Urban Air Pollution - Air Pollution and Global Warming: History, Science, and Solutions - page 97

acetaldehyde, and formaldehyde are the major carcino-
gens of concern from both gasoline and E85 exhaust.
Generally, at room temperature, E85 increases acetalde-
hyde significantly and formaldehyde to a lesser extent
butreduces benzene and 1,3-butadiene. When the pop-
ulation distribution and actual emissions at room tem-
perature throughout the United States are accounted for,
the net effect of cancer risks due to E85 and gasoline
are similar (Jacobson, 2007). However, Table 4.5 shows
that at low temperature, emissions of all four carcino-
gens increase for E85 relative to gasoline (Ginnebaugh
et al., 2010). Because emissions occur in reality across
the entire temperature range rather than at room temper-
ature alone, E85 increases the overall cancer risk com-
pared with gasoline. However, the cancer risks of both
gasoline and E85 are much higher than are those from
battery electric or hydrogen fuel cell vehicles (Chapter
13) and much lower than the ozone mortality effects
associated with either gasoline or E85 (discussed next).
Table 4.5 shows that E85 decreases nitrogen oxide
but increases organic gas emissions relative to gasoline.
Much of the additional organic gas emissions due to
E85 is in the form of unburned ethanol and acetalde-
hyde. The upper triangle of the ozone isopleth in Figure
4.12 indicates that, when NO x (g) is high relative to
ROGs (e.g., in Los Angeles or along the east coast of
the United States), both a decrease in NO x (g) and an
increase in ROGs independently increase ozone. This
suggests that a conversion from gasoline to E85 should
increase ozone in the Los Angeles Basin. Figure 4.14a
supports this supposition with a computer model sim-
ulation for 2020, in which all gasoline vehicles are
converted to E85 vehicles and emissions are at room
temperature in both cases. Such a conversion increases
ozone in the basin, a result consistent with expectations
from the isopleth. The conversion to E85 also increases
ozone-related mortality, hospitalization, and asthma by
about 9 percent in Los Angeles. If cold temperature
emissions, which apply at night and early morning and
in the winter, are considered, ozone increases further
due to E85.
Forregion where forests emit significant ROGs, such
as in the southeast United States, the ratio of ROGs to
NO x (g) is high, and ozone is governed by the lower
triangle of the isopleth in Figure 4.12. In such cases, a
decrease in NO x (g) (which occurs with E85 vs. gaso-
line) should decrease ozone, and an increase in ROGs
should have little impact on ozone. Indeed, the com-
puter simulation results in Figure 4.14b indicate that a
conversion to E85 might decrease ozone slightly in the
southeast United States. However, most populated areas

Table 4.5. Percent difference in emissions of several
chemicals between E85 and gasoline near room
temperature and at low temperature

22 ◦ C 7 ◦ C Substance −

Nitrogen oxides − 38 − 21

Carbon monoxide + 1 + 94

+ +

Nonmethane hydrocarbons 14 133

− −

Benzene 65 15

1,3-Butadiene − 66 − 0.3

Acetaldehyde + 4,500 + 8,200

Formaldehyde + 125 + 204

Sources :Ginnebaugh et al. (2010), citing data from Westerholm
et al. (2008) for nitrogen oxides and carbon monoxide averaged
overtwo vehicles, a Saab 9-5 biopower and a Volvo V50 flex
fuel vehicle run on E85 versus E5, and data from Whitney and
Fernandez (2007) for the remaining emissions averaged over
three vehicles, a 2007 Chevrolet Silverado, a 2006 Lincoln Town
Car, and a 2006 Dodge Stratus, each run on E85 at 22 ◦ CbutE70
at − 7 ◦ C.

4.3.8. Ethanol versus Gasoline Effects
on Air Pollution and Health
Current ethanol fuel blends used in vehicles range from
E6 (6 percent ethanol fuel, 94 percent gasoline) to E100
(100 percent ethanol fuel). However, in the United
States and many countries, 100 percent ethanol fuel
really contains 95 percent ethanol and 5 percent gaso-
line added as a denaturant ,which is a poisonous or
untasteful chemical added to a fuel to prevent people
from drinking it.
Many vehicles today are designed for the use of E85 ,
which is effectively 81 percent ethanol and 19 percent
gasoline due to the presence of the denaturant in the
fuel. An important question is whether the use of E85
or other blends of ethanol improve or exacerbate air pol-
lution and global warming relative to gasoline vehicles
or other vehicles, such as battery electric or hydrogen
fuel cell vehicles. These issues are discussed at length in
Chapter 13; however, a comparison of the air pollution
and health effects of vehicles powered by E85 versus
gasoline is given here.
The primary by-products of E85 combustion in
avehicle include unburned ethanol, acetaldehyde,
formaldehyde, methane, nitrogen oxides, and carbon
monoxide. Table 4.5 compares the percent change
in emissions of several important pollutants between
E85 and gasoline vehicles from data at two tempera-
tures. Among the chemicals, benzene, 1,3-butadiene,