Cars are wonderful things. You can go where you want and when. You can travel with friends or family in a weatherproof lounge-room on wheels that whisks you along far faster than you could run. But they do create air pollution.
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?
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.
