Airtoxics Workshop - comments bob sawyer

The Health Effects Institute
"A Partnership of the U.S. Environmental Protection Agency and Industry"

HEI-EPA WORKSHOP ON MOBILE SOURCE AIR TOXICS: EXPOSURE AND RISK
8 February 2000
Washington, D.C.

Perspective of the Respondent, Robert F. Sawyer, Professor of the Graduate School, University of California at Berkeley, and Member of the Health Effects Institute Research Committee

Establishing the risk to the public of mobile source air toxics suffers from a number of uncertainties. The magnitude of both on-road and off-road mobile source toxics emissions, or the carbon monoxide emissions to which they are methodologically tied, is uncertain, perhaps by a factor of two or more. The use of ambient CO as a surrogate for mobile source emissions introduces additional uncertainties in that neither evaporative hydrocarbons nor tailpipe particulates (largely from diesel engines), both important sources of toxics, are related to the tailpipe emissions from gasoline engines. Potencies for many of the toxics are similarly uncertain, by a factor of 10 or more. Toxics additional to those being considered, for example non-diesel particulates and higher aldehydes, may also be important. Uncertainties in future emissions and exposures come from growth projections and predicting the effectiveness of control measures.

The very complex models employed to estimate exposure are inconsistent with the sparse data upon which they are based. Future efforts should focus on ambient and personal exposure measurements for the most important toxics. Uncertainties notwithstanding, mobile sources appear to dominate air toxics. Fortunately, control programs now in place for ozone precursors and particulates are effective in reducing mobile source air toxics. Further reduction of benzene is anticipated through reducing gasoline benzene levels and capping aromatics. Reduction of formaldehyde will result from the recommended reduction in the use of methyl tertiary butyl ether (MTBE) as a fuel additive. Secondary formaldehyde will be reduced by the same controls that reduce ozone. It should be anticipated that an increase in the use of ethanol will increase ambient acetaldehyde. Reducing mobile source air toxics is not the sole responsibility of the USEPA. The states have an important role in the development of effective inspection and repair programs to address in-use vehicle emissions problems. They also can adopt federal reformulated gasoline and can further regulate fuels as may be effective in their particular states.

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The Health Effects Institute "A Partnership of the U.S. Environmental Protection Agency and Industry"

The Health Effects Institute
"A Partnership of the U.S. Environmental Protection Agency and Industry"