1. Local and Regional Impacts
One geographical dimension of air pollution is at the local and regional
levels where its externalities are immediately felt. Many pollutants identified
as being closely related to transportation:
Carbon Monoxide CO
- Carbon monoxide is a colorless, odorless gas, the result of the incomplete
combustion of hydrocarbons.
- Transportation accounts from 70 to 90% of total carbon monoxide emissions.
It is thus the air pollutant the most strongly associated with transportation.
Carbon monoxide is often present near major traffic intensive arterials, notably
in urban areas. Carbon monoxide is a poisonous gas.
- When inhaled, it combines with hemoglobin to form carboxyhemoglobin,
preventing absorption of oxygen and resulting in asphyxiation. 0.5% of carbon
monoxide in air may prove fatal in less than half an hour by transforming
over 50% of the hemoglobin in carboxyhemoglobin. Lower concentrations of carbon
monoxide (3 ppm) may cause poisoning symptoms and affect people with heart,
lung and circulatory system weaknesses. It also effects the respiration of
plants by inhibiting photosynthesis.
- Since carbon monoxide is not chemically very stable, direct global effects
are strongly limited (probably non existent). Indirectly, carbon monoxide
contributes to the formation of greenhouse gazes as a catalyst.
Nitrogen Oxides NOx
- Nitrogen oxide (NO or NO2) is a brown, odorless gas. A by-product
of combustion when energy is used to oxide nitrogen instead of an hydrocarbon.
- Transportation accounts from 45 to 50% of total emissions of nitrogen
oxides. Other sources are chemicals (notably nitrates) industrial production
and combustion of fossil fuels in thermal power plants.
- Nitrogen oxides are not very harmful to humans (particularly NO), but
when released from an internal combustion engine, high concentrations are
often toxic. It irritates and infects the respiratory system and the eyes.
Some decreases in the ability to resist bacterial infection were also observed
when the subject is exposed to significant concentrations of nitrogen dioxide.
Nitrogen oxides are known to prevent the growth of crops and thus reduce agricultural
yields.
- Nitrogen oxides are known to be associated with several global effects
and have increased at a rate of 0.2% annually over the last decades. They
are a catalyst for ozone, a component of acid rain and a component of smog.
Depositions of nitrogen oxides influence the nitrate cycle, particularly in
water where it influences algae blooms.
Hydrocarbons and Volatile Organic Compounds - (HC/VOC)
- Hydrocarbons (HC) are a group of chemical compound composed of carbon
and hydrogen. When in a gaseous form, HC are called Volatile Organic Compounds
(VOC). Several HC and VOC are heavy gazes or volatile compounds with a strong
odor. They are mostly the result of the incomplete combustion of gasoline
or by-products of the petrochemical industry. They include methane (CH4),
gasoline (C8H18) and diesel vapours, benzene (C6H6),
formaldehyde (CH2O), butadiene (C4H6) and
acetaldehyde (CH3CHO).
- Transportation accounts from 40 to 50% of total emissions of HC/VOC.
They can be emitted by incomplete combustion (70%), during refueling (10%)
or by evaporation from storage units (20%), particularly gas tanks. For instance,
a car parked overnight during summer emits approximately 4 grams of HC/VOC.
Other important sources are petrochemical (plastics and solvent) industries.
- All HC/VOC are carcinogen (cases of leukemia linked with benzene) to some
extent, fatal at high concentrations, harmful to crops and accumulates within
the food chain (poisoning). However, heavy hydrocarbons (like benzene) are
far more carcinogen than light hydrocarbons (like methane).
- All HC/VOC have several global effects. They are components of smog, catalysts
for ozone and components of acid rain.
Particulates
- Particulates include various solids in suspension in the atmosphere such
as smoke, soot, and dust and results of the incomplete combustion of fossil
fuels, notably coal. They may also carry traces of other toxic substances
like HC/VOC.
- Transportation accounts for around 25% of total emissions of particulates.
Diesel engines are the main emitters. Other important sources are thermal
power plants using coal.
- Particulates are carcinogen. They are also harmful to lungs tissue and
worsen respiratory and cardiovascular problems, notably if their size is smaller
than 5 microns. Particulates depositions may alter the aesthetic of structures.
- The accumulation of particulates in the atmosphere and deposition on leafs
may reduce photosynthesis and plant growth.
Smog
- Mixture of solid and liquid fog and smoke particles formed through the
accumulation of carbon monoxide, ozone, HC/VOC, nitrogen oxides, sulfur oxide,
water, particulates, and other chemical pollutants. Photochemical smog
are those with a higher concentration of ozone and HC/VOC.
