&EPA
United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
EPA-600/2-78-104
June 1978
Research and Development
Generation of
Sulfuric Acid
Aerosols for Health
Effect Studies
-------
RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development. U S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA=600/2-78-104
June 1978
GENERATION OF SULFURIC ACID AEROSOLS
FOR HEALTH EFFECT STUDIES
by
Benjamin Y. H. Liu and Jak Levi
Particle Technology Laboratory
Mechanical Engineering Department
University of Minnesota
Minneapolis, Minnesota 55455
Grant No. R801301
Project Officer
Thomas G. Dzubay
Atmospheric Chemistry and Physics Division
Environmental Sciences Research Laboratory
Research Triangle Park, NC 27711
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
-------
DISCLAIMER
This report has been reviewed by the Environmental Sciences Research
Laboratory, U.S. Environmental Protection Agency, and approved for publica-
tion. Approval does not signify that the contents necessarily reflect the
views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or
recommendation for use.
ii
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ABSTRACT
An aerosol generator has been developed for producing sulfuric acid
particles for animal exposure studies. The generator has been designed to
supply sulfuric acid aerosols at 330 liters per minute to an animal exposure
chamber of 330 liters internal volume. The sulfuric acid concentration in
3
the chamber ranges from 0.13 to 1.3 mg/m . The particle diameter ranges
from 0.04 to 0.15 ym, and the geometrical standard deviation of the aerosol
is about 1.6.
The generator operates by atomizing a sulfuric acid solution to form a
polydisperse spray. The droplets are then vaporized in a tube-furnace and
the vapor injected into filtered air at room temperature to form a high con-
centration of small sulfuric acid particles.
The aerosol generating system has been evaluated by means of several
techniques. The particle size distribution was measured by an Electrical
Aerosol Analyzer. Four independent techniques were used to measure the
aerosol concentration. These include the Electrical Aerosol Analyzer, the
Quartz-Crystal Aerosol Mass Monitor, filter collection and weighing, and
chemical analysis of collected particle samples. Good agreement has been
found.
The particular generator described in this report has been constructed
and delivered to the U.S. Environmental Protection Agency for use in its
animal exposure experiments.
This report was submitted in fulfillment of Grant No. R801301 by the
University of Minnesota under sponsorship of the U.S. Environmental Protec-
tion Agency. This report covers a period from September 1, 1976 to March 1,
1978, and work was completed as of March 1, 1978.
iii
-------
CONTENTS
Abstract ill
Figures vi
Tables vii
Acknowledgements viii
1. Introduction 1
2. Design Criteria 2
3. Theoretical Considerations 3
Coagulation Limit 3
Properties of Sulfuric Acid Solution Droplets 6
4. Description of System 11
Atomization of the Sulfuric Acid Solution 11
Evaporation of Solution Droplets 13
Condensation and Growth of the Aerosol 13
Exposure Chamber 13
5. Preliminary Experiments 15
The Atomizer 15
Vaporization Temperature 16
Uniformity of the Aerosol in the Exposure Chamber . . .21
6. Performance of the Aerosol Generating System 24
Mass Concentration 25
Size Distribution 31
Coagulation Chamber 36
7. Final Remarks 38
References 39
Appendices
A. Detailed size distribution data obtained by EAA 41
B. Operating instructions 46
Introduction 46
Unpacking and Setup 46
Operating Principles and Characteristics of the
Sulfuric Acid Aerosol Generator 49
Operating Procedure 54
Notes on the Operation of the Aerosol Generator ... .56
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FIGURES
Number Page
1 Coagulation limited mass concentration of aerosols for H-SO,
particles at 50% R.H ..... 5
2 Properties of sulfuric acid droplets 7
3 Particle size growth factor taking into account the Kelvin
effect 10
4 Schematic diagram of system for generating sulfuric acid
aerosols 12
5 Variation of total EAA current with time during warm-up for a
furnace temperature setting of "lo" 18
6 Variation of total EAA current with time during warm-up for a
furnace temperature setting of "2" 19
7 Variation of total EAA current with time during warm-up for a
furnace temperature setting of "3" 20
8 Location of sampling probe on a horizontal plane within the
exposure chamber 22
9 Schematic diagram of aerosol diluter 27
10 H.SO, and aerosol mass concentration in exposure chamber as a
function of solution normality 30
11 Aerosol size distribution for 0.1N H-SO, solution 33
12 Aerosol size distribution for l.ON H2SO, solution 34
13 Aerosol particle size as a function of solution normality for
primary dilution airflow of 30 1pm 35
Bl Photograph of evaporator-mixer 47
B2 Photograph of sulfuric acid aerosol generator installed on
the exposure chamber 47
B3 Calibration curve of orifice meter for total chamber flow. ... 55
B4 Calibration curve of rotameter for primary dilution flow 57
B5 Calibration curve of rotameter for atomizer flow 58
B6 Dimensions of pyrex evaporator tube and mixing nozzle 59
vi
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TABLES
Number Page
1 Variation of Solution pH with Time for Liquid in Atomizer. ... 16
2 Characteristics of Atomizer 16
3 Variation of Aerosol Concentration within Exposure Chamber. ... 23
4 Comparison of Aerosol Mass Measurement by Weighing and
by SO Analysis 28
5 Comparison of Aerosol Mass Concentration Measurement by Several
Different Techniques 29
6 Summary of Aerosol Size Distribution Parameters for Various
Generator Operating Conditions 32
Al Size Distribution Measurement by EAA 42
A2 Size Distribution Measurement by EAA (10 1pm primary dilution
air) 43
A3 Size Distribution Measurement by EAA (20 1pm primary dilution
air) 44
A4 Size Distribution Measurement by EAA (30 1pm primary dilution
air) 45
Bl Characteristics of Aerosol Produced by the Sulfuric Acid
Aerosol Generator 50
B2 Aerosol Particle Size as a Function of Coagulation Chamber
Volume 53
B3 Consumption and Concentration of H-SO, Solution by Atomizer
as a Function of Time 53
vii
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ACKNOWLEDGEMENTS
The authors of this report wish to thank Dr. Thomas G. Dzubay of EPA
for his help in establishing the basic design criteria for the aerosol
generator. His interest in the project and his helpful discussions are
greatly appreciated. The authors also wish to thank Mr. Mike Kirtz of EPA
for providing the animal exposure chamber used in the study. A special word
of thanks goes to Dr. David Y. H. Pui of the University of Minnesota for his
help in the preparation of the report.
This work is supported by EPA under Grant R801301.
viii
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SECTION 1
INTRODUCTION
Under the sponsorship of the Environmental Protection Agency, the Par-
ticle Technology Laboratory, University of Minnesota, undertook a study on
methods for generating sulfuric acid aerosols. The goal of the study was to
develop a generator for producing sulfuric acid aerosols in the 0.01 to 0.1
ym diameter range and at concentration levels that are sufficiently high for
studying the health effect of fine sulfuric acid particles.
The impetus for the present research came from the finding that sulfu-
ric acid particles are emitted by modern, catalyst-equipped automobiles. The
particles are formed apparently by the catalytic conversion of S02 in the ex-
haust gas due to the combustion of sulfur-containing fuel. Studies conducted
by EPA at the General Motors Proving Ground and at Los Angeles freeways con-
cerning this "sulfuric acid problem" (see the recent summary by Maugh, 1977)
showed that the particles emitted are very small in size, typically in the
0.01 to 0.1 ym diameter range (Whitby et al., 1977; Wilson et al., 1977).
Since small aerosol particles can penetrate deeply into the human respira-
tory system, the potential health effect of these fine sulfuric acid parti-
cles is of some concern. The purpose of the present research is to develop
a sulfuric acid aerosol generator for studying the health effect of fine sul-
furic acid particles.
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SECTION 2
DESIGN CRITERIA
The generator described in this report has been developed specifically
for EPA for use in its health effects studies program. The generator has
been designed for an animal exposure chamber having an internal volume of
0.33 m , and a design flow rate that would provide one complete air ex-
change per minute in the chamber volume, i.e., 330 liters per minute.
Therefore, the principal requirement of the generator is that it must be
capable of supplying the test aerosol at a sufficiently high rate to pro-
duce an adequate sulfuric acid concentration in the test chamber. The
basic design parameters have been set as follows:
3
Exposure chamber volume: 0.33 m
Chamber air flow: 330 liters per minute
Aerosol diameter range: 0.02 to 0.2 ym
3
Sulfuric acid aerosol concentration: from about 100 yg/m to a few
3
mg/m
Although the aerosol generated does not need to be monodisperse, both the
size distribution and aerosol concentration must be stable. In addition,
the generator must be capable of unattended operations and be reasonably
maintenance- and trouble-free.
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SECTION 3
THEORETICAL CONSIDERATIONS
COAGULATION LIMIT
An important consideration in the design of aerosol generating systems
to supply highly concentrated aerosols for animal exposure experiments is
the following: what is the maximum aerosol concentration that can be ob-
tained? Among the factors limiting the maximum obtainable aerosol concentra-
tion is the limit imposed by coagulation, which takes place whenever aerosol
is transported from the point of formation to where it is used. In this
Section, this limit will be determined.
