Why The Peculiar Smell After A Rainfall?

Certain volatile chemical compounds that are released by bacteria called streptomycetes inhabiting the soil are the reason for the smell after rainfall. These bacteria, grouped as actinomycetes thrive in warm soil, up to a million of them in a gram of soil. When wetted by rain after a long dry period, they release chemical compounds like 2 methyl isoborneol and geosmin. These compounds are the reason for the earthy smell that can be smelt only after the first rainfall of the season.