GUEST POST: Why do we encounter poor air quality in winter? LRAPA’s Travis Knudsen explains.

LRAPA Public Affairs Manager Travis Knudsen.

Oregon has some of the most beautiful and pristine skies in the United States. However, we can also experience poor air quality, and not just during wildfire season. In winter months, there are times when DEQ’s Air Quality Index indicates anything from “Moderate” to “Very Unhealthy” air, often due to stagnant air and inversions. Thankfully, these occurrences don’t tend to last very long.

We asked our friend, Travis Knudsen from Lane Regional Air Protection Agency, to write about this. As LRAPA’s public affairs manager and a former broadcast meteorologist, we feel he is exceedingly qualified to discuss these air quality events. His explanation follows:

An air inversion occurs when a layer of cold air is present at the surface of the Earth, while warmer air is above it. During the day, the sun warms the Earth’s surface, heating the air directly above it. As the surface air becomes warmer, it rises and the colder sinks lower. This process of air movement is known as “mixing.”

Mixing is beneficial for air quality, as it helps to displace air pollution from the Earth’s surface with colder, non-polluted air. However, during periods of air stagnation, when there is no wind or air movement, the formation of low clouds and fog (which often occurs in winter) will prevent the sun from warming air at the Earth’s surface. This creates an inversion. Then, pollution is trapped at the ground. During prolonged periods of air stagnation, the continued accumulation of pollution in the same air mass can lead to poor air quality.

Two examples of inversions, as seen from above.

Air stagnations often occur when there is a region of high pressure over Oregon or near its coast, which deflects storms away from the Pacific Northwest and towards Canada or California. “High pressure” means the air is dry and sinking. When a high pressure center persists, it creates air stagnation, which can last for several days and negatively impact air quality.

It is important for individuals to take action to reduce air pollution during periods of air stagnation. One of the biggest contributors to air pollution is wood stoves, so it is crucial to burn cleanly and efficiently. This can be achieved by using dry, seasoned firewood with a moisture content under 20%; keeping the fire small and hot; and keeping the dampers on the wood stove open, so air flows and there is less smoke production.

When inversions bring extended poor air quality to Oregon, LRAPA and DEQ do our best to alert affected communities through air quality advisories. You can sign up to receive advisories at the following:

Travis Knudsen is the public affairs manager for the Lane Regional Air Protection Agency in Lane County, Oregon. He focuses on communicating agency activities to the public, partners and other interested parties. Travis works to engage the public in all topics air quality with an intent to educate and inform, especially during smoke intrusion events during wildfires. He has a B.S. in meteorology from the University of Northern Colorado and worked as a broadcast meteorologist for over 10 years, communicating the complexity of atmospheric sciences and the forecast to a television audience every day.

Published by Oregon Department of Environmental Quality

DEQ’s mission is to be a leader in restoring, maintaining and enhancing the quality of Oregon’s air, land and water.

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