One of the great environmental success stories of the 20th Century can be seen out of any window in Pittsburgh -- the dramatic improvement in air quality that helped transform the "Smoky City" into the "Most Livable City in America."

Although there is no question that air quality here is much better than it was 60 years ago, how does our air quality today compare to other regions?

The American Lung Association claims that the Pittsburgh Region's air quality is the second worst in the country. However, their methodology is misleading, because it is based on the unusually high PM2.5 readings at the air pollution monitors in Liberty Borough and Clairton. (PM2.5 consists of soot particles less than 2.5 microns in size, which can cause heart and lung damage.)

The U.S. Environmental Protection Agency recognized that these monitors were not representative of the air quality in the rest of our region, so it designated that portion of the Mon Valley as a separate non-attainment area for PM2.5 pollution.

Much better measures of air quality have been developed by the Pittsburgh Regional Indicators Project (www.PittsburghToday.org). They average the readings from all of the pollution monitors in the region to determine the air quality that the majority of regional residents are breathing.

These new indicators show that not only are the average PM2.5 levels in the Pittsburgh Region high, they were the fifth worst among the top 40 regions in the country in 2006. (They were the fourth worst in both 2005 and 2004.) Only Atlanta, Charlotte, Los Angeles, and Riverside, Calif., had worse average PM2.5 levels than Pittsburgh in 2006.

In other words, most of us in the Pittsburgh Region are being affected by high levels of PM2.5, and our air quality is worse than in most other large regions. That's a health problem and a competitiveness problem that we need to address.

A second major type of air pollution is ground-level ozone, often called smog, which is a lung irritant and also affects agriculture. The Pittsburgh Region compares more favorably to other regions on ozone. We ranked 23rd out of the top 40 regions (with No. 1 being the worst air quality) on average ozone levels in 2006.

EPA had planned to redesignate southwestern Pennsylvania as an attainment area for ozone because of improved ozone levels over the past several years, but unfortunately, high levels of ozone that occurred during August likely will cause us to remain in nonattainment status. (EPA is also planning to tighten the ozone standard, which would return the region to nonattainment status anyway.)

Pollution problems aren't limited to the 10-county southwestern Pennsylvania region, though. PM2.5 levels across the border in West Virginia and Ohio are equally bad, and ozone levels there are slightly worse.

What's causing high levels of particulate and ozone pollution across the entire tri-state region? Power plants, industries, automobiles and even wood stoves are contributors.

However, unlike the smoke that polluted our air in the past, the sources of ozone and PM2.5 can be located many miles away. Studies conducted in the mid 1990s showed that a significant portion of the ozone here was being caused by pollution sources in upwind states. More recently, research done at Carnegie Mellon University found that as much as 80 percent of the PM2.5 pollution in our region was coming from pollution sources in upwind states.

This means that although we need to reduce emissions here, we can't make our air clean enough all by ourselves. And if we try to tighten pollution controls here unilaterally, we'll just make ourselves economically uncompetitive as well as environmentally uncompetitive.

A multi-state solution is needed. EPA's Clean Air Interstate Rule, adopted in 2005, is designed to reduce emissions in 28 states in the eastern United States, and is projected to bring southwestern Pennsylvania into attainment for both PM2.5 and ozone by 2010.

Once it's fully implemented, we'll all breathe easier.

For more insight on the region, visit www.PittsburghFuture.com and www.PittsburghToday.org.