New study finds wildfire smoke impacts respiratory health more than fine particles from other sources

Choking smoke from record wildfires blanketed Northern California last summer and fall. It turned Bay Area skies an otherworldly orange, raising health concerns over a hazard that is increasing as temperatures continue to climb and poorly managed forests burn out of control each year across the West.

With this winter being extraordinarily dry, the chances of another big wildfire year are high. But the flames may not pose the biggest danger to the most people: A new study published Friday found that tiny particles of soot from wildfires, which millions of Californians are breathing in, are up to 10 times as harmful to human respiratory health as particulate pollution from other sources, such as car exhaust, factories or power plants.

“We’ve been really successful in reducing air pollution across the country by improving standards for automobiles, trucks and power plants,” said Tom Corringham, a research economist who studies climate and atmospheric science at the Scripps Institution of Oceanography at UC-San Diego. “The trend has been a decrease in air pollution. But these wildfires are getting worse.”

Corringham and his fellow researchers studied the number of people admitted to hospitals with respiratory problems daily from 1999 to 2012 in Southern California. They compared it to data from fires, Santa Ana winds and smoke plumes from San Diego to Santa Barbara.

They found that when air pollution of tiny particles called PM 2.5 — for particulate matter 2.5 microns or smaller, so small that 30 of them can line up along the width of a human hair — increased modestly, the number of people admitted to hospitals for respiratory ailments such as asthma increased by 1% on average. But when PM 2.5 levels from wildfire smoke went up by the same amount, or 10 micrograms per cubic meter, there was a 10% increase in those hospital admissions.

The tiny particles can penetrate deep into people’s lungs, enter the bloodstream and increase the risk of heart attacks, strokes and other serious health issues.

Last year, 4.2 million acres — an area 13 times the size of the city of Los Angeles — burned in California, the most in modern times. Fires from the Santa Cruz Mountains to the Southern Sierra sent enormous plumes of smoke over the state’s largest cities and as far away as the East Coast. On Sept. 9, smoke mixed with the marine layer, turning Bay Area skies an apocalyptic orange.

The Bay Area Air Quality Management District called 30 “Spare the Air” days in a row from August 18 to September 16. Soot levels nearly as bad blanketed the Bay Area during the Camp Fire in 2018 and Wine Country fires in 2017. In the Sierra, the Sacramento Valley and parts of Southern California, air quality was even worse last year, reaching 10 to 15 times the federal health standard.

A study by Stanford researchers concluded that the fires last fall caused 1,200 excess deaths and 4,800 extra emergency room visits in California, mostly among people 65 and older with pre-existing conditions such as respiratory problems, diabetes and heart disease.

More is on the way. Wildfire risk is expected to be high this summer due to the unusually dry winter. Last fall, state and federal officials signed an agreement to double the rate of thinning forests that have grown unnaturally thick due to generations of fire suppression. Gov. Gavin Newsom added $1 billion to California’s state budget this year for increased forest management, fuel breaks, fire inspections and fire crews.

But Corringham said that as the climate continues to warm and wildfires increase, government agencies must directly address the health risks of smoke, particularly to the elderly and low-income people. More “clean room” cooling centers, rebates for home air purifiers and better public education campaigns are key, he said.

Other health officials generally agreed.

Dr. John Balmes, a professor of medicine at UC San Francisco and a member of the California Air Resources Board, said some types of particle pollution, such as diesel soot, can be more dangerous than wildfire smoke. But overall, he agreed with the Scripps researchers’ conclusions that wildfire smoke poses a growing threat to the state’s residents as the climate warms.

“There’s no question it’s a huge air quality problem that has major health impacts,” Balmes said.

“There was a ring of fire last year around the Bay Area,” he added. “We are going to have to spend billions of dollars to maintain our forests better. It is going to take years. It can’t be done overnight.”

Scientists don’t know precisely why wildfire smoke is more harmful than most other particulate pollution. One theory is that when buildings burn, everything toxic in them, from heavy metals to plastics to pesticides, is sent airborne in smoke. Another theory is that the carbon nature of the particles causes more inflammation and stress on the lungs than other types of pollution.

“They are saying that wildfire smoke is more toxic. And that’s probably true,” said Dr. Mary Prunicki, director of air pollution and health research at Stanford University’s Sean Parker Center for Allergy and Asthma Research. “Usually direct deaths from wildfires are smaller than the effects from the smoke.”