Introduction

1. PREDICTING THE CONCENTRATIONS OF AIR POLLUTANTS INSIDE MUSEUM BUILDINGS: A WEB-BASED SOFTWARE TOOL DEVELOPED BY THE EC IMPACT PROJECT Declan Kruppa, Nigel Blades and May Cassar, Centre for Sustainable Heritage, University College London, UK The IMPACT Project The work presented here is part of a European Commission funded project entitled Innovative Modelling of Museum Pollutants and Conservation Thresholds (IMPACT). IMPACT is an interdisciplinary research project involving universities (UCL & UEA); a research institute (NILU) with expertise in the study of airpollution; a manufacturer of pollution control equipment (EMCEL); amuseum (MNK) and as a sub-contractor an architecture practice (AP) specializing in heritageprojects, to give an end-user perspective to the research. It is developing a tool for estimating the levels of air pollution inside museum buildings and providing advice to museum managers on how to protect their collections. As well as developing the software tool described below, the IMPACT project includes a programme of laboratory measurements in order to further understanding of the interaction of atmospheric pollutants with materials. Treating a building as a single zone, the concentration of a particular gas inside it is related to the outdoor concentration by the following equation: I / O = ach / ( Vdep (S/V) + ach) where I = Indoor concentration O= Outdoor concentration ach = air exchange rate (hr-1) S/V = interior surface area (m2)/volume (m3) Vdep = deposition velocity (m/hr) The applet user interface. Data are input by the user on the left-hand panel and the pollutant I/O ratio calculated. The output is displayed numerically and graphically, as a function of air exchange rate on the right-hand panel. The I/O ratio can be converted to a concentration if the user has access to external pollution data, often available on national and regional websites. Multi-Zone Model A version of the web programme which can model the concentration of air pollutants in multi-zone buildings is currently under development. The programme interface is a drawing page where users can sketch the layout of their building; specify the interior surface finishes of the different rooms; the number of windows, doors and other air leakage paths and the typical external wind speed conditions. The model will calculate the airflow pattern in the building and the pollutant load from the user inputs. Introduction The reactive gases nitrogen dioxide (NO2), sulphur dioxide (SO2) and ozone (O3) damage artefacts in museums. Their concentrations need to be monitored and controlled. Many museums cannot afford to monitor routinely these gases. These air pollutants are generated outdoors and indoor concentrations are generally lower: the gases deposit on the internal surfaces of the building and are removed from the air. This process can be quantified by the deposition velocity Vdep of a gas. This is a measure of the rate at which a gas is deposited on a particular material. The graph below shows the variation of Vdep for NO2 to some common interior finishes. Materials such as cement and brick have a high deposition velocity whereas glass has a low deposition velocity. The Sainsbury Centre for Visual Arts, Norwich, UK. A museum of modern design with a large open-plan interior (i.e. low surface area to volume ratio) and with large areas of glass and painted metal. The model predicts that this building fabric will be a poor absorber of harmful air pollutants. Single Zone Model The equation has been incorporated into a computer model which calculates the concentration of air pollutants in museum buildings. The programme is written as a Java applet that runs via an internet browser on any computer system. The applet will be part of a website providing information for the user on interpreting results produced by the applet. The software tool is designed to encourage users to experiment with the input parameters and get a feel for their relative importance in determining the air pollution levels inside museum buildings. Interim Results As work progresses, further information on the software tool will be posted on the UCL Centre for Sustainable Heritage website (www.ucl.ac.uk/sustainableheritage) which will also host the final freely accessible software and associated website. For further information contact Declan Kruppa d.kruppa@ucl.ac.uk We would like to acknowledge the support of the EC 5th Framework Programme Key Action 4 ‘City of Tomorrow and Cultural Heritage’ for funding the IMPACT Project (Contract no. EVK4-CT-2000-0031 “IMPACT” ). The Pollution Model To calculate the air concentration of a pollutant in a room the sources and sinks for the pollutant must be summed up in a mass balance equation. For external air pollutants the source is a function of the air exchange with the outdoor air. The pollutant sinks are the surface finishes in the room, characterised by their surface area and the deposition velocity of the particular gas. The IMPACT applet running on a laptop at the Petrie Museum, UK. University College London (UCL) Centre for Sustainable Heritage Norwegian Institute for Air Research (NILU) University of East Anglia (UEA) School of Environmental Sciences Emcel Filters Ltd (EMCEL) National Museum of Krakow (MNK)