Local air pollution begins at homeLocal air pollution is a major health threat. It ranges in scale from cigarette smoke in a house to the photochemical smog that can cover a city.
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Key textFighting for breath We all know that air pollution makes life miserable – but what exactly is it, and what can we do about it? We are not talking here about the greenhouse effect or the hole in the ozone layer (serious though those are), we are talking about local air pollution, the stuff most of us live in and breathe every day. What is pollution? 'Air pollution' means that there is something in the air we don't want. The combination of gases which make up natural or 'fresh' air seldom do us any harm, and without the most important gas for us – oxygen – we could not live. The problem comes when unwelcome chemicals are added. In Australia the main contaminants of outside air are
Not all pollution is caused by humans – the air around a large bushfire, or on the edge of an active volcano can be even more polluted than the worst city centre. In some ways, the definition of air pollution is a bit like the definition of junk – 'something useful in the wrong place'. The things that pollute air may not be bad in themselves. Ozone, for example, is a real problem at street level, but in the stratosphere it protects us from ultraviolet rays. Lead is another example – it is a durable, easily worked metal that is ideal for waterproofing a roof, screening against X-rays, or even weighting a fishing line – but lead is very nasty when it gets into your bloodstream. Where does pollution come from? Some countries have a problem with polluted air blowing in from the neighbours – Norway has complained for many years about the dirty air from Britain's power stations blowing across the sea and poisoning its beautiful lakes with acid rain. In Australia we are luckier, because most of our pollution is 'home-made'. Not lucky because we have pollution, but because we can do something about it. By understanding the causes of air pollution better we will be able to improve things. The biggest single source of air pollution in Australia is the car (Box 1: Cars). Next comes industry and then a heap of smaller sources like backyard incinerators, cleaning chemicals, paint fumes, and even furniture and carpets (Box 2: Indoor air pollution). Most of our local air pollution problems are caused by us – and by the machines and chemicals we use. Indoor air pollution Close the windows to keep the air pollution out? Well, maybe, but definitely not if you (or someone you share your home with) smoke indoors! When cigarette tobacco burns it gives off a particularly deadly range of substances, including carbon monoxide. You don't have to smoke yourself, just sharing a closed space with someone who is smoking is damaging – even though it may take many years for it to show up. Open fires, kerosene fires, and gas fires can all cause problems if they are not properly ventilated. Carbon monoxide is again the problem here. Carbon monoxide is a fast-acting poison for all animals that have red blood cells (including humans). The gas gets into your bloodstream and attaches itself to the oxygen-carrying red cells and stops them working. Without oxygen your body cannot function properly, and it doesn't take much carbon monoxide to be a problem. As little as 10 parts per million (0.001 per cent) can cause headaches, tiredness and slow reflexes. You will die if you inhale more than 200 parts per million of carbon monoxide for more than a few minutes. The future Nearly all of us are affected by air pollution. The effects of continuous lifelong exposure to low levels of certain pollutants are still unknown. Many employers must now consider air quality as an important issue for their workers, and government agencies increasingly monitor it, while scientists research its effects. This area of environmental care is likely to become much more important in the future as we learn more about it. Related Nova topic:
Lead in petrol Lead is put in petrol to make older designs of car engine work better – but if it gets into your body it will have the opposite effect. The lead comes from the exhausts of cars running on leaded petrol and it is poisonous stuff. Babies and young children can be badly affected by lead – because it can stop their nervous systems developing properly and it can damage their brains. Once lead has found its way into your body it is difficult to get it out again, so it is obviously better to keep it out in the first place. Changing from leaded to unleaded petrol has already helped reduce the problems caused by lead poisoning. But one of the problems is that Australians tend to keep their cars for a very long time, so although unleaded petrol is used in all cars less than 10 years old, it will take a while for all the old cars using leaded petrol to vanish from our roads. Photochemical smog Photochemical smog (where ozone is generated) is the main air pollution problem in the larger Australian cities, because of our sunny weather. It is caused by the release of nitrogen oxides, mainly from motor vehicles. Under the influence of sunlight, these oxides react with certain hydrocarbon compounds to form various substances that are toxic to humans and plants. The smog irritates people's eyes, nose and throat, causing considerable discomfort. Ozone is an extremely irritating and poisonous gas, and concentrations in our cities can exceed recommended health limits for short periods during photochemical smog episodes. The air circulation patterns in some of our cities (where polluted air may recirculate for some time before being swept away) worsen the problem. (Ozone levels are rising in the lower atmosphere; the destruction of ozone in the upper atmosphere is a quite separate problem, see our Nova topic Earth's sunscreen – the ozone layer.) All of this is bad news for us and bad news for the planet – so what are we doing about it? Catalytic converters Development of catalytic converters has helped reduce pollutants in car exhaust. The converter is a special box that goes onto a car's exhaust system just past the engine. It is sealed on the outside, but inside is a heat-proof block with lots of holes through it – a bit like a big bundle of hollow spaghetti. As the car's hot exhaust gases pass through this honeycomb of holes, they come into contact with a thin coating of precious metal – usually platinum. This coating causes chemical changes to take place in the exhaust gases, which much reduce the pollutants coming out of the car. But as more and more cars take to the road, even these much cleaner cars are still a major source of pollution. Also, using a precious metal like platinum makes the converters very expensive to produce. The future For many years car engineers and scientists have been trying to find a cheap way to replace our very polluting cars with something better. The replacement would have to:
