Using lichen as indicators of air quality

Curious about the air quality in your area? Lichen are nature's own indicators of polluted or pure air. Take part in a national survey that will help give scientists a greater insight into England's air quality

Scientists at Open Air Laboratories (OPAL) have launched a national Air Survey aimed to investigate the impact of pollution on air quality in England.

The survey looks at the different species of lichen found on trees and tar spot fungus on the leaves of sycamore trees.

Different species of lichen thrive in areas with poor air quality. Other more sensitive lichens will only grow where the air is of high quality with few or no pollutants.

Lichens are actually two types of organisms living together, a fungus and an alga. The fungus makes the body that protects the alga and the alga provides the food for the fungus.

It is not known whether the fungus that causes ‘tar spots' on sycamore leaves is related to air pollution but it is hoped that by plotting them on maps with the indicator lichens scientists can learn more about the mysterious blotches.

Sensitivity to pollutants

The project, developed with experts from the British Lichen Society is being led by Imperial College London scientists. OPAL has been awarded an £11.7 million grant by the Big Lottery Fund and hopes that by getting people into the outside world to actively looking at trees with a purpose this survey will also encourage people to enjoy nature and inspire more nature enthusiasts.

Lichens have been used since the last century as indicators of air quality. Their use as an air quality meter was first discovered when they disappeared from the trees of England after the Industrial Revolution which caused increased acidity in rain.

The OPAL Air Survey uses different lichens' sensitivity to nitrogen-containing pollutants, namely oxides of nitrogen and ammonia. These oxides are the result of burning fossil fuels, vehicle exhaust emissions and intensive agricultural practices including the use of fertilisers.

Oxides of nitrogen and ammonia have detrimental effects on both human health and the natural environment. The information collected through the data gathered by people across England will be indispensable in giving scientists a greater insight into the country's air quality.

‘Everyone's contribution to this survey is valuable. Even a result of "no lichens" still tells us something about the air quality in that area,' says Pat Wolseley, of the British Lichen Society.

Anyone can participate in the survey. A free survey pack, which includes a guide and workbook, can be obtained by emailing, or downloaded from


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