The London low emission zone came into effect in 2008 covering almost all of Greater London - the largest such zone in the world. London currently has levels of air pollution among the worst in Europe and road transport related emissions account for around half of total emissions of PM10 and NOx in the capital. The Low Emission Zone targets emissions of these pollutants from older diesel-engined lorries, buses, coaches, vans, minibuses and other heavy vehicles that are derived from lorries and vans such as motor caravans and motorised horse boxes. There was a phased introduction of the scheme from 2008 through to 2012. Different vehicles were affected over time and increasingly tougher emissions standards applied.