Martin Williams is currently a Professor of air quality at King’s College, London, UK. He was until 2014 Chairman of the Executive Body of the UNECE Convention on Long Range Transboundary Air Pollution (CLRTAP) and formerly chair of the CLRTAP EMEP Steering Body. He has authored papers on urban air quality, vehicle emissions and the links between air quality and climate change including the role of lead author of the policy section of the UNEP Assessment of Short Lived Climate Forcers. Prior to this, he was Head of the Air Quality programme in Defra, the UK Environment Ministry, where he had responsibility for air quality policy, industrial pollution control and research. At King’s College, his research interests lie in the application of science to policy in air quality and climate change.