EPA-650/2-74-133
DECEMBER 1974
Environmental Protection Technology Series
DEVELOPMENT
OF A PROTOTYPE
NITRATE DETECTOR
Office of Research ond Development
Environmentol Protection Agency
Washington, DC 20460
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environ-
mental Protection Agency, have been grouped into series. These broad
categories were established to facilitate further development and applica-
tion of environmental technology. Elimination of traditional grouping was
consciously planned to foster technology transfer and maximum interface
in related fields. These 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
9. MISCELLANEOUS
This report has been assigned to the ENVIRONMENTAL PROTECTION
TECHNOLOGY series. This series describes research performed to
develop and demonstrate instrumentation, equipment and methodology
to repair or prevent environmental 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.
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EPA-650/2-74-133
DEVELOPMENT
OF A PROTOTYPE
NITRATE DETECTOR
by
J. McCoy, L. Forney,
A. Zakak, J. Ehrenfeld, J. Driscoll
Walden Research Division of Abcor
201 Vassar Street
Cambridge, Massachusetts 02139
Contract No. 68-02-0591
ROAP No. 26AEK
Program Element No. 1A1010
EPA Project Officer: T. G. Dzubay
Chemistry and Physics Laboratory
National Environmental Research Center
Research Triangle Park, North Carolina 27711
Prepared for
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
' WASHINGTON, D.C. 20460
December 1974
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EPA REVIEW NOTICE
This report has beer, reviewed by the National Environmental Research
Center - Research Triangle Park, Office of Research and Development,
EPA, and approved for publication. Approval does not signify that the
contents necessarily reflect the views and policies of the Environmental
Protection Agency , nor does mention of trade names or commercial
products constitute endorsement or recommendation for use.
This document is available to the public for sale through the National
Technical Information Service, Springfield, Virginia 22161.
11
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TABLE OF CONTENTS
TITLE PAGE
ABSTRACT ii
TABLE OF CONTENTS ill
LIST OF FIGURES iv
LIST OF TABLES v
Section
I. CONCLUSIONS 1
II. RECOMMENDATIONS 3
III. INTRODUCTION 4
IV. DISCUSSION OF PROGRAM 7
A. GENERAL 7
B. PHASE I - DEVELOPMENT AND DESIGN 7
C. PHASE II - FABRICATION AND EVALUATION 7
D. PHASE III - DELIVER AND DEMONSTRATION 8
V. INSTRUMENT 9
A. GENERAL
1. Sampler and Analysis Concepts 9
2. Description of the Prototype Instrument 13
B. LEAP SAMPLER 16
C. ION-SELECTIVE ELECTRODE 20
D. INTERFACE SYSTEM 20
1. General Function 20
2. Cell Design 26
E. BACKUP FILTER 29
F. INLET IMPACTOR 31
VI. OPERATION 34
A. GENERAL 34
B. EXPERIMENTAL TESTS 34
1. Maintenance-free Operation 34
2. Suspended Nitrate Measurements 36
3. Temporal Variations of Suspended Nitrate 38
VII. REFERENCES 41
APPENDIX A 42
APPENDIX B 44
APPENDIX C 48
11
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FIGURES
1 Nitrate Detector System 10
2 Schematic of Nitrate Monitor with Cascade Impactor 14
3 Physical Layout 15
4 Schematic of Leap Sampler 17
5 Leap Collection Efficiency 18
6 Solenoid Valve Interconnection Diagram 22
7 Program Valve Diagram 24
8 Switching Circuits Design 25
9 Cell Arrangement 27
10 Cell Response 30
11 Schematic Cutaway View of Impactor 32
12 Stage Calibration Curves 33
13 Filter 35
14 Temporal Variations 40
IV
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TABLES
1 Summary of Data from NASN and Contributing State 5
and Local Networks
2 Valve Position 23
3 Flow Rates 26
4 Unit Test Parameters 29
5 Results 37
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SECTION I
CONCLUSIONS
The results of this program indicate that a practical system for
automatically sampling and analyzing for suspended nitrate can be suc-
cessfully implemented.
The prototype nitrate monitor demonstrated adequate sensitivity to
meet the 1-100 yg/m3 concentration range specifications. Field results
3 3
obtained over a range of about 1.7 yg/m to 35 yg/m were consistent with
high-volume measurements taken as reference. The collection efficiency
of the LEAP sampler was about 80%, as expected on the basis of the manu-
facturer's design characteristics. The monitor results, including a back-
up filter, averaged about 80% of the high-volume results. The difference
is believed to be due to the loss of large-diameter, nitrate-containing
particles in the monitor intake system.
The sensitivity of the monitor at the lowest concentrations ob-
served indicates that the monitor should be able to follow concentrations
o
of the order of 1 yg/m with a time resolution of 1 hour or less.
3
Continuous measurements at 15 yg/m and above appear reasonable. Since
nitrate formation and removal dynamics must be understood before we are
able to develop optimal control programs, this instrument should become
a valuable scientific tool for the investigation of the fate of nitrogen
oxides.
Further field operations need to be carried out to gain a fuller
understanding of the ultimate sensitivity and time resolutions of the
instrument, and to characterize better its accuracy and precision.
-------
The instrument concept used in developing the continuous nitrate
monitor is very general. By introducing appropriate means of analysis,
other species, both anionic and cationic, can be monitored in a device
of similar characteristics.
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SECTION II
RECOMMENDATIONS
1. The present prototype, preferably without the inlet-mounted cascade
impactor, should be used to study the dynamic behavior of atmos-
pheric nitrates.
2. The prototype could be improved by the following:
a) increase reliability through mechanical improvements;
b) simplify operation as part of mechanical improvements above;
c) increase fine particle collection efficiency of
the electrostatic precipitation section of the LEAP sampler
or using a larger type of LEAP sampler;
d) lower the detection threshold by decreasing the collection
solution volume in the system, probably by taking advantage
of electrode miniaturization.
3. Additional field experience should be obtained in order to better
characterize the instrument performance, and to establish a de-
tailed basis for improvements.
4. Analytic schema for other species should be studied to assess the
feasibility of extending the concept. NH. and S04= ions, for
which specific ion-electrode analyses are available, appear to be
excellent choices for such extension.
