Page 322 Air Pollution Control and Climate Change Mitigation Law
VOCs that are chemically reactive HCs. VOCs
and NOx react in the presence of sunlight to pro-
duce photochemical oxidants.14 Photochemical
oxidants, which include ozone and a myriad of
less easily identiable air pollutants, are commonly
known as smog. Photochemical oxidants are nor-
mally expressed as concentrations of ozone.15 PM
from light-duty and heav y-duty trucks also is
In 2006, transportation sources in t he United
States were responsible for a large percentage of the
nation’s total emissions, including 77.6% of the CO
emissions, 58.3% of the NOx, 35.5% of the VOCs,
2.6% of the PM10, 9.0% of the PM2.5, 4.5% of the
SO2 emissions, and 8.1% of ammonia.17 From
1970 to 2006, CO emissions from transportation
sources in the United States decreased by 55.4%,
VOCs decreased by 75.9%, and NOx from the
transportation sector decreased 30.5% from 1970
to 2005.18 Mobile sources are responsible for emis-
sions of many hazardous air pollutants (HAPs).
Benzene is the toxic that poses the greatest risk of
cancer; 49% comes from onroad sources, and 19%
is released by nonroad sources. Acrolein is the most
signicant noncancer threat to public health; 14%
comes from onroad sources, and 11% comes from
onroad mobile sources.19 Haz ardous pollutants
from motor vehicles are discussed below in §4(d).
Transportation sources accounted for 31.75 %
of the United States carbon dioxide (CO2) emis-
sions from fossil fuel consumption in 2006.20 CO2
emissions are considered to be the most impor-
tant greenhouse gas (GHG) emitted in the United
States.21 Emissions estimates for CO2 were 5,934.4
million metric tons (mmts) in 2006. Methane, the
second most common GHG emission by weight,
had 605.1 mmts emitted, but only 4.8 mmts were
from transportation sources.22 Each gallon of gaso-
line used by a motor vehicle results in the release
of about 20 pounds (lbs.) of CO2 (containing 5.47
14. T F Y, E C: E
C E P 328 (1999).
17. S C. D ., T E D B
12-2, tbl. 12.1 (27th ed. 2008) [hereinafter D .].
18. Id. at 12-4, tbl. 12.3, 12-5, tbl. 12.4, 12-7, tbl. 12.6 (calculated
from the data).
19. U.S. EPA, N S A T A :
E E, C, R: T
F S (2006), available at http://www.epa.gov/ttn/atw/
20. D ., supra note 17, at 11-5, tbl. 11.4.
22. Id. at 11-4, tbl. 11.3.
lbs. of carbon) into the atmosphere.23 From 1990
to 2006, carbon emissions from United States
transportation sources have increased from 1,582.6
mmts to 1,990.1 mmts.24 However, this tonnage
increase represents an increase in the world’s overall
CO2 emissions of about 1.5% over the same period
of time.25 e worldwide contribution of emissions
of global warming gases from motor vehicles is far
more dramatic. Since 1950, the number of automo-
biles has increased worldwide from about 53 mil-
lion to more than 635 million in 2006, which has
resulted in a decrease in the U.S. percentage of the
world’s automobiles from 76.0% in 1950 to 21.3%
e fuel economy of automobiles for the model
year (MY ) 2007 average 31.0 miles per gallon
(mpg), but MY 2007 light-duty truck s average
22.9 mpg.27 Fossil fuels used for transportation
in the United States increa sed from 8.38 quadril-
lion British thermal units (or “quads”) in 195028
to 18.6 quads in 1973, and then increased to 19.8
quads in 1977 and 22.6 quads in 1990.29 In 2007,
the a mount of fossil fuels used for transportation
had climbed to 29.0 quads.30 is is an increase
in energ y use by the transportation sector for the
1973 to 2007 period of 1.3% per year; from 1997-
2007 the annual increase was 1.6%.31 Transporta-
tion accounted for 28.5% of the energy used in the
United States in 2007, and 95.1% of this energy
came from petroleum.32
Motor vehicles used in the United States today
emit signicantly less pollution per mile traveled
than did the vehicles of the 1960s. However, since
the 1970 CAA Amendments were enacted, annual
vehicle mi les traveled (V MT) increased from
slightly more than 1.10 trillion miles to more tha n
3.014 trillion miles in 2006.33 is increase in the
use of motor vehicles helped nullif y the reductions
23. Gasoline has a density of .79 that of water. us, a gallon of
gasoline weighs 6.32 lbs. Gasoline is primarily carbon and hy-
drogen with approximately 86.6% composed of carbon. is
amounts to 5.47 lbs. of carbon per gallon. When this carbon
combines with oxygen, the carbon produces approximately 20
lbs. of CO2 because the carbon in CO2 accounts for only 27%
of the weight of CO2.
24. D ., supra note 17, at 11-6, tbl. 11.5.
25. Id. at 11-2, tbl. 11.1.
26. Id. at 3-2, tbl. 3.1.
27. Id. at 4-18, tbl. 4.17, 4-19, tbl. 4.18.
28. C E Q, E
Q, 18th & 19th A R 301 (1989)
29. D ., supra note 17, at 2-3, tbl. 2.1.
32. Id. at 2-1.
33. Id. at 3-9, tbl. 3.6.