Page "Cycling" Paragraph 88

One concern often expressed ( both by non-cyclists and some cyclists ) is the thought that riding in traffic exposes the cyclist to higher levels of air pollution, especially if he or she travels on or along busy roads.

Some authors have claimed this to be untrue, showing that the pollutant and irritant count within cars is consistently higher, ( presumably because of limited circulation of air within the car and due to the air intake being directly in the stream of other traffic ).

Other authors have found small or inconsistent differences in concentrations but claim that exposure of cyclists is higher due to increased minute ventilation and is associated with minor biological changes .< ref > The significance of the associated health effect, if any, is unclear but probably much smaller than the health impacts associated with accidents and the health benefits derived from additional physical activity.