Secondhand tobacco smoke concentrations in motor vehicles: A pilot study

Context: Motor vehicles represent important micro-environments for exposure to secondhand smoke (SHS). While some countries and cities have banned smoking in cars with children present, more data are needed to develop the evidence base on SHS exposure levels in motor vehicles to inform policy and education practices aimed at supporting smoke-free motor vehicles when passengers are present. Objective: To assess exposure to secondhand tobacco smoke in motor vehicles using passive airborne nicotine samplers. Methods: 17 smokers and five non-smokers who commute to and from work in their own vehicle participated. Two passive airborne nicotine samplers were placed in each vehicle for a 24-hour period, one at the front passenger seat headrest and the other in the back seat behind the driver. At the end of the sampling period, airborne nicotine was analysed by gas chromatography. Results: Median (IQR) air nicotine concentrations in smokers' vehicles were 9.6 mg/m³ (5.3-25.5) compared to non-detectable concentrations in non-smokers' vehicles. After adjustment for vehicle size, window opening, air conditioning and sampling time, there was a 1.96-fold increase (95% CI 1.43 to 2.67) in air nicotine concentrations per cigarette smoked. Conclusions: Air nicotine concentrations in motor vehicles were much higher than air nicotine concentrations generally measured in public or private indoor places, and even higher than concentrations measured in restaurants and bars. These high levels of exposure to SHS support the need for education measures and legislation that regulate smoking in motor vehicles when passengers, especially children, are present.