- Smog is strongly linked with transportation and industrial activities,
notably in urban areas. Smog is particularly dense during a thermal inversion
(static regional air masses that enable the accumulation of pollutants).
- The effects of smog are the conjunction of those of its major components
(see the effects of carbon monoxide, sulfur dioxide, nitrogen oxide, HC/VOC,
particulates and ozone). Based upon historical observations (like London in
the 50s), the number of deaths among susceptible persons (respiratory and
cardiovascular problems) grows sharply during thermal inversions.
- Several large cities (like Los Angeles, Tokyo and Mexico) have serious
smog problems to the point that emissions reduction policies are established.
Smog impairs visibility considerably and causes different annoyances (odors,
irritations, etc.). Because of its components, smog is highly associated with
acid rains and greenhouse effects.
Lead Pb
- Lead is a toxic metal mainly used as an anti-knock agent in gasoline
(Lead tetraethyl - Pb(C2H5)4) and in
batteries (lead dioxide as an anode and lead as a cathode).
- Until recently, lead tetraethyl was a main source of atmospheric lead
emissions in developing countries. This contribution has dropped in absolute
numbers but still accounts for 30 to 40% of total emissions. Batteries are
now an important source of lead for transportation, but a very limited amount
of this lead is carried through the atmosphere (see water pollution).
- Extremely poisonous metal. Lead has effects on the metabolism and accumulates
in living tissues. May causes anemia, and mental retardation for young children.
For instance, an extremely high occurrence of mental retardation in some parts
of Mexico city was directly linked with lead poisoning. Small doses may cause
behavioral changes.
- Lead is fixed by plants and animals and re-contaminate the food chain.
It has a high potential to accumulate in the environment. Lead can also be
transported in the atmosphere over wide distances.
Odors
- Odors are the subjective perception of the sense of smell. They exists
different "shapes" of odors perceived as pleasant, neutral, or unpleasant.
A long run exposition to specific odors will attenuate their perception.
- Diesel and gasoline engines are the major sources of odors accounted
by transportation. Odors are particularly prevalent during smog conditions.
Odors are at worst an annoyance, but they are linked with the presence of
harmful air pollutants like sulfur dioxide, ozone and HC/VOC. People tend
to stay or move away from areas having a significant prevalence of odors.
2. Global Impacts
Although the pollutants below can have local and regional impacts, their
scope is more global.
Carbon Dioxide CO2
- Carbon dioxide is a colorless, odorless gas that composes 0.04% of the
atmosphere. Whenever there is combustion (oxidation) of fossil fuels, there
is an emission of carbon dioxide. Important temperature regulator for the
atmosphere, keeping it a +15oC instead of -15oC if carbon
dioxide was absent.
- Transportation accounts for around 30% of total carbon dioxide emissions
in developed countries (15% worldwide).
- About 66% of carbon dioxide emissions from transportation come from the
combustion of gasoline, 16% from diesel fuel and 15% from jet fuel.
Carbon dioxide emissions by transportation have the following modal breakdown:
cars (43%), light trucks (20%), heavy trucks (14%), airplanes (14%), rail
and marine (7%) and non-oil based (2%). Other significant natural sources
are volcanic eruptions and the metabolic respiration of living organisms (including
decomposition).
- Carbon dioxide is a harmless gas and an essential element of photosynthesis.
Although limited concentrations of carbon dioxide have no effects on human
beings, high concentrations (5000 ppm) may be harmful by causing breathing
disorders. Growing quantities of carbon dioxide in the atmosphere are assumed
to be linked with the
greenhouse effect. Concentrations of CO2 have rose on the average
of 0.4% per year over the last decades. Before the industrial revolution (early
19th century), the concentration of carbon dioxide was estimated to be around
275 ppm, while by 2002 it has reached 372 ppm. It is advocated that a level
of 400 ppm is the limit after which climate modifications become important
and difficult to predict. Levels of about 600 ppm are anticipated by the middle
of the 21st century.
Sulfur Dioxide SO2
- Sulfur dioxide is a heavy, colorless gas with a strong odour. It is the
result of the combustion of fossil fuels like coal (particularly bituminous
coal) and hydrocarbons.
- Transportation accounts for around 5% of total sulfur dioxide emissions.
Although transportation is a minor source of SO2, related activities
like steel and petrochemical industries are important emitters. One of the
most important artificial source are thermal power plants using low quality
coal. Volcanic eruptions are an important natural source of sulfur dioxide.
- Sulfur dioxide causes and worsens respiratory and cardiovascular problems.
In sufficient concentration, it irritates the eyes and causes discomfort (odor).
Sulfur is an essential nutrient for plants but sulfur dioxide is regarded
as an inhibitor of physiological activity. Most affected plants are those
having a high physiological activity like crops and commercial timber forests.
