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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 16, issue 6 | Copyright
Atmos. Chem. Phys., 16, 4171-4189, 2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 31 Mar 2016

Research article | 31 Mar 2016

Diurnal cycle and multi-decadal trend of formaldehyde in the remote atmosphere near 46° N

Bruno Franco1, Eloise A. Marais2, Benoît Bovy1, Whitney Bader1, Bernard Lejeune1, Ginette Roland1, Christian Servais1, and Emmanuel Mahieu1 Bruno Franco et al.
  • 1Institute of Astrophysics and Geophysics, University of Liège, Liège, Belgium
  • 2School of Engineering and Applied Sciences, Harvard University, Cambridge, MA, USA

Abstract. Only very few long-term records of formaldehyde (HCHO) exist that are suitable for trend analysis. Furthermore, many uncertainties remain as to its diurnal cycle, representing a large short-term variability superimposed on seasonal and inter-annual variations that should be accounted for when comparing ground-based observations to, e.g., model results. In this study, we derive a multi-decadal time series (January 1988–June 2015) of HCHO total columns from ground-based high-resolution Fourier transform infrared (FTIR) solar spectra recorded at the high-altitude station of Jungfraujoch (Swiss Alps, 46.5°N, 8.0°E, 3580ma. s. l. ), allowing for the characterization of the mid-latitudinal atmosphere for background conditions. First we investigate the HCHO diurnal variation, peaking around noontime and mainly driven by the intra-day insolation modulation and methane (CH4) oxidation. We also characterize quantitatively the diurnal cycles by adjusting a parametric model to the observations, which links the daytime to the HCHO columns according to the monthly intra-day regimes. It is then employed to scale all the individual FTIR measurements on a given daytime in order to remove the effect of the intra-day modulation for improving the trend determination and the comparison with HCHO columns simulated by the state-of-the-art GEOS-Chem v9-02 chemical transport model. Such a parametric model will be useful to scale the Jungfraujoch HCHO columns on satellite overpass times in the framework of future calibration/validation efforts of space-borne sensors. GEOS-Chem sensitivity tests suggest then that the seasonal and inter-annual HCHO column variations above Jungfraujoch are predominantly led by the atmospheric CH4 oxidation, with a maximum contribution of 25% from the anthropogenic non-methane volatile organic compound precursors during wintertime. Finally, trend analysis of the so-scaled 27-year FTIR time series reveals a long-term evolution of the HCHO columns in the remote troposphere to be related to the atmospheric CH4 fluctuations and the short-term OH variability: +2.9%year−1 between 1988 and 1995, −3.7%year−1 over 1996–2002 and +0.8%year−1 from 2003 onwards.

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The long-term evolution of HCHO in the remote troposphere is characterized using a 27-year time series of total columns from high-resolution FTIR solar spectra recorded at Jungfraujoch. A parametric model is used to remove the effect of the HCHO diurnal variations for improving the trend determination and the comparison with columns simulated by GEOS-Chem. Sensitivity tests are performed to identify the main drivers of the HCHO seasonal and inter-annual variations, as well as their contribution.
The long-term evolution of HCHO in the remote troposphere is characterized using a 27-year time...