title: Black carbon absorption at the global scale is affected by particle-scale diversity in composition.
abstract: Atmospheric black carbon (BC) exerts a strong, but uncertain, warming effect on the climate. BC that is coated with non-absorbing material absorbs more strongly than the same amount of BC in an uncoated particle, but the magnitude of this absorption enhancement (Eabs) is not well constrained. Modelling studies and laboratory measurements have found stronger absorption enhancement than has been observed in the atmosphere. Here, using a particle-resolved aerosol model to simulate diverse BC populations, we show that absorption is overestimated by as much as a factor of two if diversity is neglected and population-averaged composition is assumed across all BC-containing particles. If, instead, composition diversity is resolved, we find Eabs=1-1.5 at low relative humidity, consistent with ambient observations. This study offers not only an explanation for the discrepancy between modelled and observed absorption enhancement, but also demonstrates how particle-scale simulations can be used to develop relationships for global-scale models.
authors: Department of Environmental and Climate Sciences , Brookhaven National Laboratory, Upton, New York 11973, USA.|Visiting Scientists Program, University Corporation for Atmospheric Research, Boulder, Colorado 80307, USA.
authors: Laura
authors: L
authors: Fierce
authors: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors: Tami C
authors: TC
authors: Bond
authors: NASA Goddard Institute for Space Studies, New York City, New York 10025, USA.|The Earth Institute, Columbia University, New York City, New York 10025, USA.
authors: Susanne E
authors: SE
authors: Bauer
authors: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors: Francisco
authors: F
authors: Mena
authors: Department of Atmospheric Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
authors: Nicole
authors: N
authors: Riemer