Removal of air pollutant mixtures from museum display cases

Abstract

Laboratory studies have been carried out to investigate the feasibility of removing air pollutant mixtures using sorbents, focusing on activated carbon and Purafi1. ‘Active mode’ tests (polluted air passing through the sorbent contained in a cartridge) with activated carbon, Purafil, molecular sieves and silica gel indicated that activated carbon was the most efficient sorbent for removal of the pollutants peroxyacetyl nitrate (PAN) in pure air, PAN and oxides of nitrogen in a smog mixture, and the chlorinated hydrocarbons 1,1, 1-trichloroethane (methyl chloroform), trichloroethylene and tetrachloroethylene. In the ‘passive mode’ (pollutant removal by diffusion to a bed ofsorbent in a display case) removal by sorbents and at the display case walls obeyed first order kinetics for all pollutants tested. The corresponding passive removal rate constants and pollutant half-lives have been determined. Carbon was more efficient than Purafil in all but one passive mode test. Several passive mode experiments were also carried out to simulate possible museum conditions, including limited access to the sorbent bed, the effect of varying the size of displayed objects, and the effect of varying the display case surface-to-volume ratio. Using fugitive colorants as surrogate objects, we also showed that severe fading or color change induced by exposure of the colorants to polluted air can be suppressed or drastically reduced by simply adding a bed of activated carbon to the display case.