Most important environmental
impacts caused by energy sources are global climate change and acid rain – both
of which have the origin in the combustion of fossil fuels and lead to global
or transboundary effects.
Climate change; During the last few decades, concern has been
growing internationally that increasing concentrations of greenhouse gases in
the atmosphere will change our climate in ways detrimental to our social and
economic well-being. Climate change or global warming means a gradual increase
in the global average air temperature at the earth’s surface. Abundant data
demonstrate that global climate has warmed during the past 150 years. The
majority of scientists now believe that global warming is taking place, at a
rate of around 0,3 deg. C per decade, and that it is caused by increases in the
concentration of so-called “greenhouse gases” in the atmosphere. The most
important single component of these greenhouse gas emissions is carbon dioxide
(CO2). The major source of emissions of CO2 are power
plants, automobiles, and industry. Combustion of fossil fuels contributes
around 80 percent to total world-wide anthropogenic CO2 emissions.
Another source is global deforestation. Trees remove carbon dioxide from
the air as they grow. When they are cut and burned that CO2 is
released back into the atmosphere. Massive deforestation around the globe
is releasing large amounts of CO2 and decreasing the forests’
ability to take CO2 from the atmosphere. The second major greenhouse
gas is methane (CH4). It is a minor by-product of burning coal, and
also comes from venting of natural gas (which is nearly pure methane).
Different fossil fuels produce different amounts of CO2 per unit of
energy released. Coal is largely carbon, and so most of its combustion products
are CO2. Natural gas, which is methane, produces water as well as CO2
when it is burned, and so emits less CO2 per unit of energy than
coal. Oil falls somewhere between gas and coal in terms of CO2
emissions, as it is made up of a mixture of hydrocarbons. The amount of CO2
produced per unit of energy from coal, oil and gas is in the approximate
proportion of 2 to 1,5 to 1. This is one of the reasons why there is a move
towards greater use of natural gas instead of coal or oil in power stations,
despite the much greater abundance of coal.
The earth’s atmosphere is made up of several gases, which act as a
“greenhouse”, trapping the sun’s rays as they are reflected from the earth’s surface.
Without this mechanism, the earth would be too cold to sustain life as we know
it. Since the industrial revolution, humans have been adding huge quantities of
greenhouse gases, especially carbon dioxide (CO2) to the atmosphere.
More greenhouse gases means that more heat is trapped, which causes global
warming. By burning coal, oil and natural gas increases atmospheric
concentrations of these gases. Over the past century, increases in industry,
transportation, and electricity production have increased gas concentrations in
the atmosphere faster than natural processes can remove them leading to
human-caused warming of the globe.
Acid
rain
; Another side effect of fossil
fuels combustion and resulting emissions of pollutants is acid rain (or acid
deposition). In the process of burning fossil fuels some of gases, in
particular sulphur dioxide (SO2) and nitrogen oxides (NOx)
are created. Although natural sources of sulphur oxides and nitrogen oxides do
exist, more than 90% of the sulphur and 95% of the nitrogen emissions occurring
in North America and Europe are of human
origin. Once released into the atmosphere, they can be converted chemically
into such secondary pollutants as nitric acid and sulphuric acid, both of which
dissolve easily in water. The result is that any rain which follows is slightly
acidic. The acidic water droplets can be carried long distances by prevailing winds,
returning to Earth as acid rain, snow, or fog.
Natural factors such as volcanoes, swamps and decaying plant life all
produce sulphur dioxide, one of the contributing gases to acid rain. These
natural occurrences form some kind of acid rain. There are also some cases
where acid rain may be produced naturally, which is also bad for the
environment but occurs in much lower amounts and quantities than that of those
found in urban areas. Between the 1950’s and the 1970’s the rain over Europe increased in acidity by approximately ten times.
In the 1980’s however, acidity levels decreased, but although many countries
have started to do something about pollution that causes acid rain, the problem
is not going away. Acid rain is often phrased as “acid precipitation”. On the
pH scale, rain usually measures 5.6. Anything below this measurement is said to
be acidified rainfall. The chemical equation for acid rain is as follows:
SO2
(Sulphur
dioxide) + NO (Nitrogen Oxide) + H2O (Water) = Acid rain
Water solutions vary in their degree of acidity. If pure water is
defined as neutral, baking soda solutions are basic (alkaline) and household
ammonia is very basic (very alkaline). On the other side of this scale there
are ascending degrees of acidity; milk is slightly acidic, tomato juice is
slightly more acidic, vinegar, lemon juice is still more acidic, and battery
acid is extremely acidic. If there were no pollution at all, normal rainwater
would fall on the acid side of this scale, not the alkaline side. Normal rainwater
is less acidic than tomato juice, but more acidic than milk. What pollution
does is cause the acidity of rain to increase. In some areas of the world, rain
can be as acidic as vinegar or lemon juice.
