Distribución pasada y futura del color en edificios históricos de piedra

Abstract

The patterns of colour on stone buildings change with time. Buildings were blackened by coal soot, but now mostly diesel particles and in future, wind-driven rain may alter the patterns and oxidation of surface organics. Colouring patterns that outline or shadow architectural elements are publicly more acceptable than those that cut across them e.g. rain streaking. Thresholds of acceptability for blackening can be related to soot loading. When soot loading of the ambient air is high, e.g. near busy roads, buildings are dark and typically viewed as unacceptable. However at lower concentrations (2-3 μg m-3 elemental carbon), building appearance is typically seen as more acceptable. The future offers a potential for variation in building colour, arising through different biological growth under changing climates or the presence of different pollutants. In future urban atmospheres more dominated by organic pollutants a yellowing process may be more important. Diesel soot has many organic compounds that can oxidise to brownish-coloured humic-like (HULIS) materials.