Chapter 19 – Environmental Issues (Part 2)
Depletion of the Ozone layer
As discussed in Chapter 18, the ozone layer, most of it within a band 10–30 km above the Earth’s surface, protects life on Earth by
absorbing ultraviolet (UV) radiation. UV radiation causes skin cancer and cataracts and suppresses the immune system in humans.
Exposure can damage plant life and aquatic ecosystems. Scientists first became concerned about possible damage to the ozone
layer in 1971, with proposals to develop supersonic aircraft, which would fly at extremely high altitudes. It was suggested that the
jet engines of these aircraft would produce nitrogen oxide (NO) from the reaction between the nitrogen and oxygen in the air
drawn into the engines. The nitrogen(II) oxide produced in this reaction in the stratosphere could then act as a catalyst to break
down ozone.
The net effect of these reactions
ozone.
is: The nitrogen(II) oxide is then free for further reactions with
There is now widespread concern that other gases produced by human activities have damaged
the ozone layer. These gases are chlorofluorocarbons (CFCs) and halons. Halons are thought to
cause more damage to the ozone layer than chlorofluorocarbons. Although these compounds
are not produced widely now, it will be many years before their effect on the ozone layer
decreases significantly. CFCs are long lived because they are unreactive in the lower
atmosphere. In regions near the Earth’s surface they are virtually inert. Eventually they move
up into the stratosphere, where they can be broken down by ultraviolet light, releasing free
halogen atoms, such as chlorine. These atoms have a destructive effect on ozone similar to that
of nitrogen oxide.
Alternatives to ozone-depleting chemicals
The development of the ‘hole’ above Antarctica has been matched by a similar thinning in the northern hemisphere above the
Arctic. Together with an overall global decline in ozone levels over the last few decades, this has caused sufficient worldwide
concern to reduce the production of CFCs and halons. There have been nine international assessments, including the Montreal
Protocol (1987). Individual government regulations have been designed to reduce the production of ozone-depleting chemicals
and to find alternatives. For example, in many countries, including Australia, aerosol cans no longer use CFCs as a propellant.
The CFCs used in refrigerators and air-conditioning systems can be recycled. However, it is thought that an 85% reduction in
CFC and halon production worldwide would be needed just to stabilise the ozone depletion at current levels. As the various
Protocols and amendments begin to take effect, the incidence of skin cancer should decrease. The good news is that the ozonedepleting chemicals in the lower atmosphere have been decreasing since their highest concentrations in 1994. These chemicals are
still present in the upper atmosphere and have reached their maximum levels in the year 2000. So, in the next 10 years or so, the
hole should begin to recover.
Photochemical Smog
Many cities around the world experience photochemical smog. It is visible as a brown haze, particularly on still, sunny days. NO is
formed during the combustion of fuel in car engines. NO 2 is formed when the NO reacts with O2 as the temperature of the
combustion products drops to near air temperature. These oxides of nitrogen are important in the formation of photochemical smog.
Unfortunately, the brown haze is not harmless. It is a collection of gases, including ozone, some of which can cause severe health
problems. It is called photochemical smog, because it forms from the action of sunlight on a mixture of nitrogen oxides, unburnt
hydrocarbons (from car engines and industry) and oxygen.
When fossil fuels are burnt in an efficient engine and a plentiful supply of air, CO2 and H2O are the main wastes produced. Because
fossil fuels contain traces of sulfur, sulfur dioxide is also produced during this combustion process and released into the atmosphere.
When the supply of oxygen is insufficient, however, or in a poorly tuned engine, combustion of the fuel might not be complete.
There might not be enough oxygen for all the fuel to form carbon dioxide. Some of the fuel may produce CO instead of CO 2. As
well, some of the hydrocarbons in the gasoline escape in the exhaust gases without burning at all. For example:
where a, b and c depend on the amount of oxygen available.
Carbon monoxide is a highly poisonous gas. It combines readily with haemoglobin, the oxygen carrier in blood. When attached to
carbon monoxide, haemoglobin cannot transport oxygen around the body, which leads to oxygen starvation of tissues. At about 200
ppm, it can lead to death. The average carbon monoxide concentration in large cities is now 7 ppm, and can be as high as 120 ppm
at busy intersections in heavy traffic. It is believed that the effect of carbon monoxide on drivers is a contributing factor to many
peak-hour road accidents.
