It's been the hottest summer on record in many cities on the East Coast. And with that blistering weather has come a lot of days of unhealthy air.
On Wednesday, at least 75 areas from San Francisco to Portland, Maine, are warning their residents about high air pollution.
In the Washington, D.C., metropolitan area, local officials sent out more air pollution warnings this year than they had since 2002 -- three Code Red, 26 Code Orange and more predicted on the way.
Children Are Vulnerable
All those bad air days mean that at day care centers, like Little Flower Montessori School in Washington, D.C., children are spending a lot of time cooped up inside.
Eliana Noguchi says the children normally would go to the playground several times a day for 40 minutes each time. But with Code Red air quality, they get one short recess -- 15 minutes in a sprinkler.
"Ready, go! Who is going to be the brave one?" she squeals, urging the children into the spray of water.
As tiny feet slap the pavement in a happy sprinkler dance, Noguchi says some toddlers are missing. They have asthma and their parents picked them up early to avoid even this brief time outside.
The American Lung Association's chief medical officer, Dr. Norman Edelman, says children are especially vulnerable to bad air days, particularly if they have asthma.
"Kids are always running around so they breathe a lot more for their size than adults do. So they take in a lot more of this bad stuff," he says.
Ozone and fine particles are the two types of pollution that trigger Code Red and Orange days. Both are formed out of exhaust from power plants, cars and a lot of other things.
With ozone "the two bad chemical actors are oxides of nitrogen and hydrocarbons," Edelman says. "When they're exposed to heat and sunlight, a chemical reaction takes place which releases ozone."
And when people breathe it in, it irritates their lungs, which are as fragile as the inside of eyelids.
"So if you look down the airways of somebody exposed to excessive ozone, it would look like a bad sunburn of the airways," he says.
That can cause inflammation, and since children's airways are a lot smaller than adults, it doesn't take much swelling to cause an asthma attack or worse.
High levels of fine particles also trigger bad air days in summertime, especially in the East. Coal-fired power plants are the main culprit, and on the hottest days, they're working at full tilt to keep air conditioners running.
The elderly and people with lung and heart problems are at high risk. Studies show that air pollution kills tens of thousands of them every year.
Even The Healthy Should Be Careful
But Edelman says even if you're healthy, you shouldn't ignore bad air days. It's probably best to do outdoor exercise in the morning before the sun and exhaust have turned the air into an unhealthy soup.
Clearly a lot of people ignore this advice, like two teams of federal workers who were slugging it out on a softball field on the National Mall on a steamy Code Red day.
"It's not that bad out here," says Army Corps of Engineers shortstop Matt Unger.
He says other games were canceled, but his players are used to the heat after serving in Iraq and Afghanistan.
Turns out their opponents -- self-described bureaucrats from the Government Accountability Office -- are pretty tough too.
Still panting from her run around the bases, Kim Gianopoulos says she doesn't pay attention to air pollution alerts.
"You don't get too much opportunity these days to get out and have fun with your co-workers and do this kind of thing, so you've got to take advantage of it," Gianopoulos says.
Edelman says if you do exert yourself on a bad air day, don't ignore symptoms like burning lungs or irritated eyes.