Automobiles and the Environment
Automobiles affect the environment in many ways.
Impacts begin when a vehicle is manufactured (including the production
of all the parts and materials that go into the car) and end with
its scrappage in a junkyard (which can recycle many parts but also
involves the disposal of many wastes). Over the life of an average
motor vehicle, however, much of the environmental damage occurs
during driving and is greatly associated with fuel consumption.
Over the dozen or so years of a vehicle's life, nearly 90 percent
of lifecycle ("cradle to grave")
greenhouse gas production for a typical automobile is due to fuel
Environmental impacts start with mineral extraction and the production
of the raw materials that go into the parts of a car. For example,
iron ore gets turned into steel, which now accounts for most of the
mass in vehicles. Steel can be recycled, of course. On average, today's
automobiles are about 75 percent recyclable, and using recycled steel
helps reduce energy use and pollution. Other metal components, such
as aluminum (used in some engine parts and wheels, for example) and
copper (used for wiring) are also largely recycled. The lead and
acid in batteries are poisonous and dangerous. But batteries can
be recycled, if they are returned to a service station, a parts store,
or brought to a municipal hazardous waste facility. Plastics, which
are mostly made from petroleum, are more difficult to recycle. In
any case, some degree of pollution is associated with all of these
components, much of it due to the energy consumption, air pollution,
and releases of toxic substances that occur when automobiles are
manufactured and distributed.
Most of the environmental impact associated with motor vehicles
occurs when they are used, due to pollution in their exhaust and
pollution associated with supplying the fuel. In the United States,
nearly all of today's automobiles use gasoline; a lesser number use
diesel fuel. In some areas, various alternative fuels are being introduced,
but these are not widely available for most drivers. When gasoline,
diesel, or other fuels are burned in car engines, combustion is never
perfect, and so a mix of hazardous pollutants comes out the tailpipe.
If combustion were perfect and didn't create
noxious by-products, the exhaust would contain only water vapor
and carbon dioxide. Carbon dioxide (CO2) isn't directly harmful
to health, at least not in low concentrations. After all, CO2 is
also what we exhale after "burning" the
calories in the food we eat. However, CO2 from fossil fuels like
gasoline and diesel is very harmful to the environment because it
causes global warming-more on this pollutant shortly.
Motor fuel is itself a product and so, like a car, environmental
damage occurs throughout its lifecycle as well. For gasoline and
diesel, the product lifecycle begins at the oil well and ends when
the fuel is burned in the engine. Fuel cycle impacts are the forms
of pollution and other environmental damage that occur between the
oil well and the fuel tank. Gasoline and diesel fuel are poisonous
to humans, plants, and animals, and their vapors are toxic. Other
energy sources have their own fuel cycles. With battery-powered electric
vehicles, for example, no fuel is burned onboard the vehicle, and
so nearly all of the fuel-cycle pollution and energy use occurs at
electric power plants and in producing the fuels that run the power
plants. Many of the same air pollutants that spew from vehicle tailpipes
are also spewed from power plants and oil refineries (as well as
the tanker trucks that deliver gasoline to your local filling station).
Petroleum products now provide 96 percent of America's transportation
energy needs. Air pollution isn't the only problem associated with
these petroleum-based fuels. Oil extraction lays waste to many fragile
ecosystems, harming tropical forests in South America and Southeast
Asia, deserts and wetlands in the Middle East, our own coastal areas,
and the fragile tundra and arctic coastal plains of Alaska. Millions
of gallons of oil are spilled every year. Sometimes the disasters
are well known, such as the 1989 Exxon Valdez spill in Prince William
Sound. More often there are rarely reported but still tragic smaller
spills that occur in the oceans and in coastal waters, bays, and
rivers throughout the world. In our own communities, groundwater
is sometimes tainted by leaks from underground fuel storage tanks
and miscellaneous spills that occur during shipping and handling
of the 120 billion gallons of fuel we use each year.
In addition to these environmental harms, gasoline and diesel consumption
bring economic and security risks. The Middle East contains the largest
concentration of the world's oil. The United States maintains a global
military presence partly to maintain access to foreign oil. The 1991
war with Iraq was directly related to securing our oil supply. The
tragic situation in which the United States finds itself since September
11, 2001, presents many grave challenges for national defense and
security. Choosing more fuel-efficient vehicles to reduce our reliance
on a world oil market in which Middle Eastern countries play a dominant
role is one way we, as individuals, can assist in energy-related
aspects of national security.