This acid rain can cause damage to plant life, in some cases seriously
affecting the growth of forests, and can erode buildings and corrode metal
objects. The primary component involved in corrosion is acid rain. It is
estimated that the damage to metal buildings alone amounts to about 2 billion
dollars yearly. The highest emissions of sulphur come from those sectors, which
use the most energy and the highest sulphur-content fuels, that is solid fuels
and high sulphur heavy fuel oil. Solid fuels are the most polluting fossil
fuels locally and globally. These fuels range from hard coals to soft brown
coals and lignites, which have high proportion of combustion waste and
pollutants such as sulphur, heavy metals, moisture and ash content.
One of the major problems with acid rain is that it gets carried from a
mass acid rain producing area to areas that are usually not as badly affected.
Tall chimneys that are built to ensure that the pollution that is produced by
factories is taken away from nearby cities, puts the pollution into the
atmosphere. When the moisture in the air picks up these particles, they form
acids. As a result they become a part of the clouds. Then these clouds get
carried off by wind, which means that when the rain falls it may be a long
distance away from where the acidic particles were picked up from. An example
of this would be Central and Eastern Europe and Scandinavia.
Sweden
suffer from acid rain because of huge sulphur emissions from Eastern European
power plants with low emission standards and because of wind blowing the
particles over to their country.
Bad air quality; Beside greenhouse gases, SO2 and
NOx emissions that cause acid rain, emissions of particulate matter
contribute to bad air quality. Fuel combustion is the most important source of
anthropogenic nitrogen oxides, while fuel combustion and evaporative emissions
from motor vehicles are the main sources of anthropogenic volatile organic compounds
(VOCs). Motor vehicles account for a considerable fraction of the
total emissions of nitrogen oxides and VOCs in Europe and North America. NOx emissions also contribute
to the formation of tropospheric photochemical oxidants. Photochemical
oxidants, especially ozone (O3), are among the most important trace
gases in the atmosphere. Their distributions show signs of change due to
increasing emissions of ozone precursors (nitrogen oxides, or VOCs, methane and
carbon monoxide
According to World Health Organisation air quality guidelines for ozone
limit values are frequently exceeded in most parts of developed countries. In
the lower troposphere, close to the ground, ozone is a strong oxidant that at
elevated concentrations is harmful to human health, materials and plants. In
the upper troposphere, ozone is an important greenhouse gas and contributes
greatly to the oxidation efficiency of the atmosphere.
There are reported several ozone and other photochemical oxidants effects on
human health, materials, and crops. Increased ozone level can cause premature
ageing of lungs and other respiratory tract effects like impaired lung function
and increased bronchial reactivity. Increased incidence of asthmatic attacks,
and respiratory symptoms, have been observed. Ozone contributes to damage to
materials such as paint, textile, rubber and plastics. In the case of crops and
some sensitive natural types of vegetation or plant species, exposure to ozone
will lead leaf to damage and loss of production. Other photochemical oxidants
cause a range of acute effects including eye, nose and throat irritation, chest
discomfort, cough and headache. As a second consequence of increases in global
trace gas emissions, a further decrease is expected to occur of the
self-cleansing capacity of the troposphere. This would result in longer
atmospheric residence times of trace gases and, consequently, an enhanced
greenhouse effect and an increased influx of ozone-depleting trace gases into
the stratosphere.
Heavy metals like arsenic (As), cadmium (Cd), mercury (Hg), lead (Pb)
and zinc (Zn) are also released during fuel combustion. Lead pollution as the
result of road traffic emissions have decreased markedly since early 80s due to
increased consumption of unleaded gasoline and use of catalysts in cars.
Nevertheless this sector remains the main source of lead in atmosphere. Beside
emissions of pollutants there are also some other impacts of fossil fuel
combustion on local environment. Here microclimatic impacts like origination of
fogs, less sunshine etc. are the results of large amounts of water vapour
effluents from cooling towers of power plants.
Sea pollution; Damage caused by the
transport of oil is related to the pollution of the seas. Here as the scale of
oil production has increased during the twentieth century, the quantity of oil
transported around the world, most of it by the sea, has also increased. To
cope with this increase, in a highly competitive market, the size of oil
tankers has increased to the point where they are by far the largest commercial
ships. Even in routine operation, this results in large quantities of oil being
released into the seas. The tankers fill up with water as ballast for return
journeys. When this is emptied, significant quantities of oil are released as
well.
Despite the fact that the transport of oil is generally a
safe industry, the scale of it, and the size of tankers, means that when
accidents do occur they have a large effect. Although the number of accidents
is small in proportion to the number of tanker journeys, thousands of minor
incidents involving oil spills from tankers, and oil storage facilities occur
annually.
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