c/EPA
United States
Environmental ProU,~.'
Agency
Environmental Sciences Research EPA-600/7-80-070
Laboratory March 1980
Research Triangle Park NC 27711
Research and Development
Characterization of
Scrubbed and
Unscrubbed Power
Plant Plumes
Three Case Studies
Interagency
Energy/Environment
R&D Program
Report
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EPA-600/7-80-070
March 1980
CHARACTERIZATION OF SCRUBBED AND
UNSCRUBBED POWER PLANT PLUMES
Three Case Studies
by
Jeffrey L. Stith
Donald L. Blumenthal
Jerry A. Anderson
Meteorology Research, Inc.
3402 Mendocino Avenue
Santa Rosa, CA 95401
Contract No. 68-02-2968
Project Officer
H.M. Barnes
Atmospheric Chemistry and Physics Division
Environmental Sciences Research Laboratory
Research Triangle Park, North Carolina 27711
ENVIRONMENTAL SCIENCES RESEARCH 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 Aerosol Research Branch, U. S.
Environmental Protection Agency, and approved for publication. 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
Airborne measurements of scrubbed and unscrubbed emissions from
the Widows Creek Power Plant were carried out during August 17-25,
1978. The results of the analysis of the measurements taken during three
case study days are described.
Gas-to-particle conversion rates calculated for mixtures of scrubbed
and unscrubbed emissions were between 0.3-4% hr~ . Secondary particles
were formed in both the nuclei (particles < 0.05 jim) mode in the accumula-
tion mode (0.05 - 1.0 jjm). In one instance, in a plume consisting largely
of scrubbed emissions in relatively clean background air, most of the
secondary particles were produced in the nuclei mode. For the other cases,
the amount of aerosol volume formed in the nuclei mode amounted to bet-
ween 0.2 and 3% of the total secondary aerosol. Day to day variations in
ambient sulfate levels were at least as great as the increase in sulfate
levels due to the plume. The scrubbed plume was not a significant source
of particles greater than 1. 0 pn or of primary sulfates in the submicron
size range.
This report was submitted in partial fulfillment of Contract No. 68-02-
2968 by Meteorology Research, Inc. under the sponsorship of the U.S. En-
vironmental Protection Agency. A data volume describing the results of
the aircraft measurements is also available.
in
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CONTENTS
Abstract iU
Figures vi
Tables ix
.Acknowledgements X
1. Introduction 1
2. Conclusions 4
3. Background: The 1 978 SCRUB Program 6
The Widows Creek Power Plant 6
Data Collection: instrumentation and
methodology "
Summary of sampling program 14
4. Case Study: August 17, 1978 18
Background 18
Particle size distributions 19
Gas-to- particle conversion 23
5. Case Study: August 19, 1978 24
Background 24
Plume cross sections 25
Particle size distributions 31
Gas-to-particle conversion 37
6. Case Study: August 23, 1978 38
Background 38
Plume cross sections 39
Particle size distributions 52
Gas-to-particle conversion 56
References DQ
Appendix
A. Gas-to-Particle Conversion Rate Uncertainties .... 62
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FIGURES
Number page
1 MRI Queen Air sample inlet lines and external probes 10
2 Comparison of the sulfate concentrations from ion chroma-
tography analysis of RSP filters versus the sulfate con-
centrations determined by flash volitization/flame
photometric analysis of Two Mass filters 12
3 Particle number, surface, and volume distributions, mea-
sured in scrubbed emissions from the Widows Creek
Power Plant on August 17, 1978 22
4 Contours of sulfur dioxide concentration measured perpen-
dicular to the axis of the plume from the Widows
Creek Power Plant on August 19, 1978 26
5 Contours of ozone concentration measured perpendicular
to the axis of the plume from the Widows Creek Power
Plant on August 19, 1978 27
6 Contours of condensation nuclei concentration measured per-
pendicular to the axis of the plume from the Widows
Creek Power Plant on August 19, 1978 28
7 Contours of light scattering coefficient due to particles mea-
sured perpendicular to the axis of the plume from the
Widows Creek Power Plant on August 19, 1978 29
8 Particle number, surface, and volume distributions, mea-
sured in a mixture of scrubbed and unscrubbed emis-
sions from the Widows Creek Power Plant on August 19,
1978 at a distance of 24 km downwind and an altitude of
671 m (msl) 35
9 Particle number, surface, and volume distributions, mea-
sured in a mixture of scrubbed and unscrubbed emis-
sions from the Widows Creek Power Plant on August 19,
1978 at a distance of 75 km downwind and an altitude of
610 m (msl) 36
vi
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10 Contours of sulfur dioxide concentration measured perpen-
dicular to the axis of the plume from the Widows Creek
Power Plant on August 23, 1978 at 11 km downwind .... 40
11 Contours of ozone concentration measured perpendicular to
the axis of the plume from the Widows Creek Power
Plant on August 23, 1978 at 11 km downwind 41
12 Contours of condensation nuclei concentration measured
perpendicular to the axis of the plume from the Widows
Creek Power Plant on August 23, 1978 at 11 km down-
wind 42
13 Countours of light scattering coefficient due to particles mea-
sured perpendicular to the axis of the plume from the
Widows Creek Power Plant on August 23, 1978 at 11 km
downwind 43
14 Contours of sulfur dioxide concentration measured perpen-
dicular to the axis of the plume from the Widows Creek
Power Plant on August 23, 1978 at 50 km downwind .... 44
15 Contours of ozone concentration measured perpendicular to
the axis of the plume from the Widows Creek Power
Plant on August 23, 1978 at 50 km downwind 45
16 Contours of condensation nuclei concentration measured
perpendicular to the axis of the plume from the Widows
Creek Power Plant on August 23, 1978 at 50 km down-
wind 46
17 Contours of light scattering coefficient due to particles mea-
sured perpendicular to the axis of the plume from the
Widows Creek Power Plant on August 23, 1978 at 50 km
downwind 47
18 Contours of sulfur dioxide concentration measured parallel
to the axis of the plume (looking down from aoove) from
the Widows Creek Power Plant on August 23, 1978 48
19 Contours of ozone concentration measured parallel to the
axis of the plume (looking down from above) from the
Widows Creek Power Plant on August 23, 1978 49
20 Contours of condensation nuclei concentration measured
parallel to the axis of the plume (looking down from
above) from the Widows Creek Power Plant on August 23,
1978 50
Vll
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21 Contours of light scattering coefficient due to particles mea-
sured parallel to the axis of the plume (looking down
from above) from the Widows Creek Power Plant on
August 23, 1978 51
22 Particle number, surface, and volume distributions, mea-
sured in the plume of tiie Widows Creek Power Plant
on August 23, 1978 at 13 km downwind and at an alti-
tude of 975 m (MSL) 5g
23 Particle number, surface, and volume distributions, mea-
sured in the plume of the Widows Creek Power Plant
on August 23, 1978 at 50 km downwind and an altitude
of 975 m (MSL), and at 70 km downwind at an altitude
of 853 m 59
viii
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TABLES
Number Page
1 Queen Air Instrumentation 7
2 SCRUB Program Summary 15
3 Summary of Size Distribution Measurements Taken on the
Morning of August 17, 1978 20
4 Summary of Size Distribution Measurements Taken on the
Afternoon of August 17, 1978 21
5 Summary of NOa /NO Ratios in the Widows Creek Power Plant
On August 19, 1978 30
6 Summary of Size Distribution Measurements Taken on the
Morning of August 19, 1978 32
7 Summary of Size Distribution Measurements Taken on the
Morning of August 23, 1978 53
8 Summary of Size Distribution Measurements Taken on the
Afternoon of August 23, 1978 54
ix
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ACKNOWLEDGEMENTS
This work was supported by the U. S. Environmental Protection
Agency, Contract Number 68-02-2968. The program direction by
H. M. Barnes, EPA Project Monitor, throughout the project has been
greatly appreciated. The assistance and cooperation during the field
program by J. A. McDonald (MRI), J. Ogren (University of Washington),
P. McMurry (University of Minnesota), and J. Meagher (Tennessee
Valley Authority) was also much appreciated.
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SECTION 1
INTRODUCTION
This report presents the analysis of the results of an airborne sampling
program performed by Meteorology Research, Inc. (MRI), as part of a study
of scrubbed and unscrubbed power plant plumes (referred to as the SCRUB
project).
The production of primary and secondary pollutants has been studied
extensively in plumes of unscrubbed power plants, but only preliminary
work has been done to determine the effects of scrubbers on downwind plume
chemistry. There is mounting political pressure to reduce ambient sulfate
levels by reducing the emissions of sulfur dioxide (SO2 ), the precursor to
secondary (i. e., particles produced by gas-to-particle conversion) sulfate
particles, from coal-fired power plants. The primary methods of reducing
SO emissions are to use low sulfur coal or to use scrubbers in the stack
to reduce the amounts of SO8 produced. Since scrubbing allows the use of
higher sulfur coal, scrubbing is likely to become more common in the future,
as utilities utilize the more available higher sulfur coal.
A number of studies have been conducted to determine the rate of gas-
to-particle conversion in the atmosphere. A recent review by Hegg (1979)
lists the results of 11 separate investigations of the conversion rates of sul-
fur dioxide; conversion rate estimates in these studies range from
0 - 300% hr" . However, most recent studies (e.g., Forrest and Newman,
1977; Ursenbach et al.. 1977; Cantrell and Whitby, 1978; Gillani etal.,
1978; Husar et_al., 1978; Pueschell and Van Valin, 1978; Stith, 1978;
Hegg, 1979) indicate a conversion rate between 0 and 10% hr" .
