EPA
United States
Environmental Protection
Agency
Office of Environmental Sciences Research
Research and Laboratory
Development Research Triangle Park, North Carolina 27711
EPA-600/7-77-021
March 1977
SULFATES IN THE ATMOSPHERE
A Progress Report on
Project MISTT
Interagency
Energy-Environment
Research and Development
Program Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S.
Environmental Protection Agency, have been grouped into seven series.
These seven broad categories were established to facilitate further
development and application of environmental technology. Elimination
of traditional grouping was consciously planned to foster technology
transfer and a maximum interface in related fields. The seven series
*
*
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
This report has been assigned to the INTERAGENCY ENERGY-ENVIRC
RESEARCH AND DEVELOPMENT series. Reports in this series result from
the effort funded under the 17-agency Federal Energy/Environment
Research and Development Program. These studies relate to EPA's
mission to protect the public health and welfare from adverse effects
of pollutants associated with energy systems. The goal of the Program
is to assure the rapid development of domestic energy supplies in an
environmentally—compatible manner by providing the necessary
environmental data and control technology. Investigations include
analyses of the transport of energy-related pollutants and their health
and ecological effects; assessments of, and development of, control
technologies for energy systems; and integrated assessments of a wide
range of energy-related environmental issues.
This document is available to the public through the National Technical
Information Service, Springfield, Virginia 22161.
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EPA-600/7-77-021
March 1977
SULFATES IN THE ATMOSPHERE
A Progress Report on Project MISTT
(Midwest Interstate Sulfur Transformation and Transport)
by
William E. Wilson
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
Robert J. Charlson
University of Washington
Seattle, Washington
Rudolf B. Husar
Washington University
St. Louis, Missouri
Kenneth T. Whitby
University of Minnesota
Minneapolis, Minnesota
Donald Blumenthal
Meteorology Research, Inc.
Altadena, California
ENVIRONMENTAL SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
-------
DISCLAIMER
This report has been reviewed by the Environmental Sciences Research
Laboratory, U.S. Environmental Protection Agency, and approved for publication.
Mention of trade names or commercial products does not constitute endorsement
of recommendation for use.
-------
ABSTRACT
The size and sulfate content of atmospheric aerosols and the rate and
mechanisms for sulfate formation from sulfur dioxide in power plant plumes
are reviewed. Emphasis is given to results from the recent USEPA study,
Project MISTT (Midwest Interstate Sulfur Transformation and Transport
rate of conversion of sulfur dioxide to sulfate aerosol in power plant
plumes is low near the point of emission, but increases to several percent
per hour as ambient air mixes with the plume. Tall stacks reduce ground-
level concentrations of sulfur dioxide, resulting in a reduction of the
amount removed by dry deposition. In urban plumes, which are well-mixed
to the ground near the source, sulfur dioxide is removed more rapidly by
dry deposition. Thus, tall stacks increase the atmospheric residence time
of sulfur dioxide, which leads to an increase in atmospheric sulfur forma-
tion. These sulfate aerosols may be transported over distances of several
hundred kilometers and produce air pollution episodes far from the pollution
source.
This report covers a period from June 1974 to June 1976 and work was
completed as of June 1976.
111
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CONTENTS
Abstract .............................
Figures ............................. v
Tables .............................. vi
Acknowledgments ......................... vii
1. Introduction ...................... 1
2. Transformation Mechanisms ............... 3
3. Size Distributions ................... 5
4. Chemical Forms of Sulfate ............... 7
5. Review of Plume Studies ................ 9
6. EPA Plume Studies ................... 10
Program plan ................... 10
Plume mapping program ............... 11
Power plant plume characteristics ......... 13
Urban plumes ................... 18
Sulfate budget .................. 22
Removal processes ................. 24
Effects of tall stacks .............. 24
7. Summary ........................ 26
References ............................ 27
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FIGURES
Number Page
1 Schematic of a trimodal atmospheric aerosol size distribution
showing the principal modes, main sources of mass for
each mode, and the principal processes involved in inserting
mass and removing mass from each mode 6
2 Profiles of Aitken Nuclei concentration (AN), light scattering
aerosol (bscat), sulfur dioxide (SCL) and ozone (CO .... 12
3 Schematic of experimental method for pollutant flow measure-
ment in large plumes .................... 12
4 Flight plan of the research aircraft through the plume
showing the four altitudes at which passes were made .... 15
5 Volume size distribution of aerosol measured within the
Labadie power plant plume and background air on August
14, 1974 .................... 15
6 Aerosol volume flows in the plume as a function of time and
distance traveled compared with light scattering and
Aitken Nuclei flows ... ..... 17
7 Percentage of sulfur concentration due to aerosol sulfur for
several estimated background concentrations of aerosol
sulfur 17
8 Ozone concentration and aerosol light-scattering coefficient
(b ) downwind of St. Louis on 18 July 1975 ........ 19
scat J
9 Flow rates and related data for St. Louis plume on
18 July 1975 ...... ........... 21
10 A profile of the St. Louis urban plume taken early in the
morning of July 30, 1975, after following the plume for
18 hours ...... 21
11 Sulfur budget in urban-industrial plumes 23
12 Sulfur budget in power plant plumes 23
VI
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TABLES
Number Page
1 Mechanisms by which Sulfur Dioxide is Converted to
Sulfates (10) 4
2 Known Atmospheric Sulfates 8
3 Aerosol Size Distribution Characteristics 16
4 Plume Aerosol Flow Rates and Calculated Sulfur Conversion,
14 August 1974a 16
VII
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ACKNOWLEDGMENTS
A large number of people, in addition to the authors, made important
contributions to EPA's studies of sulfate in the atmosphere. These include
the following: Environmental Protection Agency, Jack L. Durham and Thomas
G. Ellestad; University of Washington, Allan P- Waggoner and Norman C. Ahlquist;
Washington University, Noor V. Gillani, Steven B. Fuller and Janja D. Husar;
University of Minnesota, Bruce K. Cantrell; Meteorology Research, Inc., Warren
H. White and Jerry Anderson; Environmental Measurements, Inc., William M.
Vaughan; Environmental Quality Research, Inc., William P. Dannevik; and
Rockwell International, Air Monitoring Center, Al Jones.
