Air quality in Tooele Valley this winter was much worse than last due to early snowstorms and bitter cold, state officials say. The difference is found in the numbers.
According to the Utah Division of Air Quality, from October through February the valley had 20 voluntary no-burn days and 17 mandatory no-burn days. During the 2011-2012 winter for that same time period, the valley had two voluntary no-burn days and zero mandatory noburn days.
In comparison, Salt Lake County had 14 voluntary noburn days and 35 mandatory no-burn days. During the 2011- 2012 winter, Salt Lake County had 16 voluntary no-burn days and two mandatory no-burn days, according to DAQ.
For clarification, the state previously called voluntary no-burn days “yellow air quality days,” and mandatory no-burn days “red air quality days.”
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 were not called until the standard reached 25 micrograms per cubic meter, and red alert days were not called until the standard was violated. When winter began, in an effort to reduce meeting that threshold so often, the DAQ changed its method. The new method replaced the stoplight color scheme and adopted the Environmental Protection Agency’s Air Quality Index, which is a six-color warning system. This system uses green, yellow, orange, red, maroon and purple to define air quality conditions based on the amount of micrograms per cubic meter of PM 2.5.
“For yellow days, we reduced the standard to 15 and for red days, we reduced it to 25,” said Bo Call, manager of DAQ’s air monitoring section. Because of the changes, Tooele Valley had several more voluntary and mandatory noburn days during the winter, said Call.
“We got snow early in significant quantities and then it got really cold and the snow stayed and it stayed cold,” he said.
Call said the reason why freezing temperatures and snow on the ground cause bad air quality is because there’s nothing to disrupt the inversion.
“The inversion gets trapped under the upper warm layers in the lower cold layers,” he said. “Last winter it was cold, but we didn’t have much snow so we didn’t really have that many bad air days.”
In addition, Call said when the sun shines down it reflects off the snow, so there’s not much thermal absorption in the ground.
“That means you don’t get the standard moving of air,” he said. “If the ground warms, then hot air rises, but if you don’t get that then you get pollution sticking around.”
Call said he doesn’t have any data to show if the adoption of the new method helped to improve the air quality throughout the winter, but he hopes it did.
“I know the change had some effect just because of the number of people who called me to chew me out for saying they couldn’t burn their fireplace,” he said. “Anybody who’s not burning their wood-burning fireplace is helping the air quality problem. Whether or not there’s any significant change, it’s hard to tell because there are different things that affect air quality.