In spite of the many studies of gas-to-particle conversion rates which
-------
have been conducted, there still exists considerable uncertainty as to the
formation mechanisms, and the rates of conversion. Husar et al. (1978)
and Gillani et al. (1978) have observed sulfate conversion to be directly
related to the amount of solar radiation for the coal-fired Labadie Power
Plant. Cantrell and Whitby (1978), also at the Labadie plant, found the sul-
fate fraction to monotonically increase with plume travel time. On the other
hand, Forrest and Newman (1977) and Meagher et al. (1978) found very little
change in secondary sulfates with plume travel time. Friberg (1978) sug-
gested that conversion proceeds to a fractional asymptotic limit.
Dittenhoffer and Pena (1978) found the production of Aitken particles,
in the Keystone coal-fired power plant, to be the dominant secondary product-
tion process under conditions of low humidity, near neutral stability, and
strong solar radiation; while for plumes of relative humidity near 100%,
they found that conversion occurred on pre-existing droplets.
In a study of the Labadie Power Plant, Whitby et al. (1978) found the
creation of nuclei mode particles to range from about 1700 cm" s"1 (at
6:30 in the morning) to about 1 cm"*s" at night. They found that about 5%
of the aerosol volume which formed as a result of gas-to-particle conversion
went into the nuclei mode, and was independent of the conversion rate.
They also found that coagulation of these nuclei with particles in the accumu-
lation (0. 05 - 1. O^m) mode reduced the mean size of particles in the accu-
mulation mode in the plume as compared to the background air.
One of tiie main mechanisms for the oxidation of SO (as well as NO ) is
oxidation by OH radicals. The rate of oxidation by this mechanism is be-
tween 0.4-2. 7% hr"1 for SOa fCalvert et al, 1978) and about 13% hr"1 for
NO2 (Cox, 1974). Since the OH radicals are formed photochemically, the
rate of conversion should depend on the amount of solar radiation.
SOa oxidation may also take place on the surface of existing particles
(e. g., carbon particles) or in water droplets. This liquid phase oxidation
may play an important role under cloudy or high humidity conditions (Hegg
-------
and Hobbs, 1978). Further, metal salts in fly ash act as catalysts for the
oxidation of SO8 dissolved in water droplets. Thus, the SOa conversion
rates may be affected by any droplets produced by the scrubber.
The aerosol formation mechanisms in scrubbed plumes may be different
from the unscrubbed plumes as a result of the different primary emissions.
The objective of the present study is to determine what differences, if any,
exist in the plume chemistry, aerosol size distributions, aerosol formation
rates, and transformations of aerosols among scrubbed, unscrubbed, and
mixed plumes.
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SECTION 2
CONCLUSIONS
The principal findings that have emerged from this study are:
• Particles are formed by gas-to-particle conversion in
both the nuclei and accumulation modes. In one case,
where the background air was comparatively clean, the most
significant increase in particulate volume, in a plume which most
likely consisted primarily of scrubbed emissions, occurred
in the nuclei mode. In another case, with similar pri-
mary emissions but with very dirty ambient air, most of
the increase occurred in the accumulation mode. For
the latter case, the secondary particulate volume in the
nuclei mode was about 0. 3-0. 6% of the total secondary particu-
late volume.
• In a mixture of scrubbed emissions and fly ash laden
emissions (owing to problems with the electrostatic pre-
cipitators), the fraction of secondary particulate volume
in the nuclei mode reached a maximum of ~3% at 24-25 Km
downwind and then decreased to ~0. 2% at 75 Km.
• The differences between the scrubbed and unscrubbed
emissions, aside from the expected lower SO concentra-
tions, were: the scrubbed emissions probably contained fewer
primary particles greater than 0. 05 pm in size than did
the combined emissions; and the NOa /NO ratio may be
higher in the scrubbed plume. The differences, in
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terms of the size of the secondary aerosols which are pro-
duced, are probably relatively minor compared to the day
to day variations.
The rates of gas-to-particle conversion of SO which were
observed in both types of plumes is similar to that reported
for other power plants (between 0 and 4% hr 1).
Day to day variations in ambient sulfate levels for this
particular region were at least as great as the increase
in sulfate levels caused by the plume, for both types of
plumes.
The scrubbed plume is not a significant source of primary
sulfates in the submicron size region.
The scrubbed plume is not a significant source of coarse
(> 1. 0 jjni) particles.
Significant ozone formation downwind of the Widows Creek
plant was observed. Since above ambient ozone was detected
in both a plume which contained a large scrubbed fraction and in a
mixed plume, the formation of ozone may be more influenced
by ambient conditions than by the differences between the
scrubbed and unscrubbed primary emissions.
Regions of high condensation nuclei concentration were
observed in the Widows Creek plume. One of them coin-
cided with a region of relatively high NO concentrations.
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SECTION 3
BACKGROUND: THE 1978 SCRUB PROGRAM
THE WIDOWS CREEK POWER PLANT
The power plant studied in the SCRUB project was the Tennessee
Valley Authority's (TVA) Widows Creek steam plant near Stevenson,
Alabama. The plant has six 135 MW units (units 1-6) which are connected
to a single 305 m stack. Two additional 557 MW units are each connected
to separate 152 m stacks. One of these units (#8) is equipped with a lime-
stone wet scrubber, with a design efficiency of 80% for SO removal.
Units 1-6 and unit #8 are equipped with electrostatic precipitators with
design efficiencies of greater than 99. 5%. The precipitators on unit 7 have
a design efficiency of 90%.
DATA COLLECTION: INSTRUMENTATION AND METHODOLOGY.
The aircraft used in this study was the MRI Beechcraft Queen Air,
which contains instrumentation for measuring atmospheric trace gases and
aerosols, as well as several meteorological parameters. A list of the in-
struments aboard the Queen Air is presented in Table 1. Location of
some of the instruments on the aircraft are shown in Figure 1.
Data from all continuous instruments, as well as time and event codes
are recorded on 9-track tape in digital form. These tapes are then process-
ed at MRI where the appropriate calibration factors are applied to the data.
Further, altitude corrections are made to correct for changes in the zero
and span response of various instruments as a function of altitude.
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TABLE 1. QUEEN AIR INSTRUMENTATION
Parameter
SO,
NO/NO,, *
°.
Sulfate
it
light
Scattering
Coefficient
it
Condensa-
tion Nuclei
Turbulence
Temperature
Sampler
Manufacturer
and Model
Meloy 285
Monitor Labs
8440
CSI
MRI Two-Mass
ERT RSP
Sampler
MRI 1550
MRI 1569
Environment
One Rich 100
MRI 1120
YSI/MRI
Analysis Technique
Flame Photometric
Chemiluminescence
Chemi luminescence
Flash vaporization/
flame photometric
Ion Chromatograph
Integrating
Nephclometer
"
Light Attenuation
Pressure
Fluctuations
Bead Thermistor/
Vortex Housing
Normal Measure-
ment Ranges
(Full Scale)
50, 100 ppb
ZOO, 500 ppb
200 ppb
> 3 and < 3 jim
dia
< 3 Urn dia
10""m"*
10" and 10"3 m"1
(Dual Range)
106 cm'3
0-10 cm s
-50* to +50* C
Time Response
(to 90%)
30 s
5-10 s
5 8
1 8
< 1 a
3 8
3 s (to 60%)
5 8
Approximate
Resolution
1 ppb
< 10 ppb
5 ppb
~ 1 fig m"9
~ 1 Mg m~9
0.1 x 10"*m"1
lO'*™"1
10s cm'3
0.1 erne's-1
0.5* C
* Not installed while the Mcloy 285 Particulate Sulfur Monitor was in use.
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TABLE 1 (continued)
oo
Parameter
Dew Point
Altitude
Indicated
Airspeed
Position
Data Logger
(includes
time)
Stripchart
Recorder
Aerosol
Charge
Acceptance
Partlculate
Sulfur*
Sampler
Manufacturer
and Model
Cambridge
Systems 137
Validyne
Validyne
King KX170B/
HTI DVOR
MRI Data
System
Linear
Instruments
Washington
University
Meloy 285
Analysis Technique
Cooled Mirror
Absolute Pressure
Transducer
Differential Pressure
Transducer
Aircraft DME/VOR
9- Track Tape - 6
hour capacity in con-
tinuous operation
Dual channel
Aerosol Charge
Acceptance
Upstream SO,
Scrubber /Measure-
ment of total sulfur
Normal Measure-
ment Ranges
(Full Scale)
-50* to 450* C
0>3000 m msl
23-68 m • -l
0 to 359' and
0 to ISO km from
the station
0 to ±9.99 V DC
0.01. 0. 1, I,
10 VDC
~ .Ol-.ljl
particles
66 jig S m"3
Time Response
(to 90%)
0.5 s/*C
1 8
1 s
1 s
< 1 »
~ 1 s
30 s
Approximate
Resolution
0.5* C
6 m
_i
0. 1 ma
1 * (bearing),
0.2 km (dis-
tance)
0.01 VDC
Relative changes
in particulate sul-
fur only
Not installi-d whili- the Monitor Labs 8440 NO/NO Monitor was in use.
x
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TABLE 1 (continued)
AEROSOL SIZE DISTRIBUTION MEASUREMENTS
Instrument
Size Range
Method
TSI 3030*
Royco 218/MCA*
Knollenberg ASSP
Lundgren Impactor
(modified by the Univer
sitv of Calif, at Davis)
.0056 - 1 jjm
.56 - 18
3-45
10 to< 1/2
Aerosol Charger/Mobility
Analysis
Optical Particle Counter
with Multichannel Analyzer
Axial Scattering Spec-
trometer Probe
4 stage imp actor with
final filter. Diameters of 507c
cutoff: 4,2, 1, and 0. 5
* Automatic bag sampling system for TSI 3030 and Royco 218; bagfill
requires about 4 seconds
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Bag Sampling Syst
Two-Hass
RSP Filter Inlet
1550 Nephelometer
'Dew Point
1569 Nephelometer
CNC, Charger. SO? ..
or NO/NO *
SO,. Oj *,
PI tot
Figure 1. MRI Queen Air sample inlet lines and external probes.
