Cold temperatures and inversion conditions caused the first yellow air quality alert of the winter season in Tooele County today.
“Today is the first voluntary no-burn day of the season,” said Bo Call, manager of the air monitoring section for the Division of Air Quality. “This means the air is starting to get bad, so you should start doing all you can do to prevent it.”
The violation amount for the 24-hour national air quality standard is 35 micrograms per cubic meter for PM 2.5 — small soot and dust particulate matter — which is approximately 1/40th the size of a human hair. It comes primarily from vehicle emissions, industry and wood burning stoves.
In the past, yellow alert days have not been called until the standard has reached 25 micrograms per cubic meter, and red alert days were not called until the standard was violated. This year, in an effort to reduce meeting that threshold so often, those standards have been changed, Call said.
“This year what will be different is the threshold that we use to call the red and yellow alert days has been adjusted a bit,” Call said. “For yellow days, we’ve reduced the standard to 15 and for red days, we’ve reduced it to 25. We’re trying to be more proactive. We don’t want to pass the standard anymore, so we’re asking people to not use their fireplaces and drive less earlier — before we reach the standard.”
Call said because of the change, Tooele County might see a lot more yellow and red alert days this winter. Last winter, Tooele County had two yellow air quality days — on Dec. 10 and Dec. 12 — and no red air quality days.
Salt Lake County has already had five yellow alert days this winter, including today. Tomorrow is also predicted to be a yellow art day for both Tooele and Salt Lake counties.
Call said colder temperatures and the inversion are to blame for the yellow alert day today. The rain earlier this week and the fog this morning did not change conditions either, he said.
“’We’ve got a strong enough inversion that it’s keeping the lid on reasonably tight,” Call said. “I don’t think fog is a cause for bad air quality, but just a symptom of the inversion. Rain falls through the pollution. It’s not generally rain that clears us out. It’s the winds that come in with the rain, so the air is able to change more. We didn’t have much wind with this rain.”
Call said it’s important for people to take precautions when there are yellow alert days.
“When things get to that level, what we say is for people to voluntarily not use wood or coal burning stoves, not use their fireplaces and reduce their vehicle use,” he said. “Industries should also optimize their processes to reduce emissions.”
In addition, children, the elderly and those with upper respiratory illnesses should try to limit their time outdoors.