Major recessions were triggered by oil crises in the 1970s and early
1980s, causing unemployment and inflation. Oil imports drain over
$50 billion per year from American pockets, representing lost job
opportunities even when our economy seems to be doing fine. Over
half of U.S. oil is now imported and our dependence on foreign sources
is steadily rising, perpetuating the risk of future oil crises. The
gasoline price run-ups of the past two years are just the latest
examples of how petroleum dependence can squeeze family budgets only
to enrich oil producers.
Our addiction to gasoline and diesel fuel also involves moral compromises.
It entails deals and economic arrangements with some oil-rich countries
whose standards of human rights and environmental protection may
not be the same as what we expect at home. Of course, these issues
go beyond strictly environmental concerns. Nevertheless, choosing
greener vehicles that consume less fuel not only protects the environment,
but also helps protect U.S. jobs while reducing the economic costs
and moral liabilities of oil dependence.
Major Pollutants Associated with Automobiles
Our focus in ACEEE's Green Book® is on air
pollutants related to car and truck fuel consumption, because they
are such a large part of a vehicle's environmental damage and because
they are the main impacts that can be reduced through your choice
of make and model. The adjoining figure shows the amounts of major
air pollutants caused by the average new passenger car and light
truck in a year. The pollution coming from vehicles can differ
depending on the standards they meet (and how well their emissions
controls work), how they are driven and maintained, and the quantity
and quality of the fuel they burn. Many vans, pickups, sport utilities,
and other light trucks meet less stringent emissions and fuel economy
standards than vehicles classified as passenger cars. As a result,
and as the ratings in this guide indicate, the average light truck
pollutes more than the average car.
All new vehicles must meet either the emissions standards set by
the U.S. Environmental Protection Agency (EPA) or those set by the
California Air Resources Board (CARB). Generally, California standards
are more stringent than the Federal standards. A number of Northeastern
states have adopted the California standards, and vehicles meeting
these stricter standards are now commonly available nationwide.
Vehicles are also tested for fuel economy, as
measured by miles per gallon-MPG. Fuel economy standards apply
to manufacturers, rather than individual vehicles, and are set
so that an automaker can sell a variety of vehicles as long as
the average MPG of its sales meets the applicable standard. Manufacturers
calculate the fuel economy of each model they sell using laboratory
tests similar to those conducted to determine tailpipe emissions.
Because these tests give fuel economy estimates higher than what
most people experience in real-world driving, the MPG measurements
are adjusted downward by EPA. These adjusted MPG numbers are printed
on new vehicle stickers and listed here in ACEEE's Green Book®.
Although a wide variety of pollutants are formed
in the various stages of an automobile's lifecycle, our ratings
are mainly based on the serious air pollutants that are regulated
to control vehicle emissions. All of these pollutants are more
damaging to health when emitted from vehicle tailpipes than when
a similar quantity is emitted from a power plant, since tailpipe
pollution is literally "in
your face," subjecting people to more direct exposures during
Particulate Matter (PM)
Fine airborne particles are an established cause of lung problems,
from shortness of breath to worsening of respiratory and cardiovascular
disease, damage to lung tissues, and cancer. Certain people are particularly
vulnerable to breathing air polluted by fine particles, among them
asthmatics, individuals with the flu and with chronic heart or lung
diseases, as well as children and the elderly. PM also soils and
damages buildings and materials. It forms haze that obscures visibility
in many regions. Soot and smoke coming from exhaust pipes are obvious
sources of PM, but among the most deadly forms of airborne particulate
matter are the invisible fine particles that lodge deeply in the
lungs. PM has been regulated for some time, but the regulations were
based on counting all particles up to 10 microns in size (PM10).
However, PM10 standards fail to adequately control the most dangerous,
very fine particles. The U.S. EPA has recently started to regulate
fine particles up to 2.5 microns in size (PM2.5), which better focuses
on the most damaging category.