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Three types of flight maneuvers were used in this study: traverses,
spirals, and orbits. Traverses are used to determine the horizontal dis-
tribution of the various measured parameters, while spirals are used to
determine their vertical distribution. Generally, when sampling a plume,
such as the plume from the Widows Creek plant, these traverses are done
perpendicular to the axis of the plume, at various altitudes and distances
downwind. In this way, the three-dimensional structure of the plume can be
determined for cases where the plume does not change radically during the
period of the sampling mission. The spirals done upwind of the plant are
especially useful for determining background concentrations and the structure
of the mixing layer. Orbits are done to provide filter or impactor samples
at one specific location.
Ground reference points are used to determine the endpoints of each
traverse, and the location of each spiral.
For producing plume cross sections, the data from the traverses are
plotted in vertical or horizontal cross sections, using the endpoints of each
traverse to fix the location of the aircraft. A contour analysis is then done.
Since the data for one cross section requires ~ 15-60 minutes to collect,
these cross sections represent the true plume cross sections only for steady
state plumes.
Particulate sulfur (sulfate) concentrations were determined by flash
volitization and flame photometric analysis of Two-Mass filters and by ion
chromatography analysis of RSP filters. The filter material for the Two-
Mass samples is glass fiber, the RSP filters are Teflon coated quartz.
When activated, the filter samplers sample continuously from the sampling
ports outside the aircraft (Figure 1). The flow rates are about 50 and 25
1 m for the RSP and Two-Mass samplers, respectively. All sample volumes
were reduced to standard conditions of 25" C and 1013.2 mbar. Both sam-
plers have a similar particle size cutoff (~3jum). A comparison of RSP data
with the Two-Mass data, collected at the same time, is presented in Figure
2. These data are from a combination of in-plume and background samples.
11
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t\>
10
15
Figure 2.
ION CHROMOTOGRAPHY SULFUR (jigS rrr3)
Comparison of the sulfate concentrations from ion chromatography
analysis of RSP filters versus the sulfate concentrations determined
by flash volitization/flame photometric analysis of Two Mass filters.
Each filter was exposed over the same period of time. The slope of
the regression line which fits the data is 0. 52; the correlation coef-
ficient is 0. 86.
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The two methods are reasonably correlated (correlation coefficient
of 0. 86); however, the sulfur concentrations derived from the RSP filters
are, on the average, about twice as high as the Two-Mass results. Since
many more Two-Mass filters were generally exposed than were RSP filters,
sulfate concentrations used in this study are from the Two-Mass results.
RSP filters were also analyzed for nitrate by ion chromatography.
These results are somewhat uncertain, as the nitrate levels on the filters
are near the values found on blank filters.
Elemental analyses of the Lundgren impactor samples were also
conducted using Ion Excited X-ray Emission (IEXE). Some of these re-
sults are available in the SCRUB data volume (Stith. et al.,1979); addition-
al results are available upon request to MRI. Sulfur concentrations deter-
mined by the IEXE analyses were often higher than RSP or Two-Mass values.
The systematic difference between the Two-Mass, RSP, and impactor
results have been consistent through several field programs. At present,
the ion chromatography analyses of RSP filters appear to give the most
reasonable results; however, these differences have not yet been resolved.
SO conversion rates were calculated following the procedure used by
Husar et al. (1978): the conversion rate is given as the charge in the frac-
tion of total sulfur present as sulfate per unit plume travel time. This
method will overestimate the conversion rate if there is significant removal
of SO before the measurements are made. Most of the plumes sampled
in this study were either above the terrain entirely, or had the main portion
of the plume above the terrain; consequently, little removal of SO should have
taken place. These conversion rates may also be low (perhaps by as much as
a factor of 2), since the sulfate concentrations which are used are from the
Two-Mass results. Plume travel times were determined from the average
•windspeed at plume elevation and the distances downwind. Windspeeds were
determined by pibal measurements made by TVA. More details on these cal-
culations are provided in Appendix A.
13
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Particle size distributions are presented as number concentration in
each instrument channel (dN), normalized by the finite difference between the
base 10 log of the instrumental channel boundaries (d log D), versus the geo-
metric mean of the channel boundaries. Particle surface and volume dis-
tributions are computed from the number distributions, assuming spherical
particles.
Following Whitby (1978), we refer to three modes which describe the
aerosol size distribution. These modes appear as three additive log-normal
functions, and are most easily observed on the particle surface or volume
distributions, with the nuclei mode in the 0.005 - 0.05 ^.m range, the accumu-
lation mode in the 0. 05 - 1. 0 jim range, and the coarse particle mode greate
than 1. 0 ^m. Nuclei mode particles are usually fresh condensation products
from chemical or high temperature (e.g., combustion) processes, while
accumulation mode particles result from condensation and from coagulation
of nuclei mode particles. Coarse particles are produced usually by grinding
or impaction or may result from windblown dust.
Particles formed by photooxidation of SOa are usually in the nuclei
mode range, unless there is sufficient aerosol surface area (greater than
2 .a
~ 500 /^m cm ) that condensation on existing particles, rather than the
formation of new particles, is the dominant particle formation mechanism
For more details see, for example, Whitby (1978) or Bouland et al. (1978)
Gas-to-particle conversion by liquid phase oxidation should produce par-
ticles in the accumulation mode size range, owing in part to the original siz
of the droplet condensation nucleus, which for most natural clouds is in the
range 0.05 - 0.5
SUMMARY OF SAMPLING PROGRAM
A total of ten flights were conducted by MRI at the Widows Creek site
during August 17-25, 1978. A short summary of the flights made by MRI
is given in Table 2. The data collected by MRI are available in the form
of a Data Volume (Stith et al. , 1979 ) and on magnetic tape.
14
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TABLE 2. SCRUB PROGRAM SUMMARY
Cartf/
Date
29/
17 Aug
30 /
17 Aug
31/
19 Aug
32/
19 Aug
33/
Zl Aug
34/
Z2 Aug
}5/
23 Aug
Flight Objective
Characterization
of unit 18
(scrubbed) plume
Duplication of AM
sampling for AM/
PM comparison
Long range plume
characterization
Continuation of
AM flight
NO^ plume chem-
at ry ilctermina-
ion; comparison
flights with TVA
iclicopter
Sunrise experi-
ment on unit 16
>lumc
'jong ranjje plume
characterization
liglit; sampling
n conjunction
ivilh TVA
Sampling
Period
(CDT)
0845-1224
1551-191
0630-1108
1407-1741
0647-1031
0609-0835
0915-1322
Plume
Sampling
Distances
(km)
0.5.3.9
downwind
0.5,2,7
0.5. 9.
20.45, 75
'. 9, 13,
17,25,30
15-20.30
0.5,10
15, 50
No. of
Traverses/
Spirals/
Orbits*
0/2/16
0/2/15
10/3/10
8/3/7
14/2/1
6/2/10
13/2/2
No. of Samples
RSP
3
4
6
2
3
1
5
Lmpactor
5
5
5
2
3
1
5
Two-Mass
8
7
13
10
7
4
6
Comments
Unit 17 not operating
Unit #7 not operating
Good plume characterization; Pre-
cipitators out of service.
Vertical structure determination at
•~-25 km downwind; near source char
actcrization; plume spread out and
patchy beyond 10 km; Precipitators
out of service.
Plume spread out and shifting - poor
characterization data
Experiment terminated due to low
clouds and fog; limited sampling
within 10 km of plant; poor plume
definition - shifting winds
(iood plume characterization data;
documentation of NO, NOX and O^
cliemist ry; documentation of plume
O^ bulge; unit #7 not operating
-Circles around the bt.icks are included us cirbits.
-------
TABLE 2 (continued)
Cart |/
Date
36 /
23 Aug
37 /
Z5 Aug
38/
25 Aug
Flight Objective
Continuation of
AM sampling;
sampling in con-
junction with TV A
Sunrise stud/ -
document history
of plume and
background be-
fore, during, and
after sunrise
Continuation of
AM flight
Sampling
Period
(COT)
1441-1907
0511-0936
1030-1316
Plume
Sampling
Distances
(km)
13,50,70
1,8.20
43-50,70
No. of
Traverses/
Spirals/
Orbits41
7/1/5
2/2/19
6/1/4
No. of Samples
RSP
1
0
0
[mpactor
1
7
4
Two-Mass
13
8
4
Comments
Unit 17 not operating
Sun first visible 0620; close in plume
samples were of the plumes from
units 17 and 18
Good (light) plume definition at 48
km not found at 70 km
*Circli-s around the stack arc included as orbit*.
-------
Other groups have participated in the SCRUB program. TVA performed
airborne sampling of trace gases and particles using an instrumented heli-
copter. The University of Minnesota performed similar sampling from an
instrumented van. TVA also provided plant operation and meteorological
data. Midwest Research, Inc. performed emission characterization mea-
surements on the scrubbed unit.
Several of the flights conducted by MRI provide detailed case studies
of the scrubbed and unscrubbed plumes. On August 17 and 23 morning and
afternoon flights were made. On these days unit #7 (the largest unscrubbed
unit) was not operating. The data from these days provide case studies of
scrubbed and mixed plumes. On August 19 , morning and afternoon flight?..
were made while all the units were operating; however, some of the pre-
cipitators were out of service These primary emissions should be quite
d iff r rent from the August 17 and 23 emissions.
In the following chapters, the results of the analyses of these case
studies are presented.
17
-------
SECTION 4
CASE STUDY: AUGUST 17, 1978
BACKGROUND
On August 17, 1978, morning and afternoon flights were conducted
while the largest unscrubbed unit (#7) was not operating. Thus, much of
the sampling was in the scrubbed plume.
