Atmospheric Measurement Techniques Discussions www.atmos-meas-tech-discuss.net 1867-8610 1 1 2008 10.5194/amtd-1-481-2008 http://www.atmos-meas-tech-discuss.net/1/481/2008/ http://www.atmos-meas-tech-discuss.net/1/481/2008/amtd-1-481-2008.html http://www.atmos-meas-tech-discuss.net/1/481/2008/amtd-1-481-2008.pdf 481 507 2008-12-23 Broadband Cavity Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS) &ndash; applicability and corrections U. Platt ulrich.platt@iup.uni-heidelberg.de J. Meinen D. Pöhler T. Leisner Institute for Environmental Physics (IUP), Ruprecht-Karls-University, Heidelberg, Germany Institute for Meteorology and Climate Research, Aerosols and Heterogeneous Chemistry in the Atmosphere (IMK-AAF), Forschungszentrum Karlsruhe GmbH, Germany Atmospheric trace gas measurements by cavity assisted long-path absorption spectroscopy are an emerging technology. An interesting approach is the combination of CEAS with broad band light sources, the broad-band CEAS (BB-CEAS). BB-CEAS lends itself to the application of the DOAS technique to analyse the derived absorption spectra. While the DOAS approach has enormous advantages in terms of sensitivity and specificity of the measurement, an important implication is the reduction of the light path by the trace gas absorption, since cavity losses due to absorption by gases reduce the quality (<I>Q</I>) of the cavity. In fact, at wavelength, where the quality of the BB-CEAS cavity is dominated by the trace gas absorption (esp. at very high mirror reflectivity), the light path will vary inversely with the trace gas concentration and the strength of the band will become nearly independent of the trace gas concentration <I>c</I> in the cavity, rendering the CEAS Method useless for trace gas measurements. 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