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Radiative Effects of Atmospheric Aerosols and Regional Haze

Radiative Effects of Atmospheric Aerosols and Regional Haze. Jin Xu DAS Science Talk February 17, 2004. Aerosol Radiative Effects. Regional Haze, Air Quality and Visibility (COHA, FAQS) Photochemical Reaction (Atlanta Supersite) Photosynthesis and Crop Yields (ChinaMAP)

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Radiative Effects of Atmospheric Aerosols and Regional Haze

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  1. Radiative Effects of Atmospheric Aerosols and Regional Haze Jin Xu DAS Science Talk February 17, 2004

  2. 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

  3. Scattering and Absorption of Light by Aerosols I=Light Detector (W/m2) L=Path Length Io=Light Source (W/m2)

  4. 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

  5. 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

  6. 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

  7. Visibility Impairment of Aerosols Based on Aerosol Chemical Speciation Data • Bext = 3F(RH)[Sulfate] + 3F(RH)[Nitrate] + 4[OMC] + 10[LAC] + 1[Soil] + 0.6[CM]+ 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

  8. 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 29

  9. 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]. 30

  10. 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. 34

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