It's that time of year again: the leaves change color, the temperature begins to drop, and the pumpkin spice lattes start popping up on café menus. Of course, those aren't the only things that fall brings. There's also that distinct, but somewhat indescribable scent of autumn that mysteriously starts filling the air, as if pumped in by an enormous machine. But why? Why is it that fall smells so different from every other season? We made it our mission to find out. (And for more incredible trivia you can share with your friends, check out these 75 Weird But Wonderful Facts That Will Leave You Totally Amazed.)
The primary reason fall has a distinct smell has to do with the temperature. Higher temperatures can increase the intensity of certain smells, and lower temperatures can diminish them. For example, a pile of garbage in an alleyway might overpower other smells on a hot day, but when things cool down, you may barely smell that once-overpowering stench of trash.
In addition to that, there are also different scents in the air to begin with. One of the strongest smells you might pick up on in the fall is that of dying leaves and decomposing plant matter. "When the leaves fall, they die," meteorologist Matthew Cappucci wrote for The Washington Post. "As they take their last breath, they 'exhale' all sorts of gases." Cappucci says those gases smell "a bit like chlorine or the exhaust of a dryer vent."
Smell is also linked to the stimulation of a nerve in your brain called the trigeminal nerve, which is responsible for the sensations in your face, including your nose. When you breathe in, that nerve gets turned on, which is why your brain associates the cooler air with a "scent."
But it's not all about the science of nerves and gaseous emissions. "Smell is much more arbitrary than just molecules," Rachel Herz, an expert on the psychology of smell and author of the book, The Scent of Desire: Discovering Our Enigmatic Sense of Smell, told Radiolab. "Scent is a confluence of what we are seeing, hearing, and feeling, emotionally and physically."
Herz adds that if we bottled up some "distinct" scents, including that of fall, and sniffed them in a lab, we might not even recognize them. So yes, fall does have a distinct smell. But whether you'd be able to notice it without all the crunchy leaves, Halloween decorations, pumpkin-flavored drinks, and crisp air is seriously debatable.
Regardless, it's one of the best smells in the world—so go ahead and take a whiff while you can! And for more help to guide you on your quest for knowledge this fall, don't miss these 100 Random Facts So Interesting You'll Stop and Say, "Wow!"