Jean-Paul Rodrigue (2017), New York:
Routledge, 440 pages.
Pollutants Emitted by Transport Systems (Air, Water and Noise)
Author: Dr. Jean-Paul Rodrigue
One geographical dimension of air pollution is at the local and regional
levels where its externalities are immediately felt. The higher the
level of concentration of transport activities, the higher their
environmental impacts are being felt by the local community. This is
particularly the case for large transport terminals, such as ports,
rail yards and airports. A salient example is Hong Kong, one of the
world's most important container port. The container terminals are
centrally located with with an acute concentration of large ships
and tens of thousands of truck movements per day. Many air pollutants
identified as being closely related to transportation:
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
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 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
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 vapors, 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 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.
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
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 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.
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
Sulfur dioxide is a heavy, colorless gas with a strong odor.
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 climatic models.
Ozone is a pale blue gas with a strong odor 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
Acid Rain and Acid Depositions (Sulfuric and Nitric Acid (H2SO4,
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.
CFCs are colorless 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 during 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).
Transportation contributes significantly to the pollution of the
hydrosphere in various ways ranging from air pollution fallouts to the
construction and maintenance of infrastructure such as roads, railways
and ports. The first type of impacts are related to the transport modes.
Fallouts occur when a pollutant goes from an airborne state
(gas, solid or liquid) towards a solute or colloidal state. Water
is a very good solvent for several pollutants, notably acid depositions.
Fallouts are accelerated and concentrated in an area by rainy conditions. As an important source of air pollution, transportation accounts
on a similar scale for fallouts. In some areas transportation may
account for up to 25% of nitrogen fallouts in water. It is
estimated that acid rains may account for more than 75% of the growth
of acidity of lakes.
Since fallouts are a continuous accumulation and occur over
a longer period than most water pollution sources, they have a higher
impact on still-water (lentic) environments than running-water (lotic).
The most notable and destructive fallouts are sulfuric and nitric
acids that may alter the pH of water if they are present in sufficient
concentrations. Several northeastern United States and eastern Canadian
lakes have seen their entire fish population destroyed as a result
of increased acidity levels. It also includes damage to forests
like reduced photosynthesis (sparse foliage) and acidified soils
(limited nutrients). Nitrous oxides may affect the ecological balance
of marine life by favoring algae blooms.
Other fallouts such as HC/VOC and lead are poisonous and may
disrupt marine life if they accumulate in the aquatic food chain.
Particulate fallouts, when in sufficient quantities, may increase
the turbidity of water and thus reduce the photosynthesis capacity
of aquatic plants. A long term accumulation of air pollution fallouts
of various nature will contaminate and disrupt whole aquatic ecosystems.
Marine Vessels Discharges and Spills
After unloading their bulk loads like oil, coal, nitrates and
mineral products, marine vessels require cleaning. Since this practice
is restricted in several port and coastal areas, operators wait
until they are in international waters to proceed. Oil products
residuals carried by tankers are the major source for discharges. It is estimated that
for every million tons of oil carried,
one ton is spilled through washouts. Once a spill has occurred,
it is extremely difficult to contain it. Annually, an average of 1.1 million
tons of oil comes from discharges and 400,000 tons are spilled.
They depend on the nature of the residue discharged. Petroleum products are the most harmful and include environmental
effects like the destruction/disruption of aquatic plant/animal
life and of shore ecosystems. Since most marine life is in neritic
(continental shelf) and epipelagic (less then 100 meters) zones,
it is particularly vulnerable to
De-Icing of Infrastructure and Runoffs
Salt (NaCl) has the characteristic of lowering the melting point
of water and thus presents an useful compound for keeping safe road
conditions in sub-zero climates. Other elements like sand and gravel
are also added to provide adherence. Runoffs occur when substances accumulated by a surface (notably
a road) are dissolved / carried by water and evacuated elsewhere.
It is often the convergence of a surface to a point. De-icing of
transportation infrastructure (roads, parking lots, airfields etc.)
is almost the only artificial source of salt release in the environment.
Salt mostly comes from mining (halite) or in fewer proportions from
sea water evaporation. Other compounds like calcium and magnesium
can be used, but they work more slowly and cost ten times as much. Lubricants (from car leakages - engine, brakes, and transmission),
heavy metals (Zn, Cd, Cu, Ni, Cr and Fe from abrasion of tires and
brake linings) and dry fallouts (HC/VOC, particulates) account for
harmful sources of runoffs.
Since road infrastructure (parking lots, roads, drainage systems)
occupy a significant land surface in developed countries, it is
the major source of runoffs. For instance, while highways occupy
5-8% of the urban catchment area, it contributes for as much as
50% of the total suspended solids, 16% of the total HC and 75% of
the total metal inputs to a receiving stream. High concentrations of salt, notably chlorine ions, in fresh
water environments disrupt life cycles and may be fatal to some
organisms like larvae. Runoffs from infrastructure will alter the
turbidity and the oxygen level of water (warm water holds less oxygen),
and contaminate the food chain. It may increase the eutrophication
process of several lakes, particularly in recreational areas where
dirt roads are dense. De-icing salt has the tendency to accumulate
in snow and soils beside roadways. During early springtime, nearly
all the salt accumulated will be released in the hydrographic system
where it will contaminate ground water and interfere with the growth
of plants and the reproduction cycle of aquatic life, particularly
vulnerable at this time of year. Infrastructure runoffs collected by the sewage system of urban
areas often converge at evacuation points and contaminate whole
hydrographic systems at high concentrations. It is worth noting
that most cities have 30 to 70% of their surface occupied by roads
and parking space. They thus represent important sources of runoffs.
