High-speed video of falling droplets releasing petrichor, a key ingredient of the distinctive post-rainfall scent.
From Quark To Quasars explains: "The smell itself comes about when increased humidity – a pre-cursor to rain – fills the pores of stones (rocks, soil, etc) with tiny amounts of water. While it’s only a minuscule amount, it is enough to flush the oil from the stone and release petrichor into the air. This is further accelerated when actual rain arrives and makes contact with the earth, spreading the scent into the wind."
