Mobile Source Air Pollution Control
| Author | Arnold W. Reitze, Jr. |
| Pages | 321-375 |
Page 321
Chapter 11:
Mobile Source Air Pollution Control
§1. Introduction
In 1970, the present era of a ir pollution control
commenced when Congress provided for atmo-
spheric national ambient air quality standards
(NAAQS)1 that are established for six criteria pol-
lutants: (1) particulate matter with a diameter of 10
microns or less (PM10) and particulate matter with
a dia meter of 2.5 microns or less (PM2.5); (2) su l-
fur d ioxide (SO2); (3) carbon monoxide (CO); (4)
nitrogen dioxide (NO2); (5) ozone; and (6) lead.2
In addition, volatile organic compounds (VOCs)
and nitrogen oxides (NOx) are regulated as ozone
precursors.3 Criteria pollutants and their precur-
sors are controlled to reduce atmospheric concen-
trations of these regulated pollutants in order to
achieve the NA AQS. e program is administered
by the U.S. Environmental Protection A gency
(EPA or “the Agency”), but it is primarily a pro-
gram implemented by the states.4 EPA uses the
threat of sanctions to force each state to develop
a state implementation plan (SIP) detailing the
process by which it intends to control emissions
of criteria pollutants and their precursors.5 Clean
Air Act (CAA) §110 mandates the use of SIPs to
control stationar y source s, transportation sources,
and other sources of emissions to the extent neces-
sary to meet the NAAQS.6 EPA must approve each
SIP, and it retains jurisdiction to impose federal
requirements or penalties if a state fails to perform
its duties under the CAA .7
1. Clean Air Act (CAA) Amendments of 1970, Pub. L. No. 91-604,
§4, 84 Stat. 1678 (codied as amended at 42 U.S.C. §7408,
§7409, CAA §108, §109).
2. 40 C.F.R. §§51.4- .12.
3. See, e.g., 42 U.S.C. §7511a(b)(1), (f), CAA §182(b)(1), (f ).
4. Id.§§7401-7515, CAA §§101-193.
5. See, e.g., id. §7509, CAA §179(b).
6. Id. §7410, CAA §180.
7. Id. §7410(k) & (m), CAA §110(k) & (m).
One signicant exception to t he reliance on
the state for implementation of the CAA is the
program designed to control emissions from new
motor vehicles based on the provisions of Subchap-
ter II of the CAA.8 Since 1967 the federal gov-
ernment has preempted the control of emissions
from new motor vehicles. ere is an exception in
§209(b) for California that waives the application
of federa l law if California’s standards will be “at
least as protective of public health and welfare as
applicable federal standards.”9 Congress enacted
a four-pronged approach to control air pollution
from motor vehicles in the CA A Amendments of
1970,10 wh ich, with numerous modications, stil l
persists after the Act’s subsequent amendments.11
e major mobile source progra m regulates motor
vehicle manufacturers in order to limit emissions
from new engines and vehicles.12 Other CAA pro-
grams regulate fuels and fuel additives in §211;
provisions in §182(c)(3) regulate emissions from in-
use vehicles; and §176(c) imposes tra nsportation-
planning requirements. is chapter discusses the
requirements for new light-duty and heavy-duty
engines and vehicles. It also discusses other pro-
grams under Subchapter II: the regulation of emis-
sions from nonroad engines, locomotives, ships,
and aircraft.
e major regulated pollutants emitted from
motor vehicles are CO, NOx, and hydrocarbons
(HCs).13 Some HC controls are in the form of con-
trols on nonmethane hydroca rbons (NMHCs), or
8. Id. §§7521-7590, CAA §§202-250.
9. Id. §7543, CAA §209.
10. Pub. L. No. 91-604, 84 Stat. 1676 (1970).
11. See generally Arnold W. Reitze Jr., e Legislative History of U.S.
Air Pollution Control, 36 H. L. R. 679 (1999).
12. 42 U.S.C. §§7521-7543, 7547-7590, CAA §§202-209, 213-250.
13. Id. §7521, CAA §202. See generally D.J. P N.A.
H, E F C E T
C ().
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
regulated.16
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).
15. Id.
§51.100(s). Diesels are discussed infra §6(g).
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/
nata1999/natanalfact.html.
20. D ., supra note 17, at 11-5, tbl. 11.4.
21. Id.
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%
in 2006.26
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.
