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Institute of Energy and Climate Research

# Photochemistry and Radicals

Free radicals (OH, HO2 und NO3) play an important role for the degradation of trace gases in the atmosphere. They are substantial species in the formation of secondary pollutants like ozone and particulate matter. The hydroxyl radical (OH) is the most important oxidising species. OH provides about 90% of the cleansing capacity of the atmosphere on a global scale. The experimental observation of radicals and their precursors yields direct understanding of the relevant chemical processes which control the atmospheric trace gas concentrations.

### The working groups

• Laser induced Fluoreszence - Measurement of OH, HO2 and RO2 radical concentrations and chemical OH lifetimes by Laser Induced Fluorescence (LIF).  The LIF technique is deployed in ground-based field campaigns, in airborne missions on research aircraft and Zeppelin, and in the atmosphere simulation chamber SAPHIR.

• DOAS and SAPHIR - Concentrations of free radicals and reactive trace gases are measured in the troposphere by Differential Optical Absorption Spectroscopy (DOAS). The atmosphere simulation chamber SAPHIR is operated for experimental studies of chemical gas-phase and aerosol processes.

• Photolysisfrequencies - Investigation of the production of free radicals by photolysis of atmospheric trace gases and measurement of solar radiation.
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