A study of the air quality of Toronto’s subway system, conduced by the Toronto Public Health, has found levels of air pollutants on the subway are higher than those in outdoor air and contain “high levels of some metals.”

CBC News »

“Air quality data collected in the Toronto subway system shows that, as is the case for other similar subway systems, levels of fine particulate matter air pollution (PM2.5) are elevated,” De Villa wrote.

PM2.5, or particles less than 2.5 microns in diameter, are associated with cardiovascular and respiratory health issues.