Fig. 1

The mounting of Teflon membrane and quartz filters on the cardboard plate (A), the vertical exposure of the filters, and exposure of the passive gas samplers (also seen in the enlargement) under the Aula gallery balustrade (B), and the view towards the paintings in the Aula from the gallery (C) in 1955, when grid-like thermal soiling deposits over the stretchers of the paintings on the left and right could be observed. The present room arrangement of the Aula is close to that in the photograph. C reproduced with permission from the UiO Universitetshistorisk fotobase