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Title:
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Nephelometer-derived and measured optical depth: first Europeancolumn closure experiment
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Author(s):
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Published by:
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Publication date:
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ECN
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1995
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ECN report number:
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Document type:
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ECN-RX--95-002
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Other
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Number of pages:
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Full text:
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26
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Download PDF
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Abstract:
During a period with cloudless skies and high aerosol mass loadings inthe Netherlands, the aerosol optical depth was determined both from direct
solar irradiance measurements and from extrapolation of nephelometry. The
vertical profile of the aerosol was obtained from lidar measurements. From
humidity controlled nephelometry at the ground and humidity profiles from
soundings the scattering aerosol extinction as a function of height was
assessed. Integration of the extinction over the aerosol layer gave the
aerosol optical depth. The optical depth at a narrow band was translated to a
broadband value, assuming an Angstrom wavelength exponent of 1.5, a typical
value for the Netherlands. It was found that the boundary layer aerosol
contributed on average 80#+#10% to the total optical depth. Ammonium nitrate
dominated the light scattering. This is an anthropogenic aerosol component.
The radiative forcing caused by reflection on the anthropogenic aerosol was
estimated assuming an upward scattered fraction in accordance with the
aerosol site distribution measured in the period. A value of -11 Wm"-2 was
found. This value corresponds to an absolute increase in planetary albedo of
0.03, a 15% increase in the estimated value of 0.2. 2 figs., 2 tabs., 13 refs.
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