FADING OF COLORANTS BY ATMOSPHERIC POLLUTANTS - REFLECTANCE SPECTROSCOPY STUDIES

Artists' colorants coated on cellulose paper have been exposed, in the dark and at ambient temperature and humidity, to purified air (contro l test) and to purified air containing parts per billion levels of the following air pollutants: formaldehyde, sulfur dioxide, ozone, nitrog en dioxide, peroxyacetyl nitrate (PAN) and a mixture of photochemical oxidants (O3 + NO2 + PAN). Color changes (L, a*, b* and DELTAE) have been measured using a reflectance color analyzer after 1, 2, 3, 4, 6, 8, 10 and 12 weeks exposure. Color parameters (x, y, X, Y, Z, L, a* a nd b) were also calculated from the 380-700 nm spectra, recorded with a reflectance spectrophotometer, of unexposed and air pollutant-expos ed colorants. The two measurement methods were in good agreement. Subs tantial color changes were recorded for several compounds exposed to p hotochemical oxidants (O3, NO2, PAN) both singly and as a mixture. Inc reasing the humidity from 46 to 83% resulted in a large increase in co lor change for several colorants exposed to the mixture of oxidants. C olor changes are discussed in terms of pollutant dose (dose = product of pollutant concentration and exposure duration) and for their implic ations with respect to air pollution damage to colored objects in muse um collections.