Pollutants in our air
Pollutants are substances which, when present at high enough
concentrations, produce harmful effects on people and/or the environment.
A number of pollutants affecting urban and/or regional air quality are
listed in Table 1.
Sulfur dioxide is produced when coal and oil are burnt
or when minerals are "roasted" to remove the sulfur. In some
countries, particularly in the northern hemisphere, coal and oil contain
significant amounts of sulfur. Unless special steps are taken to remove
sulfur dioxide, it is released into the atmosphere. Power stations and
industrial plants, which are often sited close to cities, can produce
large quantities of the gas.
As well as affecting human health, sulfur dioxide can be harmful to plants,
turning leaves yellow and drying, bleaching, and even killing, foliage.
In the atmosphere, sulfur dioxide can form acidic particles, or react
with cloud droplets, contributing to acid rain.
Particles in the air (also known as aerosol) come from
a number of sources, including motor vehicles, industrial processes and
wood burning. Secondary formation of particles (formation from gaseous
emissions) can also contribute significantly to particle levels. Some
atmospheric particles are from natural sources. These include wind-blown
dust, pollen, sea salt, and material from volcanic eruptions.
Fine particles (particles with a diameter of 10 micrometres or less)
can be inhaled deeply into the lungs and have been associated with a wide
range of adverse respiratory symptoms. Long- and short-term exposure to
such particles has been linked with increased deaths from heart and lung
Lead compounds, which are emitted by motor vehicles fuelled with leaded
petrol, are cumulative poisons. They slowly build up in the body.
Urban haze is mainly due to fine particles, which cause
scattering or absorption of light. Haze is typically brown and limits
Studies by CSIRO scientists have found that there are several types of
particles present in haze in Australian cities: organic carbon compounds,
elemental carbon or soot, salt, sulfates, nitrates and dust.
The term air toxics is often used when referring to atmospheric
pollutants. Air toxics are gaseous, aerosol or particulate pollutants,
which are present in the air in low concentrations with characteristics
such as toxicity or persistence so as to be a hazard to human, plant or
Sometimes, under certain meteorological conditions, the
combined effects of a number of air pollutants are worse than the individual
effects. Photochemical smog, sometimes seen as a whitish haze present
over cities during summer, is an example of this.
Photochemical smog is formed on still days when the sun shines on air
containing volatile organic compounds (VOCs) and oxides of nitrogen. Volatile
organic compounds include hydrocarbons, as well as alcohols, aldehydes
and ethers. VOCs in the air arise mainly from automotive fuels and industrial
solvents. Chemical reactions driven by sunlight and involving VOCs and
oxides of nitrogen form ozone, a gas harmful to humans, animals and plants.
Table 1 Major pollutants in our air
Motor vehicles, burning of fossil fuels.
Blood absorbs carbon monoxide more readily than oxygen, reducing the amount of oxygen being carried through the body.
Carbon monoxide can produce tiredness and headaches. People with heart problems are particularly at risk
Coal and oil burning power stations, mineral ore processing and chemical manufacture.
Attacks the throat and lungs. People with breathing problems can suffer severe illness.
Affects the throat and lungs.
Volatile organic compounds
Motor vehicles, fuel combustion, solvent use.
Some VOCs cause eye and skin irritation, headaches or nausea, while some are classed as carcinogens.
Formed from nitrogen oxides and hydrocarbons in sunny conditions. These chemicals are released by motor vehicles and industry.
Ozone attacks the tissue of the throat and lungs and irritates the eyes.
Exhaust gases from motor vehicles that use leaded petrol, smelters.
Particles containing lead in the air can enter the lungs. The lead can then be absorbed into the blood stream. Over a period lead can affect the
nervous system and the body's ability to produce blood.
Motor vehicles, burning of plant materials, bushfires.
May cause breathing difficulties and worsen respiratory diseases. Some particles contain cancer-producing materials.
