To ask the Secretary of State for Transport, what comparative assessment he has made of exposure to particulate matter between commuting at (a) street level and (b) on the London Underground; and if he will make a statement.

My Department has not carried out such an assessment. Air quality in London, and on the London Underground is the responsibility of the Mayor of London. The Committee on the Health Effects of Air Pollution did publish a review of air quality on the London Underground last January, which was discussed with Transport for London.