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SECTION III
INTRODUCTION
Nitrate in atmospheric particles probably represents the atmospheric
end product of the nitrogen oxides produced in combustion processes. The
original sources of nitrogen oxides and the intermediate chemical steps
are dynamic processes which vary not only from day to day but also during
the course of a single day, due to automative traffic flow, solar radia-
tion, etc. A useful tool in studying this dynamic process is a real-
time nitrate monitor. At present, almost all data on suspended nitrate
concentration has been collected by the National Air Sampling Network
(NASN). These data were produced by the colorimetric analysis of the
warm water extract from 24-hour, high-volume filter samples. Hence, from
this data the finest time resolution on the behavior of suspended nitrate
is day-to-day variations.
The one-day average concentration levels of suspended nitrate range
from much less than 1 ug/m3 to well over 10 ug/m3. Summary data from
the NASN are presented in Table 1. The particulate-bearing nitrate is
in the fine particle size range. Data of Lee and Patterson -'indicate
that the particle size is approximately 0.4 pm (mmd).
The approach taken in developing a nitrate monitor is as outlined
below. Suspended atmospheric particulate is sampled by use of a com-
mercially available air sampler (Environmental Research Corp., LEAP Model
3440). LEAP samplers are designed to concentrate by a large factor, on
a continuous basis, the particles in a large volume of air into a small
volume of solution. In this approach aqueous collection solution is used
and the highly soluble nitrate is dissolved. Then, the nitrate concen-
tration of the resulting solution is analyzed with a nitrate ion-selective
electrode technique using commercially available electrodes (Orion Re-
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TABLE I
SUMMARY OF DATA FROM NASN AND CONTRIBUTING
STATE AND LOCAL NETWORKS
(Values in yg/m )
Urban
Non-Urban
Pollutant
Suspended Particulates
Nitrates
Nitrogen Dioxide (gas)
No. of
Stations
217
132
47
Arith.
Average
102
2.9
141
Max. Station
Average
254
13.5
333
No. of
Stations
30
29
Arith.
Average
38
1.3
Max. Sta
Averagi
79
2.5
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search). The nitrate concentration of the solution is then related back
to the suspended atmospheric nitrate concentration through the operating
parameters of the system such as, sample air flow, solution volume, and
time.
The principle design task in the program was the design and fabrica-
tion of an interface system between the LEAP sampler and the nitrate ion-
selective electrode. This system incorporates the functions of solution
handling, timing, calibration and sampling mode. In the following task
evaluation of the system was performed. The design specifications for
the monitor require automatic measurements of atmospheric nitrate concentra-
tions from 1 to 100 yg/m with an analysis time of one hour or less. The
monitor designed and fabricated in this program successfully meets these
specifications.
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SECTION IV
DISCUSSION OF PROGRAM
A. GENERAL
The development program was divided into three phases, viz.
Phase I - Design
Phase II - Fabrication
Phase III - Delivery and Demonstration
B. PHASE I - DEVELOPMENT AND DESIGN
The Phase I activities were directed toward gathering background
performance data on the LEAP sampler and the nitrate ion-selective electrode.
Also criteria for sampling and calibration modes were established. An
initial total design of the prototype instrument was generated and presented
for Project Officer approval in an informal interim report and oral presenta-
tion.
C. PHASE II - FABRICATION AND EVALUATION
Following Project Officer approval of the initial design, fabrication
of the instrument was implemented. Following fabrication the instrument
was operated to determine suitable operating parameters such as flow rates,
solution concentrations operation mode times. Also, preliminary sampling
of atmospheric air was performed.
In the course of this evaluation a problem was observed, namely air
bubbles attached to the sensing surface of the nitrate ion-selective electrode.
When this happened data were lost unless the electrode was removed from the
sensing cell and the gas bubble removed by washing the sensing surface with a
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jet from e wash bottle. The scope of work was increased to eliminate
this problem and also to modify the instrument for 7-day operation including
the placement of a coarse screen and cascade impactor U7 urn, cutoff) at
the air sample inlet.
Additionally, a series of 10 comparative tests of the nitrate monitor
with the high-volume samplers were included and performed in the increased
scope of work.
D. PHASE III - DELIVERY AND DEMONSTRATION
After completing the Phase II Fabrication and Evaluation, the nitrate
monitor was delivered to the EPA and operation of the prototype was demonstrated.
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SECTION V
INSTRUMENT
A. GENERAL
1. SAMPLING AMD ANALYSIS CONCEPTS
The concept behind the design of this monitor is the concentra-
tion of the particles from a large volume sample of ambient air into a very
small volume of solution. The very soluble nitrate compounds in the particles
are readily dissolved. The resulting solution is then analyzed by a nitrate
ion-selective electrode. Figure 1 depicts a block diagram of this process.
The LEAP sampler performs the functions of air sampling and concentrating the
sampled aerosol into a collecting solution. The interface provides control
for two sampling modes and two electrode calibration modes. The electrodes
used are a nitrate ion-selective and a fluoride reference electrode. The
mil li voltmeter measures and displays the electrical potential difference
between the nitrate and reference electrodes.
The general relationship between the measured nitrate concentra-
tion in solution and the suspended nitrate in the atmosphere is given by the
following general relationship:
v.'here
C is the atmospheric nitrate concentration
c is the solution nitrate concentration
v is the solution volume
v is the sampled atmospheric volume
a
REGION HI LIBRARY
ENVIRONMENTAL PROTECTION AGENCY
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ATMOSPHERIC
PARTICULATE
NITRATE
LEAP
SAMPLER
INTERFACE
i
ELECTRODES
..i.
MILLIVCLTMETER
J
SIGNAL CUT PUT
TO
CE'.'7 RATION
Figure 1. Nitrate Detector System.
ID
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This monitor has two sampling modes, continuous and recircula-
tion. In the continuous mode, solution is passed only once through the
system, and in the recirculation mode, solution is recirculated for a fixed
time period.
For the continuous mode of operation, Equation (1) is rewritten
in terms of the flow rates, viz.,
C = c{j. (2)
where
Q is the air sample rate
q is the solution flow rate
If the threshold of the nitrate ion-selective electrode is taken at ~5 x 10"
molar and if the air sample rate and solution flow is taken at -600 Jl/min and
~3 ml/min respectively, then the threshold sensitivity of the detector is
-15 yg/m .
For the recirculation mode of operation, Equation (1) is rewritten
in terms of air sample rate and sample time (t), viz.,
C = COT
If the operating parameters from the above calculation are used with 60 ml of
recirculation solution and a sample time of 60 min, then the threshold
3
sensitivity is ~1 yg/m . Mote howe'
achieved by a longer sampling time.
