Stone-built heritage as a proxy archive for long-term historical air quality: A study of weathering crusts on three generations of stone sculptures on Broad Street, Oxford

Katrin Wilhelm; Jack Longman; Scott Allan Orr; Heather Viles

doi:10.1016/j.scitotenv.2020.143916

Stone-built heritage as a proxy archive for long-term historical air quality: A study of weathering crusts on three generations of stone sculptures on Broad Street, Oxford

Sci Total Environ. 2021 Mar 10:759:143916. doi: 10.1016/j.scitotenv.2020.143916. Epub 2020 Dec 3.

Authors

Katrin Wilhelm¹, Jack Longman², Scott Allan Orr³, Heather Viles⁴

Affiliations

¹ Oxford Resilient Buildings and Landscapes Laboratory (OxRBL), School of Geography and the Environment, University of Oxford, South Parks Road, Oxford OX1 3QY, UK. Electronic address: Katrin.wilhelm@ouce.ox.ac.uk.
² Marine Isotope Geochemistry, Institute for Chemistry and Biology of the Marine Environment (ICBM), University of Oldenburg, Carl-von-Ossietzky-Str. 9-11, 26129 Oldenburg, Germany. Electronic address: jack.longman@uni-oldenburg.de.
³ Bartlett School Environment, Energy and Resources, Faculty of the Built Environment, University College London, UK. Electronic address: scott.orr@ucl.ac.uk.
⁴ Oxford Resilient Buildings and Landscapes Laboratory (OxRBL), School of Geography and the Environment, University of Oxford, South Parks Road, Oxford OX1 3QY, UK. Electronic address: Heather.viles@ouce.ox.ac.uk.

PMID: 33338691
DOI: 10.1016/j.scitotenv.2020.143916

Abstract

Black crusts on historic buildings are mainly known for their aesthetic and deteriorative impacts, yet they also can advance air pollution research. Past air pollutants accumulate in distinct layers of weathering crusts. Recent studies have used these crusts to reconstruct pollution to improve our understanding of its effects on stone-built heritage. However, the majority of the studies provide only coarse resolution reconstruction of pollution, able to distinguish between 'inner = old' and 'outer = modern' crust layers. In contrast, very few studies have linked distinct periods of exposure to pollution variations in the composition of these crusts. Here we address this research gap by developing a finer-scale resolution pollution record. Our study explored the unique configuration of limestone sculptures in central Oxford, which have been exposed over the last 350 years to three different periods of atmospheric pollution; the early Industrial Revolution, the Victorian period and the 20th century. When the first two generations of sculptures were moved to less polluted areas, their 'pollution clocks' were stopped. Here we discuss the potential of investigating the 'pollution clock' recorded in the geochemical makeup of each sculpture generation's weathering crust layers. We found the analysed crusts record clear changes related to the evolution of modes of transport and industrial and technological development in Oxford. Higher levels of Arsenic (As), Selenium (Se) are linked to pollution from coal burning during Victorian times and Lead (Pb) indicated leaded petrol use in modern times. Our work shows that stone-built heritage with a known history of air pollution exposure allows improving the pollution reconstruction resolution of these weathering crusts. The results provide the basis for calibrating long-term geochemical archives. This approach may be used to reconstruct past air quality and has the potential to inform stone weathering research and conservation, in addition to improving the reconstruction of historical pollution.

Keywords: Black crusts; Coal burning; Environmental pollution; Geochemical archives; Heavy metals; Palaeopollution.