Thermal response characteristics of stone: Implications for weathering of soiled surfaces in urban environments

Soiling of stone surfaces by particulate deposition increases absorption of radiant energy, raises surface/subsurface temperature gradients and accentuates rates of surface temperature change. Short-term fluctuation of raised surface temperatures, in response to variations in windspeed and cloud cover, may ultimately contribute to stone breakdown through 'fatigue' effects which reduce cohesive strength of intergranular bonds and initiate microfracture development. The effects of soiling are particularly marked for stone with low thermal conductivity and high albedo when clean. Albedo change has implications for the effectiveness of weathering processes and the durability of building stone by creating microenvironmental conditions which are more severe than those indicated by macroenvironmental regimes.