So serious are the effects of air pollution on human health - the WHO recently categorised it as carcinogenic, responsible for 223,000 deaths a year worldwide - that it is easy to neglect its wider impact.
Air pollution damages ecosystems, building materials, and cultural heritage. While health is and will remain the key problem to be addressed, there has been renewed concern recently about the damage to electronic circuitry, particularly in highly polluted cities in India and China.
This was noticed 40 ago when Bell Laboratories realised that telephone switchboards had a shortened service life when used in polluted areas. Acidic air pollutants react with the electrical contacts made of copper and tin, causing a build up of corrosion products which interfere with electrical current, causing switches to fail. While this is clearly a problem, the reaction of air pollutants with the solid state components found in electronics also has some uses, for example as air pollution sensors. These still suffer from drift and low sensitivity, but one can envisage a future where tiny air pollution monitors could easily fit into a mobile phone and provide local air pollutant levels.
The range of air pollution impacts not related to health is very large. In 2010 the world was surprised by the natural pollutants ejected into the atmosphere when the Eyjafjallajökull volcano erupted in Iceland. This caused the most substantial disruption of air traffic in 50 years, with the transatlantic routes affected of such importance that it cost the airline industry an estimated US$1.7 billion.
A number of serious incidents in the 1980s occurred when aircraft engines shut down after airliners ran through volcanic ash clouds. In response the International Civil Aviation Organisation began to use information provided by Volcanic Ash Advisory Centres to warn of airborne ash dangers. Where volcanic eruptions are very intense and explosive they can drive gases and dust high into the stratosphere, which can lower global temperatures and extend the whole in the ozone layer.
Small holes, large problems
Another much smaller “ozone hole”, but one that can be just as important on a personal level, was the discovery in the 1980s that the ozone produced in photochemical smog attacked the thin latex of condoms causing them to degrade after just a few days. It forced the industry to think about production and packaging.
Chemically speaking, rubber (for example natural rubber, known as polyisoprene; CH2=C(CH3)CH=CH2) has many double bonds that easily react and combine with ozone (O3). In a similar way, ozone-rich smogs can attack modern building materials such as plastic fittings, polymer coatings and sealants. Some metals, most notably copper and aluminium that are widely used in modern architecture, are sensitive to these oxidising pollutants typically found in cities.
Our modern atmosphere is quite different from the smoke-filled air of cities in the past. The Roman poet Horace was much concerned about the smoke-begrimed temples of his ancient city. More than a thousand years later architect Christopher Wren described sulphate crusts on Westminster Abbey that had grown four inches thick from long exposure to coal smoke in London.
Today buildings rarely exhibit such thick sulphate crusts as the days of coal have largely gone. Instead damage is more subtle. In the past the sulphur-laden coal smoke had also killed off lichen that attach to buildings. Now sulphur dioxide pollution has been replaced by nitrogen oxides, which form deposits on stone facades, essentially providing a fertiliser of sorts that encourages biological growth.
Outdoor damage indoors
Air pollutants can also leak indoors, and potentially damage objects in museums, art galleries and historic houses. To some extent the problem can be alleviated in museums and art galleries, but historic houses are not well suited to modern air conditioning. Even visitors themselves can be a source of damage - their presence changes the humidity of indoor air and they shed pollutant dust and fibres from their clothes as they move among the displays. The current enthusiasm for open displays means these deposited pollutants must be regularly cleaned off.
However, the aesthetic impact of air pollution is not always negative. Some of the chemical reactions taking place in the atmosphere contribute to our appreciation of landscapes. Natural chemicals given off from trees, such as pinene from coniferous forests or eucalyptol from eucalyptus trees in Australia, react to form fine particles. In the case of eucalyptol, these particles scatter blue light, making distant objects appear blue – hence the appearance of the Blue Mountains. The importance of cool tones in depicting distant objects was described long ago by Leonardo da Vinci.
In its own way air pollution has had a great impact on art. Take the abstraction evident in Monet’s paintings of Westminster done more than a century ago. He particularly chose to visit London in winter to capture the vivid colours of its famous polluted fog. Victorian fog became a metaphor for confusion and lack of clarity, hence its use in Sherlock Holmes stories. Even today it can be used to wield the same symbolism: in The King’s Speech, a film about King George VI and Lionel Logue, a confused Duke of York wanders off into the fog. Clearly, the effects of air pollution in all its forms is much broader than one would think.