Recent Developments in IN SITU Size Spectrum Measurement of Submicron Aerosols

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Abstract
This paper reports the recent developments for in situ atmospheric aerosol size spectrometry in the diameter range below a few microns. Such particles are responsible for most of the visibility reduction and believed to be most dangerous to the human health. The use of optical single particle counters for aerosol size spectrometry is reviewed, and the main factors in counter design and aerosol characteristics affecting their performance are discussed. The paper reports the main characteristics of a modified Climet Instruments, Inc. counter, intended primarily for high size resolution atmospheric aerosol measurement in the 0.25 to 3.0 µm particle diameter range. Its main feature is an ellipsoid mirror scattered light collector. The design, operation, calibration, and size resolution of the University of Minnesota's Electrical Aerosol Analyzer is discussed. The instrument is capable of measuring aerosol size spectra in situ in the diameter range from about 0.004 to 0.5 µm with its size resolution being best at about 0.01 µm. A simple device, the diffusion battery can be used for rough size distribution measurement in the range 0.002 to 0.1 µm. Its principle of operation, design, and use is discussed.