3
sensitivity is ~1 yg/m . Mote however any threshold sensitivity may be
For both modes, the higher limit of detection is four decades
higher than threshold, due to the four decade range of the nitrate electrode.
11
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The electrode measurement is the potential difference between
the nitrate and fluoride ion-selective electrodes. At operating conditions
the potential of the nitrate ion-selective electrode is given by:
El Eol
and at the fluoride electrode by,
where
E = reference potentials
= Nernst constant (-59 mv/decade)
[NO"] = nitrate concentration
O
[F~] = fluoride concentration
The millivolt meter reading (E) is the difference between these two potentials,
viz.,
AE = E, - E9 = AEn - S-^F- log [NOl] - log [F~]
I f~ U r O
or
o o DT [NO!
AC AC 2.3r)RT , L ;
AE = AE - F log
0 r r i-~ -
12
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Rearranging the last equation we see that the nitrate and
fluoride concentration ratio is actually measured, i.e.,
[NC]
_ exp
(AE -AE )
o
2.3nRT
This relation also holds for the ratio of the mass of nitrate ion and
fluoride ion in the system. The collecting medium used in the monitor
contains fluoride ion of known concentration, sufficiently large that the
small amounts of fluoride ion or cations that tie up fluoride ion present
in the atmosphere will not significantly change the concentration. The
solution used in these experiments contained 10 molar fluoride ion
concentration.
Changes in the collection medium volume due to evaporation
or dilution from atmospheric condensation over the collecting plate will
not affect the analytic results.
2. DESCRIPTION OF THE PROTOTYPE INSTRUMENT
In final form, the prototype nitrate detector has plumbing,
valving and timing devices to permit sampling in either the continuous
mode, or more importantly in terms of sensitivity, in the recirculate mode,
Provisions exist for calibrating the ion-selective electrode by injection
of two levels of calibration solution either automatically or manually.
Provision is made for stablizing the temperature of the test solution by
a temperature sensor controlling arc immersion cooler in the cell and
for eliminating nonhomogenetics by stirring the solution in the cell.
The liquid level sensor/controller is provided to prevent the system
from drying out due to evaporation while operating in the recirculate
mode. A schematic of the monitor showing the various sub-systems is
shown in Figure 2. A pictorial layout is shown in Figure 3. A
descriptive list of specific components is presented in Appendix A.
13
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Air In
Cascade Impactor
.iquid In
Temperature
Controller
Digital
pH/mv Meter
Sensing Cell
Test Solution
-
I
1
Leap Sampler
Liquid Out -*l
Freezer
Liquid Level
Controller
Liquid Out
Figure2
Schematic of Nitrate Monitor With Cascade Impactor
14
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jr-jr
IN
OUT
Control
&
Output
Module
Make-up Solution
Two Stage
Cascade
Impactor
- Leap
Sampler
y$h Voltage
Wy V.
r i
Collection Solution
,
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B. LEAP SAMPLER
The performance characteristics of the LEAP sampler determine the
sampling properties of the Nitrate Detector. LEAP samplers were developed
several years ago to collect biologically active particles from the
atmosphere. A schematic of a LEAP sampler is shown in Figure 4. During
sampling, ambient air is drawn into the sampler through the top as shown.
The large suspended particles in the sample are impacted near the axis of
the rotating collection disk. Within the instrument, the sampled air is
deflected to flow radially outward between the grounded rotating collection
disk and the high voltage plate. The sample air is drawn through the ring
of corona needles which emit a continuous negative corona. Suspended particles
are charged passing through the corona field. The charged particles are
then precipitated onto the collection disk by the electrostatic force due
to the electric field existing between the high voltage plate and the
grounded collection disk.
The peristaltic liquid pump supplies a small flow of collection
solution onto the center of the rotating collection disk. Centrifugal force
spreads the liquid out into a thin film. This thin film is the collection
surface for the electrostatically precipitated particles.
The particular LEAP sampler used in this program (ERC Model 3440)
has adjustable air sample rates from 0-1.20 m -min" , liquid flow rates from
0-10 ml-min" and an applied voltage from 0-20kv. Particle collection efficiency
is a function of particle size, applied precipitation voltage and flow rate
as shown in Figure 5. We found it convenient to operate at an air sample
rate of 600 liters per min with an applied precipitator voltage of about
15 kv. To avoid evaporation of solution on the collection plate a minimum
solution flow of about 3 to 4 ml-min" was found necessary. This provided a
reasonable collection efficiency for the particle size of interest, i.e.,
16
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A',R
COLLECTION
DiSK
STATIC PICKUP
DRIVE MOTOR
...GolD PUMP
c.., r:'c- uf 1ZV? s£.r.?lsr (after £.
-------
100
FRECIPITi-CR VOLTAGE: 15KV
0.3 1.0 2.0
RTrCLE SIZE, MICRONS
LEAP collection etflciency ,*fter BUC
1969-1970).
Figure 5
18
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-0.4 ym. Further discussion on collective efficiency is presented in
the section on results.
The LEAP sampler is a very poor collector of gases. This is shown
by calculation in Appendix B. For this reason, the Nitrate Detector is
not expected to be affected by such gaseous interferences as NCL.
19
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C. ION-SELECTIVE ELECTRODES
As stated earlier in the general description of the instrument,
a nitrate ion-selective electrode is used to sense the nitrate ion
concentration of the resulting collection solution and a fluoride ion-
selective electrode is used as a reference electrode. The nitrate and
fluoride ion-selective electrodes are Orion Research Models 92-07 and
94-09 respectively. The ion-selective electrode sensing was selected for
simplicity and ease of application over the more procedurally complicated
colorimetric procedures of nitrate analysis.
A manual method using these electrodes has been investigated for
measuring suspended nitrate concentration. The results of this study are
discussed by Williams, et al., 1972. In the course of this study it was
shown that the possible interferences due to Cl", Br", l", V0~ and Se04 may
be eliminated by precipitation out of the measurement solution by adding
silver fluoride. As indicated by Driscoll and Forney, 1973, and Williams, et al.,
1972, Br" from automobile exhaust is the most likely interference. As a
precaution the collection solution has been doped with a concentration of
10~4 molar AgF. Since the nitrate ion-selective electrode selectivity
constant K = 0.13 for Br' versus KX = 1 for nitrate, and AgBr" is virtually
insoluble; the Br" interference is removed from at least equal concentra-
tion of Br" and NO".
