Can nature tell you if the air is clean? Three signs to look out for

For many urban dwellers, a lichen-covered tree or a garden buzzing with insects can feel almost unfamiliar. As cities expand and natural habitats become increasingly fragmented, some of the small organisms that once made ecosystems feel alive can become harder to encounter. Research has linked increasing urbanisation with declines in wild bee and butterfly diversity, while studies have also found that air pollution can affect the diversity and composition of lichens and other pollution-sensitive organisms. 

Some organisms are particularly sensitive to atmospheric pollutants and can act as bioindicators, responding to changes in air quality over time. They cannot give you an AQI reading, and spotting one does not prove that an area has clean air. But their presence, abundance and condition can offer useful clues about the environment we share with them. Here are three signs to look out for if you want to read the air through the living world around you.

Lichens are among the most established biological indicators of air pollution. Because they absorb substances from the atmosphere, they can accumulate airborne pollutants and respond to changes in air quality. Scientists study the diversity, abundance and composition of lichen communities to assess pollution, including exposure to sulphur dioxide, nitrogen compounds and heavy metals. Lichen-based indices have also been used to map pollution gradients. 

Mosses can act as natural collectors of atmospheric pollution. Their tissues can accumulate substances deposited from the air, including heavy metals and persistent organic pollutants. This makes them useful for comparing patterns of atmospheric pollution across locations and over time, and moss biomonitoring is now an established area of environmental research. 

Some plants are particularly sensitive to specific air pollutants and can be used by scientists as biomonitors. The best-known example is the ozone-sensitive tobacco cultivar Bel-W3, whose leaves develop characteristic injury when exposed to elevated ground-level ozone. Other plants used in air-pollution biomonitoring include spiderwort, Italian ryegrass and curly kale, which can accumulate or respond to different atmospheric pollutants. Certain beans, grapes and gourds can also show visible ozone injury. The characteristic responses of these plants are what make them useful in biomonitoring studies. 

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