Properly functioning new, fuel-injected gasoline
vehicles directly emit very little PM2.5. But they indirectly cause
significant PM pollution as a result of their NOx, SO2, and HC
emissions, not only from tailpipes but also from vehicle manufacturing
and fuel refining (see below). These emissions result in "secondary" particle
formation. This phenomenon refers to the way that the gaseous pollutants
agglomerate ("glom up") at microscopic scales to form fine
particles that are largely invisible but cause the health problems
mentioned. Transportation sources account for about 20 percent of
directly emitted PM2.5. Diesel engines are the major source of direct
PM emissions from motor vehicles. Although most such emissions come
from heavy trucks and diesel buses, even the smaller diesel engines
in some cars and light trucks emit significant amounts of fine PM.
Nitrogen Oxides (NOx)
NOx refers mainly to two chemicals, nitrogen
oxide (NO) and nitrogen dioxide (NO2), that are formed when nitrogen
gas, which comprises 78 percent of air, reacts with oxygen during
the high temperatures that occur during fuel combustion. NOx is
truly a noxious pollutant in many ways. It is directly hazardous,
an irritant to the lungs that can aggravate respiratory problems.
It reacts with organic compounds in the air to cause ozone, which
is the main reason for "smog
alerts" that still happen too often in many cities and regions.
NOx is a precursor of fine particles, which cause respiratory problems
and lead to thousands of premature deaths each year. It is also a
precursor of acid rain, which harms lakes, waterways, forests, and
other ecosystems, as well as damaging buildings and crops. Airborne
NOx also contributes to nitrification-essentially an over-fertilization-of
wetlands and bays, leading to algae blooms and fish kills.
As an air pollutant, NOx is one of the most difficult to control
since it is such a pervasive product of combustion. Nationwide, most
NOx comes from electric power plants and industrial sources. Natural
gas and oil-fired home furnaces and water heaters also produce NOx
in their flue gases. Motor vehicles account for about one-third of
nationwide NOx emissions. Many of these emissions come from heavy-duty
diesel trucks, but cars and light trucks are also a major source.
NOx has also been one of the most difficult pollutants to get out
of our air. EPA air quality regulations have helped keep emissions
from growing as fast as they might have, and inventories show a modest
decline in NOx emissions over the past five years. Transportation-related
NOx emissions continue to increase, however, preventing faster progress
Sulfur Dioxide (SO2)
Gasoline and diesel fuels also contain varying amounts of sulfur,
which burns in the engine to produce sulfur dioxide (SO2). This gaseous
chemical is another source of secondary particulate formation, and
is itself a lung irritant as well as a cause of acid rain. SO2 also
interferes with the operation of catalytic converters. Some of the
cleaner, reformulated versions of gasoline have very low sulfur levels.
Most gasoline sold nationwide still has too much sulfur, but levels
are being reduced under recently established EPA regulations.
Cars and light trucks are not the largest source of SO2 emissions,
which come mainly from power plants and industrial facilities. However,
because cars and light trucks are so numerous and gasoline has a
high average sulfur content, cars and light trucks cause twice as
much fine PM pollution as heavy freight trucks. Making all gasoline
as clean as the cleaner, low-sulfur fuels already available in California
would greatly reduce this PM pollution from all cars and trucks on
the road, both new and used.
Hydrocarbons are a broad class of chemicals
containing carbon and hydrogen. Those hydrocarbons that cause various
forms of air pollution are also known as volatile organic compounds
since they are forms of HC that are either gases or readily evaporate
into the air. Many forms of HC are directly hazardous, contributing
to what are collectively called "air toxics." These compounds
can be directly irritating to the lungs and other tissues and they
can also cause cancer, contribute to birth defects, and cause other
illnesses. During daylight hours, and particularly during hot summer
weather, HC reacts with NOx to form ozone smog (see box below).
Controlling ozone is one of the major environmental challenges
in the United States. Although progress has been made over the
past several decades, many cities and regions still have smog alerts
when ozone levels get too high.
