09 May 2022
09 May 2022
Status: this preprint is currently under review for the journal CP.

Is it possible to estimate aerosol optical depth from historic colour paintings?

Christian von Savigny1, Anna Lange1, Anne Hemkendreis2, Christoph Hoffmann1, and Alexei Rozanov3 Christian von Savigny et al.
  • 1Institute of Physics, University of Greifswald, Felix-Hausdorff-Str. 6, 17489 Greifswald, Germany
  • 2Institute of Art History, Albert-Ludwigs-University of Freiburg, Platz der Universität 3, 79085 Freiburg, Germany
  • 3Institute of Environmental Physics, University of Bremen, Otto-Hahn-Allee 1, 28359 Bremen, Germany

Abstract. The idea of estimating stratospheric aerosol optical thickness from the twilight colours in historic paintings – particularly under conditions of volcanically enhanced stratospheric aerosol loading – is very tantalising, because it would provide information on the stratospheric aerosol loading over a period of several centuries. This idea has in fact been applied in a few studies in order to provide quantitative estimates of the aerosol optical depth after some of the major volcanic eruptions that occurred during the past 500 years. In this study we critically review this approach and come to the conclusion that the uncertainties of the estimated aerosol optical depths are so large that the values have to be considered highly questionable. We show that several auxiliary parameters – which are typically poorly known for historic eruptions – can have a similar effect on the red-green colour ratio as a change in optical depth typically associated with eruptions such as, e.g. Tambora in 1815 or Krakatao in 1883. Among the effects considered here, uncertainties in the aerosol particle size distribution have the largest impact on the colour ratios and hence the aerosol optical depth estimate. For solar zenith angles exceeding 80 degrees, uncertainties in the stratospheric ozone amount can also have a significant impact on the colour ratios. In addition, for solar zenith angles exceeding 90 degrees the colour ratios exhibit a dramatic dependence on solar zenith angle, rendering the estimation of aerosol optical depth essentially impossible.

Christian von Savigny et al.

Status: open (until 04 Jul 2022)

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Christian von Savigny et al.

Christian von Savigny et al.


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Short summary
This study investigates the possibility to infer information on aerosol optical depth from photographs of historic paintings. The idea – which has been applied in previous studies – is very interesting, because it would provide an archive of the atmospheric aerosol loading covering many centuries. We show that twilight colours do not only depend on the aerosol optical thickness, but also on several other parameters, making a quantitative estimate of aerosol optical depth essentially impossible.