Thunderstorm over prairie grassWhen I was a kid, I loved going outside after it rained because it just smelled so good! (And I enjoyed jumping in mud puddles – like all children) I always asked myself, why does rain smell? I didn’t bother to find out until recently.

So Why Does Rain Smell?

As it turns out there isn’t one catch-all answer to that question. The smell after it rains will likely vary from place-to-place and from storm to storm based on different circumstances. However, there are a few things that naturally cause the air to smell great after it rains. Some of them just might surprise you!

Ozone

This is actually the reason I had always heard for why rain smells so good. If the rain came from a thunderstorm, then you will likely be able to smell the ozone generated by the lightning. Lightning produces nitrogen oxides that react with other chemicals in the air to produce ozone. Most of this ozone is generated inside the storm which is miles above the earth’s surface. However, some of it is generated or filters down to ground-level where we smell it.

Bacteria

After ozone, this may be the biggest contributor to why rain smells. There are some forms of bacteria that thrive in damp and warm conditions. They are called actinomycetes[1889] (don’t worry, I can’t pronounce it either). This bacterium is present in many areas of the world, so it gets credit for one of the universal smells of rain. When the soil is dry, the bacteria produce spores that are spread through the dry earth. When it rains, these spores are kicked up into the air and are carried away to our nostrils.

I know it sounds kind of gross that what you smell after a rain shower are bacteria spores. But hey, I’m not making it up! This is the main cause of that rich “earthy” smell after it rains. This idea kind of disturbed me at first, but I’m okay with it now. There’s already plenty of bacteria growing in my body already, I’ll just go back to enjoying the sweet smell of rain.

Acidic Rain

If the rain in your area is acidic (possible if you live in a highly-populated and/or polluted area), then the acid in the rain will likely react with chemicals and organic content on the ground. These reactions can create smells that we smell after a rain shower. Sometimes, if the rain is particularly acidic (due to pollution) then these smells may be very unpleasant. If you live in the country, you’ve probably never experienced a bad smell after rain though.

Oils

Some plants and trees release oils that collect on leaves and hard surfaces on the ground such as rocks. When it rains, the acidic nature of the rainwater reacts with the oils and carries it through the air for us to smell (similar to the way we smell the bacteria in the air).

I hope this settles your curiosity about the smell of rain. You’re also well equipped to answer your child’s question next time he asks you “Why does rain smell?”