The powerful scent of fresh rain is 
a mixture of plant oils, bacterial spores and ozone.

In moist, forested areas, a soil-dwelling bacteria known as actinomycetes - produced a chemical - geosmin. The bacteria secrete the compound when they produce spores, then the force of rain landing on the ground sends these spores up into the air, and the moist air conveys the chemical into our noses.*

*Joseph Stromberg in What Makes Rain Smell So Good, [April 2, 2013]