Articles | Volume 6, issue 1
Atmos. Meas. Tech., 6, 167–185, 2013

Special issue: Cabauw Intercomparison campaign for Nitrogen Dioxide measuring...

Atmos. Meas. Tech., 6, 167–185, 2013

Research article 31 Jan 2013

Research article | 31 Jan 2013

MAX-DOAS formaldehyde slant column measurements during CINDI: intercomparison and analysis improvement

G. Pinardi1, M. Van Roozendael1, N. Abuhassan4, C. Adams2, A. Cede4, K. Clémer1,*, C. Fayt1, U. Frieß5, M. Gil6, J. Herman4, C. Hermans1, F. Hendrick1, H. Irie7,**, A. Merlaud1, M. Navarro Comas6, E. Peters8, A. J. M. Piters9, O. Puentedura6, A. Richter8, A. Schönhardt8, R. Shaiganfar3, E. Spinei10, K. Strong2, H. Takashima7,***, M. Vrekoussis8,11, T. Wagner3, F. Wittrock8, and S. Yilmaz5 G. Pinardi et al.
  • 1Department of Physics, University of Toronto, Ontario, Canada
  • 2BIRA-IASB – Belgian Institute for Space Aeronomy, Brussels, Belgium
  • 3Max Planck Institute for Chemistry, Mainz, Germany
  • 4NASA/Goddard Space Flight Center, GSFC, Greenbelt, MD, USA
  • 5Institute of Environmental Physics, University of Heidelberg, Heidelberg, Germany
  • 6National Institute for Aerospace technology, INTA, Madrid, Spain
  • 7Research Institute for Global Change, JAMSTEC, Yokohama, Japan
  • 8Institute of Environmental Physics, University of Bremen, Bremen, Germany
  • 9Royal Netherlands Meteorological Institute, KNMI, De Bilt, The Netherlands
  • 10Laboratory for Atmospheric Research, Washington State University, Pullman, WA, USA
  • 11Energy, Environment and Water Research Center, The Cyprus Institute, Nicosia, Cyprus
  • *now at: Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Leuven, Belgium
  • **now at: Center for Environmental Remote Sensing, Chiba University, Chiba, Japan
  • ***now at: Department of Earth System Science, Faculty of Science, Fukuoka University, Fukuoka, Japan

Abstract. We present intercomparison results for formaldehyde (HCHO) slant column measurements performed during the Cabauw Intercomparison campaign of Nitrogen Dioxide measuring Instruments (CINDI) that took place in Cabauw, the Netherlands, in summer 2009. During two months, nine atmospheric research groups simultaneously operated MAX-DOAS (MultiAXis Differential Optical Absorption Spectroscopy) instruments of various designs to record UV-visible spectra of scattered sunlight at different elevation angles that were analysed using common retrieval settings. The resulting HCHO data set was found to be highly consistent, the mean difference between instruments generally not exceeding 15% or 7.5 × 1015 molec cm−2, for all viewing elevation angles. Furthermore, a sensitivity analysis was performed to investigate the uncertainties in the HCHO slant column retrieval when varying key input parameters such as the molecular absorption cross sections, correction terms for the Ring effect or the width and position of the fitting interval. This study led to the identification of potentially important sources of errors associated with cross-correlation effects involving the Ring effect, O4, HCHO and BrO cross sections and the DOAS closure polynomial. As a result, a set of updated recommendations was formulated for HCHO slant column retrieval in the 336.5–359 nm wavelength range. To conclude, an error budget is proposed which distinguishes between systematic and random uncertainties. The total systematic error is estimated to be of the order of 20% and is dominated by uncertainties in absorption cross sections and related spectral cross-correlation effects. For a typical integration time of one minute, random uncertainties range between 5 and 30%, depending on the noise level of individual instruments.

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