If you live in a place that gets winter, you know (or may be) a person who steps outdoors, sniffs the airs, and declares it “smells like snow.” Others might not be keen on weather prediction, but swear the fluffy, white flakes have a distinctive aroma. Can you tell when it’s going to snow? Do snowflakes have a scent? Based on science, the answer to both questions is yes.
The Way It Smells Before It Snows
Air smells different before it snows both because of what it contains and what it lacks. For snow to fall, temperatures need to drop near the freezing point of water. When the air gets this cold, humidity is low. When humidity is low, the human sense of smell is deadened because mucus around olfactory receptors in the nose dries up. On an ordinary winter day, the air smells dry and maybe even dusty. Just before a snow storm, humidity rises and atmospheric pressure changes. The scent of the air subtly changes, plus the cold and pressure change stimulate the trigeminal nerve. The trigeminal nerve sends information that isn’t the same as scent, but is often associated with it (e.g., the coolness of mint or the heat of hot peppers). The end result is the human nervous system perceives a difference in the weather that may account for the smell of snow.
The Smell of Fallen Snow
After it has fallen, the scent of snow depends on its location. This is because ice crystals readily absorb molecules from the air, especially volatile organic compounds (VOCs).
Snow that falls over a field may smell earthy, perhaps bearing a lingering scent of grass. Snow that falls on trees carries the clean scent of terpenes from the plants, including pinenes, limonene, myrcene, phellandrene, and camphene. So, snow in rural areas smells fresh and maybe even a bit woodsy.
Snow that falls in urban areas can smell oily, dirty, and toxic. Snow efficiently filters dust, soot, and VOCs from air. The VOCs may be toxic or carcinogenic, such as benzene, pesticides, and trichloroethene. The good news is that snow cleans air and is particularly effective at removing automobile exhaust. The bad news is that the first snow smells bad and is not safe to eat. However, as the snow continues to fall, the air gets cleaner and the snow smells fresh.
References
- Herbert, B.M.J.; Villa, S.; Halsall, C.J. (2006). “Chemical interactions with snow: Understanding the behavior and fate of semi-volatile organic compounds in snow.” Ecotoxicology and Environmental Safety 63(1):3-16. doi:10.1016/j.ecoenv.2005.05.012
- Kos, G.; Kanthasami, V.; Adechina, N.; Ariya, P.A. (2014). “Volatile organic compounds in Arctic snow: concentrations and implications for atmospheric processes.” Environ. Sci. Process Impacts 16(11):2592-603. doi:10.1039/c4em00410h
- Starokozhev, E.; Fries, E.; Cycura, A.; Puttmann, W. (2009). “Distribution of VOCs between air and snow at the Jungfraujoch high alpine research station, Switzerland, during CLACE 5 (winter 2006).” Atmos. Chem. Phys. Discuss. 9, 3197–3207.