HELENA, Mont. (AP) -- Katie Gray-Murphy spent the last weekend of her summer vacation shuttered in her house, the windows closed against a gray shroud of wildfire smoke.
"If there was no fires or smoke going on, I could go out and do whatever I wanted," said the 15-year-old, who has lived with asthma most of her life.
Most of the Northern Rockies are cloaked in a stinky, dingy cloud of wood smoke from wildfires that have burned millions of acres this summer. In Helena, the shroud is often so dense Katie must check the local air quality hot line before going for a walk.
"I read, watch TV or do chores," she said. "It gets really boring, just doing the same thing over and over."
For others, the smoke is more than boring -- it's a matter of life and death. Each new day is a danger to those with existing respiratory or cardiac problems.
"There are people on the ragged edge of dying anyway, and this kind of air could be the triggering cause," said John Coefield, a meteorologist with the state Department of Environmental Quality.
The fires have spawned a massive plume of smoke that extends the 500-mile breadth of Montana, east into the Dakotas and beyond. In Des Moines, the Iowa Department of Natural Resources warned people with respiratory problems to stay indoors Monday.
"The longer it lasts, the more people are going to be affected," said Shannon Therriault, air quality specialist for the Missoula City-County Health Department.
For Montana, the Big Sky is almost permanently gray over nearly all the state's 145,000 square miles. A blend of wind and temperatures can change the haze into air pungent with the smell of burning wood and laced with ash that leaves a dusting on cars parked overnight.
Some cities and towns in the Bitterroot Valley have had air considered so hazardous that everyone is urged to avoid any strenuous activities outdoors. The elderly, children and those with breathing or heart problems are told to stay home.
State officials said pharmacies are reporting runs on inhalers, used by asthmatics and others with respiratory problems. Some stores are selling two or three times what they normally do this time of year.
The data backs up the fear: While a typical summer day would measure a pollution level of 30 micrograms or less per cubic meter of air, Missoula has reached 500 micrograms during the worst smokestorms.
Darby, a small town near the heart of the Bitterroot's worst fires, has measured pollution at 750 micrograms -- 25 times more polluted than normal for August.
Lungs compensate for smoke by constricting, reducing air flow and causing blood pressure to rise -- putting an added strain on the heart, said Dr. Michael Spence.
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