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Wildfires churning out dense plumes of smoke as they scorch part of the U.S. West Coast have exposed more than 8 million people to hazardous pollution levels, according to an Associated Press analysis.

Unhealthy particles carried by the smoke caused emergency room visits to spike and potentially thousands of deaths among the elderly and infirm, according to physicians, health authorities and researchers.

Major cities in Oregon last month suffered the highest pollution levels they’ve ever recorded when powerful winds supercharged fires in remote areas and sent smoke into Portland and other cities.

Stanford University researchers estimated on Sept. 11 that between 1,200 and 3,000 people aged 65 and older may have died prematurely due to exposure to wildfire smoke in California since Aug 1. 

“We are in the midst of the COVID pandemic, and this has as-yet-unknown implications for our understanding of how air pollution affects health outcomes,” the Stanford researchers wrote. “Early evidence seems to suggest that poor air quality could worsen COVID-related outcomes, and if that’s the case then our numbers above could be lower bounds.”

A University of Montana study of residents of the western Montana town of Seeley Lake found that wildfire smoke leaves lung damage long after the air clears.

Los Angeles saw weeks of unhealthy air quality as the Bobcat Fire burned.

When an area records an air quality index range of 151 to 200, “everyone may begin to experience some adverse health effects, and residents with higher sensitivity to air pollution may experience more serious effects,” South Coast Air Quality Management District officials said.

When the AQI reaches a range of 201 to 300, residents may experience more serious health effects.

People with heart or lung disease, older residents and children are at a greater risk from exposure to air pollution.

Symptoms from wildfire smoke include burning eyes, runny nose, scratchy throat, headaches and illness like bronchitis. Those with sensitive conditions can experience difficulty breathing, wheezing, coughing, fatigue and chest pain.