Electric cars have been developed to high technical standards – but they do not stop pollution, they just move it somewhere else – back to the power station that produces the electricity they run on! And there is still a major problem with the weight and the short 'run time' of the batteries electric cars have to use. Other people have tried to use hydrogen as a fuel. Hydrogen is environmentally clean and gives you good performance – but it is very difficult to carry safely. Another idea is to use 'fuel cells' (a bit like the ones used to power the space shuttle's electrical system). Fuel cells work by producing energy for a reaction between oxygen and hydrogen, triggered by a platinum catalyst. Chrysler in the US is developing a fuel cell system which uses petrol (a hydrocarbon) and provides better fuel economy than a conventional engine – and produces no harmful pollutants. Related sites
Related Nova topics
The foam in the cushions of a sofa is manufactured from a variety of chemicals and some of those chemicals remain active long after the furniture has left the factory. Toxic organic compounds such as formaldehyde (CH2 O) may be emitted in small quantities from carpets, soft furnishings and fabrics. Household pesticides and cleaning solvents may contain volatile toxic compounds. And asbestos insulation – once used to keep the heat in – is dangerous if its fibres are inhaled. Sick building syndrome If a home, or office, or classroom is well-ventilated there should be no problem from these things – but with growing awareness of energy conservation, many rooms are now quite well sealed against draughts and get less fresh air. In extreme cases this can lead to the same stale polluted air being circulated round and round inside a closed and sealed 'air conditioned' building. Not surprisingly this causes a lot of health problems, and can lead to what has been called the 'sick building syndrome'. When this happens, many of the inhabitants get eye irritation, headaches, and feelings of nausea and tiredness. These so-called 'sick buildings' often have higher than average levels of fungi spores and bacteria in the air. The answer is not to go back to cold draughty buildings, but to cause less pollution. Building materials The materials used to build the house itself can cause problems. Builders use all sorts of glues, sealers and fillers in modern building – and most of these use some sort of solvent as their base. The pollution levels in a new house can be quite high, and builders may have to find ways to reduce it. Good ventilation will help disperse most of the air-borne pollutants, but some items emit lower levels of pollutants for years. We may soon see house and furniture buyers being a lot more choosy about the health effects of their purchases. The home kitchen can also be a source of pollution. This is particularly true where the kitchen has a gas oven and a less than adequate fume extraction system. One solution is to keep a window open or use an extractor fan (the type that blows the air outside) to help remove the fumes. Solutions Overseas, people are trying to find ways to reduce indoor pollution, and here in Australia CSIRO has been testing furniture in a special sterile chamber. When more is known about what items give off what kind of pollution, it should be possible to find ways of improving products at the design and manufacturing stage. We might also be seeing a new system of labelling used to tell buyers how 'polluting' their new furniture is! It will probably be a bit like the 'star' rated energy labels now used on fridges and other appliances. Related sites
Materials (for the class)
Procedure
Teachers notes Comparisons can be based on the amount of time needed to produce a visible film on the filter paper, the colour of the deposit or the amount of deposit observed over a fixed time. The biggest limitation to sample collection is the length of the extension cords! A more elaborate version of this experiment, including calculations to determine the concentration of black carbon in the air, can be found at How to sample black carbon air pollution.
People often assume that a correlation implies a causal link between factors, that is, that one thing is causing the other. Sometimes this is true: for example, there is a clear correlation between smoking cigarettes and dying of lung cancer years later and there appears to be a causal link between these two factors. But there are also plenty of correlations that do not have a causal link. For example, consider the fact that most people in car accidents were wearing seats belts. Does wearing a seat belt cause you to have a car accident? You know that this isn't true because of your knowledge of what is likely to cause car accidents and because you know that most people who do not have car accidents also wear seat belts. (However, seat belts do tend to reduce certain types of injury to the occupants in car accidents.) Sometimes two correlated factors may be linked because a third, hidden, factor causes both of them to happen. In that case, neither of the two measured factors directly influences the other, although they may always occur together. This activity, using fictitious data, is designed to help you think about correlations, and to help you learn what conclusions it is reasonable to draw from limited data.
Here is some information about the other 19,373 cars also tested in that study.
Teachers notes
Australasian Science July 2007, page 33-35 Humane research into air toxicity (by Amanda Hayes) Investigates more humane methods to assess the toxicity of air pollutants.