D. INTERFACE SYSTEM
1. GENERAL FUNCTIONS
The functions of the interface system is the following:
a. convey liquid sample from the LEAP sampler to
the electrodes
b. control the sample modes
20
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c. control the calibration modes
d. program the flush cycle on recirculation sampling
e. thermally stabilize the electrode measurement
f. control volume of recirculation solution
g. mix the sample solution
A schematic of the elements of interface system is shown in
Figure 2. Figure 6 shows a solenoid valve interconnecting diagram of
the system connecting the LEAP sampler with the electrode in the cells.
When the Detector is operating in the continuous sampling mode solution is
pumped out from the LEAP sampler through V4 to the cell. Solution from the
cell pumped through V2 to the LEAP sampler. Any decrease in recirculation
solution volume due to evaporation is sensed and deionized water is added
through V9 to maintain constant solution volume. At the end of a sample "
cycle the recirculation solution is flushed out and replaced by fresh
collective solution. The flush is initiated either automatically or
manually. Collection solution flows under gravity through V8 to the cell.
Solution from the cell flows out through the overflow indicated. Fresh
solution is also pumped into the LEAP sampler through VI. (It is necessary
to maintain a continuous flow on the collection plate of the LEAP sampler
or liquid will be splashed about shorting out the applied high voltage).
During calibration, calibration solution flows through either
V5 or V6 to the cell. Solution in the cell flows out the indicated over-
flow port.
The valve position for each function is shown in Table 2.
The method of controlling the solenoid valves is shown in Figure 7.
Figure 8 shows the wiring schematic for the solenoid valve switching and
timing.
21
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Gravity Flow
2
I v
i._._
Gravity Flow \
L.
-
-------
TABLE 2
VALVE POSITION
Continuous
V V V V V V V
V3 V4 V5 V6 V7 V8 V9
Open X X
Closed XX X X x X
Calibration A
V1 V2 V3 V4 V5 V6 V7 V8 V9
Open XXX
Closed X X X x X X
Calibration B
V1 V2 V3 V4 V5 V6 V7 V8 V9
Open XX X
Closed X XX XX X
Recirculate
V1 V2 V3 V4 V5 V6 V7 V8 V9
Open XX (On Demand)
Closed X X X X X X
Flush Between Recirculation
V1 V2 V3 V4 V5 V6 V7 V8 V9
Open XX X
Closed X X X Y X
23
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24
-------
Figure 8 Switching Circuits Design
J^'.
I. '.
-e-
© o
LINE
TIMCR'Z
LICUIO
ICVCL
COHTPOLUEB
NITRATE MONITOR SWITCHING DIAGRAM
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2. CELL DESIGN
The cell was designed to hold the following:
a. solution to be analyzed
b. nitrate and fluoride electrodes
c. temperature sensing probe
d. liquid level sensing probes
e. cold finger
f. magnetic stirring bar
These elements are shown schematically in Figure 2. The cell was
machined from lucite as shown in Figure 9. With all components installed
the solution capacity of the conical cavity is about 45 ml. The conical
cavity was chosen to provide a small solution holding volume while providing
space to accommodate all the required elements plus provide a sensitive
liquid level detector for sensing small changes in solution volume.
The volumetric flow rates through the cell are listed in
Table 3.
TABLE 3
Flow Rates
Operating Mode ml min" Method
Continuous 0-12 Leap Pump
Recirculate 0-12 Leap Pump
Calibrate 15-20 Gravity
Flush -25 Gravity
An effort was made to give the solution cavity the
characteristics of an ideal stirred vessel in which entering solution is
dispersed instantaneously throughout. Assuming an ideal stirred vessel
26
-------
Temperature
Probe
Fluor ide--
Electrode
Liquid Level
Controller
Liquid Inlet
and Vent
Top Flange
Nitrate
Electrode
Cold Finger
Overflow
[
1
!
Mm
i
!
i
!/'
/
/
1 1
i i
[
1
1
1
1
L
/
/
k
1
1
1
1
1 1 I
1 ll 1
" ,'
ii
Si1 1 f«
!> 1
-f1 1
~\
\
\
\
i
i .. . i.
Figure 9 Cell Arrancerv.ent
5
SCALF
7 K5 i C
27
-------
of volume V through which a solution is slowing at rate Q, one has the
relationship [4].
t/T
[N0~] = ([N0~]o - [N03]i) e + [N03]i
where [NO"] = [NOJ at t = 0 and = V/Q the solution residence time.
o o u
Moreover, if the concentration of NOZ within the vessel is measured with
a nitrate and fluoride reference electrode operating within the Nerstian
-5 2
region (~5 x 10 - 10 M N0~) where the electrode voltage response is
O
given by
AE - AEQ - ln
[NO]
These equations can be combined to yield:
AE - AE.
RT/nF
= -In
[NOji
t/i
+ 1
- In
To check the validity of this equation, two tests were conducted using a
gravity feed NO" solution to the flow-through unit. The results of both
tests are shown in Figure 10, where the parameters of the system are
summarized in Table 4 below.
28
-------
TABLE 4
UNIT TEST PARAMETERS
AE = 73 mv
o
RT/nF = 26.9
T = 38.5°C
n = 1
[F~] = 10~2 M
V = 44 cc.
As can be seen in Figure 10 the flow-through unit response
conformed closely to that of a well-stirred vessel (solid lines). The
small drift in the data relative to theory was a result of a decrease
in head above the unit as the experiment progressed. From this result
the cell behaves as a well-stirred vessel, hence the cell response time
for an e-fold time chance to a step change in concentration is simply V/Q.
E. BACKUP FILTER
The design of the prototype instrument incorporated the provision
for using a backup filter on the LEAP Sampler. A high volume filter may
be installed to filter the exhausted gas from the LEAP sampler. Originally
a full-size high volume sampler sheet was used. However, due to the small
quantity of nitrate particles which penetrate the sampler relative to the
background of nitrate or filter paper blanks, the effective filtering area
was reduced to a diameter of about 7 cm. This provided a more favorable
signal to raise ratio. Data were gathered on the efficiency of the LEAP
Sampler for atmospheric suspended nitrate. This data is presented in the
Section IV.
