Plant ecosystems exchange reactive trace gases, such as nitrogen oxides (NOx), ozone, and volatile organic compounds (VOCs), and particles. While some of these compounds are anthropogenically produced, many are biotic in origin and are emitted in-situ or produced from rapid photochemistry in the canopy. The oxidation products include low-volatility organic compounds that readily partition to the aerosol phase, particularly in the presence of anthropogenic pollutants such as ammonium, nitrate and sulphate. In addition to being strong sources, soil and leaves represent major sinks of these reaction products, with deposition to the surface also as a function of surface wetness and uptake into the leaf via the stomata. The canopy region thus represents a dynamic and rapidly changing environment in which a myriad biological, chemical and physical processes occur over very short time and spatial scales. Advanced techniques of flux measurements provide good knowledge of the overall net fluxes of these compounds above canopies, while additional in-canopy measurements enable more detailed study and understanding of the individual processes and reactions driving these fluxes. These rapidly advancing measurements can support parametrization of models for a mechanistic understanding of in-canopy dynamics of deposition and emission of these reactive gases, which can in turn allow fuller interpretation of in-situ measurements and inform the design of field experiments to test specific hypotheses. This session, sponsored by ILEAPS (Integrated Land Ecosystem Atmosphere Process Study), encourages the submission of contributions based on in-situ measurements and/or modeling that improve our understanding of biosphere-atmosphere exchange of reactive gases and aerosols and in-canopy processes.