Theoretical and Experimental Analysis of the Optec NGN Nephelometer

Molenar, John

The integrating nephelometer directly measures the scattering coefficient of atmospheric aerosols. The Optec NGN integrating nephelometer was designed to operate in low power, low maintenance, and ambient field conditions. This required two main compromises in the optical design:-- The use of a photodiode rather than a photomultiplier tube (PMT) detector, and--· A wide band filter to compensate for the reduced sensitivity of the photodiode compared to a PMT. The following is a theoretical examination of the effect of these design requirements on the measurement accuracy of the Optec NGN integrating nephelometer and an experimental determination of the measurement precision of the instrument. Included in the theoretical analysis are comparisons to three other currently available integrating nephelometers:-- TSI 3563: TSI, Inc., St. Paul, Minnesota-- Belfort 1590 : Belfort Instrument Company, Baltimore, Maryland-- Radiance Research M903: Radiance Research Inc., Seattle, Washington