29
-------
"T i I i
1 I _ L JL L
Figure 10. Cell Response
-------
F. INLET IMPACTOR
A contract requirement was the installation of our impactor with
a particle cut-off of 7 ± 2 urn. Upstream of the LEAP sampler inlet,a BGI-30
(BGI-Incorporated) high volume cascade impactor was installed to remove the
particles greater than approximately 7 ± 2 ym. The BGI-30 is a four stage
impactor (Figure 11) with particle penetration characteristics as shown
in Figure 12 for a sample flow rate of 0.85 m -min . Since the LEAP
sampler is operated at 0.60 m -min" , the particle size penetration was
assumed to be approximated by increasing particle size by the ratio of the
flow rates. For example the 50% penetration of the second stage (Figure 12)
is taken as:
Particle size = 3.8 ym -85 (m -mm
x .60 (m -min"1
Since this is within our tolerance of 7 ± 2 ym, the impactor was used with
the first two stages installed. Actual penetration was not measured.
In conventional impactor operation, the collection stages are greased
to decrease re-intrainment of impacted particles. However, in our operation
where it was required to measure the total nitrate in the sample stream, the
stages were not greased because the grease interferred with a subsequent
manual analysis (ion-selective electrode method) for nitrate on the collection
stages.
31
-------
OJ
Filter
IrnpacMon
Plato
Tie Rod
Nut
Flowmefr©r
Tap
Figure 11 Schematic Cutaway View of Impactor
-------
100
00
OJ
345
SCLE SIZE -
Figure 12 Stage Calibration Curves
-------
SECTION VI
OPERATION
A. GENERAL
Two types of experimental tests were made. The first was a test
of long-term maintenance-free operation. The second was a set of
suspended nitrate measurements using the prototype detector along with
three high-volume samplers run in parallel. During the latter set of
.tests, the collection efficiency of the LEAP sampler was measured as well as
the difference between the prototype measurement and the high-volume sampler
measurement.
B. EXPERIMENTAL TESTS
1. MAINTENANCE-FREE OPERATION
One objective of this test was to obtain 7 days of maintenance-
free operation. The prototype instrument was set-up to sample in the
recirculate mode. In this mode, the instrument recirculated collection
solution for 105 minutes, then automatically flushed out the system (15
minutes) and initiated another 105 minute recirculation sample cycle.
Every six hours, the analyzer was automatically calibrated with two levels
of calibration solution. A liquid filter was installed at the liquid output
from the LEAP sampler to trap the preponderance of insoluble particles
collected by the sampler. This filter is depicted in Figure 13.
The test ended after almost four days of continuous operation.
Termination was due to particles clogging the liquid filter. Also the
liquid level controller failed about the same time, due to fine particles
collecting on the grounded electrode of the sensor probe, thus insulating
34
-------
Flow Direction
Glass
Sand
Glass Wool
Figure 13 Filter
35
-------
this electrode from the level sensing system. It was also observed that
the tubing of the peristaltic pump in the LEAP sampler had begun to leak.
(This tubing had considerably more than four days of testing and this
failure was not a direct result of this test.)
During this test period, an old five-story building across
the street from the test-site was being demolished. This produced very
heavy dust concentrations which made these four days an extremely severe
test of the instrument. Under ordinary conditions, a much longer uninter-
rupted test period could have been expected.
2. SUSPENDED NITRATE MEASUREMENTS
A series of ten, 24-hour tests were run in which the ambient
atmosphere at our Cambridge facilities was sampled for suspended nitrate
concentration. The prototype Nitrate Detector was operated with inlet
impactor and backup filter installed as explained in Section V.
The referee measurement consisted of three high-volume sampler
measurements made simultaneously and in proximity to the sample intake of
the prototype detector, which was a conventional hi-vol shelter. There
were about 6-8 meters of 10 cm diameter flexible hose connecting the
detector to the sample intake. All analyses for nitrate were performed by
selective ion electrode techniques. All filter and impaction stages were
extracted and analyzed by techniques similar to those reported by Williams
et al.(2) Nitrate collected by the LEAP Sampler was analyzed automatically
in the detector cell.
The results are presented in Table 5. Detailed data for
individual tests are presented in Appendix C. In reporting the results,
the impactor catch is summed with cell collection and reported as the
"Detector Results." These values are summed because the impactor is not a
36
-------
TABLE 5
RESULTS
Te'st "~ Hi-Vol , Detector Results Total Catch Impactor3Catch Backup Filter Sample
No Results (pg/m3) (ug/m5) (yg/m3) (yg/mj) Catch (yg/m ) Cycle Time
13.3 Mean Std.Dev.
12.5 13.3 .7
14.0
7.1
8.3
0.6
1.2
24 hr.
5. I
4.9 5.0 .1
4.9
4.3
4.7
0.4
0.4
24 hr.
4.7
4.3 4.6 .2
4.7
3.7.
4.4
0.4
0.7
24 hr.
00
I
4.4
4.5 4.7 .4
5.2
1.7
1.4 1.7 .3
2.0
3.1
2.1
3.8
2.7
0.1
nil
0.7
0.6
1.75 hr.
1.75 hr.
3.0
2.7 3.2 .7
4.0
1.5
2.0
0.1
0.5
1.75 hr.
7.1
6.7 7.1 .4
7.6
35. 5
24^6 35.5 10.5
45.7
1.9
4.1
2.5
4.9
0.2
0.6
0.6
0.8
1.75 hr.
1.75 hr.
10
9.9
3.9 4.5 .5
4.7
1.7
1.7 1.8 .2
2.1
3.7
1.8
4.6
1.8
0.4
nil
0.9
24 hr.
not used 24 hr
-------
necessary element for the operation of the Nitrate Detector, and it
is assumed that the large particles caught in the impactor would be
readily caught by the LEAP sampler, then analyzed automatically by the
cell if the impactor was not installed. The sum of the "Detector Catch"
and the backup filter catch is reported as "Total Catch".
For five of the ten days of testing the detector was
operated continuously in recirculation mode for 24 hours. In the
remaining five tests the detector was operated in two-hour cycles with
recirculation sampling for 1.75 hours and flush for 0.25 hours. The
average of values for the 2 hour cycle is reported as the 24-hour value.
The operation mode for each test is indicated in Table 5 under "sample
cycle time."
