Radiative%20Effects%20of%20Atmospheric%20Aerosols%20and%20Regional%20Haze

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Radiative Effects of Atmospheric Aerosols and
Regional Haze

• Jin Xu
• DAS Science Talk
• February 17, 2004

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Aerosol Radiative Effects

• Regional Haze, Air Quality and Visibility (COHA,
  FAQS)
• Photochemical Reaction (Atlanta Supersite)
• Photosynthesis and Crop Yields (ChinaMAP)
• Climate Change - Whitehouse Effect (ACE-Asia,
  ChinaMAP)
• Directly - Scattering Absorption
  of Solar Radiation
• Indirectly - Modifying Cloud Properties

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Scattering and Absorption of Light by Aerosols
ILight Detector (W/m2)
LPath Length
IoLight Source (W/m2)
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Scattering Model of an Aerosol Layer
F0 incident solar flux (wm-2) Ac fraction of
the surface covered by clouds Ta fractional
transmittance of the atmosphere
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Aerosol Scattering and Absorption Coefficients
Where l Wavelength (m) Dp Particle Diameter
(m) ascat, aabs Mass Scattering and Absorption
Efficiencies (m2/g) ri Refractive Index m(Dp)
Aerosol Mass Size Distribution
Note Aerosol Extinction Depends on Wavelength
(Ångstrom Exponent, å - d log ?ext / d log ? ),
Chemical Composition, and Size
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Major Aerosol Chemical Species that Contribute to
the Light Extinction

• Sulfate Aerosols
  SO2 from Fossil Fuel
  Combustion
• Carbonaceous Aerosols
• Organic Compounds (OC)
• Biomass Burning, Automobile Emissions, Fossil
  Fuel Combustion, Gas-to-particle Conversion of
  Hydrocarbons
• Elemental Carbon (EC) (Absorption, Warming
  Effect)
• Incomplete Combustion of Fossil and Biomass
  Fuels
• Mineral Dust Aerosols
  Desert Dust,
  Construction, Road Dust
• Nitrate Aerosols
  Industrial and Automobile
  Emissions

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Visibility Impairment of Aerosols Based on
Aerosol Chemical Speciation Data

• Bext 3F(RH)Sulfate 3F(RH)Nitrate 4OMC
  10LAC 1Soil 0.6CM 10 (Rayleigh Gas
  Scattering)
• Visual Range (V.R.) K/Bext
• Where K is the Koschmieder Coefficient the log
  of the contrast threshold of the human eye, K
  3 3.9

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GOES View of the Dust Streak Across North
America, April 17
GOES10 view of dust streak on the morning of
April 17
GOES8 view of dust streak on the evening of April
17
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Transport of the Asian dust to the United States
The common weather conditions are usually
associated with the upper low pressure trough /
cut-ff low and surface low pressure system (low
formed by a strong cyclonic vortex) over
northeast China and north Korea Kim et al.,
2002. Under this weather conditions, Asian dust
can move fast along the zonal wind distribution
due to the jet streak Kim et al., 2002.
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Origin of the Asian Dust
Strong low pressure system sitting in northeast
Mongolia caused surface wind speeds to be as high
as 30 m/s Given suitable weather conditions,
dust can be lifted from the dry surface of the
Asian Gobi desert region and transported to the
United States in about 7-10 days.
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