EPA-600/4-77-040
August 1977
Environmental Monitoring Series
SULFUR DIOXIDE BUBBLER
TEMPERATURE STUDY
Environmental Monitoring and Support Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
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SULFUR DIOXIDE BUBBLER TEMPERATURE STUDY
By
Barry E. Martin
Field Studies Section
Environmental Monitoring and Support Laboratory
Research Triangle Park, North Carolina 27711
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and Support
Laboratory, U. S. Environmental Protection Agency, and approved for publica-
tion. Mention of trade names or commercial products does not constitute
endorsement or recommendation for use.
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ABSTRACT
The instability of sulfur dioxide collected in the absorbing reagent
specified by the Federal Register Method has been shown to result in sub-
stantial errors at ambient temperatures above 21°C (70°F) by several investi-
gators.
A series of temperature controlled studies was designed by the Field
Studies Section, Environmental Monitoring Branch, to determine the temperature
characteristics of the typical Indoor and All Weather Five-Gas Samplers used
to collect 24 hour integrated samples of sulfur dioxide from ambient air.
These studies included tests to determine the temperature inside the samplers
using 32°C (90°F) thermal heating strips. The results of these tests suggest
that the temperature maintained in both samplers is elevated enough to cause
decay of S02 collected by the Federal Reference Method. Several methods were
investigated to control the temperature of the sulfur dioxide absorbing
reagent, potassium tetrachloromercurate, before, during and after sampling. A
small commercially available refrigerator was evaluated as an inexpensive
method of controlling the absorbing reagent temperature. With certain modifi-
cations, the refrigerator was found to be an acceptable method of maintaining
the necessary temperature control during sampling. A thermoelectric cooler
was also evaluated and found to be acceptable. As the result of this investi-
gation, a contract was funded to develop an acceptable prototype thermo-
electric cooler which could be incorporated into the existing All Weather
iii
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Five-Gas Sampler" to maintain the temperature control of 12±5°C during various
atmospheric temperature ranges. Two companies responded to the invitation to
bid. Evaluations were performed on these thermoelectric systems and data show
that the systems will control the temperature of the absorbing solution within
the acceptable range.
A method of controlling the temperature of the collected solution during
shipping was also investigated. A styrofoam shipping container using a
eutectic mixture for cooling was evaluated. It was found a 21°C temperature
was maintained in the sulfur dioxide - tetrachloromercurate solution for a
period of 50 hours at ambient temperatures up to 50°C.
iv
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CONTENTS
Abstract iii
Figures vl
Tables vii
Acknowledgement viii
1. Introduction 1
2. Conclusions 3
3. Results and Discussion 5
References 22
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FIGURES
Number Page
1 Temperature inside S02 samplers under varied
temperatures 6
2 Effects of ambient conditions on the temperature inside
all weather sampler 7
3 Temperature inside an indoor sampler using standard
32 C heater under varied temperatures 8
4 Modified refrigerator system 11
5 Modified Bendix permeation chamber system 12
6 Effects of chamber temperature variations on TCM solution
temperature using Bendix permeation chamber 13
7 Hilton Industries Model 2125 Sampling Train Assembly .... 15
8 RAC Sampling Train Assembly 15
9 Effects of constant temperature of 50°C on TCM solution
stored in a Trans Temp Cool Pak 19
10 Effects of time on the TCM solution temperature stored
in a Trans Temp Cool Pak exposed to variable high tem-
perature 20
vi
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TABLES
Number Page
I Effects of time and temperature on collected
S02 9
II Temperature of TCM solution during ambient
sampling 17
vii
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ACKNOWLEDGEMENT
The author would like to express appreciation to Joel Vernon Daughtridge
for his assistance in the testing of the SO^ samplers and thermoelectric
temperature controlled systems.
