Recording of pre-industrial atmospheric environment by ancient crusts on stone monuments

The interaction between today’s polluted urban atmosphere and materials leads to the formation of sulphated black crusts containing industrial fly-ash. While many historical documents report the existence of polluted air in towns prior to the modern industrial era, such descriptions have not so far been substantiated by any scientific analysis of samples of older interactions. A new approach is proposed, based on the study of crusts found in Arles and Bologna, which formed in the periods 1180–1636, and 1530–1887, respectively. They are grey, mostly calcitic, and contain wood debris and micrometric siliceous or alumino-silicated spherules. The same tracers were also encountered in the smoke from experimental wood fires. This approach confirms the presence of air polluted by wood combustion in the towns of Southern France and Northern Italy during the Medieval up to pre-industrial age. Such information, near to the source, completes the evidence provided in written documents, as well as the data obtainable, farther from the sources, using core samples of glaciers, lakes and marine sediments.