In the Great White North, snowstorms are a matter of life and death. Or, at least, that’s what it looks like these days, as a new snow-clearing method is making some streets look like the site of a bloody massacre. This week in Calgary, Alberta, city officials took to the snowy streets with a mixture of salt and beet juice, which they say is a more eco-friendly and cost-effective way to de-ice roads than using only salt.
The CBC reported on Tuesday that Calgary is expanding its use of beet juice after previous small trial runs proved successful. The snowy city is following in the footsteps of towns such as Laval and Cowansville, both in Quebec, as well as Toronto — all cities that have previously used similar beet-juice mixtures on roads in preparation for storms. In Calgary, the mixture of beet juice and salt is being sprayed directly onto the streets from a two-ton truck that can hold 40,000 liters of beet juice.
Cities that are hard-hit by winter storms have been seeking alternatives to salt for several years now, as excessive amounts of sodium chloride not only harm cars, roads, and personal property but also affect the environment. In 2016, the Toronto and Region Conservation Authority stated that declining fish and bug populations were likely linked to the city’s reliance on salt during the winter months.
The reason salt is such an efficient road de-icer in the first place is that it lowers the freezing point of the water around it. All ice has a very thin film of liquid water on its surface, and when a chunk of ice mixes with that liquid, it lowers its freezing point, which raises its temperature — in turn causing the ice around it to melt, and so on. This process becomes more and more effective as the salt concentration becomes higher. For example, a 10 percent salt solution freezes at 20 degrees Fahrenheit (-6 degrees Celcius), and a 20 percent solution freezes at 2 degrees F (-16 degrees C).
On a molecular level, this happens because the salt molecules intersperse with the water molecules, making it harder for the latter to come together in the molecular crystal that constitutes ice. Here’s how physicists at the University of Illinois at Urbana-Champaign explain it:
Say you have a cup of pure water and a cup of somewhat salty water. As you lower the temperature some of the pure water starts to form ice crystals. The reason is that although the frozen water molecules, lined up into a crystal, have fewer ways to move around (lower “entropy”) than the liquid molecules, they release heat when they freeze and that raises the entropy of the surroundings even more. So the net entropy goes up as the water freezes, as it always does on the way to any equilibrium state.
What about in the salty water? There’s one extra term in the entropy change. The salt doesn’t fit into the ice crystals. So as they form, the remaining salt is left with less room to roam around in, and thus less entropy. So you have to get the salt water even colder before you get a net entropy gain from freezing it.
But sodium chloride isn’t the only molecule that can disrupt a water crystal. The sugar molecules from the beet juice have a similar effect, which means that if beet sugar is added to the 20 percent salt solution and sprayed on ice, the melting point of the ice will be even lower than 15 degrees F. What most Canadian cities have tried is mixing together sugar beet molasses, a waste byproduct of beet sugar refining, together with existing salt solutions in order to cut down on the concentration of salt needed to produce the same ice-melting effects. The stickiness of the molasses additionally helps bond the salt to the surface of the road, where it can maximize its effects.
The only downside to the beet juice hack, National Geographic reported in 2014, is that it can sometimes leak into streams, where the sugar attracts bacteria that suck up all of the oxygen in the water on which animals rely.
Of course, there’s the issue of the beet juice turning the streets into a red-brown mess, as if it were the oxidized remains of a bloody battle. Some cities, like Laval, have used juice from white beets to avoid the stain, but others have simply learned to embrace the bad with the good. At the very least, the sweet concoction is said to smell like a Tootsie Roll.
If you liked this article, check out this video about a trash “monster” that is able to eat floating garbage.