The weather in the area was characterized by warm humid flow over
the area accompanied by afternoon and evening convective activity. A
radiation inversion was present in the area during the early morning hours,
breaking up about 0930 CDT. Ground fog was present in the area prior to
this time. The afternoon was unstable with light precipitation from late
afternoon thunder showers. Winds during the morning near plume elevation
were between 2 - 6 m s" from the west-southwest. The wind died down
during the afternoon.
Aircraft sampling was conducted near the plant by flying circles around
the stacks, penetrating the plume at about 0. 5 km downwind. In-plume
orbits were then conducted at a near (3 km) range and a far (9 km during the
morning flight and 7 km during the afternoon flight) range. Shallow back-
ground spirals, covering the plume vertical extent were done to provide data
in background air.
The plume from the tall stack (units 1-6, unscrubbed) was observed
to be above the aircraft during the passes at 0. 5 Km. At the further dis-
tances, the tall stack plume may have mixed with the lower plume.
The plume during the morning flight was relatively well defined;
however, during the afternoon the plume was more spread out. Traces
18
-------
of old plume may have also been in the area.
During the period 0500 - 2400 (CDT), unit #8 (scrubbed) was operating
at a relatively steady level with hourly gross generation between 275 - 320
MW.
PARTICLE SIZE DISTRIBUTIONS
Many bagfills were collected during the plume orbits, and the particle
size distributions determined. Tables 3 and 4 summarize these results
in terms of the particle volume concentration in the nuclei and accumulation
modes, along with the sulfate concentrations which were measured while
these bagfills were obtained. Examples of the particle number, surface,
and volume distributions are presented in Figure 3, for the morning
flight. As is clearly evident from Table 3 and Figure 3, there was a
significant increase in the nuclei mode concentration at the 9 km distance
during the morning flight. At the 3 km distance, the nuclei mode concen-
trations were similar to that in the background. Accumulation mode concen-
trations were little different from background levels at both ranges, for the
morning flight. A coarse particle mode (particles greater than 1.0 jim) is
also seen in both the plume and background (Figure 3). The coarse mode
is highly variable, hence the slight differences in this mode in Figure 3
are not a result of the plume.
The results from the afternoon flight were quite different from the
results obtained during the morning. Although, on average, there was a
slight increase in the nuclei mode, the differences are not significant as
were the earlier results. SO concentrations were about a factor of 2
lower than at similar distances downwind during the morning.
The nuclei mode concentrations were generally lower in the afternoon,
both in the plume and out, than they were in the morning . The accum-
ulation mode was greater in the afternoon than in the morning. These re-
sults indicate that the afternoon airmass had characteristics of a more aged
a.irmass than did the airmass present during the morning. It is difficult,
19
-------
TABLE 3. SUMMARY OF SIZE DISTRIBUTION MEASUREMENTS
TAKEN ON THE MORNING OF AUGUST 17, 1978
Time
10:24:39
10:31:01
10:39:00
11:01:07
11:05:24
11:08:58
11:11:57
11:28:52
11:34:17
11:40:11
11:44:31
11:53:57
09:51:22
09:54:27
09:57:10
Nuclei Mode
Volume
Concentration
(jim cm )
0.16
0.13
0.087
0.095
0. 14
0.16
0.098
0. 12 , 0.031
0.64
0.69
0.52
0.46
0.56
0. 57 , 0.092
0.083
0.048
0.089
0. 073 , 0.022
A ccumulation
Mode Volume
Concentration
/ * -*\
(jim cm )
10.
8.9
6.9
6.0
6.4
6.7
6.6
7.4, 1.5
8.6
11.
8.8
6.5
11.
9.2, 1.9
9.8
7.4
5.3
7.5 , 2.3
C one entr ation
(ppb)
20.
41.
62.
30.
41.
51.
45.
41., 14.
57.
112.
42.
29.
24.
53. , 35
\ -0.5
-0.5
Sulfate *
Concentration
(MgS m" )
^
\ 0.89
J
\
I 1.3
f
)
1.1 , 0.29
1.5
)1 0
1.2
1.4 , 0.21
| 0.75
0.75
Comments
^
3 km downwind
\ 457 m altitude
Plume orbit
J
Average and standard
deviation at 3 km
9 km downwind
457 m altitude
Plume orbit
Average and standard
deviation at 9 km
1 Background
j 426 - 495 m
Average and standard devi-
ation of background samples
* Sulfate concentrations are from Two-Mass filters which were being exposed while the bag samples
were obtained; often several bagfills were obtained while one filter was being exposed.
-------
TABLE 4. SUMMARY OF SIZE DISTRIBUTION MEASUREMENTS
TAKEN ON THE AFTERNOON OF AUGUST 17, 1978
Time
17:32:43
17:40:32
17:45:34
17:51:48
18:29:03
18:33:40
18:37:07
18:41:03
18:44:55
18:48:16
16:56:26
16:59:03
17:01:50
17:05:09
Nuclei Mode
Volume
Concentration
(fjm cm )
0.070
0.069
0.029
0.078
0.062 , 0. 022
0.046
0.080
0.050
0. 086
0.090
0.046
0.066 , 0.021
0. 033
0. 013
0.073
0. 078
0.049 , 0.031
Accumulation
Mode Volume
C one ent ration
I * "3 %
(jim cm )
14.
12.
14.
12.
13. , 1.2
11.
13.
8.8
11.
13.
9.2
11. , 1.8
9.8
9.8
10.
8. 2
9.4 , 0.84
soa
Concentration
(ppb)
23.
17.
40.
16.
24. , 11.
30.
41.
17.
13.
50.
14.
28. , 15.
N
V ~0 5
J
-0.5
Sulfate *
Concentration
(MgS rrfa)
^
} 1.6
J
1.4
1.5 , 0.14
A 4 9
J '*
^\
\l 6
J
3.3 , 2.3
^1
>1 3
/ 1.3
J
1.3
Comments
"*\ 3 km downwind
I 457 m altitude
1 Plume orbit
J
Average and standard
deviation at 3 km
>^
7 km downwind
457 m altitude
) Plume orbit. Possible
portion of another plume
J
Average and standard
deviation at 7 km
>v
1 Background sampling
) 400 - 500 m
)
Average and standard devi-
ation of background samples
* Sulfate concentrations are from Two-Mass filters which were being exposed while the bag samples
were obtained; often several bagfills were obtained while one filter was being exposed.
-------
E
~ w*-
«•-
? •' =
ts>
K
UJ
0
O
O
ilill
11 mi
IBM
W* «• W1 «•
PARTICLE DIAMETER D
Ml
PARTICLE DIAMETER D
Ml
tat
Figure 3.
PARTICLE DIAMETER D (jim)
Particle number (dN/dlog D), surface (dS/dlog D), and volume (dV/dlog D)
distributions, measured in scrubbed emissions from the Widows Creek
Power Plant on August 17,1978 at 9 km downwind (dotted line) and at an
altitude of 457 m (MSL). A distribution taken in the background air at an
altitude of 459 m is also presented (solid line).
-------
however, to compare the in-plume results obtained in the afternoon to the
morning results, since the afternoon plume was more spotty, and may have
mixed with traces of old plume (of some sort) which was in the area.
GAS-TO-PARTICLE CONVERSION
Sulfate levels in-plume during the morning flight generally increased
to about twice the background level (Table 3). Two sulfate filters were
exposed during each plume orbit during the morning flight. The sulfate con-
centrations measured during the 3 Km orbit were 0.89 and 1. 3 ^gS m" .
Above ambient total sulfur concentrations measured while these filters were
exposed were 39 and 54 ^gS m" , respectively. The ambient sulfate con-
centration was 0.75 jigS m" . Thus, the fraction of total sulfur as sulfate
at the 3 Km distance was 0.36 and 1.0%, or an average of 0.68% with stand-
ard deviation of 0.45%. At the 9 Km distance the sulfate concentrations were
1.5 and 1.2 pgS m" . Above ambient total sulfur concentrations measured
•while these filters were exposed were 63 and 28 jigS m , respectively.
Thus, the fraction of total sulfur as sulfate at the 9 Km distance was 1.2 and
1.6%, or an average of 1.4% with standard deviation of 0.28%. Based on a
windspeed of 3 m s"1 , which existed during the sampling period, this results
in a gas-to-particle conversion rate of 1.3 dt 0.737o hr'1 . However, these
results may be low by a factor of 2, as a result of the systematic errors dis-
cussed in Section 3. A discussion of the uncertainty in this value is given in
Appendix A.
Background sulfate levels were about a factor of 2 higher in the after-
noon than during the morning flight. It is difficult to estimate a conversion
rate from these data, since the sulfate concentrations in the plume were
generally not very different from background values (Table 4). Further,
the winds died down during the afternoon.
23
-------
SECTION 5
CASE STUDY: AUGUST 19, 1978
BACKGROUND
On August 19, 1978, morning and afternoon flights were conducted
while all of the units were operating. However, only about half the precip-
itators on units 1-6 were functioning, and the precipitator on unit 7 was
shut down. Consequently, this plume presents a much more particulate
laden plume than was present earlier.
A maritime tropical airmass was present in the area, associated with
a subtropical high pressure system over the southeastern United States.
A radiation inversion was developed to about 650 meters altitude, during the
morning hours, with final breakup occurring by about 1000 CDT. Winds at
plume elevation were between 2 - 4 m s , out of the northwest during the
morning. Windspeed was slightly higher during the afternoon and was out
of the southwest. No precipitation occurred.
During the morning flight, aircraft sampling near the plant was conduc-
ted by flying circles around the stack and penetrating the plume at about
0. 5 km downwind. The aircraft then moved out to successively further
distances downwind, where a series of traverses through the plume and orbits
in the plume were conducted. The plume was followed out to a distance of
about 75 km. In all, plume sampling was done at 0.5, 9, 8, 24, 25, 45,
47, 70, and 75 km downwind. Thus, the morning flight provides a very good
long range characterization of the plume.
