Evaluating different methods for elevation calibration of MAX-DOAS (Multi AXis Differential Optical Absorption Spectroscopy) instruments during the CINDI-2 campaign

Abstract. We present different methods for in-field elevation calibration of MAX-DOAS (Multi AXis Differential Optical Absorption Spectroscopy) instruments that were applied and inter-compared during the second Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI-2). One necessary prerequisite of consistent MAX-DOAS retrievals is a precise and accurate calibration of the elevation angles of the different measuring systems. Therefore, different methods for this calibration were applied to several instruments during the campaign, and the results were inter-compared. This work first introduces and explains the different methods, namely far- and near-lamp measurements, white-stripe scans, horizon scans and sun scans, using data and results for only one (mainly the Max Planck Institute for Chemistry) instrument. In the second part, the far-lamp measurements and the horizon scans are examined for all participating groups. Here, the results for both methods are first inter-compared for the different instruments; secondly, the two methods are compared amongst each other. All methods turned out to be well-suited for the calibration of the elevation angles of MAX-DOAS systems, with each of them having individual advantages and drawbacks. Considering the results of this study, the systematic uncertainties of the methods can be estimated as ± 0.05 ∘ for the far-lamp measurements and the sun scans, ± 0.25 ∘ for the horizon scans, and around ± 0.1 ∘ for the white-stripe and near-lamp measurements. When comparing the results of far-lamp and horizon-scan measurements, a spread of around 0.9 ∘ in the elevation calibrations is found between the participating instruments for both methods. This spread is of the order of a typical field of view (FOV) of a MAX-DOAS instrument and therefore affecting the retrieval results. Further, consistent (wavelength dependent) offsets of 0.32 ∘ and 0.40 ∘ between far-lamp measurements and horizon scans are found, which can be explained by the fact that, despite the flat topography around the measurement site, obstacles such as trees might mark the visible horizon during daytime. The observed wavelength dependence can be explained by surface albedo effects. Lastly, the results are discussed and recommendations for future campaigns are given.

[1]  K. Kreher,et al.  Intercomparison of NO2, O4, O3 and HCHO slant column measurements by MAX-DOAS and zenith-sky UV–visible spectrometers during CINDI-2 , 2020, Atmospheric Measurement Techniques.

[2]  J. Burrows,et al.  Dual ground-based MAX-DOAS observations in Vienna, Austria: Evaluation of horizontal and temporal NO2, HCHO, and CHOCHO distributions and comparison with independent data sets , 2020 .

[3]  K. Kreher,et al.  Intercomparison of NO2, O4, O3 and HCHO slant column measurements by MAX-DOAS and zenith-sky UV-Visible spectrometers during the CINDI-2 campaign , 2019 .

[4]  A. Bais,et al.  Comparisons of ground-based tropospheric NO 2 MAX-DOAS measurements to satellite observations with the aid of an air quality model over the Thessaloniki area, Greece , 2016 .

[5]  Steffen Beirle,et al.  Intercomparison of aerosol extinction profiles retrieved from MAX-DOAS measurements , 2016 .

[6]  Sebastian Donner.  Mobile MAX-DOAS measurements of the tropospheric formaldehyde column in the Rhein-Main region , 2016 .

[7]  J. Lampel,et al.  The impact of vibrational Raman scattering of air on DOAS measurements of atmospheric trace gases , 2015 .

[8]  Ilya Bruchkouski,et al.  Seasonal variability of the atmospheric trace constituents in Antarctica , 2014, 2014 IEEE Geoscience and Remote Sensing Symposium.

[9]  John P. Burrows,et al.  Formaldehyde and nitrogen dioxide over the remote western Pacific Ocean: SCIAMACHY and GOME-2 validation using ship-based MAX-DOAS observations , 2012 .

[10]  Hisahiro Takashima,et al.  MAX-DOAS formaldehyde slant column measurements during CINDI: intercomparison and analysis improvement , 2012 .

[11]  Steffen Beirle,et al.  Inversion of tropospheric profiles of aerosol extinction and HCHO and NO 2 mixing ratios from MAX-DOAS observations in Milano during the summer of 2003 and comparison with independent data sets , 2011 .

[12]  Steffen Beirle,et al.  The Cabauw Intercomparison campaign for Nitrogen Dioxide measuring Instruments (CINDI): design, execution, and early results , 2011 .

[13]  Yugo Kanaya,et al.  Intercomparison of slant column measurements of NO 2 and O 4 by MAX-DOAS and zenith-sky UV and visible spectrometers , 2010 .

[14]  F. Hendrick,et al.  Multiple wavelength retrieval of tropospheric aerosol optical properties from MAXDOAS measurements in Beijing , 2010 .

[15]  J. Drummond,et al.  The Polar Environment Atmospheric Research Laboratory UV-visible Ground-Based Spectrometer: First measurements of O-3, NO2, BrO, and OClO columns , 2009 .

[16]  Christopher A. Cantrell,et al.  Technical Note: Review of methods for linear least-squares fitting of data and application to atmospheric chemistry problems , 2008 .

[17]  Yugo Kanaya,et al.  First retrieval of tropospheric aerosol profiles using MAX-DOAS and comparison with lidar and sky radiometer measurements , 2008 .

[18]  Ulrich Platt,et al.  MAX‐DOAS O4 measurements: A new technique to derive information on atmospheric aerosols: 2. Modeling studies , 2006 .

[19]  Ulrich Platt,et al.  MAX‐DOAS O4 measurements: A new technique to derive information on atmospheric aerosols—Principles and information content , 2004 .

[20]  J. Lambert,et al.  Retrieval of Tropospheric BrO and NO2 from UV-Visible Observations , 2004 .

[21]  John P. Burrows,et al.  MAX-DOAS measurements of atmospheric trace gases in Ny- ˚ Alesund - Radiative transfer studies and their application , 2004 .

[22]  P. Zieger,et al.  Retrieval of Aerosol Profiles using Multi-Axis Differential Optical Absorption Spectroscopy (MAX-DOAS) , 2003 .

[23]  Ulrich Platt,et al.  Observations of BrO and its vertical distribution during surface ozone depletion at Alert , 2002 .