Abstrakt
Airborne particles deposited on cultural heritage artefacts have many negative effects. Beside soiling and abrasion of surfaces particles can also cause material deterioration by chemical reactions.
Ultrafine atmospheric particles, penetrating indoors from the outdoor environment, contain soot and organic matter from traffic that are hygroscopic and effective for transport of acids. Fine particles consist of secondary organic matter, ammonium sulphate and ammonium nitrate, and sometimes sulphuric acid.
Coarse particles, formed predominantly by resuspended dust, contain crustal elements and in the indoor environment also alkaline particles emitted from concrete structures (Nazaroff et al., 1993, Hatchfield, 2005). Dry deposition is considered to occur by a combination of Brownian and eddy diffusion and gravitational settling (Nazaroff and Cass, 1989, Lai and Nazaroff, 2000) where prevailing deposition mechanism depends on the particle size.
Coarse particles are deposited on upward-facing surfaces by gravitational settling and fine particles predominantly by diffusion on surfaces of any orientation. In principle the submicron particles can penetrate by diffusion also between books and even into the gaps between pages and thus can be deposited on the inner surfaces of books.
To test this hypothesis we examined deposition of particles on Whatman filters located on the free shelf of the library.