viii
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SECTION 1
INTRODUCTION
The dichlorosulfito-mercurate (S02-TCM) solutions collected by the
Federal Reference Method have been shown to be unstable during storage at
2 3
temperatures above 21°C (70°F) . Since there is a stability problem with
the collected SO^-TCM solutions at elevated temperatures, the S02 collected by
the potassium tetrachloromercurate (TCM) may be decaying prior to analysis
during sampling and storage, indicating S02 concentrations lower than those
actually collected. Based on a temperature-time decay table developed by the
Quality Assurance Branch of the Environmental Monitoring and Support Labora-
tory (QAB/EMSL), a minimum temperature decay range of 12°C±5°C was selected as
the desirable TCM solution sampling temperature. Temperature studies were
performed to characterize elevated temperatures that SOp - TCM solutions might
be exposed to before, during, and after ambient air sampling. Studies were
also designed to develop a temperature controlled sampling system which will
maintain the desired temperature of 12°C±5°C in temperature ranges expected
during summer months.
To perform these evaluation studies, two commercially available sampling
shelters were utilized. One design consisted of a thermostated compartment in
which the five-gas sampling system is housed. The sampling pump system is a
separate component and "is not housed in the shelter. This sampler is designed
1
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for indoor use. It is commonly referred to as the Indoor Five-Gas Sampler.
The second design consists of an All Weather shelter which houses a temper-
ature controlled Five-gas sampler in one section and the sampling pump in a
separate ventilated section. This sampler is designed for use outdoors and is
referred to as the All Weather Five-Gas Sampler.
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SECTION 2
CONCLUSIONS
The results of the tests on the typical Indoor and All Weather Five-Gas
Samplers indicate that at ambient temperatures above 20°C, the temperature
inside the samplers was elevated enough to cause decay of collected S02» when
the Federal Reference Method (FRM) is used. Data show that it js_ necessary to
control temperature inside both samplers (Indoor and All-Weather) to limit
decay of the S02 collected by the FRM. The results from testing new prototype
systems to control the temperature show that several units adequately maintain
the TCM solution temperature below the temperature at which decay of collected
S02 occurs. These devices may be as simple as a small properly modified
refrigerator or as sophisticated as a special thermoelectrical control to
maintain the solution temperature. A-means of controlling the TCM solution
temperature during sampling and storage must be implemented immediately to
insure good quality data collected by the Federal Reference Method at sites
where the TCM bubbler would be exposed to elevated temperatures above 25°C.
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SECTION 3
RESULTS AND DISCUSSION
The environmental chamber used to obtain test temperatures was Model B5-
67M manufactured by Forma Scientific, Inc. This chamber maintains a desired
temperature at ± 0.3°C with a uniformity of ±0.5°C over the range of 0°C to
50°C. All of the temperatures monitored in this study were measured using
Yellow Springs Instrument Company (YSI) 700 series thermilinear (linear therm-
istors) probes. These probes are teflon coated which allowed them to be
inserted in the SO^ sampling solution without affecting their performance.
YSI Sostman Series 740A thermivolt signal conditioners were used to convert
the signal from the probe into a linear temperature analog millivolt signal.
These units cover a temperature span from 0°C to 100°C with a system accuracy
of ±0.4°C including the probes. The YSI systems were verified using an ASTM
thermometer prior to initiation of the study. The output of the signal condi-
tioners was monitored using a Model 680 Hewlett Packard recorder to provide a
continuous record of the temperatures being measured.
Initially, tests were conducted to determine if a potential temperature
problem existed in the Indoor and the All-Weather 5-gas samplers. For this
test, the temperature probes were not placed in the sampler solution, but were
located at the approximate position of the S02 bubbler. Both types of samplers
equipped with the standard 32°C heater were placed in the temperature con-
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trolled environmental chamber. The Indoor sampler was not sampling during
this temperature check. The All-Weather sampler has a built-in sampling pump
which acts as a source of heat. Therefore, during this temperature check, the
All-Weather sampler was sampling the environmental chamber air at a flowrate
of 200 cm /min. Fifty (50) ml of water was substituted for the TCM solution
in the S02 bubbler in both samplers. After the initial stabilization period,
the temperature inside both samplers remained constant for 24 hours. Figure 1
is a plot of the chamber temperature versus the temperature inside the S02
samplers. Figure 1 indicates that the temperature inside the All-Weather
sampler is one to six degrees higher than the temperature inside the Indoor
sampler under similar conditions. This difference i.s attributable to the heat
generated by the sampling pump.
