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On Oct. 1, the Environmental Protection Agency revised the national standards for ground-level ozone, one of the primary components of photochemical smog.

This was a modest action but one that will help protect the health of many Americans.

Ground-level ozone is formed through chemical reactions involving nitrogen oxides and volatile organic compounds emitted from transportation, energy production and industrial activities.

In contrast to its role in the stratosphere, where ozone absorbs harmful ultraviolet radiation, ozone at the ground level can cause serious health effects, including respiratory irritation that can lead to coughing, wheezing, tightness of the chest and nasal congestion.

Ozone can aggravate existing health problems such as asthma, emphysema, pneumonia and bronchitis. Long-term exposure could injure the lungs, permanently reducing lung function, and lead to premature death.

While natural levels of ground-level ozone are generally in the range of 5-30 parts per billion, ozone levels have more than doubled since 1900, reaching several hundred ppb in many urban areas.

This is not the first time the ozone standard has been strengthened. To ensure that the standards continue to provide public health protection with an adequate margin of safety, the Clean Air Act requires the EPA to review air quality standards every five years and to revise the standards as scientific understanding shifts.

The original ozone standard of 120 ppb was reduced to 84 ppb in 1997, and the current standard of 75 ppb was set in 2008. It's the Clean Air Scientific Advisory Committee that provides advice on setting the standards.

In 2007, the committee recommended that the standard be reduced to between 60 ppb and 70 ppb based on research demonstrating observable adverse impacts at ozone levels as low as 72 ppb. But the Bush administration EPA chose to lower the standard only to the current level of 75 ppb, against the advice of the advisory committee.

For this current review, the committee again recommended a standard between 60 ppb and 70 ppb, but advised that 70 ppb might not provide an adequate margin of safety, as more recent scientific studies provided some evidence of adverse health effects at this level. But because the science is more uncertain about what occurs at lower levels of exposure, the EPA decided to set the standard at 70 ppb, the upper end of the recommended range.

As in the past, industry and utility groups have claimed that the cost of compliance will kill jobs and hurt the economy.

However, recent history has clearly demonstrated the economic benefits of improving air quality. Since 1970, air pollution has decreased by 70 percent, while the U.S. economy has tripled.

The EPA estimates that the public health benefits of the new ozone standard would be between $2.9 billion to $5.9 billion annually by 2025 compared with estimated annual costs of $1.4 billion, and it projects that by 2025, more than 90 percent of counties outside of California that currently do not meet the standard will have ozone levels below 70 ppb.

To put this into perspective, 90 percent of the 115 areas violating the 84 ppb standard in 1997 meet that standard today. In 2012, only 46 areas violated the 75 ppb standard, while over one third has met that standard today.

As before, industry and utilities will have time and flexibility to meet the new standard. Based on history, these groups should give themselves more credit for meeting the technological and economic challenges of reducing emissions that lead to improved air quality in order to protect the health of the citizens of this country.

Are EPA's new ozone rules reasonable and necessary? The science says they are. The law says they are. And history says everyone will benefit.

— Philip S. Stevens is the James H. Rudy Professor in the School of Public Environmental Affairs and the Department of Chemistry at Indiana University Bloomington.

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