Introduction Despite progress in adoption of smoke-free policies, smoking in casinos is allowed in some US states, including Nevada. In 2020, for the first time, a resort-style casino in Las Vegas prohibited smoking voluntarily. This study is the first to assess air quality in this casino and compare results with similar casinos that allow smoking.

Methods A real-time personal aerosol monitor evaluated particulate matter with a diameter <2.5 µm (PM2.5), a surrogate for secondhand smoke (SHS). PM2.5 was measured at eight Las Vegas casinos, including the smoke-free casino. Each casino was visited twice, and PM2.5 was assessed in smoking-permitted gaming areas and areas where smoking is otherwise prohibited.

Results Average PM2.5 levels were significantly higher in casinos that allow smoking, for both casino gaming areas and areas where smoking is otherwise prohibited (p<0.05). Mean PM2.5 in gaming areas was 164.9 µg/m³ in casinos that allow smoking and 30.5 µg/m³ in the smoke-free casino. Mean PM2.5 in areas where smoking is otherwise prohibited was 83.2 µg/m³ in casinos which allowed smoking in gaming areas, and 48.1 µg/m³ in the smoke-free casino.

Conclusion Despite robust evidence about the harms of SHS, tens of thousands of casino employees and tens of millions of tourists are exposed to high levels of SHS in Las Vegas casinos annually, with PM2.5 levels 5.4 times higher in gaming areas when compared with a smoke-free casino. The only way to protect people from SHS exposure is to prohibit smoking in all indoor areas.