Consider a monodisperse aerosol undergoing coagulation according to the
following equation:
f - - KN2 (1)
dt
where N is the aerosol number concentration and K is the coagulation coeffi-
cient. Separating variables and integrating between appropriate limits, we
have:
N J>T ft
(2)
(3)
where N0 is the initial aerosol concentration and N is the aerosol concen-
tration at the time t. It follows from Equation (3) that,
N ^y- (4)
which can be approximated by
N
No
L
1 ~
dN
~ 2 ~
N
t
Kdt
0
1
IN o
-------
N -
if No > ^TT. The above result states that, if the initial aerosol concen-
Kt
tration, N0, is sufficiently high, the aerosol concentration N at time t
will be independent of the initial concentration, the concentration N being
solely a function of the coagulation time, t.
The coagulation coefficient for monodisperse aerosols is a function of
particle size. The following table, taken from Fuchs (1964), gives the coag-
ulation coefficient for various particle sizes:
D , ym 0.02 0.04 0.1 0.2
K, cm3/sec 12 x 10~10 11 x 10~10 7.2 x 10~10 5.2 x 10"10
Over the particle size range from 0.02 to 0.2 pm, the coagulation coeffi-
cient does not vary greatly. For the present purpose of making an estimate
-9
of the limiting particle concentration that can be obtained, K = 10
3
cm /sec will be used as an approximate average for the coagulation coeffi-
cient in the above-mentioned size range.
-9 3
Using Equation (5) and the coagulation coefficient of K = 10 cm /sec,
we have for the coagulation-limited number concentrations at various coagu-
lation times:
t, sec 1 10 100
N, cm"3 109 108 107
The corresponding mass concentration of the aerosol is related to the number
concentration by:
M = 7'7rD3pN (6)
b p
where p is the particle density.
In Figure 1, the mass concentration of a coagulation-limited aerosol
based upon the above analysis is shown as a function of particle size for
various coagulation times. The particles are sulfuric acid droplets in
equilibrium with ambient air at 50% relative humidity. At this humidity,
the equilibrium sulfuric acid concentration in the solution is 42.5% by mass,
-------
'l 1 a 4 567*91 a a 4 5676*1 a 34567891
.001 .01 .1 i
PARTICLE DIAMETER, urn
Figure 1. Coagulation limited mass concentration of aerosols
for H2SO particles at 50% R.H.
-------
3
and the solution density is p = 1.325 g/cm . Similar graphs for other humid-
ity conditions can easily be constructed.
From the above analysis, it is clear that coagulation imposes a limit
on the maximum aerosol concentration that can be obtained. For example, sup-
pose that a certain animal exposure experiment requires that sulfuric acid
particles be transported from where they are formed to where they are inhaled
by the test animals in 30 seconds. Then, according to Figure 1, the maximum
sulfuric acid concentration will be 79 yg/m if the particle diameter is
0.02 ym. If the ambient relative humidity is 50%, the maximum aerosol mass
concentration (sulfuric acid plus associated liquid water) will be 185 yg/m ,
also from Figure 1. Any attempt to increase the aerosol concentration to a
level above these limits would only result in more coagulation and the pro-
duction of larger particles. This is an important factor that must be taken
into account in designing human or animal exposure experiments in health ef-
fect studies.
PROPERTIES OF SULFURIC ACID SOLUTION DROPLETS
Sulfuric acid droplets are hygroscopic particles whose size will change
in response to changes in ambient humidity. To facilitate calculations,
Figure 2 has been prepared (Liu, Pui and Kousaka, 1977).
In Figure 2, the pertinent sulfuric acid solution properties are shown
plotted against x, the solution concentration expressed in g H»SO,/g solu-
tion. Included in the plot are the equilibrium relative humidity over a flat
solution surface, the solution density, p, the boiling point, B.P., and the
surface tension, a. The data have been taken from the Chemical Engineers
Handbook (Perry and Chilton, 1973) and from Sabinina and Terpugow (1935),
as indicated in the figure. In addition, several calculated parameters are
shown. These include the solution normality, the product, xp, the particle
growth factor, D /D , and the Kelvin effect parameter, D In — , which are
defined below. To illustrate the use of the various plotted quantities, the
following example is given.
Consider a 1 ym diameter sulfuric acid solution droplet in equilibrium
with relative humidity at 50%. Using the curve denoted by R.H. in Figure 2,
-------
O o
g «
It (M
11 I I I I
D. 'iNIOd
o
o
I I I I I I I I I I I I I I I
ui9/*uXp • a • NOISN31
1 1 1 1 1 it 1 1 1 1 1 1 1 1 1 1
su»/6 '
-------
we find that the solution concentration, x, is 0.425 g of H?SO, per g of
solution, or a concentration of 42.5% by mass. At this concentration, the
3
solution has a density, p, of 1.32 g/cm , a boiling point, B.P., of 115°C, a
surface tension, a, of 76 dyne/cm, a normality of UN, and a mass concentra-
3
tion, xp, of 0.55 g lUSO, per cm of solution. The particle size growth
factor, D /D , is 1.48, and the Kelvin effect parameter, D InCp/p^), is
11.3 x 10 ym. The last two parameters are explained in more detail below.
The particle size growth factor, D /D , shown in Figure 2, is the
ratio of the actual diameter of the particle, D , to the diameter of the
particle, D , if the water associated with the droplet is completely re-
moved. In the example given above, the 1 ym diameter sulfuric acid solution
droplet will become a droplet of pure sulfuric acid of 1/1.48 = 0»68 ym if
water is removed. Similarly, if the ambient humidity is now increased to
90%, then according to Figure 2, the equilibrium solution concentration is
17% by mass and the particle size growth factor is 2.12. Consequently, the
1 ym diameter particle at 50% R.H. will now become a particle of (2.12/1.48)
(1) = 1.43 ym diameter at 90% R.H. Thus, the particle size growth factor
can be used to predict changes in particle size when ambient relative humid-
ity around the particles is changed.
In the above discussion of particle size change, the Kelvin effect has
been ignored. The Kelvin effect relates the increase in equilibrium vapor
pressure, p, over a curved surface to that over a flat surface, p ,
-i / / \ 2 a M ,_.
^fr'"-' ' RTp-7 (7)
where a is the surface tension of the solution, M is the molecular weight of
water, R is the gas constant for water, T is the absolute temperature, p is
the solution density, and a is the particle radius. The quantity plotted in
Figure 2 is the ratio D InCp/p^) which, according to Equation (7), is:
V
where D has the same meaning as that discussed above. It should be noted
that the quantity on the right-hand side of Equation (8) involves only
solution and vapor properties, which are functions of x, the solution
8
-------
concentration. Consequently, the Kelvin effect parameter is also a function
of x.
To illustrate the use of the Kelvin effect parameter, let us consider
the example discussed earlier, viz. the 1 ym diameter sulfuric acid solution
droplet at 50% R.H. Since D =0.68 ym, and the Kelvin effect parameter is
-4 P° -4 -4
11.3 x 10 ym, we have InCp/pJ = 11.3 x 10 /0.68 = 16.62 x 10 . Conse-
quently, P/P,,,, = 1.00166. For this case, the Kelvin effect is negligible;
the increase in water vapor pressure is only 0.166% above that for a flat
surface.
Let us now consider a 0.01 ym diameter sulfuric acid particle at 50%
humidity. Since D = 0.01/1.48 = 0.0068 ym in this case, we have InCp/p^)
= 11.3 x 10/0.0068 = 0.166, which gives p/pm » 1.18. Consequently, the
Kelvin effect will cause the equilibrium vapor pressure over the curved drop-
let surface to be 18% higher than that over a corresponding flat surface.
Thus, the effect is substantial and generally cannot be ignored. In Figure
3, the particle size growth factor, D /D , taking into account the Kelvin
effect has been calculated and shown as a function of the relative humidity.
-------
100
80
^
>-"
9
ID
UJ
>
UJ
or
60
40
20
,...., WITHOUT KELVIN EFFECT
!(INDEPENDENT OF PARTICLE SIZE)
PARTICLE SIZE GROWTH FACTOR
TAKING INTO ACCOUNT THE
KELVIN EFFECT
1.5 2.0
PARTICLE SIZE GROWTH FACTOR, Dp/Dp0
Figure 3. Particle size growth factor taking into account
the Kelvin effect.
-------
SECTION 4
DESCRIPTION OF SYSTEM
There are three main steps involved in the method chosen for generating
H_SO, particles, and they can be summarized, as follows:
(a) Atomization of the sulfuric acid solution
(b) Evaporation of the solution droplets
(c) Condensation and growth of the aerosol
The complete system is shown in Figure 4.
ATOMIZATION OF THE SULFURIC ACID SOLUTION
Since sulfuric acid is to be used in the experiments, it is necessary
that the aerosol generator be made of an acid-resistant material. Also, it
is very important that under steady state conditions, the concentration of
the particles should remain constant at the outlet of the atomizing device
used. The atomizer shown in Figure 4 proved to be most reliable in this re-
spect. The atomizer is made of 304 stainless steel, and all other parts in
contact with the acid solution are made of either polyethylene or Teflon.
The basic atomizer design has been adapted from that described by Liu and
Lee (1975). The only difference is that in the system described by Liu and
Lee, a syringe pump is used to feed the liquid continuously to the atomizer,
whereas in the present case, the liquid is drawn into the atomizer head by
suction, and the excess, non-aerosolized liquid is returned to the same
liquid reservoir. The atomizer is normally operated with dry, filtered com-
pressed air at 35 psig (241 kPa). At this pressure, the flowrate through
the atomizer is 2.4 1pm, as measured downstream of the atomizer as shown in
Figure 4.