Oxides of nitrogen are also released by motor vehicles. These are not produced by the combustion of the fuel itself. A side reaction
occurs because one of the important features of this type of engine is that the gases in its cylinders reach temperatures as high as
2000°C. At such high temperatures, some of the nitrogen and oxygen gases in the air entering the
combustion chamber combine to produce NO:
As the combustion products are released into the atmosphere, they experience a sudden temperature drop. At the lower temperature,
some of the NO reacts further with oxygen to produce NO2:
In summary, the exhaust gases from a car engine include:
 unreacted nitrogen gas
 carbon dioxide, water and sulfur dioxide gases from the complete burning of fuel


carbon monoxide and unburnt hydrocarbons from the incomplete burning of fuel
Nitrogen(II) oxide from the high temperature reaction between nitrogen and oxygen in the combustion chamber of the
engine.
The formation of photochemical smog tends to be favoured by particular weather conditions. Normally, warm air near the
Earth’s surface will rise and carry any smog with it, dispersing it into the atmosphere. Temperature inversions begin on calm,
clear nights when the Earth’s surface cools rapidly as heat radiates away from it. The air near the ground becomes colder than the
air higher up and this denser, colder layer becomes trapped by the warmer air above it. Any smog formed during the day in this
bottom layer is also trapped and this gives more time for the reactions between the sunlight and the gases which produce smog to
increase the concentrations of pollutants. These conditions can last for several days until the smog is dispersed by winds.
The nitrogen oxides (NOx) and the unburnt hydrocarbons emitted into the atmosphere, mainly from car exhausts and industry,
are called primary pollutants. These then take part in a complex, and not fully understood, series of reactions together with
oxygen, and in the presence of sunlight, to form a mixture of secondary pollutants, which have no direct emission sources. They
include ozone (O3) (which is the most common), aldehydes, peroxyacetyl nitrate (PAN) and other organic compounds. Ozone is
considered a pollutant in these circumstances because it is produced in the wrong place. In the lower atmosphere, ozone can be an
irritant, especially to those with respiratory problems. Even in very low concentrations, ozone damages plants and causes rubber
to deteriorate. However, in the upper atmosphere, ozone is an essential ultraviolet light filter.
Enhanced Greenhouse Effect
Greenhouse gases have enabled the Earth to maintain its average
temperature over time because of a balance created between the radiation
received from the Sun and the heat radiated back into space. Carbon dioxide is
one greenhouse gas. Other greenhouse gases include water vapour, methane,
CFCs, nitrogen(II) oxide and ozone.
The greenhouse effect itself is not a problem. The enhanced greenhouse
effect describes an imbalance that has arisen with the levels of greenhouse
gases in the atmosphere, in particular carbon dioxide, methane and CFCs
increasing too quickly. This increase has upset the balance and has caused
global warming to occur too rapidly for living things to adjust.
Why are the concentrations of greenhouse gases increasing?
1. Carbon Dioxide - Since the industrial revolution in the late 18th and early 19th centuries, the concentration of CO 2 in the
atmosphere has risen dramatically. At present, the level is increasing by about 0.5% each year. The increase is largely due to the
greater consumption of fossil fuels to meet an increased demand for energy in industrialised countries. The combustion of 1 tonne
of coal produces 4 tonnes of carbon dioxide. About half of the carbon dioxide produced has accumulated in the atmosphere; the
remainder has either dissolved in the oceans or has been used by plant life in photosynthesis. The continued clearing of forests,
particularly in tropical areas, contributes to the accumulation of carbon dioxide. Carbon dioxide is released when the trees are
burnt or left to decay. In addition, the clearing of forests means there is less carbon dioxide removed from the atmosphere by
photosynthesis. It is estimated that carbon dioxide is contributing to about half of the warming effect produced by increasing
concentrations of greenhouse gases. Although carbon dioxide is essential to life, it is detrimental to the environment when its
concentration is too high—when its production is not balanced by its consumption.
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2. Methane - The concentration of CH4, another greenhouse gas, is currently increasing by about 0.4% per year. Methane is
produced by bacterial action in the digestive tracts of ruminant animals. It also enters the atmosphere from rice paddies; termite
mounds; natural gas fields; industrial activities, involving the burning of wood and fossil fuels; and garbage dumps.
