How dust pollution from shrinking Great Salt Lake affects communities disproportionately

The findings suggest restoring the lake to a healthy water level would reduce disparities in harmful dust exposure experienced by different racial/ethnic and socioeconomic groups, along with delivering other ecological and economic benefits.

Exposure to particulate pollution arising from dry portions of the playa is highest among Pacific Islanders and Hispanics and lowest among white people compared to other racial/ethnic groups, according to the findings reported June 21 in the journal One Earth. It was also higher for individuals without a high school diploma. 

This is likely because Salt Lake City's lower-income neighborhoods are more likely to lie in the path of windblown dust from Great Salt Lake, which has shrunk to less than half its historical size, leaving about 800 square miles of lakebed exposed.

More than two decades of drought and unrelenting upstream diversions have contributed to the decline of the saline terminal lake located immediately west and north of Utah's main population corridor along the Wasatch Front.

"People here in Utah are concerned about the lake for a variety of reasons -- the ski industry, the brine shrimp, the migratory birds, recreation -- and this study adds environmental justice and the equity implications of the drying lake to the conversation," said lead author Sara Grineski, a professor of sociology and environmental studies.

Grineski led an interdisciplinary team of U faculty, largely associated with the Wilkes Center for Climate Science and Policy, from both the College of Social and Behavioral Science (CSBS) and the College of Science. Co-authors are Timothy Collins and Malcolm Araos (geography); John Lin, Derek Mallia and Kevin Perry (atmospheric sciences); and William Anderegg (biology).

The study analyzed data from the Utah Department of Environmental Quality's air-quality monitoring network, which screens for fine particulate matter, or PM_2.5. Comprised of ultra tiny particles that can penetrate lung tissue, this pollution is linked to myriad health problems, including cardiovascular disease and asthma.

During dust storms, current levels expose residents to 26 micrograms per cubic meter, or μg/m³, of PM_2.5 on average, according to the study, significantly higher than the World Health Organization's threshold of 15 μg/m³. Were the lake to dry up completely, exposure could rise to 32 μg/m³, while restoring the lake could reduce exposure to 24 μg/m³ during these wind events, according to the study.

The study examined four such events in 2022 on April 19, 20 and 21 and May 7, when spikes of recorded PM_2.5 coincided with high winds.

For the study, which was funded by the National Science Foundation, researcher Derek Mallia developed a model for predicting exposure levels for the three counties abutting the lake's east and south shores -- Salt Lake, Davis and Weber, home to 1.8 million residents -- under four different lake level scenarios. It uses a weather model that simulates wind direction and speed, and includes a wind-blown dust model, which measures how much dust is emitted from an erodible surface, such as the Great Salt Lake playa, and is primarily based on the wind speed and soil texture and characteristics.

"We have to use weather models, since we cannot physically go out to the lake and remove/add water to see how much more/less dust it would emit," Mallia said. "Models like the one that I developed let us run these hypothetical scenarios."

The study's scenarios range from a totally dry lake, to very low lake level, to current lake, to 'healthy' lake level designated as 4,200 feet above sea level. The lake's South Arm currently sits at 4,194.4 feet, almost 6 feet higher than the historic low of 4,188.7 registered at the end of 2022.

According to the model, neighborhood disparities in exposure levels would increase when the lake level drops.

"We frame it the converse. Lake levels rise, overall levels of dust go down during the dust events and the gap, especially between Hispanic and Pacific Islander people, narrows with respect to the level of dust exposure for non-Hispanic white people," Grineski said. "So if we can take better care of the lake, the dust for everyone goes down and the gap in exposure between these groups goes down too."

Her team's prior research has previously documented disparities of PM_2.5 exposure generally in the Salt Lake Valley

"There is a really strong pattern of inequality with respect to race and ethnicity," she added. "It's sort of a hopeful finding that if we can raise the lake to a 'healthy' level we can at least with respect to lake dust we can reduce some of that inequality."

Most dust from the playa is PM₁₀, pollution comprised of much larger particles that are only measured at a few of Utah's air quality monitoring stations. Without a robust PM₁₀ monitoring network, researchers and regulators are deprived of a key data source that could give a more complete assessment of the lakebed dust threat, according to co-author Kevin Perry. He said the study points to the need for Utah to expand its network of PM₁₀ monitors since windblown lakebed dust contains about six times more PM₁₀ than PM_2.5.

"We have to use the PM_2.5 data because that's the network that we have available. It's not what I would design and not what I would like to do," he said. "Because of the network being so sparse, I can't even answer a really basic question, like how many dust events do we have a year that are impacting these communities. And that's super frustrating."

A professor of atmospheric science, Perry is known as "Dr. Dust" thanks to his tireless bicycle forays across the vast lakebed gathering sediment samples. These sediments were found to be contaminated with heavy metals in some places.

He noted that potentially harmful dust events typically occur in the spring and fall when cold fronts pass through the Wasatch Front.

"Before a cold front gets here, we have really strong winds from the south that will last for 12 or 18 hours," Perry said. "And where's it pushing that dust? It's pushing it to Layton, Syracuse, Ogden, Brigham City where we have almost no PM₁₀ monitors at all, and then the wind reverses and we'll get three to four or five hours of stuff coming into Salt Lake Valley where we do have monitors."

Because of its ability to infiltrate living tissue, PM_2.5 is considered more harmful to human health than PM₁₀, which is also classified as a criteria pollutant under the federal Clean Air Act.