s-xEPA
                                 United States
                                 Environmental Protection .
                                 Agency
                                 Environmental Sciences Research - ,
                                 Laboratory                  ",  ' '
                                 Research Triangle ParkNC 27711   '' >
                                 Research and Development
                                 EPA-600/S3-81-041  Oct. 1981
Project  Summary
                                Characterization  of
                                Scrubbed  and  Unscrubbed
                                Power  Plant  Plumes
                                H. M. Barnes
                                  Airborne measurements of scrubbed
                                and unscrubbed plumes from the
                                Widows Creek Steam Plant were
                                made during August 17 to 25,1978,
                                under the SCRUB program. Data from
                                the flight program (except size distri-
                                bution data) and preliminary data
                                analysis results have been previously
                                published in a Data Volume.
                                  This report  briefly describes the
                                flight program and methodology of
                                SCRUB and gives an analysis of the
                                data gathered. The results cover
                                plume chemistry, primary aerosol,
                                aerosol size distributions, and aerosol
                                formation rates among the scrubbed
                                and mixed plumes.
                                  Little difference was seen in photo-
                                chemical aerosol and sulfate formation
                                in the scrubbed and  unscrubbed
                                plumes. However, measurement noise
                                and plume mixing may have obscured
                                moderate differences. The  submicron
                                primary emissions from the scrubbed
                                unit were only about 14  percent of
                                those from the unscrubbed unit.
                                  Sulfur dioxide to sulfate conversion
                                rates in the plumes were between 0
                                and 3.2 percent per hour. Aerosol
                                formation rates varied between 0 and
                                0.30 microns3/(ppb SO2 - hr - cm3).
                                More sulfate  was measured  than
                                could be accounted for by the aerosol
                                measurements.
                                  Ozone bulges of 40 ppb were typical
                                in the afternoon 50 kilometers down-
                                wind of the plant.
                                  Photochemical reactions were most
                                rapid when the plume was dilute and
                                the sunlight strong.
                                  Submicron primary emissions from
                                all units appeared to be mostly sulf uric
                                acid.
                                  This Project Summary was devel-
                                oped by EPA's Environmental Sci-
                                ences Research Laboratory, Research
                                Triangle Park, NC, to announce key
                                findings of the research project that is
                                fully documented in a separate report
                                of the same title (see Project Report
                                ordering information at back).


                                Introduction
                                  The production of primary and sec-
                                ondary pollutants has been studied
                                extensively in the plumes of unscrubbed
                                power plants, but little work has been
                                done to study the  effects of wet
                                scrubbers on downwind plume chemis-
                                try. The  environmental  laws coupled
                                with the cost of low sulfur coal are such
                                that the installation of SO2 wet scrubbers
                                are certain to become more common in
                                the future. Therefore, it is necessary to
                                obtain information on  any possible
                                adverse effects from using wet scrubbers
                                to control SOz emissions from utility
                                boilers.
                                  A number of studies have been
                                conducted to establish gas to particle
                                conversion rates in urban and in
                                conventional  power plant plumes.
                                These studies indicate conversion rates

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for SC>2 to sulfate aerosols of between 0
and 10 percent per hour.
  One of the principal pathways leading
to sulfate formation in the atmosphere
is the S02 + OH radical reaction. Since
the hydroxyl radical is formed  photo-
chemically, the conversion  rate  should
depend on the amount of solar radiation.
  SC>2 oxidation may also take place on
the surface of existing particles or in
water  droplets.  This liquid  phase
oxidation  may  play an important role
under high tiumidity conditions or in
moisture  laden power plant plumes.
Thus, the  S02  conversion rate may be
affected by the droplets produced by a
wet scrubber on a power plant.
  The  purpose of the study was to
investigate the S02 conversion  rate in
the plume and to determine if it differed
significantly from that  found  in  un-
scrubbed power plant plumes.