During the afternoon another long range characterization flight was
attempted. However, the wind had shifted, and the plume was much more
24
-------
broken up and hard to follow. Consequently, the sampling which was done
was rather limited. The results presented in this section are from the
morning flight.
Units 7 (unscrubbed) and 8 (scrubbed) were operating at a relatively-
steady load during the morning flight, with operating levels between 305 -
330 MW and 245 - 250 MW for units 7 and 8, respectively. During the
period 0900 - 1000 the output of units 1-6 (unscrubbed, tall stacks)
increased from about 450 to 690 MW. In-stack opacity on unit #7 increased
considerably during the period 0600 - 0800, which was due to the shutdown
of the precipitators.
PLUME CROSS SECTIONS
Cross sections of the concentrations of SO , O , and condensation
3 d
nuclei (CN) and the light scattering coefficient due to particles, bsp, mea-
sured at 24 km downwind, are presented in Figures 4 to 7, respectively.
It is evident from these cross sections that the lower portion of the plume
was much different than the upper portion. The lower region contained
less SO ; hence, it may likely be the plume from the scrubbed stack.
However, both regions of the plume had a similar impact on the bSp. The
possibility of contamination from some other source of CN cannot be ruled
out; however, it is highly unlikely because the CN plume and the plume
from the power plant exactly coincide. At the 75 km distance downwind,
a slight ozone bulge (~ 10 ppb) was observed.
Another unusual aspect of the plume is that the lower portion of the
plume contained higher levels of NOa relative to NO than did the rest of the
plume. These results are summarized in Table 5. As can be seen in
Table 5, this ratio is consistently higher in the lower portion of the plume.
The usual increase in this ratio with distance downwind is also noted, a re-
sult of conversion of the NO produced by the plant into NO by ambient
ozone. The observed ozone deficit in the plume is approximately equal to
the amount of NO which has been converted to NO . Virtually all of the
Z5
-------
800
700
111
O
600
500
10 SQ MO 200 100 10 20
86420246
DISTANCE FROM PLUME CENTERLINE (km)
8
Figure 4. Contours of sulfur dioxide concentration (in ppb) measured perpendicular
to the axis of the plume from the Widows Creek Power Plant on
August 19, 1978 at 24 km downwind. The plume was comprised of a
mixture of scrubbed and unscrubbed emissions. The concentration of
sulfur dioxide in background air was between 0 and S ppb.
-------
800
700
E"
UJ
Q
ID
600 -
500
6420246
DISTANCE FROM PLUME CENTERLINE (km)
8
Figure 5. Contours of ozone concentration (in ppb) measured pc-rpcndicvilar to the
axis of the plume from the Widows Crt-ek Power Plant on August 19,
1978 at 24 km downwind. The plume was comprised of a mixture of
scrubbed and unscrubbcd emissions. The cr-onc concentration in back-
ground air was between 56 and 70 ppb.
-------
800 r
700
•l
UJ
O
00
600
500
864202468
DISTANCE FROM PLUME CENTERLINE (km)
Figure 6. Contours of condensation nuclei concentration (in units of 10 cm )
measured perpendicular to the axis of the plume from the Widows
Creek Power Plant on August 19, 1978 at 24 km downwind. The plume
was comprised of a mixture of scrubbed and unacrubbed emissions.
The background CN concentration was between 3x10 and 10 cm .
-------
800 r
700 -
E
UJ
o
IS)
600 -
500
6420246
DISTANCE FROM PLUME CENTERLINE (km)
8
.-•
Figure 7. Contour• of light scattering coefficient due to particles (in units of 10
measured perpendicular to the axis of the plume from the Widows Creek
Power Plant on August 19, 1978 at 24 km downwind. The plume was com-
prised of a mixture of scrubbed and unscrubbed emissions.
-.
m )
-------
TABLE 5. SUMMARY OF NO. /NO RATIOS IN THE WIDOWS
CREEK POWER PLANT ON AUGUST 19, 1978
Altitude
(m, MSL)
762
670
610
549
488
610
549
488
762
671
610
549
Distance
Downwind/
Travel Time
km/hr.
~0.5/0.05
-0.5/0.05
'-O. 5/0. 05
-0.5/0.05
-0.5/0.05
9/0.8
9/0.8
9/0.8
24/2.2
24/2.2
24/2.2
24/2.2
Peak
NO /NO
Ratio
0. 24
0.19
0.20
0.32
1.78
0.32
0.33
1.62
1.45
1.60
2.08
4.33
SO Peak
Concentration
(ppb)
428
1377
1398
1393
292
703
1387
333
221
206
149
114
30
-------
NO which was present in the upper portions of the plume at the 24 km dis-
8
tance could be accounted for as having resulted from this conversion. How-
ever, for the lower portion of the plume (549m, altitude), there was an ex-
cess (~14 ppb at 24 km downwind) of NOs. This indicates that one of the units
may have been a primary source of NO . This may result from electrical
discharges occurring in a precipitator which is not functioning properly. The
electrical discharge produces ozone which quickly reacts with NO to increase
the NOa level. If the observed NOg excess is due to precipitator problems,
the unit which is responsible is probably the scrubbed unit, since the pre-
cipitators on unit 7 (unscrubbed) were shut down and the excess occurred in
the region of lower SO3 concentration near the bottom of the plume. It is
interesting to note that this region of higher NOa coincides with the region
of high CN concentrations.
PARTICLE SIZE DISTRIBUTIONS
A summary of some of the results of the size distribution analyses of
bagfills which were obtained at the various distances downwind at roughly
similar altitudes are presented in Table 6. Sulfate concentrations which
were measured while the bagfills were being taken are also presented.
As is seen in Table 6, the nuclei mode concentration remained rela-
tively constant until 75 km, where the concentration decreased to near back-
ground levels. In contrast to the August 17 results, the accumulation mode
concentrations were significantly higher than background levels. The accu-
mulation mode concentrations remained relatively constant out to the 75 km
range. However, since the plume was diluting as it moved out to the 75km
range, it is clear that there was creation of particulate volume in both the
nuclei and accumulation mode ranges by gas-to-particle conversion. Using
(from Table 6) the average plume above ambient nuclei and accumulation
mode concentrations, and normalizing by the average plume above ambient
SO concentration, we see that this ratio was 1.2x10", 0.0013, 0.0032, and
4.2 x 10^* \t.m3 cm"3 ppb'1 for the nuclei mode and 0.028, 0.044, 0.11, and
0.26 fim3 cm"8 ppb'1 for the accumulation mode at the 9, 24-25, 45, and 75
31
-------
TABLE 6. SUMMARY OF SIZE DISTRIBUTION MEASUREMENTS
TAKEN ON THE MORNING OF AUGUST 19, 1978
Time
08:21:06
08:25:03
08:55:01
09:16:59
09:21:57
09:26:54
10:05:15
10:18:30
10:23:28
Nuclei Mode
Volume
Concentration
(jim cm~ )
0. 27
0. 070
0. 17 , 0. 14
0.087
0.39
0. 21
0.25
0. 23 , 0.12
0.10
0. 24
0.51
0. 28 , 0. 21
A ccumulation
Mode Volume
Concentration
(jim cm" )
56.
25.
40. , 22.
19.
17.
19.
18.
18. , 0.96
19.
19.
22.
20. , 1.7
soa
C one ent r ation
(ppb)
1388.
639.
1014. , 530.
197.
108.
138.
105.
137. , 43.
76.
67.
76.
73. , 5.2
Sulfate *
C one entr ation
(MgS m" )
)7.4
7.4
2.8
>
)3'7
3.25, 0.64
3.9
) 4. 9
4.4 , 0.71
Comment a
)9 km downwind
610 m altitude
Average and standard
deviation at 9 km
>>
1 24 - 25 km downwind
/ 671 m altitude
Average and standard
deviation at 24 - 25 km
^ 45 km downwind
J 610 m altitude
Average and standard
deviation at 45 km
ts>
* Sulfate concentrations are from Two-Mass filters which were being exposed while the bag samples
were obtained; often several bagfJUs were obtained while one filter was being exposed.
-------
TABLE 6 (continued)
Time
10:42:36
10:45:20
10:48:0
10:50:46
06:37:05
06:40:23
06:58:49
Nuclei Mode
Volume
Concentration
(/im cm )
0. 091
0.074
0.042
0.038
0. 061 , 0. 026
0.038
0.054
0.059
0.050 , 0.011
A c cumulation
ivlode Volume
Concentration
(fjm cm" )
19.
18.
16.
23.
19. ,2.9
14.
13.
10.
12. , 2.1
soa
C one entration
(ppb)
27.
26.
25.
28.
27. , 1.3
1 -0.5
-0.5
Sulfate *
Concentration
(MgS m" )
}"
J
4.2
) 2.6
2.4
2.5 , 0.14
Comments
1 75 km downwind
/ 610 m altitude
)
Average and standard
deviation at 75 km
"^ Background
} 439 - 879 m
Average and standard devi-
ation of background samples
w
Sulfate concentrations are from Two-Mass filters which were being exposed while the bag samples
were obtained; often several bagfills were obtained while one filter was being exposed.
-------
km distances downwind, respectively. Thus, though the volume in the
nuclei mode was initially increasing at a faster rate than the volume in the
accumulation mode, most of the volume was created into the accumulation
mode. The fraction of secondary particulate volume in the nuclei mode was
about 0.4, 3, 3, and 0. 2% at the 9, 24-25, 45, and 75 km distances, re-
spectively.
These results are similar to what is typically observed in smog
chambers (e. g. , Whitby et al., 1978; Bouland et al.. 1978): the concen-
tration of nuclei tends to increase until the point where the formation rate
is equal to the coagulation rate, and then the concentration decreases.
