Don't Worry, It's a Dry Cold

When people first move to Edmonton, they quickly begin hearing tales of how cold our winters are. These tales are met with the exasperated shout of disbelief: "It gets HOW cold?!" To which native prairie dwellers, such as myself, reply: "Don't worry, it's a dry cold." So what? Ever wonder why it feels way colder at -10 in Guelph than it does at -20 in Edmonton? It has to do with humidity (or the lack of) and a branch of chemistry referred to as "thermochemistry".

Our story begins with James Joule (1818-1920) and the first law of thermodynamics. Joule, being a brewer by trade, also shows us that chemists are rarely far from ethanol. 

First Law of Thermodynamics: energy can neither be created nor destroyed, only converted from one form to another. Heat is a form of energy. It can be transferred across the boundary between a system and its surroundings. Temperature is the measure of heat. Also important to know it that the direction of heat transfer is always from the thing that has the heat to the thing that doesn't. So leaving your front door open in the winter will not let any cold air in. It is physically impossible; however, you can let a whole lot of heat out. Another important term to know is heat capacity: the amount of heat required to change the temperature of a system by 1 degree. 

It is currently a balmy +1 in Edmonton right now.  The North Saskatchewan river isn't even frozen over, but I can tell you with certainty, I will not be jumping in for a swim. Even though the temperature of that river is actually warmer than the air surrounding it, it still feels a heck of a lot colder. This is because heat transfer is more efficient between a liquid and a solid than it is between a solid and gas. Heat is lost, at a molecular level, by collisions between the warmer body (you) and the colder body (the river or the air). Because of the fact that a liquid is more dense than a gas (especially a gas at cold temperature), there are more opportunities for molecules to collide, meaning more opportunities for heat transfer. The other important point is that the heat capacity of water is really big. Meaning that it takes a lot of heat to warm the water just one degree. If there is a lot of water in the air, it can condense on you, giving you that "wet" feeling. This will lead to more opportunity for heat transfer, making you feel much colder at -10, than if you are living in a place like Edmonton, where it is so dry that your skin begins to feel like an exoskeleton that you are much too big for. (I recommend Moisturel as a moisturiser for anyone looking to combat dry skin.) 

This heat capacity of water isn't all bad though. Ask people in Vancouver. See, because water takes so long to heat, it also takes a really long time to cool. Meaning that in the winter, places near water, like Vancouver, don't get that cold. Of course, one big snow storm and the whole city shuts down because they only own one snow plow, and have no idea how to function in weather that gives the rest of Canada the monicker "The Great White North". You can also use this heat capacity to your advantage when cooking dinner. Want to thaw your frozen meat faster? Stick it in room temperature water. 

So Edmontonians, when that mercury dips, and your skin and hair desiccate to a point beyond all recognition, be thankful for it. After all, it's a dry cold, so it really isn't that bad. Just bundle up.  

References:

Petrucci, R. H.; Harwood, W. S.; Herring, F. G. General Chemistry 2002 Prentice Hall Inc., Upper Saddle River, NJ.

Balchin, J. Quantum Leaps: 100 Scientists Who Changed the World 2010 Arcturus Publishin Limited, London.

Laidler, K. J.; Meiser, J. H.; Sanctuary, B. C. Physical Chemistry 4th ed. 2003 Houghton Mifflin Company, Boston, MA.