The authors would also like to thank Stephen J. Gage, Deputy Assistant
Administrator, Office of Energy, Minerals, and Industry, for his continuing
interest in this program and for providing financial supporth through the
Interagency Energy/Environment R&D Program. We would also like to thank
Gregory D'Alessio, OEMI, for his administrative assistance.
VI11.
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SECTION 1
INTRODUCTION
Sulfate is a pollutant of note, having been linked in epidemiological
and laboratory studies with adverse effects on human health (1,2). Epidemio-
logical studies have, in fact, indicated that sulfate may be more toxic than
sulfur dioxide or total suspended particulates. Sulfates are also known to
be major contributors to reductions in visual range caused by atmospheric
aerosols (3). Studies of acid precipitation in Scandinavia (4) have impli-
cated sulfuric acid in a variety of adverse ecological effects.
The known adverse health effects of sulfur dioxide (S0~) led to the
control of this pollutant (5). Reduction in urban SO- emissions and concen-
trations effected by the mandatory use of low-sulfur fuels, however, were
not accompanied by a proportional decrease in urban sulfate (6).
The observed lack of a proportional decrease has four possible explana-
tions: (1) sulfates can be biogenic in origin, resulting from transformations
of hydrogen sulfide, methyl disulfide, and methyl mercaptans, which are
natural products; (2) measured sulfate values are not real but anomalous,
resulting from conversion of S0« to sulfates on filters used in sampling;
(3) observed sulfates are primary pollutants produced from the combustion of
high-vanadium oil or from combustion in small, inefficient furnaces; and
(4) observed sulfates may be explained by the transformation-transport theory.
Reductions in urban SO,., emissions have been accompanied by increases in
rural SO,., emissions from new power plants located outside cities. S09 from
these power plants may be transformed to sulfate in the atmosphere and trans-
ported over long distances to urban areas.
The fourth possibility, the transformation-transport theory, is
supported by Scandinavian (4) and U.S. studies (7) and could account for the
increased sulfate levels observed in rural areas and the static sulfate
-------
levels observed in urban areas in the U.S. (6). Early information on the
rate of conversion of SCL to sulfate in power plant plumes suggested that the
rate of conversion was too low to result in significant formation, and sub-
sequent transport, of sulfate (7). However, studies of the flux of sulfur
out of various areas, e.g., studies by Smith and Jeffrey (8) and of Waggoner
et al. (9), successfully showed that some of the sulfur transported from
source areas like the United Kingdom arrived in Scandinavia as sulfates.
The transformation-transport theory remains, then, a viable hypothesis
for the US and is the subject of this paper.
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SECTION 2
TRANSFORMATION MECHANISMS
Though they are not well understood, the mechanisms by which SO- is
oxidized to sulfates are important because they determine the rate of forma-
tion and, to some extent, the final form of sulfate. Atmospheric S0_ may
be oxidized to sulfur trioxide (SO.,) and converted to sulfuric acid aerosol,
or it may form sulfite ions that are then oxidized to sulfate. Subsequent
to the oxidation, sulfuric acid or sulfate may interact with other materials
to form other sulfate compounds. The most important sulfate formation
mechanisms identified to date are summarized in Table 1.
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TABLE 1. MECHANISMS BY WHICH SULFUR DIOXIDE IS CONVERTED TO SULFATES (10)
Mechanism
Overall reaction
Factors on which
sulfate formation
primarily depends
Direct photo-
oxidation.
Indirect photo-
oxidation.
3. Air oxidation in
liquid droplets.
4. Catalyzed oxidation
in liquid droplets.
5. Catalyzed oxidation
on dry surfaces.
SO,,
SO,.
H2S04
light, oxygen
water
smog, water, NOX
organic, oxidants,
hydroxyl radical (OH)
liquid water
SO,
Oxygen
->NH, + SO,
4 4
oxygen, liquid water
SO ^ SO,
2 heavy metal ions
oxygen, water
SO.
"carbon, particulate
Sulfur dioxide concen-
tration, sunlight
intensity.
Sulfur dioxide concen-
tration, organic oxidant
concentration, OH, NO .
Ammonia concentration.
Concentration of heavy
metal (Fe, V, Mn) ions.
Carbon-particle concen-
tration (surface area),
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SECTION 3
SIZE DISTRIBUTION
Studies (11) over the past 5 years of the size distribution of particles
in both sulfate aerosols and general atmospheric aerosols have led to impor-
tant changes in our understanding of the behavior of aerosols such as sulfates
in the ambient atmosphere. A schematic diagram of a typical atmospheric
aerosol size distribution is shown in Figure 1. The three principal modes
(particle-size ranges), the main sources of mass for each mode, and the
principal processes involved in inserting and removing mass from each mode
are shown. Particles in the Aitken nuclei mode, 0.005 to 0.05 ym diameter,
are formed by condensation of vapors produced either by high temperatures
or chemical processes. The accumulation mode, which includes particles from
0.05 to 2 ym in diameter, is formed by coagulation of particles in the nuclei
mode and by growth of particles in the nuclei mode through condensation of
vapors onto the particles. Coarse particles are formed by mechanical pro-
cesses such as grinding or rubbing—for example soil, street dust, and rubber
tire wear—and by evaporation of liquid droplets. Accumulation mode particles
do not continue to grow into coarse particles, however, because the more
abundant small particles have a higher gas-aerosol collision rate and dominate
the condensational growth process. Sulfates formed by the conversion of SO,.,
are found in the accumulation mode; MgSO, from sea salt, Na-SO, from paper
pulping, and CaSO, from gypsum are found in the "coarse particle mode."
