lower and lower 8-hour standards promulgated by the EPA may never be met consistently in many areas of the United States. During cool, wet periods, the standard will be met. During hot, dry periods, the standard may be violated at some sites if the 8-hour standard continues to be lowered much below the 0.070 ppb level.

Our research is actively continuing to carefully evaluate the research results associated with the controlled human health laboratory studies. A.S.L. & Associates and its team of research collaborators is working to identify a much more relevant form of the human health standard that will overcome the inconsistency problems associated with the use of the 8-hour averaging form of the current ozone standard.

Referernces

Adams, W. C. (2003) Comparison of chamber and face mask 6.6-hour exposure to 0.08 ppm ozone via square-wave and triangular profiles on pulmonary responses. Inhalation Toxicology 15: 265-281.

Adams, W. C. (2006). Comparison of Chamber 6.6-h Exposures to 0.04 - 0.08 ppm Ozone Via Square-Wave and Triangular Profiles on Pulmonary Responses. Inhal Toxicol. Inhalation Toxicology 18, 127-136.

Hazucha, M. J.; Folinsbee, L. J.; Seal, E., Jr. (1992) Effects of steady-state and variable ozone concentration profiles on pulmonary function. Am. Rev. Respir. Dis. 146: 1487-1493.

Hazucha, M. J.; Lefohn, A. S. (2007) Nonlinearity in Human Health Response to Ozone: Experimental Laboratory Considerations. Atmospheric Environment. 41:4559-4570.

Lefohn, A.S., Foley, J.K., 1993. Establishing ozone standards to protect human health and vegetation: exposure/dose-response considerations. Journal of the Air Waste Management Association 43 (2), 106-112.

Plopper, C.G., Paige, R., Schelegle, E., Buckpitt, A., Wong, V., Tarkington, B., Putney, L., Hyde, D., 2000. Time-response profiles: implications for injury, repair and adaptation to ozone. In: Heinrich, U., Mohr, U. (Eds.), Relationships Between Acute and Chronic Effects of Air Pollution. ILSI Press, Washington, DC, pp. 23-37.

Rombout, P.J.A., Lioy, P.J., Goldstein, B.D., 1986. Rationale for an eight-hour ozone standard. Journal of Air Pollution Control Association 36 (8), 913-917.

US Environmental Protection Agency, US EPA, 2006. Air quality criteria for ozone and related photochemical oxidants. Report Nos. EPA/600/R-05/004af, Office of Research and Development, Research Triangle Park, NC, February 2006.