60
40
<
C/3
20
ALL WEATHER SAMPLER TEMP. - O
INDOOR SAMPLER TEMP. -A
I
I
20 40 60
CHAMBER TEMPERATURE, °C
Figure 1. Temperature inside SO2 samplers under varied
temperatures.
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Another temperature check was performed on the All-Weather sampler
equipped with the 32°C heater strip under actual sampling conditions for
ambient S02 at the Environmental Research Center, Research Triangle Park, N.C.
During the test, the ambient temperature monitored varied from -3°C to 20°C.
For this ambient temperature range, the 32°C heater strip controlled the
temperature inside the sampler from 9° to 30°C. Figure 2 is a plot of the
ambient temperature versus the temperature inside the sampler. The wide
scatter observed on the graph suggests that the temperature inside the sampler
is affected by external meteorological conditions such as wind speed and wind
direction. At an ambient temperature of 20°C, the temperature inside the All
Weather sampler reached 30°C.
K
UJ
<
CO
40
30
20
10
10 20
AMBIENT TEMPERATURE. °C
30
40
Figure 2. Effects of ambient conditions on the temperature inside
all weather sampler.
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A further study was performed to determine the temperature in the Indoor
sampler equipped with the 32°C heater strip under various chamber temperatures.
Figure 3 is a plot of the environmental chamber temperature versus the TCM
solution temperature. Data showed that if the Indoor sampler is used with the
32°C heater strip operational, decay of S02 in the TCM absorbing solution
occurs when ambient temperatures are in excess of 8°C.
30
u
e
<
cc
cc
LU
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The Quality Assurance Branch (QAB) supplied the Field Studies Section
(FSS) with a temperature-time decay table for S02 collected by the Federal
Reference Method. See Table I. Table I shows the percent SOp remaining in
the TCM solution after exposure to various temperatures. From this table, a
minimum temperature decay range of 12°C ± 5°C was selected by the Field Studies
Section (FSS) as the desirable TCM solution sampling temperature. Since there
is decay of the collected SO^ at elevated temperatures, a means of controlling
the TCM temperature within the desired range during sampling and shipping is
needed.
TABLE I. EFFECTS OF TIME AND TEMPERATURE ON COLLECTED S02
°c
5
10
15
20
25
30
35
40
45
50
°F
41
50
59
68
77
86
95
104
113
122
At End
Of sampling
99.
99.
99.
99.
98.
97.
95.
87.
75.
56.
9
9
8
6
9
4
1
6
3
3
1
99.
99.
99.
98.
96.
92.
84.
66.
41.
15.
8
8
4
7
7
2
0
8
4
6
2
99.8
99.7
99.0
97.8
94.4
87.4
74.1
50.8
22.7
4.3
% S02 REMAINING
Days After Sampling
345
99.8
99.6
98.6
96.9
92.2
82.8
65.5
38.7
12.5
1.2
99.7
99.5
98.2
96.1
90.2
78.5
57.9
29.5
6.9
0.9
99.7
99.4
97.8
95.2
88.1
74.3
51.3
22.5
3.8
0.1
6
99.6
93.5
97.4
94.3
86.1
70.4
45.2
17.2
1.9
0
7
99.6
99.2
97.0
93.5
84.2
66.7
39.9
13.0
1.1
0
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One method of controlling the TCM solution temperature during sampling
was the use of a small commercially available 1.5 ft refrigerator (Sanyo
Model SR 4801). The only required modification to this refrigerator was the
drilling of two 1/4" holes in the back of the refrigerator for the sample and
exhaust lines. The results indicate that the small refrigerator is capable of
maintaining 12°C±5°C at ambient temperatures of 25°C to 50°C. However, if the
ambient temperature is below 20°C, it will be necessary to install a small
strip heater in the refrigerator to keep the temperature inside the refrig-
erator above 7°C.
