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
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
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.
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
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.