Dear Umbra,
Is there a relationship between air quality and temperature? I thought about this on my bike ride to work this morning when the smell of exhaust from cars seemed more potent, and the fumes were certainly more visible in the 32-degree air. I know that air quality in Los Angeles is worse during the summer. And "code red" or "code orange" air quality days occur in the summer in Washington, D.C., and in Richmond. But I have heard that in really cold places like Fairbanks, Alaska, where people leave their cars running while doing errands, the air quality is worse in the winter.
Mary Reynolds
Richmond, Va.
Dearest Mary,
What biking inspiration! Neither rain, nor sleet, etc. Good for you.
Can weather chill pollution levels?
Photo: iStockphoto
There is indeed a relationship between air quality and temperature. We tend to think of smoggy skies as a summertime problem, because sunlight plays a key role in forming ozone -- and maybe because there are more hours of daylight for smog-gazing. But air quality suffers in winter too, for a number of reasons. These reasons have less to do with geography than with weather patterns and human behavior.
Let's back up for a moment. Air pollutants are produced by cars, power plants, forest fires, metal processing plants, dusty roads, construction sites, woodstoves ... I'm trying to make a long list, but most air pollutants come from vehicles and power generation. By far. Particulate matter is the pollutant that adds a little diversity to our list of sources, because it rises from construction sites and chimneys. Lead makes our list diverse, too; now that gasoline is unleaded in the U.S., the main domestic sources of airborne lead are businesses that process metals. But our compounds of chief concern spew from cars and power plants: nitrogen oxides, the precursors to ground-level ozone formation; sulfur dioxide, a main ingredient in acid rain; and carbon monoxide, which directly messes with the human body.
So pollution is emitted from cars and burning of fuels and wafts through the air. Air quality, in turn, depends on how wafty the air is, and this is where the weather comes in. When air is stagnant, pollutants will lurk. Perhaps they come from far away and reach a stagnant spot and loiter there, perhaps on your bike route they stagnate directly behind the emitting cars.
The air can be stagnant due to lack of wind. But in winter, pollution is often trapped during inversions -- that is, when a layer of warm air lies atop a layer of cold air. Until this arrangement is ended, the convection that normally carries away pollutants will not occur, and air quality plummets, especially if the area under an inversion includes many vehicles or power plants. By midmorning, the sun will generally warm the layer of air down where we humans are, causing the polluted air to expand and the contaminants to disperse. But I'm guessing that your bike commute takes place earlier than that, which means you may be riding through a wintry haze.
Another thing that can make pollution worse in winter -- and this is something you should be aware of, given your commuting proximity to tailpipes -- is that cold weather can keep car emissions control systems from being as effective as they should be, leading to higher carbon monoxide levels in the air. Add an inversion, and whammo: you're in a soup of CO.
A third part of this equation is human behavior. When temperatures drop, people use their cars differently (idling them to warm them up, for instance) and crank up their woodstoves. Many cities, including Fairbanks but also those with less extreme winters, issue advisories and tips for cutting down on cold-weather pollution, for everyone from construction workers to drivers. These tips include reducing or eliminating wood burning, weatherizing your home to create less of a need for heating with wood, avoiding letting your car idle longer than 30 seconds, and -- my favorite, always -- driving less.
Your local weatherpeople probably issue an air-quality alert or index number on a regular basis. They should be able to tell you more if you wish to further investigate this phenomenon.
Coughily,
Umbra
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Comments
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rivergal Posted 4:56 am
21 Feb 2007
I don't believe that NOx are much of a problem here in the winter -- engine temperatures and/or compression ratios have to be high to form NOx.
Here in Anchorage there are daily advisories to plug in engine block heaters when night time lows are 20 F or below, and the block heaters are subsidized. In Fairbanks, where it is frequently -40 F or colder even during the day (days only last 3.5 hours there in late December), leaving your engine on while you run an errand is NOT just to keep the car warm for the driver and passengers. It is sometimes the only way you can get around at all -- engines simply won't restart when they get too cold, plus all the car's plastic components (door handles, heat and vent levers, etc.) get brittle and break if you don't leave them set where they need to be when you turn the car on. Then there's the square tire issue -- if you don't keep them round by driving around the parking lot while someone else runs into the store, your tires will get a flat spot on the bottom and driving will be pretty bumpy for the first few miles. Virtually all outdoor parking spaces in Fairbanks have power outlets for block heaters, but keep in mind that the electricity used comes from nearby fossil fuel plants . . .
