A University of Colorado-Boulder study suggests U.S. air quality regulations may not effectively target a large source of fine, organic particle pollutants.

Researchers said they've determined a much smaller percentage of pollutants from vehicles and industrial processes is to blame for the organic haze seen over many larger cities. Instead, 75 percent of the fine, organic particulate pollutants form from reactive gases called VOCs -- or volatile organic compounds -- when they are oxidized and condense onto existing particles in the air.

"Air quality regulations today effectively target most sources of 'primary,' or directly emitted particles," said Ken Docherty, the study's lead author. "Yet our study indicates that the 'secondary,' or chemically formed particles, contribute more significantly to poor air quality, even in very polluted urban regions.

"Our study suggests that regulations need to focus much more attention on the gases -- such as gasoline vapors -- that form secondary organic particles and create visible haze," he said, noting other examples of VOCs include vapors from paints, varnishes, cleaning supplies, automotive products and dry-cleaned clothing.

The study is to be published in the journal Environmental Science and Technology and is now available online at the journal's Web site.