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Utah’s otherwise ‘benign’ ozone season punctuated by pollution from holiday fireworks

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Hazy skies obscure the south end of the Salt Lake Valley as vehicles travel along Main Street in Salt Lake City on Wednesday, July 15, 2020.

Steve Griffin, Deseret News

SALT LAKE CITY — The Wasatch Front has not suffered terribly from ozone pollution this summer, but extremely active and long-lasting fireworks celebrations over July Fourth drove fine particulate pollution to extremely high levels.

“My own neighborhood was nuts. I didn’t need to go to a fireworks show. I just sat in my backyard,” said Bo Call, manager of the Utah Division of Air Quality’s air monitoring section.

The federal threshold for unhealthy levels of PM2.5, or fine particulate pollution most often dominant in the winter, is 35 micrograms per cubic meter. This particular pollution, roughly 25 times smaller than the diameter of a human hair, is the primary culprit driving the state’s notorious wintertime inversions that are harmful to human health and trap people indoors, especially the very young and elderly.

Over the July Fourth holiday, however, exploding fireworks blanketed the atmosphere with extremely high levels of PM2.5, with the division recording values over 200 micrograms per cubic meter, and for a duration of an hour or more.

“The fireworks also seemed to last longer,” Call said, noting that in the past fireworks would go off around dusk and continue for 45 minutes or so. This year, celebrants started putting flame to fireworks about 8 p.m. and lit up the sky until 11 p.m. or midnight, Call said.

“That may be where the coronavirus stimulus check went,” Call mused.

Otherwise this summer, Call said ozone levels have not been particularly troublesome due to a favorable weather pattern that has brought rain, wind and cloud cover on many days.

Ozone forms as the result of photovoltaic chemistry — it needs sunlight to kick-start — so Call said Mother Nature has been a pollution ally this summer.

“So far this summer has been pretty benign,” he said.

Call did say when there were ozone levels that eclipsed the eight-hour 70 parts per billion federal standard — about three instances so far — the measurements were pretty extreme.

“That is the part that is bothersome,” he said. “When you see values that are 80 or above, you have to scratch your head and wonder what is going on.”

The division’s monitoring section is also closely eyeing pollution levels this summer as it relates to potential COVID-19 impacts.

When the pandemic forced a lockdown this spring, Call said it was tough to tell how much the drastic declines in traffic and business activity affected pollution levels because spring is a time when pollutants are naturally diminished.

As the summer wears on, and with it the potentially sweltering heat, Call said the division will be watching ozone levels if spikes in COVID-19 cases or deaths spur a return to lockdown conditions.

“We will be paying particular attention to see if there is anything that could be identified or linked to coronavirus,” he said. “If vehicle traffic reduces by 20 to 30%, we would really pay attention to that and tease it out to see if the values are going lower ... it would be interesting to see if those numbers materialize or not.”

While ozone has not been a particularly troublesome pollutant this summer, Call said that could change if hot, sunny and stagnant weather sets in.

“It is the dog days of summer when you have nothing but crickets and locusts and hot sun and no wind — that is when we expect to see high values.”