Local air pollution begins at home
acid rain. A form of acid deposition. When fossil fuels are burnt, sulfur dioxide (SO2) and oxides of nitrogen (NOx ) are released into the atmosphere. They can react with water vapour (or chemicals derived from it) to form acids. If these attach to particulates in the air, they may fall as acid soot close to the source of the pollution. This is acid deposition. The acid can also fall in rain, snow or hail (collectively known as acid precipitation) often far away from the original pollution (eg, Canada receives acid rain from US pollution).
carbon monoxide. Carbon monoxide (CO) is a colourless, odourless, very poisonous gas. It is produced by the incomplete combustion of carbon-containing fuels. For example, it is a product of combustion of petrol in car engines.
It is a fast-acting poison for all animals (including humans) that use the red pigment haemoglobin to carry oxygen within the body. The gas attaches to haemoglobin, which then is unable to function. Thus, carbon monoxide stops the blood from carrying oxygen efficiently. Even at concentrations as low as 10 parts per million (0.001 per cent) CO can cause headaches, tiredness and slow reflexes, as a small proportion of the haemoglobin molecules are put out of action. Daily exposure to low levels of CO is linked with lack of fitness, a tendency to form blood clots, and disease of the heart, arteries and lungs. At concentrations above 200 ppm, exposure to CO for more than a few minutes is fatal.
The maximum acceptable level for CO in air is usually set at 30 ppm. Australian suburbs in general seldom exceed this, but busy city centres with many vehicles (such as during rush hour) and with poor air circulation may sometimes suffer a build-up of CO, sufficient to cause the first symptoms of poisoning in some individuals. Garages and road tunnels are places where CO can increase to more dangerous proportions.
nitrogen oxides. Chemical formula NOx . Covers the gases nitric oxide (NO) and nitrogen dioxide (NO2). Both can be toxic but nitrogen dioxide is considered to be of most concern for asthmatics. The main source of the gases in urban areas are motor vehicle exhaust and gas cookers and kerosene heaters indoors. The brown haze sometimes seen over cities is mainly nitrogen oxides. These gases are also partly responsible for the generation of ozone, when acted upon by sunlight in the presence of other chemicals. Although air pollution can cause irritating symptoms and increased asthma symptoms in some people, it is unlikely to be an important cause of asthma in Australia.
ozone. Ozone (O3) is a form of oxygen. It is a colourless gas that has a very pungent odour. It exists naturally at low concentrations in the stratosphere, where it absorbs ultraviolet radiation. In the troposphere it exists naturally at extremely low concentrations. But these concentrations increase when sunlight acts on various gases coming mainly from vehicle exhausts, and ozone then becomes a pollutant in the troposphere. Ozone is a highly corrosive gas and is poisonous to most organisms. At concentrations as low as 0.00001 per cent (or 10 parts per hundred million) it can irritate the membranes lining the nose, throat and airways and can trigger or exacerbate asthma attacks.
particles. Very small pieces of solid or liquid matter. Particles of dust, sea salt, and material from volcanic eruptions occur naturally in the atmosphere. Sulfate particles are also produced naturally from gases emitted by marine organisms. Industry and motor vehicles add significantly to the concentration of particles in the atmosphere high concentrations are found in big cities and industrial areas. These particles remain airborne for long periods, lowering visibility. The brown haze which is often seen over large cities in autumn, winter and spring is due mainly to particles.
Particles in the air can cause breathing difficulties and worsen respiratory diseases. Some particles contain cancer-producing materials.
sulfur dioxide. Sulfur dioxide (SO2) is an acrid-smelling gas that even at low concentrations irritates the membranes of the nose and respiratory system. It is thought to exacerbate many respiratory diseases, including asthma. Sulfur dioxide is produced whenever sulfur-containing compounds are burnt. Its commonest source in Australia is power-stations burning coal containing slight sulfur impurities.
Posted August 1997.