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CHEMICAL CONVERSION
OF GASES TO LOW
VOLATILITY VAPORS
.1 12
PARTICLE DIAHETEP, MICROMETER
100
TRANSIENT NUCLEI OR
AITKE:: NUCLEI r_-vxcE~
ACCUMULATION
~ RANGE
!!ECHANICALLY CEMENTED
— AEROSOL RANGE —
Figure 1. Schematic of a trimodal atmospheric aerosol size distri-
bution showing the principal modes, main sources of mass for each mode,
and the principal processes involved in inserting mass and removing
mass from each mode.
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SECTION 4
CHEMICAL FORMS OF SULFATE
Several different sulfates are among the molecular forms naturally
produced as sulfur is cycled through the atmosphere. Table 2 is a list of
sulfate forms known to exist in air, along with some of their more outstanding
chemical characteristics. As the table shows, sulfate per se is not a single
molecular form, and several sulfates are known to be produced from the oxida-
tion of S0«. All seven compounds listed are sensed as "sulfate," but they
have radically different chemical properties dictated by their molecular
nature. They will also have different sizes, depending largely on their mode
of formation. Sulfates in the fine-particle size range are respirable and
also reduce visibility. Sulfates are also found in the coarse particle mode.
Sulfates are either produced and emitted into the air as such, or they
are formed in the atmosphere from gas-particle conversions. The first four
substances in Table 2 (H-SO, and its products of neutralization with NH_)
seem to be formed from S0? oxidation. The remainder of the sulfates are
emitted directly by industrial or by natural sources; that is, they are
primary rather than secondary pollutants. The chemical nature of these
substances varies from the strongly acid nature of H_SO, and NH.HSO, to
the relatively inert salts. Water solubility and hygroscopicity and/or
deliquescence vary from extremely high (H~SO,) to quite low (CaSO,).
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TABLE 2. KNOWN ATMOSPHERIC SULFATES
Formula Names
Sulfuric acid (oil of
H2SO vitrol)
NH.HSO. Acid ammonium sulfate
4 4
(NH, ) H(SO )? Triammonium acid disul-
fate (Letovicite)
Ammonium sulfate
(NH,)0SO, (Mascagnite)
Sodium sulfate
Ka,,SO (Glauber's salt)
Calcium sulfate
CaSO, (gypsum)
Magnesium sulfate
MgSO, (Epsom salts)
Sources
Atmospheric oxidation
of SO,,; direct from
manufacturing .
Oxidation of SO with
NH addition.
Oxidation of SO,, plus
NH3.
Oxidation of SO. plus
NH3 .
Paper pulping by
kraft process.
(1) Wind-tlown dust.
(2) Manufacture of
gypsum products.
(1) Sea spray.
(2) Paper pulping.
Notable chemical
proper t ies
Strong acid, very
hygroscopic (drying
agent at low RH) .
Strong acid,
hygroscopic .
Acidic, del iquenscent
(?) at -v65% RH.
Weak acid, water-
soluble, deliques-
cent at 80% RH.
Water-soluble,
deliquescent at 84%
RH; relatively inert.
Low solubility in
H,,0; relatively
inert
Very hugroscopic;
relatively inert
and non-toxic.
Probable Size
class by mass
particle
Diameter, Dp
0.1 - 1.0 urn
0.1 - 1.0 urn
0.1 - 1.0 urn
0.1 - 1.0 vim
D > 0.5 un
(uncontrolled
pulp mill)
D > 1 pm
F
Dp > 1 y3i
(sea spray)
Dp > 0.5 um
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SECTION 5
REVIEW OF PLUME STUDIES
Information on the rate of conversion of S09 to sulfate in power plant
plumes was needed to quantify the contributions of power plants to atmospheric
sulfates. A critical review of plume studies (7) revealed no reliable infor-
mation on conversion rates, and only two studies that provided information on
the amount of S0_ converted to sulfate. The early work of Gartrell et al.
(12) indicated little conversion of S0~ to sulfate except at relative humidi-
ties greater than 75 percent. However, at high relative humidity, conversion
of S0? to sulfate may occur either on the filter surface or within the aerosol
particles collected on the filter. Therefore, Gartrell's results cannot be
accepted unless verified by other techniques.
Investigators at the Brookhaven National Laboratory used two techniques
to study sulfate formation in power plant plumes (13,14): the sulfur isotope
technique and direct measurements of S0_ and sulfate. The isotope technique
is considered erroneous because of the presence of several competing reactions
having different isotope effects (7). The direct measurement of S0« and
sulfate is considered experimentally valid. The Brookhaven workers measured
conversion from 0 to 8.5 percent per hour in coal-fired power plant plumes
(13) and 0 to 26 percent per hour in oil-fired power plant plumes (14).
The Brookhaven work has previously been interpreted to indicate an average
conversion rate in coal-fired plumes of 1 percent per hour or less and a
substantially higher rate in oil-fired plumes. However, a careful analysis
of the data, after discarding the isotope results, indicates that no dif-
ference has been established between oil- and coal-fired plumes and that,
depending on conditions, conversion rates of substantially greater than 1
percent per hour are possible (7). The sampling techniques and flight patterns
used were such that an accurate measurement of the conversion rate could not
be obtained (7).
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SECTION 6
EPA PLUME STUDIES
PROGRAM PLAN
In order to obtain a better understanding of the physical and chemical
processes occurring in power plant plumes, a new series of field studies
were undertaken. During July, August and February of 1975, extensive studies
involving three-dimensional mapping of large plumes were carried out in the
St. Louis area as part of the Midwest Interstate Sulfur Transport and Trans-
formation Study (MISTT). Preliminary studies were conducted during July and
August of 1973 and 1974.
These plume studies differed from earlier ones in that: (1) more gas
and aerosol parameters were measured; (2) horizontal and vertical profiles
were measured; (3) data were interpreted in terms of mass flows instead of
ratios; (4) the background air mixing with the plume was characterized; (5)
the chemical composition and size distribution of the aerosols in the plume
were determined; and (6) measurements were made in approximately the same
air mass as it moved downwind.
