Changing patterns of soiling and microbial growth on building stone in Oxford, England after implementation of a major traffic scheme

Surfaces of freshly cut Bath limestone exposed along various roadsides before and after the reduction of traffic in the historical city centre of Oxford, England (following the Oxford Transport Strategy or OTS), presented an opportunity to investigate changes in soiling and fungal growth in relation to changing traffic pollution. Spectrophotometric data using an X-Rite SP68 sphere spectrophotometer provided quantitative information on soiling before and after the OTS. Scanning electron microscopy (SEM) provided a means to view and quantify the microbial inhabitants in detail, using a technique which registered and counted branching beaded structures. Results indicated that at Longwall Street soiling became more pronounced and microbial cover lower, with the reverse occurring at High Street where the greatest improvements in surface lightness were found. Other sites showed less clearcut responses in soiling and microbial growth. Overall, microbial growth was pronounced within hollows on stone surfaces before the OTS, with some signs of spreading of growths away from hollows after the OTS. A complex relationship between air pollution, soiling, and microfloral growths is revealed by the study which needs to be taken into account in soiling management strategies.