11
-------
OVEN
MIXING NOZZLES
(PYREX)
0-30J
Ipmr/ Ipm i
ATOMIZER
PTAMETE
VALVES
-_ 1": SOLUTION
AEROSOL (12.4 - 32.4 Ipm)
»
ORIFICE
OPTIONAL
20 LITER
COAGULATION
CHAMBER
T
FILTER
— AIR IN
EXPOSURE
CHAMBER
(O.33m3)
AP
CHAMBER
PRESSURE
BLOWER
-•-EXHAUST
REGULATOR
COMPRESSED
AIR
ACCUMULATION
CHAMBER
_
FILTER DRYER FILTER
Figure 4. Schematic diagram of system for generating sulfuric acid aerosols.
-------
EVAPORATION OF SOLUTION DROPLETS
The atomizer produces a spray of solution droplets, which are polydis-
perse and relatively coarse. This spray is passed through an accumulation
chamber to remove the liquid collecting on the walls of the connecting
tubing, and then introduced into a Pyrex evaporator tube. The evaporator
tube is placed within a tube furnace, which is kept at a constant tempera-
ture of about 400°F (204°C). The residence time of the flow in the tube is
three seconds, and the gas is heated to a temperature of approximately 220°F
(104°C) at the exit. At this temperature, the solution droplets are com-
»
pletely vaporized. The specific furnace used is the Lindberg Model 55035
(Solar Basic Industries, 304 Hart St., Watertown, WI 53094). Under normal
operation, the furnace temperature control is set to "lo" in order to produce
the required furnace temperature of 400°F (204°C) at steady state.
CONDENSATION AND GROWTH OF THE AEROSOL
The hot gas leaving the evaporator is injected through a small orifice
at the end of the evaporator tube to form a turbulent jet, which is then
mixed with the primary dilution air at room temperature. The dilution air
is obtained from a filtered air supply and is metered to the mixing nozzle
through a 0 - 30 1pm rotameter, as shown in Figure 4. The rapid mixing of
the two streams causes the nucleation and condensation of the vapor and the
subsequent coagulation and growth of the sulfuric acid particles.
The aerosol is then introduced into the exposure chamber by means of
a 1.27 cm i.d., 60 cm long Tygon tubing. The volume of the flow passages
between the point where the hot gas first comes in contact with the dilution
air to where the aerosol is further diluted by the exposure chamber air flow
3
is 125 cm . This results in a residence time of 0.25 sec for a primary dilu-
tion air flow of 30 1pm. This residence time is normally too short to cause
substantial particle growth by coagulation. If further coagulation is de-
sired, an optional coagulation chamber can be used, as shown in Figure 4, to
increase the size of particles produced.
EXPOSURE CHAMBER
The exposure chamber is roughly cubical in shape, and has an internal
3
volume of 0.33 m . An exhaust blower at the chamber outlet provides the
13
-------
needed air flow of 330 1pm. This air flow is metered by an orifice meter of
1" (2.54 cm) diameter at the chamber inlet. The aerosol is introduced into
the chamber just upstream of the orifice. The rapid mixing of the aerosol
with the main chamber flow quickly dilutes the aerosol and causes the aerosol
size distribution to be "frozen" at that point. Since the total chamber flow
of 330 1pm is much higher than the aerosol flow of 12.4 to 32.4 1pm, the hu-
midity of the aerosol in the exposure chamber is approximately the same as
the humidity of air at the chamber inlet. In the experiments described below,
the main chamber air was taken from the air-conditioned laboratory room, and
the relative humidity was between 42 and 48%, with a mean of 45%.
14
-------
SECTION 5
PRELIMINARY EXPERIMENTS
Several preliminary experiments were performed in order to establish the
performance characteristics of the major system components, and the best
operating conditions for the system. These are described below, together
with the results obtained.
THE ATOMIZER
The flowrate of the atomizer was measured by connecting a rotameter
downstream of the atomizer and operating the atomizer with compressed air at
35 psig (241 kPa). The flowrate was found to be 2.4 liters per minute.
Next, the atomizer was operated for 24 hours, and the quantity of liquid
consumed was measured. The rate of liquid consumption was found to be 6..4
ml/hr.
Since not all the liquid consumed by the atomizer was aerosolized —
some was lost through evaporation — an experiment was performed to determine
the evaporative loss of liquid from the reservoir. This was done by placing
200 ml of the nominal 0.1 N H-SO, stock solution in the atomizer and mea-
suring the pH of the solution in the reservoir as a function of time. The pH
was measured by periodically withdrawing 1 ml samples from the reservoir,
diluting the sample by a factor of 1000 with distilled water, and measuring
the resulting pH with a high resolution (0.001 pH) pH meter (Model 701, Orion
Research, Inc., 11 Blackstone St., Cambridge, MA 02139). The result is shown
in Table 1. It is seen that as water evaporated, the solution in the reser-
voir became more concentrated, resulting in a lowering of the pH, and an
increase in the solution normality. The rate of evaporation of water was
calculated and found to be 1.9 ml/hr, or 30% of the total liquid consumption
rate of 6.4 ml/hr.
15
-------
TABLE 1. VARIATION OF SOLUTION pH WITH TIME FOR LIQUID IN ATOMIZER
Time, hr
0
7
20
24
Vol. of Solution
in Reservoir, ml
200
46
pH
(1000:1 dilution)
3.83
3.71
3.58
3.54
The liquid consumption and evaporation rates determined above were ob-
tained by operating the atomizer with dry, filtered compressed air at 35 psig
(241 kPa). The relative humidity of the air, after expanding to atmospheric
pressure, was found to be 20%.
In Table 2, the principal atomizer characteristics are summarized.
TABLE 2. CHARACTERISTICS OF ATOMIZER
Operating Pressure: 35 psig (241 kPa)
Flowrate: 2.4 liters per minute
Liquid Consumption Rate: 6.4 ml/hr.
Liquid Evaporation Rate: 1.9 ml/hr.
Reservoir Capacity: 1,000 ml
VAPORIZATION TEMPERATURE
To determine the furnace temperature needed to vaporize the sulfuric
acid solution droplets, the following experiments were performed. All ex-
periments were carried out with a 0.1 N solution in the atomizer reservoir.
First, a steady flow was established in the system by turning on the
compressed air supply and the exhaust blower. An Electrical Aerosol Analyzer
(EAA) (Model 3030, TSI Inc., P. 0. Box 3394, St. Paul, MN 55165) was then
used to monitor the aerosol in the exposure chamber.
16
-------
Next, the furnace was turned on, and the total EAA current was recorded
on a strip chart. The temperature, as indicated by the furnace temperature
indicator, was also recorded at regular intervals up to the maximum attain-
able temperature.
The furnace was then allowed to cool down to room temperature. A ther-
mocouple introduced into the exit orifice of the evaporator tube provided
the gas temperature at that point. The furnace was then turned on, and the
gas temperature, as sensed by the probe, was recorded on a strip chart on the
same time scale as before. Recordings from the two runs were mapped to give
the EAA current variation with time and with furnace and gas temperatures.
The runs were repeated for three furnace settings, resulting in three steady
state temperatures. The plots are shown in Figures 5, 6, and 7. From these
plots, the following observations or conclusions can be made:
1) As the furnace began to warm up, there was initially no change in
the total EAA current, indicating that the size distribution of the
aerosol was not affected by the initial warming of the furnace.
This initial warming period varied between 33 minutes, for a furnace
temperature setting of "lo", and 9 minutes, for a higher temperature
setting of "3".
2) At an exit gas temperature of 138°F (54°C), the total EAA current
began to rise sharply, reaching a peak at a gas temperature of 180°F
(82°C). Thereafter, the EAA current decreased and then finally
stabilized. The variation in EAA current was due to the fact that
the instrument sensitivity is a function of particle size, and that
as sulfuric acid droplets vaporized and recondensed, the size dis-
tribution of the aerosol was changed. The result indicates that
the minimum vaporization temperature for sulfuric acid droplets
was 130°F (59°C), and that complete vaporization of the droplets
could be obtained at a somewhat higher temperature.
3) The time for the EAA current to become steady varied from 50 minutes
for a furnace temperature setting of "3" to 130 minutes for a tem-
perature setting of "lo". Thus, sufficient time should be allowed
17
-------
oo
135
200
160
250
190
300
210
350
220 ~ GAS T (°F)
375 — OVEN T (°F)
40
60
80 100
TIME, MINUTES
120
140
160
180
200
Figure 5. Variation of total EAA current with time during warm-up
for a furnace temperature setting of "lo".
-------
115 155
150 250
200
350
14
12
10
240 260
450 500
280
550
320 — GAS T (°F)
625 — OVEN T (°F)
OVEN SETTING: 2
! I ,
-f-
r
i
i
T'
i
„ i_
4 -
20 40 60 80 100
TIME, MINUTES
120
140
160
Figure 6. Variation of total EAA current with time during
warm-up for a furnace temperature setting of "2",
-------
12
10
120 158 198 240 300 380 430
175 275 350 450 575 750 800
560 - GAS T(°F)
1000 - OVEN T(°F)
T r
OVEN SETTING:
r
j_._ _.
i r
20 40 60 80 100 120
TIME, MINUTES
140
160
180
200
220
Figure 7. Variation of total EAA current with time during warm-up
for a furnace temperature setting of "3".
-------
for the system to stabilize before any size distribution measurement
was made.
4) A furnace temperature setting of "lo" was adequate to completely
vaporize the sulfuric acid droplets. At this setting, the furnace
reached a steady operating temperature of 400°F (204°C) and the gas,
220°F (104°C).