Due to the cool temperature maintained by the refrigerator, water condensed
in the sample inlet lines and in the bubblers. This condensation will be a
problem in sampling on high relative humidity days. Therefore, a study was
conducted using a sample stream saturated with water to determine the amount
of condensation in the sample inlet lines and in the bubbler. Using an
uninsulated sample inlet line, enough water condensed in the sample line
inside the refrigerator to stop the sample flow and to increase the total
volume of solution at the end of sampling to 52 ml. Since water is added to
the TCM solution under high relative humidity conditions, it may be necessary
to use less than 50 ml of the TCM solutions. Using a sample inlet line insu-
lated with standard water pipe insulation, only a few drops of moisture were
evident in the sample inlet line. To prevent any accumulation of moisture,
the sample inlet line inside the refrigerator should be wrapped with heater
tape. The voltage to the heater tape should be adjusted so that the temperature
of the sample inlet line is near the average ambient temperature. Under these
conditions, water condensation in the sample inlet line should not occur or at
10
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least be minimized and not interfere with the collection of S02 in the bub-
blers. Figure 4 is a diagram of this system. A small refrigerator such as
the one used in this experiment could be used as an inexpensive means of
maintaining sub-ambient temperatures during the hot summer months. If nec-
essary, as many as five bubblers could be installed in the refrigerator.
SAMPLE PROBE INLET
FILTER
\
TIMER
EXHAUST MANIFOLD
PUMP
MODIFIED 1.5 ft3 REFRIGERATOR
Figure 4. Modified refrigerator system.
11
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Another device investigated to determine the feasibility of controlling
the temperature of the TCM solution at sub-ambient levels was the permeation
chamber utilized in the Bendix Calibrator Model 8851. For this test, a
o
sample flow rate of 200 cm /min was used. The temperature probe was placed in
the TCM solution. The Bendix permeation chamber was then placed in the tempera-
ture controlled environmental chamber and the chamber temperature was varied.
These results indicate that this thermoelectrically controlled permeation
chamber is capable of maintaining a temperature cool enough to limit S02 decay
in the TCM solution during sampling. These thermoelectric permeation chambers
and controllers are expensive and therefore may not be practical for field
use. Figure 5 is a diagram of this experimental set-up.
RECORDER
TEMP. PRO BE
SAMPLE
INLET
EXHAUST
PUMP
BENDIX PERMEATION
CHAMBER
TEMP. CONTROLLED CHAMBER
Figure 5. Modified Bendix permeation chamber system.
Figure 6 is a plot of the chamber temperature versus the TCM solution
temperature using the Bendix permeation chamber.
12
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^ 50
uf
oc
5 «
oc
Ul
a.
m 30
z
o
^ 20
-i
o
u 10
i i r
j i
10 20 30 40 50
CHAMBER TEMPERATURE, °C
60
Figure 6. Effects of chamber temperature varia-
tions on TCM solution temperature using Bendix
permeation chamber.
Research Appliance Corporation (RAC) and Hilton Industries were con-
tracted to build prototype thermoelectric temperature controlled holders for
the S02 bubbler train. Ideally, these temperature controlled systems should
maintain the TCM bubbler solution temperature at 12°C ± 5°C for an ambient
temperature range of 0°C - 50°C. Hilton Industries manufactured a prototype
thermoelectric temperature controlled holder which controlled the temperature
of only one sample holder and which restricts the total number of possible
samples to two. This unit could be installed in the existing sample train of
either the Indoor or All-Weather sampler. The addition of this controller to
either sampler requires modifications to the sampler box for ventilation of
the thermoelectric cooler. This can be accomplished by cutting a 5 inch
diameter hole in the inner wall of the All Weather sampler or cutting a 5 inch
diameter hole in an external wall of the Indoor sampler. During testing in
13
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the environmental chamber, this unit did not meet the original purchase speci-
fications of 12°C ± 5°C over a temperature range of 0°C -50°C. After several
modifications by the manufacturer, the unit met the purchase specifications
when tested in the environmental chamber and would maintain the desired
temperature range. This unit (Model 1125) is presently available from Hilton
Industries for $300.
