Estimation of the historical dry deposition of air pollution indoors to the monumental paintings by Edvard Munch in the University Aula, in Oslo, Norway

Heritage Science

Table 2 Expected indoor (Oslo University Aula) to outdoor (Oslo central urban background) concentration ratios and pollutant dry deposition velocities

Pollutant	Indoor/outdoor concentration ratio^a	Indoor dry deposition velocity (cm s⁻¹)
SO₂	0.23^b	0.057^g
NO₂	0.9^c	0.004^h
O₃	0.5^d	0.021ⁱ–0.077^g
PM_2.5 before 1975	0.5–0.8^e	0.02^j
PM_2.5 after 1975 (with mechanical ventilation filtration)	0.1–0.4^f	0.02^j

^aSee also Additional file 1
^bMeasured in the National Gallery of Oslo.
^cSuggested probable value based on data from the National Gallery and the literature, allowing a slight reduction to the indoors.
^dMeasured in the Aula in the winter 2019.
^eBased on [60] and the assumption that there will probably have been some reduction to the indoors.
^fBased on evaluations of possible variations in the PM_2.5 I/O ratio from the measured average ion I/O ratio in the Aula (Table 1) and the considerable general uncertainty.
^gAverage of surface dry deposition velocity to paintings at RH = 30% and RH = 50% [56].
^hA two times higher value (0.008 cm s⁻¹) was reported from measurements [56] at RH = 30% than from RH = 50–90% (0.004 cm s⁻¹) The value of 0.008 cm s⁻¹ seems anomalous and it was decided to use the value of 0.004 cm s⁻¹, for the situation with RH = 40% in the Oslo University Aula.
ⁱObtained by modelling to measurements by [57, 58] report a typical value of 0.051 cm s⁻¹ “based on studies by [61] and by [62]”
^jAverage experimental dry deposition velocity to the indoor building surfaces of the historic house museum of Apsley House in London [60]. Simulation of the mechanically ventilated room in the house (Waterloo Gallery) showed the same value [63]