Air pollution is everything from the gases produced from burning fuels to the very fine particles that come from damage to brake pads, wear and tear on the roads, building sites and general dust.

Research shows gases like nitrogen dioxide and tiny particles, known as particulate matter or PM, can reach deep into the body with the danger of causing lasting damage.

The most obvious effects are on our breathing: increasing the risk of asthma attacks and inflammation of the lungs.

The BBC's Science Editor, David Shukman, explains how air pollution has also been linked to strokes, lung cancer, heart disease and possibly dementia.