Passenger Vehicle Ventilation and Secondhand Smoke Particulate Measurements

One in four Minnesota middle school students report that they have ridden in a car with someone who was smoking cigarettes in the preceding week (Minnesota Youth Tobacco and Asthma Survey, 2011), yet only eight US states have policies prohibiting smoking with youth in vehicles (www.no-smoke.org). This study expands on previous research by measuring ventilation rates and secondhand smoke particulate concentrations under a variety of conditions that affect passenger exposure. A total of 170 trials were conducted, including duplicate trials to determine reliability. The monitoring included continuous photometer measurements of fine particles (PM_2.5) before, during, and after a participant drove and smoked a cigarette. The instruments were installed in 3 to 5 locations inside the vehicle and 1 outside to measure and compensate for ambient air particulates. Carbon dioxide injection and decay were used to compute the ventilation rate and the PM_2.5decay rate was analyzed to determine the total removal rates that included ventilation and absorption. The monitoring was conducted for 3 vehicle types (sedan, mini-van, SUV), 2 driving speeds, 4 window positions, and multiple ventilation operating conditions over both summer and winter conditions. With windows closed and the vent fan on, the average PM_2.5 concentration during smoking ranged from 138 to 2,694 with an average of 1,020 ug/m³. After smoking stopped, it took from 4 to 25 minutes for the particulate level to decrease to the background level. When the activate smoking and post-smoking periods were combined, the passenger’s total PM_2.5 exposure averaged 165 ug/m³ * hr. The average exposure was 61% higher for city driving (30mph) than highway driving (60mph). The exposure in the rear seats compared to the front varied with window position. Overall, for about half of the trials, the SHS concentration was greater in the rear seats than in the front passenger seat. Opening windows greatly increased ventilation and reduced exposure levels. Opening windows just 2 inches reduced exposure by almost an order of magnitude and fully opening at least one window reduced exposure by a factor of 34.