An alternative form and level of the human health ozone standard

Controlled human laboratory studies have shown that there is a disproportionately greater pulmonary function response from higher hourly average ozone (O3) concentrations than from lower hourly average values and thus, a nonlinear relationship exists between O3 dose and pulmonary function (FEV1) response. The nonlinear dose-response relationship affects the efficacy of the current 8-h O3 standard to describe adequately the observed spirometric response to typical diurnal O3 exposure patterns. We have reanalyzed data from five controlled human response to O3 health laboratory experiments as reported by Hazucha et al. (1992), Adams (2003, 2006a, 2006b), and Schelegle et al. (2009). These investigators exposed subjects to multi-hour variable/stepwise O3 concentration profiles that mimicked typical diurnal patterns of ambient O3 concentrations. Our findings indicate a common response pattern across most of the studies that provides valuable information for the development of a lung function (FEV1)-based alternate form for the O3 standard. Based on our reanalysis of the realistic exposure profiles used in these experiments, we suggest that an alternative form of the human health standard, similar to the proposed secondary (i.e., vegetation) standard form, be considered. The suggested form is an adjusted 5-h cumulative concentration weighted O3 exposure index, which addresses both the delay associated with the onset of response (FEV1 decrement) and the nonlinearity of response (i.e., the greater effect of higher concentrations over the mid- and low-range values) on an hourly basis.