In previous studies, the fractional conversion of S0_ to sulfate was
calculated from the ratio of S02 to sulfate collected as integrated filter
samples while circling in random portions of the plume at various downwind
distances. This technique can overestimate conversion if any S0? is removed
by dry deposition to ground surfaces. For this reason and because of the
need to collect large amounts of S0?, samples were usually collected in
cohesive plumes which had undergone minimal dilution with background air.
This technique can also lead to errors if conversion varies in different
parts of the plume or if conversion is influenced by the extent to which the
plume has been diluted by background air. That this can indeed be the case
is demonstrated in Figure 2, in which the nuclei formation rate is seen to
10
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be much greater at the edges of the plume than in the center. Although such
a dramatic difference was not often observed, current interpretation of
sulfate formation mechanisms suggests that the conversion rate will be
higher in those portions of the plume, such as the edges, in which dilution
has led to conversion of plume NO to NO- by background 0» (15). To overcome
these problems the EPA plume mapping studies were designed to measure S0~
and sulfate mass flow rates at increasing distances from the source in both
cohesive and well-mixed plumes. From the change in flow rate with distance,
it is possible to calculate transformation and removal rates for individual
pollutants (16,17).
In the EPA study, the SO- mass flow rates were determined by a continuous
SO- monitor. A two-dimensional plot of S0~ concentrations in a plane perpen-
dicular to the plume axis was constructed from the horizontal and vertical
profiles. The mass flow of SO- was calculated from the SO- concentration and
the wind speed and direction. Since no continuous monitor for sulfate was
available, the continuous light-scattering (b ) measurement was used as an
SC3.U
indication of the sulfate concentration distribution. Sulfate, collected in
filter samples during each pass through the plume, was analyzed by the flash
vaporization-flame photometric detection method—a new, highly sensitive
technique modified for aircraft use (18,19). The sulfate flow was calculated
from the b /sulfate concentration ratio, integrated over a pass, and the
scat
b flow. Similarly, b -to-aerosol volume ratios were used to calculate
scat scat
an aerosol volume flow.
PLUME MAPPING PROGRAM
Two instrumented aircraft, an instrumented van, and three mobile single-
theodolite pilot-balloon units were used in a coordinated measurement program
(Figure 3). The primary sampling platform was a single-engine aircraft (20)
equipped for continuous monitoring of the gaseous pollutants (0_, NO, NO ,
-3 X
S07); three aerosol parameters (condensation-nuclei count, light-scattering
coefficient, and aerosol charge); several meteorological variables (tempera-
ture, relative humidity, dew point, and turbulent dissipation); and naviga-
tional parameters. Particulate sulfur samples were gathered by a sequential
filter tape sampler equipped with a respirable-particle size separator. An
11
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.08
K06
E
CL
CL
.04 oT
a
o
.02
O L0
5 Km
10 Km
Figure 2. Profiles of Aitken Nuclei concentration (AN), light
scattering aerosol (b ), sulfur dioxide (SO,.) and ozone (()„).
scat 2. j
PRIMARY
AIRCRAFT
SCOUT
"• L'fig '.
SOURCT
Q(x)=//c(x,y,zjU(zJdydz
plume
Figure 3. Schematic experimental method for pollutant flow
measurement in large plumes.
12
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array of four cascade impactors collected size-differentiated aerosol samples
for later chemical and microscopic analyses. An optical counter and an
electrical-mobility analyzer provided details of the in situ particle-size
distribution of grab samples.
An instrumented "scout" aircraft located the plume, laid out the sampling
path of the primary aircraft, and directed the three mobile pilot-balloon
(pibal) units to their respective positions in the center and at the edges
of the plume. Coordinated with the aircraft sampling, a van equipped with a
correlation spectrometer (COSPEC) made lateral traverses under the plume and
measured the integrated overhead burden of SCL and NCL (21). Data collected
aboard the two aircraft and in the van were recorded automatically at 1- to
10-second intervals on magnetic tapes for subsequent computer processing.
The operations headquarters coordinated the mobile units by radio communication.
The flight pattern of the primary aircraft was designed to enable charac-
terization of the plume at discrete distances downwind from the source. At
each distance, horizontal traverses were made in the plume perpendicular to
the plume axis at three or more elevations. These were supplemented by
vertical spirals within and outside the plume. The continuous instruments
monitored the distribution of pollutants along each pass, and the sequential
filter samples, analyzed later by a sensitive flash-vaporization, flame-
photometric technique (17), yielded the average particulate sulfur concentra-
tion for each pass. From the three-dimensional pollutant concentration field
obtained in this manner, together with the vertical profiles of wind velocity
measured every half-hour by the three pibal units, the horizontal flow rates
of pollutants at each downwind distance were directly calculated. Under
well-defined wind conditions (unidirectional, steady wind field), the
reproducibility of the pollutant flow measurement was ± 20 percent.
POWER PLANT PLUME CHARACTERISTICS
Aerosol Volume (22)
An electrical aerosol analyzer and an optical particle counter were used
to measure, in each of a number of size ranges, the number of particles per
o
cm of air. By assuming spherical particles, the volume of aerosol material
33 33
in ym per cm of air may be calculated (volume concentration, ym /cm ). Thus
13
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from size distribution measurements made during horizontal passes and from
upwind spirals, as shown in Figure 4, and at the distances given in Tables 3
and 4, it was possible to calculate aerosol volume flows. Wind velocities
at each distance were measured with pilot balloons.
Size distributions were also measured, usually near the plume center, as
shown in Figure 4. In contrast to the bi- or tri-modal distributions found
at ground level (Figure 2), the size distributions at plume height (Figure
5) were unimodal, nuclei apparently having been removed by coagulation and
coarse particles by sedimentation. Therefore, these distributions were
characterized by fitting them with a single log-normal distribution. The
resulting geometric mean diameters and geometric standard deviations are
tabulated in Table 3. These show that, although the mean size increased
from 0.24 ym at 10 km to 0.29 ym at 45 km, particle sizes in the plume are
not significantly different from the average found in the upwind, background
spiral.
