Claus Jørgen Nielsen

My research is currently focused on fundamental physico-chemical properties related to atmospheric chemistry and global change. Global change depends critically on the concentrations of gases present in the atmosphere at trace levels and the balance between the production and the loss terms governs the concentration of these gases. We determine the characteristic isotopic signatures of atmospheric photolysis and OH radical reactions in our laboratory. In combination with observed stable isotope abundances this provides insight to the sources and to the regional and global transformations of the greenhouse gases. In particular the additional information obtained from the construction of an isotopologue budget reduces the uncertainties in the grand budget. The kinetic information from studies of isotopologues also provides additional information on how chemical reactions occur, and the results from our laboratory studies are used as benchmarks for quantum chemical calculations.

Atmospheric aerosols interact with solar and terrestrial radiation. A significant amount of aerosols are of anthropogenic origin and aerosols therefore contribute to man made impact on climate. Aerosols have a significant direct impact on the radiative balance by scattering and absorption of solar radiation. Aerosols influence the radiative balance indirectly by acting as cloud condensation nuclei and thus affect the cloud microphysics and the albedo of the earth. Aerosols act as sites for heterogeneous chemistry and are thereby linked to trace gas partitioning in general. We determine the optical properties of individual aerosol constituents in the UV-Visible and infrared regions of the solar spectrum. These results are then used in calculations of aerosol scattering and absorption.

• Photochemical and photolytic degradation of atmospheric trace gases
• Studies of particle formation on the molecular level
• Optical properties of aerosol constituents
• Molecular properties

INTROP: Interdisciplinary Tropospheric Research: from the Laboratory to Global Change.  Flyer