United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 2771 1
Research and Development
EPA-600/S3-83-093 Dec. 1983
Project Summary
Chemistry and Visual
Impact of the Plumes from the
Four Corners Power Plant and
San Manuel Copper Smelter
Judith 0. Zwicker, Edward S. Macias, Jerry A. Anderson,
D.L Blumenthat, and James R. Ouimette
This paper presents a study of the
conversion of SO2 to participate sulfur
in a western power plant plume and in a
western copper smelter plume, the
impact of these plumes on visibility, and
the relative contributions of primary
and secondary aerosols to this impact.
For plume ages greater than 3 h, the
rates of conversion in the power plant
and smelter plumes were similar (0.4 to
0.8% h"1) with the higher rate in the
smelter plume. For very young plumes,
the conversion rates differed substantial-
ly. The low conversion rate (0-0.1 % h~1)
in the very young plume of the power
plant appeared to be related to the
depletion of oxidant by nitrogen oxides.
The very high conversion rate (2-4% h'1)
in the smelter plume of less than 1 h
plume age was due in part to the
absence of nitrogen oxides in the
smelter plume. In the Four Corners
region, most of the paniculate sulfur
was in the form of ammonium sulfate
during the sampling period. The data
suggest that most but not all of the
particulate sulfur in the San Manuel
plume and background was in the form
of sulfate.
The major contribution to excess light
extinction due to the plumes at the Four
Corners power plant and the San
Manuel smelter was light scattering by
primary particles. This accounted for
about 90% of the excess extinction from
5 km to 10 km downwind and decreased
to about 70% at 25 km to 30 km
downwind. Light scattering by primary
sulfate particles was found to contribute
very little to the extinction in the Four
Corners power plant plume—2% of
extinction at 5 and 25 km from the
plant. In the San Manuel smelter plume,
light scattering by primary sulfate
particles contributed much more— 55%
of extinction at 10 km and 22% at 35
km from the smelter. Light scattering by
secondary sulfate particles made a
minor contribution to the plume excess
extinction at Four Corners (2 to 5%),
while at San Manuel it contributed ~7
to —34%. The larger contribution in the
smelter plume was due to higher
conversion rates and the lack of IMOa in
the plume. Light absorption due to NO2
did not contribute to the San Manuel
plume excess extinction but made a
modest contribution to the Four Corners
plume excess extinction, increasing
from 6% at 5 km to 18% at 25 km
downwind.
This Project Summary was developed
by EPA's Environmental Sciences
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
It is now generally recognized that haze
is present in all parts of the continental
United States, even in the relatively
pristine desert of the Southwest. The U.S.
Environmental Protection Agency under-
took Project VISTTA(Visibility Impairment
Due to Sulfur Transport and Transformation
in the Atmosphere) in order to study the
haze in the Southwest and to assess the
-------
contributions of various sources to
visibility reduction.
In this paper, we discuss the results of
the second VISTTA field program (Fall of
1978) in which the plumes from a
western coal-fired power plant and from
a copper smelter were studied to deter-
mine the important components of the
visibility reducing aerosol from these two
sources.
Five days were spent studying the
plume and background of the Four
Corners (NM) power plant located 30 km
SW of Farmington (NM). The plant has
five units and produces a maximum
output of 2100 MW. During the study
period, the plant output varied from 900
to 2100 MW. The SOa emissions during
the study period were estimated to range
from 182 to 384 tons/day. The San
Manuel (AZ) smelter plume was studied
on two days with the most useful data
coming from the flights on September 27,
1 978, at downwind distances of 10 to 90
km.
The measurements, made by aircraft-
based sampling of the plumes, were
carried out on 1 1 days as summarized in
Table 1 . The aircraft was equipped with
the instruments listed in Table 2.
Results
Sulfur conversion rate calculations
from the Four Corners data fell into a
pattern of low conversion rates of 0.1 to
0.2% h'1 from 0.2 to 1 h plume age rising
to a maximum of 0.4% h~1 from 3 to 5 h
plume age. Alternately, the limited San
Manuel smelter data indicated a maximum
sulfur conversion rate of 4% h"1 from 0.5
to 1 h plume age, which leveled off to
0.8% at 1 to 10 h plume age.
