Aerosols of KBr and AgNO3 were mixed, exposed to light in a glass tube and collected in the dark. About 15% of the collected material was reduced to silver upon development. Thus, two aerosols of particles that react to form a photo-reducible compound can be used to measure coagulation efficiency

Boyd, A.

Dimmick, R. L.

Wolochow, H.

English

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A SIMPLE METHOD FOR ESTIMATION OF COAGULATION EFFICIENCY
IN MIXED AEROSOLS
R. L. Dimmick, Alvin Boyd, H. Wolochow
Naval Biomedical Research Laboratory
School of Public Health, University of California, Berkeley
Naval Supply Center
Oakland, California 94625
ABSTRACT
Two aerosols of particles that can react to form a photo-reducible
compound can be used to measure coagulation efficiency. Aerosols of KBr
and AgNO3 were mixed, exposed to light in a glass tube and collected in
the dark. About 15% of the collected material was reduced to silver upon
development.
(NASA-CR-142041) A SIMPLE METHOD FOR N75-1613
ESTIMATION OF COAGULATION EFFICIENCY IN
MIXED AEROSOLS (Naval Biomedical Research
Lab., Oakland) 9 p HC $3.25 CSCL 13B Unclas
G3/45 09141
https://ntrs.nasa.gov/search.jsp?R=19750008059 2020-03-23T00:59:17+00:00Z
A SIMPLE METHOD FOR ESTIMATION OF COAGULATION EFFICIENCY
IN MIXED AEROSOLS
R. L. Dimmick, Alvin Boyd, H. Wolochow
Naval Biomedical Research Laboratory
School of Public Health, University of California, Berkeley
Naval Supply Center
Oakland, California 94625
We needed an approximate measurement of the coagulation efficiency
of mixed aerosols generated from two Wells-type refluxing atomizers to be
used in another experiment where a restrictive orifice seemed to increase
coagulation. With non-homogeneous aerosols, and with unknown conditions
of.turbulence in inlet tubing to an aerosol chamber, and no knowledge of
electrostatic charge on the particles or true particulate number, it was
impossible to calculate an expected value for our particular set up.
After consideration of several methods, it became evident that a three-
phase system was needed; i.e., two types of aerosols (A and B) and a
"catalyst" that could form a reaction product from collisions of A and B
only while the coagulated particles were airborne and not after they had
been collected (e.g., in an impinger).
The system finally chosen consisted of mixed aerosols of AgNO3 (2%)
and KBr (2%) conducted through a glass tube (2.3 cm ID, 90 cm long) irradiated
by a 300 watt incandescent lamp prior to collection in distilled water
Dimmick, et al. 2
contained in AGI-30 impingers either enclosed in aluminum foil or not,
depending upon whether the coagulation product of silver or the total
possible production of silver was the desired datum. The selected concen-
trations corresponded to tht dissolved solids used in the other experiment.
The experimental set up is shown in Figure 1. The combined air
output of the two Wells-type atomizers was about 181 liters per minute
and the collection rate of the impingers was 12.5 liters per minute, so
back-flow of room air was negligible. The mass median diameter of equili-
brated particles from these atomizers was about 2.3 pm and the distribution
was approximately log-normal. Without the orifice, which was a disk with
a central hole one-half the diameter of the copper tubing, flow in the
tubing was only marginally turbulent (Reynolds, number 4 x 103).
The procedure to establish standards was to operate both atomizers
simultaneously, collect the output in a 20 ml volume of water for 30, 60,
90, 120, and 150 second intervals, add 0.25 ml of developer (Kodak DK 50),
allow the impinger to remain in the light for 15 minutes, add 0.25 ml of
fixative (Kodak Rapid Fixer) and determine the optical density (OD) at
640 nm. The 0 D values were plotted against percentage recovered, with
150 seconds collection as 100 percent (Fig. 2). This range of intervals
represent the useful limits of the system under these conditions.
To estimate coagulation efficiency, the impinger was wrapped in foil
and the mixed aerosols were collected in a darkened room for a 5-minute
Dimmick, et al. 3
interval. Thus, only silver cations that had contacted bromine anions
in the lighted tube would form silver after development. Developer was
immediately added to the impinger fluid via an hypodermic needle through
the rubber tubing connected to the inlet tube, fixative was added after
two minutes and the OD was then determined as before.
Initially, tests were made without the orifice (Fig. 1) and coagulation
efficiency was less than 5%; i.e., barely detectable by the method used.
When the orifice was inserted, values of coagulation between 15 - 21% were
found. Values for coagulation are shown in Fig. 2. We believe this
variability was influenced by differences in resonances in the tee section
(and hence, different turbulence) caused by unequal starting of the two
atomizers and by the fact that the glass inlet tube to the impinger could have
served as a "light pipe". We have not investigated either possibility.
Although our interest was only to obtain an estimate of coagulation
under special conditions, we believe the method could be improved. For
example, the ends of the inlet and outlet tubes of the impinger could be
ground and painted black to reduce stray light, or an impinger could be
constructed of metal or opaque plastic, or another sampling method might
be used. The silver could be measured by oxidometric methods, or by
volt-ammetry, after removal of the soluble silver salts.
If it can be demonstrated that an aerosol developer can function as
a developer or an aerosol of fixer as a fixer, the possibilities would
Dimmick, et al. 4
exist of a study of interactions of aerosols composed of 3 or 4 species
of particles. Other variables, such as number and sizes of particles,
and their ratios, are also amenable to study.
Finally, the method described here measures only the A-B coagulation
fraction, which is only one-half of the total coagulation in the mixed
aerosols containing A-A and B-B fractions.
This work was supported in part by NASA (Office of Planetary Quarantine)
Contract No.W 13,450, and in part by the Office of Naval Research.
Di mick, et al. 5
Figure 1. Experimental set-up to measure coagulation
Legend: The copper tube was 1.5 cm inside diameter and 33 cm long,
and was bent to permit later use within a closed hood.
Dimmick, et al. 6
Figure 2. Relationship between mass of aerosols of AgNO3 and KBr
collected and optical density after development. Percentages
for coagulation shown must be divided by two to correct for
5-minute sample.
0. 9
0. 7-
0 collected in
total light
O0.5 " collected in
covered impinger
during 5 minutes.
Exposed to light
only in glass tube.
0.3
. I I " I
10- -20-- -30--- -40 -50
Percent of total silver formed on basis of 5'minute sample
ATOMIZERS
COPPER TUBE' COPPER TEE
LAMP I. @ TO PRESSURE, lOpsi
GLASS TUBE, 30 cm,~ y3 ,
TO VACUUM A=OR IFICE (see text)


A simple method for estimation of coagulation efficiency in mixed aerosols

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