Assessing the effect of Michigan's smoke-free law on air quality inside restaurants and casinos: a before-and-after observational study

OBJECTIVES To assess the effect of Michigan's smoke-free air (SFA) law on the air quality inside selected restaurants and casinos. The hypothesis of the study: if the SFA law is effectively implemented in restaurants and casinos, there will be a significant reduction in the particulate matter PM2.5 measured in the same establishments after the law is implemented. SETTING Prelaw and postlaw design study. PARTICIPANTS 78 restaurants in 14 Michigan cities from six major regions of the state, and three Detroit casinos. METHODS We monitored the real-time PM2.5 in 78 restaurants and three Detroit casinos before the SFA law, and again monitored the same restaurants and casinos after implementation of the law, which was enacted on 1 May 2010. PRIMARY AND SECONDARY OUTCOME MEASURES Concentration measurements of secondhand smoke (SHS) fine particles (PM2.5) were compared in each restaurant in the prelaw period to measurements of PM2.5 in the same restaurants during the postlaw period. A second comparison was made for PM2.5 levels in three Detroit casinos prelaw and postlaw; these casinos were exempted from the SFA law. RESULTS Prelaw data indicated that 85% of the restaurants had poor to hazardous air quality, with the average venue having 'unhealthy' air according to Michigan's Air Quality Index for PM2.5. Postlaw, air quality in 93% of the restaurants improved to 'good'. The differences were statistically significant (p<0.0001). By comparison, the three casinos measured had 'unhealthy' air both before and after the law. CONCLUSIONS The significant air quality improvement in the Michigan restaurants after implementation of the SFA law indicates that the law was very effective in reducing exposure to SHS. Since the Detroit casinos were exempted from the law, the air quality was unchanged, and remained unhealthy in both prelaw and postlaw periods.