This work presents results of particle mass, number and size measurements inside passenger cars (PCs),
vans and urban buses. Effects of the in-cabin air purifier on particle concentrations and average size
inside a vehicle are studied. Use of the air purifier leads to a dramatic reduction, by 95e99%, in the
measured ultrafine particles number concentration inside a vehicle compared with outside readings.
Extremely low particle concentrations may be reached without a danger of vehicle occupants’ exposure
to elevated CO2 levels. The lowest values of particle concentrations inside a PC without air purifier are
registered under the recirculation ventilation mode, but the issue of CO2 accumulation limits the use of
this mode to very short driving events. Lower PM concentrations are found inside newer cars, if this
ventilation mode is used. Great differences by a factor of 2.5e3 in PM10 concentrations are found
between the PCs and the buses. Smoking inside a car leads to a dramatic increase, by approximately 90
times, in PM2.5 concentrations.