The science behind inversions

By Camille St. Onge, Communications

Let's talk inversion and I'm not referring to a yoga pose.

Ecology often times has to call burn bans because of inversions and a lot of folks throughout the state are perplexed. The sky is clear and they don't understand why a ban is needed. That's where inversions come in.

How inversions work 

Normally, the air closest to the ground is warmer than the air higher up.  This allows air pollution like smoke, vehicle exhaust and dust  to disperse and not reach high levels below in the air we breathe. During the winter, sometimes these conditions are reversed—cold air below and warmer air up high. This is called, not surprisingly, an inversion.

Forecasting weather and monitoring air quality 

There are nine air authority agencies in Washington with forecasters that monitor weather patterns and assess air quality on a daily basis. Forecasters watch weather and air quality models closely to identify areas with weather and pollution patterns that will cause air quality to reach unacceptable levels.

Air monitors placed throughout the state provide valuable data about air pollution. Through air monitoring and weather modeling, forecasters are able to identify communities that will experience air pollution problems during inversions. Once a community is identified for an air pollution problem a burn ban is put in place to help keep air pollution at acceptable levels.

Some areas are more susceptible than others for air pollution buildup because of the geographic makeup of the region. Good examples are Leavenworth and Colville, which are in narrow valleys. Other areas are less obvious bowl-shaped areas like Spokane. Cold, dense air gets trapped in these areas and pollution builds up near the ground.

Because outdoor burning and indoor wood heating contribute significantly to air pollution during inversions, residents and businesses may be required to restrict burning. Washington has two stages of burn bans: Stage 1 is applied when air pollution levels are elevated and are expected to continue to increase to unhealthy levels; Stage 2 is applied when air pollution levels are approaching unhealthy levels and the air cannot accommodate any more pollution without becoming unhealthy.

To check out air quality in your neck of the woods, visit our statewide network of air monitors: Washington Air Monitors.

Ecology has several resources available about indoor burning, including a list of approved wood stoves, fireplace inserts and other devices on the Air Quality pages. You also can find tips for burning properly in a previous blog story: How you burn makes a difference in your pocket and in the air.

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