AEROSOL SPECTROMETER AND ITS APPLICATION 
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Fria. 11—Size spectra of artificial NaCl aerosols without (O) and with (T) traces of turpentine vapor 
at various relative humidities (14-80%) in Cs , and nebulizer temperatures (Ty = 0° C or 24° C); the 
ordinate presents the light scattering intensities C-S/ in arbitrary units, the abcissa indicates the par- 
ticle diameter (Stokes) in terms of dehydrated salt ds; and of a saturated salt solution dy 
NaCl aerosol amounts thus to about 1.9 mg/min, 
representing a salt concentration of 380 ug/lt at 
the flow of 5 lit/min in C,. Since the flow addi- 
tion from IT and III amounted to 20 lit/min, the 
aerosol concentration of about 76 ug/lit results 
in Cz, C3. A one per cent monodisperse poly- 
styrene latex suspension of, for example, 0.3 u 
particles produces thus under the same conditions 
an aerosol density of about 10° particles /lit. The 
reaction rate of the aerosol can be estimated from 
the variation of the average residence times 
7™, T2 MN Ci, Co, effected by changing the air 
volume for the same flow rates. So far two sizes 
of C, , representing 7; = 2 sec and 80 sec as well 
as of C2 for 72 = 5 sec and 120 sec were used, 
causing the variation of 71 + 72 of 7 sec and 200 
sec at the entry into the AS. 
The hydration state of the NaCl-aerosol in 
C, can in this setup be varied by the temperature 
Ty of the nebulizer. The equilibrium in C, for 
Ty = 0° C corresponded to 35% < rh < 45% 
and thus to a fairly dehydrated aerosol prior to 
contact with the air flow, while for Ty = 24° C 
the relative humidity was 60% to 70%, and 
should thus result in (supersaturated) hydrated 
NaCl-particles. Contact with the air flow in C2 
can thus either hydrate or dehydrate the nuclei, 
depending upon the rh in Cz [Orr and others, 
1958a]. 
Spectra of various NaCl aerosols—The selection 
of size spectra of artificial aerosols (Fig. 11) from 
more than a hundred tests is to be considered 
still of exploratory character. The aim of the 
particular test conditions was the study of the 
variation of the size distribution caused by con- 
tacting either a hydrated or dehydrated (but 
stable) aerosol with an air stream of varying 
humidity, and sampling it within a few seconds 
thereafter. (Such conditions should be indicative 
of the effect by organic traces in the air stream 
