The series has been edited by Professors Hester and Harrison since it began in 1994. Professor Roy Harrison OBE is listed by ISI Thomson Scientific (on ISI Web of Knowledge) as a Highly Cited Researcher in the Environmental Science/Ecology category. He has an h-index of 84 (i.e. 84 of his papers have received 84 or more citations in the literature). In 2004 he was appointed OBE for services to environmental science in the New Year Honours List and in 2017 was elected a Fellow of the Royal Society. He was profiled by the Journal of Environmental Monitoring (Vol 5, pp 39N-41N, 2003). Professor Harrison’s research interests lie in the field of environment and human health. His main specialism is in air pollution, from emissions through atmospheric chemical and physical transformations to exposure and effects on human health. Much of this work is designed to inform the development of policy. Now an emeritus professor, Professor Ron Hester's current activities in chemistry are mainly as an editor and as an external examiner and assessor. He also retains appointments as external examiner and assessor / adviser on courses, individual promotions, and departmental / subject area evaluations both in the UK and abroad.