Outside Susan Holmes' house in southeastern Oklahoma, visitors are welcomed by an entryway lined with oxygen bottles and a machine that collects and concentrates oxygen from the air.
"I take two inhalers twice a day," Holmes says. "And I have a nebulizer that I use four times a day, and I use oxygen at night."
She says her asthma returned when she moved to Bokoshe, a decaying town of about 500 people that is flanked by old coal mines. The huge pits have now been filled with hundreds of thousands of tons of coal ash.