Hilton Industries also manufactured a prototype thermoelectric temperature
controlled dual sample holder (Model 2125) that replaced the existing sampling
train holder and controlled the temperature in both sampling cells to 12°C ±
5°C. Ventilation for the unit must be provided as described for the Model
1125. On the actual test run in our laboratory, the prototype of this model
did not meet the purchase specifications and had to be modified by the manu-
facturer. Since modifications, this unit has undergone extensive testing and
will control the TCM solution temperature in both bubblers to 12°C ±- 5°C for
an ambient temperature range of 0°C - 50°C. The Model 2125 is presently
available from Hilton Industries for $320. Figure 7 is a picture of the
Hilton Industries Model 2125 thermoelectric sampling train assembly.
RAC manufactured a prototype three gas sampler to replace the five-gas
samplers. This unit underwent similar temperature testing in the environ-
mental chamber as did the Hilton units. The actual TCM solution temperature
showed more variance than was observed in the Hilton units, but remained
within the purchase specifications. The unit controls only the TCM bubbler
and not the remaining two bubblers. The temperature of the solution inside
the nontemperature controlled bubblers which is heated to 25°C ± 5°C by a
thermostated heater ranged from 25°C at 0°C environmental chamber temperature
14
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Figure 7. Hilton Industries Model 2125 Sampling Train Assembly.
Figure 8. RAC Sampling Train Assembly.
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to 63°C at 50°C environmental chamber temperature. At ambient temperatures
above 25°C, the temperature inside the non-temperature controlled bubblers is
determined by the ambient temperature. During testing, this unit developed an
electrical problem and subsequently blew several fuses. RAC was informed of
this and modifications were made in the production line model to eliminate any
recurrence of this problem. After receipt of two RAC thermostatically con-
trolled All-Weather production units, testing showed that these models did not
meet the high temperature specifications. However, after additional modifi-
cations by the manufacturer, the modified production models met the original
temperature specification of 12°C ± 5°C for the environmental chamber tem-
perature range of 0°C-50°C. RAC offers a complete sampling system and a
modification kit to convert existing units. A complete unit consists of the
temperature controlled shelter, 3 gas sampling train, pump and necessary
supplies. The modification kit consists of a new temperature controlled
shelter and 3 gas sampling train. The cost for the complete unit is approxi-
mately $800 and the cost of the modification kit is approximately $600. See
Figure 8 for a picture of the RAC sampling train assembly that goes in the All
Weather sampler-
A sampling program has been initiated at the Durham Air Monitoring and
Demonstration Facility (DAMDF) Durham, N.C., to determine the long term dura-
bility of the Hilton and RAC thermoelectric bubbler units under actual sampling
conditions. This study will last approximately one year. Since no major
problems arose during the initial tests on each system, which ran for approxi-
mately 60 operating days, no problems are anticipated during this durability
study. Table II shows the temperature inside the bubblers during an actual
run under ambient conditions at the DAMDF. The RAC unit tested is the
16
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prototype and not the latest production model. The production model is now
being tested under ambient conditions. The temperatures measured under
ambient conditions for the thermoelectric holders are slightly higher than
those taken in the environmental chamber tests. This difference may be caused
by the effect of ambient conditions on the signal conditioners used to convert
the signal to millivolts. The signal cable was not of sufficient length to
allow the conditioners to be placed in a temperature controlled facility.
However, the temperatures measured were controlled at low enough levels to
sufficiently reduce decay of collected S02.
TABLE II. TEMPERATURE OF TCM SOLUTION DURING AMBIENT SAMPLING
Hilton Bubbler RAC Bubbler
Ambi ent
Temp, °C Temp, °C
Hour Temp. °C 1 2 1 2_
15 20 18 11
16 4 20 19 11 28
17 3 20 19 11 27
18 1 20 19 12 26
19 -1 20 19 12 26
20 -2 20 18 12 25
21 -3 19 18 12 24
22 -3 19 18 12 24
23 -4 19 18 12 23
24 -4 19 18 15 23
1 -5 19 18 18 23
2 -5 19 18 18 22
3 -6 19 19 18 22
4 -6 19 19 17 22
5 -6 19 19 17 22
6 -6 19 19 17 22
7 -4 19 19 18 22
8 -2 20 19 19 23
9 1 20 19 20 23
10 1 20 19 21 24
11 -1 20 19 20 24
12 0 20 19 19 23
13 0 20 19 19 23
14 1 20 19 19 23
17
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A test was conducted to determine the maximum length of time that the S02
bubbler solution could spend in transit from a field site in a Trans Temp Cool
Pak shipping container. Two of the Trans Temp Cool Paks (eutectic mixtures) were
charged in a freezer for at least 24 hours. The Cool Paks were then placed
in a Trans Temp shipping container. An S02 bubbler filled with TCM solution
was also placed in the Trans Temp shipping container. This shipping container
was then placed in a 50°C (122°F) environmental chamber. The temperature of
the TCM solution was monitored. Figure 9 is a plot showing time versus temper-
ature using the Trans Temp Cool Pak shipping container. Within one (1)
hour, the temperature of the TCM solution was below 0°C. After 24 hours, the
TCM solution temperature had risen to 8°C. At the end of 50 hours, the solution
temperature was 21°C (70°F).
