Elsevier

Building and Environment

Volume 38, Issues 9–10, September–October 2003, Pages 1217-1224
Building and Environment

Soiling and microbial colonisation on urban roadside limestone: a three year study in Oxford, England

https://doi.org/10.1016/S0360-1323(03)00078-7Get rights and content

Abstract

An exposure programme has been carried out to study the impact of traffic on building limestone soiling and decay. After 1–3 years of exposure it was found that busier roads experience faster soiling, and all sites show extensive colonization by bacteria, fungi, and phototrophs, deposition of particulate matter and calcite dissolution. In all cases, fungal colonisation is preferentially located within hollows on the stone surface. Fungi appear to be an important component of soiling as confirmed by SEM observations and isolation experiments. However, no clear pattern of microorganism colonisation has been observed between sites, although the urban background site experienced higher colonization of all organisms after three years.

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. 200m 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 L 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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