from the paper you cited: "Nevertheless, we should mention that the inhalation dose of commuters could be different from the exposure levels. Dons et al. (2012

from the paper you cited: "Nevertheless, we should mention that the inhalation dose of commuters could be different from the exposure levels. Dons et al. (2012) found that exposure to BC during travel in motorised transport was clearly higher than exposure while walking or biking (6.3 μg/m3 versus 3.4 μg/m3), but when accounting for inhaled doses, this relationship was reversed. Cyclists seem to receive the highest inhaled PM2.5 dose followed by bus and car passengers (McNabola et al., 2008). However, in the present study we do not examine the inhaled dose of pollutants during commuting due to the lack of studies determining it and also its complexity of interacting factors such as breathing rate, ventilation and/or particle deposition to the respiratory system." Also, in the study, they said they drove with air-recirculation off, which I believe would mean the outside air does not get filtered. And outside air seems to be a major source of inhaled pollution, since electric vehicles have even higher measured pollution levels than gasoline.