Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 10 8 2010 10.5194/acp-10-3901-2010 http://www.atmos-chem-phys.net/10/3901/2010/ http://www.atmos-chem-phys.net/10/3901/2010/acp-10-3901-2010.html http://www.atmos-chem-phys.net/10/3901/2010/acp-10-3901-2010.pdf 3901 3914 2010-04-27 Technical Note: Using a high finesse optical resonator to provide a long light path for differential optical absorption spectroscopy: CE-DOAS J. Meinen jan.meinen@imk.fzk.de J. Thieser U. Platt T. Leisner Institute for Meteorology and Climate Research, Aerosols and Heterogeneous Chemistry in the Atmosphere (IMK-AAF), Karlsruhe Institute of Technology (KIT), Germany Institut for Environmental Physics (IUP), Atmosphere and Remote Sensing, Ruprecht-Karls-Universität Heidelberg, Germany now at: Department of Atmospheric Chemistry, Max Planck Institute for Chemistry, Mainz Germany Cavity enhanced methods in absorption spectroscopy have seen a considerable increase in popularity during the past decade. Especially Cavity Enhanced Absorption Spectroscopy (CEAS) established itself in atmospheric trace gas detection by providing tens of kilometers of effective light path length using a cavity as short as 1 m. In this paper we report on the construction and testing of a compact and power efficient light emitting diode based broadband Cavity Enhanced Differential Optical Absorption Spectrometer (CE-DOAS) for in situ observation of atmospheric NO₃. This device combines the small size of the cavity with the advantages of the DOAS approach in terms of sensitivity, specificity and insensivity to intensity fluctuations of the light source. In particular, no selective removal of the analyte (here NO₃) is necessary for calibration of the instrument if appropriate corrections are applied to the CEAS theory. Therefore the CE-DOAS technique can – in principle – measure any gas detectable by DOAS. We will discuss the advantages of using a light emitting diode (LED) as light source particularly the precautions which have to be considered for the use of LEDs with a broad wavelength range. The instrument was tested in the lab by detecting NO₃ formed by mixing of NO₂ and O₃ in air. It was then compared to other trace gas detection techniques in an intercomparison campaign in the atmosphere simulation chamber SAPHIR at Forschungszentrum Jülich at NO₃ concentrations as low as 6.3 ppt. % vor jede Referenz Atkinson, R., Baulch, D. L., Cox, R. 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