Regulation of Fuels and Fuel Additives: Renewable Fuel Standard ...

increase in ambient ozone levels is roughly twice as high, or 0.250-0.268 ppb. This
increase represents about 0.32 percent of the standard.
There are a number of important caveats concerning these estimates. First, the
emission effects of adding ethanol to gasoline are based on extremely limited data for
recent vehicles and equipment. Second, the Ozone RSM does not account for changes in
CO emissions. As shown above, ethanol use should reduce CO emissions significantly,
directionally reducing ambient ozone levels in those areas where ozone formation is
VOC-limited. (Ozone levels in areas which are NOx-limited are unlikely to be affected
by a change in CO emissions.) The Ozone RSM also does not account for changes in
VOC reactivity. With additional ethanol use, the ethanol content of VOC should
increase. Ethanol is less reactive than the average VOC. Therefore, this change should
also reduce ambient ozone levels in a way not addressed by the Ozone RSM, again in
those areas where ozone formation is predominantly VOC-limited.
Moving to health effects, exposure to ozone has been linked to a variety of
respiratory effects including premature mortality, hospital admissions and illnesses
resulting in school absences. Ozone can also adversely affect the agricultural and
forestry sectors by decreasing yields of crops and forests. Although the health and
welfare impacts of changes in ambient ozone levels are typically quantified in regulatory
impact analyses, we do not evaluate them for this analysis. On average, the changes
ambient ozone levels shown above are small and would be even smaller if changes in CO
emissions and VOC reactivity were taken into account. The increase in ozone would
likely lead to negligible monetized impacts. We therefore do not estimate and monetize
ozone health impacts for the changes in renewable use due to the small magnitude of this
change, and the uncertainty present in the air quality modeling conducted here, as well as
the uncertainty in the underlying emission effects themselves discussed earlier.
2. Particulate Matter
Ambient PM can come from two distinct sources. First, PM can be directly
emitted into the atmosphere. Second, PM can be formed in the atmosphere from gaseous
pollutants. Gasoline-fueled vehicles and equipment contribute to ambient PM
concentrations in both ways.
As described above, we are not currently able to predict the impact of fuel quality
on direct PM emissions from gasoline-fueled vehicles or equipment. Therefore, we are
unable at this time to project the effect that increased ethanol use will have on levels of
directly emitted PM in the atmosphere.
PM can also be formed in the atmosphere (termed secondary PM here) from
several gaseous pollutants emitted by gasoline-fueled vehicles and equipment. Sulfur
dioxide emissions contribute to ambient sulfate PM. NOx emissions contribute to
ambient nitrate PM. VOC emissions contribute to ambient organic PM, particularly the
portion of this PM comprised of organic carbon. Increased ethanol use is not expected to
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