The chemistry of rain Rain has an awful lot of suppositions and accusations connected to it. And doesn t every sensible almanac reader know that the leaves on trees turn over to catch the coming rain. First, lets look at the olfactory side of rain. Not a chance, but when the ground and plants are warmer, you can smell something.
Plants release oils that enter the soil and blend with the other earthy odors.
These odors are released into the air when the relative humidity at ground level exceeds 75 percent. Moist humid air will transmit odors far better than dry air. In these moist humid conditions we notice these odors more readily. And since rain is so often connected with moist humid air, we tend to associate one with the other. This has been rather hotly debated between medical groups.