Gasoline vapor contains a mix of hydrocarbons. Thus, HC pollution
is produced whenever we fill our tanks. Some regions have special
nozzles on fuel pumps to help trap such vapors. Other HC vapors are
released at various stages along the way from the refinery to the
filling station. Vapors seep out, even when a car is parked and turned
off, due to the imperfect sealing of the fuel tank, pipes and hoses,
and other components leading to the engine. HC also comes out of
the tailpipe, as a result of incomplete combustion and the less-than-perfect
cleanup of exhaust gases by catalytic converters and other vehicle
emissions controls. Diesel fuel is less volatile than gasoline, so
evaporation is less of a problem. Nevertheless, diesel exhaust still
contains many toxic hydrocarbons and other compounds. Overall, transportation
is responsible for about 36 percent of man-made HC emissions in the
Ozone: Helpful in the Stratosphere, But Harmful in the Air We Breathe
Ozone (O3) is a highly reactive form of oxygen that occurs naturally
in various parts of the atmosphere but gets artificially produced
in dangerously high concentrations due to emissions from cars, trucks,
and other combustion sources.
Up in the stratosphere, ozone helps protect us from ultraviolet
radiation. Loss of this protective ozone layer at high altitudes
can lead to increased skin cancer. Such concerns have led to restrictions
on ozone-depleting chemicals such as those once found in some spray
cans and others that have been phased out of use in refrigerators
and air conditioners (including automotive air conditioners).
Down in the lower atmosphere, in the air the we breathe, ozone is
a health hazard. It is the main ingredient of the smog that causes
pollution alerts in many cities around the country. Ozone produced
by pollution at low altitudes is of no help in restoring the protective
ozone layer at high altitudes. Inhaling air polluted by ozone damages
the lungs, reduces breathing ability, and makes us more susceptible
to other respiratory problems. Ozone can be deadly to individuals
with asthma and other lung conditions, as well as to people with
heart conditions. It is also harmful to both adults and children
who are otherwise healthy. The risks of shortness of breath, chest
pain, lung congestion, and other symptoms caused by ozone are the
reasons why public health officials warn us to stay inside and avoid
strenuous exercise on severe air pollution days.
Although cars and trucks do not directly emit ozone, they are a
major cause of ozone smog. They add to the amount of HC in the air,
and tailpipe NOx reacts with HC to form ozone. Cities without major
industries and power plants still have serious smog problems, mostly
caused by pollution from cars, trucks, and vans. Although many U.S.
cities are seeing better air quality, we'll have to do better at
cutting motor vehicle pollution to ensure progress.
Toxic releases are just that—any number
of a wide range of chemicals that can cause cancer, birth defects,
cardiovascular, respiratory and neurological damage, or other forms
of health harm. Many smog-forming hydrocarbons are directly toxic;
for example, the benzenes found in gasoline are carcinogens.
Other toxics include solvents and metallic compounds such as lead
and chromium. Toxics are released during many industrial activities,
and car and truck manufacturing is a significant source. Workers
and communities near factories and scrappage facilities are at the
highest risk. When vehicles are scrapped, bioaccumulative toxins
such as lead, chromium, and mercury make their way into the soil,
water, and air where they can last for a long time and build up in
our bodies and those of other organisms. Vehicles also emit toxics
in use, due to fuel evaporation while the tank is being filled or
while the car sits in the sun, for example, as well as toxic emissions
from the tailpipe. Diesel exhaust, in particular, has been implicated
as a harmful toxic release.
Toxic emissions from cars and trucks, as well as toxic releases
during the production and assembly of vehicles and their components,
are controlled by various regulations. Factories and other manufacturing
facilities are required to report toxic emissions from each site.
But controls are far from perfect, and there are many ways in which
industry could do a better job of preventing toxic pollution. You
can find out the source and amount of toxics that are emitted in
your community from the Environmental Defense toxic pollution scorecard.
Carbon Monoxide (CO)
Carbon monoxide is an odorless, colorless, but potentially deadly
gas that is created by the incomplete combustion of any carbon-containing
fuel, including gasoline and diesel. When inhaled, CO combines with
the hemoglobin in our blood, impairing the flow of oxygen to our
brain and other parts of the body. We've all heard stories of people
being killed by carbon monoxide poisoning, from vehicles in closed
garages, during fires, or in homes when indoor CO concentrations
are raised by malfunctioning stoves or furnaces. Even if it doesn't
cause death, CO exposure can cause permanent damage to the nervous
system. At lower concentrations, CO is still harmful, particularly
for people with heart disease. In some areas, cars and trucks can
create enough CO to cause health risks outdoors.
