Utah’s dark skies, painted with vibrant colors and splashing flames when fireworks light the night, are quite the spectacle during the state’s two July celebrations.

But the rockets’ red glare and the lingering smoke in the air can also yield their share of toxic chemicals and pesky pollutants.

State data over the past 15 years shows that particulate pollution, primarily from PM 2.5, frequently climbed to unhealthy or even hazardous levels during those nighttime displays on July 4 and 24, peaking between 9 p.m. and midnight.

During that period, a Salt Lake Tribune analysis found, fireworks-fueled pollution was much higher on Independence Day than Pioneer Day. The analysis also revealed that the maximum nighttime PM 2.5 levels on those days across Utah have been lower in recent years.

Even so, clean-air advocates note that holiday pollution remains evident during those spikes and argue that more needs to be done to reduce emissions.

‘Pollution burden’

PM 2.5 levels are measured in micrograms per cubic meter of air (µg/m³). Nationally, PM 2.5 concentrations are 42 percent higher on July Fourth than the days surrounding the holiday, according to a 2015 study.

Air becomes unhealthy when the PM 2.5 level falls between 55.5 and 150.4 µg/m³, according to the Air Quality Index established by the U.S. Environmental Protection Agency. It’s considered very unhealthy at 150.5 and hazardous above 250.5.

The Utah Division of Air Quality has set up monitoring stations in 12 counties across Utah to track PM 2.5 levels. Since 2004, the air frequently reached unhealthy levels at 13 stations in six counties on July Fourth. It shot up to hazardous levels on Independence Day at three stations in Ogden, Lindon and the Rose Park neighborhood in west Salt Lake City.

In Ogden, where the highest PM 2.5 level was recorded, PM 2.5 concentration skyrocketed to 900.5 µg/m³ at 10 p.m. on July Fourth in 2014, almost 70 times higher than daytime levels.

“To put that in context, that’s 30 times higher than the EPA’s 24-hour standard [of good or moderate air quality],” said Brian Moench, board president of Utah Physicians for a Healthy Environment.

“It’s a significant pollution burden,” he said.

PM 2.5 can travel to every cell and organ, enter the bloodstream and trigger all kinds of diseases, Moench warned. “Particulate matter is associated with increased rates of heart attacks and strokes and sudden death, just about every respiratory disease that we know of."

Some particulates emitted during fireworks displays take longer to dissipate, Moench said. “The smallest subset of those particles of PM 2.5 ... the ultra-fines, can remain in the atmosphere for several days afterwards."

Heavy metals — included in chemicals that create the colors — are also packed into fireworks and can be more harmful than the typical particles, said Bryce Bird, director of the Utah Division of Air Quality.

“We encourage people to be careful with fireworks, to enjoy the large community displays," Bird said, “and to ... watch your children and the elderly who are particularly susceptible to the impacts from air pollutants of that size and type.”

Down but not out

Despite those sharp nighttime upswings on July holidays, the maximum PM 2.5 levels have fallen in recent years, state data shows.

For instance, over the past four years, the average peak-hour PM 2.5 levels across the state during the July festivities never topped 100 µg/m³, according to the data.

In Salt Lake County, however, where the population density is highest, several stations recorded their highest peak-hour values during the past four years. PM 2.5 hit 204 µg/m³ at Hawthorne Elementary School in Salt Lake City in 2016.

Most stations with years of history experienced their highest levels of PM 2.5 concentration before 2016, the data shows. PM 2.5 levels from stations across the state averaged 318.63 µg/m³ at 10 p.m. on Independence Day in 2007, a historic high over the past 15 years.

Thom Carter, executive director of the Utah Clean Air Partnership, said he has seen a reduction of PM 2.5 emissions through the years even as the population continued to swell, a trend he attributed to technology development and a growing awareness to protect the air.

“More people are realizing that it’s better, safer and wiser to just participate in the larger-scale municipal ones," Carter said, “than just to light their backyards.”

In 2018, the Legislature scaled back the total number of July days people are allowed to light fireworks from 14 to eight.

Carter said the restrictions helped dial down emissions as well. “What we always like to say is regulation and personal choice are really what get us to a better place.”

Moench maintains more can be done, noting that many other states allow for a smaller window for legal fireworks. He hopes Utah policymakers will reach beyond the July holidays and tighten the rules on fireworks for other events.

“They need to be aggressive," Moench said, “in helping all of those entities understand that for them to set off huge fireworks does really create a pollution burden for the community.”