The results from these tests indicated that the Nitrate
Detector performs well. The "total catch" on the average was about 80%
of the high-volume sampler measurement, with moderate scattering. The
failure to account for all nitrate is thought to be due, in part at least,
to the loss of nitrate present on large particles in the sampling line
connecting the Detector to the sample inlet. Variations in the quantity
of nitrate on large particles and/or variations in the large particle
size distribution could result in the variability of the "total catch"
results relative to the hi-vol determination. The "detector results-
are about 81% of the "total catch". This result is as expected due
to the collection efficiency of the LEAP sampler and previously reported
particle size (mmd) for nitrate bearing particles in the atmosphere - .
3. TEMPORAL VARIATION OF SUSPENDED NITRATE
During the test period temporal variations of suspended
nitrate were measured. These data were collected in tests where the
Nitrate Detector was operated with a 1.75 hour sample recycle time
38
-------
(see Figure 14)- These data are important, since it is the first data
we know of which shows the temporal variation of suspended nitrate within
a 24-hour period, and it indicates that this prototype instrument is
capable of obtaining the dynamic data needed for experimentally
investigating models for the fate of oxides of nitrogen in the atmos-
phere. Since only the cell collection fraction of the suspended nitrate
is shown (the impactor collected the large particle fraction, ~7 um)
care should be used in theorizing with the data presented.
39
-------
lr> f,
F 5:-
UJ :
t-
-------
REFERENCES
1. Lee, R.F. and R. K. Patterson, Atn. Environment. 1969, Vol. 3,
pp.'249-255.
2 William, D., J. Driscoll, C. Curtin and R. Hebert, "Methods for
the Rapid and Accurate Measurement of Nitrate and Sulfate in
Atmospheric Particles", Final EPA report on Contract No. 68-02-0564,
EPA-650/2-73-050, December,1973.
3 Driscoll, J. and L. Forney, Chapter 8, Analytical Methods Applied
to Air Pollution Measurements, Stevens and Herget (eds.), Ann
Arbor Science Publisher, Ann Arbor, 1974.
4. Perry, J.H. fFd.l. Chemical Engineers' Handbook McGraw-Hill (1963)
41
-------
APPENDIX A
LIST OF COMPONENTS
Component
Electrode, Nitrate
Electrode, Reference, Fluoride
Electrode Meter (pH/mv)
Cell and base
Lead Sampler
Cascade Impactor
Peristaltic pump silicone
rubber tube
Liquid Level Controller
Liquid Level Controller Probe
Temperature Controller
Temperature Controller Probe
Immersion Cooler
Refrigerator
Pump
S
Sl
S2
S3
Magnetic Stirrer
Stirring Bar
14 Relays [K K]
Description
Orion Model 92-07
Orion Model 94-09
Orion Model 701
Fabricated from Plexiglass
Environmental Research Corp. Model 3440
BGI-30 High Volume Cascade Impactor
2 stages (No. 1 and 2)BGI Inc.Waltham.Ma.
Silichem 1/8" Bore, 1/4" O.D.,
New Brunswick
Scientific International Inc., New
Brunswick, New Jersey.
Dyna-Sense Controller, Model 7188
Dyna-Sense Sensing Probe Cat.No. 7186-12
Versa Therm Model 2158
Versa Therm Liquid Immersion 8446
Fabricated from Glass
1.5 ft3 Sears Cat. No. 3467370N, Sears
Roebuck & Co.
Oscillating type, Model 7103-10 cap. 1/2
GPM at O'head, Cole Palmer Inst. Co.,
Chicago, II.
4 circuit Egal BL 340 Timer, 6 hr.
Daton 2E026, Prog. Time Control (Variable
On-off 4/hr to I/day in 96 steps)
SPST Switch
SP3T Switch
SP2T Switch
SPST Switch
Fabricated using 240 Kpm sychronour motor
3/8" Dia x 3/8"
Daton, 4 x 809, 115 V SPOT Relay
42
-------
APPENDIX A
LIST OF COMPONENTS (CONTINUED)
Component Description
9 Valves [V - V ] Asco Solenoid Valve, Cat. No. 836015
Connecting Tubing Teflon, 1 mm Dia.
4 Reservoirs 2 Gal and 1/2 Gal Plastic Carboy
Cabinet Bud CR 1737
43
-------
APPENDIX B
ESTIMATE OF ABSORPTION IN LEAP SAMPLER
44
-------
The geometry of the LEAP sampler is schematically shown below.
We shall examine the absorption from the gas stream entering at the
center and flowing outward to the edge of the dish. This portion of the
inlet gas will exhibit maximum absorption. We will neglect any rotational
effects due to the motion of the collecting plate. Considering an in-
finitesmal annual section at radius, r, from the center, we can write a
material balance for the absorbent species in the gas, for example, nitro-
gen dioxide, as follows:
FC - F
fc + {£drj - k 27rr dr [C - C.] = 0
(C-l)
where F = gas flow rate in cc/min
2
k = mass transfer coefficient in cm /min
C = concentration of absorbed species in moles/cc
C. = equilibrium concentration above liquid
This reduces to:
FJJt.-khrCC-C,]
and can be integrated between any two radii as:
(C-2)
45
-------
dc - rdr (C-3)
C-C ~ F
1 ri
or
The equilibrium concentration of. nitrogen oxide is essentially zero so
this simplifies to
c2 4
^- e F 2 ] (C-5)
Ll
In order to evaluate the expression on the right, we must know the
value of the mass transfer coefficient. Being conservative, we assume
the diffusion is mass transfer controlled (gas side). This is the fastest
rate feasible, even if liquid-side chemical reaction is infinitely rapid.
Consider the case of flow over a flat plate. For gases (air), the
Schmidt number (N ) is approximately unity, so that
O w
Nsh = 0.6 Re°'5 (C-6)
kr
where N , = Sherwood number = -~-
Re = Reynolds number =
y
k = mass transfer coefficient
r = radius
D = diffusivity in cm/sec
p = gas density in gm/cc
y = gas in viscosity
V = velocity in cm/sec
46
-------
Using dimensions, characteristic of the sampler, at 500 1/min flow,
the Reynolds number is
Re = 103
so that
^= 6 x (lOOO)0'5 = 19 (C-7)
2
For gas, the diffusivity is about 0.1 cm /sec, so that for a total
travel distance (r) of 15 cm,
k = 0.12 cm/sec = 7.2 cm/mi n
Now, returning to Equation C-5, we find that the ratio of concentration
from center to edge is
~ = e
and, at
F = 500 1/min = 5 x 10 cc/min
we find that
C
2 ~ -0.01 - ,
~ " e " '
This calculation indicates that no significant absorption will occur
during the passage of the gas through the sampler.