UNIFORMITY OF THE AEROSOL IN THE EXPOSURE CHAMBER
The exposure chamber was probed at 27 different locations in order to
obtain an accurate picture of the uniformity of aerosol distribution within
the chamber. Figure 8 shows the nine probe locations on each of three hori-
zontal planes, and the location of these planes within the chamber. For each
experiment, the aerosol was sampled at the indicated probe locations with the
EAA, and the total EAA current was recorded. Table 3 lists the results for
several dilution and chamber air flows. The data include the average EAA
current and the standard deviation of current in each plane, as well as the
average current and the standard deviation for the entire 27 probe locations.
As one would expect, increasing the chamber flow generally resulted in more
uniform aerosol distributions. For instance, at a chamber flow of 132 1pm,
the standard deviation of the total EAA current was only 6.2% of the average
EAA current. This indicates that the exact probe location in the chamber is
not critical for determining the aerosol concentration, since the aerosol
distribution within the chamber is quite uniform.
21
-------
to
to
Oi
4»-
6
•10"-
— 26".
3"
--O2
10"
03
10"-
•SAMPLING LOCATION
11"
2"
FRONT
26"
Figure 8. Location of sampling probe on a horizontal plane within the exposure chamber.
-------
TABLE 3. VARIATION OF AEROSOL CONCENTRATION WITHIN EXPOSURE CHAMBER
Sampling Q-- 10 1pm
Point Q-- 132 1pm
I. ID'11 A
*
1-1
1-2
1-3
1-4
1-5
1-6
1-7
1-8
1-9
2-1
2-2
2-3
2-4
2-5
2-6
2-7
2-8
2-9
3-1
3-2
3-3
3-4
3-5
3-6
3-7
3-8
3-9
2.40
2.31
2.35
2.32 1=2.44
2.26 0=0.16
2.37 0/1=0.066
2.60
2.58
2.77
2.05
2.29
2.35
2.45 T-2.37
2.27 a-0.17
2.34 o/T-0.072
2.35
2.49
2.72
2.36
2.40
2.45
2.38 1-2.43
2.38 a-0.10
2.41 o/Y-0.041
2.30
2.50
2.65
Overall: Y-2.41
0-0.15
o/T-0.062
0- 28 1pm Q-- 10 1pm
Q2- 132 1pm Q-- 44 1pm
I, 10~U A I, 10~U A
4.00
3.89
4.20
3.85
3.92
4.10
4.40
4.48
4.40
4.20
3.87
3.83
3.64
3.53
3.51
4.00
4.00
4.50
3.84
3.80
3.92
3.60
3.50
3.55
3.80
3o38
4.45
3.95
3.50
3.15
1=4.14 3.50 1-3.57
0=0.23 3.27 0-0.33
o/Y-0.056 3.61 o/T-0.092
3.28
3.63
4.27
3.00
2.82
• 2.85
Y-3.90 2.61 Y-2.81
0=0.30 2.61 0-0.18
o/Y-0.077 2.50 o/Y-0.064
2.90
2.94
3.06
2.61
2.75
2.78
1-3.76 2.48 1-2.66
0-0.30 2.58 a-0.13
a/I-0.080 2.55 o/T-0.049
2.64
2.62
2.94
1-3.93 1-3.01
0-0.32 0-0.46
o/T-0.081 o/T-0.153
Q." 28 1pm
Q2- 44 1pm
I, 10~U A
4.45
4.23
4.00
4.48 1=4.49
4.13 0-0.33
4.79 0/1=0.073
4.40
4.92
5.02
3.60
3.45
3.60
3.61 Y-3.49
3.22 0-0.12
3.58 o/Y-0.034
3.38
3.47
3.48
3.35
3.30
3.33
3.40 Y-3.35
3.20 o-O.ll
3.41 o/Y-0.033
3.27
3.26
3.61
Y-3.78
0-0.55
o/Y-0.146
Q- • primary dilution air flow
Q2 • total chamber air flow
The first digit indicates the plane location and the second digit, the
location of the probe on that plane. Thus, 2-5 indicates plane 2 and
probe location 5 (see Figure 8).
23
-------
SECTION 6
PERFORMANCE OF THE AEROSOL GENERATING SYSTEM
As a result of the preliminary experiments described above, the fol-
lowing operating conditions were adopted as the standard for the aerosol
generating system:
Atomizer pressure: 35 psig (241 kPa)
Furnace temperature: Control set to "lo" giving a steady state furnace
temperature of 400°F (204°C) and a gas temperature of 220°F (104°C)
Chamber air flow: 350 liters per minute*
The system was then evaluated under these conditions.
The experiments to evaluate system performance were carried out using an
auxiliary blower, rather than with the exhaust blower on the chamber, since
the latter was found to have inadequate capacity to draw the needed chamber
flow through the absolute filter at the chamber intake, as shown in Figure 4.
During these experiments, two filters were used, one at the inlet to the
chamber, as shown in Figure 4, and the other at the chamber outlet and up-
stream of the exhaust blower. This arrangement insured that there would be
no leakage of the sulfuric acid aerosol into the laboratory room, the whole
.system being under vacuum.
In each experiment, the chamber flow was always turned on prior to the
atomizer flow. When both flows were on, the furnace would be switched on and
set to the "lo" setting, or if the heating process was to be speeded up, the
dial would be set to "high" for a couple of minutes and the furnace tempera-
ture closely watched. When a temperature of 400°F (204°C) was reached,
the temperature control was then returned to "lo". Usually hali an hour
* In these experiments, a Variac was used to vary the blower speed. It
was difficult to set the chamber flow exactly to 330 1pm. All the ex-
periments were consequently made with the chamber flow at 350 1pm.
24
-------
was allowed after the furnace had reached a steady temperature and before
any measurements were made.
MASS CONCENTRATION
Four different methods were used to measure the aerosol mass concentra-
tion in the exposure chamber.
3
The aerosol was collected by drawing a sample flow of at least 1 m
through a 1.0 ym pore Fluoropore filter (Millipore Corp., Bedford, MA 01730).
This was achieved by timing a flow of 14 1pm through a critical orifice for
a minimum of 71 minutes. The filter was weighted before and after the ex-
periment, and the mass concentration of the aerosol was deduced. An elec-
tronic microbalance (Model AD-1, Perkin Elmer Corp., Main Ave., Norwalk, CT
06856) was used for this purpose. The filters were subsequently analyzed by
wet chemical methods at EPA to give the SO, concentration. Previous ex-
periments (Liu and Kuhlmey, 1977) have shown that the efficiency of the
Fluoropore filter is in excess of 99.9%.
A quartz-crystal mass monitor (QCMM) (Model 3500 Piezobalance, TSI Inc.,
P. 0. Box 3394, St. Paul, MN 55165) was used simultaneously during the ex-
periments. The instrument measures the aerosol mass concentration by sensing
the change in vibrational frequency of a quartz crystal as particles are
deposited onto its surface by a small electrostatic precipitator. The sam-
pling period of the instrument is 24 seconds for high mass concentrations or
120 seconds for low concentrations. Several readings were taken for each
run and averaged to give a representative concentration.
The fourth method used was the Electrical Aerosol Analyzer, or EAA.
This instrument measures the size distribution of the aerosol in the 0.0032
to 1.0 ym diameter range by charging the particles and measuring the result-
ing particle mobilities. The operating principle of the instrument has been
described by Liu and Pui (1975) and Liu et al. (1976), who also presented the
basic calibration data for the instrument. However, in order to convert the
instrument readings into a size distribution, a "data reduction scheme" must
be used. In the present case, the "simplex minimization" technique described
by Liu and Kapadia (1977) was used. From the measured size distribution, the
aerosol volume was calculated. The mass concentration was then calculated by
25
-------
3
multiplying the aerosol volume concentration by 1.35 g/cm , which is the den-
sity of sulfuric acid droplets at 45% relative humidity.
The EAA measurement was made by drawing all the required 50 1pm flow
from the exposure chamber. Except for the case of the 0.1 N solution, all
EAA samplings required a dilution. This diluter is shown in Figure 9, and
the flow of aerosol to the diluter was monitored by a linear flowmeter in
order to obtain the dilution ratio (130 to 1 dilution was used in these ex-
periments) .
The experiments were performed with 0.1 N and 1.0 N H.SO, solutions.
Table 4 shows a comparison of the measured aerosol mass by filter weighing
and by SO, analysis. The agreement between the two methods is seen to be
satisfactory — the mean difference is about 13%, and the maximum difference,
29%.
The discrepancy between the two methods of measurement for samples A
and C may have been due in part to the partial neutralization of the col-
lected H,,SO, by ammonia in the laboratory air. Neutralization of H_SO, on
the filter would not affect the measured SO, mass by chemical analysis.
However, if the collected H_SO, particles had been partially neutralized by
ammonium at the time of weighing of the filter, the particle mass would be
reduced. The calculated SO, mass would then also be lower, since it was
calculated assuming no neutralization had taken place. This may have been
an important factor contributing to the discrepancy between measurement
methods for samples A and C, since the total collected mass for these samples
was quite small (about 0.1 of that for samples D, E, and F).
In Table 5, the aerosol mass concentrations measured by the several
techniques described above are summarized and compared. Again, there is good
agreement among the four independent measurement techniques. In view of the
differences in the operating principles involved, the agreement may indeed be
considered as excellent.
