Monitoring of atmospheric pollutants by passive sampling for the protection of historic buildings and monuments.

When considering the various possibilities to assess the effects of SO2 and NO2 on historic buildings and monuments, a distinction can be made according to the completeness of the scope of the assessment itself. A first approach can be limited to gathering data as they become available through the official bodies established under air quality legislation. This approach is based on a single point measurement where a "general purpose" monitoring station is located, often quite far from the monument to protect and often without investigating local and temporal variations. A more comprehensive assessment should include a generalisation that covers the territory. This can be made on the basis of the knowledge of the spatial distribution of concentrations and the knowledge of the causes of air pollution. Passive samplers allow the measurement of air quality in numerous sites and to assess the pollutant spatial distribution over a large area with a high resolution. As an application of the method, the spatial distribution of SO2 and NO2 in the city of Siracusa, Sicily, Italy, has been studied to identify areas of high deposition fluxes in relation to the protection of buildings and monuments of the historic centre.