Winter time inversions in Anchorage and Fairbanks do not tend to disappear during the day because there isn't enough solar heating, so we breathe a nasty mixture of ice fog with uncombusted gasoline, woodsmoke and natural gas (from home heating) for too much of the winter. Outdoor air in Fairbanks can taste and smell like the inside of an underground parking garage. Some intrepid souls take public transportation -- but this is a real sacrifice, involving walking in the dark and waiting at unheated bus stops in temperatures that freeze exposed flesh in seconds.
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nicolejc83 Posted 5:06 am
21 Feb 2007
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ltellis Posted 6:01 am
21 Feb 2007
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ccdangelo Posted 3:55 pm
21 Feb 2007
The best, of course, as Umbra says, is to drive less.
Oh.. and also.. don't support Dominion's crazy bill, SB 1416, to become a monopoly and kill us all with their hobnobbery! Or.. at least, contribute more to air pollution with more coal plants.
Cheers!
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TheSSG Posted 5:12 am
22 Feb 2007
Un fortunately, "warming up" your car causes two Main Problems:
It simply warms the engine and coolant. This makes people more inclined to drive aggressively before the other parts of their car "warm up," mainly the tires and assorted bushings which warm up via friction, which comes with USE.
When the Engine is cold, the oil is a less effective lubricant. This increases friction, which increases Engine wear, which decreases engine life. The PRIMARY concern for an owner is TO GET HE ENGINE AS WARM AS POSSIBLE. The ABSOLUTE quickest way to achieve this is to put a load on the engine; to drive it (Do NOT simply raise the RPMs up while idling. Yes, this will warm it quicker, but a cold engie should NEVER EVER be Rev'ed higher than 3,000RPM). 5 minutes of driving will warm a car, versus 15 minutes of idling.
So, THE BEST thing for your car is to get in, start it, and drive slowly and carefully until the engine reaches operating temperature. By this time, the short amount it is, the engine will be ready to rev, and any or all other components of the car will be "limbered" up, making them less fragile, and less likely to give out.
And I live in N. IL, so I know it sounds inconvenient, but it's very possible. You'd be suprised how quick it will warm up. I think that saved gas alone is worth the 5 minutes I have to keep my gloves on inside the car...
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TheSSG Posted 5:14 am
22 Feb 2007
The Primary concern is to:
Get the engine as Warm as possible, AS SOON as possible...
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edunlea Posted 6:39 am
22 Feb 2007
In the winter, sunlight is weaker, which does two things: One, as Umbra so nicely explains, this inversion layer that forms (referred to as the "boundary layer") is lower to the ground meaning that pollution is mixing into a smaller box; this means primary pollutant concentrations are generally higher. Two, the sunlight-driven chemistry of the atmosphere is slower, making secondary pollutants relatively lower.
In the summer, the opposite happens - primary pollutants are relatively lower because they mix into a larger volume (higher boundary layer), but secondary pollutants are relatively higher because the sun is cooking things more intensly. This is why you generally get poor air quality warnings during the summer (high ozone levels), but you see (and if you are riding a bike, often taste) the pollution during the winter (high carbon monoxide and some particulate matter - see next paragraph).
Interestingly, particulate matter, which you will often hear as "PM", has both primary and secondary sources. The stuff that you see coming out of a diesel truck for example is primary PM. Secondary PM is the stuff that you can't see, and this is generally the stuff that is more detrimental to human health because it is generally smaller and thus penetrates into the lungs further.
There are of course lots of complicating factors to this whole picture, including emission patterns, which Umbra and others discuss above. But, in general, some pollution gets relatively worse in winter (primary) and some gets relatively worse in summer (secondary), but none of it is fun to ride a bike through.
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aklorax Posted 7:18 am
24 Feb 2007
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nicolejc83 Posted 9:45 am
24 Feb 2007
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sidereally Posted 2:10 am
28 Feb 2007
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vociferous Posted 5:04 am
17 Nov 2008
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