The flow rates, Q(x), of light-scattering aerosols (b ) and Aitken
scat
nuclei (AN) were obtained for each plume cross section from the double
integral of the concentration (x,y,z), and wind velocity, U(z) (17). Since
the aerosol volume concentrations calculated from the size distributions
could only be determined at discrete points in the plume, the aerosol volume
integrals were estimated using the ratios of aerosol volume to b deter-
scat
mined at discrete points. The assumption that the aerosol volume integral
is proportional to b implies that the aerosol size distribution is
S Celt
constant along a traverse. This is thought to be an acceptable assumption
because of the consistency of the size distribution along the plume as shown
in Figure 4 and Table 3. Wind velocities at each distance were calculated
from pilot balloon observations. The flow rate for each aerosol parameter
is the sum of that due to the background plus that contributed by the plume.
The background was measured on both sides of the plume in order to separate
the two flow rates.
Plume-associated flow rates for b , AN, and aerosol volume measured
SC3.L
in the Labadie power plant plume on 4 and 14 August 1974 are shown in Figure
6. The volume flows are also given in Table 3. From Figure 6 it is seen
14
-------
UPWIND SPIRAL
Aerosol Sample Position
Plume Traverse Cross Section
Portion of Plume Cross Section
Not Sampled
PLUME TRAVERSE
STATIONS
DOWNWIND SPIRAL
THROUGH PLUME
Power
Plant
Figure 4. Flight plan of the research aircraft through the
plume showing the four altitudes at which passes were made,
the upwind and in-plume spirals, and the points at which
aerosol size distributions were measured. Only two traverses
out of four are shown.
Background Spiral
10 Km Traverse
a Average 21 632
Km Traverse
Figure 5. Volume size distribution of aerosol measured
within the Labadie power plant plume and background air
on August 14, 1974.
15
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TABLE 3. AEROSOL SIZE DISTRIBUTION CHARACTERISTICS
Geometric
Geometric mean standard
Date
8-5
8-5
8-5
8-5
8-14
8-14
8-14
8-14
Location
Background (upwind)
spiral
2-km traverse
4-km traverse
18-km traverse
Background spiral
(upwind)
10-km traverse
Avg. 21 and 3 2 -km
traverse
45-km traverse
diameter, urn
0.20 + .04
0.20 + .01
0.22 + .006
0.21 + -001
0.30 + .04
0.24 + .05
0.28 + .04
0.29 + .06
TABLE 4. PLUME AEROSOL FLOW
SULFUR CONVERSION,
Distance
km
0
10
21
32
45
, Time flow
hr
0
0.70
1.49
2.29
3.17
Aerosol volume
above background,
cm /sec
185
388
640
1378
deviat ion
2.09 ± .13
1.95 ± .04
1.93 ± .06
1.90 + .06
2.19 + .2
2.14 + .14
2.31 + .12
2.20 + .19
RATES AND CALCULATED
14 AUGUST 1974a
S°2 b
converted ,
%
1.1
2.3
3.7
8.0
Avg. vol . ,
um3/cm
19.3 ± 5.2
22.1 + 1.6
36.5 + 4.2
42.3 + 7.6
17.9 + 4.6
35.8 + 9.3
38.7 + 9.0
47.0 + 16.7
so2
conversion
rate, %/hr
1.5
1.8
4.9
Assuming the aerosol is 1LSO, in equilibrium with water vapor.
Based on the average SO,, flow of 4.08 kg/sec and a relative humidity of 75%.
16
-------
1800-
1600
1400
. 1200
o
o
en
^ IOOO
6
o
i 800
>
u_
600
4OO
200
o>
'g
x
F, Aersol Volume Flow, Labadie !4-Aug.-74
Fv Aersol Volume Flow, Labadie 5-Aug.'74
F»,| Aitken Nuclei Flow, Labadie !4-Aug.-74
//
bSCQ( Integral over plume cross section, Labadie l4-Aug.-74/y I —
// /\
*-*••"
t(Hr.)
0 10 20 30 40
d(Km)
Figure 6. Aerosol volume flows in the plume as a function of time
and distance traveled compared with light scattering and Aitken
Nuclei flows. Excess aerosol flow due to the plume has increased
seven times from 10 to 45 km. Note also the four fold increase in
the rate of aerosol formation after 2 hours.
20
1 15
10
cc
=3
O
CC
LABADIE PLUME
AUGUST 14,1974
BACKGROUND
2 jug/m3
10
20 30
DISTANCE FROM SOURCE, km
40
50
Figure 7. Percentage of sulfur concentration due to aerosol
sulfur for several estimated background concentrations of
aerosol sulfur.
17
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that on 14 August the growth was two-stage, the growth rate increasing by a
factor of 4 after about 2 hours, at a distance of about 30 km.
One of the chief objectives of this study was to determine the rate at
which S0? is converted to sulfate in plumes. It was assumed that the excess
aerosol formed in the plume was sulfuric acid in equilibrium with water
vapor at the ambient humidity. The fraction converted and the rate of con-
version was determined from the ratio of the calculated sulfur in the aerosol
to the total sulfur flow calculated from the S02 measurements and the
estimated sulfuric acid. These results, presented in the last two columns
of Table 4, show that at 45 km 8 percent of the S02 was converted to aerosol
and that the conversion rate varies from 1.5 percent/hr at 10 km to 4.9
percent/hr at 45 km.
Sulfate Measurements
During these experiments, the concentration of soluble sulfate was
also measured with a filter apparatus. These filter samples were integrated
from one plume edge to the other during the four passes at each distance.