To understand the effect of UV radiation
on the conversion of S02 to particulate
sulfur, the sulfur-particle to sulfur-gas
ratio (Sp/Sa) values were plotted against
UV radiation (2950 to 3850 A) for the Four
Corners and San Manuel data. The Four
Corners data were separated into two
groups. The group with the higher slope
[0.09% (W h m"2)'1] was from the
September 16, 1978, measurements.
Two features in particular distinguish this
day from the others in the Four Corners
Plume Study: the plume was dispersed
early in the morning beyond 1 2 km from
the stack and the water vapor pressure
was the highest. The data from the other
days at Four Corners were much lower.
For the San Manuel smelter, Sp/Sg
ratios plotted against UV radiation pro-
duced slopes of 0. 1 3 to 0. 1 6% (W h m'2)'1.
which were slightly greater than those for
Table 1 . Sampling Schedule at Four Corners and San Manuel Plants
Date Flights
9/12/78 Los Angeles
to Farmington
9/14/78 Four Comers power
plant (NM) plume
9/15/78 Four Corners plume
9/16/78 Four Corners plume
9/18/78 Four Corners plume
9/20/78 Four Corners plume
9/2 1/78 Regional sampling near
Four Corners plant
Farmington (NM) to
Tucson (AZ/
9/23/78 San Manuel copper smelter
(AZJ plume
9/26/78 Regional Sampling
near smelters
9/27/78 San Manuel copper smelter
plume
9/28/78 Tucson to
Los Angeles
Table 2. Aircraft Instrumentation
Sampler
Manufacturer
Parameter and Model
A erosols
Integral Size
Light Scattering MR1 1569
Coefficient
Aerosol Charge Washington
Acceptance University
Condensation Environment
Nuclei One Rich 100
Aerosols
Differential Size Thermal Systems.
Inc. 3030°
Royco218"
Knollenberg ASSP
Aerosol Samples
Total Sulfur MRI TWOMASS
Sampler/ Glass
Fiber Filter
Sulfate and Bendix 240.
Nitrate Cyclone/Teflon
Impregnated Glass
Fiber Filters
"Automatic bag sampling system for TSI 3030
Flight Times
(MDT) Flight
Start Stop Hours
14:40 - 19:08 4.5
6:50-11:30 4.7
10:17-14:00 3.7
16:00 - 20:05 4. 1
7:49 - 1 1:35 3.8
6:31 -8:15 1.7
7:54-13:37 5.7
16:00-17:38 1.5
8:23 -12:15 3.9
14:38 - 17:40 3.0
9:12 - 13:25 4.2
1 1:43 - 20:33 8.8
9:29 - 16:43 7.2
15:53 - 20:43 4.8
Analysis Technique
Integrating
Nephelometer
Aerosol Charge
Acceptance
Light Attenuation
Aerosol Charger-
Mobility Analysis
Optical Particle
Counter with
Multichannel Analyzer
Axial Scattering
Spectrometer Probe
Flash Vaporization/
Flame Photometric
Detection
Ion Chromatography
Plume Samp/ing
Distances (km)
Regional
20,40
5,25
5
2, 12.34.55
20
20.40,65
0-5
Regional
Regional
10
Regional
10,35.90,Bkg
Regional
Particle
Size Range
(urn)
-0.1-1
-.01 -.1
~005-.fi
.0056-?
0.56-18
3-45
<3
<3
and Roy co 218;bagfill requires about 4. 5 seconds
-------
Table 2.
Parameter
(cont'd)
Sampler
Manufacturer
and Model
Analysis Technique
Particle
Size Range
(um)
Total Mass
Total Sulfur
Al-Pb
Gases
Sulfur Dioxide
Ozone
Nitrogen Oxides
Other
Dew Point
Temperature
Turbulence
Altitude
Indicated
Air Speed
Position
Visual Range
UV Radiation
Bendix 240
Cyclone/Teflon
Impregnated Glass
Fiber Filters
Low Pressure
Impactor/
Vaseline- Coated
Stainless Steel
Lundgren
Impactor/Greased
Mylar Stages Followed
by Nuclepore after
Filter
Meloy 285
Monitor Labs 8410
Monitor Labs 8440
Cambridge
Systems 137
MRI Airborne
Instrument Package
Aircraft
Navigation System
Optical Photography
Telephotometer
Eppley Radiometer
Gravimetric Weighing
Flash Vaporization/
Flame Photometric
Detection
Particle-Induced
X-Ray Emission
Some Samples Analyzed
by X-Ray Fluorescence
Flame Photometric
Chemiluminescence
Chemiluminescence
<3
0.05 -0.075
0.075 - 0.12
0.12-0.26
0.26 - 0.50
0.50 - 1.0
1.0 -2.0
2.0 - 4.0
<0.5
0.5 - 1.0
1.0-2.0
2.0 - 4.0
>4.0
Barrier-Layer
Photocell
the Four Corners data set of September
16. 1978. The higher slope for data
collected close to the smelter indicates
that some factor besides or in addition to
UV radiation, perhaps heterogenous con-
version on the primary particulate emis-
sions, is important to the conversion in
the young smelter plumes.
