Black Carbon Trends

Declining Concentrations of Black Carbon

Long-term pollutant concentration trends can be useful for evaluating air quality effects of emission controls and historical transitions in energy sources.

A recent study employed archival records of coefficient of haze (COH), a now-retired measure of light-absorbing particulate matter, to reconstruct historical black carbon concentrations at urban locations in the United States. Estimated BC concentrations in ten states stretching from the East to West Coast decreased markedly between 1965 and 1980: 5-fold in Illinois, Ohio, and Virginia, 4-fold in Missouri, and 2.5-fold in Pennsylvania.

From the mid-1960s to the early 2000s, annual average black carbon concentrations in New Jersey and California decreased from 13 to 2 µg m3 and 4 to 1 µg m3, respectively, despite concurrent increases in fossil fuel consumption from 1.6 to 2.1 EJ in New Jersey and 4.2 to 6.4 EJ in California. New Jersey's greater reliance on black carbon-producing heavy fuel oils and coal in the 1960s and early 1970s and subsequent transition to cleaner fuels explains why the decrease was larger in New Jersey than California.

Over the period of study, declining concentrations of black carbon, a potent and shortlived climate warming pollutant, contrast increasing fossil fuel CO2 emissions in the U.S.