Fact Sheet OMS-11
Motor Vehicles and the 1990 Clean Air Act
The Clean Air Act of 1970 set a national goal of clean and
healthy air for all. It established the first specific
responsibilities for government and private industry to reduce
emissions from vehicles, factories, and other pollution sources.
In many ways, the far-reaching law has been a great success.
Today's cars, for example, typically emit 70 to 90 percent less
pollution over their lifetimes than their 1970 counterparts.
Despite considerable progress, the overall goal of clean and
healthy air continues to elude much of the country. Unhealthy
air pollution levels still plague virtually every major city in
the United States. This is largely because development and
urban sprawl have created new pollution sources and have
contributed to a doubling of vehicle travel since 1970.
Furthermore, scientists and now the public have become concerned
about previously unrecognized environmental threats such as
global warming, acid rain and air toxics.
With these issues in mind, Congress and the Administration in
1990 amended and updated the Clean Air Act for the first time
since 1977. The 1990 Clean Air Act includes provisions to
further control ground-level ozone (urban smog), carbon
monoxide, and particulate emissions from diesel engines and to
address air toxics and acid rain. Motor vehicles contribute to
all these problems. This fact sheet focuses on the mobile
source provisions of the 1990 law, which together will reduce
most vehicle-related pollutants by more than 40 percent.
The 1990 Clean Air Act - What's New?
The new Clean Air Act strengthens components of the earlier law.
The tailpipe standards for cars, buses, and trucks have been
tightened, and Inspection and Maintenance (I/M) programs have
been expanded to include more areas and allow for more stringent
The 1990 law also introduces several entirely new concepts with
regard to reducing motor vehicle-related air pollution. For the
first time, fuel is considered along with vehicle technology as
a potential source of emission reductions. And more attention
is focused on reducing the growth in vehicle travel. The new
The act mandates that improved gasoline formulations be sold in
some polluted cities to reduce emissions of carbon monoxide or
ozone-forming hydrocarbons. Other programs set low vehicle
emission standards to stimulate the introduction of even cleaner
cars and fuels.
The 1990 Clean Air Act requires the U.S. Environmental
Protection Agency (EPA) to consider emissions from off-highway
vehicles as well as from highway vehicles such as cars and
trucks. The so-called "nonroad" category includes boats, farm
equipment, bulldozers, lawn and garden devices, and construction
machinery. Because nonroad engines have not been previously
regulated for pollution, they can be very dirty. EPA has
determined that emissions from nonroad engines are a significant
source of urban air pollution and is working with industry and
the public to develop effective control strategies.
The law requires the smoggiest cities to limit growth in vehicle
travel by encouraging alternatives to solo driving. In areas
where ozone levels exceed certain criteria, employers of 100 or
more will be asked to find ways to increase the average number
of passengers in each vehicle for commutes to work and during
work-related driving trips.
The 1990 Amendments: The View from the Driver's Seat
Typical drivers will probably not be aware of many vehicle and
fuel changes manufacturers are making in response to the 1990
Clean Air Act, although these changes could add $200 to the cost
of a car and a few cents per gallon to the cost of gasoline.
But there are other programs that drivers will notice,
especially in areas with air pollution problems.
New 1994 and later model cars must be equipped with "onboard
diagnostic systems." These systems feature dashboard warning
lights that alert drivers to malfunctioning emission control
equipment. Controlled by the vehicle's computer, the onboard
diagnostic system must also be capable of storing trouble codes
that help mechanics pinpoint the malfunction.
Another change involves tampering and misfueling. Such
activities have always been discouraged, but were previously
illegal only for commercial operations. "Backyard mechanics"
now are also subject to stiff penalties for deliberate
For drivers in polluted cities, more changes will be apparent.
Some cities will have to start I/M programs to check vehicle
emissions on a regular basis. Areas that already require I/M
testing may have to institute more stringent programs.
A Summary of Some Specific Clean Air Act Programs
Tailpipe (exhaust) standards for cars have been reduced under
the 1990 law. The previous standards of 0.41 gram per mile
(gpm) total hydrocarbons, 3.4 gpm carbon monoxide, and 1.0 gpm
nitrogen oxides have been replaced with standards of 0.25 gpm
nonmethane hydrocarbons and 0.4 gpm nitrogen oxides (the 3.4
gpm standard for carbon monoxide does not change). These
standards will be fully phased in with 1996 models. EPA is
required to study whether even tighter standards are needed,
technologically feasible, and economical. If EPA determines by
1999 that lower standards are warranted, the standards will be
cut in half beginning with 2004 model year vehicles.
