ECN publication
Nephelometer-derived and measured optical depth: first Europeancolumn closure experiment
Published by: Publication date:
ECN 1995
ECN report number: Document type:
ECN-RX--95-002 Other
Number of pages: Full text:
26 Download PDF  

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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