Improving Air Quality in Eugene

How trees can help address winter inversions

Residents of Eugene and Springfield are very familiar with inversions. On a cold, clear winter day, pollutants get trapped in the valley, hanging low like a fog and causing notably poor air quality for people on the ground.

“On a cold, dry day, you can pretty much expect an inversion,” says Friends of Trees Eugene Director Erik Burke. “It’s not uncommon to see air quality alerts in winter.”

In the Eugene metro area, the main culprits are car emissions and wood smoke. Particulates in the air get trapped in the valley by warmer air above. It can lead to uncomfortable and even dangerous levels of air pollution. Because Eugene is at the southern end of the Willamette Valley and further away from winds coming from the Columbia River, it’s more susceptible to inversions than the Portland metro region.

One thing that can help? You guessed it, more trees! Trees improve air quality by providing surface area for airborne particulates to stick to. Those particulates are then washed by rain into the soil, where microorganisms break them down into something less harmful.

By breaking down pollutants, soil functions like a kidney of sorts. Trees help guide and slow water through the soil, making trees huge contributors to both air and water quality in both natural and urban environments. As Erik puts it, “trees are stormwater facilities.”

Like in plenty of other cities, the neighborhoods that are closest to polluters in Eugene are low income neighborhoods. Air quality is one of the many benefits of trees that low-canopy neighborhoods are deprived of. Friends of Trees plantings in the Bethel neighborhood are in part to address air quality concerns there.

“All trees are good at improving air quality,” Erik says. “We’re trying to get trees in the ground where air quality is worst.”

This is one of the reasons Friends of Trees plants along the railyard and the Northwest Expressway, where idling locomotives and automobiles are releasing particulates.

While all trees improve air quality, evergreens are particularly useful because they keep their leaves or needles all year.

“Most of our rain comes in winter,” Erik says, “so evergreens are essential. We have a lot to learn about evergreens and air quality.”

Most of the evergreens in Eugene’s urban forest are conifers rather than broadleaf evergreens. While we often think of conifers when we think of evergreens, other species like California live oaks, holm oak and California bay laurel also keep their leaves year-round. Many evergreens grow to be quite large, so the Eugene team is looking to incorporate smaller evergreens like toyon into their plantings.