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Title: Morphology of diesel soot residuals from supercooled water droplets and ice crystals: Implications for optical properties

Freshly emitted soot particles are fractal-like aggregates, but atmospheric processing often transforms their morphology. Morphology of soot particles plays an important role in determining their optical properties, life cycle and hence their effect on Earth’s radiative balance. However, little is known about the morphology of soot particles that participated in cold cloud processes. Here we report results from laboratory experiments that simulate cold cloud processing of diesel soot particles by allowing them to form supercooled droplets and ice crystals at -20 and -40°C, respectively. Electron microscopy revealed that soot residuals from ice crystals were more compact (roundness~0.55) than those from supercooled droplets (roundness ~0.45), while nascent soot particles were the least compact (roundness~0.41). Optical simulations using the discrete dipole approximation showed that the more compact structure enhances soot single scattering albedo by a factor up to 1.4, thereby reducing the top-of-the-atmosphere direct radiative forcing by ~63%. Lastly, these results underscore that climate models should consider the morphological evolution of soot particles due to cold cloud processing to improve the estimate of direct radiative forcing of soot.
 [1] ;  [2] ;  [3] ;  [4] ;  [2] ;  [2] ;  [2] ;  [2] ;  [2] ;  [5] ;  [6] ;  [6] ;  [2] ;  [2] ;  [4]
  1. Michigan Technological Univ., Houghton, MI (United States); Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
  3. Naval Postgraduate School, Monterey, CA (United States)
  4. Michigan Technological Univ., Houghton, MI (United States)
  5. Los Alamos National Lab. (LANL), Los Alamos, NM (United States); Univ. of Colorado, Boulder, CO (United States)
  6. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Report Number(s):
Journal ID: ISSN 1748-9326; KP1704020; KP1701000
Grant/Contract Number:
AC05-76RL01830; SC0010019
Published Article
Journal Name:
Environmental Research Letters
Additional Journal Information:
Journal Volume: 10; Journal Issue: 11; Journal ID: ISSN 1748-9326
IOP Publishing
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org:
Country of Publication:
United States
54 ENVIRONMENTAL SCIENCES; soot; morphology; ice cloud processing; optical properties; radiative forcing
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1226403; OSTI ID: 1239045