Further, in particularly dirty air (where the particle surface area is
a .a
greater than or equal to ~500 iim cm ), the secondary products may
condense directly on the surface of existing particles rather than form new
particles. Since the surface area concentration on August 19 was generally
a -a
between 100 - 500 ^m cm in the plume, much of the secondary products
may have formed on existing accumulation mode particles (most of the sur-
face area was in the accumulation mode, as in Figures 8 and 9).
Examples of some of the particle number, surface, and volume dis-
tributions are presented in Figures 8 and 9 for the 24 and 75 km distances
downwind. A background size distribution is also included in Figure 9
Unlike the earlier scrubbed plume samples from August 17, a significant
coarse particle mode is evident at the 24 km range (Figure 8), which was
most likely a result of the shutdown of the precipitaters. This was not
observed at the 75 km range, however. Unit 7 should normally be a
source of coarse particles, since it has a precipitator of only 90% effic-
iency. The generally higher particle concentrations in the accumulation
mode in both the plume and the background air as compared to August 17
are also evident in Figures 8 and 9.
34
-------
u>
in
•o
•o
O
cc
H
tu
O
O
CC
Ul
CO
•t* I i HUM i HIM i HIM I niiai | i yim
PARTICLE DIAMETER D
t.i i.t
PARTICLE DIAMETER D
w.t
Ml 11
PARTICLE DIAMETER D
Figure 8. Particle number (dN/dlog D), surface (dS/dlog D), and volume (dV/dlog D)
distributions, measured in a mixture of scrubbed and unscrubbed emissions
from the Widows Creek Power Plant on August 19, 1978 at a distance of
24 km downwind and an altitude of 671 m (MSL).
-------
OJ
•o
z
•o
oc
H
UJ
u
g - i
OC
UJ
00
0.01
too
PARTICLE DIAMETER D
Z
UJ
O
»•-
uj s
I Illl
I Hill
10 -
10* ir* 10t 10* lo1
PARTICLE DIAMETER D
10*
•01
10.0
PARTICLE DIAMETER D
Figure 9. Particle number (dN/dlog D), surface (dS/dlog D), and volume (dV/dlog D)
distributions, measured in a mixture of scrubbed and unscrubbed emissions
from the Widows Creek Power Plant on August 19, 1978 at a distance of
75 km downwind and an altitude of 610 m (MSL) (dotted line). A distribution
taken in the background air at an altitude of 422 m is also included (solid line).
-------
CAS-TO-PARTICLE CONVERSION
Sulfate levels both in the plume and in the background air were much
higher than on August 17. The best data for plume chemistry were obtained
during orbits which were done in the background air and in-plume at 8, 25,
45 and 75 km downwind. The sulfate concentrations which were measured
during the orbits are 7.4, 3.7, 4.9, and 4.2 pgS m and the correspond-
ing above ambient total sulfur concentrations are 1230, 147, 92, and 36
ugS m" at the 8, 25, 45, and 75 km distances, respectively. The back-
ground sulfate concentration at plume elevation was 2.4 /:gS m~ . Thus,
the fraction of above ambient sulfur as sulfate steadily increased downwind;
thU ratio was 0.41, 0.88, 2.7, and 5.0% at the 8, 25, 45, and 75 km dis-
tances, respectively. Based on the average windspeed of 3 m s"1 this gives
conversion rates of: 0.3%hr-l between 8 and 25 km, 0.99% hr'1 between
25 and 45 km, and 0. 83% hr"* between 45 and 75 km. The average con-
version rate is about 0.71% hr-1 with a standard deviation of 0. 36% hr"1.
The standard deviation provides a measure of the errors inherent in the
determination of the conversion rate and of the natural variation in this
rate which may result from differences in the amount of solar radiation
received by the plume (these emissions were produced between about
0400 to HOC CDT). Further, these results may be low by about a factor
of 2 as a result of systematic errors in the sulfate measurements, as
discussed in Section 3.
37
-------
SECTION 6
CASE STUDY: AUGUST 23, 1978
BACKGROUND
As was the case during the earlier flights on August 17, the
main unscrubbed unit (#7) was not operating on August 23. Thus, the sam-
pling which was done was in either the scrubbed plume or the mixed plurre
Morning and afternoon flights were made.
The background air was quite polluted with levels of b between
.* .* .1 SP
2. 5x10 to 3. 5x10 m . The radiation inversion which had formed by
early morning to about 800 meters had broken up entirely by about 0930.
Winds at plume elevation were rather strong (~ 6 - 7 m s~ ) during the
early morning hours, but by 1000 had died down to about 3 m s~ from
the southerly direction where they remained for the rest of the sampling
period. Scattered to broken clouds were in the area, with bases at about
1700 m; no precipitation was noted.
During the morning flight a series of traverses were made at 11 - 14
km and at 50 km downwind of the plant. A spiral through the plume and a
background orbit were also done. During the afternoon flight a series of
traverses and orbits were made starting at 70 km downwind, and these were
then repeated at 50 and 13 km downwind.
During the period of these measurements the scrubbed unit (#8) was
operating at a steady level (235 - 245 MW, hourly gross generation).
Units 1-6 (tall stack, unscrubbed) were also operating at a steady hourly
gross generation level of about 775 MW.
38
-------
PLUME CROSS SECTIONS
Cross sections of the concentrations of SO8, O^, CN, and bSp for the
morning flight are presented in Figures 10 to 13 for the 11 km distance
downwind, and in Figures 14 to 17 for the 50 km distance. These cross
sections are drawn perpendicular to the axis of the plume looking toward
the south (i. e. , facing the power plant).
The lower levels of SO in this plume (Figure 10) compared to the
levels measured on August 19 (Figure 4), at over twice the distance down-
•wind, are evident. This is probably a consequence of the shutdown of
unit f 7. The small plume to the side of the main plume is probably the plume
from a nearby pulp mill, rather than a portion of the Widows Creek plume.
The SO concentrations in the plume on August 23 at 11 km downwind were
higher than were measured in the August 17 plume at 9 km downwind, even
though on both days unit 7 was shutdown. Evidently the scrubbed plume on
August 23 had mixed with the plume from units 1-6, while the emissions sam-
pled on August 17 may have been entirely from the scrubbed unit. Different
mixing with the background air may also be a factor. At 11 km range, the
Widows Creek plume only had a rather slight effect on the levels of bsp
(Figure 13, while at the 50 km distance it had a much greater impact
(Figure 17).
As can be seen from the cross sections of ozone concentration (Figures
11 and 15), the ozone levels in the plume went from a deficit to a slight
increase between the 11 and 50 km downwind distance. The concentration
of CN in the plume at the 50 km distance was about the same as the levels
»t the 11 km distance (Figures 12 and 16), even though the plume had diluted
considerably. Clearly the formation of new CN was occurring by gas-to-
particle conversion.
Cross sections of the afternoon plume, looking down from above, arc
presented in Figures 18 to 21. The plume created an ozone excess of
considerable extent downwind of the plant (Figure 19). Generally, bsp
39
-------
1100
c/J 1000
s
E
UJ
Q
900
800
700
10 50 50 20
4202468
DISTANCE FROM PLUME CENTERLINE (km)
10
Figure 10. Contours of sulfur dioxide concentration (in ppb) measured perpendicular
to the axis of the plume from the Widows Creek Power Plant on
August 23, 1978 at 11 km downwind. The concentration of sulfur
dioxide in background air was between 0 and 5 ppb.
-------
1100
7060 60 70
UJ
Q
900
800
700
4202468
DISTANCE FROM PLUME CENTERLINE (km)
10
Figure 11. Contours of ozone concentration (in ppb) measured perpendicular to the
axis of the plume from the Widows Creek Power Plant on August 23,
1978 at 11 km downwind. The ozone concentration in background air was
between 70 and 85 ppb.
-------
1100
ts>
<7> 1000
5
j:
ui 900
Q
13
H
^ 800
700
15 20 20 15
4 202468
DISTANCE FROM PLUME CENTERLINE (km)
10
3 _3
Figure 12. Contours of condensation nuclei concentration (in units of 10 cm )
measured perpendicular to the axis of the plume from the Widows
Creek Power Plant on August 23, 1978 at 11 km downwind. The
concentration of CN in background air was between 8x10'
15 x 10" cm"".
and
-------
1100
250 280
1000
UJ
Q
900
800
250
250
700
4202468 10
DISTANCE FROM PLUME CENTERLINE (km)
Figure 13.
_6
_ _
Contours of light scattering coefficient due to particles (in units of 10 m )
measured perpendicular to the axis of the plume from the Widows
Creek Power Plant on August 23, 1978 at 11 km downwind.
-------
1000
900
g 800
700
600
10 20 20 10 5
5 5
12
8404 8 12 16 20
DISTANCE FROM PLUME CENTERLINE (km)
24
Figure 14. Contours of sulfur dioxide concentration (in ppb) measured perpendicular
to the axis of the plume from the Widows Creek Power Plant on
August 23, 1978 at 50 km downwind. The sulfur dioxide concentration
in background air was between 1 and 4 ppb.
-------
1000
5 900
E
m
9 800
700
600
100
90
U
12
8 4 04 8 12 16 20
DISTANCE FROM PLUME CENTERLINE (km)
24
Figure 15. Contours of ozone concentration (in ppb) measured perpendicular to the
axis of the plume from the Widows Creek Power Plant on August 23,
1978 at 50 km downwind.
-------
1000 -
20 25 30 35
E 900
UJ
o
800
700
25 20 20 25
600
12 8 4 04 8 12 16 20 24
DISTANCE FROM PLUME CENTERLINE (km)
3 _a
Figure 16. Contours of condensation nuclei concentration (in units of 10 cm )
measured perpendicular to the axis of the plume from the Widows
Creek Power Plant on August 23, 1978 at 50 km downwind. The
concentration, of CN in the background air was between 8x10 and
15 x I0"cm"".