The experimental results obtained above are summarized and plotted in
Figure 10, showing the aerosol concentration in the exposure chamber as a
function of the normality of the H^SO, solution in the atomizer. Also shown
in Figure 10 are the results obtained by the EAA for several intermediate
26
-------
IN
(0.38 - 1.38 1pm)
CAPILLARY TUBE U — ... Clu '
FLOWMETER I •&* \ \
LS* p— -I H ^ 2 cm T—^ ™J^ .
1pm) [/^°\J 1
L
Px
L^
i
r \ r~"" ou ipm;
r— =*- ^ ^ |
J \ — i mm DIA. NOZZLE
pi ABSOLUTE
pJ FILTER
i
DILUTION AIR
(48.6 - 49.6 1pm)
Figure 9. Schematic diagram of aerosol diluter.
-------
TABLE 4. COMPARISON OF AEROSOL MASS MEASUREMENT BY WEIGHING
AND BY S04~ ANALYSIS
Sample
A
B
C
D
E
F
Cone.
0.1 N
0.1 N
0.1 N
1.0 N
1.0 N
1.0 N
Primary
Dilution
Air , 1pm
10
20
30
10
20
30
Sample
Volume ,
3
m
1.0
1.24
1.06
1.35
1.48
1.44
Aerosol
Mass,
mg
0.24
0.34
0.25
4.41
4.87
4.92
SO ™
4
by Aerosol*
Mass,
0.106
0.150
0.110
1.945
2.148
2.170
Mass
Measured,
0.121
0.148
0.154
1.66
1.97
1.98
Ratio
VM2
0.88
1.01
0.71
1.17
1.09
1.10
* The values given are obtained by multiplying the measured aerosol
mass by the factor
Off) (0.45) = 0.441
where 96 and 98 are respectively the molecular weights of SO,
and H_SO,, and 0.45 is the equilibrium mass concentration of
HS0 in the solution droplet at an R.H. of 45%.
28
-------
TABLE 5. COMPARISON OF AEROSOL MASS CONCENTRATION MEASUREMENT
BY SEVERAL DIFFERENT TECHNIQUES*
H_SO, Concentration 0.1 N 1.0 N
Primary Dilution Air, 1pm 10 20 30 10 20 30
Aerosol Mass Concentration
(H2S04 + H20), mg/m3
Filter Weighing .24 .27 .24 3.26 3.29 3.42
S04~~ Analysis** .27 .27 .33 2.79 3.02 3.12
QCMM .16 .25 .24 2.75 3.00 3.00
EAA*** .25 .30 .27 2.73 3.00 2.65
* Measured at 45% relative humidity.
** Obtained by multiplying the measured SO, concentration by
(1/0.45)(98/96) = 2.27, where 0.45 is the mass concentration of
H_SO in the solution droplet at 45% R.H., 98 is the molecular
weight of H2S04, and 96, that of S04~.
*** Obtained by multiplying the measurement aerosol volume concen-
tration by.
at 45% R.H.
3
tration by.1.35 g/cm , the density of the sulfuric acid droplet
29
-------
2000
-rrrt 5000
0.1 0.2
NORMALITY OF
0.5
SOLUTION
co
a
00
2000
1000
Oi
0
O
o
CM
O
CO
Csl
as
o
M
H
S CONC
SOL
AE
Figure 10. I^SO^ and aerosol mass concentration in exposure chamber
as a function of solution normality.
30
-------
solution normalities. These additional EAA measurements are described in
more detail in the next section.
It is interesting to note in Figure 10 that the aerosol mass concentra-
tion is proportional to the solution normality, and that over the normality
range of 0.1 N to 1.0 N, the H-SO, mass concentration in the chamber varied
3
from 0.13 to 1.3 mg/m .
SIZE DISTRIBUTION
The aerosol size distribution was measured by the EAA for various sul-
furic acid concentrations and for primary dilution airflow of 10, 20, and 30
1pm. The data were reduced by means of the "Simplex Minimization" technique
of Liu and Kapadia (1977). The results are summarized in Table 6, and a few
selected size distribution curves are plotted and compared in Figures 11 and
12. More complete size distribution data are given in Tables Al to A4 in
Appendix A.
Although the aerosol volume concentration is not greatly affected by
primary dilution airflow, the particle size is seen to decrease with in-
creasing dilution airflow. This is to be expected, since the aerosol volume
concentration is determined primarily by the atomizer output, which was un-
changed in these experiments. The smaller particle size obtained at the
higher primary dilution airflows was apparently the result of the more rapid
mixing of the vapor with the dilution air. With more rapid mixing, a greater
number of small particles are produced, resulting in a reduction in the over-
all size distribution of the aerosol. In all cases, the a of the aerosol
O
was not greatly affected, the a being in the range from 1.5 to 2.0 with an
O
average of about 1.7.
Experience with the aerosol generator shows that the generator has good
operational stability when the primary dilution air was kept above 20 1pm.
The result in Table 6 shows that the measured size distribution of the aero-
sol was quite stable when primary dilution airflows of 20 and 30 1pm were
used, whereas at a primary dilution airflow of 10 1pm, less stable results
were obtained. Consequently, 30 1pm has been chosen as the standard operat-
ing flowrate for the primary dilution air. In Figure 13, the variation of
31
-------
TABLE 6. SUMMARY OF AEROSOL SIZE DISTRIBUTION PARAMETERS FOR VARIOUS GENERATOR OPERATING CONDITIONS
to
Solution
Normality
0.1 N 0.2 N
Primary
Dilution (1pm) 10 20
VMD
VMD
a
g
CT
g
\*
\
* t
(2)f
(1)
(2)
(1)
(2)
.14 .056
.082
1.9 1.7
1.8
189 226
215
30 10 20 30
.041
.038 .077 .051 .049
1.5
1.6 1.7 1.6 1.7
204
167 424 425 408
10
.077
.083
1.7
1.7
823
787
0.3 N
20
.058
.058
1.6
1.6
680
640
30
.056
.072
1.7
1.8
622
718
0.6 N
10 20 30 10
.088
.093 .080 .081 .16
1.5
1.6 1.7 1.8 2.0
2060
1530 1430 1400 1830
1.0 N
20
.082
.11
1.5
1.8
2264
2077
30
.082
.089
1.7
1.7
2000
1910
*
VMD = geometrical volume mean diameter, ym
(1) and (2) refer to the first and second runs, respectively
3, 3
+ 3
V , total volume in urn /m
-------
600
u>
(-0
1 DILUTION VOLUME, D
•! 1 , ^ P»v
••' AIR, 1pm ymJ/cm-> ym
i PRIMARY
DILUTION
AIR, 1pm
.005
0.01
0.05
0.1
0.5
1.0
PARTICLE DIAMETER, D , ym
Figure 11. Aerosol size distribution for 0.1N H?SO, solution.
-------
SOLUTION NORMALITY: 1.0 N
DILUTION VOLUME
! AIR, 1pm um^/cm* pm" ag
30 1910 0.09 1.7
10 1830 0.16 2.0
0.005
0.01
0.05
0.1
0.5
1.0
PARTICLE DIAMETER, D , urn
Figure 12. Aerosol size distribution for l.ON H2SO, solution.
-------
0.1
u>
0.05
0.02
0.01
0.08 0.1
0.2
NORMALITY OF
1.0
SOLUTION
Figure 13. Aerosol particle size as a function of solution normality
for primary dilution airflow of 30 1pm.
-------
the geometrical mean volume diameter of the aerosol with solution normality
is shown for a primary dilution airflow of 30 1pm.
COAGULATION CHAMBER
The result of the above-described studies shows that the aerosol gener-
ator is capable of generating sulfuric acid aerosols in the 0.04 to 0.087 ym
diameter range when sulfuric acid solutions in the 0.1 N to 1.0 N range is
used. Although larger particles can be produced by means of more concen-
trated solutions, it was decided to investigate the use of a coagulation
chamber for increasing the size of particles produced.
The experiment was performed with 1.0 N solution in the atomizer. The
size distribution of the aerosol was measured with and without the optional
20 liter coagulation chamber shown in Figure 4. It was found that the geo-
metrical mean volume diameter increased from 0.087 ym when no coagulation
chamber was used, to 0.130 ym when a 20 liter chamber is inserted into the
system. It was found that the measured aerosol volume concentration remained
essentially unchanged, indicating that there was negligible aerosol loss in
the coagulation chamber.
To determine the aerosol particle diameter for other coagulation chamber
volumes, we note that for a coagulation-limited aerosol, the number concen-
tration, N, is inversely proportional to the coagulation time, t, according
to Equation (5). Since t a V, we have
N cc (1/v1) (9)
where V1 is the total effective coagulation volume in the system. In addi-
tion, the aerosol mass concentration is given by
m = Or Dp3/6)(N)(p) (10)
If there is no loss of aerosol mass during coagulation, we have, according to
-1/3
Equation (10), D <* N , and with Equation (9),
D <* (V')1/3 (11)
P
The total effective coagulation chamber volume in the system is the sum of
36
-------
the coagulation chamber volume, V , in the absence of a coagulation chamber,
and the volume, V, of the coagulation chamber, or
V = V + VQ (12)
By means of Equations (11) and (12), we have
1/3
D oc (V + V ) ' (13)
p o
Using the experimental result,
D = 0.087 ym for V = 0
P
(14)
D = 0.13 ym for V = 20 liters
P
and treating V in Equation (13) as an empirically adjustable parameter,
we have
Dp = (^|~)1/3(0.087), ym (15)
which can be used as an interpolation or extrapolation formula to estimate
the aerosol particle size for various coagulation chamber volumes. The re-
sult of the calculation is shown in Table B2 in Appendix B. The result shows
that with a 30 liter coagulation chamber, particles as large as 0.144 ym can
be obtained using a 1.0 N solution in the atomizer.
