Influence of epilithic microorganisms on the surface temperature of building walls

Abstract

Despite numerous investigations on the role of epilithic microorganisms in the biodegradation and weathering of historical monuments, the influence of cyanobacteria (cyanophytes), green algae, and lichens on the surface temperature of outer walls of buildings is only poorly understood. Reported herein are the results of a combined microscopic and infrared imaging radiometry study focusing on the localization of microorganisms on mortar walls in Israel, and on the temperature regime on the surfaces of such colonized walls. We decided to investigate whether such lithobionts could affect the microclimate on and around buildings in rural and urban areas. Scanning electron microscopy revealed the presence of unicellular cyanobacteria, multicellular colonies of the cyanobacterium Gloeocapsa biformis st. dermochrous, and unicellular Trebouxia-like green algae on mortar wall surfaces. Older walls were found to be covered by the lichen Caloplaca citrina, which changed the blackish colour of these walls into a lemon yellow. We found that blackish surfaces on mortar walls colonized mostly by cyanobacteria were up to 8 °C warmer than noncolonized areas, which suggests that such microorganisms may affect the temperature regime on walls in built-up areas. Key words: lithobionts, infrared radiometry.