Melting City Snow Unleashes Toxic Pollutants

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Snow absorbs pollutants from car emissions, prompting chemical changes that create brand new pollutants with different toxicity, new research reveals.

Ah, city snow. Few things are as romantic as an urban landscape glittering in a blanket of fresh wintry white. By the next day, however, the sparkle begins to adopt a gray cast. After a week, we’re talking black ice mountains.

As the snow melts, it releases any number of treasures that wandered into its frozen clutches; leaves, garbage, dog waste ... and now it turns out, according to researchers, it also releases “a toxic cocktail from car emissions.” Is nothing sacred??

"We found that snow absorbs certain polycyclic aromatic hydrocarbons which are organic pollutants known to be toxic and carcinogenic," says Yevgen Nazarenko, who worked on the study with Parisa A. Ariya, professor at McGill's Department of Atmospheric and Oceanic Sciences and Department of Chemistry, and collaborating with Patrice Seers' team at École de technologie supérieure.

"Understanding how these pollutants interact with the environment, including snow, is crucial if we are to reduce the hundreds of thousands of premature deaths caused by mild air pollution in North America. Worldwide, air pollution claims as many as 8 million lives," says Ariya, senior author of the study.

City snow

© Environmental Pollution

Curious about why the smell of fresh snow is “crisp,” before turning into a flatter less-pleasant smell, the researchers decided to investigate the relationship between snow and air pollutants. They looked at how snow takes up pollutants from car emissions and discovered that snow absorbs airborne particulate matter and actually alters the concentrations of the smallest particles found in air pollution. They note:

These tiny particles have been linked to numerous health problems. Unexpectedly, colder temperatures and interaction with snow increased the relative presence of smaller nanoparticles in the polluted air above the snow.
Once in the snowpack, air pollutants may undergo chemical transformations that create additional pollutants with different toxicity and carcinogenicity. Some compounds, including more toxic and carcinogenic chemicals, may volatilize back into the air, while others accumulate in the snow and are released with meltwater.

"These releases could lead to a higher short-term concentration of certain pollutants in the air, soil and surface water bodies where the meltwater runs to," says Nazarenko.

Is this something city residents need to start worrying about in the wintry day-to-day? Hopefully not, but it serves as a potent reminder that fuel-burning cars and their emissions do their dirty work in ways far beyond what the imagination might expect. For now, studies and environmental monitoring could help identify the most harmful pollutants, the researchers conclude, "and which ones should be targeted for reduction in gasoline formulations and in optimization of engines and exhaust treatment technologies." Or, we could just stop driving emission-spewing cars.

The study was published in Environmental Pollution.