Opinion: Atmospheric multiphase chemistry – past, present, and future

Abstract. Multiphase chemistry occurs between chemicals in different atmospheric phases, typically involving gas–solid and gas–liquid interactions. The importance of atmospheric multiphase chemistry has long been recognized. Its central role extends from acid precipitation and stratospheric ozone depletion to its impact on the oxidizing capacity of the troposphere and to the roles that aerosol particles play in driving chemistry–climate interactions and affecting human health. This opinion article briefly introduces the subject of multiphase chemistry and tracks its development before and after the start of Atmospheric Chemistry and Physics. Most of the article focuses on research opportunities and challenges in the field. Central themes are that a fundamental understanding of the chemistry at the molecular level underpins the ability of atmospheric chemistry to accurately predict environmental change and that the discipline of multiphase chemistry is strongest when tightly connected to atmospheric modeling and field observations.