If the plume is oxidant limited, SO2 is
expected to compete with NO and NOz
for oxidant species, and the faster
reactions NOx will be favored. This
competition was evident in the Four
Corners plume when the SP/Sg ratio (an
indicator of SO2 conversion) was examined
against the NCVNOx ratio (an indicator
of NO oxidation). An increase in Sp/Sa
due to secondary particulate sulfur
formation appeared only at relatively high
NO2/NOx ratios (low NO concentrations).
In the San Manuel smelter plume, no
measureable NOX above background was
observed. This was also observed in
passes near smelters during regional
flights and is consistent with other
VISTTA measurements.
The concentrations of gaseous nitrogen
compounds and ozone for the various
plume and background orbits at the Four
Corners power plant are consistent with
the generally accepted photostationary
steady state model which leads to the
conservation of the sum of NO? plus Os.
This conservation relationship can be
tested with our data using the ratio
(ANOa+AOal/ANO*. The values of the
ratio near the plant ranged from 0.04 to
0.09. While fluctuations were probably
due to experimental uncertainties, negative
values may be related to HNO3 production.
The photostationary steady state reactions
are not the only reactions involving Os,
NO, NOa, but the invariance of the ratio
indicates that they are the most important.
The chemical composition of both the
power plant and smelter plume aerosol
showed obvious differences between the
two plumes at the same downwind
distances. These differences may be use-
ful in determining the contribution of
each type of source to the regional haze.
The power plant always had higher
concentrations of Al, Si, Ti, and V while
the smelter always had higher concentra-
tions of S, K, Cr, Cu, Sn, and Pb.
A trimodal mass size distribution of
particulate sulfur with an ultrafine
aerosol peak at 0.09 /um, a fine aerosol
peak at 0.9 jum and coarse aerosol peak at
9 /urn was seen in aerial plume measure-
ments close to the Four Corners power
plant (5 km) on the morning of September
15, 1978. The ultrafine mode was also
present in morning ground-based plume
measurements at 3 km and 25 km from
the stacks. The ultrafine mode was not
present in late afternoon aerial plume
measurements when temperatures were
10 to 20°C higher than the morning
measurements. This small particle mode
might be due to condensation of sulfuric
acid vapor into droplets.
The average percentage of coarse
particle sulfur (diameter >2 um) to total
gaseous sulfur in the plume at 5 km was
0.08% which can be used as an indication
of primary particulate sulfur from the
flyash. No significant particle sulfur
concentrations were observed on the
ground because of the low cutpoint of the
cyclone used.
The sulfur concentration associated
with particles of aerodynamic diameter
>1 /um was quite low in all background
measurements. The mass mean size of
particle sulfur in the background was
about 0.24 um. The Stokes mass mean
diameter was 0.10 to 0.15 /um.
In the Four Corners plume and in the
background, the sulfur appeared to be in
the form of ammonium sulfate. Ammonium
ion concentrations were determined only
for the ground site sampling. For the
samples in which ammonium, sulfate,
and nitrate ion concentrations were
determined, the average concentrations
were 14 nmol sulfate/m3, 34 nmol
ammonium/m3, and 2 nmol/m3 of
nitrate. These balance to within the
sampling errors, indicating that sulfur
was in the form of ammonium sulfate at
the ground site near the Four Corners
power plant. At the San Manuel copper
smelter, most of the sulfur appeared to be
in the form of water-soluble sulfate
except close to the plant where large
primary sulfur particles (>4 um) made a
significant contribution.
