December 08, 2009

Air Quality Drops

Tonight may end up the coldest night of the entire winter for many. Cold air has settled over the region and differences in pressure have decreased (see graphic of pressures over the region), resulting in weakening winds. Winds help to stir up the low-level atmosphere...mixing up warmer air from above the surface to the ground.

Why is the air warmer above the surface on these clear nights? Because the earth can effectively emit infrared radiation to space (better than the air) and thus the surface cools down faster. Thus, on clear, nearly calm nights we can develop inversions in which the temperature WARMS with height.

You can see the inversion forming tonight in the figure below, which shows conditions above North Seattle.
Inversions act as stable layers or lids that keep the air from mixing and allows pollutant levels to rise. And this build up of pollutants increases further on cold nights when people run their heating units more and especially when they burn wood in their fireplaces and stoves. Burning wood injects a huge array of particles and toxic substances into the air. I know. A fire can be nice on a cold night and the odor even a bit attractive...but this is really bad stuff. Full of particles that interfere with lung function and chemicals that cause cancer.

As a result of the developing inversion and increasing woodburning, air quality is declining fairly rapidly in many locations. Take a look at the graphics for reporting stations in Everett, Lake Forest Park, and Bremerton. Air has either attained unhealthy status or will soon be there (see graphics).

The Puget Sound Clean Air Agency has placed a stage 2 burn ban out for Snohomish County. During such burn bans
  • No burning is allowed in any fireplace, pellet stove or wood stove (certified or not), unless it is your only adequate source of heat.

  • You can use natural gas or propane fireplaces.

  • No visible smoke is allowed from any solid fuel burning device at any time.
For more info on local air quality check their web site: I think you can expect them to extend this band to other locations.

There have been a number of studies, some done at the UW, showing how bad wood smoke can be for vulnerable individuals (like those with asthma, breathing problems, or heart conditions). The smoke tends to settle in low hollows and valleys. The valley of Lake Forest Park is infamous for poor air. I live at the bottom of a hill and when people uphill from me use fireplaces..and particularly when they use wet scrap wood...the smoke becomes palpable in my home and very unpleasant. One time it even set off my fire alarms. I asked them to stop and they did.

But it is good to know that if you have some problem uphill neighbors sending smoke your way you can call the clean air agency and they will talk to those in the problem household. And if there is visible smoke they have the power to levy fines.


  1. I remember in January of this year there was an intense temperature inversion at nearly 1000 feet exactly. I drove up to the top of a hill in Bellevue where "the summit" subdivision is (near cougar mountain) and at the top of the hill (which is at about 1190 feet) you could have a perfect view of mount rainier and the sky was crystal clear blue but look down the hill across towards seattle and see this nasty layer of smog being restricted to the 1000' level... it was really cool to witness.

  2. Oh, and here is a link to a photo of the inversion from last January:

  3. I noticed a lot of wood smoke in the air (by odor) when driving from Redmond back to Bellevue tonight.

    I hope it's not super-cold tonight but I bet it will be. Last night at this time it was 24 on the way down to our low of 17.3F; now it's 19.1 on the way down to 12? would be my guess.

  4. What about the snow report today? Yesterday you wrote: "Thursday could have some scattered snow showers, but the real threat is over the weekend as we transition to a warmer, wetter regime...more on that tomorrow." Can you write about that tomorrow?

  5. Fines and scolding are all well and good, but maybe the Puget Sound Clean Air Agency would get better results by educating people on how to burn cleanly, without smoke, by using good wood and getting the fire hot. It seems pretty obvious that the issue is ignorance.

    I sympathize with those having fires now: I have electric wall heaters, and they are barely an adequate source of heat. They run constantly and can't keep up with the cooling--and the apartment was re-insulated a year or two ago. If the fireplace hadn't be decommissioned before I moved in, I would choose that for my source of heat.

  6. Properly seasoned wood fires that aren't being dampered down (meaning they are getting enough air) do not emit any smoke, especially in a good wood stove. The even heat that radiates from a woodstove is second to none in comfort.

  7. As someone who heats with wood it's good to remember that for some, it's either bad wood or no heat. For others it's ignorance. Leave the fines and threats to one side and focus on education.

    Speaking of threats, let discuss the threat of snow on Friday or what will happen when moisture hits this super cold ground and road surface. My Davis station read at 10.8 degrees at 7:30 am.

    Love your blog Cliff. Thanks for doing it.

  8. Know plenty of wildland firefighters who have been in the smoke for over 25 years and are not dying of cancer. Inversions are nasty though. No mixing at the surface. Car fumes have more chemicals and more of an impact. But then again not everybody burns high efficient modalities whether wood stoves or automobiles.

  9. First recorded 100 degree temperature swing.
    In the upper Snoqualmie Valley 2009 will go down as one of the most extreme weather seasons on record.
    Just one of those events will be the 100 degree swing from July 29th when we registered 107 to this morning when out in the Middle Fork of the Snoqualmie it was 7 degrees at 6 AM.
    I've only lived out in this valley for about 50 years and been keeping records since 1974 so I'm not an expect but, I don't see anything close to this since 1974.
    Oh and by the way, no air inversions up here, sky is crystal clear with a light NE breeze.

  10. Lunch break, morning run of GFS has -32C 925mb temps just north of the border and a 20mb pressure gradiant along the east slopes monday, comical.

  11. Thanks everyone for the comments about the burn ban. We do have a variety of year-round educational efforts. But unfortunately it’s usually during burn bans when we get people's attention. So, key messages are critical: heat with wood if you absolutely must, do it cleanly, or you could get fined. You have touched on elements of "burning clean", which is great! Here's a more official list: burn only dry wood that has been well seasoned (12 months or more around here); never burn garbage; keep your fire small and hot; and give your fire plenty of air. Visit our website ( for more tips, including an educational video. It's up to all of us to keep our air clean!

  12. Thom - such extremes of temperature are sure sign of climate change.


Please make sure your comments are civil. Name calling and personal attacks are not appropriate.

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