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Kristin Murphy, Deseret News
Traffic passes by the Big West Oil LLC refinery in North Salt Lake on Thursday, Aug. 2, 2018.

SALT LAKE CITY — Despite population growth, more energy development and additional motorists on the road, hazardous air pollutants have dropped significantly across the country since 1990, a new report shows.

The U.S. Environmental Protection Agency released its annual report this week tracking air pollution trends across the nation, noting double digit decreases in concentrations of hazardous pollutants.

Since 1990, eight-hour measurements of carbon monoxide have plunged by 77 percent, annual measurements of nitrogen dioxides diminished by 56 percent and eight-hour ozone levels are down by 22 percent.

The report notes that between 1970 and 2016, the combined emissions from six common pollutants dropped by 73 percent.

Bryce Bird, director of the Utah Division of Air Quality, said federal clean air standards have evolved over time to become more stringent, driving down emissions from a variety of polluting sources, including industry, homes and automobiles.

At the same time, technology developments are fueling cleaner ways for the industry to operate and for people to live their lives by minimizing their carbon footprint, he noted.

"Over the past 35 to 40 years we have been addressing air pollution challenges along the Wasatch Front," Bird said. "We have seen actual improvements in air quality even though we have been growing."

The EPA report looked at the number of days in 35 major U.S. cities, including the Salt Lake metro area, that air pollution levels hit the level of "unhealthy for sensitive groups" or higher mark.

Jeffrey D. Allred, Deseret News
Motorists travel on I-215 in Salt Lake City on Thursday, Aug. 2, 2018.

In 2000, across those cities, there were 2,076 days where there were exceedances for ozone or PM2.5, or what's known as fine particulate levels. In 2016, that number was 697.

The Salt Lake City metro area experienced 65 of those days in 2002 — the highest in a 17-year period. In 2016, that number was 28.

The Utah Department of Environmental Quality points to population increases of 26 percent between 2002 and 2014, yet a statewide decline in emissions by 30 percent.

According to the EPA report, visibility standards are also improving at some of Utah's national parks, which come under a regional haze rule designed to enhance viewsheds in wilderness and other prime outdoor spaces.

It cites significant improvement at Bryce Canyon National Park and at the Canyonlands National Park's Island in the Sky area and possible improvements for Capitol Reef National Park.

The heavy lifting is far from over, however.

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The state is continuing to craft ways to tamp air pollution and is crafting a new state implementation plan identifying emissions control measures for industry, small businesses and household products.

Scott G Winterton, Scott G Winterton, Deseret News
A smoggy view of the Salt Lake valley.

That plan to address PM2.5 levels is required by the EPA because the Salt Lake area was classified as "serious" nonattainment.

A similar challenges exists for the state's ozone levels, which Bird said have spiked this summer due to the hot and stagnant weather pattern.

"So far we have exceeded the standard 11 times in Salt Lake County," he said.

Utah is also engaged in the largest study of its kind probing the formation of winter-time ozone in eastern Utah.