47
-------
APPENDIX C
ATMOSPHERIC TEST DATA
BY TEST
This Appendix shows the test data by individual tests. The
following notations were used:
B.F. - backup filter to the LEAP sampler
S, = first inspection stage
S9 = second inspection stage
F = multiplying factor where analysis was
performed on 1/2 or 1/4, etc. of filter area.
48
-------
Test No. 1
Date: (8/21/74)-
Sampling Rate, Sampling Time
(m /min) (min)
Hi Vol A
Hi Vol B
Hi Vol C
Av. Hi Vols.
B.F.
Sl
s2
Cell
1.67
1.47
1.75
0.57
0.57
0.57
0.57
1455
1455
1455
1455
1455
1455
1455
Total
Sampled
, Volume,
(m3)
2430
2139
2546
829
829
829
829
Moles N03
Collected
(y moles)
58.0
48.0
64.0
4.1 -
2.05
1.75
87.0
F
X
9
9
9
4
2
2
1-
Total Moles
(u moles)
522
432
576
16.4
4.1
3.5
87.0
Weight Nitrate
Collected
fog)
32364
26784
35712
1016.8
254.2
217.0
5394.0
Nitrate
Concentration
(yq/m3)
13.3
12.5
14.0
13.3
1.2
0.31
0.26
6.5
-------
Test No. 2
Date: (8/22/74)
Sampling Rate,
(m /mi n )
Hi Vol. A 1.27
Hi Vol. B 1.41
Hi Vol. C 1.39
Av. Hi Vols.
B.F. 0.60
S1 0.60
S2 0.60
Cell 0.60
Sampled Moles NO- Total Moles Weight Nitrate Nitrate
Sampling Time, VoTume, Collected F N03 . Collected Concentration
(min) (m3) (u moles) X (y moles) (vjo) (]^J.
1425 1810 37.2. 4 148.8 9225.6 5.1
1425 2009 40.0 4 160.0 9920.0 4.9
1425 1980 39.2 4 156.8 9721.6 4.9
4.9 .
1425 855 1.7 4 6.8 421.6 0.50
1425 855 0.8 2 1.6 99.2 0.12
1425 855 2.1 2 4.2 260.4 0.30
1425 855 54.0 1 54.0 3348 3.9
-------
Test No. 3
Date: (8/26/74)
Hi Vol.
Hi Vol.
Hi Vol ,
Av. Hi
B.F.
Sl
S2
Cell
Sampling Rate,
o
(m /min)
A 1.27
B 1.47
. C 1.39
Vol.
0.6
0.6
0.6
0.6
Sampling Time,
(min)
1300
1300
1300
1300
1300
1300
1300
Total
Sampled
Volume,
(m3)
1651
1911
1807
780
780
780
780
Moles N03
Collected
(u moles)
31.4
33.4
34.2
2.07
0.56
1.83
41.4
F
X
4
' 4
4
4
2
2
1
Total Moles
N03
(u moles)
125.6 .
133.6
136.8
8.3
1.1
3.7
41.4
Weight Nitrate
Collected
(yg)
7787.2
8283.2
8481 . 6
514.6
68.2
229.4
2566.8
Nitrate
Concentration
4.7
4.3
4.7
4.6
0.66
0.09
0.29
3.3
-------
en
r-o
Test No. 4
Date:(8/29/74)
Sampling Rate,
(m /min)
Hi Vol. A 1-42
Hi Vol. B 1.61
Hi Vol. C 1.47
Av. Hi Vols.
B.F. 0.6
S, 0.6
1
S9 0.6
2
Cell 1 0.6
2
3
4
5li
6
7
Total
Sampled Moles NO-
Sampling Time, Volume, Collected
(min)
1425
1425
1425
1425
1425
1425
105
u
ll
u
ll
M
ll
(m ) (u moles)
2023 35.6
2294 41.6
2095 43.6
855 2.3
855 0.02 .
855 0.55
63 2.7
3.3
2.04
2.04
2.04
4.5
5.1
Total Moles
F N03
X (u moles)
4 142.4
4 166.4
4 174.4
4 9.31
2 0.04
2 1-10
1 2.7
3.3
2.04
2.04
2.04
4.5
5.1
Weight Nitrate
Collected
(ua)
8829
10317
10813
577
2.5
68
167
205
126
126
126
279
316
Nitrate
Concentration
/ / 3\
diq/m )
4.4
4.5
5. 2
4.7
0.68
0.00
0.08
2.65
3.25
2.01
4.23
5.02
3.02 .
Cell Av.
-------
Test No. 5
Date: (9/3/74)
tn
CO
Sampling Rate,
(m /mi n )
Hi Vol. A 1.29
Hi Vol. B 1.63
Hi Vol. C 1.44
Av. Hi VolS.
B.F. 0.6
S, 0.6
|
l
Sp 0.6
Cell 1 0.6
2
3
4
5
6
7
8
9
Cell Av.
Sampling Time,
(min)
1465
1465
1465
1465
1465
1465
105
ll
ll
ll
II
"
ll
ll
75
Total
Sampled
Volume,
(m3)
1890
2388
2110
879
879
879
63
II
ll
ll
II
It
ll
11
45
Moles N03
Collected
(u moles)
12.6
13.0
16.6
2.0
0.0
0.14
3.9
2.6
2.4
2.3
2.4
2.4
1.3
1.3
0.7
Total Moles
F N03
X (y moles)
4 50.4
4 52.0
4 66.4
4 8.0
2 0.0
2 0.3
1 3.9
2.6
2.4
2.3
2.4
2.4
1.3
1.3
0.7
Weight Nitrate
Collected
3125
3224
4117
496
0.0
18.6
242
161
149
143
149
149
81
81
43
Nitrate
Concentration
(yg/m3)
1.7
1.4
2.0
1.6
0.56
0.0
0.02
3.8
2.6
2.4
2.2
2.4
2.4
1.3
1.3
1.0
2.1
-------
Test No. 6
Sampling Rate,
(m /mi n )
Hi Vol. A 1.39
Hi Vol. B 1.64
Hi Vol. C 1.44
Av. Hi Vols
B. F. 0.6
S1 0.6
S2 0.6
Cell 1 0.6
2
3
4
5
6
7
P
9
10
Cell Av.
