Up In The Air: Inversion Season Is Ending in Boise, But Air Quality Still Matters 

"That pollution just continues to increase and increase and increase, and it mixes at ground level, so there's no real relief."

According to the Idaho Department of Environmental Quality, winter inversion season kicks off at Thanksgiving and wraps up around Valentine's Day, which means that this year, Boiseans got lucky—a host of quickly changing weather systems kept the worst of the inversions away. But in most years, as long-term Boiseans know, the winter air in the City of Trees can get dismally dark and polluted for days or even weeks at a time.

For newcomers who have yet to experience the Treasure Valley's signature smog, Airshed Coordinator Michael Toole, who works out of the DEQ's Boise Regional Office, said inversions are a kind of cold-air "cap" over the valley that shelters pollution beneath it. Normally, emissions from vehicles, buildings and wood-burning fires rise and drift away, but during an inversion they're trapped in the area, building up a toxic atmosphere just like a full trash can left decomposing in a closed-off kitchen.

"That pollution just continues to increase and increase and increase, and it mixes at ground level, so there's no real relief," Toole said. "When we get those inversions we can see [pollution levels] go from green, to yellow, even up into the orange over a couple days. And then it can stay in that orange and even maybe get into the red, which is unhealthy for everyone, until we get a weather system or something that can come in and, essentially, for lack of a better term, rip the lid off of that inversion."

Still, as miserable as inversions are, people tend to forget about them almost the moment they lift, and they only worry about air quality when the next one strikes or wildfire season begins, replacing smog with smoke. For Austin Hopkins, senior conservation associate for the Idaho Conservation League, this boom-and-bust awareness cycle is a problem, because while inversions are at base an act of nature, people can play a role in preventing them from getting too hazardous.

"We can't control the weather, per se, but we can control the amount of pollution we release that gets trapped," Hopkins said. "So, you know, we can drive less, we can burn less, we can do all sorts of things that help us reduce the amount of pollution we're exposed to."

Knowing just how much gunk is floating around in the air outside your home is a good place to start. While most people check on the state of the air by looking out the window or listen for the DEQ's color-coded warnings during an inversion, Hopkins has a different method: He pulls up the website for PurpleAir and watches its dozens of Treasure Valley dots fade from green, to yellow, to orange.

click to enlarge This was the air quality in the U.S. according to PurpleAir's map on Friday, Feb. 8.  - LEX NELSON
  • Lex Nelson
  • This was the air quality in the U.S. according to PurpleAir's map on Friday, Feb. 8.

Each of those dots represents a PurpleAir monitor—a small, cylindrical device that can be mounted to a buildings' exterior to measure local air quality. Hopkins attached one to the side of ICL's North End headquarters, where it uses laser beams to measure the density of particles in the air, then uploads the data to PurpleAir's website via a WiFi link.

"There's a small fan that sucks air in very gently," Hopkins explained. "As air passes over that laser, the more pieces of material, called particulate matter, that are in the air the more the beam of that laser will get scattered around. And essentially that's how this records air quality."

click to enlarge ICL's PurpleAir monitor is attached to its headquarters in the North End. - LEX NELSON
  • Lex Nelson
  • ICL's PurpleAir monitor is attached to its headquarters in the North End.

The little gizmos cost between $200 and $250 on purpleair.com, which can be cost-prohibitive, but businesses, schools and neighborhood groups have bought them to increase awareness of dips in air quality year-round.

"The data is totally free for everyone, so that's one of the really cool things about PurpleAir. Once someone installs a monitor, everyone gets the benefit of it," Hopkins said.

The map of monitors at purpleair.com is available for free to the public, and even the DEQ, which has its own fleet of expensive air monitors carefully calibrated to reflect EPA standards and set up strategically across the valley, checks on PupleAir from time to time.

"We don't know the accuracy of those data points," Toole said, noting that the ad hoc monitors are less reliable because they aren't calibrated as often, and can be accidentally placed near emitters like chimneys or vents that slant the readings, "... but we do look at that map and it does provide additional information for us to look at what's going on in other areas, maybe a trend, maybe a pattern."

Once you're aware of the air quality, the next step is checking your personal emissions. This is particularly important during inversions (including the less-intense summer inversions, which Toole noted often hit Boise in the mornings and lift by mid-day), when you're stuck breathing whatever you emit, but establishing low-pollution habits even when the air is clear can help fight off orange, red and purple air quality readings year-round.

"Inversions and wildfires, the poor air quality, it's kind of a gateway into making smart choices year-round," Hopkins said.

Find the ILC's list of those smart choices—including carpooling, telecommuting and taking public transportation—in the PDF below.

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