A new study looking at the effects of climate change predicts an extra week of dangerous ozone levels every year across the U.S. by the year 2050.
That's even though levels of the dangerous compound drop off on the hottest days, the team at Harvard University and the National Center for Atmospheric Research found.
California, already the state with the most air pollution; the Southwest, and the Northeast could all get up to nine extra days a year when ozone levels pass safe levels, their calculations predicted.
"In the coming decades, global climate change will likely cause more heat waves during the summer, which in turn could cause a 70 to 100 percent increase in ozone episodes, depending on the region," Lu Shen, a graduate student at Harvard's School of Engineering and Applied Sciences, who led the study, said in a statement.
Shen's team looked at what would happen across the country as temperatures rise.
"We find an average increase of 2.3 days … in ozone episodes across the United States by the 2050s," they wrote in their report, published in Geophysical Research Letters.
That's even taking into account a phenomenon called ozone suppression — when ozone levels stop rising at the highest temperatures.
"Ozone production accelerates at high temperatures, and emissions of the natural components of ozone increase. High temperatures are also accompanied by weak winds, causing the atmosphere to stagnate. So the air just cooks and ozone levels can build up," said Harvard's Loretta Mickley, who also worked on the study.
Ozone is invisible, but it often goes along with smog.
Ozone high in the atmosphere helps shield the planet from radiation. That's why scientists worry about the ozone layer.
At ground level, it's not so good. Ozone is a gas molecule made up of three oxygen atoms. Most oxygen — called O2 — has two molecules. That third molecule makes ozone unstable and it can cause harmful chemical reactions in the body.
According to the American Lung Association, they include:
- shortness of breath, wheezing and coughing
- asthma attacks
- increased risk of respiratory infections
High levels of ozone may also cause heart effects such as irregular heartbeats. When ozone levels soar, so do visits to emergency rooms and so do deaths.
That's why the Environmental Protection Agency wants to limit ozone levels.
"Our results point to the need for ambitious emission controls to offset this penalty, especially in the Northeast and Southwest," the team wrote.