37
-------
SECTION 7
FINAL REMARKS
The aerosol generator described in this report may be considered as a
developmental prototype. Although it performed satisfactorily during the
evaluating phase of the program, we believe certain improvements can and
should be made. In addition, certain precautions need to be taken in order
to insure proper operation of the generator. These are described below.
1) Due to its availability in our Laboratory, Tygon tubing was used
throughout as the connecting tubeing in the generator. For long-
term operation, a more chemically inert tubing such as Teflon
should be used. It is recommended that the existing tubing be
replaced with Teflon for long-term operation of the generator and
in any new generator to be constructed following the basic design
reported here.
2) To avoid neutralizing the generated sulfuric aerosol particles by
NH_, which may be present in the compressed air line or in the
supply air for the main chamber air flow, it is recommended that
these airstreams be purified by passing through an absorbent mate-
rial with high affinity for NH~.
3) Although the generator has been found to be quite stable during
its operation over a period of several days, its true long-term
stability needs to be established. It is recommended that during
the operation of the generator in the actual animal exposure experi-
ments, the performance of the generator be monitored closely in
order to obtain some practical working experience to determine how
frequently the generating system needs to be cleaned and serviced.
38
-------
REFERENCES
Fuchs, N. A. 1964. The Mechanics of Aerosols. MacMlllan Company,
New York. 408 pp.
Liu, B. Y. H., and A. Kapadia. 1977. A Computer Data Reduction Program
for the Electrical Aerosol Analyzer. Publication Number 325, Particle
Technology Laboratory, Department of Mechanical Engineering, University
of Minnesota, Minneapolis, MN 55455. 26 pp.
Liu, B. Y. H., and G. A. Kuhlmey. 1977. Efficiency of Air Sampling Filter
Media. In: X-Ray Fluorescence Analysis of Environmental Samples, T. G.
Dzubay, ed. Ann Arbor Science, Ann Arbor, MI. pp. 107-119.
Liu, B. Y. H., and K. W. Lee. 1975. An Aerosol Generator of High Stability.
Am. Ind. Hyg. Assoc. J., 36:861-865.
Liu, B. Y. H., and D. Y. H. Pui. 1975. On the Performance of the Electrical
Aerosol Analyzer. J. Aerosol Sci., 6:249-264.
Liu, B. Y. H., D. Y. H. Pui, and A. Kapadia. 1976. Electrical Aerosol
Analyzer: History, Principle and Data Reduction. Presented at the
Aerosol Measurement Workshop, University of Florida, Gainesville, FL,
March 24-26, 1976. To be published in the Proceedings of the Workshop.
Liu, B. Y. H., D. Y. H. Pui, and Y. Kousaka. 1977. Properties of ^SCyp
H20 Solution Droplets. Particle Technology Laboratory, University of
Minnesota, Minneapolis, MN 55455.
Maugh, T. H., II. 1977. Sulfuric Acid from Cars: A Problem that Never
Materialized. Science, 198:280-284.
Perry, R. H., and C. H. Chilton, eds. 1973. Chemical Engineers1 Handbook,
5th Edition. McGraw-Hill Book Company, New York.
Sabinina, L. and L. Terpugow. 1935. Die Oberflachenspannung des Systems
Schwefelsaure-Wasser. Z. Phys. Chem., A173:237-241.
Whitby, K. T., D. B. Kittelson, B. K. Cantrell, N. J. Barsic, and D. F.
Dolan. 1976. Aerosol Size Distributions and Concentrations Measured
during the General Motors Proving Grounds Sulfate Study. Presented
before the Division of Environmental Chemistry, American Chemical
Society, San Francisco, CA, August, 1976.
39
-------
Wilson, W. E., L. L. Spiller, T. G. Ellestad, P. J. Lamothe, T. G. Dzubay,
R. K. Stevens, E. S. Macias, R. A. Fletcher, J. D. Husar, R. B. Husar,
K. T. Whitby, D. B. Kittelson, and B. K. Cantrell. 1977. General
Motors Sulfate Dispersion Experiment: Summary of EPA Measurements.
J. Air Pollut. Control Assoc., 27:46-51.
-------
APPENDIX A
DETAILED SIZE DISTRIBUTION DATA OBTAINED BY EAA
41
-------
TABLE Al. SIZE DISTRIBUTION MEASUREMENT BY EAA
M
Date of Experiment: July 11 (0.1 N) and July 14 (1.0 N) , 1977
Solution Normality 0.1 N
Primary Dilution
Air. 1pm 10 20 30
AT AV AT AV AT AV
AlogD "* AlogD "•"• AlogD
P P P
Channel, D , pm
.0100 - .0178 .3 .64 6.0 12.8 10 21.2
.0178 - .0316 2.4 8.2 27 114.8 45 204.8
.0316 - .0562 1.7 43.8 11 300 13 343
.0562 - .100 4.3 195.7 11.2 382 10.1 222.8
.100 - .178 2.45 263.7 2.34 79.2 1.6 12.7
.178 - .316 .61 173 .32 14 .2 .64
.316 - .562 .14 53.7 .07 .68 .04
.562 - 1.00 .04 8.4 .02 .036 .01
> 1.00 .06 — .05 — .05 —
Measured Aerosol
Volume, pm3/cm3 186.8 225.8 201.4
Dilution No No No
Aerosol Volume in
Chamber, um3/cm3 186.8 225.8 201.4
Geometric Mean Volume
Diameter, pm .14 .056 .041
o 1.9 1.7 1.5
g
1.0 N
10 20 30
AT AV AT AV AT AV
AlogD Ui AlogD "* AlogD
P P P
0 0 0 0 .05 .104
.2 .35 .35 .76 .60 2.07
.3 7.6 .42 11.2 .45 12.28
.7 35.9 .82 40 .70 30.68
.255 18.2 .265 16 .215 13.96
.035 1.96 .035 1.72 .027 2.64
.007 .048 .007 .04 .005 .20
.003 — .003 — .003 .016
000—00
16.0 17.5 15.49
129:1 129:1 129:1
2064 2258 1998
.088 .082 .082
1.5 1.5 1.7
* ,T ,,,-11, AV pm3
AI. 10 A* — — — J-—
* • AlogD ' 3 *
6 p cm
-------
TABLE A2. SIZE DISTRIBUTION MEASUREMENT BY EAA (10 LPM PRIMARY DILUTION AIR)
u>
Date of Experiment: July 21, 1977
Solution Normality
Channel,
.0100
.0178
.0316
.0562
.100
.178
.316
.562
Measured
Dp, urn
- .0178
- .0316
- .0562
- .100
- .178
- .316
- .562
- 1.00
> 1.00
Aerosol
3 3
Volume, vim /cm
Dilution
0.
AI
3.0
13
7.3
10.2
2.14
.25
.04
.01
.06
1 N
AV
AlogD
P
6.4
52
197
420
147
36
4.4
.4
—
215.4
Ho
0.2 N
AV
AlogD
P
2.0 4.0
23 84
15 412
20.7 868
4.5 272
.54 52
.13 4
.03 —
.08 —
424
No
0.3 N
AI AV
AlogD
P
.1 .22
.9 3.3
.7 19
.99 43
.258 17
.036 4
.009 .6
.003 —
.004 —
21.9
36:1
0.6
AI
.05
.9
1
1.83
.55
.086
.018
.008
.008
42.
36:
N
AV
AlogD
P
.1
3
27
86
43
11
1
—
—
5
1
1.0
AI
.1
.4
.3
.99
.7
.154
.033
.012
.011
50.
36:
N
AV
AlogD
P
.2
1
8
45
80
49
16
4
—
8
1
Aerosol Volume in
3 3
Chamber, vim /cm
Geometric Mean Volume
Diameter, ym
215.4
.082
1.84
424
.077
1.7
787
.083
1.72
1530
.093
1.64
1830
.16
1.97
* -11
AI, 10 A;
AV
-------
TABLE A3. SIZE DISTRIBUTION MEASUREMENT BY EAA (20 LPM PRIMARY DILUTION AIR)
Date of
Experiment: July 21, 1977
Solution Normality
Channel ,
.0100
.0178
.0316
.0562
.100
.178
.316
.562
Measured
Volume,
Dilution
Dp, urn
- .0178
- .0316
- .0562
- .100
- .178
- .316
- .562
- 1.00
> 1.00
Aerosol
3 3
pm /cm
0.1 N 0.2 N
AT AV AT AV
AlogD " AlogD
P P
11 24
54 232
25 688
21.7 672
3.6 76
.45 8
.09
.03
.09
425
No
0.3 N
AT AV
AlogD
P
.22 .4
1.74 7
.88 25
.92 32
.195 6
.032 .8
.006
.003
.004
17.8
36:1
0.6
AI
0
1.9
1.3
1.83
.47
.073
.015
.005
.007
39.
36:
N
AV
AlogD
P
0
7
36
79
30
7
.6
— -
—
7
1
1.0
AI
.2
1.1
.9
2.17
.76
.123
.026
.009
.012
57.
