Waking up on a summer’s morning after a night of rainfall, you step outside and take a breath. What do you smell? That distinctive, earthy scent rising from the damp ground often brings a wave of nostalgia or calm. This is the unmistakable smell of rain, called petrichor. But what exactly causes this familiar aroma?
At the heart of this scent is a molecule called geosmin. Geosmin is a bicyclic alcohol with the molecular formula C12H22O (Figure 1). Its structure includes two fused carbon rings, a single hydroxyl group (–OH) and two methyl side chains. Geosmin is produced by certain soil-dwelling bacteria, such as Streptomyces, and is released into the air when raindrops disturb the soil surface.
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