Experimental Approach
  The  Tennessee  Valley Authority
Widows Creek Steam  Station  near
Stevenson, Alabama,  was studied in
this  project. The  plant's six 135 MW
units (Units 1-6)  are connected  to a
single 1000 foot stack. Two additional
557  MW units have individual 500 foot
stacks and electrostatic precipitators of
90% efficiency. Unit 8 is equipped with a
combined  venturi  and limestone wet
scrubber having a design efficiency of
80% for  SOz  removal.  The effective
paniculate removal efficiency for Unit 8
is 99.5% by weight. Ammonia (about 10
ppm) is added to the Unit 7 flue gas to
increase  the  particulate collection
efficiency.  Units  1 -6  burn  1  percent
sulfur coal; Units 7 and 8 burn 4 percent
sulfur coal.
  The field study  involved sampling in
the power plant plume using a  Beech-
craft Queen Air fixed wing airplane to
carry the sampling equipment. The
sampling and monitoring equipment is
listed in Table 1.
  Three types of flight maneuvers were
used in the program: traverses,  spirals,
and  orbits. Traverses gave horizontal
distributions of measured parameters.
Spirals gave vertical distributions of the
important species. Orbits were per-
formed to obtain filter or impactor
samples at a specific location.
  To produce  plume  cross sectional
plots, the  data from the traverses were
plotted in cross  sections with the
endpoints of  each traverse fixing the
traverse  line. Contours  were  then
drawn. Since completing a traverse
Table 1.    Queen Air Instrumentation

 Parameter        Manufacturer/Model
                         Analysis Technique
 SOZ
 03
 Sulfate
 Light Scattering

 Condensation
  Nuclei
 Turbulence
 Temperature
 Elemental
  Analysis
 Dew Point
 Altitude
Meloy 285
Monitor Labs 8440
CSI
MRI Two-Mass

ERT RSP sampler
MRI 1550
MRI 1569
Environment One
Rich 100
MRI 1120
YSI/MRI
Lundgren 4-stage
Impactor
Cambridge Systems 137
Validyne
Flame Photometric
Chemiluminescence
Chemiluminescence
Flash vaporization/flame
photometric
Ion Chromatography
Integrating nephelometer

Light Attenuation

Pressure Fluctuations
Bead Thermistor
Analysis by PIXE

Cooled Mirror
Absolute Pressure Transducer
Airspeed
Position
Aerosol Charge
Acceptance
Data Logger
Stripchart
Recorder
Particulate
Sulfur
Aerosol Size
Distribution
Aerosol Size
Distribution
Aerosol Size
Distribution
Validyne
King KX1 70B/HTI DVOR
Washington U.

MR! Data System
Linear Instruments

Meloy 285

TSI 3030

Roy co 218

Knollenberg ASSP

Differential Pressure Transducer
Aircraft DME/VOR
Aerosol Charge Acceptance

9 -Track Tape - 6 hr. Capacity
Dual channel

Upstream SOz Scrubber/
Measurement of Total Sulfur
Charger/Mobility Analysis i

Optical Particle Counter

Axial Scattering Spectrometry

requires 15 to 60 minutes, these cross
sections give true plume concentrations
only for steady state situations.
  A total  of ten flights  were flown
during August 17-25, 1978. All data
collected are available in a Data Volume
and on magnetic tape. Several flights
provided studies of the scrubbed and
unscrubbed plumes. On August 17 and
23, Unit 7, the largest unscrubbed unit,
was not operating; flights on those days
gave data  on the scrubbed and mixed
plumes. On August 19, morning and
afternoon flights were made while all
units were operating.
  The weather varied little during the
study period. The days were clear and
the plume well mixed by 10 or 11 a.m.
each day. A moderate to strong inversion
formed each night and broke up by 9
a.m. the following morning. Winds were
moderate at plume elevation, typically
10-15km/hr.
                     Results and  Discussion

                        Photochemical aerosol formation  in
                     the plume was calculated in two ways:
                     (1) using sulfate concentration deter-
                     mined from filter samples and (2) using
                     aerosol  size distributions measured
                     with  the electrical aerosol  analyzer
                     (EAA) and the bag sampling system. The
                     sulfate results are discussed, then the
                     EAA, and finally a comparison is made
                     between the two techniques.

