Petrichor

The pleasant smell that we get after the first rain ending a dry spell is known as Petrichor.
When the organic substances like nitrates and other carbon compounds  react with the rain water and produce the vapour of this sweet smell .This vapour is carried by the wind and reaches our nose.

Everyone will like this smell and some relish when experienced after a long time.

But we don't get that sweet smell after heavy rain as the organic substances  are washed away .

These organic substances are the product of decomposition process when the microbes and earthworms of the soil feed on the dead plants and animals.