In-vehicle exposure to NO2 and PM2.5: influences of environmental, vehicle and driving factors

In many developed cities, commuters spend more than 1.5-h inside vehicles daily, which may result in elevated exposures to traffic-related NO₂ and PM_2.5, which are known to have harmful health effects. In addition, time spend inside vehicles is likely to be greater for professional drivers, whereas the impacts of these exposures may be greater for vulnerable groups such as the elderly or obese. Therefore, reducing in-vehicle exposure and the associated risk for adverse health effects is very important.

This study measured in-vehicle NO₂ and PM_2.5 during repeated transects of the same route on city streets for 10 vehicles under real-world conditions, and as a function of ventilation settings and cabin filters. The results were used to assess personal exposure for driver/passengers, and to develop stepwise general additive models in order to identify important controllable factors that can reduce in-vehicle exposure.

The overall variability of in-vehicle exposure explained by these models was R² = 0.58 and 0.52, for NO₂ and PM_2.5 respectively. From the model’s explained variability, the most significant predictor for both pollutants was on-road NO₂ and PM_2.5 levels accounting for 25.4 and 35.6% respectively. Vehicle-based predictors included car type, odometer, use of activated carbon filter, air exchange rate and use of air conditioning/air recirculation ventilation settings that, in combination, explained 48.9% and 61.1%, of NO₂ and PM_2.5, variability, respectively. Driving-based predictors included road traffic conditions, presence of traffic lights roundabouts and high emitters, explained 25.7% and 3.3% of NO₂ and PM_2.5 in-vehicle concentration variability, respectively. By carefully regulating vehicle-based factors under driver or passenger control, such as ventilation and filtration options, vehicle occupants can significantly reduce their exposure to NO₂ and PM_2.5.