Each year, the American Lung Association ranks the air quality of the country's largest metro areas. And this year's State of the Air report has good news for Monroe County.

The Lung Association gave the county high marks on its air quality. The county received an A grade for ground level ozone, and a B for short-term particle pollution. The report, which is based on averages from 2009 to 2011, says the county had no days with high ozone levels and a less than one day when short-term particle pollution was a problem.

The numbers in this year's report are a far cry from just four years ago, when Monroe County received an F on ozone pollution and a C on short-term particle pollution. Both of the pollutants are the result of burning fossil fuels, particularly coal and diesel gasoline. And they can pose risks to people with respiratory or cardiovascular problems.

The Lung Association says that, nationally, particle pollution is down because of cleaner diesel formulas and advances in engine technology. It's likely that local residents also benefit from Rochester Gas and Electric's decision to shut down the coal-fired Russell Station power plant in 2008.

Michael Seilback, vice president of public policy and communications for the Lung Association's Northeast office, says the same factors would contribute to a decrease in ozone. He says actions that decrease one air pollutant often decrease others, too.

But the association says that the federal government still needs to enact tougher ozone pollution standards, particularly limiting sulfur dioxide and nitrogen oxide emissions.

Ozone is generated when certain emissions react with each other, which generally happens on hot days. And since 2012 was very hot, I don't think the low average will hold.

A table published by the state Department of Environmental Conservation says that Rochester exceeded federal ozone standards twice this past summer, though it came close on several other days. When it did exceed the standards, however, it never exceeded what the Lung Association considers "unhealthy for sensitive populations." Sensitive populations include children, the elderly, people with asthma, and people with cardiovascular disease.

Seilback says that if climate change results in longer or hotter summers, elevated ozone levels could be present during more days per year.