More Like Shades of Gray: the Effects of Black Carbon in Aerosols

McComiskey, A. C., Brookhaven National Laboratory

Aerosol Properties

Aerosol Life Cycle

Cappa CD, TB Onasch, P Massoli, DR Worsnop, TS Bates, ES Cross, P Davidovits, J Hakala, KL Hayden, BT Jobson, KR Kolesar, DA Lack, BM Lerner, SM Li, D Mellon, I Nuaaman, JS Olfert, T Petaja, PK Quinn, C Song, R Subramanian, EJ Williams, and RA Zaveri. 2012. "Radiative Absorption Enhancements Due to the Mixing State of Atmospheric Black Carbon." Science, 337(6098), 10.1126/science.1223447.

Black to the core: Scientists are combining field and laboratory measurements to understand more about the physical properties of aerosols containing black carbon and how they impact global warming.

Black to the core: Scientists are combining field and laboratory measurements to understand more about the physical properties of aerosols containing black carbon and how they impact global warming.

Every day, the incomplete combustion of fossil fuels, biofuels, and biomass forms black carbon particles in the atmosphere. Once deposited in the Arctic, these black carbon particles darken the surface of snow and ice, increasing the amount of the sun’s energy converted to heat rather than reflected back to space. At a larger scale, sunlight absorbed by atmospheric black carbon is also converted into heat and increases temperatures, affecting atmospheric circulation and cloud development. What researchers want to know is how much heating takes place and how that change affects global climate.

Through measurements in the field and in the laboratory, research projects in the last year have advanced the understanding of the impacts from black carbon aerosol in the following ways:

  • In examining how the amount of black carbon aerosol and the size of snow grains affect heat generation at the Earth’s surface, researchers confirmed model predictions and found that the larger the grains of snow, the more heat was generated by the black carbon contamination.
  • Research into the different physical characteristics of individual black carbon particles mixed together with other components—commonly modeled as a light-absorbing inner core surrounded by a non-absorbing shell—revealed that many particles are actually shaped differently.
  • Measurements of black carbon in the atmosphere around urban centers in California indicate that when black carbon mixes with other atmospheric components, the particle’s ability to absorb light and generate heat is significantly less pronounced than often simulated in global climate models.

Various research efforts coupled laboratory and field measurements to yield a better understanding of the concentrations and physical characteristics of aerosols containing black carbon. The research confirmed that black carbon contamination on snow contributes to near world-wide melting of ice, which exacerbates global warming. Using sophisticated instruments, scientists also determined that black carbon particles can adopt a range of internal configurations, which may affect their ability to absorb sunlight and heat the atmosphere. Finally, measurements at specific locations showed that black carbon’s influence on light absorption may need to be modeled differently. When combined, the research demonstrates that a more accurate representation of the physical characteristics of black carbon in models can greatly affect the calculated influence of black carbon on global warming and supports development of more effective ways to mitigate its impacts.

To determine the effect of black carbon and snow grains on heating, researchers generated snow in the laboratory and measured the effects of adding various amounts of black carbon. To learn more about the structure of black carbon, scientists used the Single Particle Soot Photometer, or SP2, one of the few instruments that can quantitatively characterize black carbon down to individual particles. Two of the projects also used observations from a large field measurement campaign funded by DOE, the Carbonaceous Aerosols and Radiative Effects Study (CARES), as the basis for their analyses.

References: Cappa, CD, et al. 2012. “Radiative absorption enhancements due to the mixing state of atmospheric black carbon.” Science 337:1078, doi:10.1126/science.1223447.

Hadley, OL, and TW Kirchstetter. 2012. “Black-carbon reduction of snow albedo.” Nature Climate Change Letters: doi:10.1038/NCLIMATE1433.

Sedlacek, AJ, et al. 2012. “Determination of and evidence for non-core-shell structure of particles containing black carbon using the Single-Particle Soot Photometer (SP2).” Geophysical Research Letters 39: L06802, doi:10.1029/2012GL050905.