It's isn't just the heat. It isn't just the humidity, either.
It's the air quality.
The heat wave that has the East Coast sweating is threatening not only the skin of those brave enough to leave the comfort of air-conditioning, but also anyone who breathes.
Today, from Virginia to New Hampshire, air quality is expected to be unhealthy, especially for those most sensitive to bad air.
With heat and sun comes ozone, an air pollutant whose potency has become better understood in recent years. Ozone, a main component of smog, forms when tailpipe and smokestack pollutions reacts to heat and sunlight. In the stratosphere, it protects us from harmful UV rays, but at the ground level it can scar lung tissue, trigger asthma attacks and, together with tiny particulate pollution, reach into the circulatory system and damage the heart.
"Ozone smog threatens the health of infants, children, seniors, and people who have asthma, emphysema, chronic bronchitis, and other lung diseases. For these people, breathing smog-polluted air can make them cough and wheeze, restrict their airways, worsen their diseases, force them to the hospital and even kill them," Bernadette Toomey, president and CEO of the American Lung Association said in March. "Even healthy young adults and people who exercise or work outdoors can suffer from high levels of ozone pollution."
The rate of hospitalizations on hot days is higher, as is the rate of death, partially because of air pollution.
On hot summer days, health officials recommend limiting outdoor activity, particularly strenuous activity like exercise, to the early morning hours. Ozone builds up over time, and unhealthy conditions can linger even after the sun has gone down. But short-term and cumulative exposure are a concern.
While the Environmental Protection Agency recently tightened the health standard governing allowable ozone in the air, health and environmental groups criticized it as too weak, based on the state of scientific understanding about ozone.
Here's a look at the latest air quality forecast for the United States:
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