Thick clouds of smoke from wildfires in the United States have exposed millions of people to harmful levels of pollution. The smoke is causing emergency room visits to jump and may have led to the death of thousands of older and sick people. That information comes from a study of pollution records by The Associated Press, or AP news agency.

The AP also spoke with doctors, health officials and researchers about conditions on the U.S. West Coast.

For at least one day, smoke from the wildfires topped concentration levels that the government says increase health risks. In recent weeks, the smoke has covered areas where more than 8 million people live, the news agency said.

The state of Oregon has been hit especially hard by the wildfires. Last month, Oregon's major cities suffered the highest pollution they have ever recorded. Powerful winds worsened fires that had been burning in remote areas and sent them toward the city of Portland.

Medical problems began while communities were still covered in smoke. It led to hundreds of additional hospital emergency room visits each day in Oregon, state health officials say.

Barb Trout is a 64-year-old retiree who lives south of Portland, in the Willamette Valley. The experience has been hard on her, she says. She was taken to the emergency room, or ER, two times after suffering severe asthmatic reactions. It is something that had never happened to her before.

Trout had sheltered inside her home as soon as smoke rolled into the Willamette Valley early last month. But within days, she had an asthma attack that left her struggling for air and landed her in the ER. Two weeks later, smoke from fires in California moved into the valley. That is when she had what she thinks was a near-death experience.

"It hit me quick and hard – more so than the first one. I wasn't hardly even breathing," Trout told The AP. After getting treatment, she was sent home. But the chance of a third attack worries her, so she and her husband put in a warning system. With it, she can press a button to call for help.

Martin Johnson is Trout's doctor and a heart specialist. He lives in nearby Salem, Oregon. Johnson says people with existing breathing conditions started showing up at his hospital or calling his office right after the smoke arrived. Many were struggling to breathe. The Salem area had eight days of pollution at dangerous levels during a short period. These are some of the worst conditions the West has seen over the past 20 years, the AP study found.

Most of Johnson's patients are expected to recover, but some could have permanent loss of lung function, he said. Then there are the "hidden" victims. These are people who Johnson suspects died from heart attacks or other problems resulting from the poor air quality. But their causes of death are being listed as something else.

Stanford University researchers say up to 3,000 people in California, all over the age of 65, died earlier than expected after exposure to smoke for six weeks last summer. Their findings are based on earlier studies of pollution-related deaths and the number of people exposed to recent wildfires.

Hundreds more deaths could have happened in Washington state over weeks of bad air from the fires, say University of Washington researchers.

The findings for both states have not been reported in scientific publications. No such estimate was available for Oregon.

A California heat wave last week led to warnings of extreme fire danger. And electric companies turned off some power lines for safety reasons.

Wildfires happen each year in Western states. But over the years, they have gotten more intense and dangerous as a changing climate dries out forests and other plant life. Particles that are too small to see make the smoke a health risk. They can be breathed in and cause breathing problems.

On any day, western fires can make 10 times more particles than other sources including vehicles and factories, notes Shawn Urbanski. He is a smoke scientist with the U.S. Forest Service.

Fires across the West released more than a million tons of the particles in 2012, 2015 and 2017, and almost as much in 2018. That year, a wildfire in Paradise, California killed 85 people and burned 14,000 houses. It created thick smoke that covered parts of Northern California for weeks.

This year, a combination of weather events made the smoke especially bad.

Smoke particles enter the lungs, get down deep, and irritate the lining, said University of Montana professor Erin Landguth. They may also get into your blood, she said. "We're seeing the effects."

The coronavirus health crisis raises another set of worries: Research is linking higher air pollution with higher rates of infection and more severe symptoms, notes Gabriela Goldfarb of the Oregon Health Authority.

Climate experts say people on the West Coast and in the northern Rocky Mountains can expect more major smoke events in the future.

I'm Alice Bryant.

The Associated Press reported this story. Alice Bryant adapted it for VOA Learning English. George Grow was the editor.

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expose - v. to leave (something) without covering or protection

concentration - n. the amount of a component in a given area or volume

remote - adj. far away

asthmatic - adj. relating to asthma, a lung disorder that causes periods of wheezing, coughing, and difficulty with breathing

button - n. a small part of a machine that you push to make the machine work

function - n. the special purpose or activity for which a thing exists or is used

source - n. the cause of something; someone or something that provides what is wanted or needed

ton - n. a measure of weight equal either to 2000 pounds (about 907 kilograms) (short ton) or 2240 pounds (about 1016 kilograms; long ton ) with the short ton being more frequently used in the United States and Canada

irritate - v. to make (someone) impatient, angry, or annoyed

symptom - n. a change in the body or mind which indicates that a disease is present