Figure 5: Shows concentrations in the car cabin (red) and how it varies compared to tunnel concentrations (blue) while travelling through a 6 km road tunnel. The concentration ratio between the car cabin and the tunnel approaches a constant value equal to the proportion passing the filter, in this case 50% was employed. Air exchange rate or turnover time in the car cabin was set to 30 minutes in the left figure and 3 minutes in the right figure.