Air pollution control in museums and galleries

REGNATEDACTIVATEDCARB

Air pollution control in museums and galleries Museums and galleries are suffering badly from the generally higher levels of air pollution in cities. Careful control of such contamination requires strict monitoring, and the use of the most appropriate materials. Alan Singleton of Sutcllffe Speakman Carbons explains the benefits of impregnated activated carbons, and reports on an application at the National Gallery in London.

here is little doubt that certain air pollutants can have a damaging effect on objets d’art throughout galleries and museums and, with today’s levels of pollution, the need to maintain a stable en&onment has never been more important in preventing material decay. Furthermore, as galleries borrow and lend paintings - to increase public access to them and to advance knowledge and understanding of the pictures strict environmental control is often a condition of the loan. The pressure to create and maintain a controlled environment for both objects and people is intense. Yet, how can a controlled environment be achieved and, once in place, how can its function be verified? Over recent years, air purification companies have been willing to promote the benefits of different filtration media to galleries, but how can a gallery manager be sure that once a system is in place it is the most suitable to meet the gallery’s needs? There will no doubt be galleries believing that their environment is being carefully controlled, when in fact the filter system is either not removing all the necessary pollutants to prevent corrosion, or even no longer functioning correctly. Are you really protecting your assets? A 198 1 technical report prepared for the UK Department of the Environment’s Property Services Agency, on ‘The Control

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of Atmospheric Sulphur Dioxide in Air Conditioned Buildings’, stated that positive information was scarce, and that treatment of air can be expensive without any certainty of the degree of improvement that could be achieved. So, in 1994, what help is available to ensure that galleries are being effectively protected? It is widely believed that the most harmful air pollutants for galleries are sulphur and nitrogen oxides, since under certain ambient atmospheric conditions - they can undergo further oxidation to acidic oxides and ozone, with obviouslyn greater corrosive potential. It is therefore essential to incorporate some means of reducing the concentration of these oxides to as low a level as possible. In 1981, an investigation into the relative efficiency of various methods of reducing levels of sulphur compounds (including H,S) to achieve the most efficient and economic result was com-

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pleted by the Stevenage, UK-based Warren Spring Laboratoly, commissioned by the Department of the Environment’s Property Services Agency. It was concluded that, in making an economic choice between adsorbent filters of acceptable efficiency, considerations should include the retention capacity of each material, the relative maintenance requirement, and the relative cost of adsorbent filters. The report also suggested that claims for any new or alternative agents should be supported by a test report from an independent authority, showing direct comparison with an agent of known efficiency. However, as the nature of pollution has changed, so the increase in the level of organic gases and solvents presents further complications on the fight against pollution damage. To guarantee complete protection against airborne contaminants, a large inventory of substances such as sulphur and nitrogen oxides, organic gases and solvent vapours must be adsorbed. However, not all filter media can adsorb all of these contaminants. For example, independent assessments such as those carried out by the Warren Spring Laboratory have shown that prepared specialist carbons containing suitable catalytic agents offer an optimal performance level, operating with more than twice the effectiveness at the concentration ranges encountered in museum air as potassium permanganate impregnated on alumina. Utilising a combined effect of chemical reaction and adsorption to remove contaminants (gases are reacted on the surface by catalysis over a chemical which is fixed on the exterior), impregnated activated carbons remove contaminants which are not readily adsorbed by base carbon or other media alone. This should provide peace of mind for galleries and museums worldwide, by removing all organic gases and organic solvents.

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REGNATEDACTIVATEDCARB Implementation at the National Gallery Users of impregnated activated carbon as a filter medium include the National Gallery in London. The recent installation of the replacement air-purification system contains impregnated carbons, which actively remove sulphur compounds and trace organics from the air. Offering protection for the many paintings housed within the 8268 m2 of air-conditioned picture galleries, conditions are carefully monitored and maintained, which is critical to the successful preservation of the nation’s paintings. In response to the requirements of the National Gallery’s Building Department, a leading manufacturer and supplier of specified impregnated carbons, Sutcliffe Speakman Carbons Ltd, provided the highquality chemically impregnated activated carbon suitable for the effective removal of sulphur compounds. With ensured easily maintainable operation, the filters can be refilled with pourable granular carbon. Ironically, air-conditioning equipment often recirculates polluted air, and increases the possibility of corrosion from airborne contaminants. It is therefore vital to incorporate some means of reducing the concentration of contaminants to as low a level as possible within the air conditioning system. Unfortunately, active carbons when sold cannot guarantee the safe removal of all

airborne contaminants for a defined period of time, because of the inevitable variations in equipment design, filling techniques etc. The company stresses that it is therefore vital that museums and galleries consider competitive readings of different media, to ensure they are employing the most effective filter material available. The carbon supplied to the National Gallery retains an adsorption capacity which can cope with not only the contaminants found in day-today pollution, but which can adsorb the unusually high levels of contaminants required during pollution episodes, such as those in London in December 1991 and this summer. In short, the National Gallery needed a very high-quality filter performance to satis& its conservation needs. By testing the carbon after an agreed period, Sutcliffe Speakman can estimate the levels of contaminant present and evaluate the renewal time. Test results are vital to ensure that the filter medium is operating satisfactorily. To underline this view, the UK Building Services Research & Information Association is currently working on a f150,OOO research project on advanced air filtration, with 50% funded by the Department of the Environment, to examine a variety of techniques - including activated carbons - to remove gaseous pollutants from air streams. In particular, the project will

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address the test methods employed, in order to verify their effectiveness, and the ultimate aim is to develop a draft test standard. Specialist impregnated carbon manufacturers hope that this will provide a muchneeded benchmark against which to evaluate different filter media, and so help galleries in the assessment and provision of different carbons. The problem of pollution is escalating, not diminishing, and the need to secure practical protection has never been more important. In reacting now, galleries can put an end to the unseen sources of material decay, by investing in systems which can effectively maintain a controlled environment. Guardian Speciality Activated Carbon is a trao!mmrk of Sutcliffe Speakman Carbons Ltd.

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