- A major component favoring the genesis of acid rain. Sulfur dioxide has
a counter effect on greenhouse gases by blocking
radiation. This effect is significant enough to be included in global warming
climatic models.
Ozone
- Ozone is a pale blue gas with a strong odour and a powerful oxidant. It
is the most common photochemical oxidant. Ozone is created naturally in the
high atmosphere when an oxygen molecule is broken apart by ultraviolet radiation
and combines with another oxygen molecule.
- Ozone is also the result of the action of light over a mixture of HC/VOC
and nitrogen oxides in the lower atmosphere. It is thus directly linked
with transport emissions, notably in urban areas.
- Ozone is poisonous, hampers breathing and irritates the eyes and the respiratory
system at concentrations higher than 0.15 ppm. The normal/natural concentration
is around 0.01 ppm at ground levels. It degrades structures (metal and concrete)
through oxidation. It damages crops and vegetation and leads to losses of
leafs. Depending on the crops and the concentration involved, ozone may reduce
yields from 1 to 20%. Ozone impairs visibility.
- Ozone is essential in the upper atmosphere, as it absorbs light in the
ultraviolet band. A drop of 5% in the concentration of ozone may lead to an
increase of 10% of skin cancer and eye cataracts. Ozone is also a
greenhouse gas.
Acid Rain and Acid Depositions (Sulfuric and Nitric Acid - H2SO4,
HNO3)
- Sulfuric acid is a corrosive, oily colorless liquid, which forms when
sulfur oxides and water vapors are mixed. Nitric acid is a corrosive and colorless
liquid and forms when nitrogen oxides and water vapor are mixed. The level
of formation of acid (sulfuric and nitric) is influenced by the level of exposition
to sun light. It may also exists in dry form, which is called acid deposition.
When dissolved in water, sulfuric and nitric acids lower the pH (higher concentrations
of hydrogen ions). The standard pH of fresh water ranges between 6.5 and 7.5.
- Since transportation accounts for 5% of sulfur dioxide emissions,
45% of nitrogen oxides emissions and for 40% of HC/HOV emissions, sources
may range from 10 to 30% of acid rains, depending on regions. This
figure is of 25% in Western Europe.
- Sufficient concentrations of sulfuric of nitric acids are known to damage
artificial structures, thus historical monuments are particularly vulnerable.
When inhaled as a mist, may cause respiratory organs irritation.
- Change the chemical composition of soils by breaking down complex organic
matter in simpler elements. At a small scale, this is beneficial, but at a
large scale, it reduces the available biomass. By altering the pH of fresh
water, acid rains gradually destroy life in lake and rivers.
- Sulfuric and nitric acids are carried over large distances through weather
systems. It later falls down either as rain or fog. Acid rain and acid depositions
are known to alter the ecological balance of continental ecosystems, notably
in industrialized areas.
Chlorofluorocarbons (CFCs)
- CFCs are colourless and poisonless gases (or liquids). They are very stable,
non-flammable and non-toxic components and they have been widely used as dispersing
agents (aerosols) or as refrigerants (notably Freon, R-12).
- For transportation, motor vehicle air-conditioning systems are
the main source and account for about 20% of all CFCs emissions. In
fact, during its life cycle, an air-conditioning system will release 100%
of its CFCs in the atmosphere. With recent legislations, CFCs emissions
have
considerably subsided in developed countries but not in developing countries.
- Because of its chemical properties (stable and non-toxic), CFCs have no
noticed effects on living organisms.
- Current concentrations of CFCs in the atmosphere reach about 0.35 ppm
(all types of CFCs) but the most widely used type, R12, has 20,000 times more
infrared absorbency than carbon dioxide. Thus one ton of Freon will have the
same
greenhouse effect than 2,000 tons of carbon dioxide. CFCs reduce the concentration
of stratospheric ozone, which absorbs harmful ultraviolet rays. CFCs may stay
in the atmosphere from 70 to 200 years, due to their extremely stable properties.
They are a long term component of the atmosphere. CFCs emitted in the 1990s
are likely to damage the ozone layer for 200 years.
- Indirect effects of CFCs (increase in ultraviolet rays exposition) include
growths in the incidence of skin cancer, eye cataracts, damage to crops and
plants, deficiencies of the immune system and increase of ozone at ground
levels (through photochemical smog).
Even though transportation contributes significantly to the emission of air
pollutants new technologies (catalytic converters) and policies have
reduced emissions significantly, notably in the United States.
Copyright © 1998-2008, Dr. Jean-Paul Rodrigue, Dept. of Economics & Geography,
Hofstra University. For personal or classroom use ONLY. This material (including
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