Chapter 3 Holistic Modeling of Gas and Aerosol Deposition and the Degradation of Cultural Objects

Abstract

This chapter addresses the deposition of gases and aerosols both inside and outside museums and the possible effects that such deposition may have on cultural objects. This issue is addressed through the concept of holistic modeling, where all critical factors controlling the deposition and degradation process are defined and linked together. The types and sizes of particulates both within and exterior to a museum are outlined. The types of gases found within a dwelling and their relations to exterior pollutants are described. The aerosol and gas deposition mechanisms and the equations for each mechanism are outlined. In order to define conditions for gas deposition, the factors controlling condensation and formation of moisture layers are also presented. These principles and equations are then illustrated by analysis of the generation, transport and deposition of aerosols on cultural objects in the external environment, followed by a similar analysis for inside buildings. In the case of deposition inside buildings, the literature is first reviewed, and then three case studies are analyzed that represent significant cases or highlight unresolved issues in the literature. The case studies clarify the relative importance of each deposition mechanism. It is evident that the major mechanisms within a building are gravity, vortex shedding and, in case of significant air flows, momentum-dominated impact. Factors controlling the attachment and detachment of pollutants both within and outside dwellings are then outlined, as are the common damage forms that result for some pollutants. Throughout the chapter and especially towards the end, the implications of the findings to design and maintenance strategies are discussed.