Tunnels serve as enclosed particle loaded environments where mostly stagnant and stable abiotic conditions prevail throughout the year. In-vehicle exposure to ultra-fine particles (UFP) is therefore significant while driving through long tunnels. The objective of this study was to assess exposure to UFP while driving a car through a 3.4 km long highway tunnel system in Austria and to calculate the associated lung deposition. On board a mobile Scanning Mobility Particle Sizer (SMPS, Grimm model 5403) was used to monitor the particle number concentration in the size range of 5.5 nm to 350 nm. The influence of various air ventilation settings inside the passenger cabin of the car was investigated in terms of UFP concentrations. These ventilation settings and hence the associated particle concentrations inside the cabin were used in the lung deposition model IDEAL to determine their fate in the lung. To examine a real life situation, this heavily frequented highway tunnel system was chosen to serve as a particle laden environment. The data were obtained over several days throughout the year to analyze the effect of traffic mix on the resulting particle regime.
Our study revealed a decrease of in-cabin air pollution by up to 88% while using recirculating air (RA) settings in combination with the air-conditioning system. This mode of operation in comparison to plain tunnel air (TA) reduced the corresponding lung deposition by up to 95%. Our observations thus suggest making use of recirculating air setting while driving through poorly ventilated areas such as tunnels. Doing so considerably reduces the resultant particle deposition in the lung.