Effects of cabin ventilation on in-vehicle exposure to PM and VOCs in passenger cars.

This study simultaneously measured in-cabin and ambient air quality in a passenger car under real-world driving conditions to evaluate the influence of different ventilation modes (recirculation, fresh air, and open windows) on the cabin concentrations of volatile organic compounds (VOCs) and particulate matter (PM). A single passenger car was tested in order to control for confounding factors related to vehicle design. Ventilation efficiencies were quantitatively assessed using air changes per hour (ACH), estimated using the carbon dioxide (CO2) mass balance method. Results showed that the recirculation mode effectively suppressed the infiltration of ambient fine particles (PM2.5), with I/O ratios ranging from 0.10 to 0.13. However, due to inadequate ventilation (ACH ≈3.2-3.5 h- 1), cabin CO2 concentration surpassed 4000 ppm. In contrast, the fresh air mode significantly increased ACH to 55-66 h-1, keeping CO2 concentrations below 1000 ppm. However, both fresh air and open-window modes led to a pronounced increase in cabin concentrations of PM and VOCs. Of the detected VOCs, acetone, ethanol, and formaldehyde had I/O ratios >1, suggesting in-cabin sources, whereas benzene, ethylbenzene, xylenes, and MTBE had I/O <1, indicating the presence of their dominant sources outside the vehicle cabin. These findings indicate a trade-off between reducing exposure to ambient pollutants and maintaining adequate ventilation, highlighting the need for optimized cabin ventilation strategies that balance ventilation, occupant comfort, and cabin air quality.Implications: When ventilation systems are inadequately designed or operated, vehicle cabins may become highly polluted microenvironments, exposing occupants to elevated levels of air pollutants due to the infiltration of roadside air contaminated by vehicle exhaust, emissions from in-cabin sources, and the confined nature of the cabin space. The observed trade-off between minimizing exposure to pollutants and ensuring sufficient ventilation highlights the need for optimized cabin ventilation strategies that balance air exchange, occupant comfort, and in-cabin air quality.