Airtoxics Workshop - comments michael walsh

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

Mobile Source Air Toxics Workshop
Conclusions - Michael Walsh

The presentations, especially those from the State and Local experts make clear that at the present time, toxic emissions from motor vehicles and ambient toxics levels represent a serious health hazard. In fact, comparisons of actual measured levels in ambient air tend to exceed those levels predicted by the EPA models.

The new emissions control programs recently adopted by the US EPA, especially the Tier 2 standards and low sulfur gasoline, and the expected future programs such as stringent heavy duty engine standards combined with low sulfur diesel fuel, should substantially reduce the motor vehicle related toxics risk. However, whether these reductions will be sufficient to eliminate the residual toxics risk is highly uncertain. One reason for this uncertainty is the lack of reliable toxics emissions factors. In some cases, the factors used by EPA seem fundamentally flawed in a systematic way. This concern applies to particulate emissions factors which essentially assume no deterioration in use, an assumption which seems to inherently understate future emissions. Similarly, the assumption of zero deterioration in emissions of all pollutants (including hydrocarbons) from heavy duty vehicles and engines inherently understates the problems.

Other emissions factors from gasoline fueled cars meeting Tier 2 standards are difficult to estimate because the cars are not yet in existence in other than the prototype stage. However, in carrying out a sensitivity analysis to determine the residual risk it seems prudent to carry out a worst case assessment along with the best judgement. Estimating twice the deterioration doesn’t seem to truly reflect worst case. Emission factors for off road vehicles and engines should get a similar worst case assessment. Ultimately the precautionary principle should apply.

Another problem that was raised is the utility of CO as a surrogate for vehicle emissions since CO doesn’t necessarily correlate well with evaporative hydrocarbons, account for reactivity and the secondary transformation of toxics. CO is also an inadequate surrogate for diesel particulate both directly emitted and its physical persistence in the urban environment. Therefore difficult as it may be, it seems worthwhile to at least explore alternative methodologies.

Finally micro environments such as residential garages and within vehicles seem to be important sources of exposure to toxics and deserve greater attention.

Areas which seem especially ripe in terms of future control efforts include both fuels and off road vehicles and engines. Fuel controls have the special advantage of having an immediate impact as soon as implemented compared to vehicle controls which take many years to have their full impact. Retrofit strategies can have similar benefits.

The bottom line recommendation is that EPA should not in its April 28^th proposal or December 22^nd final rules preclude future actions which may turn out to be appropriate as the available data and methodologies improve.

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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"