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.
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 spots...like 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.