Before or after (or occasionally during) a rainstorm, a very fresh smell hangs in the air that I associate with rain. What am I smelling, specifically?
I could not say specifically, but I would venture ozone. Ozone and fresh soil that is.
Some ozone.
Also geosmins.
I’ve often commented that it was going to rain, because I could smell it in the air. I’ve been chided for my observation, but I’ve often been right also.
Wow, prompt response. Thanks, guys!
But why is the smell of fall rain different in San Jose than in the suburbs of Portland, OR?
Different soil bacteria.
Hippies.
Not ozone, I’m reliably informed. By a curious coincidence I’ve just read an article about this by [in the book Butter Side Up.
Plants release scented oils ([url=http://en.wikipedia.org/wiki/Petrichor] petrichor](]Magnus Pyke[/url)) which are absorbed into the soil. On first rain after a dry spell, the scent of the oils are released into the air.
So there are three answers in this thread, which one is correct? 
That’s Magnus Pyke for those who don’t know him.
Ozone might be part of the smell if there was lightning involved with the rain.
In southern Arizona, creasote bushes lend most of the smell to the rain, what little comes. The smell preceeds the rain because the wind bringing the rain clouds blows along smell from plants that already got rained on.
Rain in Hawaii and California smelled completely different. Another vote for local differences in flora producing different rain smells.
It could be the particular ozone depleter that permeates the area. San Jose and Santa Clara were mostly saturated with Trichlorotrifluoroethane, while Aloha and Hillsboro were partial to Dichlorodifluromethane. They both have Intel Inside! 
Seriously, I do not think that it is related to the smell, but the two locations that you mentioned were known for using gratuitous amounts of CFCs in the chip manufacturing process along with other more persistent harmful chemicals. Much of the Bay Area is now designated as remediated Superfund sites due to abuses of the semiconductor industry.
But wouldn’t that only be smellable after it rained? The “smell of rain” that I’m familiar with can be smelled before it starts to rain … or at least befpre ot starts to rain where I’m at.
Once geosmins, petrichlor, ozone and funny wet cement smells are in the air, they’ll be carried ahead of the rain by any breezes.
“Where your at” is key. Rain cools the air, causing a downward verticle wind where the shower is at. When it confronts the ground, it flows outward in all directions, but farthest in the direction the “normal” wind is blowing, which will be the direction the shower is moving toward. The downward verticle blast of air, and resulting outflow is the same “verticle wind shear” that routinely brought down low altitude airliners when “on time performance” statistics began to be published, and dopler radar had not yet been widely deployed.
Wow, that’s fascinating. So I guess that means that if you happen to be at the place where rain first starts falling in a particular area, you won’t smell the “smell of rain” beforehand?
I think the smell I usually associate with a light rain is the smell of wet asphalt.
Yep, me too. Especially on a hot day when it hasn’t rained for a while. But what is the volatile component of asphalt that is released when it gets wet?