Why spend so much money on fancy schmancy expensive equipment to measure air quality when you can figure it out for free using lichens?
What's a lichen, you ask? Some lichens are extremely cool examples of eukaryotic symbiosis, where two organisms mutually benefit from each other in perfect harmony. Lichens are two separate organisms, such as photosynthetic algae and fungus, working together. The fungi makes a nice pad for the algae to live in, and the algae pays the fungi back for the sweet living arrangement by providing food (specifically, with carbohydrates the algae make from photosynthesis). As a combo, these two are like peanut butter and jelly.
Lichens put up shop in a range of habitats. Neither organism has roots or a vascular system like plants do, which gives them the freedom to grow on surfaces like rocks and trees. But, without roots and shoots to transport food from the ground, they have to take up nutrients from the air around them.
An example of lichens growing merrily on a rock. Image from here.
Without roots, lichens get the nutrients they need from absorbing the atmosphere around them. Not only do they absorb yummy nutrients from the air, they also absorb the gross stuff, too. This means lichens can be used as indicators of air quality. They are super sensitive to changes in the environment. They can be used to map out microclimates in different areas of the world and map out itty-bitty individual areas of slightly different temperature, moisture, and chemical stressors. Lichens essentially can sense environmental stress before the rest of us know what's coming by absorbing small amounts from the air.
Lichens can therefore replace all the fancy shmancy expensive equipment used to measure air quality. Case in point: lichens were used to tell scientists about air-borne toxins following the Chernobyl Nuclear Power plant meltdown back in 1986. Lichens accumulate more radioactivity than most other organisms by sucking it out of the air. Scientists were then use lichen for use as a relevant indicator of radioactive contamination in different areas resulting from the catastrophe.
So, next time you're wondering what's going on in the world, just ask a lichen, "What's up?"