Air pollution: what are the effects on humans?
Air pollution is everything from the gases produced from burning of fuels to the very fine particles that come from damage to brake pads, wear and tear on the roads, building sites and general dust.
It's mostly invisible to the naked eye.
Research shows gases like nitrogen dioxide and tiny particles, known as particulate matter or PM, can get into our lungs, our blood and even our brains.
Here the BBC's Science Editor, David Shukman explains how air pollution has also been linked to strokes, lung cancer, heart disease and possible dementia.