Alastair Lewis is professor of atmospheric chemistry at the University of York and the National Centre for Atmospheric Science. He is an experimental scientist who has studied the composition of the atmosphere and the impacts of pollution from polar regions to megacities, open oceans to tropical forests. He has received the John Jeyes Prize for Environment, Energy and Sustainability and the biennial Royal Society of Chemistry prize for contributions to science policy. Alastair has been Chair of the Defra Air Quality Expert Group (AQEG) since 2019, Chair of the Department for Transport Science Advisory Council since 2021 and a member of the Environmental Sustainability Panel of the Civil Aviation Authority. He has been a contributor to >300 scientific papers, chapters and reports on topics spanning transport and combustion emissions and environmental impacts, measurement technology, global, regional and urban air pollution and health impacts.