The actual conversion rate determined by the sulfate flow rate method will
depend on the sulfate background. Figure 7 shows the pattern for several
background concentrations. Adequate background sulfate concentrations were
not obtained during this experiment. The drop in percent converted between
10 and 21 km may be due to fall out of large particles which escaped the
electrostatic precipitator or it may be due to measurement errors. Measure-
ments of SCL in the plume are most difficult nearest the stack because of
the high concentration gradients and plume inhomogeniety.
URBAN PLUMES
Similar techniques were used to map the three-dimensional flow of aerosols
and trace gases in the air leaving the St. Louis area. It was found that
under certain summer, daytime meteorological conditions the aggregate pollu-
tant emissions from metropolitan St. Louis often formed a cohesive, well-
defined "urban plume" downwind of the city (16,17,23,24). Such a plume can
be identified in Figure 8, which shows ozone concentrations and light-
scattering coefficients measured within the mixing layer northeast of St.
Louis on 18 July 1975 (24).
18
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SCALE, kilometers
i—ZOO
T-150
SPRINGFIELD
•MOO
•-,../-^ x -
4 V
ILLINOIS
T-50
WINDS
J-o
A POWER PLANT
• REFINERY
OZONE
- ~ bSCAT
Figure 8. Ozone concentration and aerosol light-scattering coefficient
(bscat) downwind of St. Louis on 18 July 1975. Data is taken from
horizontal traverses by instrumented aircraft at altitudes between 460
and 760 m msl. Sampling paths are along graph baselines; note that
baseline concentrations are not zero (24).
19
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On that day, the St. Louis plume incorporated the emissions of major
coal-fired power plants at Labadie (Mo.) and Portage des Sioux (Mo.) and
of a refinery complex near Wood River (111.), in addition to emissions from
industries and automotive traffic of the St. Louis-East St. Louis urban area
itself. The concentrated individual plumes immediately downwind of large
combustion sources can be identified in Figure 8 by their ozone "deficits ;
the depressed concentrations of 0» in these plumes reflect the high concen-
tration of NO in effluents.
The width of the plume, approximately 40 km, did not change much along
its 150-km-length. Apparently, horizontal diffusion at the boundaries of
the urban plume was by means of a rather slow dilution mechanism. It appears
likely that the elevated ozone concentrations in this plume and the reduced
visibility caused by the plume were exported well beyond Decatur (111.).
Unlike the primary pollutants NO and S0?, ozone and light-scattering
aerosols attained their maximum concentrations well downwind of St. Louis on
18 July 1975. The ozone and most of the aerosol were not emitted but were
products of chemical and physical transformations in the atmosphere; their
secondary origin is evident in Figure 9, which shows flow rates of ozone and
aerosol in the St. Louis plume increasing with distance from the city. The
flow rates in Figure 9 represent only the contribution of the St. Louis
plume, and are calculated from the measured winds within the plume and from
the difference between pollutant concentrations inside and outside the plume.
Based on a number of experiments in 1974 and 1975, the following features
of the urban plume were observed to be typical: 1. The St. Louis plume
significantly degraded the air quality of communities as far as 150 km from
the city. 2. The most conspicuous components of the St. Louis plume 50 km
or more downwind of the city were the reaction products formed along the way.
3. Most of the aerosol responsible for the high b and resulting decrease
scat °
in visibility within the St. Louis urban plume was formed in the atmosphere.
The sulfate concentrations in the 18 July 1975 urban plume attained a
maximum of 20 yg/m . This is not an extremely high value. On 29-30 July 1975
the urban plume was followed for 18 hours and measurements were made both
in the evening and the following morning. During this experiment sulfate con-
20
-------
- 250 2500
200 g 2000
_c :
s. <
Hi 50 ,„ 1500 ]
100 , , 1000
1 50
o
M
O
500
Figure 9. Flow rates and related data for St. Louis plume on 18 July
1975. Values are plotted against distance downwind of the St. Louis
Gateway Arch, with equivalent travel times for a constant mean wind
speed of 45 km/hr shown for comparison. The mass flow rate of ozone
and the flow rate of the aerosol light-scattering coefficient (bscat)
are shown.
Pf*
125
ST. LOUS URBAN PLUME
JULY 28 8 29, 1975
DISTANCE, miles
Figure 10. A profile of the St. Louis urban plume taken early in
the morning of July 30, 1975, after following the plume for 18
hours. Profiles are shown for ozone (» ) , sulfur dioxide ( --- ),
(•""")> an^ aerosol sulfate.
21
-------
o
centrations of 60 yg/m were measured, as shown in Figure 10. This set of
measurements demonstrates that at least under some conditions sulfate formation
can exceed removal and dilution and can lead to the accumulation of very
high sulfate concentrations.
SULFATE BUDGET
By examining the total flow of sulfur—both SC>2 and sulfate—we can
draw some interesting conclusions regarding the transformation and removal
of S0? in the two classes of plumes, that is, power plant plumes and urban
plumes (17).
The experimental results representing pollutant flow data for gaseous
and particulate sulfur are shown in Figures 11 and 12. Pollutant flow
measurements in urban plumes are shown in Figure 11. Data are reported here
only for those days in which the wind direction was such that the plumes of
the rural power plants (tall stacks, > 700 ft.) were well separated from the
urban plume which contained emissions from low stacks (< 350 ft.) and near
ground level sources. In such plumes, the total sulfur flow rate (gaseous
plus particulate) has been found to decrease with distance. The pollutant
flow rate, as determined from both the aircraft-measured concentrations and
correlation spectrometer data, shows a decay in excess of the estimated
experimental uncertainty of the methods (± 20 percent).
Sulfur depletion in the urban plumes appears to be equivalent to an
exponential rate of decay with a characteristic (1/e) decay time of 3 to 4
hours. Our results show, therefore, that in such plumes only about one-
third of the original emissions are transported beyond a radius of 100 km
and that formation of new sulfate aerosol is undetectable up to a distance
of 50 km. There is evidence that during the daytime the formation of aerosol,
including sulfate in an urban plume, begins after an aging time of 1 or 2
hours.
