The U.S. Environmental Protection Agency has set a new ozone pollution standard in an effort to clean up the air and improve overall public health.

"Ozone pollution is still making people sick and we still have a lot of work to do," EPA Administrator Gina McCarthy said Thursday, according to Yahoo! News.

The previous 2008 standard is no longer strong enough to ensure public health, the EPA says. The new standard will help to lower pollutants in the air that are linked to asthma and other respiratory illnesses.

The previous ozone limit, 75 parts per billion, has been lowered to 70 parts per billion. Denver and 10 other American cities have already recently been cited for failing to meet the current standards, according to The Denver Post. As a result, they will need to work hard to meet the new standard.

"We've made progress. We'll probably continue to make progress. But it's going to be a challenge," Ken Lloyd, director of the Regional Air Quality Council, said of the EPA standards.

"Our job is to set science-based standards that protect the health of the American people. Today's action is one of the most important measures we can take for improving public health, reducing the costs of illness and protecting our children's health," McCarthy said, according to Environmental Protection Online.