                     Sulfate Measurements
                        Three  methods were used  to deter-
                     mine sulfate concentrations. Sulfate in
                     the  Lundgren  impactor samples was
                     measured as total sulfur by  proton
                     induced X-Ray Emission.  The sulfur
                     values on the  impactor filter and last
                     stage were added together to give the
                     sulfur in particles less than one  micron
                     in size. Sulfate on the Two Mass filter^

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was measured by flash vaporization
followed by flame photometric analysis.
Sulfate on the Teflon™ coated glass
fiber filters was extracted with water
and measured by ion chromatography.
Of the three methods the 1C analysis
of the Teflon™ coated filters was judged
to be the most accurate because of its
simplicity and because the technique
was unlikely to introduce errors. Pair-
wise comparisons among the three data
sets showed good correlation (rz=0.74)
between the flash vaporization/FPD
and the 1C values. Other correlations
were not very good. In all data analysis
the FPD values were used since they
correlated well with the 1C results and
since many more FPD samples were
available than 1C ones.
Table 2 shows the sulfate formation
rates obtained using the FPD data.
The data set exhibits significant
'scatter, i.e., some excessively large
sulfate numbers and several negative
values, which are physically unrealistic.
As an entity, the data appear to be
reasonable and generally consistent
with results from other studies showing
0-10% hr"1 conversion rates of SO2 to
sulfate aerosol.

Aerosol Formation
Aerosol formation rates were calcu-
lated using the EAA size distribution
data. The data are shown inTable 3. The
plume excess aerosol volume has been
divided by the S02 concentration to
reduce the impact of plume dilution in
the comparison. Plume excess volumes.
Vpe were calculated using_the following
equation: Vp, = VE_- VB - S02(VVS02*)
where Vp and S02 are the average
aerosol volume and SOz concentration
in the plume at a given distance, VB is
the average aerosol concentration in
the background air, and V*/S~02* is the
ratio of primary source aerosol concen-
tration to S02 concentration obtained
from measurements close to the source.
Table 3 shows that aerosol formation
did not occur significantly near the
source or early in the morning even on
sunny days. Maximum rates were
observed near noon or in the early
afternoon.
The SOz conversion to aerosol was of
interest in these calculations. Using the
EAA data, the SOz conversion rate is the
normalized volume formation rate times
a constant, Cs, which depends on the
aerosol composition. The following
assumptions were made: (1 ) the sulf uric
acid formed by S02 oxidation was
Table 2.


Date
8/17



8/17




8/17
8/19







8/19


8/19



8/21




8/21

8/23


8/23

8/25




8/25

8/25




8/25
In Plume Sulfate


Sample Times
Morning
0853-0933
1024-1116
1129-1159
Afternoon
1551-1635
1732-1805
1821-1852

A verage
0853-1852
Early Morning
071 7-0736
0756-0826
0845-0944
0917-0932
0955-1007
1011-1026
1038-1053
Average
071 7-0826
0955-1053
Afternoon
1407-1424
1516-1529
1553-1618
Morning
0734-0844
0857-0925
0936-1031
0949-0959
A verage
0734-1031
Morning
0944-0950
1134-1231
1252-1259
Afternoon
1441-1531
1710-1719
1822-1828
Morning
0543-0645
0652-0736
0830-0845
O857-0912
A verage
0543-0912
Late Morning
1053-1108
1240-1255
1301-1316

Average
1240-1316
11 May be left over plume.
n. a. - not
applJcable
Formation Based on Filter Measurements

Distance
(km)

0.5
3
9

0.5
3.01
7.0

<9

0.5
9
24
25
45
47
75

<9
45-75

58
0.5
9-13

15-20
30
15
20

15-30

11-14
50
50
70
50
13

0.5
0.5
20
8



45
50
45

47.5
travel time

Sulfur Conversion Rates
(%/hr)
From Start From Previous Distance

n.a
n.a.


n.a.
n.a.


n.a.

n.a.
n.a.
0.6 0.4
0.4 <0
1.4 2.7
1.1 1.6
1.3 1.4


1.3±0. 1 1.9±0.4

2.1

6.82

0.2
.8
0.4


0.5±0.2



0.7


n.a.
n.a.





