Chemically it's the smell of beet red. Most people describe it vastly differently because the retro nasal smell makes it feel like something else. Pretty interesting if you ask me.
It's hard to describe I suppose. First the smell of rain hitting dry stone and dirt, and how that smell slowly swells and then fades as they become waterlogged... Then the heat rises as the thunderstorm comes, and the air itself smells warm and wet.
I don't think I have ever spoken to someone who hasn't experienced the smell of rain on dry soil. Not trying to be rude, or pry too deep, but....uhmmm....how? How have you never smelt that before? It's so far outside my own personal experience, I just don't really understand it.
I have an O3 air purifier, not that I ever run it when I'm going to be in the same room. But getting a whiff on the way to airing it out the room after a session, yeah, I think I do pick up that smell also in very active thunderstorms.