At 12 km downwind of the stack, the
visual range through the copper smelter
-------
plume was reduced from 105 km in the
background to 42 km with the plume
present (60% reduction). The visibility
reduction decreased farther downwind of
the plant. For example, at 90 km downwind,
the visual range was 92 km with the
plume present (13% visibility reduction
relative to the background). The impact of
the power plant is greatest when the
plume is well defined in early morning
and decreases at farther downwind
distances. The impact was greatest on
September 14, 1978, the only day when
all five units were in operation during the
VISTTA study. The reduction in visibility
(51%) was significantly greater at 20 km
downwind on the 14th when the load was
—2100 MW than the reduction in visibility
(35%) when the load was 1200 MW.
Conclusions
The major conclusions of the study are:
1. The conversion of S02 to particulate
sulfate in the Four Corners power
plant plume and in the San Manuel
copper smelter plume at ages
greater than 1 h is consistent with
homogeneous gas phase oxidation
by OH radical. Rates of 0.4% h"1 for
Four Corners on September 16,
1978 and 0.8% h"1 for San Manuel
on September 27, 1978 were
observed.
2. Conversion of S02 in the young (<1
h) smelter plume under daylight
conditions is possibly dominated by
heterogenous conversion on primary
particles. The high conversion rate
of —4% h"1 was seen only close to
the stacks where SOa and particulate
concentrations were high.
3. In the Four Corners power plant
plume, significant amounts of large
diameter particles (>2 /um) contain-
ing sulfur were measured at 4 and
25 km downwind. Sulfur associated
with fine particles (diameters
between 0.1 and 2fjm) was seen in
some plume samples. Very small
particle sulfur (<0.1 //m aerody-
namic diameter) was measured in
high concentrations when ambient
temperatures were below 18°C in
sampling from the ground and
from an airplane in the mixed layer.
Sulfur was not present in the very
small particle mode in samples
taken at higher ambient tempera-
tures.
4. In the background of the Four
Corners power plant plume, no
significant concentration of large
particle sulfur (diameter > 2 /urn)
was present either in ground-based
or aerial measurements. The aerody-
namic sulfur mass median diameter
from these background measurements
was 0.2 fjtrn.
5. The particulate composition in the
Four Corners power plant plume
was consistent with flyash analyses
from this plant. Sulfur was enriched
relative to iron at increasing down-
wind distances from the plant,
indicating particulate sulfur formation
in the plume.
6. The particulate composition in the
San Manuel copper smelter plume
was consistent with copper ore.
Again sulfur enrichment indicated
particulate sulfur formed from SOa
in the plume.
7. Light scattering by primary particles
was the major contribution to
excess light extinction due to the
plume at the Four Corners power
plant and at the San Manuel
smelter. This accounted for about
90% of the excess extinction from 5
km to 10 km downwind and decreased
to about 70% by 25 km to 30 km
downwind.
8. Light scattering by primary sulfate
particles was found to contribute
very little to the extinction in the
Four Corners power plant plume—
2% of extinction at 5 and 25 km
from the plant. In the San Manuel
smelter plume, light scattering by
primary sulfate particles contributed
much more—55% of extinction at
10 km and 22% at 35 km from the
smelter.
9. Light scattering by secondary
sulfate particles made a minor
contribution to the plume excess
extinction at Four Corners (2 to 5%),
while at San Manuel it contributed
~7 to —34%. The larger contribution
in the smelter plume was due to
higher conversion rates and the
lack of NC>2 in the plume.
10. Light absorption due to NOz did not
contribute to the San Manuel
plume excess extinction but made a
modest contribution to the Four
Corners plume excess extinction,
increasing from 6 to 18% from 5 km
to 25 km downwind.
Judith O. Zwicker and Edward S. Mad as are with Washington University. St. Louis,
MO 63120; Jerry A. Anderson and D. L Blumenthal are presently with Sonoma
Technology, Inc., Santa Rosa, CA; and James R. Ouimette is presently with
Chevron Research Company, Richmond, CA.
Will/am Wilson and William Conner are the EPA Project Officers (see below).
The complete report, entitled "Chemistry and Visual Impact of the Plumes from the
Four Corners Power Plant and San Manuel Copper Smelter," (Order No. PB
83-264 457; Cost $ 10.00, 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 Officers can be contacted at:
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
-------
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
BULK RATE
U.S. POSTAGE
PAID
Cincinnati, Ohic
Permit No. G35
Official Business
Penalty for Private Use $300
•e, U.S. GOVERNMENT PRINTING OFFICE: 1984-759-1
Q?Jt
------- |