Challenges in remote sensing of CCN concentration An assessment based on airborne observations of AOD, CCN, chemical composition, size distribution, light scattering/absorption and humidity response over North America

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Challenges in remote sensing of CCN
concentrationAn assessment based on airborne
observations of AOD, CCN, chemical composition,
size distribution, light scattering/absorption
and humidity response over North America

• Yohei Shinozuka, Jens Redemann, Phil Russell,
  John Livingston, Roy Johnson, S. Ramachandran,
  Qin Zhang (NASA Ames Research Center),
• Tony Clarke, Steve Howell, Volodia Kapustin, Vera
  Brekhovskikh, Cameron McNaughton, Steffen Freitag
  (University of Hawaii),
• Terry Lathem, Thanos Nenes (Georgia Institute of
  Technology)
• NASA Postdoctoral Program, yohei_at_hawaii.edu

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In this talk

• Goal and method
• Preliminary findings

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Goal

• To assess challenges in remote sensing of CCN
  concentration
• To quantify uncertainties associated with
• aerosol chemical composition,
• size distribution,
• humidity response of light extinction and
• vertical structure,
• using ARCTAS data.

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Andreae, ACP 2009 Campaign averages.
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AOD and CCN Concentration

• The CCN concentration can be constrained by AOD
  to within a factor of 3

Georgia Tech
AATS-14
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AOD and CCN Concentration

• The CCN concentration can be constrained by AOD
  to within a factor of 3, and

• by the light extinction of dried particles, a
  factor of 2.

Georgia Tech
Georgia Tech
AATS-14
HiGEAR (U. Hawaii) nephPSAP
Difference is attributable to the vertical
structure and humidity response of light
extinction.
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ARCTAS Airborne Measurements

• humidity response of light extinction (fRH nephs)
• vertical structure (AATS-14, nephPSAP, lidar)
• aerosol chemical composition (AMS, SP2)
• size distribution (DMA, OPC)
• CCN concentration (CCN counter)
• for isolating the factors affecting the
  relationship of column integral optical
  properties to near-surface CCN concentration.

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CCN Diameter

• The critical dry diameter at 0.3 supersaturation
  (right axis) derived from direct CCN measurement
  and long DMA size distribution is larger than 100
  nm for 65 of ARCTAS Canada data, including
  almost all in forest fire smoke (high extinction
  horizontal axis) near the surface (filled
  marker).

Georgia Tech CCN counter HiGEAR (U. Hawaii) long
DMA, neph, PSAP
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Comparing sunphotometer and nephPSAP measurements
450 nm
Layer AOD for vertical profiles with ?alt. gt1
km HiGEAR layer AODs were typically within
(100.02) of the AATS-14. Russell et al.
poster Thurs. PM Shinozuka et al., in
preparation
? AOD/(100 m) for segments of vertical profiles
with ?alt. 100 m.
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Example Extinction Spectra

• Two extinction spectra of
• similar near-UV extinction coefficients
• different near-IR wavelength dependences
• vastly different number concentrations

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Optically constraining particle concentration

• The number concentration of fine particles (100
  400 nm) per extinction tends to increase with the
  extinction Angstrom exponent for comparable
  wavelengths, as expected.

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Optically constraining particle concentration

• The relationship is stratified by the wavelength
  dependence of near infrared extinction.

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AATS-14 fine-mode fraction compared with in situ
data

• FMF derived from the spectral curvature after
  ONeill et al. 2001.
• SMF measured with nephPSAP, with and without an
  impactor.
• More on AATS-14 tomorrow Redemann et al. talk
  815 AM, Russell et al. and Livingston et al.,
  poster afternoon

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Conclusions

• Among the NASA P-3 data during ARCTAS Canada,
• the CCN concentration below 1 km can be
  constrained by AOD to within a factor of 3, and
  by dry extinction, 2.
• The critical dry diameter derived for 0.3
  supersaturation is larger than 100 nm for most
  cases.
• Near UV and near IR extinction helps to constrain
  the number concentration of fine particles.
• We are in the process of quantifying the factors
  that affect the relationship of aerosol optical
  properties to near-surface CCN concentration.

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Extra slides
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Including all altitudes, note the log scale.
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Figures not used in the text.
The hygroscopicity parameterization by Petters
and Kreidenweis 2007
Approximation where ? is large,
? is a function of critical diameter (Dd) and
supersaturation (Sc), when surface tension (ss/a)
and temperature (T) are assumed to be
constant. Dd ?(-1/3) 70 nm at 0.2
supersaturation
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aerosol composition and smoke type
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White smoke from smoldering fires
White smoldering and black flaming identified
based on Tony Clarkes flight report.
Dark smoke from flaming fires
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Smoke after evolution, or pollution from other
sources? To be investigated.
White smoke from smoldering fires
Aerosol evolution in downwind transport?
Characterization of smoke types and age with the
wavelength dependence of scattering and SSA
Dark smoke from flaming fires