Coarse particulate matter deriving from California’s largest lake is linked to an increased risk of respiratory-related hospitalizations.
By Katherine Kornei, EOS
California’s Salton Sea is impressive—it’s the largest lake by surface area in the Golden State and a haven for migratory birds. But its waters also contain high levels of agricultural runoff. As the lake evaporates, those pollutants are becoming increasingly concentrated, and the Salton Sea’s shrinking shorelines are leaving behind a perimeter of dry, toxic dust.
Researchers recently mined hospitalization records and showed that people are more likely to experience respiratory distress when particulate matter blows from over the Salton Sea. These findings could inform efforts to limit the health impacts of Salton Sea–derived particulates, according to the team.
Located roughly 260 kilometers (160 miles) southeast of Los Angeles, the Salton Sea is a vast inland lake. But it’s shrinking: Water levels have fallen by more than 3 meters (9 feet) over the past 25 years. That’s because the rate of water flowing into the lake—mainly due to agricultural runoff from farms in the surrounding Coachella and Imperial Valleys—is far lower than the rate of evaporation. As the Salton Sea shrinks, wide swaths of dusty, dry lake bed known as playa are continuously being exposed. At the same time, the lake’s waters are becoming more saline and rich in agriculturally important compounds such as nitrogen and phosphorus, conditions that can promote algal blooms.
“The air quality in the area is pretty darn suspect.”
William Porter, an atmospheric physicist at the University of California, Riverside, and his colleagues wanted to understand the implications of those shifts. “For decades, there have been concerns about what that means for the ecology, what that means for animals in the environment, and what that means for people,” Porter said.
Dust levels in the Coachella Valley routinely exceed national standards set by the U.S. EPA, and previous work showed that children living near the Salton Sea suffer from asthma at nearly twice the national rate.
“The air quality in the area is pretty darn suspect,” said Amato Evan, an atmospheric scientist at the Scripps Institution of Oceanography in La Jolla, Calif., who was not involved in the research.
Yaning Miao, previously a graduate student in Porter’s research group, led the new work. Miao and her colleagues collected records of airborne particulate matter from six ground stations—three to the north of the Salton Sea and three to the south.
Tiny airborne particles can be readily inhaled and become lodged in the lungs, where they can have deleterious health effects. The researchers focused on coarse particulate matter, which ranges in diameter from 2.5 to 10.0 micrometers. They gathered 12 years’ worth of hourly data from 2008 to 2019, amounting to more than 630,000 individual measurements.
From Whence It Came

The team then used simulations of atmospheric transport to investigate what types of surfaces the dusty air had passed over before being measured. That step allowed the researchers to estimate how much dust had originated from various sources, including the Salton Sea. “For all the observations of particulate matter that are taken up and down the valley, we ran thousands and thousands of back trajectories to see where it was arriving from,” Porter said.
Most of the dust the team analyzed came from landscapes dominated by shrubs or crops; less than 3% of the total dust mass likely came from the Salton Sea, the researchers estimated. But the big question was whether that Salton Sea–derived dust was more harmful than dust from other types of landscapes.
Miao and her collaborators analyzed public hospitalization records for individuals living in zip codes within 5 kilometers (3 miles) of each of the ground stations. But working with health data is challenging, Porter said, because there are so many different factors that affect how many people are hospitalized on a given day. Day-of-week, seasonal, and annual trends can all have a significant impact on hospitalization numbers, he said.
The team tried to control for as many confounding variables as possible by comparing records from a particular day with the same day of the week in the same month of the same year. “We’re only comparing apples to apples,” Porter said.
“This is a problem for many, many other communities.”
The researchers found that the risk of respiratory-related hospitalizations increased by about 9% for each 10-microgram-per-cubic-meter increase in coarse particulate matter coming from the Salton Sea. A similar uptick in dust from the other nine landscape types was not statistically correlated with an increase in respiratory-related hospitalizations.
Furthermore, the same increase in coarse particulate matter from the Salton Sea was associated with a nearly 25% increase in the risk of respiratory-related hospitalizations during times of algal blooms. Those numbers suggest that particulate matter coming from the water itself is particularly harmful to human health, Porter said. That finding can inform mitigation strategies.
Current efforts to address the poor air quality in the Salton Sea region have been largely focused on the playa surfaces. “We’re talking about millions of dollars’ worth of infrastructure work,” Evan said. But such efforts may not be getting at the root of the problem, which appears to be particulate matter deriving from the water surface itself, he said. “This is a new finding.”
These results were published in Environmental Research: Health.
Unfortunately, the situation at the Salton Sea isn’t unique—similar situations are playing out at other lakes worldwide, Porter said. Utah’s Great Salt Lake is a prime example, he said. “This is a problem for many, many other communities.”
—Katherine Kornei (@KatherineKornei), Science Writer