0.6
2.9
3.2

3.0±0.2
very uncertain. 2I Number unreliable.


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Table 3. Aerosol Growth Rate Calculations
Aerosol Growth
Excess
Plume
Distance Vol./
Date Time (km) S02
8/17 Morning
1024-1115 3 <0
1128-1158 9 <0

8/17 Late Afternoon
1732-1751 3 0.055*
8/19 Early Morning
O7 59 -08 25 9 <0
\J / *J& W ^tJ *^ ^»V
0847-0907 24 
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Table 4. Comparison
Sample
Time
8/17 Morning

8/17 Late Afternoon


8/19 Early Morning






8/19 Late Afternoon

8/21 Morning



8/23 Morning

8/23 Afternoon


8/25 Early Morning



8/25 Late Morning


of Sulfate and Aerosol Measurements
Sulfate As*
Aerosol Volume
Distance
(km)
0.5
3
9
0.5
3
7
0.5
9
24
25
45
47
75
9-13
58
15-20
15
20
30
11-14
50
13
50
70
0.5
0.5
8
20
45
45
50
Measured Aerosol*
Volume by EAA
3.8
3.1
5.4
0
2
30
0.58
2.3
4.6
3.3
16
9.1
8.8
58
4.3
4.1
0.9
<0
1.7
16
-0.2
1.1
24
6.7
0.58
8.4
<0
<0
3.9
0.50
1.2
3. The EAA data should be better
corrected for altitude and channel
cross sensitivity. This adjustment
might improve the estimates of the
aerosol formation rates. The in-
verted data may then be analyzed
to establish the relative contribu-
tions of gas and liquid phase
chemical reactions to aerosol
formation.



























  *Plume excess including primary emissions.
 indicated by ozone formation in  the
 plume, was observed about  50 km
 downwind on occasions when Unit 7
 was and was not operating. The ozone
 formation in the plume was more a
 factor of solar insolation  and plume
 mixing with background air than of the
 presence or absence of the scrubbed or
 unscrubbed plume.  The maximum
 aerosol formation  was measured for
 downwind (40 km  or  more) when the
 plume was well mixed and sunlight was
 strong. When expressed as pseudo first
 order sulfur conversion rates, average
 aerosol formation rates of  2.5 percent
 per hour were typical between 10 am
 and 5 pm. The aerosol concentrations
 predicted from the plume excess sulfate
 measurements were  usually about 3
 times higher than  the measured con-
 centrations; this large disagreement
rprooably has more  than one cause. No
useful nitrate formation data were
obtained because the amount of nitrate
collected  on the filters was near the
blank values. Observations  of N0«
removal from the plume indicate  an
afternoon removal rate of 25  percent
per hour, a value much higher than  for
S02.
  The results of the  study indicate
several linesof future research. Specific
recommendations include:

  1.  The  large difference between the
     sulfate and aerosol measurements
     should  be resolved, possibly  by
     comparing  bscat  measurements
     with the sulfate and aerosol data.
  2.  The near source aerosol formation
     rates  should be  investigated,
     possibly by computing changes in
     nuclei  mode particle concentra-
     tions.

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The EPA author H. M. Barnes (also the EPA Project Officer, see below) is with
  the Environmental Sciences Research Laboratory, Research Triangle Park, NC
  27711.
The complete report,  entitled "Characterization of Scrubbed and Unscrubbed
  Power Plant Plumes," was authored by G. R. Markowski, J. L Stith, and L.
  Richards of Meteorology Research. Inc., Santa Rosa, CA 95401  (Order No.
  PB 82-101 346; Cost: $8.00,  subject to change) will be available only from:
       National Technical Information Service
       5285 Port Royal Road
       Springfield. VA 22161
        Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
       Environmental Sciences Research Laboratory
       U.S. Environmental Protection Agency
       Research Triangle Park, NC 27711
                                                                         *U.S. GOVERNMENT PRINTING OFFICE:1981--559-092/3351

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