A second test similar to the above was run varying the chamber temperature
from 25°C to 40°C. This temperature range was chosen to determine the maximum
length of time that the TCM bubblers could spend in transit under variable
elevated temperature conditions. Figure 10, is a plot showing time versus
temperature using the Trans Temp Cool Pak shipping container. Under the speci-
fic conditions outlined in Figure 10, the TCM solution temperature reached 21°C
(70°F) in 62 hours. Obviously, if the chamber temperature was maintained at
a lower temperature, the solution temperature would remain below 21°C for a
longer time.
The 3M Company manufactures a time/temperature tag ("Monitormark") which
can be used as an indication of the maximum temperature to which a sample was
exposed during transit. These tags can be purchased for certain specified
time/temperature ranges and are available for as little as $0.25 each when
purchased in large quantities. The "Monitormark" tags could be used as a
18
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10
30 40
TIME, hours
50
60
70
Figure 9. Effects of constant temperature of 50° C on TCM solution stored in a Trans
Temp Cool Pak.
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u
o
UJ
OC
LU
24
20
i I i r
oc 16
UJ
0.
12
8
CHAMBER TEMPERATURE
16hrsAT25°
5 hrs AT 30°
16hrsAT35°
30 hrs AT 40°
I I I
10 20 30 40
50
60
70
TIME, hours
Figure 10. Effects of time on the TCM solution temperature
stored in a Trans Temp Cool Pak exposed to variable high
temperature.
' 20
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quality assurance measure during shipping. These "Monitor-mark" tags were
not evaluated during this project. However, several sample tags were obtained
and sent to the Rockwell International Corporation, Newbury Park, California
for evaluation. The results of their evaluation are not available at present.
21
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REFERENCES
1. Title 40 - Protection of Environment, National Primary and Secondary
Ambient Air Standards, Appendix A - Reference Method for the Determination of
Sulfur Dioxide in the Atmosphere (Pararosaniline Method). Federal Register 36
(228): 22385 - 22388, Nov. 25, 1971.
2. Fuerst, R. G., Scaringelli, F. P., Margeson, J. H., "Effect of Tempera-
ture on Stability of Sulfur Dioxide Collected by the Federal Reference Method",
EPA - 600/4-76-024, May, 1976.
3. Scaringelli, F. P., L. Elfers, D. Norris, and S. Hochheiser, Anal. Chem.
42: (14): 1818-1820, December, 1970.
22
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TECHNICAL flE"ORT DATA
(Please read liiUniclions i>n l:.c reverse before comi'lclini:)
I. REPORT NO.
EPA-600/4-77-040
3. RECIPIENT'S ACCESSION-NO.
4. TITLE ANDSUBTITLE
SULFUR DIOXIDE BUBBLER TEMPERATURE STUDY
5. REPORT DATE
August 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Barry E. Martin
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
1AD606
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
J.S. Environmental Protection Agency
Dffice of Research and Development, EMSL
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Tnhouse
14. SPONSORING AGENCY CODE
EPA/600/08
15. SUPPLEMENTARY NOTES
16. ABSTRACT
This paper describes a series of temperature-controlled studies designed to
determine the temperature characteristics of several thermostated systems used to
collect sulfur dioxide from the ambient air by the EPA Federal Reference Method.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Held/Group
13. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
31
20. SECURITY CLASS (This page)
•UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
23
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