What causes the distinctive smell of the beginning of a rainstorm?

Answer 1

probably ozone from the associated lighting in the rain clouds

Answer 2

I've made several Tesla Coils and static electricity generators, and I'd say it's ozone. It doesn't actually require full lightning, the rain falling down has what is called a tribo-electric effect upon the air. The rest of the smell is probably water related.

Short answer: the smell is caused by a complex electro-chemical reaction.

Answer 3

Ozone has an acrid and unpleasant smell. The smell of rain is pertrichor. Volatiles are released by plants on hot dry days and are absorbed by the earth and rocks. When it rains, these oils are released and we smell them. There is also a fungus which releases its spores in rain and these also have a pleasant smell.

The wind usually precedes a shower or a thundesrtorm coming from the shower to you and it brings the scents with it so you smell the petrichor before the rain reaches you.

Answer 4

Nitrogen. Smells sooooo good, doesn't it? (You should catch a whiff of the ancient, locked-in primordial aromas that are released when a chunk of glacier falls off). The nitrogen before a rainstorm is sorta fractured off air molecules by static electricity. There's a "nitrogen" cycle in nature just like there's a "water" cycle. Tons of nitrogen fall to the ground in rain and lightning storms and enrichen the soil. Here's a link to an article from the University of Edinburgh that describes this "nitrogen fixation" caused by lightning and how it benefits plants:
http://helios.bto.ed.ac.uk/bto/microbes/nitrogen.htm

Answer 5

Ozone. It is very strong and causes animals to run for cover the molecules in the atmosphere are heavily laden with the water and chemical compound of ozone which bothers the breathing capacity of people and animals.

Answer 6

The water..
And probably the wetness of the earth and the water.

It's a very good smell, if I may say so myself.