Atmos. Chem. Phys. Discuss., 13, 33145-33176, 2013
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Further evidence of important environmental information content in red-to-green ratios as depicted in paintings by great masters
C. S. Zerefos1,2, P. Tetsis1, A. Kazantzidis3, V. Amiridis4, S. C. Zerefos5, J. Luterbacher6, K. Eleftheratos7, E. Gerasopoulos2,8, S. Kazadzis8, and A. Papayannis9
1Academy of Athens, Athens, Greece
2Navarino Environmental Observatory (N.E.O.), Messinia, Greece
3Laboratory of Atmospheric Physics, Physics Department, University of Patras, Greece
4Institute of Astronomy, Astrophysics, Space Application and Remote Sensing, National Observatory of Athens, Greece
5Hellenic Open University, Patras, Greece
6University of Giessen, Germany
7Faculty of Geology and Geoenvironment, University of Athens, Greece
8Institute of Environmental Research and Sustainable Development, National Observatory of Athens, Greece
9National Technical University of Athens, Athens, Greece

Abstract. This work is a follow-up study of a research carried out since 2005 and presents evidence supporting the findings of an earlier paper (Zerefos et al., 2007), which postulated that sunsets painted by famous artists provide independent proxy information on the aerosol optical depth after major volcanic eruptions. The series of these and additional paintings have been revisited and comparisons between coarser digital images with those derived from precision colour protocols, match together confirming the earlier results as discussed in the text. It was also found that aerosol optical depths (AODs) at 550 nm calculated by feeding Red-to-Green (R/G) ratios from a large number of paintings to a radiative transfer model, were well correlated with independent proxies from stratospheric AOD and optical extinction data, the dust veil index and others. AODs calculated from paintings have been grouped into 50 yr intervals from 1500 to 2000. From each 50 yr time period the year of the eruption and the 3 following years have been excluded. The remaining years have been termed "non-volcanic" and they provide additional evidence of a multidecadal increase in the atmospheric optical depths during the industrial "revolution". The increase of AOD at 550 nm calculated from the paintings, is estimated to range from 0.15 in the middle 19th century to about 0.20 by the end of the 20th century. To corroborate our findings, an experiment was designed in which a master painter/colourist painted successive sunsets during and after the passage of Saharan aerosols over the island of Hydra in Greece. Independent solar radiometric measurements confirmed that the master colourist's R/G ratios which were used to model his AODs, matched to the AOD values measured in situ by the co-located sunphotometers at the declining phase of the Sahara aerosol. Our work concludes that regardless of the school, red-to-green ratios from great masters can provide independent proxy AODs that correlate with widely accepted proxies and with independent measurements.

Citation: Zerefos, C. S., Tetsis, P., Kazantzidis, A., Amiridis, V., Zerefos, S. C., Luterbacher, J., Eleftheratos, K., Gerasopoulos, E., Kazadzis, S., and Papayannis, A.: Further evidence of important environmental information content in red-to-green ratios as depicted in paintings by great masters, Atmos. Chem. Phys. Discuss., 13, 33145-33176, doi:10.5194/acpd-13-33145-2013, 2013.
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