The Environmental Impact of Vehicle Emissions
From: Illinois EPA
http://www.epa.state.il.us/air/vim/guide/air_pollution.html
Emissions from an individual car are generally low, relative to the smokestack image many
people associate with air pollution; however, in numerous cities across the country, the
personal automobile is one of the single greatest sources of air pollution as emissions from
millions of vehicles on the road add up. Vehicle emissions are responsible for up to 50 percent
of the emissions that form ground-level ozone and up to 90 percent of carbon monoxide in
major metropolitan areas. Driving a private car is probably a typical citizen's most "polluting"
daily activity.
The power to move a car comes from burning fuel in an engine. Pollution from cars comes
from:


by products of this combustion process (exhaust) and,
from evaporation of the fuel itself
(Emissions generated by brakes and tires are not mentioned in this
article but they are also an important source of emission)
Gasoline and diesel fuels are mixtures of hydrocarbons -- compounds that contain hydrogen
and carbon atoms. In a "perfect" engine, oxygen in the air would convert all the hydrogen in
the fuel to water and all the carbon in the fuel to carbon dioxide. Nitrogen in the air would
remain unaffected. In reality, the combustion process cannot be "perfect," and automotive
engines emit several types of pollutants.
"Perfect" Combustion:
Fuel (hydrocarbons) + air (oxygen and nitrogen) = carbon dioxide + water + unaffected
nitrogen
Typical Engine Combustion:
Fuel + air = unburned hydrocarbons + nitrogen oxides + carbon monoxide + carbon dioxide +
water
Exhaust Pollutants
Hydrocarbons (HC): Hydrocarbon emissions result when fuel molecules in the engine do
not burn or burn only partially. Hydrocarbons react in the presence of nitrogen oxides and
sunlight to form ground-level ozone, a major component of smog. Ozone irritates the eyes,
damages the lungs, and aggravates respiratory problems. It is our most widespread and
intractable urban air pollution problem. A number of exhaust hydrocarbons are also toxic, with
the potential to cause cancer.
Nitrogen oxides (NOx): Under the high pressure and temperature conditions in an
engine, nitrogen and oxygen atoms in the air react to form various nitrogen oxides,
collectively known as NOx. Nitrogen oxides, like hydrocarbons, are precursors to the formation
of ozone. They also contribute to the formation of acid rain.
Carbon monoxide (CO): Carbon monoxide is a product of incomplete combustion and
occurs when carbon in the fuel is partially oxidized rather than fully oxidized to carbon dioxide.
Carbon monoxide reduces the flow of oxygen in the bloodstream and is particularly dangerous
to persons with heart disease.
Carbon dioxide (CO2): In recent years, the U.S. Environmental Protection Agency has
started to view carbon dioxide, a product of "perfect" combustion, as a pollution concern.
Carbon dioxide does not directly impair human health, but it is a "greenhouse gas" that traps
the earth's heat and contributes to the potential for global warming.
Evaporative Emissions
Hydrocarbon pollutants also escape into the air through fuel evaporation. With today's efficient
exhaust emission controls and modern gasoline formulations, evaporative losses can account
for a majority of the total hydrocarbon pollution from current model cars on hot days when
ozone levels are highest. Evaporative emissions occur several ways:
Diurnal: Gasoline evaporation increases as the temperature rises during the day, heating
the fuel tank and venting gasoline vapors.
Running Losses: The hot engine and exhaust system can vaporize gasoline when the car
is running
Hot Soak: The engine remains hot for a period of time after the car is turned off, and
gasoline evaporation continues when the car is parked.
Refueling: Gasoline vapors are always present in fuel tanks. These vapors are forced out
when the tank is filled with liquid fuel.
Federal standards dictate how much pollution autos may emit, and automakers decide how to
achieve the pollution limits. The emission reductions of the 1970's came about because of
fundamental improvements in engine design, plus the addition of charcoal canisters to collect
hydrocarbon vapors and exhaust gas recirculation valves to reduce nitrogen oxides.
The advent of "first generation" catalytic converters in 1975 significantly reduced hydrocarbon
and carbon monoxide emissions. The use of catalytic converters provided a huge indirect
benefit as well. Because lead inactivates the catalyst, 1975 saw the widespread introduction of
unleaded gasoline. This resulted in dramatic reductions in ambient lead levels and alleviated
many serious environmental and human health concerns associated with lead pollution.