Sampling Time,
(min)
1430
1430
1430
1430
1430
1430
105
II
ll
li
ll
"
ll
ll
n
ll
Total
Sampled
Volume,
(m3)
1988
2345
2059
858
858
858
63
ll
II
ll
II .
ll
II
ll
"
ll
\ -" / / /
Moles NO-
Collected
(u moles)
24.3
25.5
33.1
1.7
0.25
0.65
1.38
1.38
1.44
1.08
1.08
1.44
1.44
1.56
1.44
1.56
F
X
4
4
' 4
4
2
2
1
ll
ll
ll
ll
ll
ll
ll
M
II
Total Moles
(u moles)
97.2
102
132.4
6.8
0.5
1.3
1.38
1.38
1.44
1.08
1.08
1.44
1.44
1.56
1.44
1.56
Weight Nitrate
Collected
(yg)
.6026
6324
8209
422
31
81
86
86
89
67
67
89
89
97
89
97
Nitrate
Concentration
(yg/m3)
3.0
2.7 .
4.0
3 2
:
0.5
0.03
0.09
1.4
1.4
1.4
1.1
1.1
1.4
1-4
1.5
1.4
1.5
1.4
-------
Test No. 7
Date: (9/9/74)
Sampling Rate,
o
(m /min)
Hi Vol . A 1.39
Hi Vol. B 1.58
Hi Vol. C 1.44
Av. Hi Vols.
B.F. 0.6
S1 0.6
S2 0.6
Cell 1 0.6
2
3
4
5
6
7
8
9
10
11
12
r * 1 1 A . ,
Total
Sampled
Sampling Time, Volume,
(min) (m )
1410 1960
1410 2228
1410 2030.
1410 846
1410 846
1410 846
105 63
H H
n H
n n
n i>
n "
n n
n n
M II
II H
II II
II II
Holes NO.
Collected
(u moles)
56.2
60.2
62.2
2.3
0.42
0.77
2.0
1.3
1.3
1.5
1.2
1.3
1.5
1.9
2.5
2.0
1.8
2.4
F
X
4
4
4
4
2
2
1
ll
M
ll
ll
M
11
II
II
11
II
II
Total Moles
N03
(y moles)
224.8
240.8
248.8
9.1
0.8
1.5
2.0
1.3
1.3
1.5
1.2
1.3
1.5
1.9
2.5
2.0
1.8
2.4
Weight Nitrate
Collected
(yg)
13938
14929
15426
565
52
95
124
81
81
93
74
81
93
118
155
124
112
149
Nitrate
Concentration
(yg/m3)
7.1
6.7
7.6
7.1
0.67
0.06
0.11
2.0
1.3
1.3
1.5
1.2
1.3
1.5
1.8
2.. 5
2.0
1.8
2.4
1 .7
-------
Test No. 8
Date: (9/10/74)
cr>
Hi Vol
Hi Vol
Hi Vol.
Av. Hi
B F
U.I
Sl
S2
Cell
Cell
. A
. B
. C
Vol
2
3
4
5
7
8
9
10
11
12
Av.
Sampling Rate,
I m /mi n \
1.30
1.50
1.35
s.
0.57
0.57
0.57
0.6
0.6
0.6
0.6
0.5
Or
. b
0.5
0.5
0.6
0.6
0.6
0.6
Sampling Time,
(min)
1595
1595
1595
1595
1595
1595
105
ii
ll
ti
II
M
II
II
II
II
II
II
Total
Sampled
Volume,
(m3)
2073
2393
2153
909
909
909
63
63
63
63
52
52
52
52
63
63
63
63
Moles N03
Collected
(u moles)
297
237
397
5.6
2.0
2.6
3.6
2.5
2.4
2.4
2.9
4.0
4.6
3.6
2.9
4.1
4.3
3.1
Total Moles
F NO,
X (u moles)
4 1188
4 948
4 1588
2 U
2 4
2 5
1 3.6
2.5
2.4
2.4
2.9
4.0
4.6
3.6
2.9
4.1
4.3
3.1
Weight Nitrate
Collected
(yg)
73656
58776
98456
696
248
310
223
155
149
149
. 180
248
285
223
180
254
267
192
Nitrate
Concentration
35.5
24.6
45.7
o c n
3b. U
0.76
0.27
0.34
3.5
2.5
2.4
2.4
3.4
4.7
5.4
4.2
2.8
4.0
4.2
3.0
3.5,
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Test No. 9
Date: (9/12/74)
Total
Sampled Moles NO, Total Moles Weight Nitrate
Sampling Rate, Sampling Time, Volume, Collected F N03 Collected
(m3/min) (min) (m3) (u moles) X (u moles) (yg)
Hi Vol. A 1.2 1440 1728 34.0 4 136.0 8432
Hi Vol. B 1.5 1440 2160 34.0 4 136.0 8432
Hi Vol. C 1.3 1440 1872 35.6 4 142.4 8829
Av. Hi Vols.
B.F. 0.5 ' 1440 720 2.7 4 10.9 677
s 0.5 1440 720 0.8 2 1.6 99
s 0.5 1440 720 1.6 2 3.2 201
Cell 1 0.5 1440 720 39 1 39 2418
2
3
Nitrate
Concentration
(yg/m3)
4.9
3.9
4.7
4.5
0.93
0.14
0.28
3.3
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Test No. 10
en
00
ua i.c . \?/ivii ^j , .
Sampling Rate
o
(m /mirO
Hi Vol. A 1.39
Hi Vol. B
Hi Vol. C
Av. Hi Vols.
B.F.
Sl
S2
Cell
1.58
1.44
none
0.6
0.6
0.6
Sampled Moles NO, Total Moles Weight Nitrate
. Sampling Time, Volume, Collected F NO., Collected
(mini (m3) (H moles) X (u moles) .... (vg)
1440 2002 13.8 4 55 3422
1440 2275 15.8 .4 63 3918
1440 2074 17.8 4 71 4414
V
used
1440 864 -02 ~0 -0
1440 864 0.2 2 0.4 26
1440 864 25.8 1 26 1600
Nitrate
Con cent rat Jon
(yg/m3)
1.7
1.7
2.1
1.8
~0
0.03
1.8
-------
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14B
£'-
RELEASE TO PUBLIC
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