Soiling and microbial colonisation on urban roadside limestone: a three year study in Oxford, England
Section snippets
Background
As defined by Newby et al. [1] soiling of building materials is ‘an optical effect, a darkening of the surface that can be measured as a change in light reflectance, and is generally related to the deposition of airborne particulate matter onto the building surface’. Soiling can result from the deposition of particulates (from natural sources as well as pollutants), from chemical changes to the surface (e.g. oxidation crusts or conservation treatments) and from microorganism growth. Many if not
Aims and objectives
The main aim of this study was to investigate the spatial and temporal pattern of soiling and microbial colonization on stone exposed adjacent to roads with different traffic flows in Oxford. In order to do this an exposure trial was set up, using lighting columns as a way of mounting fresh stone samples near the side of roads and away from vandalism.
Materials and methods
Ten exposure trial sites were established; three along a busy road with a lot of heavy diesel traffic (High Street), three along a reasonably busy road with few buses (Longwall Street); three along a relatively quite road (Broad Street) and one in an urban garden in the city centre but ca. away from any roads (Worcester College gardens). Information on traffic flows and NO2 concentrations at the different sites is given in Table 1. Although the street with the highest traffic levels (High
Results
Fig. 2 shows the spectrophotometry results from each site along the three roads studied and the urban background site. Darker samples plot towards the left-hand side of the horizontal axis (i.e. lower values), and more colourful samples plot towards the top of the y-axis (i.e. higher c values). Fig. 2a shows the trend for the High Street sites with rapid darkening (in comparison with the control value) over each exposure time period. A gentle decrease in colourfulness is also recorded. The
Discussion and conclusions
Over a 3 year period soiling rates (as measured by colour changes by spectrophotometry) vary between an urban background site (with low amounts of soiling even after 3 years) and a busy road, with much diesel traffic (with a high soiling rate over 3 years). The two roads with low to medium traffic flows and relatively low concentrations of diesel-powered vehicles show intermediate soiling rates. Standard microbiological techniques to quantify microorganism presence do not show any clear
Acknowledgements
We are grateful to the EMITS partners, as well as Dr. Mark Taylor, Renate Kort, Clare Cox and Dr. Tim Yates for help with providing data and support for this project, and to the EU Life Programme for funding.
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