Journal
PHYSICAL REVIEW LETTERS
Volume 121, Issue 21, Pages -Publisher
AMER PHYSICAL SOC
DOI: 10.1103/PhysRevLett.121.218701
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Funding
- U.S. National Science Foundation [AGS-1455215, CBET-1511964, AGS-PRF-1624814]
- National Aeronautics and Space Administration Radiation Sciences Program [NNX15AI66G]
- Atmospheric Radiation Measurement (ARM) Program - US Department of Energy (DOE), Office of Biological and Environmental Research (OBER)
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Black carbon (BC) aerosol, the strongest absorber of visible solar radiation in the atmosphere, contributes to a large uncertainty in direct radiative forcing estimates. A primary reason for this uncertainty is inaccurate parametrizations of the BC mass absorption cross section (MAC(Bc)) and its enhancement factor (E-MAC(BC))-resulting from internal mixing with nonrefractory and nonlight absorbing materials-in climate models. Here, applying scaling theory to numerically exact electromagnetic calculations of simulated BC particles and observational data on BC light absorption, we show that MAC(BC) and E-MAC(BC) evolve with increasing internal mixing ratios in simple power-law exponents of 1/3. Remarkably, MAC(BC) remains inversely proportional to the wavelength of light at any mixing ratio. When mixing states are represented using mass-equivalent core-shell spheres, as is done in current climate models, it results in significant underprediction of MAC(BC). We elucidate the responsible mechanism based on shielding of photons by a sphere's skin depth and establish a correction factor that scales with a 3/4 power-law exponent.
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