Professor Mark Sutton is an environmental physicist based at the UK Centre for Ecology & Hydrology (UKCEH), in Edinburgh. An expert on atmospheric ammonia, he leads international research activities on nitrogen at the science–policy interface. He is a former chair of the International Nitrogen Initiative (INI) and currently directs the UNEP/GEF International Nitrogen Management System (INMS) and the UKRI Global Challenges Research Fund’s South Asian Nitrogen Hub.