In addition to ozone, photochemical smog contains a number
of other harmful secondary pollutants such as peroxyacetyl nitrate and
aldehydes, which are severe irritants, particularly to the eyes. (Ironically,
ozone in the stratosphere is essential for life as we know it. This ozone
layer prevents much of the sun's harmful ultraviolet light reaching us.)
Air quality indoors
Australians on average spend about ninety-five percent
of their time indoors and many pollutants occur at higher concentrations
indoors than outdoors because of the materials and appliances used in
Many peoples main exposure to air pollutants occurs when they are
indoors, such as at home, in the workplace or in entertainment venues.
Researchers are working towards measuring individual exposure
to pollutants. That is, a measure of the actual exposure that people have
to air pollutants during their daily routines, rather than measures of
pollution at fixed locations.
CSIRO regularly uses personal air pollution detectors, which monitor
concentrations of pollutants that people breathe. The inexpensive samplers
offer scientists, environmentalists, engineers and others a simple but
accurate way of measuring selected pollutants in air. The sampler, based
on a Swedish design, is small and requires no electricity so is ideal
for remote use. Nitrogen dioxide, sulfur dioxide, ammonia and other gases
can be measured with the device.
Pure rainwater is slightly acidic, primarily because of
dissolved carbon dioxide. Air also contains naturally occurring organic
acids and acidic particles. The pH of unpolluted rainwater ranges from
about 6 to just below 5.
Fossil fuel combustion and industrial processes release into the air
compounds containing oxides of sulfur and nitrogen. These compounds may
then dissolve in cloud droplets, making rainwater more acidic.
As well, sulfur- and nitrogen-containing particles may mix through the
atmosphere, eventually coming into direct contact with the ground and
vegetation. In other words, the pollutants can reach the ground in a wet
or dry form. Both forms can harm soil, lakes, plants, buildings and people.
Emissions from power stations, motor vehicles, and industry do contribute
to acid rain. In some parts of Australia, these activities are making
rainwater slightly more acidic.
Acidic pollutants released by one country can travel hundreds, or even
thousands, of kilometres before being deposited. Acid rain is a real problem
in Scandinavian countries, a large fraction being due to pollution released
by other European countries.
There is more industrial activity in the northern hemisphere than in
the southern hemisphere. Industry also tends to be concentrated in particular
regions. This is why acid rain problems are worse in the northern hemisphere.
The main regions affected are north-western Europe and eastern United
States and Canada. Japan and parts of China also have acidity problems.
Air pollution in Australia
Compared with cities such as Los Angeles, Mexico City and
Athens, air pollution problems in Australia are minor. In part, this is
due to the fact that we have fewer sources of pollution, and local winds
tend to rapidly disperse pollution over our cities.
Australia has a relatively small population. We are surrounded by oceans
and do not receive masses of polluted air from other countries. Our oil
and coal contain less sulfur than much of the oil and coal produced in
Nevertheless, each year, Sydney, Melbourne and other large Australian
cities experience days of high air pollution. Summer and autumn are usually
the worst times of the year.
Percentage contribution to air pollution emissions
by motor vehicles in Melbourne
Reducing air pollution
Government legislation and tighter emission controls by
industry have produced a marked improvement in air quality in many parts
of the world. Many methods of lowering emissions have been developed.
In Australia, the emphasis is on prevention and early identification
of air quality problems.
Domestic burning off adds to air pollution. In Australian cities, many
municipalities have banned the use of incinerators. Agricultural and forest
management practices that do not involve burning can also reduce the release
of visibility-reducing particles.
However, motor vehicles present a significant and growing air pollution
threat and are Australias single greatest source of atmospheric
Since 1986, new cars in Australia have had catalytic converters in their
exhaust systems. These converters reduce the amounts of oxides of nitrogen,
carbon monoxide and unburnt petrol escaping into the air. Use of unleaded
petrol is lowering the amount of lead in the urban environment.
Industrial activity, power generation and vehicle numbers in Australia
are still increasing. Action today will help prevent us suffering the
major air pollution problems currently being experienced in many other
parts of the world.
Paul Holper and Julie Noonan