The next major milestone in vehicle emission control technology came in 1980-81. In response
to tighter standards, manufacturers equipped new cars with even more sophisticated emission
control systems. These systems generally include a new catalyst, plus an on board computer
and oxygen sensor. This equipment helps optimize the efficiency of the catalytic converter.
Efforts by government and industry since 1970 have greatly reduced typical vehicle emissions.
Since then, however, the number of miles we drive has more than doubled. The increase in
travel has offset much of the emission control progress.
The net result is a modest reduction in each automotive pollutant except lead, for
which aggregate emissions have dropped by more than 95 percent.
From Wikipedia, the free encyclopedia
List the following sources of emissions must be considered:
Life cycle emissions: These are produced in activities associated
with the manufacturing, maintenance, and disposal of the
automobile and include such items as:
1. Manufacturing plant power requirements
2. Volatile solvents utilized in the manufacturing process (auto
paint finishes, etc)
3. Outgassing of synthetic materials utilized to reduce weight
and simplify manufacturing
4. Maintenance requirements such as oil and filter changes,
battery replacement, etc.
5. Disposal requirements including contaminated lubricants,
tires, heavy metals, and landfill
Heath Effects of Pollution from Vehicle Engines
Research indicates that approximately 3,700 premature deaths and thousands of medical
emergencies are linked to air pollution in the greater metropolitan Chicago and East St. Louis
areas each year. Carbon monoxide and hydrocarbons are the two main exhaust gases
produced by the combustion process in gasoline powered vehicles.
Carbon monoxide is a colorless, odorless, toxic gas. It is a by-product of incomplete
combustion. Motor vehicles produce more than two-thirds of the man-made carbon monoxide
in the atmosphere. Carbon monoxide reduces the volume of oxygen that enters the
bloodstream and can slow reflexes, cause drowsiness, impair judgment and vision and even
cause death.
Hydrocarbons are unburned fuel vapors. When hydrocarbons and other pollutants are
exposed to sunlight, a chemical reaction occurs that produces ground-level ozone (smog),
which is harmful to our health and the environment. Vehicles are responsible for about 50
percent of the emissions that form ozone.
Nitrogen oxides, like hydrocarbons, are precursors to the formation of ozone. They also
contribute to the formation of acid rain.
What is Ozone?
Ozone is a form of molecular oxygen that consists of three oxygen atoms linked together.
Ozone in the upper atmosphere (the "ozone layer") occurs naturally and protects life on earth
by filtering out ultraviolet radiation from the sun. Ozone at ground level is a noxious pollutant.
It is the major component of smog and presents this country's most intractable urban air
quality problem.
Ozone is a severe irritant. It is responsible for the choking, coughing, and stinging eyes
associated with smog. Ozone damages lung tissue, aggravates respiratory disease, and makes
people more susceptible to respiratory infections. Children are especially vulnerable to ozone's
harmful effects, as are adults with existing disease. Even otherwise healthy individuals may
experience impaired health from breathing ozone-polluted air. Elevated ozone levels also
inhibit plant growth and can cause widespread damage to crops and forests.
Ozone is not emitted directly. It is formed in the atmosphere through a complex set of
chemical reactions involving hydrocarbons, oxides of nitrogen, and sunlight. The rate at which
the reactions proceed is related to both temperature and intensity of the sunlight. Because of
this, problematic ozone levels occur most frequently on hot summer afternoons.
Hydrocarbons and nitrogen oxides come from a great variety of industrial and combustion
processes. In typical urban areas, at least half of those pollutants come from cars, buses,
trucks, and off highway mobile sources such as construction vehicles and boats.
Why Aren't Ozone Levels Dropping?
Ozone levels in many cities have come down with the introduction of lower volatility gasoline
and as newer cars with improved emission control systems replaced older models. Although
there has been significant progress since 1970 in reducing emissions per mile traveled, the
number of cars on the road -- and the miles they travel -- almost doubled in the same time
frame. In the ten years from 1991 to 2001, fuel sold and vehicle miles traveled increased
about 25 percent.