Mobile sources are the primary cause of carbon monoxide
pollution in the United States. The 1990 Clean Air Act sets up
two programs to address this problem. For the first time,
carbon monoxide emissions will be regulated at cold
temperatures. Carbon monoxide emissions can be very high in
cold weather because both fuel combustion and pollution control
equipment operate less efficiently in the cold. In the past,
tailpipe standards applied only at 75 ¡F. so manufacturers
optimized emission control equipment for that temperature. The
1990 Clean Air Act requires cars to meet a carbon monoxide
standard at 20 ¡F. The phase-in of a 10 gpm standard began with
1994 models. If, by 1997, carbon monoxide levels are still too
high in six or more cities, the cold temperature emission
standard will drop to 3.4 gpm for 2002 models. The second new
provision involves increasing the oxygen content of gasoline
sold during the winter in cities that exceed national air
quality standards for carbon monoxide pollution. The oxygen
helps reduce carbon monoxide emissions by enhancing fuel
combustion. The wintertime fuel requirements began in 1992.
Ground-level ozone, a primary component of smog, exceeds healthy
levels in cities across the United States. It is our most
serious and persistent air quality problem. A major thrust of
the 1990 Clean Air Act involves reducing urban ozone levels. As
a complement to stricter tailpipe standards, the new law
introduces several programs to minimize pollution from
evaporating gasoline. Evaporative emissions are a major source
of the hydrocarbon compounds that form ground-level ozone.
Devices that trap gasoline vapors from the engine and fuel
system will be improved. In addition, gasoline volatility will
be capped, reducing the propensity for gasoline to evaporate in
the first place.
Most provisions requiring cleaner cars and fuels will
dramatically lower vehicle toxic emissions. In addition, EPA
has completed a study of air toxics emissions and may, if
warranted, regulate emissions of benzene, formaldehyde, and
other toxic air pollutants.
By 1995, all gasoline sold in the country's worst ozone areas
must contain a minimum oxygen content and a maximum benzene
content. Through refining changes that will not be apparent to
motorists, reformulated gasoline will achieve a 15 to 17 percent
reduction in both ozone forming hydrocarbons and toxic emissions
from motor vehicles. By 2000, gasoline sold in these cities
will achieve a 25 to 29 percent hydrocarbon reduction, a 20 to
22 percent toxics reduction, and a 9 to 10 percent reduction in
nitrogen oxide emissions. Many cities have voluntarily chosen
to use this cleaner gasoline.
Beginning in 1993, the diesel particulate standard for urban
buses was reduced by 60 percent, from 0.25 to 0.1 gram per
brake-horsepower per hour (g/bhp-hr).
The standard, which applies to urban transit buses, dropped to
0.07 g/bhp-hr in 1994 and to 0.05 g/bhp-hr in 1996. If
monitoring data show that buses in actual use are not meeting
the standard, EPA must implement a "low-polluting fuels" program
for new buses in large cities. Possible fuels include methanol,
ethanol and compressed natural gas.
Beginning in 1998, 30 percent of new vehicles purchased by
centrally-fueled fleets in certain cities will be required to
use clean fuels and meet tailpipe standards that are lower than
those in place for general passenger cars (0.075 gpm
hydrocarbons, 3.4 gpm carbon monoxide, and 0.2 gram per mile
nitrogen oxides). The purchase requirement will grow to 70
percent by the year 2000. The program, which is intended to
stimulate development of new, low-polluting fuel/vehicle
combinations, will affect 22 metropolitan areas in 19 states
across the country where pollution levels are high.
California Pilot Program
Like the fleets program, the California Pilot program is
designed to encourage production of clean fuels and vehicles.
Beginning in 1996, manufacturers must produce at least 150,000
"clean" cars (capable of meeting a 0.125 gpm hydrocarbon, 3.4
gpm carbon monoxide, and 0.4 gpm nitrogen oxide standard) for
sale in California. The number increases to 300,000 by the year
1999. In 2001, the standards drop to the fleets program
levels. Other states may petition EPA to adopt this program.
Timetable for Selected Mobile Source Provisions
of the 1990 Clean Air Act
Limits on maximum gasoline vapor pressure became law nationwide.
Regulations setting minimum oxygen content for gasoline took
effect in areas where carbon monoxide levels exceed national
Production of vehicles requiring leaded gasoline became illegal.
New standards for sulfur content of diesel fuel took effect,
reducing the maximum sulfur level by 80 percent.
Phase-in of tighter tailpipe standards for light-duty vehicles
Enhanced Inspection and Maintenance programs begin in some
Phase-in of cold temperature carbon monoxide standards for
light-duty vehicles begins.
Trucks and buses must meet stringent diesel particulate emission
New cars must be equipped with on-board diagnostic systems.
Reformulated gasoline provisions take effect in the nation's
smoggiest cities and in other areas that voluntarily join the
New warranty provisions on emission control systems take effect.
Phase-in of California Clean Fuels pilot program begins.
Lead banned from use in motor vehicle fuel.
All new vehicles (1996 model year cars and light trucks) must
meet new tailpipe and cold-temperature carbon monoxide
Clean-fuel fleet programs begin in ozone and carbon
monoxide non-attainment areas in 19 states.
Second phase of the Fleets and California Pilot clean fuels
For More Information:
The Office of Mobile Sources is the national center for research
and policy on air pollution from highway and off-highway motor
vehicles and equipment. You can write to us at the EPA National
Vehicle and Fuel Emissions Laboratory, 2565 Plymouth Road, Ann
Arbor, MI 48105. Our phone number is (313) 668-4333.