Jeff S. Gaffney, a professor of chemistry at the University of Arkansas at Little Rock, told NPR that if we were to package snow and put it on grocery store shelves, the ingredient list would be, “Primarily water,” but also “various and sundry things depending on where it [comes from]” — things like sulphates, nitrates, formaldehyde or mercury.
As it falls through the sky, snow, with its intricate latticework, forms a sort of net for catching pollutants that may be in the atmosphere. The most common is black carbon, or soot, released by coal-fired plants and wood-burning stoves.
That’s why John Pomeroy, a researcher who studies water resources and climate change at the University of Saskatchewan, suggests it’s better to wait until a few hours into the snowfall to gather your fresh catch. Snow acts like a kind of atmospheric “scrubbing brush,” he explains. The longer the snow falls, the lower the pollution levels in the air, and thus in the snow.
But even if you start to collect as soon as it begins to flurry, Gaffney reassures me that contaminants in snow are “all at levels well below toxic.”