Dirty sparrows provide a historic look at soot

Evolutionary biologist Shane G. DuBay and art historian and photographer Carl C. Fuldner of the University of Chicago were studying bird specimens in natural history museum collections when they began noticing that birds collected more than 100 years ago are much dirtier than recently collected birds. That observation led them in a new direction to use the soot embedded in bird feathers to estimate past black carbon aerosol pollution stemming from burning wood and coal (Proc. Natl. Acad. Sci. USA 2017, DOI: 10.1073/pnas.1710239114). The team used electron microscopy to gather photometric reflectance data on feathers from more than 1,300 bird specimens collected from 1880 to 2015 in the U.S. manufacturing belt, which includes Chicago, Detroit, and Pittsburgh. The researchers used the data to estimate black carbon concentrations, finding that levels peaked between 1900 and 1910 and that levels before 1910 were higher than previously thought—estimates were inexact until the mid-1950s when atmospheric sampling became common. Black carbon remained relatively high in the sampling region until about 1960, when concentrations began to fall because of more efficient coal burning, environmental regulations, and a shift to cleaner-burning natural gas. Besides noting the reduced breathing hazard to people and wildlife over time, the researchers say their findings suggest black carbon’s contribution to past climate change has been underestimated and that the results should help improve models estimating future climate change.