Olfactorins
Those lovely, unknown, rain-smelling molecules released from the ground into the night air after the first rains, ready to hit the olfactory receptors of your own still-a-bit-asleep-nose as you wake up to a new dawn.
"She is aware the air on the plateau is filled with the scent of olfactorins after the first rains as she continues to pound her way onwards: her eyes focussed now on her distant goal, the two, upside-down baobabs at the edge of the escarpment."