Volatile Organic Compounds in Rainwater: A New Frontier in Atmosphere–Biosphere Interactions

Abstract

Rainwater is a key vector of atmospheric deposition, linking the atmosphere with terrestrial and aquatic ecosystems. While the inorganic chemistry of precipitation (dominated by sulfate, nitrate, ammonium, and trace metals) has been extensively studied, organic compounds in rainwater have received less attention, and Volatile Organic Compounds (VOCs) in particular have been practically overlooked. Recent methodological advances have revealed that a diverse suite of VOCs can be detected in rainwater along with VOC‐derived compounds, challenging the long‐held assumption that wet deposition plays a negligible role in VOC cycling. Although wet deposition is generally thought to be a minor atmospheric sink for VOCs (∼13.3% of total VOC emissions), rainborne VOCs are chemically reactive and biologically labile, such that even small quantities may exert disproportionate effects on soil microbial activity, plants, short‐term biogeochemical cycling, and water chemistry at local to regional scales. This article combines a synthesis of the current state of knowledge on rainborne VOCs and VOCs‐derived compounds with a particular focus on VOC occurrence, sources, partitioning, and transformation processes, with a forward‐looking perspective on the potential significance of rainborne VOCs for carbon cycling and atmosphere–biosphere interactions. We identify major gaps in observations, analytical capability, and modeling frameworks that limit quantitative understanding of VOC wet deposition and its ecological significance. Finally, we outline priority research directions, including improved sampling strategies, advanced analytical techniques, and integration into Earth system models. Together, these advances are needed to reassess the role of precipitation not only as a passive sink for atmospheric pollutants, but as an active driver of ecosystem functioning and Earth system processes in a changing climate.