Why do we get a smell immediatly after the first shower of rain?

Capuchin

There are a few different causes that you could be picking up on. In a wooded area you will normally smell spores created by bacteria in soil which are kicked up by the rain. The smell could be caused by the acidity of chemicals in the rain itself reacting with things on the ground and creating aromatic compounds. Another possibility are the smells that trees and plants secrete as oils, which are picked up by the rain and released into the air.

More info here: Howstuffworks "What causes the smell after rain?"