Increased sales of sport utility vehicles and trucks also contribute to the problem. Sales of
SUVs and light trucks have increased 270 percent since 1976. In 2001, SUVs and trucks
overtook cars in sales, and accounted for almost 55 percent of the vehicles sold in 2003.
However, these vehicles won’t have to meet passenger car emissions standards until model
year 2004.
A second reason that ozone levels remain high is that emission control systems do not always
perform as designed over the full useful life of the vehicle. Routine aging and deterioration,
poor maintenance, and tampering with emission control devices can all increase vehicle
emissions. In fact, a major portion of ozone forming hydrocarbons can be attributed to a
relatively small number of "super dirty" cars whose emission control systems are not working
properly.
Unless we dramatically reduce the amount of pollution vehicles emit in actual use, or
drastically cut back on the amount we drive, smog free air will continue to elude us.
Fine Particulate Matter
Source: Ontario Minister of the Environment
What is fine particulate matter?
Particulate matter is characterized according to size - mainly because of the different
health effects associated with particles of different diameters. Particulate matter is the
general term used for a mixture of solid particles and liquid droplets in the air. It includes
aerosols, smoke, fumes, dust, ash and pollen. The composition of particulate matter
varies with place, season and weather conditions. Fine particulate matter is particulate
matter that is 2.5 microns in diameter and less. It is also known as PM2.5 or respirable
particles because it penetrates the respiratory system further than larger particles.
PM2.5 in Ontario is largely made up of sulphate and nitrate particles, elemental and
organic carbon and soil.
What are the sources of fine particulate matter?
PM2.5 material is primarily formed from chemical reactions in the atmosphere and
through fuel combustion (e.g., motor vehicles, power generation, industrial facilities
residential fire places, wood stoves and agricultural burning). Significant amounts of
PM2.5 are carried into Ontario from the U.S. During periods of widespread elevated levels
of fine particulate matter, it is estimated that more than 50 per cent of Ontario's PM2.5
comes from the U.S.
PM 2 . 5 Composition/Emissions
Pie Chart
Category
Percent
Elemental and Organic Carbon1 (Combustion
Related)
30% 50%
Sulphate4
30% 40%
Nitrate2
10% 20%
Soil3
3% - 10%
Notes:
1.
2.
3.
4.
Transportation, wood burning, utility/commercial fuel combustion, plus secondary organic aerosols formed from precursor VOC emissions.
Formed from NOx emitted from regional and local sources: transportation, utilities, and industries.
Fugitive dust (paved roads, construction), and industries.
Formed from SO2 and SO4 emitted from regional and local sources: oil and coal-fired utility and commercial/industrial boilers, small combustion
sources, transportation, smelters.
What are the effects of fine particulate matter?
The greatest effect on health is from particles 2.5 microns or less in diameter. Exposure
to fine particulate matter has been associated with hospital admissions and several serious
health effects, including premature death. People with asthma, cardiovascular or lung
disease, as well as children and elderly people, are considered to be the most sensitive to
the effects of fine particulate matter. Adverse health effects have been associated with
exposure to PM2.5 over both short periods (such as a day) and longer periods (a year or
more).
Fine particulate matter is also responsible for environmental effects such as corrosion,
soiling, and damage to vegetation and reduced visibility.
The following table shows the health effects of different AQI levels caused by fine
particulate matter.
Greenhouse Gases
Source: Wikipedia
Greenhouse gases are components of the atmosphere that contribute to the greenhouse
effect. Some greenhouse gases occur naturally in the atmosphere, while others result from
human activities. Naturally occurring greenhouse gases include water vapor, carbon
dioxide, methane, nitrous oxide, and ozone. Certain human activities, however, add to the
levels of most of these naturally occurring gases.[1]
This figure shows the relative fraction of man-made greenhouse gases coming from each
of eight categories of sources, as estimated by the Emission Database for Global
Atmospheric Research version 3.2, fast track 2000 project [1]. These values are intended
to provide a snapshot of global annual greenhouse gas emissions in the year 2000.
The top panel shows the sum over all man-made greenhouse gases, weighted by their
global warming potential over the next 100 years. This consists of 72% carbon dioxide,
18% methane, 9% nitrous oxide and 1% other gases. Lower panels show the comparable
information for each of these three primary greenhouse gases, with the same coloring of
sectors as used in the top chart. Segments with less than 1% fraction are not labeled.
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