30. Id.
31. Id.
32. Id. at 2-1.
33. Id. at 3-9, tbl. 3.6.
Mobile Source Air Pollution Control Page 323
in exhaust emissions per VMT achieved through
the use of a ir pollution controls. Nevertheless,
improvements in overall emissions from highway
vehicles were made while annua l VMT increased
because the eectiveness of control tech nology
exceeded the impact of VMT growth.
In 1970, there were 89.243 million automo-
biles and 18.797 million trucks in use in the
United States; in 2006 the number had increased
to 135.400 mil lion automobiles and 107.944 mil-
lion trucks.34 In 2007, 14,870 million light-duty
vehicles were sold in the United States; 50.9% were
cars, and 49.1 were light-duty trucks and sport
utility vehicles (SUVs).35 Large SUVs accounted for
0.6% of light-duty vehicle sales in 1975 and 23.4%
in 2006.36 e increased use of trucks and SUVs
results in higher emissions, and because of lower
fuel economy f rom light-duty trucks and SUVs,
CO2 emissions are higher.
§2. Vehicle Emission Control
Technology
Emissions from motor vehicles t hat lack air pol-
lution controls include crankca se vapor releases,
evaporative losses, and exhaust gas emissions.37
Prior to MY 1968, when emissions were not lim-
ited by the CA A, an estimated 55% of the vehicu-
lar HCs came from exhaust gas emissions, 26%
came from cra nkcase blow-by, and 18% resulted
from evaporation losses.38 Other sources of data in
the 1970s commonly used a 60-20-20% division.39
However, evaporative losses were probably under-
estimated. Nearly all the CO and NOx are emitted
in the exhaust ga s.40
§2(a). Crankcase Emissions
In a vehicle without any emission controls, crank-
case vapors primarily consist of HC from unburned
fuel.41 When f uel burns in t he cylinder of an
34. Id. at 3-5, tbl. 3.3 (based on Federal Highway Administration
data).
35. Id. at 4-8, tbl. 4.8.
36. Id. at 4-9, tbl. 4.9.
37. F G ., T A R
I I E 119 (1974).
38. Id.
39. See, e.g., D I. S., CSU, M V
E C B F: F E C
S 4-7 (1977).
40. E F. O, I C E A
P 368 (1973).
41. B F: F E C S, supra note
39, at 4-7.
engine, some fuel and exhaust gases compressed by
the piston escape as “blow-by” a round the pistons
into the crankcase. As an engine ages, cylinder and
piston ring wear causes blow-by to increase. Blow-
by is controlled by directing it from the crankcase
to the engine intake using a positive crankcase ven-
tilation (PCV) va lve to control the ow. When the
engine is not running, the vapors remain in the
crankcase. When the engine runs, it provides vac-
uum that opens the PCV valve, allowing the vapors
to move to the engine’s intake where they combine
with the air and f uel mixture and are burned in
the engine.42 Modern vehicles use a charcoal-lled
canister to store vapors until the PCV valve opens
to allow vapors to be combusted. Crankcase emis-
sions have been controlled on California vehicles
since 196143 and on most U.S. automobiles manu-
factured after 1962.44 ey have been eectively
controlled nationwide since MY 1968 by a “closed”
PCV system, which is used a lmost universally.45
§2(b). Evaporative Hydrocarbon Losses
During refueling, evaporative HC losses occur that
can be controlled by vapor recovery devices at the
gasoline station’s pump or with an “onboard” sys-
tem insta lled in the vehicle.46 To control evapora-
tive losses at gas stations when their tanks are lled
from tank trucks involves the u se of devices called
Stage I vapor recovery. Devices to control evapora-
tive losses during the fueling of customers’ vehi-
cles are called Stage II vapor recovery. Evaporative
losses a lso c ome from parked vehicles t hat relea se
HC vapors from the fuel tank hoses, gaskets, the
fuel injector system, and from other components
of the fuel system. e highest losses occur during
the period of “hot soa k,” which is the time follow-
ing a n eng ine shutdown until it cools to ambient
temperature.47
Running losses (losses that occur while the
vehicle is operating ) occur because heated fuel
vaporizes and escapes from the fuel tan k and
associated fuel lines when heated by engine and
42. D I. S., CSU, M V E-
C B O: P C V
S 1-10 (1977).
43. Id. at 1-9.
44. Id.
45. Id. at 1-17.
46. 42 U.S.C. §§7511a(b)(3) & 7521(a)(6), CAA §§182(b)(3) &
202(a)(6).
47. T P D’, M F, V
E C S, V , (1977).
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