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Winter ExhaustHave you ever noticed that when the weather gets cold, it’s a little harder to breath in busy city streets?  It’s not just because of the cold air you’re sucking into your lungs.  It may be because you’re taking in more automobile exhaust, too.

As David Sullivan, a Research Associate at the Center for Energy and Environmental Resources at The University of Texas, explained to me,


In the winter, the wind speeds are slower, and temperature inversions prevent vertical mixing leading to higher accumulations of local pollutants.  In the summer, the sun stirs things up more and the energetic atmosphere mixes and dilutes local pollutants.


In other words, in the winter, the exhaust from cars, trucks, and busses doesn’t go up and disperse above us as quickly is it does when it’s warmer.  Instead, it sticks around in the space where we do our breathing.

(Dave adds that the increase in fumes may also have to do with some vehicle engines having difficulty coping with the cold air, which results in higher vehicle emissions.)

Since nearly all of us are pedestrians at some point or another, you’ve probably experienced this if you ever spent any time in a city when it’s cold.  Bicyclists are particularly aware of this when they get behind a large vehicle like a truck or bus where there is a greater concentration of exhaust coming at you in one place.  Wearing some sort of cloth like a bandana or balaclava over your mouth can sometimes help, but that can also make some people uncomfortable.

Regardless of the season, vehicle pollution is a big problem contributing to global climate change and serious health problems.  And as we continue to sprawl, the problem will continue to get worse.  The more we do to make our communities efficient, compact, and convenient, the better off you are and the better off the planet is.