CHEYENNE, Wyo. (AP) — A study conducted by anti-smoking groups found that air quality improved in Casper businesses that ceased to allow smoking when a city-wide smoking ban took effect.

Air quality as gauged by the U.S. Environmental Protection Agency improved from "very healthy" to "good."

The Associated Press reports the study was conducted by SmokeFree Natrona County along with the American Cancer Society Cancer Action Network.

The organizations monitored air quality in October 2010 at four bars and restaurants that allowed smoking. The groups re-sampled the air in the same businesses in March, six months after Casper's smoking ban took effect in September.

Jason Mincer with the cancer network says the findings are significant because even small levels of second-hand smoke can trigger asthma or even heart attacks.