Construction and Maintenance of Infrastructure
Several transportation infrastructures have important territorial
handholds. When a transportation infrastructure is built over a
hydrological environment like a river, wetland or a coastal area,
disruption occurs. The maintenance of transportation infrastructure, particularly
harbor and waterways (dredging), have also a significant impact.
Each mode needs a specific set of infrastructure that interfere
with hydric systems. Road infrastructure accounts for most of the territorial
handhold of transportation with structures like bridges and
parking facilities. Railways have also an important handhold over
continental hydric systems. Maritime transportation, by its intrinsic
link with hydric systems have several disruptive infrastructure
like piers, canals, harbors and terminals. Airports have similar
effects when constructed over wetland. Dredging accounts alone for
80% of the waste released in aquatic environments.
The most widespread effect of transportation infrastructure
on hydric systems is the removal of natural habitats along shorelines.
The aquatic / land interface to which several animal and vegetal
species depend is considerably reduced. Further, a modification
of the aquatic environment occurs, particularly during dredging
in port harbors and along waterways. This notably influences the
turbidity of water and destroys habitats. Roads and rails, when
running through wetland, reduce the water regeneration / purification
capacity by splitting available areas and disrupting water flows.
Large ports occupy extensive areas along the shorelines of waterways
and coasts. The construction and maintenance of those infrastructure
have thus extensive impacts over aquatic environments. The construction
of canals changes whole hydrographic systems by altering water flows
(quantity and speed) at regional and often at continental levels.
Road accounts for approximately
70% of total noise emissions by transportation. It must be noted
that different road transportation modes have different scales of
noise emissions. Main sources of noise come from the engine and the
friction of the wheels over the road surface. Further, travel
speed and the intensity of traffic are directly linked with its
intensity of noise. For instance, one truck moving at 90 km/hr makes
as much noise as 28 cars moving at the same speed. Ambient noise is a frequent result of road transportation
in urban areas, which is the cumulative outcome of all the noise generated by
vehicles (ranging from
45 to 65 db), which impairs the quality of life and
thus property values. Nearby
road arterials, ambient noise
is replaced by direct noise and vibrations. The acoustics created
by the surrounding environment (hills, buildings, trees, open space,
etc.) alleviate or worsen local conditions. Noise level grows arithmetically with speed. For instance
a car traveling at 20 km/hr emits 55 db of rolling noise, at 40
km/hr 65 db, at 80 km/hr 75 db and at 100 km/hr 80 db. Available
evidence underlines that around 45% of the population in developed
countries live in high levels of noise intensity (over 55 db) generated
by road transportation. Along major highway arterials in inter-urban
areas, noise emissions are likely to alter the living environment
of wildlife species.
Rail accounts for 10% of total
noise emissions by transportation. Noise comes from the engine
(mostly diesel), the friction of wheels over the rails, and whistle
blowing. Furthermore, when trains are moving at high speed, areoacoustic
noise becomes more important than other sources. Depending of
the train aerodynamics, noise emissions are from 50 to 80 times
the logarithm of train speed and become significant at speeds higher
than 200 km/hr. When rail / truck transshipment is involved, the convergence
of trucks towards railyards provides an additional source of noise
related to rail transportation activities. Around 3% of the population may be exposed to high noise levels
from rail transportation in OECD countries. The level of exposure
is obviously related to the importance and
location of rail transportation infrastructure.
The most important noise impacts of rail operations are in urban
areas where the majority transshipment functions are performed.
Furthermore, rail terminals are often located in the central and
high density areas of cities.
Air transportation accounts for 20% of total noise emissions
by transportation. As air transportation took a growing importance
in inter-city transportation and that jet engines were predominantly
used, noise emissions have increased significantly to the point
of becoming a major concern near airports. Noise comes from the
jet engine, the aerodynamic friction
and ground craft operations. Even if the turbofan is the
least noisy jet propulsion technology available, aircrafts are an
acute source of noise in several urban areas. Noise from aircraft
operation is known to have direct impact on property values around
airports. This effect is distributed
along major approach and takeoff lanes. The establishment of heavily used flight paths between major
cities creates noise corridors where ambient noise is almost prevalent.
This is particularly noted when those corridors are over densely
populated areas. Operations at several airports are impacted.
For instance, in 2011, the airport of Frankfurt (Flughafen Frankfurt am
Main) imposed a night curfew on operations, effectively closing the
airport from 11PM to 5AM. This had a negative impact on cargo operations
that usually use airport facilities during the night.