A new study from the Wisconsin Department of Health Services and the University of Wisconsin Carbone Comprehensive Cancer Center reports a marked improvement in air quality in bars and restaurants as a result of Wisconsin’s smoke-free air law.

The study looked at air quality data recorded in more than 200 businesses before and after the July 5 implementation of the smoke-free law. Smoking was allowed in the businesses before July 5.

Before the law took effect, air quality in 21 percent of the tested businesses was classified as “hazardous,” the highest level, according to Wisconsin Department of Natural Resources’ standards.

Some 28 percent of the businesses had air classified as “very unhealthy,” with 38 percent classified as having “unhealthy” air. Only 13 percent of the surveyed businesses had “good” or “satisfactory” air quality.

Those numbers improved sharply following the enactment of the smoke-free law. Post-July 5 testing found that 97 percent of the bars and restaurants had “good” or “satisfactory” air. The study also saw small-particle levels from cigarette smoke drop from 160 to 13 micrograms.

“This study clearly demonstrates the public health impact of smoke-free laws” said Sandy Bernier, Five Counties for Tobacco-Free Living program coordinator, in a news release. “Wisconsin’s workplaces are safer, and employees and customers are reaping the benefits by being able to breathe healthier air.”

Study data was collected around the state by public health agencies.

Air quality testing equipment was used to collect air samples in the same businesses in the pre- and post-testing.

The majority of testing was done on weekends when the businesses were most likely to be busy and more employees and customers could potentially be exposed to secondhand smoke.