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Determinants of In-Vehicle Exposure to Traffic-Induced Emissions

The past two decades have witnessed a growing concern about in-vehicle air quality with an emphasis on passenger cars, with greater levels of exposure to traffic-induced emissions recorded of all transport modes. In this study, in-vehicle exposure to carbon monoxide (CO) is examined under eight ventilation modes on a 2,333-m circuit in the Hamra–Bliss Area of Beirut, Lebanon, and the influence of ventilation mode, outdoor CO concentrations, and wind speed on in-vehicle exposure is assessed. The highest mean CO exposure was experienced for ventilation settings with the windows closed and vents closed and the windows closed and air conditioning on recirculation, with mean CO levels of 37.4 and 30.8 ppm, respectively, exceeding the 1-h air quality guidelines. In-vehicle CO levels revealed moderate to good correlation with out-of-vehicle CO levels for ventilation modes allowing outdoor air intake and no correlation with ambient CO levels and wind speed. A mass balance modeling with measured out-of-vehicle CO levels and a trip-specific movement record as boundary conditions ascertained a contribution to in-vehicle exposure of self-pollution, or the ingression of a vehicle's own engine fumes into the vehicle compartment.