Martin Lloyd Williams (22 November 1947–21 September 2020)[1] was a Welshchemist and environmental scientist who made important contributions to the science of air pollution and its incorporation into public policy in the United Kingdom.[2] Williams was one of the first scientists to recognize the harmful health effects of ground-level ozone, in papers published in Nature in the mid-1970s,[3][4] and one of the first to study vehicle emissions in the real world (rather than under artificial laboratory conditions).[2][5] He also established the first systematic programme to produce inventories of UK national air pollution emissions.[6]