Atmospheric Composition

This session welcomes contributions related to chemical and compositional processes in the atmosphere relevant to complex environments including mountainous areas. While the physical modification by orography has been largely acknowledged, the status of atmospheric composition is much less understood. Atmospheric chemistry in mountainous regions is made complex by the interplay between dynamical effects and a diverse precursor mix of ozone and aerosol-forming compounds. Early modelling attempts found an underestimation of tropospheric ozone (e.g. ALPNAP) in the greater Alpine region. Another interesting aspect relates to aerosol formation processes, that have been observed to be amplified in the presence of complex topography. From a remote sensing point of view, only now atmospheric composition starts being resolved at spatial scales that can capture individual valleys (e.g. CAMS, COPERNICUS). Past shortcomings in remote sensing observations of the atmosphere over mountains therefore need to be urgently addressed by taking advantage of new high resolution models and a wide array of in-situ observations. From a chemical point of view, complex does not necessarily only relate to topography, but also to situations where highly heterogenous and complex surface emissions impact the chemistry of the atmosphere. We therefore would like to solicitate observational (remote sensing and in-situ) and modelling contributions from all aspects where complexity plays a role, this certainly includes regions impacted by mountains, but should not exclude regions where complexity is defined in a different context.