Secondhand tobacco smoke (SHS) in enclosed spaces is a major source of potentially harmful airborne particles. To quantify exposure to PM2.5 because of SHS and to investigate the interaction between pollutants from SHS and vehicular emissions, number concentration of PM2.5 were measured inside a moving vehicle under different ventilation conditions. Air purification was found to have a significant effect on PM2.5 in the cabins of vehicles. Purification can achieve higher and more consistent results in terms of protecting drivers from SHS while commuting on the roads. Moreover, air purifiers are economically and technically easier to implement than other chemical technologies currently in use. Because the study with the air purifier was conducted in only one vehicle, more vehicles should be tested with and without air purifiers to achieve a statistically robust conclusion regarding their performance.