Utah has made laudable strides combating PM2.5 and ozone, the two leading air quality challenges for the Wasatch Front that have long threatened residents’ health.  But that progress is being overshadowed by two growing menaces, dust and wildfire smoke, according to presentations made by University of Utah atmospheric scientists last month at the College of Law’s 30th annual Wallace Stegner Center Symposium.

Both are associated with climate change, which is making the West drier and warmer. Neither can be controlled through traditional emission-reduction programs that have helped reduce smog all over the West, especially in Los Angeles.

The symposium’s keynote speaker Nsedu Obot Witherspoon, executive director of the Children’s Environmental Health Network, explored the need for greater equity in how we protect children from air pollution. The other featured speaker, UCLA law professor Ann Carlson, discussed the progress Los Angeles has made in recent decades to rein in emissions responsible for its once-notorious air pollution and what lessons it offers for other cities struggling with bad air.

Reducing vehicle and industrial emissions alleviates particulate and ozone pollution, but such measures make little difference for smoke and dust.

A new Dust Bowl?

Salt Lake City is affected by countless dust sources—gravel quarries, the long-dried Sevier Lake, roads and lands disturbed by cattle grazing and off-roading. But the most troubling could be the shrinking Great Salt Lake, yet the state of Utah has yet to deploy the monitoring equipment to know for sure, said Kevin Perry, a professor in the Department of Atmospheric Sciences. His tireless sampling forays by bike have earned him the moniker of Dr. Dust.

According to Perry’s research, there are four major “hotspots” on the 750 square miles of exposed playa where winds can lift dust into the air and potentially push it into populated areas and nearby mountains, Perry said on a panel devoted to the dust issue. These spots occur where the lakebed crusts have been disturbed, exposing the underlying sediments to the influence of the wind.

Hotspots closest to residential areas are in Farmington Bay, as well as in Bear River Bay, where most of the dust sources are located at elevations above 4,202 feet, nearly 10 feet above where the lake level stands, Perry said. The Farmington Bay spots tend to be at lower elevations.

“You can cover up a significant quantity of these dust hotspots at a lake elevation of 4,200 feet and get 70% coverage at 4,202,” he said. The lake’s ever-fluctuating level is currently at 4,193, a good 5 feet below what officials say is needed to restore Great Salt Lake’s ecological health.

“All of these dust hotspots that I’ve measured are currently exposed. They’re too wet to blow right now, but that’ll change as we move into the drier season,” Perry said. “Even if you bring that lake up to 4,198 feet, that will only cover up about 40% of the dust hotspots.”

Wind events, especially in spring, drive a big share of the Wasatch Front’s dust problem, pushing particulate pollution from the lake and other sources into the cities of Salt Lake, Davis and Weber counties and into the mountains where it settles onto the snowpack. Research shows this dust contains elevated levels of cadmium, arsenic, lead and other hazardous metals, depending on its source.

“Before a cold front hits our valley, we have really strong winds from the south that scream 25 mph or more for up to 18 hours. As that front passes, the winds change and move from the west to the northwest and stay strong for a few hours. So if you look at the data from the airport at Salt Lake International Airport, when we have these strong wind events that create these big dust storms, 75% of the time the dust is moving north to communities of Layton and Syracuse and Ogden.”

Perry and his colleagues are eager to quantify the impact of lake playa dust on Wasatch Front cities, but there is currently not sufficient data being collected along the lake’s populated eastern shore, he said.

Smoke on the horizon

Poor air quality should be considered a climate-related hazard that kills way more people than other forms of severe weather, such as tornadoes and hurricanes, said Derek Mallia, a research professor of atmospheric sciences who studies wildfire.

“Air quality events across the western U.S. are becoming more severe and this is ultimately being driven by drier conditions. If we have drier conditions, we have more wildfires and we have more wind-blown dust,” said Mallia, speaking on the panel devoted to wildfire. He believes the West has entered an “era of mega fires” that will worsen until at least the 2060s.

“It’s the largest wildfires that are seeing the most rapid growth,” he said. “Our bigger fires are becoming much bigger.”

The largest fires have increased in size by about 800%, and even though they make up a small fraction of total fires, they burn the most land and produce the most smoke. And their “plume rises” is growing taller.

“It’s that buoyant column of smoke that’s lofting smoke from the fire vertically up into the atmosphere. The reason why we care about this is that this can actually impact the geographical coverage of smoke,” Mallia said. “This wildfire plume rise acts as a chimney where it carries smoke up to, in some cases, the cruising altitude of a plane. This can actually spread out the smoke over a much larger geographic region, increasing the likelihood that that smoke gets caught in the jet stream.”

Over the past 20 years, plume rises on average have increased by a quarter mile, injecting more aerosols into the atmosphere, according to research by U atmospheric scientists.

“This is being driven by the fact that these fires are burning hotter, they’re adding more buoyancy to the atmosphere, so like a hot air balloon, it’s going to rise up more quickly,” Mallia said.

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Banner photograph, shot by Liberty Blake, shows a dust cloud blowing into Salt Lake City. Videos of the S.J. Quinney College of Law’s 30th annual Stegner Symposium presentations can be found here.

• Brian Maffly Science writer, University of Utah Communications
  801-573-2382 brian.maffly@utah.edu