In power plant plumes (Figure 12), total sulfur flow measurements
showed no loss of sulfur within the limits of experimental uncertainty. The
aerosol fraction of total sulfur flow on 14 August 1974 was 6 percent at 10
km and 13 percent at 40 km from the source. As seen in Figure 10 and 11,
most of the particulate sulfur formation occurred between 30 and 50 km from
22
-------
o
o>
O
LU
h-
CO
CO
7.5
5.0
4.0 -
3.0-
2.5 -
2.0
1.5
CO
1.0
T I I I I I I I I
URBAN a INDUSTRIAL PLUMES
-AEROSOL
20%/HOUR LOSS RATE
-s AT IMS m/sec
10 20 30 40 50 60 70 80 90 100 110 120
DOWNWIND DISTANCE, X (km)
Figure 11. Sulfur budget in urban-industrial plumes. The shaded area
represents the particulate sulfur contributions, the solid lines are
gaseous sulfur.
-, 4-0
o
0)
^ 3.0
. 2.0
UJ
I-
o: i.5
o
u.
CO 1.0
CO
2
cc.
U-
D
CO
0.5
I I I I I I I
POWER PLANT PLUMES
I
I
I
I
10 20 30 40 50 60 70 80 90 100 110 120
DOWNWIND DISTANCE, X (km)
Figure 12. Sulfur budget in power plant plumes. D 8.14.1974; A 8.5.1974;
o 7.29.1975 (COSPEC). Note the increase of particulate sulfur between
30 and 50 km on 8.14.1974.
23
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the source. The SO flow data for 30 July 1975 were obtained by the correla-
tion spectrometer, unaugmented by particulate sulfur measurements. These
power plant plume measurements, all performed during daytime conditions,
demonstrate that there is little removal of the sulfur emitted from tall
stacks within a region of 50 to 100 km from the plant. During these measure-
ments, dry deposition was minimal either because the plumes had not touched
the ground or because they were very dilute at ground level.
REMOVAL PROCESSES
It is important to understand that most sulfate aerosol is secondary,
i.e., formed by gas-to-particle conversion in the atmosphere after emission,
and occurs in the accumulation mode. Particles in this size range have very
long lifetimes. Some confusion has existed regarding the relative removal
rates for SO and sulfate aerosol by deposition. The deposition velocity of
aerosols depends on the particle size and reaches a minimum in the accumula-
tion size range of 0.1 to 1.0 ym. The deposition velocity of gaseous S0_
depends on the chemical reactivity of the surface. Both deposition velocities
depend on the friction velocity and the surface roughness. However, since
the diffusion of accumulation mode aerosols through the surface boundard
layer (0.001 to 1 cm) is much slower than the diffusion and surface reaction
of an SO,., molecule, the deposition velocity of sulfate aerosol is always
significantly smaller than for gaseous S09 (25,26,27). Consequently, though
SO,, is removed fairly rapidly by dry deposition on soil, vegetation, and
other surfaces, the removal processes become slower once the S0? has been
converted to sulfate. Therefore, sulfates can travel long distances before
their removal by fallout, rainout, or deposition.
EFFECTS OF TALL STACKS
These aspects of reaction mechanisms, aerosol size, and deposition rates
are critical to an understanding of the possible effects of tall stacks. When
S02 is emitted near the ground, as from home heating units, the SO- can be
removed by surface removal mechanisms (dry deposition). When S0? is emitted
higher in the air, as from the tall stacks of fossil-fuel-fired electric
power plants, the SO- is diluted before it reaches the ground, and the surface
removal rates are reduced. Emissions may, in fact, be trapped above an
24
-------
inversion layer and remain trapped for hours. Thus, elevated stacks theo-
retically permit a longer residence time in the ambient atmosphere for S0~
and promote fine particulate sulfate formation by the mechanisms discussed
previously. On the other hand, they provide for increased dilution of the
sulfate and SCL and thus reduce the impact of emissions in the vicinity of
the source.
25
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SECTION 7
SUMMARY
Earlier work had shown that the rate of conversion of S0» to sulfate in
power plant plumes was slow except at very high relative humidity. In the
recent EPA program, consistent conversion of several percent per hour at
normal levels of relative humidity has been measured. The conversion of SCL
to sulfate aerosol in power plant plumes is slow in the early part of the
plume; that is, close to the point of emission. As ambient air mixes with
the plume, the rate of conversion increases. Thus tall stacks reduce
ground-level concentrations of SCL but increase sulfate aerosol formation by
reducing surface losses of SCL and by increasing the atmospheric residence
time, which results in increased SCL-to-sulfate conversion. In urban plumes,
which are well-mixed to the ground, S0~ may be removed by reaction with
plants and by deposition. The SCL dry deposition rates vary with vegetation,
with the nature of the surface, and with time of year.
Urban plumes have been sampled out to 250 km from their sources and
power plant plumes out to 60 km. Sampling at these distances revealed that
sulfate, generated from SO- in power plant and urban plumes, and ozone,
generated from hydrocarbons and nitrogen oxides in urban plumes, may be
transported at least hundreds of km and may cause air pollution episodes
and other problems far from the source of pollution. These air pollution
problems cannot be controlled by the government entity where the air
pollution impact actually occurs.
26
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REFERENCES
1. Amdur, M.O., T.R. Lewis, M.P- Fitzhand and K.I. Campbell. Toxicology
of Atmospheric Sulfur Dioxide Decay Products. Publication No. AP-111,
U.S. Environmental Protection Agency, Research Triangle Park, NC 1972.
47 pp.
2. Health Consequences of Sulfur Oxides: A Report from CHESS 1970-1971.
EPA-650/1-74-004, U.S. Environmental Protection Agency, Research Triangle
Park, NC, 1974. 428 pp.
3. Waggoner, A.P., A.H. Vanderpol, R.J. Charlson, L. Granat, C. Tragard
and S. Laisen. Sulfates as a Cause of Tropospheric Haze. Report AC-33,
Dept. of Meteorology, University of Stockholm, Sweden. UDC 551.510
4:535.33, 1975.
