What are the indicators of air pollution?
The most common source of air pollution is the combustion of fossil fuels. Sulfur dioxide is released if the fuel contains sulfur compounds. This gas contributes to acid rain. Lichens can be used as air pollution indicators, especially of the concentration of sulfur dioxide in the atmosphere.
Lichens are plants that grow in exposed places such as rocks or tree bark. They are very good at absorbing water and nutrients to grow there. Rainwater contains just enough nutrients to keep them alive. Air pollutants dissolved in rainwater, especially sulfur dioxide, can damage lichens, and prevent them from growing. This makes lichens natural indicators of air pollution. For example:
- bushy lichens need really clean air
- leafy lichens can survive a small amount of air pollution
- crusty lichens can survive in more polluted air.
In places where no lichens are growing, it is often a sign that the air is heavily polluted with sulfur dioxide.
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