Petrichor: a smell of rain

Petrichor is a pleasant, musky aroma that is released after rain. The smell is similar to the one gardeners smell when they turn the soil.

Why does the air smell good after the rain?

Often, after a rain, there is a distinctive smell in the air, a kind of musky scent. This pleasant scent is most frequently experienced during rains that follow a period of drought.

This phenomenon is called petrichorFrom the Greek roots petra (stone) and ichor (the blood of the gods). If you are a gardener, you will find that this smell is similar to the smell you get when you turn your soil over and you would be right. Good organic soils contain bacteria and one bacterium that is abundant in warm, moist soils is the actinomycete.

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The origin of petrichor: actinomycetes

Actinomycetes also known as "radiating fungi" are a key ingredient in the decomposition of organic matter in the soil. They thrive when the soil is moist. When the soil dries out, actinomycetes produce tiny spores, which are part of their reproductive cycle.

Rain lifts these spores when the raindrops hit the ground and makes them airborne. The air movements then disperse the spores and carry some of them to our nose, where we detect an aroma, similar to the smells of plants and nature.

Actinomycetes are very common in the wilderness, which explains the after-rain odours found in many places. The oil exuded by some plants during dry periods also contributes to this natural, plant-like smell.

More frequent odour after a light rainfall

You may have noticed that the smell of petrichor is more common after light rain than heavy rain. High-speed photography has shown that light rain causes small bubbles to form in the raindrop on the soil surface, which can carry soil microbes when the bubble bursts.