-------
1000
360
400 440
360
360
320
900
800
UJ
Q
D
H
<
700
600
12 8 4 0 4 8 12 16
DISTANCE FROM PLUME CENTERLINE (km)
20 24
_6
Figure 17. Contours of light scattering coefficient due to particles (in units of 10" m
measured perpendicular to the axis of the plume from the Widows Creek
Power Plant on August 23, 1978 at 50 km downwind.
-------
WIDOWS CREEK
POWER PLANT *
Figure 18. Contours of sulfur dioxide concentration (in ppb)
measured parallel to the axis of the plume
(looking down from above) from the Widows Creek
Power Plant on August 23, 1978 at an altitude of
975 m (MSL). The sulfur dioxide concentration
in background air was between 1-2 ppb. The flight
paths of the aircraft are indicated by the dashed lines.
48
-------
C? WHITWELL
CHATTANOOGA
801 90
BRIDGEPORT
WIDOWS CREEK
POWER PLANT *
0
10
20
•JKm
Figure 19. Contours of ozone concentration (in ppb) measured
parallel to the axis of the plume (looking down
from above) from the Widows Creek Power Plant on
August 23, 1978 at an altitude of 975 m (MSL). The
ozone concentration in background air was between
80 and 90 ppb. The flight paths of the aircraft are
indicated by the dashed lines.
49
-------
SEWANEE
RACY CITY
Ł? WHITWELL
CHATTANOOGA
BRIDGEPORT
WIDOWS CREEK
POWER PLANT *
0
10
20
•JKm
Figure 20. Contours of condensation nuclei concentration (in
units of 10 cm ) measured parallel to the
axis of the plume (looking down from above) from
the Widows Creek Power Plant on August 23, 1978
at an altitude of 975 m (MSL). The concentration
of CN in the background air was between 9x10
and 15 x 10 cm" . The flight paths of the aircraft
are indicated by the dashed lines.
50
-------
340
SEWANEE
C? WHITWELL
CHATTANOOGA
BRIDGEPORT
WIDOWS CREEK
POWER PLANT *
10
20
•JKm
Figure 21. Contours of light scattering coefficient due to particles
(in units of 10" m" ) measured parallel to the
axis of the plume (looking down from above) from the
Widows Creek Power Plant on August 23, 1978 at
an altitude of 975 m (MSL). The light scattering
coefficient due to particles, in the background air,
increased downwind of the Widows Creek Plant; at
13 km downwind it was between 2.5x10 "* and
3.0x10 m and at 50 -70 km downwind it was
between 3.0 x 10" and 3.4 x 10" m" . The flight
paths of the aircraft are indicated by the dashed lines.
51
-------
increased downwind in both the background and in the plume; however a
maximum in the plume is evident beginning at the 50 - 70 km distance.
The concentration of CN reached a maximum value at the 50 km distance,
then decreased in the region which displays the higher levels of bst)
(Figures 20 and 21).
PARTICLE SIZE DISTRIBUTIONS
A summary of some of the size distribution results from the morning
and afternoon flights are presented in Tables 7 and 8, respectively, along
with the sulfate concentrations which were measured while the bagfills were
obtained. As is seen in Table 7, during the morning flight the nuclei mode
concentration was slightly higher in the plume at both distances downwind.
The accumulation mode concentration was at about background levels at
11-14 km range, and higher than background levels at the 50 km range.
These results confirm the increases in light scattering which were observed
(Figures 13 and 17). Between these two ranges, the plume had diluted by
about a factor of 4. Normalizing the average plume above ambient nuclei
and accumulation mode volume concentrations, by the above ambient SO3
concentrations, we find the ratio to be ~4 x 10"* and 0.002|im3 cm"3 ppb'1
for the nuclei mode and -JQ and 0.32 jim3 cm"3 ppb" for the accumulation
mode at the 11-14 km and 50 km distances downwind, respectively. Thus,
both of these modes were increasing downwind. The secondary particle
volume in the nuclei mode amounted to about 0.6% of the total secondary
particle volume, at the 50 km distance.
During the afternoon flight, both the nuclei and accumulation mode con-
centrations were near background levels at the 13 km distance (Table 8),
but were above background at the further distances. The ratio of the average
plume above ambient nuclei and accumulation mode volume concentrations
to the above ambient SO concentrations are about 0.013 and 0. 006 pn" cm"3
ppb for the nuclei mode, and 2.0 and 2. 3 ^m cm ppb for the accumu-
lation mode at the 50 and 70 km distances, respectively.
5Z
-------
TABJ.E 7. SUMMARY OF SIZE DISTRIBUTION MEASUREMENTS
TAKEN ON THE MORNING OF AUGUST 23, 1978
Time
09:58:17
10:15:3Z
10:24:54
10:32:22
10:41:06
11:52:03
12:05:49
12:14:51
12:28:22
12:36:41
11:08:34
11:15:12
11:19:26
Nuclei Mode
Volume
Concentration
(l*m cm )
0.051
0. 12
0. 15
0.11
0.065
0. 099 , 0. 041
0.061
0. 12
0. 11
0. 14
0. 14
0. 11 , 0. 032
0.042
0.088
0.054
0. 061 , 0.024
Accumulation
Mode Volume
C one entr ation
i * -•»
(pm cm )
24.
12.
17
20.
17.
18. , 4.4
29.
29.
29.
25.
35.
29. , 3.6
21.
23.
22.
22. , 1.0
soa
Concentration
(ppb)
77.
100.
116.
90.
46.
86. , 27.
22.
29.
21.
23.
20.
23. , 3.5
0.
1.
2.
~1.
Sulfate *
Concentration
(JZgS m~9)
^
>
1.8
1.8
«^
5.8
J
5.8
J 4.4
4.4
Comments
762 m altitude >
792 m altitude
853 m altitude
914 m altitude
975 m altitude J
11-14 km
downwind
Average and standard devi-
ation at 11-14 km
762 m altitude *\
701 m altitude
792 m altitude
853 m altitude
975 m altitude J
50 km
i
downwind
Average and standard devi-
ation at 50 km
914m altitude ^Ba'ck d
914 m altitude ) °
914m altitude/ 8amples
Average and standard devi-
ation of background samples
(Jl
Ul
* Sulfate concentrations are from Two-Mass filters which were being exposed while the bag samples
were obtained; often several bagfills were obtained while one filter was being exposed.
-------
TABLE 8. SUMMARY OF SIZE DISTRIBUTION MEASUREMENTS
TAKEN ON THE AFTERNOON OF AUGUST 23, 1978
Time
14:50:30
15:04:17
17:14:49
17:23:10
17:28:22
17:32:54
18:15:14
18:36:25
18:41:06
18:45:45
Nuclei Mode
Volume
Concentration
(jim cm )
0. 12
0.057
0. 088 , 0. 044
0.14
0.11
0.15
0.11
0. 13 , 0.021
0.087
0.037
0.063
0.090
0. 069 , 0. 025
A ccumulation
Mode Volume
Concentration
(pm cm" )
23.
22.
22. , 0.71
24.
24.
23.
24.
24. , 0.50
15.
17.
15.
15.
16. » 1.0
S0a
C one ent r ation
(ppb)
4.
4.
4.
4.
4.
7.
7.
5.5 , 1.7
26.
13.
12.
39.
22. , 13.
Sulfate *
C one entr jition
(MgS m )
6.7
6.6
6.6 , 0.071
7.0
I7'1
7.0 , 0.071
5.6
) ^
^
5.5 , 0. 14
Comments
853 m altitude \ 70 km
792 m altitude / downwind
Average and standard devi-
ation at 70 km
N
I 975 m altitude
/ 50 km downwind
Average and standard devi-
ation at 50 km
1 975 m altitude
/ 13 km downwind
Average and standard devi-
ation at 13 km
Ul
* Sulfate concentrations are from Two-Mass filters which were being exposed while the bag samples
were obtained; often several bagfills were obtained while one filter was being exposed.
-------
TABLE 8 (continued)
Time
17:48:09
17:52:16
17:56:14
18:52:08
18:54:59
Nuclei Mode
Volume
Concentration
(lim cm" )
0.060
0.048
0.061
0.10
0.082
0. 070 , 0. 021
Accumulation
Mode Volume
C oncentr ati on
(fjm cm )
15.
14.
14.
13.
17.
15. , 1.5
SO,
Concentration
(ppb)
1.
1.
1.
0.
2.
1. , 0.71
Sulfate *
Concentration
(jigS m"*)
.
) 6.4
/
5.4 , 1.3
Comments
^
1 975 m altitude
/ Background samples
J
Average and standard devi-
ation of background samples
* Sulfate concentrations are from Two-Mass filters which were being exposed while the bag samples
were obtained; often several bagfills were obtained while one filter was being exposed.
-------
Since the concentrations were near background levels at thr 13 km
)
distance, both modes increased between 13 and 50 km. The secondary
particle volume in the nuclei mode was about 0. 6% of the total secondary
particle volume at the 50 km distance and about 0. 3% at the 70 km dis-
tance. As was the case on August 19, the nuclei mode decreased at the
farthest range downwind (70 km).
Some examples of the particle number, surface, and volume distri-
butions, for the afternoon flight, measured at the 13, 50, 70 km distances
and in the background air are presented in Figures 22 and 23. The
increase in the accumulation mode at 50 and 70 km is evident in Figures
21 and 23. The relative depression of the portion of the number dis-
tribution less than O.OS^m, at the 70 km range (Figure 23), is evident,
in agreement with the lower concentration of condensation nuclei observ-
ed at this range (Figure 20). As was the case on August 17, these
emissions are not a significant source of coarse (>1.0 pm) particles.
GAS-TO-PARTICLE CONVERSION
The sulfate levels measured in both the plume and the background
air were among the highest observed during the entire SCRUB project.