36:
N
AV
AlogD
P
.4
3.8
24
98
72
27
6
.7
—
7
1
Aerosol Volume in
Chamber, urn /cm
Geometric Mean Volume
Diameter, urn
425
.051
1.61
640
.058
1.6
1430
.08
1.67
2077
.11
1.82
* -11
AI, 10 A}
AV
-------
TABLE A4. SIZE DISTRIBUTION MEASUREMENT BY EAA (30 LPM PRIMARY DILUTION AIR)
Date of Experiment: July 21, 1977
Solution
Channel,
.0100
.0178
.0316
.0562
.100
.178
.316
.562
Measured
Volume ,
Dilution
D , um
P
- .0178
- .0316
- .0562
- .100
- .178
- .316
- .562
- 1.00
> 1.00
Aerosol
Urn /cm
0.1 N
AT AV
AlogD
P
14 30
45 209
11 280
7 139
.83 5.6
.09 .3
.02 —
.01 —
.05 —
167
No
0.2 N
AT Av
AlogD
P
22 48
69 304
22 588
20 600
3.3 80
.5 14
.08 ~
.03
.09
408
No
0
AI
.2
2.08
.83
.86
.185
.03
.077
.003
.005
Normality
.3 N
AV
AlogD
P
.4
9
22
34
11
3
.4
—
—
20
36:1
0.6
AI
.2
2.4
1.2
1.74
.465
.065
.016
.005
.009
N
AV
AlogD
P
.4
9
33
72
31
8
1
.1
—
39
36:
1
1.0
AI
.1
1.7
1.4
2.25
.7
.105
.022
.011
.012
N
AV
AlogD_
•
6
38
101
52
13
1
•
—
V
2
1
53
36:
1
Aerosol Volume In
Chamber, um /cm
Geometric Mean Volume
Diameter, um
167
.038
1.56
408
.049
1.68
718
.072
1.82
1400
.081
1.77
1910
.089
1.70
* -11
AI, 10 A;
AV
AlogD ' 3 '
p cm
-------
APPENDIX B
OPERATING INSTRUCTIONS
INTRODUCTION
The sulfuric acid aerosol generator described in this manual has been
developed at the Particle Technology Laboratory, University of Minnesota.
The generator was designed for the Environmental Protection Agency for use
3
with its 0.33 m animal exposure chamber. It was tested with the chamber
at the University of Minnesota and shipped to EPA together with the test
chamber.
This manual covers the operating instructions for the aerosol generator
only. More detailed information concerning the generator is given in the
main body of this report.
UNPACKING AND SETUP
As the schematic diagram of the system in the next section shows, there
are three main parts to the generator: (1) an atomizer sub-assembly, (2) a
flow control panel, and (3) an evaporator-mixer unit. The atomizer sub-
assembly, the flow control panel, and the evaporator-mixer are placed within
the test chamber during shipment, whereas the furnace for the evaporator is
shipped separately in its own container.
Following the receipt of the shipment at EPA, carefully unpack and
remove the contents from the test chamber. Carefully unwrap the atomizer
sub-assembly, the flow control panel, and the evaporator-mixer. The
evaporator-mixer is made of pyrex glass (see Figure Bl). Be careful not
to break it. Two units are supplied, one to be used in the generator, and
the other as a spare. A detailed drawing of the evaporator-mixer is shown
in Figure B6.
Set up the system as follows:
46
-------
Figure Bl. Photograph of evaporator-mixer,
Figure B2.
Photograph of sulfuric acid aerosol generator installed
on the exposure chamber.
-------
1. Mount the atomizer sub-assembly on the front of the test chamber
near the upper left-hand corner as in Figure B2. The acrylic back
panel of the atomizer sub-assembly is fastened to the front of the
test chamber with eight screws.
2. Mount the flow control panel on the front of the test chamber above
the chamber door as in Figure B2. The panel is fastened to the
stainless steel bracket - the original mounting bracket for the
Magnehelic pressure gauge - with four screws.
3. Set up the furnace on top of the test chamber on the piece of ply-
wood supplied. Set up the metal stand and clamp, and install the
evaporator-mixer in the furnace as shown in Figure B2. Adjust the
evaporator-mixer so that the evaporator is inserted all the way
into the furnace.
4. Make the following interconnections with tubings supplied:
a) Connect the outlet of the atomizer-flow rotameter to the com-
pressed air inlet of the atomizer with the 1/4" nylon tubing
and Swagelok fitting.
b) Connect the outlet of the settling chamber to the inlet of the
evaporator with the 5/16" i.d. Tygon tubing supplied.
c) Connect the outlet of the primary dilution air rotameter to the
side-inlet on the mixing nozzle with the 5/16" i.d. Tygon tubing
supplied.
d) Connect the outlet of the mixing nozzle to the aerosol inlet of
the test chamber with the 1/2" i.d. Tygon tubing supplied.
e) Connect the Magnehelic gauge to the orifice meter with the
3/16" i.d. Tygon tubing supplied.
The completed system should appear as in Figure B2. Compare the con-
nections you have made with those shown in the photograph.
48
-------
OPERATING PRINCIPLES AND CHARACTERISTICS OF
THE SULFURIC ACID AEROSOL GENERATOR
This section provides a brief description of the operating principles
and characteristics of the aerosol generator. A schematic diagram of the
system is shown in Figure 4.
Dry, filtered and regulated compressed air at 35 psig (241 kPa) is sup-
plied to the atomizer via a 0 - 9 1pm rotameter. In the atomizer, the H»SO,
solution is atomized to form a polydisperse spray. The spray is then intro-
duced into a one-liter settling chamber to remove the large drops and to
allow any accumulated liquid on the connecting tubing to settle. The spray
then enters the evaporating tube, which is heated externally by the tube
furnace. In the evaporating tube, the droplets are vaporized. The vapor
is then injected into the mixing nozzle where it encounters the primary
dilution air supplied to the nozzle via the 0-30 1pm rotameter. The rapid
mixing of the vapor and the primary dilution air causes a fine H«SO, aerosol
to be formed. This aerosol is then introduced into the chamber inlet where
it is further diluted by the chamber air flow just upstream of the orifice
flowmeter. This diluted aerosol is used in the test chamber.
Under normal operating conditions, the temperature control on the tube
furnace is set to "lo". At this setting, the furnace will reach a steady
operating temperature of 350 - 400°F according to the front-panel meter on
the furnace. The actual gas temperature at the exit of the evaporator will
be approximately 220°F.
Under a given set of operating conditions, e.g., for a fixed furnace
temperature and fixed primary and secondary dilution air flows, the size and
the concentration of the sulfuric acid aerosol produced by the generator are
determined by the concentration of the H»SO, solution used in the atomizer.
This is the primary means by which the aerosol size and concentration are
varied. Table Bl shows the characteristics of the aerosol produced by the
generator for various H^SO, solution concentrations. Normally, H^SO,
solutions in the 0.1 N to 1 N concentration range are used. This results
3
in an H2SO, mass concentration of 130 to 1,300 yg/m . The corresponding
particle size range is from 0.04 to 0.87 urn diameter.
49
-------
TABLE Bl. CHARACTERISTICS OF AEROSOL PRODUCED BY THE SULFURIC ACID AEROSOL GENERATOR
Primary dilution air flow = 30 1pm (see Note 1)
Chamber air flow = 350 1pm
Relative Humidity = 45% (see Note 2)
Ln
O
Run 1
Run 2
Measured Values
3
Filter: Mass Cone., yg/m
3
TSI Piezobalance: Mass Cone., yg/m
3 3
EAA: Volume Cone., ym /cm
D (volume median dia.). ym
P
a
g 3
EPA sulfate: yg/m of sulfate
3 3
EAA: Volume Cone., ym /cm
D (volume median dia.)> ym
P
a
g
0.1
240
240
204
0.041
1.5
145
167
0.038
1.6
H_SO, Solution Normality
0.2 0.3 0.6 1.0
3420
3000
2000
0.056 0.082
1.7 1.7
1375
408 718 1400 1910
0.049 0.072 .081 0.089
1.7 1.8 1.8 1.7
Calculated Mass Concentration of H2SO,, yg/m
Run 1
Run 2
Filter x , _,.
> (see Note 3)
TSI Piezobalance
EAA (see Note 4)
EPA Sulfate (see Note 5)
EAA (see Note 4)
108
108
128
148
101
1540
1350
1220
1400
248 437 851 1160
(continued)
-------
TABLE Bl (continued)
Notes
Note 1 Due to flow instability, the experiments were run with a mean chamber
flow of 350 1pm rather than the standard chamber flow of 330 1pm.
It is expected that reducing the chamber flow from 350 to 330 1pm
will have a negligible effect on the measured aerosol characteristics.
Note 2 The relative humidity varied between 42 and 48% during these experi-
ments, with a mean of 45%. At a 45% relative humidity, the droplet
will have an equilibrium concentration of 0.45 g of H~SO, per gram
of solution and a solution density of 1.35 g/cc.
Note 3 Obtained by multiplying the measured aerosol mass concentration by 0.45.
Note 4 Obtained by multiplying the measured aerosol volume concentration by
(1.35M0.45) = 0.608.
Note 5 Obtained by multiplying the measured SO, concentration by the ratio
of molecular weights of H2SO, and SO, or (98/96) = 1.021.
