The American Lung Association’s annual State of the Air Report suggests that approximately 60 percent of Americans reside in areas with air pollution levels being so unhealthy that they can result in sickness.

Pittsburgh topped the association’s list of 25 worst cities for particulate matter pollution – the three-year analysis, from 2005 to 2007, being based on the data gathered from almost 900 monitoring sites across the country.

In order to gauge the air quality of different cities, the researchers depended largely on three main criteria - long-term particle pollution, short-term particle pollution and ozone concentration. It was observed that all of the three forms of pollution have negative health effects.

The findings of the report indicate that "air pollution remains widespread and dangerous," and almost every big city is burdened either by pollution from ozone or particle pollution, which is a blend of minute specks of dust, soot, ash, and aerosols in the air.

While Pittsburgh and Bakersfield, California, reported the maximum amount of particle pollution; Los Angeles topped the ozone rankings, indicating that it could likely the smoggiest place in the country.

The surprise element of the findings is that some cities that were earlier considered pristine now have dirty air, thereby giving a blow to the supposedly-escalating "green" movement in the US!