A study out today suggests the air quality on the Toronto subway system is as bad as the air quality in smog-prone Beijing on an average day.

The study published in the Journal of Environment Science and Technology found concentrations of fine particulate matter in the Toronto system was about ten times higher than what a person would experience out on the street.

University of Toronto engineering professor and study co-author Greg Evans says the levels could be a concern for people with pre-existing medical conditions.

But Evans the replacement of subway cars on the Yonge-University Line may have already improved the air quality in the system.

He says another option is to clean out the subway tunnels at night and the Toronto Transit Commission is exploring that.