Smoky bars and casinos have up to 50 times more cancer-causing particles in the air than highways and city streets clogged with diesel trucks at rush hour, according to a study that also shows indoor air pollution virtually disappears once smoking is banned.

Conducted by the researcher who first showed secondhand smoke causes thousands of U.S. lung cancer deaths each year, the study found casino and bar workers are exposed to particulate pollution at far greater levels than the government allows outdoors.

"This paper will help localities pass smoking bans," predicted the author, James Repace, a biophysicist who works as a secondhand-smoke consultant after spending 30 years as a federal researcher. "It shows how beneficial smoking bans are for hospitality workers and patrons."

Repace tested air in a casino, a pool hall and six taverns in Delaware in November 2002 and in January 2003, two months after the state imposed a strict indoor smoking ban.

His detectors measured two substances blamed for tobacco-related cancers: a group of chemicals called particulate polycyclic aromatic hydrocarbons, or PPAHs, and respirable particles - airborne soot small enough to penetrate the lungs.

"They are the most dangerous" substances in secondhand smoke, said Repace, a visiting assistant clinical professor at Tufts University School of Medicine in Boston.

Repace said his research also showed that ventilation systems - sometimes touted by tavern, restaurant and casino groups as an alternative to smoking bans - cannot exchange air fast enough to keep up with the smoke.

The study, published in the September issue of the Journal of Occupational and Environmental Medicine, was partly funded by the nation's largest philanthropic organization devoted to health care, the Robert Wood Johnson Foundation of Plainsboro, N.J.