Have you noticed a distinctive smell after the rain? If you have, it is not the incoming rain that has the earthy scent, but the moistening ground.

The smell from the rain is called petrichor. It is a fragrant compound made of oils from plants and actinobacteria which are tiny micro-organisms.

Actinobacteria help the decomposition of dead or decaying matter which then becomes nutrients for plants. The combination of plant and actinobacteria activity creates the compound geosmin, contributing to the petrichor smell.

With no rain, the productivity of the actinobacteria declines. Just before rainfall, the air becomes humid and actinobacteria productivity increases moistening the ground and creating geosmin.

When rain falls, the raindrops splatter on the ground ejecting tiny aerosols. The petrichor elements including geosmin, which have dissolved in the raindrops are then released and carried by the wind, and this is what we smell.

After some heavy downpours this Bank Holiday weekend, see if you can smell the scent of the rain.