Characterizing in-cabin air quality and vehicular air filtering performance for passenger cars in China

The rapidly growing vehicle population has become a crucial contributor to severe air-pollution and public health issues. In urban areas, vehicles have become one of the important sources of air pollutants such as nitrogen oxides and fine particulate matter (PM2.5). In particular, the on-road concentrations of traffic-related air pollutants (TRAPs) are typically many times higher than normal ambient concentrations, potentially leading to high in-vehicle exposure levels to TRAPs. Limited studies have focused on the variability in in-vehicle concentrations of TRAPs and linked the pollution level to both out-cabin conditions and the in-cabin filtration performance during real-world travels. Therefore, this study measured on-roadway, in-cabin concentrations of PM2.5 and carbon dioxide (CO2) by using well-calibrated low-cost sensors during various conditions. Our results indicate that, although in-cabin PM2.5 concentrations are correlated to out-cabin PM2.5 concentration levels, the control efficiency would be affected by the ventilation mode and the adoption of vehicular filtration device. The PM2.5 reduction efficiencies could achieve 45% and 77% for in-use and new filters made by vehicle manufacturers respectively, with the average CO2 concentration remained at a safe level (<800 ppm) under the in-vehicle outside air ventilation. The application of a high-efficiency cabin air (HECA) filter can further enhance the PM2.5 filtration efficiency up to 85–96%, indicating the significance of advanced cabin air filtration technology for improving in-cabin air quality and reducing health risk of Chinese drivers.