TY - JOUR
T1 - Radiative absorption enhancements by black carbon controlled by particle-to-particle heterogeneity in composition
AU - Fierce, Laura
AU - Onasch, Timothy B.
AU - Cappa, Christopher D.
AU - Mazzoleni, Claudio
AU - China, Swarup
AU - Bhandari, Janarjan
AU - Davidovits, Paul
AU - Al Fischer, D.
AU - Helgestad, Taylor
AU - Lambe, Andrew T.
AU - Sedlacek, Arthur J.
AU - Smith, Geoffrey D.
AU - Wolff, Lindsay
N1 - Publisher Copyright:
© 2020 National Academy of Sciences. All rights reserved.
PY - 2020/3/10
Y1 - 2020/3/10
N2 - Black carbon (BC) absorbs solar radiation, leading to a strong but uncertain warming effect on climate. A key challenge in modeling and quantifying BC’s radiative effect on climate is predicting enhancements in light absorption that result from internal mixing between BC and other aerosol components. Modeling and laboratory studies show that BC, when mixed with other aerosol components, absorbs more strongly than pure, uncoated BC; however, some ambient observations suggest more variable and weaker absorption enhancement. We show that the lower-than-expected enhancements in ambient measurements result from a combination of two factors. First, the often used spherical, concentric core-shell approximation generally overestimates the absorption by BC. Second, and more importantly, inadequate consideration of heterogeneity in particle-to-particle composition engenders substantial overestimation in absorption by the total particle population, with greater heterogeneity associated with larger model–measurement differences. We show that accounting for these two effects—variability in per-particle composition and deviations from the core-shell approximation—reconciles absorption enhancement predictions with laboratory and field observations and resolves the apparent discrepancy. Furthermore, our consistent model framework provides a path forward for improving predictions of BC’s radiative effect on climate.
AB - Black carbon (BC) absorbs solar radiation, leading to a strong but uncertain warming effect on climate. A key challenge in modeling and quantifying BC’s radiative effect on climate is predicting enhancements in light absorption that result from internal mixing between BC and other aerosol components. Modeling and laboratory studies show that BC, when mixed with other aerosol components, absorbs more strongly than pure, uncoated BC; however, some ambient observations suggest more variable and weaker absorption enhancement. We show that the lower-than-expected enhancements in ambient measurements result from a combination of two factors. First, the often used spherical, concentric core-shell approximation generally overestimates the absorption by BC. Second, and more importantly, inadequate consideration of heterogeneity in particle-to-particle composition engenders substantial overestimation in absorption by the total particle population, with greater heterogeneity associated with larger model–measurement differences. We show that accounting for these two effects—variability in per-particle composition and deviations from the core-shell approximation—reconciles absorption enhancement predictions with laboratory and field observations and resolves the apparent discrepancy. Furthermore, our consistent model framework provides a path forward for improving predictions of BC’s radiative effect on climate.
KW - Absorption enhancement
KW - Aerosol mixing state
KW - Black carbon
KW - Direct radiative forcing
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U2 - 10.1073/pnas.1919723117
DO - 10.1073/pnas.1919723117
M3 - Article
C2 - 32098848
AN - SCOPUS:85081682846
SN - 0027-8424
VL - 117
SP - 5196
EP - 5203
JO - Proceedings of the National Academy of Sciences of the United States of America
JF - Proceedings of the National Academy of Sciences of the United States of America
IS - 10
ER -