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Soot Superaggregates from Flaming Wildfires and Their Direct Radiative ForcingWildfires contribute significantly to global soot emissions, yet their aerosol formation mechanisms and resulting particle properties are poorly understood and parameterized in climate models. The conventional view holds that soot is formed via the cluster-dilute aggregation mechanism in wildfires and emitted as aggregates with fractal dimension D(sub f) approximately equals 1.8 mobility diameter D(sub m) (is) less than or equal to 1 micron, and aerodynamic diameter D(sub a) (is) less than or equal to 300 nm. Here we report the ubiquitous presence of soot superaggregates (SAs) in the outflow from a major wildfire in India. SAs are porous, low-density aggregates of cluster-dilute aggregates with characteristic D(sub f) approximately equals 2.6,D(sub m) (is) greater than 1 micron, and D(sub a) is less than or equal to 300 nm that form via the cluster-dense aggregation mechanism.We present additional observations of soot SAs in wildfire smoke-laden air masses over Northern California, New Mexico, and Mexico City. We estimate that SAs contribute, per unit optical depth, up to 35% less atmospheric warming than freshly-emitted (D(sub f) approximately equals 1.8) aggregates, and approximately equals 90% more warming than the volume-equivalent spherical soot particles simulated in climate models.

Document ID
20140017420
Acquisition Source
Goddard Space Flight Center
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Chakrabarty, Rajan K.
(Washington Univ. Saint Louis, MO, United States)
Beres, Nicholas D.
(Nevada System of Higher Education Reno, NV, United States)
Moosmuller,Hans
(Nevada System of Higher Education Reno, NV, United States)
China, Swarup
(Michigan Technological Univ. Houghton, MI, United States)
Mazzoleni, Claudio
(Michigan Technological Univ. Houghton, MI, United States)
Dubey, Manvendra K.
(Los Alamos National Lab. NM, United States)
Liu, Li
(Columbia Univ. New York, NY, United States)
Mishchenko, Michael I.
(NASA Goddard Inst. for Space Studies New York, NY, United States)
Date Acquired
December 16, 2014
Publication Date
July 1, 2014
Publication Information
Publication: Scientific Reports
Publisher: Nature Publishing Group
Volume: 4
Subject Category
Meteorology And Climatology
Environment Pollution
Report/Patent Number
GSFC-E-DAA-TN16365
Funding Number(s)
CONTRACT_GRANT: NNX10AU63A
CONTRACT_GRANT: NNX10AR89A
CONTRACT_GRANT: NNX11AB79G
WBS: WBS 281945.02.03.03.27
Distribution Limits
Public
Copyright
Public Use Permitted.
Keywords
SAS
climate models
soot
deuterium fluorides
aggregates
aerosols
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