Crusts From The Tower Of London Suggest Yellowing In The Future

In the study, Peter Brimblecombe and colleagues investigated the origin and transformation of elemental carbon (EC) and organic carbon (OC) from simple organic compounds in the black crusts that have formed over the centuries on stone walls in the tower complex. The blackening of the past, they note, is from EC in coal smoke released since the late 13th Century.

Air pollution control efforts are reducing the amount of sulfur dioxide from coal, with increased OC emissions from motor vehicle exhaust. With less sulfur dioxide (toxic to microorganisms) and more OC, microbes can grow in crusts on buildings and transform compounds contributing a color change.

"In particular, one should note that modern deposits have taken on a slightly different color and now appear more brownish," the reports states. "These changes may arise from oxidation processes in the organic rich materials. The color change is particularly evident here at the Tower of London, where yellowing may become of greater concern than the habitual blackening in the near future."

Article: "Carbon in Black Crusts from the Tower of London"

The research is scheduled for publication in the June 15 issue of ACS' Environmental Science & Technology.