Johan Lundstrom, a professor of clinical neuroscience who describes himself as a “smell researcher” at Monell Chemical Senses Center in Philadelphia, said because snow’s smell reflects the impurities in the air, the flakes in Wisconsin smell different from snow in Sweden, and from snow in a city. Lundstrom said that people notice smells more in the summer because the humid and warmer air intensifies odor molecules, in the same way perfume smells more intense and different on the skin than when it is sprayed in the air. But the cold and dry air of winter makes for a “poor odor environment.”

Climate change is affecting the way snow smells, said Parisa A. Ariya, a chemist and chair of the Atmospheric and Oceanic Sciences Department at McGill University. As the ground and air get warmer, that encourages the circulation — and intensity — of the odor molecules.

“The increases in temperature have been suggested to increase the toxicity of certain contaminants and enhance the chemical reaction rates and degradation processes,” Ariya said.