The objective of this project was to increase the protection of objects placed in display cases or other microenvironments from air pollutants.

The project had three main research activities. These included:

• literature research and materials characterization, which involved collecting adsorbents and their literature and developing a deep understanding of the materials' physical chemistry and properties;
• measurement of capacity and breakthrough curves for selected pairs of pairs of pollutants and adsorbents—specifically, two acids at three different relative humidities with 18 adsorbents;
• rank the adsorbents' performance for each acid and humidity, and derive a final figure of merit value predictive of adsorption behavior at any relative humidity.

Background
The last thirty years have seen increased interest in the role pollutants play in the deterioration of works of art indoors and within indoor microenvironments. Much work has been carried out in designing hermetically sealed display cases with inert materials and in the use of barrier films to restrict materials off-gassing (see "The Good, the Bad, and the Ugly" by Jean Tétreault). However, the use of adsorbents to intercept pollutants—matching adsorbent capacities to specific gases and determining how long these materials last—had never been systematically explored.

The most commonly used adsorbents adapted for microenvironments have been those borrowed from museum air conditioning filtration applications. These are classic high performance media but because they pose a potential soiling problem in close proximity to delicate artifacts, conservators can benefit by having more options available to them. This project has sought to broaden those options. Even absorbents whose capacities are low, when it is possible to use them in larger quantities, may have attributes such as humidity buffering that makes them unique for certain applications.

Overview
The Performance of Pollutant Adsorbents project had several research objectives, which included:

• measuring the adsorption capacity of selected zeolites, activated carbon, potassium permanganate impregnated alumina, potassium hydroxide impregnated activated alumina/carbon, silica gel, normal precipitated calcium carbonate, microporous calcium carbonate, and five types of clays to acetic and formic acids;
• determining capacities with standard breakthrough curve measurements, thermal desorption/mass spectrometry (TG/DTA/MS), and elemental analysis;
• conducting exposures using calibrated diffusion and permeation devices as well as carboxylic acids in saturated salt solutions at 30 percent, 50 percent, and 84 percent relative humidity;
• determining desorption rates for many physisorbents in clean air at 50 percent RH and—for the more important adsorbents—measure the specific effects of high humidity on pollutant desorption;
• from these individual exposure experiments, ranking all adsorbents and awarding a figure of merit for overall expected performance, under the range of conditions tested.