Hygroscopic Properties of Asian Aerosols

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Hygroscopic Properties of Asian Aerosols and
Their Effects on Aerosol Radiative Forcing
J. Kim, S.-C. Yoon, S.W. Kim, and A. Jefferson
SEES, Seoul National University,
Korea NOAA/CMDL, USA
The University Allied Workshop for Climate and
Environmental Modeling, 11-13 July 2005, Busan,
Korea
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Background and Motivation
IPCC TAR (p. 368-369) The treatment of the
effects of relative humidity appear to be
particularly important in determining the
radiative forcing a stronger radiative forcing
when sulfate resides near the surface because the
RH and subsequent hygroscopic growth of sulfate
particles is higher

• Short lifetime 1week (relative to GHGs)
• Spatial and temporal inhomogeneity
• Wide size range( 10-9 to 10-5 m), complex
  composition
• Physico-chemical interaction with gases and
  particles
• Complex interaction with atmospheric radiation

Source IPCC Third Assessment Report
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What is Hygroscopic Growth? Why Important?
f(RH) ? ssp(RH85)/ssp(RH40) increase of the
aerosol scattering coefficient as a result of
water uptake by the hygroscopic aerosols (e.g.,
sulfate, sea salt).
particle growth with RH increase gt increase of
light scattering by aerosols gt changes in AOD,
SSA, and asymmetry parameter gt changes in
aerosol radiative forcing at the surface and TOA
Kotchenruther et al.(JGR, 1998 and 1999)
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High Aerosol Loadings over East Asia

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Objectives of this study

• What is the characteristics of the hygroscopic
  properties of Asian aerosols?
• How do the key aerosol properties relevant to
  radiative forcing change with relative humidity?
• How much can the aerosol hygroscopic growth
  affect direct aerosol radiative forcing?

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Measurements at Gosan during ACE-Asia 2001
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f(RH) of Asian Aerosols
Smoke 1.16
Pollution Dust Smoke 2.32
Kotchenruther and Hobbs (JGR, 1998) Amazon,
Aug.Sept. 1995
Pollution 2.15
Kotchenruther et al.(JGR, 1999) US East Coast,
July 1996
This study 2001.4. 10.-5.17., Gosan
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High Variability of f(RH) in Spring
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The Change of f(RH) with increasing RH
Slide 16
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Aerosol Optical Closure Studies
MEASUED Chemical Composition of Major Aerosol
Components (Sea Salt, Water-Soluble, Soot, and
Mineral Dust)
Calculation of mass, scattering, and absorption
coefficients of single particle using an optical
model (Hess et al., 1998)
Determination of aerosol number concentration
from single particle mass data for each aerosol
component
Calculation of scattering, absorption, and
extinction coefficients using mass
scattering absorption efficiencies
Comparison with the measured and calculated
scattering and absorption coefficients
Modeling the changes of aerosol optical
properties (scattering, absorption, asymmetry
parameter, and so on) in the solar and
terrestrial spectrum range with RH
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Chemical and f(RH) Changes of PM10
PM10 Aerodynamic particle size less than 10 ?m
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Aerosol Number Size Distribution
4/10-27
4/10-12
4/25-26
TSEMS Twin Scanning Electrical Mobility Sizer
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Biomass Burning originated from NK and Russian
Forest Fires
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Closure Studies by Aerosol-Optical Model
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Chemical Apportionment of Light Extinction
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Changes of the Optical Properties by Water Uptake
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Temporal and Spatial Distribution of RH
Fig. Daily variation of hourly-averaged relative
humidity at Gosan in April 2001. The thick red
and blue line in the box indicate mean and median
value of RH each day, respectively. The boundary
of the box closest to zero indicates the 25th
percentile, and the boundary of the box farthest
from zero indicates the 75th percentile. Whiskers
below and above the box indicate the 10th and
90th percentiles. Dots below and above the box
indicate the 5th and 95th percentiles.
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Effects of RH on Aerosol Radiative Forcing
1.98
Slide 16
1.55
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Conclusion

• Large hygroscopic growth was mainly caused by
  water-soluble component (mainly composed by
  sulfate, nitrate, ammonium and OC). A
  contribution by sea salt was minor.
• The less hygroscopic growth was appeared for
  biomass burning smoke transported from NK and
  Russian boreal forest fires.
• Closure studies show that there is well
  agreement between the measured and modeled values
  for aerosol physical, chemical, and optical
  properties.
• The remarkable enhancement of aerosol radiative
  forcing due to the hygroscopic growth may be
  attributable to ubiquitous anthropogenic
  pollution over East Asia