The terrestrial biosphere (vegetation and soil) is an important source and/or sink for reactive air constituents contributing to chemical processes in the atmosphere. These relatively short-lived compounds include reactive trace gases like ozone, oxidized and reduced nitrogen and sulphur compounds, volatile organic compounds (VOC), as well as aerosols. All compounds are important for air quality with potential impacts on ecosystems through dry and wet deposition (nutrients or toxic effect) and on human health. Some compounds also have a direct or indirect effect on the atmosphere radiative properties.

The distribution of reactive atmospheric compounds near the surface and exchange with the biosphere is more complex than for inert trace gases due to influences from biological and chemical (homogeneous and heterogeneous) processes, surface interactions, and turbulent transfer within and above the vegetation canopy that all act on similar time scales. Due to these complex interactions as well as due to instrumental and methodological difficulties there exist major uncertainties associated with the description, quantification and modelling the near-surface concentration and surface-atmosphere exchange of reactive trace gases and aerosols.

The session is addressed to experimentalists and modelers working on various spatial scales to understand the near-surface concentration and surface-atmosphere exchange of reactive trace gases and aerosols. It is open to a wide range of studies including the development and application of new measurement devices, methods, and model approaches as well as field observations and process studies. Presentations concerning all types of reactive compounds and (semi-) natural or agricultural ecosystems are welcome. Contributions from recent studies on ammonia measurements are especially encouraged.