How Does Pollution Affect Construction Materials?

By Nidhi DhullReviewed by Susha Cheriyedath, M.Sc.May 15 2024

A recent study featured in the journal Sustainability examined the black crust and soiling on Lipowiec Castle in Babice, Southern Poland, revealing how pollution is impacting structures in the construction industry. The research highlighted how these historic buildings serve as natural indicators of air quality, offering valuable insights into the environmental challenges faced by the construction sector.

Background

The exteriors of historic castles and other heritage buildings, constructed from stone, are extremely vulnerable to atmospheric weathering. At the same time, particulate matter (PM), various gases (such as NO_x, CO₂, SO₂, H₂S, and HCl), and dusty pollutants from the burning of coal, other fossil fuels, vehicular emissions, and industrial activities significantly degrade air quality in both urban and rural settings. As a result, these exposed stone surfaces often darken and become covered with thin black layers known as soiling,

Additionally, a deteriorated surface layer known as black crust, composed of hard and fragile stone material, forms on parts of buildings shielded from direct rainfall or water runoff, especially in urban environments. This crust serves as a reactive surface, containing carbonaceous particles and metallic compounds from particulate matter (PM). Significant reactions on the stone surface can cause the black crust to detach. Therefore, the presence of black crust and soiling on heritage buildings can provide valuable insights into air quality over extended periods through continuous studies.

Methods

The study examined black crust and soiling on the external materials of Lipowiec Castle, a medieval structure located in southern Poland. The castle, constructed using local and partially dolomitic limestones, dolomites, other limestone types, and bricks during 20th-century renovations, displayed soiling and crust formation on the substrata of Triassic and Jurassic carbonate rocks and bricks.

Sampling occurred on the west, south, and north wings during the 2022 conservation campaign (the eastern part was inaccessible for security reasons). Samples were collected from each side at heights of approximately 1 to 1.5 meters above ground level, focusing on areas that showed signs of black crust and surface soiling on different building materials: limestone, dolomitic limestone, and a combination of dolomite and brick.

The study utilized non-destructive Raman micro-spectroscopy (RS) and scanning electron microscopy with energy-dispersive spectrometry (SEM-EDS) to analyze these crust and soiling components, secondary mineral phases, and anthropogenic PM. This analysis helped identify the components and characteristics of the black crust, providing insights into potential pollution sources affecting the castle

Study Results

The black crust analyzed on Lipowiec Castle was relatively uniform in composition, primarily consisting of gypsum with traces of hydrated magnesium sulfates in certain samples. It also contained a mix of carbonaceous matter, spherical silicon-aluminum glass particles, iron oxides, and various heavy metals including chromium, iron, manganese, copper, zinc, lead, and arsenic.

These elements are indicative of air pollution stemming from the combustion of solid fuels in both industrial power plants and local domestic furnaces, as well as from zinc-lead ore mining and smelting activities in the nearby industrial centers, which were operational until 2021.

Additionally, the crust included carbonaceous soot, siliceous fly ash, and spherical metallic particles containing iron, manganese, titanium, zinc, copper, lead, and chromium. These particles were interspersed within the sulfate crust layers rather than forming a solid, continuous layer. The presence of these dispersed carbonaceous elements suggests a self-cleaning characteristic of the castle's stone surfaces, which, when exposed to wind and rainfall, can naturally wash away some of the black deposits.

Despite its rural setting, Lipowiec Castle's proximity to large industrial and urban areas, coupled with prevailing northwest winds, subjects it to a significant influx of pollutants from these nearby centers. The specific composition of the particles analyzed reflects the influence of these sources of air pollution on the region.

Conclusion

The in-depth analysis highlighted that despite its seemingly isolated rural setting, Lipowiec Castle has endured prolonged exposure to pollution due to its proximity to major industrial hubs. Consequently, the black crust studied on the castle's surfaces serves as a valuable environmental indicator, revealing the types of air pollution affecting the region. This study is notably the first to investigate pollution impacts on this historical site and its rural surroundings.

The comprehensive examination of soiling and black crust on the historic stones provides a unique lens to assess air pollution trends and historical levels. This information is crucial for effective heritage management, aiding in the development of projects that enhance the valorization of such sites.

Overall, the research methodologies employed in this study offer a model for preventive conservation of heritage buildings. By identifying environmental risks early, these methods enable the implementation of effective strategies to mitigate potential damage, thus ensuring the prolonged preservation of our architectural heritage. This approach not only helps in maintaining air quality and environmental safety but also enhances the health and longevity of both the monuments and the communities around them.

Journal Reference

Marszałek, M., Dudek, K., & Gaweł, A. (2024). Black Crust from Historic Buildings as a Natural Indicator of Air Pollution: A Case Study of the Lipowiec Castle, Babice, Southern Poland. Sustainability, 16(9), 3816. https://doi.org/10.3390/su16093816, https://www.mdpi.com/2071-1050/16/9/3816

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