March 2007, pages 9 Pollution keeps northern Australia wet Reports that northern Australia has become wetter since the 1950s due to pollution from Asia.
May 2006, page 7 A cure for sick buildings? Describes two methods to destroy the volatile organic compounds present in the air of buildings.
Ecos Issue 134, 2007 page 5 'Asian haze' impact on Australian rainfall Reports on the impact of particle emissions from Asia on Australia's tropical rainfall.
No. 130, 2006, page 5 Formaldehyde levels high in wood panel products Claims that many imported wood panel products in Australia contain dangerous levels of formaldehyde.
Freshscience 2000 Air pollution: Size counts Presents information about atmospheric particles from vehicles and wood burning that adversely affect our health.
New Scientist 13 January 2007, pages 46-47 Interview: Win or lose, it’s fighting back that counts (by Diane Martindale) An interview with Zhang Jingjing about pollution in China.
9 September 2006, pages 26-27 Where to find the freshest air in town (by Michael Reilly) Describes how cheap detectors can be used by anyone to monitor pollution.
26 August 2006, page 12 Pollutant damages child immunity (by Michael Reilly) Suggests that a banned pollutant may be damaging children’s health before they can properly develop.
5 August 2006, page 9 Falling behind on clean air (by Andy Coghlan) Says that plans to rid the air of toxic pollutants in the US are behind schedule.
29 April 2006, pages 8-9 A nation struggling to catch its breath (by Matt Walker) Describes the problem of atmospheric pollution in China.
2 February 2006, page 29 Pigeons to set up a smog blog Pigeons fitted with a GPS receiver and sensors are being used to measure air pollution.
11 January 2006 More pollution in taxis than on sidewalks (by Kurt Kleiner) Reports on a study measuring the exposure of people using different forms of transport to particles.
29 June 2005 Clearing smoke may trigger global warming rise (by Fred Pearce) Research suggests that the rate of warming will increase as pollution decreases.
21 May 2005, page 56 Apocalypse then (by Stephanie Pain) Describes the effects of a volcanic eruption in 1783 suspected of causing 30,000 deaths.
9 May 2005, page 26 The filthy truth about diesel 'mules' (by Mick Hamer) Chinese rural vehicles account for about a quarter of China’s diesel use and pollution.
5 May 2005 Clearing smog has led to 'global brightening' (by Fred Pearce) Describes research that suggests that decreasing smog pollution is accelerating global warming.
11 March 2005 US pollution cuts could save 17,000 lives a year (by Maggie McKee) The US Clean Air Interstate rule promises to significantly decrease sulfur dioxide and nitrogen oxide pollutants from coal fired electricity plants.
16 November 2004 City deaths rise with ozone levels (by Maggie McKee) Reports on a study suggesting that short-term increases in ozone pollution contribute to thousands of deaths in the US each year.
12 October 2004 World's pollution hotspots revealed from space (by Katharine Davis) Provides a map of nitrogen dioxide pollution hotspots around the globe.
7 September 2004 European deaths from air pollution set to rise (by Anna Gosline) Reports that deaths will increase due to the combined effects of climate change and pollution.
24 August 2004 Cigarettes more polluting than diesel exhaust (by Gaia Vince) Describes a study indicating that three filter cigarettes produce more pollutants than a diesel car.
3 July 2004, page 14 Air pollution damages DNA long before birth (by Anna Gosline) Reports on a study showing foetal DNA damage caused by pollutants.
29 May 2004 Blackout gave cities a breath of fresh air (by Jenny Hogan) Scientists took the opportunity to measure pollutants produced by coal-fired power station emissions.
30 September 2003, page 47 Home grown pollution (by Ian Lowe) Looks at the quality of indoor air in Australia.
Scientific American August 2008, pages 52-59 China's children of smoke (by Dan Fagin) Looks at the impact of air pollution on children in China.
Velocity March 2007 Tackling international air pollution Looks at the use of ion beam analysis to monitor atmospheric particles.
Motor vehicle emissions (Environment Protection Authority Victoria, Australia)
Describes the pollutants from motor vehicles and ways to improve vehicle emissions.
Outdoor air pollution and lung disease (Australian Lung Foundation)
Information about what air pollution is and how it can harm people.
Australian Government Department of the Environment, Water, Heritage and the Arts
Total Environment Centre (Australia)
Australian Broadcasting Corporation
Using pot plants to clean indoor air (Technical Nursery Papers, Nursery and Garden Industry Australia)
Describes research indicating that plants can take up volatile organic compounds and clean indoor air.
Glossaryacid 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. hydrocarbon. Compound containing only the two elements, carbon and hydrogen. 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.
External sites are not endorsed by the Australian Academy of Science. Posted August 1997. The Australian Foundation for Science is also a supporter of Nova. This topic is sponsored by BHP
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