3. Chlorofluorocarbons and other gases - As well as contributing to the depletion of the ozone layer, CFCs are also effective
greenhouse gases. They are up to 10 000 times more efficient at absorbing infrared radiation than an equal amount of carbon
dioxide. At present, the concentration of CFCs is increasing by 5–7% per year. At this rate, by early next century the warming
effect of CFCs may approach that of carbon dioxide. Other greenhouse gases thought to be contributing to the climatic warming
are water vapour and nitrogen oxides, including nitrogen(II) oxide (NO) from the use of agricultural fertilisers.
Consequences of global warming
There has been much speculation about the effects of the increased concentration of greenhouse gases in the atmosphere. The
Earth’s mean temperature has risen by about 0.6°C since the 1890s, and many scientists are now confident that is due largely to
an increased greenhouse effect. At present, this warming seems to be continuing at about 0.3% per decade, and the rate may
increase if action is not taken to limit the increase in concentration of greenhouse gases. Scientists predict that the Earth’s
temperature could rise by 2.5–5°C in the next 30 years due to the increasing concentrations of greenhouse gases.
The various predictions about the consequences of such a rapid global warming include:
 Rising sea levels. The sea level could by rise up to 1.5 m within the next 30 years due to the expansion of water as the
temperature of the oceans increases. Prolonged global warming could also melt the polar ice caps and sea levels would
then rise much further.
 Climatic changes in different parts of the world. For example, south-eastern Australia is predicted to have increased Summer
rainfall and decreased winter rainfall. Extreme weather conditions, such as droughts and floods, would be more frequent,
and tropical cyclones could also become more frequent and extend further. In alpine areas the snow-line would rise.

Ecological changes. These would occur as a result of rising sea levels and climatic change. For example, there could be a
loss of natural wetlands. Such changes would affect the habitats of many of the world’s plants and animals, particularly
those in mid-latitudes and Arctic regions.
Planning for the future
There is much public discussion about ways of slowing the increase of greenhouse gases. These include:
 reducing the consumption of fossil fuels by conserving energy measures and developing renewable energy sources
 slowing the rate at which forests are being cleared, and planting more forests, which would also slow the increase in
carbon dioxide levels. The current rate of deforestation is about ten times the rate of reafforestation
 phasing out the use of chlorofluorocarbons. This is gaining worldwide acceptance as it will reduce greenhouse gases in
addition to protecting the ozone layer.
If global warming cannot be prevented, many countries, including Australia, will need to examine issues such as the planning and
design of housing, particularly in low-lying areas subject to increased flooding and erosion. Any climatic change will affect
agricultural production. Some of the world’s major food production areas could become considerably drier as a result of global
warming. Flood plains and river delta regions that currently grow a significant proportion of the world’s food would be
permanently under water.
The Kyoto Protocol
The Protocol was negotiated in Kyoto, Japan, in 1997 and is an international agreement designed to limit greenhouse gas
emissions. By signing the 1997 protocol, countries agreed to continue to develop and refine the rules and conditions laid down in
the agreement, but did not consent to be bound by it. In November 2001, countries were asked to ratify or confirm their intentions
to abide by the agreement once it came into force in February 2005. The major feature of the Kyoto Protocol is that it sets binding
targets for 37 industrialized countries and the European community for reducing greenhouse gas (GHG) emissions .These
amount to an average of five per cent against 1990 levels over the five-year period 2008-2012.
Recognizing that developed countries are principally responsible for the current high levels of GHG emissions in the atmosphere
as a result of more than 150 years of industrial activity, the Protocol places a heavier burden on developed nations under the
principle of “common but differentiated responsibilities.”
A solution to the Enhanced Greenhouse Effect
A report from the United Nations Framework Convention on Climate Change proposed that carbon dioxide could be stored in
underground formations such as old, exhausted oil or gas fields or salt mines. A trial has been conducted, over the past 10 years,
where 5 million tonnes of carbon dioxide have been pumped under the North Sea. The gas is buried a kilometre beneath the ocean
floor. The cost of capturing the CO2 from power stations would be significant and we still don’t know what effect the CO 2 would
have on aquatic life. This technology might provide a short-term solution, but it would be preferable to develop alternative sources
of energy that produce less pollution especially of CO 2.
Chapter 19 – Q 4, 5, 7a, 8, 9, 10, 11, 14, 16, 17, 20,