PROJECTION OF HEALTH BENEFITS FROM AMBIENT OZONE REDUCTION RELATED TOTHE USE OF METHYL TERTIARY BUTYL ETHER (MTBE) IN THE REFORMULATED GASOLINE PROGRAM

To estimate potential public health benefits from ozone (O-3) pollutio n reduction attributable to the use of methyl tertiary-butyl ether (MT BE) in gasoline, O-3 dose-response estimates from the biomedical liter ature were combined with model estimates of O-3 reduction. Modeling em ployed EPA MOBILE5a and Complex models to predict emission changes, in dustry AQIRP techniques to predict ambient O-3 changes, and the Nation al Exposure Model to predict human exposures. Human health effects con sidered were lung function decrements and respiratory irritant symptom s (using dose-response functions measured in laboratory and field stud ies), and increased death rates (using concentration-response function s inferred statistically from public-health data). Other reported heal th effects, such as lung inflammation, increases in asthma attacks, an d hospitalizations, were not addressed because of inadequate dose-resp onse information. Even for the health responses considered, quantitati on of improvements due to MTBE use is problematical, because MTBE affe cts only a small percentage of existing O-3 pollution, and because exp osure-response relationships are not well understood for population su bgroups most likely to be affected. Nevertheless, it is reasonable to conclude that even small MTBE-associated reductions in peak ambient O- 3 levels (1-5 ppb, according to model estimates) should yield consider able public health benefits. Tens of millions of Americans are potenti ally exposed to O-3 in the concentration range associated with health effects. Even if only a small percentage of them are susceptible, any incremental reduction in O-3 (as with MTBE use) must mitigate or preve nt effects for a meaningful number of people. Better quantitative esti mates of benefit must await a more detailed understanding of each link in the chain of causation.