Large amounts of CO are produced when a vehicle first starts up
and its engine is cold. Poorly designed and malfunctioning engines
and emission controls systems are also responsible for excess CO
pollution. Motor vehicles are responsible for about 60 percent of
CO emissions nationwide.
Cars, Trucks, and Global Warming
The gasoline-powered automobile was invented
just over 100 years ago, when the industrial revolution was still
young. Streams had long been dammed to turn mills, and coal was
on its way to widespread use—it was already powering steamships
and locomotives. But most energy used by humans still came from
traditional fuels such as wood. In 1890, the world population was
about 1.5 billion but growing rapidly. The amount of carbon dioxide
(CO2) in the atmosphere was just over 290 parts per million, not
yet noticeably over its level throughout pre-industrial civilization.
The world population has now topped six billion and is still growing
rapidly. During the past century, the amount of fossil fuel we consume
has risen nearly five times faster than population. As a result,
the amount of CO2 in the atmosphere is now over 360 parts per million
and climbing. This rapid increase in CO2 concentration represents
the enormous impact of our energy-consumptive lifestyle on the planet,
and it is causing dangerous changes to the earth's climate. The past
decade has already seen many years with above-normal temperatures.
The changes in weather patterns and increases in severe events are
consistent with climate disruption. Recent years have been among
the warmest ever recorded.
Carbon dioxide is the most important of what are known as greenhouse
gases, compounds that enable the earth's atmosphere to trap heat,
like a greenhouse, but on a global scale. Too much greenhouse gas
in the atmosphere causes global warming, an increase in global average
temperatures above what they normally would be.
The risks of global warming are many. Human health is threatened
by more frequent and severe heat waves and the spread of tropical
diseases. Lives can be lost because of rising sea levels and more
severe storms, which can also damage regional and national economies.
The disruptions to climate are unpredictable but certainly risky.
While some areas may see greater coastal flooding and inundating
rains, other regions may experience droughts. Both agriculture and
natural habitats can be harmed. Future generations will bear the
brunt of these risks, but the effects of global warming have already
been detected. Although we cannot attribute any given event to climate
change, the increased risks have created a call for action to curtail
CO2 emissions around the world.
Oil is now the world's dominant fuel. There
are over 600 million cars and trucks in the world. Both here and
abroad, transportation accounts for most oil use. In the United
States, we now have more motor vehicles than licensed drivers,
and we travel over 2 trillion miles per year, burning 120 billion
gallons of gasoline. Not counting the "upstream" emissions
from producing the fuel, the result is over a billion tons of CO2
pollution each year.
U.S. cars and light trucks alone account for more energy-related
CO2 than the nationwide emissions of all but four other countries
in the world (China, Russia, Japan, and India). Our vehicles produce
nearly as much CO2 as all of India, which has more than triple our
population. U.S. cars and trucks emit more than twice as much fossil-fuel
CO2 as the economies of either South Korea or Mexico, and over three
times as much as the whole of Brazil. Although some of these countries
are growing and industrializing rapidly, it will be decades before
their level of CO2 pollution per person approaches ours.
Fuel Economy and Air Pollution
The amount of CO2 emitted by a vehicle is essentially proportional
to the amount of fuel burned. Thus, fuel-efficient vehicles are the
best choice for helping to stop global warming. And gas guzzlers
are global polluters.
For other forms of air pollution, the relation between fuel economy
and emissions is more complex. Automobile emissions are regulated
to a given number of grams per mile, independently of a vehicle's
fuel economy, but standards are weaker for many gas-guzzling light
trucks. Moreover, several factors cause NOx, HC, CO, and PM pollution
to be higher when a vehicle's fuel economy is lower.
In real-world use, most vehicles' emissions are much higher than
the standards levels. The reasons include the fact that automakers'
and EPA's emissions tests fail to fully represent real-world driving,
malfunction of emissions control systems, deterioration of components,
inadequate or incorrect maintenance, and sometimes tampering. A portion
of this excess pollution is proportional to a vehicle's rate of fuel
consumption. Automobiles that meet a more stringent emissions standard
are generally cleaner than those that meet a less stringent standard.
However, among vehicles that meet the same standard, those with higher
fuel economy generally produce less air pollution.
