At the air quality monitoring station just across the Deschutes River from downtown Bend, air circulates through the tubes of a nephelometer — a device that shines a light through air samples once a second.
It detects tiny smoke or exhaust particles that get in the way of the light beam to measure the amount of pollution in the air swirling around Bend.
But over the last decade, fewer pollutants have passed through the device, due in part to changes in wood stove use and better vehicle emission technology.
“That's the exciting story about Bend — why Bend has been able to grow and improve air quality at the same time,” said Larry Calkins, air quality specialist with the Oregon Department of Environmental Quality.
Over the last 10 years, measurements of fine particles only a fraction of the width of a human hair have shown an overall downward trend, said Anthony Barnack, ambient air monitoring coordinator with the DEQ.
“Compared to the rest of the state, you're doing pretty well,” he said.
Those small particles from things like fires, wood stoves, diesel combustion and more, called PM 2.5, concern environmental regulators because they can lodge in lungs and cause health problems.
The DEQ previously measured the amounts of slightly bigger pollutants — up to four times as big as what's measured now — but in part because Bend's numbers were so low, the DEQ stopped measuring it locally, Barnack said.
“We also had a carbon monoxide monitor in Bend, but (measurements were) very low,” he said. “We shut it down to save money.”
So now, most of the agency's monitoring in the area is focused on measuring PM 2.5.
At the downtown Bend site, a machine draws air through a filter for 24 hours, once every six days, to get the official pollutant count. For a more up-to-the-minute, unofficial count, the nephelometer takes instant readings so the agency can warn people if a wildfire or inversion is causing a decline in the air quality, potentially posing a health hazard.
The DEQ is also focusing its attention on the amount of ozone in Bend — not because it's been a problem, Barnack said, but because of the size of the growing population. Ozone is an easily measurable component of smog, so it lets officials track how big of a problem smog is in an area.
“That's a large area not to be monitoring,” Barnack said. “Most everything we do now is because of the population — air quality is doing pretty well relative to other cities.”
The DEQ started measuring ozone in Bend in August 2008, and each of the 41 measurements the department took that year fell in the “good” category, according to the agency's annual report.
Concern over Prineville
But one nearby area of concern, agency officials said, is Prineville.
“We've gone back to Prineville with more stringent standards,” Calkins said. “EPA keeps changing the standard, and improving it so that people can breathe cleaner and cleaner air.”
In November 2008, the DEQ started monitoring PM 2.5 in Prineville, and in the first 49 days of measurements, the city had one day during which the air was classified as “unhealthy,” and four days when it was “unhealthy for sensitive groups” — referring to people with respiratory problems as well as children and seniors.
The problem is that Prineville has cold, still air at night, Calkins said. So when people use their wood stoves, the smoke sticks around.
“The two just build up pollution at night, and then you have problems,” he said.
Since Nov. 15 of this year, Prineville has had one “unhealthy” and one “unhealthy for sensitive groups” days, according to the DEQ's Web site — the rest of the days were fairly evenly split between “good” and “moderate.” If the air quality is unhealthy, officials recommend people avoid strenuous exercise or stay inside if they have a house with a filtered air system.
In contrast, Bend's ratings for the past month have been “good,” except for two days that were “moderate.”
The DEQ has been working with officials from Prineville and Crook County, Calkins said, to encourage people to burn small, hot fires, use alternate heat sources on bad air quality days, and change out old, inefficient stoves for EPA-certified models.
Bend's air quality has turned around in the last couple of decades, said Gregory McClarren, who was a member of the city's clean air committee that formed in the late 1980s.
“We're nowhere (near) as bad off as we were 10 years ago,” he said. “They've taken most of the monitoring equipment out of Bend because it's so much of an improvement, and there are other hot, or dirty, spots in the state.”
Some of the things that helped, he said, were educational outreaches focusing on wood stoves, and Bend's adoption of an ordinance that stated people could not sell a house with an old, uncertified stove — it had to be replaced with either a certified model or a natural gas version.
Improved technology that cut down on vehicle emissions and better quality of gasoline fuels also helped, he said, as did less burning of slash piles from timber sales.
“It all made for cleaner air,” he said.
But there are still problems, McClarren said, adding that he would like to see field burning regulated more in certain areas.
And Bend still has those “moderate” air quality days.
Ripdeep Mangat, a Bend allergy and asthma specialist, said he had seen an increase in patients whose asthma had picked up recently — timing that corresponds to the cold, still nights the second week of December, when the air quality wasn't as clear as usual.
And wildfires and burning can contribute to the problem in the summer.
“We certainly see, whenever the fires occur, that sensitive people and people with asthma have problems,” he said.