Wildfire smoke may cause tens of thousands of premature deaths

Wildfire season got off to an early start in Northern California with the Corral Fire, which started burning grasslands in San Joaquin County on June 1 and grew to cover more than 50 square kilometers. A new modeling study estimates the health effects on the state’s population due to plumes of smoke from fires like this one — not only in the first few days, but also after years of exposure.

Researchers estimate that fine particulate matter pollution spewing from California wildfires from 2008 through 2018 was responsible for 52,500 to 55,700 premature deaths in the state. The estimated economic benefit of reducing that early mortality is $432 billion to $456 billion, the team reports June 7 in Science Advances.

The study finds “quite a considerable impact” from wildfire smoke exposure over time, says environmental health scientist Stephanie Cleland of Simon Fraser University in Burnaby, Canada, and the Vancouver Coastal Health Research Institute. Health impact assessments like this underscore the benefit of investments to build smoke resiliency, says Cleland, who wasn’t involved in the study.

Fine particulate matter, called PM_2.5, describes airborne particles of pollution that have a diameter of 2.5 micrometers or smaller. Once inhaled, these microscopic particles can travel all the way to the lungs’ alveoli, the delicate air sacs surrounded by tiny blood vessels, where oxygen is exchanged for carbon dioxide. There’s evidence that the particles can even enter the bloodstream.

Studies have found that exposure to fine particulate matter pollution is linked to lung damage, an increased risk of a heart attack and reduced life expectancy (SN: 8/22/2018). Along with wildfires, sources of PM_2.5 include fossil fuel combustion, factories and agriculture operations (SN: 7/30/20).

Historically, the research field has treated exposure to wildfire smoke as “this very acute event — it comes in, people are exposed to really high concentrations and then it leaves,” Cleland says. Studies have reported health harms in the short term, including upticks in hospital visits for chronic lung conditions (SN: 9/18/20). But there’s been a recent shift to understanding the health risks “when someone’s exposed to years’ worth of smoke,” Cleland says.

Michael Jerrett, an environmental health scientist at UCLA’s Fielding School of Public Health, and his colleagues created a mathematical model to tackle the issue. The team used annual averages of wildfire smoke exposures over an 11-year period to try to capture the long-term effect on mortality. With early evidence suggesting that PM_2.5 from wildfires may be more toxic than fine particulate matter from other sources, the team built that assumption into the model. The researchers also estimated the exposure to PM_2.5 specifically from wildfires, rather than from a composite of sources.

To get a better understanding of the long-term effect of wildfire smoke exposure, the next step is to follow a group of people over a decades or two to compare the death rates between those who’ve been exposed to higher concentrations of wildfire smoke and those who’ve experienced less, Jerrett says. But considering the amount of time such a study takes, his research team started with the mathematical model approach.

With how often wildfires are occurring and how they are projected to get worse with climate change, “it was really important to get some overall estimate of the size of this problem.”