People commuting by public transport faced up to eight times more pollution than car users, according to new research.
Even though motorists produced the most pollution per commuter, they were least exposed to harmful particulate matter (PM) as they were sealed off from the outside, the study found.
According to the researchers at the University of Surrey, the findings pointed to an "environmental injustice" at play, with those who created the most pollution having the least exposure to it.
The researchers compared how commuters who used cars, buses and the underground in different areas of London suffered exposure to a range of pollutants.
According to the study published in the journal Environment International, commuters on some underground lines were the most exposed to poor air quality, followed by those on buses.
Monitors worn by commuters revealed that on the tube were commuters were exposed to 68 micrograms of PM10, tiny particles of soot that are breathed into the lungs, as against eight micrograms of exposure experienced by motorists.
The researchers found that on newer trains that did not have opening windows, PM exposure was much lower than on tube trains with opening windows.
Bus users were exposed to higher levels of black carbon and particles than car users, the study found.
Air pollution is known to cause 40,000 UK premature deaths a year and two thirds of UK citizens suffering with asthma said poor air quality made their condition worse.
As bus trips were typically longer than car journeys they led to greater exposure, the University of Surrey study found.
London mayor Sadiq Khan, who plans a £10 daily ''toxicity charge'' on pre-2005 diesel cars, had called for a national scrappage scheme to encourage diesel drivers to buy vehicles with less deadly emissions.