-------
The mass concentration of the sulfuric acid aerosol was measured with
several different techniques as shown in Table Bl. The techniques used in-
clude filter collection and weighing, the integration of the measured size
distribution by the electrical aerosol analyzer to obtain the total aerosol
volume, direct mass measurement by the quartz-crystal microbalance (TSI
Model 3500 Piezobalance) and sulfate measurement by the EPA wet chemical
technique. The agreement is seen to be good with the spread of data gener-
ally within ±20% from the mean. The results are also shown plotted in
Figures 10 and 13, which can be used to interpolate between the measured
values.
To generate sulfuric acid aerosols larger than can be obtained by the
use of a 1 N solution, an optional coagulation chamber is inserted between
the aerosol generator and the test chamber as shown in Figure 4. This causes
the particles to coagulate and grow to a larger size. Experiments show that
with a 20-liter coagulation chamber, the 0.087 ]im diameter aerosol produced
by a 1 N solution with a 30 1pm primary dilution air flow will grow to a
size of 0.13 pm diameter with negligible reduction in mass concentration.
Other chamber sizes can also be used. The corresponding particle size at
the chamber can be estimated by means of Table B2.
The rate of liquid consumption by the atomizer has been measured and
found to be 6.4 ml/hr when dry, filtered compressed air at 35 psig (241 kPa)
was used as the atomizing air. Of this, 1.9 ml/hr, or 30%, represents an
evaporative loss, and the remaining 4.5 ml/hr, or 70%, represents the actual
liquid consumed by atomization. Due to evaporation, the solution in the
atomizer reservoir will become more concentrated during operation. The rate
of increase in solution concentration will depend upon the amount of liquid
that is in the atomizer reservoir. Table B3 shows the calculated volume of
liquid remaining in the atomizer reservoir and the concentration of the re-
maining liquid at various times for an initial liquid volume of 1,000 ml.
As the table shows, although 1,000 ml will provide sufficient liquid to op-
erate the generator continuously for six days, the increase in solution con-
centration due to evaporation will necessitate more frequent liquid changes.
For instance, if the solution concentration in the reservoir is to be main-
tained within 30% of the initial concentration, the solution must be replaced
52
-------
TABLE B2. AEROSOL PARTICLE SIZE AS A FUNCTION OF
COAGULATION CHAMBER VOLUME
Chamber Volume, liters Volume Mean Diameter, ym
0 0.087 (measured)
5 0.101
10 0.113
20 0.130 (measured)
30 0.144
Calculated by means of the interpolation formula
DP = Nds^]13 (0-087) *m
where V is the volume of the coagulation chamber in liters.
TABLE B3. CONSUMPTION AND CONCENTRATION OF H-SO, SOLUTION
BY ATOMIZER AS A FUNCTION OF TIME
Time,
hr
0
16
31
47
63
78
94
109
125
141
Liquid Volume in
Atomizer, ml
1,000
900
800
700
600
500
400
300
200
100
H2S04 Cone, at t
fc ° H-SO, Cone, at t = 0
1.00
1.03
1.07
1.13
1.20
1.30
1.45
1.69
2.19
3.68
53
-------
whenever the liquid volume in the reservoir is down to 500 ml, or after about
78 hours of continuous operation. Other solution changing intervals can be
easily determined from Table B3 when the maximum allowable concentration
change is known.
OPERATING PROCEDURE
In order to operate the aerosol generator, you will need a source of
regulated compressed air. The compressed air should be dried and filtered
as shown in Figure 4 before it is introduced into the aerosol generator.
A suitable filtered air supply unit is available commercially (Model 3074
Filtered Air Supply, TSI Inc., P. 0. Box 3394, St. Paul, MN 55165).
Connect the compressed air supply to the inlet of the rotameters as
shown in Figure B2. Then operate the generator as follows: .
1. Set the pressure regulator on the filtered air supply unit to zero
output pressure.
2. Fill the atomizer reservoir with H-SO, solution of the desired
concentration. Use more or less liquid in the reservoir depending
upon the length of operating time needed. One full bottle (one
liter) will provide sufficient liquid to operate the generator
continuously for about six days, or three days if the concentra-
tion change is to be kept within 30% of its initial value (see
preceding section).
3. Turn on the exhaust blower on the test chamber and adjust the flow
to obtain a deflection of 0.7" H~0 on the Magnehelic gauge. This
will provide a chamber air flow of 330 1pm, or one chamber volume
per minute. (For other chamber air flows, refer to the calibration
curve for the orifice meter given in Figure B3.)
4. With the rotameter inlet valves closed, adjust the pressure regu-
lator to obtain an output pressure of 35 psig (241 kPa).
5. Adjust the inlet valve on the primary dilution air rotameter to
obtain a full-scale reading of 150 mm. This will produce a primary
dilution air flow of 30 1pm. (To obtain other dilution air flows,
refer to the calibration curve in Figure B4 for the rotameter.)
54
-------
CHAMBER INLET ORIFICE
For Air at 21°C and 1 atmosphere
O ASME Orifice
O Gas Meter
200
Flovrate, 1pm
Figure B3. Calibration curve of orifice meter for total chamber flow.
55
-------
6. Open the inlet valve on the atomizer flow rotameter. The rotameter
should read 25 mm on the scale corresponding to an atomizer flow of
2.4 1pm. If the reading is substantially lower, the orifice in the
atomizer is probably plugged. The atomizer should then be cleaned.
(See Figure B5 for the rotameter calibration curve provided by the
manufacturer.)
7. Turn on the furnace and set the temperature control to "lo". When
starting with a cold furnace, it will take about two hours for the
generator output to become steady. If the heating process is to be
speeded up, the temperature control dial can be set to "high" for
a couple of minutes and the \furnace temperature closely watched.
When a temperature of 400°F (204°C) is reached, the dial should
then be returned to "lo".
8. To shut down the generator, turn off the compressed air supply and
the furnace. If the aerosol generator is to be shut down tempo-
rarily for short periods, say from a few hours to overnight, the
furnace may be left on its "lo" setting. Simply turn off the com-
pressed air. When the generator is started up again with a warm
furnace, it will take only one hour for the output to become steady.
NOTES ON THE OPERATION OF THE AEROSOL GENERATOR
1. Under no circumstances should the furnace be operated above a tem-
perature of 1000°F, corresponding to a temperature control setting
of "3". The pyrex evaporator will soften or melt at high tempera-
tures.
2. When changing from a concentrated H-SO, solution to a more dilute
solution, the atomizer reservoir, the settling chamber, the
evaporator-mixer, and all connecting tubing in contact with H^SO,
aerosol or vapor should be thoroughly cleaned and dried. Over a
period of time, H^SO, solution will accumulate at various points
in the system. If the system is not cleaned, the H_SO, solution
may act as a desiccant, a humidifier, or as a source of H^SO, vapor
to change the characteristics of aerosols produced by the generator.
56
-------
ROTAMETER
PRIMARY DILUTION AIR
For Air at 21°C and 1 atmosphere
Tube Number: FM044-40S
12 16 20
Flowrate, 1pm
Figure B4. Calibration curve of rotameter for primary dilution flow.
-------
1140
L/i
CO
ROTAMETER
ATOMIZER FLOW
For Air at 21°C and 1 atmosphere
Tube Number: FM034-39G
Figure B5. Calibration curve of rotameter for atomizer flow.
-------
VO
* IT V »
* 13. 0 *
II . . II -i_
r
1
- •' — o
4" to
| ^
//
rr
l/4
2"
fc^
Figure B6. Dimensions of pyrex evaporator tube and mixing nozzle.
-------
TECHNICAL REPORT DATA
(Please read Instructions on the rvvrsc before completing)
1. REPORT NO.
EPA-600/2-78-104
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
GENERATION OF SULFURIC ACID AEROSOLS
FOR HEALTH EFFECT STUDIES
6. PERFORMING ORGANIZATION CODE
5. REPORT DATE
June 1978
7. AUTHOR(S)
B. Y. H. Liu and J. Levi
8. PERFORMING ORGANIZATION REPORT NO,
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Particle Technology Laboratory
Mechanical Engineering Department
University of Minnesota
Minneapolis, MN 55455
10. PROGRAM ELEMENT NO.
1AA601 CA-24 (FY-78)
11. CONTRACT/GRANT NO.
R-801301
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory - RTF, NC
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
Interim 9/76-3/78
14. SPONSORING AGENCY CODE
EPA/600/09
15. SUPPLEMENTARY NOTES
16. ABSTRACT
A generator has been developed and constructed for producing sulfuric acid
aerosols at 330 liters per minute to an animal exposure chamber of 330 liters
internal volume. Sulfuric acid concentrations in the chamber range from 0.13 to
1.3 mg/m3. Geometrical mean volume diameters of the aerosol range from 0.04 to
0.15 urn, and the geometrical standard deviation of the aerosol is about 1.6.
The generator operates by atomizing a sulfuric acid solution to form a poly-
disperse spray. The droplets are then vaporized in a tube-furnace and the vapor
injected into filtered air at room temperature to form a high concentration of
small sulfuric acid particles.
The aerosol generating system has been evaluated by means of several tech-
niques. Particle size distribution was measured by an Electrical Aerosol Analyzer.
Four independent techniques were used to measure the aerosol concentration: an
Electrical Aerosol Analyzer, a Quartz-Crystal Aerosol Mass Monitor, filter col-
lection and weighing, and chemical analysis of collected particle samples. Good
agreement was found.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
* Air pollution
* Aerosols
* Sulfuric acid
* Aerosol generators
* Development
13B
07D
07B
13D
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
68
20. ."CCURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
60
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