These measurements (see Tables 7 and 8) indicate that the sulfate
concentrations in the plume were increasing downwind during the morning
and afternoon flights. However, the concentration in the background air
was also increasing during this sampling period. Consequently, the amount
of sulfate produced by the plume is uncertain.
Most of the sulfate filter samples which were collected during the
morning flight were collected by activating the Two-Mass sampler at the
beginning of the aircraft traverse and then shutting it off at the end of the
traverse. This was repeated, using the same filter sample, until the srt
of traverses at that distance downwind were completed. For these traverses
the aircraft was generally in the plume for less than half of the time the
56
-------
filter was being exposed. Consequently, the sulfate samples obtained
during the plume traverses at 11-14 km and 50 km downwind are probably
highly diluted by background air.
57
-------
u
o
s
T3
VJl
00
UJ
o
o
o
K
Ul
CD
Figure 22.
•«-.
O „«
•1 -,
i mil
LLlill
I I UU
PARTICLE DIAMETER D
O.O1
W.O
PARTICLE DIAMETER D
PARTICLE DIAMETER D
Particle number (dN/dlog D), surface (dS/dlog D), and volume (dV/dlog D)
distributions, measured in the plume of the Widows Creek Power Plant on
August 23, 1978 at 13 km downwind (dotted line) and at an altitude of 975 m
(MSL). A distribution taken in the background air at an altitude of 975 m is
also presented (solid line).
-------
Ul
vO
o
S "4i
TJ
I --fc
2 «»
o
5 .•-Ł
O
Ul w*
a
z u «_
ui »L •"-
0 I.
z <3-«w-
?«••
51..
(O
\V
ni i t i i rtlf^^_^L»
l.t
PARTICLE DIAMETER D
M i linn* i ni»m i inimt 1 1 mm
PARTICLE DIAMETER D (>im)
PARTICLE DIAMETER D
Figure 23. Particle number (dN/dlog D), surface (dS/dlog D), and volume (dV/dlog D)
distributions, measured in the plume of the Widows Creek Power Plant on
August 23, 1978 at 50 km downwind and an altitude of 975 m (MSL) (dotted
line), and at 70 km downwind at an altitude of 853 m (solid line).
-------
REFERENCES
Bevington, P. R., 1969: Data Reduction and Error Analysis in the Physical
Sciences, New York, McGraw-Hill, 336 pp.
Bouland, D. , J. Bricard, and G. Madelaine, 1978: Aerosol growth kinetics
during SO oxidation. Atinos, Envir. , 12, 171-177.
^ ^•••^•MIMHB^M M^^M^WBM^ BHBBM
Calvert, J. G. , F. Su, J. W. Bottenheim, and O. P. Strausz, 1978:
Mechanism of the homogeneous oxidation of sulfur dioxide in the
troposphere. Atmos^ Envir. ]2_, 197-226.
Cantrell, B. K., and K. T. Whitby, 1978: Aerosol size distributions and
aerosol volume formation for a coal-fired power plant plume.
Atmos. Envir. . 12, 297-306.
Cox, R. A. , 1974: Particle formation from homogeneous reactions of sul-
fur dioxide and nitrogen dioxide. Tellus, 26, 235-240.
Dittenhoffer, A. C., and R. G. De Pena, 1978: A study of production and
growth of sulfate particles in plumes from a coal-fired power plant.
Atmos. Envir. , 12, 297-306.
Forrest, J. , and L. Newman, 1977: Further studies on the oxidation of
sulfur dioxide in coal-fired power plant plumes. Atmos. Envir. ,
U., 465-474.
Friberg, J. , 1978: Conversion limit and characteristic time of SO
oxidation in plumes. Atmos. Envir. , 12, 339-347.
Gillani, N. V. , R. Husar, D. E. Patterson, and W. E. Wilson, 1978:
Project MISTT: kinetics of particulate sulfur formation in a power
plant plume out to 300 km. Atmos. Envir. , 12, 589-598.
Hegg, D. A. , 1979: Gas-to-particle conversion in the plumes from coa^-
fired electric power plants. Ph. D. dissertation, University of
Washington.
60
-------
Hegg, D. A. , and P. V. Hobbs, 1978: Oxidation of sulfur dioxide in
aqueous systems with particular reference to the atmosphere.
Atmos. Envir. , 1_2, 241-254.
Husar, R. , D. Patterson, J. D. Husar, F. V. Gillani, and W. E. Wilson,
1978: Sulfur budget of a power plant plume. Atmos. Envir., 12,
549-568.
Meagher, J.F., L. Stockburger, E. M. Bailey, and O. Huff, 1978:
The oxidation of sulfur dioxide to sulfate aerosols in the plume
of a coal-fired power plant. Atmos. Envir. , 12, 2197-2203.
Pueschel, R.V., andC.C. Van Valin, 1978: Cloud nucleus formation
in a power plant plume. Atmos. Envir. , 12, 307-312.
Stith, J. L., 1978: A comparison of some natural and anthropogenic
sources of particles and gases in the atmosphere. Ph. D. disser-
tation, University of Washington.
Stith, J. L. , J. A. Anderson, J. A. McDonald, and D. L. Blumenthal,
1979a: Airborne measurements of scrubbed and^inscrubbed emissions
from the Widows Creek Power Plant; Data Volume. MRI 79-DV-1707.
Meteorology Research, Inc., 3402 Mendocino Ave., Santa Rosa, CA
95401, 347 pp.
Ursenbach, W. O. , A.C. Hill, W. H. Edwards, and S. M. Kunen, 1977:
Conversion rate of SOg to submicron sulfate in the plumes of a
coal-fired power plant in the western United States. Presented at
7J3th Annual Meeting of the Air Pollution Control Association.
Toronto, Canada, June 20-24.
Whitby, K. , B. Cantrell, and D. B. Kittelson, 1978: Nuclei formation
rates in a coal-fired power plant plume. Atmos. Envir. , 1^2, 313-322.
Whitby, K. T. , 1978: The physical characteristics of sulfur aerosols.
Atmos. Envir. . 12, 135-169.
61
-------
APPENDIX A
GAS- TO- PARTICLE CONVERSION RATE UNCERTAINTIES
In this appendix the uncertainties in the rate of gas-to-particle con-
version are estimated for the August 17 case study. If the uncertainty in
each of the measurements of the sulfate function (i.e. the ratio of the
above ambient sulfate to the above ambient total sulfur) is given by the
standard deviation of the values, 0" , then the uncertainty in the mean value,
0"m, is given by* 0" /\/N, where N is the number of measurements.
N = 2 for the measurements made at 3 and 9 km downwind on August 17.
The standard deviations of the sulfate fraction (see Section 4) are 0.45%
and 0. 28% for the 3 and 9 km distances, respectively. Thus the uncertain-
ties in the mean sulfate function at 3 and 9 km are 0. 32 and 0.20%, re-
spectively. The rate of gas-to-particle conversion, R, between the two
distances is
R =~ (fg - f3), A-l
where T is the travel time between the two distances, f is the mean sulfate
fraction and the subscript refers to the distance downwind. The uncertainty
in R Ls given by *
..2 rf2 _
°R= *rn9 «- m3
where 0-r- is the uncertainty in the plume travel time which is estimated
to be about 20% of T (T = . 55 hr) or . 11 hr. Then, from A-l and A-2,
4 = *2m9 T"2 + ^m3 T"2 + 4
Substituting in values (fg = 1.4%, f$ = 0.68%, see Section 4) we find On = 0.75%
* For the derivation of these formulas see, for example, Bevlngttm (1969)
62
-------
provides a measure of the errors in the conversion rate associated
with the random sampling errors. These errors are about 56% of the con-
version rate. As was noted in Section 3 there may be additional systematic
errors associated with the measurement technique which suggest that the
sulfate concentrations may be low by about a factor of 2. The conversion
rate would be low by the same factor (see equation A-l).
63
-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
i. REPORT NO.
EPA-600/7-80-070
4. TITLE AND SUBTITLE
CHARACTERIZATION OF SCRUBBED AND UNSCRUBBED
POWER PLANT PLUMES
Three Case Studies
6. PERFORMING ORGANIZATION CODE
3. RECIPIENT'S ACCESSIOf*NO.
5. REPORT DATE
March 1980
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Jeffrey L. Stith, Donald L. Blumenthal, and
Jprry A. Anderson
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Meteorology Research, Inc.
3402 Mendocino Avenue
Santa Rosa, California 95401
10. PROGRAM ELEMENT NO.
1NE625 EA30 (FY78)
11. CONTRACT/GRANT NO.
68-02-2968
12. SPONSORING AGENCY NAME AND ADDRESS
Environmental Sciences Research Laboratory - RTP, NC
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA-600/09
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Airborne measurements of scrubbed and unscrubbed emissions from the Widows
Creek Power Plant were carried out during August 17-25, 1978. The results of the
analysis of the measurements taken during three case study days are described.
S02 gas-to-particle conversion rates calculated for mixtures of scrubbed and
unscrubbed emissions were between 0.3-4% hr'l. Secondary particles were formed in
both the nuclei (particles <0.05 ym) mode in the accumulation mode (0.05-1.0 ym).
In one instance, in a plume consisting largely of scrubbed emissions in relatively
clean background air, most of the secondary particles were produced in the nuclei
mode amounted to between 0.2 and 3% of the total secondary aerosol. Day to day
variations in ambient sulfate levels were at least as great as the increase in
sulfate levels due to the plume. The scrubbed plume was not a significant source
of particles greater than 1.0 ym or of primary sulfates in the submicron size range.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
COSATI Field/Group
*Air pollution
*Evaluation
*Aerosols
*Plumes
*Electric power plants
Scrubbers
13B
07D
10B
07A
131
13. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21 NO. OF PAGES
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
64
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