A significant amount of pollution also occurs in supplying vehicles
with fuel. These so-called upstream emissions occur everywhere from
the oil well and refinery to the filling station and gas tank, before
the fuel gets to the engine. Upstream emissions associated with a
vehicle are proportional to its fuel consumption. For an average
car, upstream hydrocarbon and PM10 emissions are about twice the
tailpipe emissions of those pollutants. Lesser but still-significant
amounts of other pollutants are also related to the amount of fuel
burned. Examples include NOx from tanker trucks delivering gasoline
and a whole soup of pollutants from oil refineries. Thus, higher
fuel consumption implies greater pollution.
Efficiency and Safety
Other things being equal, a smaller, lighter vehicle is more fuel
efficient and less polluting than a larger, heavier vehicle. But
are smaller, lighter vehicles less safe? The answer is more complex
than one might think. In a two-car collision, occupants of the heavier
vehicle are typically subjected to lower crash forces. However, the
heavier vehicle generally inflicts higher forces on the occupants
of the lighter vehicle. Thus, while individuals may gain a measure
of protection by driving heavier vehicles, they do so at others'
expense. In and of itself, weight does not improve overall safety.
Any type of vehicle, including a small car, can be safe when it has
well-designed features that improve occupant protection (such as
stable, energy-absorbing structures), and properly used occupant
restraints (like seat belts, air bags, and child safety seats).
Many of these safety-enhancing features are reflected in crash-test
scores and the related safety ratings published by National Highway
Traffic Safety Administration (NHTSA) and several consumer publications
which we list at the end of this section. These safety ratings are
particularly helpful for identifying vehicles that have superior
structures, since such features are engineered into a vehicle and
are not obvious based on size, shape, or body style.
Better vehicle structures absorb crash energy,
cushioning occupants from the severity of an impact. Well-designed
structures also act as a "safety cage" that protects
occupants from being crushed or otherwise injured by intruding
parts of a crashing vehicle. Seat belts protect occupants from
striking the inside parts of a vehicle or being thrown out of it.
Using seat belts doubles the chance of surviving a serious crash
in any vehicle, and air bags further enhance that protection. Improved
stability lowers the risk of rollover, a form of accident associated
with high fatalities and serious injuries. All of these design
features improve safety without adverse trade-offs.
Large and heavy personal vehicles are a mixed
bag when it comes to safety. For one thing, heavier vehicles are
a greater menace to others on the road, including pedestrians,
bicyclists, motorcyclists and occupants of smaller vehicles. Sport
utility vehicles (SUVs) illustrate the fallacy of "larger is safer" simplistic
thinking. While SUVs are heavier on average than passenger cars,
they don't necessarily have lower fatality rates. Not only are SUVs
more hazardous to others on the road, they threaten their own occupants
with higher rollover risks. Many SUVs are less stable than passenger
cars and provide poor occupant protection in rollovers. Pickup trucks
have the same safety deficiencies as SUVs and many vans are only
moderately better. Newer "crossover" body styles, such
as all-wheel-drive wagons and sport wagons, reduce some of the safety
liabilities of traditional SUVs. In general, because they are detrimental
to both safety and the environment, SUVs should be avoided by consumers
without an ongoing need for their larger power, capacity, or off-road
The best guidance is to check the safety ratings
as well as the Green Scores of models that you are considering,
so that you can find the safest and greenest vehicle that meets
your needs. The government safety ratings measure how well a car
or truck protects its occupants in various crash tests; recently
added rollover ratings indicate how stable a vehicle is. The ratings
do not tell the whole story about vehicle safety, since they fail
to account for how harmful a vehicle is to others on the road and
how well it protects its own occupants in a rollover crash. Nevertheless,
crash-test scores are a good comparison of the relative safety
of vehicles within a given size class. Look for the "Buying a Safer Car" feature
on NHTSA's website (www.nhtsa.dot.gov). Additional advice, information
on crashworthiness, and descriptions of safety features by make and
model are provided by The Ultimate Car Book and Consumer Reports.
back to top
How to buy green
Sorting out Standards
EPA Fuel Economy Estimation (Cars and Light Trucks)
Why Buy Green?
Automobiles and the environment
Major Pollutants Associated with Automobiles
Cars, Trucks, and Global Warming