Why did pollution in the 19th century make the bark of many trees go black?

In the 19th century, pollution from industrial activities, particularly coal burning, released large amounts of soot and particulate matter into the atmosphere. This soot settled on tree bark, coating it and causing it to appear black. The phenomenon was especially pronounced in urban areas, where factory emissions were concentrated. This change in coloration also impacted the visibility of tree species, influencing natural selection, as darker trees became more prevalent in polluted environments.