4. Air Pollution Across National Boundaries. The Impact on the Environment
of Sulfur in Air and Precipitation. Sweden's Case Study for the United
Nations Conference on the Human Environment. Bert Bolin, ed. Kungl.
Boktryckeriert P.A. Nortsedt & Soner 710396. Stockholm, Sweden, 1971.
5. Air Quality Criteria for Sulfur Oxides. Publication No. AP-50, U.S.
Department of Health, Education, and Welfare, Public Health Service,
Washington, B.C., 1969.
6. Position Paper on Regulation of Atmospheric Sulfates. EPA-450/2-75-007,
U.S. Environmental Protection Agency, Research Triangle Park, NC, 1975.
108 pp.
7. Wilson, W.E. Sulfate Formation in Power Plant Plumes: A Critical Review.
Project MISTT Report #2. Submitted for publication.
8. Smith, F.B. and G.H. Jeffrey. Airborne Transport of Sulfur Dioxide from
the U.K. Atmospheric Environment, 9:643-659, 1975.
9. Waggoner, A.P., A.H. Vanderpol, R.J. Charlson, L. Granat, C. Tragard and
S. Laisen. The Sulfate Light Scattering Ratio: An Index of the Role of
Sulfur in Tropospheric Optics. Report AC-33, Dept. of Meteorology,
Stockholm University, Sweden. Accepted, Nature.
10. Scientific and Technical Assessment Report on Suspended Sulfates and
Sulfuric Acid Aerosols. J.R. Smith, ed. Office of Research and Develop-
ment, U.S. Environmental Protection Agency, Washington, D.C.
27
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11. Whitby, K.T. Modeling of Atmospheric Aerosol Size Distribution.
Progress Report, EPA Research Grant No. R800971, April 1975.
12. Gartrell, F.E., F.W. Thomas and S.B. Carpenter. Atmospheric Oxidation
of SO in Coal-Burning Power Plant Plumes. Am. Ind. Hyg. J., 24:113-120,
1963.
13. Newman, L. , J. Forrest and B. Manowitz. The Application of An Isotopic
Ratio Technique to the Study of the Atmospheric Oxidation of Sulfur
Dioxide in the Plume From a Oil Fired Power Plant. Atmos. Environ.,
9:954, 1975.
14. Newman, L., J. Forrest and B. Manowitz. The Application of An Isotopic
Ratio Technique to the Study of the Atmospheric Oxidation of Sulfur
Dioxide in the Plume From a Coal Fired Power Plant. Atmos. Environ.,
9:969, 1975.
15. Wilson, W.E., R.B. Husar, K.T. Whitby, D.B. Kittleson and W.H. White.
Chemical Reactions in Power Plant Plumes. In: Proceedings of the 171st
National ACS Meeting, Div. of Environ. Chem., New York, N.Y., April 1976.
16. Husar, R.B., B.L. Blumenthal, J. Anderson and W.E. Wilson. The Urban
Plume of St. Louis. In: Proceedings of the 167th National ACS Meeting,
Div. of Environ. Chem., Los Angeles, CA, April 1974.
17. Husar, R.B., J.D. Husar, N.V. Gillani, S.B. Fuller, W.H. White, J.A.
Anderson, W.M. Vaughan and W.E. Wilson. Pollutant Flow Rate Measurement
in Large Plumes: Sulfur Budget in Power Plant and Area Source Plumes
in the St. Louis Region. In: Proceedings of the 171st National ACS
Meeting, Div. of Environ. Chem., New York, N.Y., April 1976.
18. Husar, J.D., R.B. Husar and P.K. Stubits. Determination of Submicrogram
Amounts of Atmospheric Particulate Sulfur. Anal. Chem., 47:2062, 1975.
19. Husar, J.D., R.B. Husar, E.S. Macias, W.E. Wilson, J.L. Durham, W.K.
Shepherd and J.A. Anderson. Particulate Sulfur Analysis: Application
to High Time Resolution Aircraft Sampling in Plumes. Atmos. Environ.,
in press.
20. White, W.H., J.A. Anderson, W.R. Knuth, D.L. Blumenthal, J.C. Hsiung
and R.B. Husar. Midwest Interstate Sulfur Transformation and Transport
Project: Aerial Measurements of Urban and Power Plant Plumes, Summer
1974. EPA-600/3-76-110, U.S. Environmental Protection Agency, Research
Triangle Park, NC, 1976. 125 pp.
21. Vaughan, W.M., R.B. Sperling, N.V. Gillani and R.B. Husar. Horizontal
S02 Mass Flow Measurements in Plumes: A Comparison of Correlation
Spectrometer Data with a Dispersion and Removal Model. Paper # 75-17.2,
68th Annual Meeting of the Air Pollution Control Association, Boston,
Mass., 1975.
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22. Whitby, K.T., B.C. Cantrell, R.B. Husar, N.V. Gillani, J.A. Anderson,
D.L. Blumenthal and W.E. Wilson. Aerosol Formation in a Coal Fired
Power Plant Plume. In: Proceedings of the 171st National ACS Meeting,
Div. of Environ. Chem., New York, N.Y., April 1976.
23. White, W.H., J.A. Anderson, D.L. Blumenthal, R.B. Husar, N.V. Gillani,
S.B. Fuller, K.T. Whitby and W.E. Wilson. Formation of Ozone and
Light-Scattering Aerosols in the St. Louis Urban Plume. In: Proceedings
of the 171st National ACS Meeting, Div. of Environ. Chem., New York,
N.Y., April 1976.
24. White, W.H., J.A. Anderson, D.L. Blumenthal, R.B. Husar, N.V. Gillani,
J.D. Husar and W.E. Wilson, Jr. Formation and Transport of Secondary
Air Pollutants: Ozone and Aerosols in the St. Louis Urban Plume.
Science 194:187-189, 1976.
25. Sehmel, G.A. Particle Diffusivities and Deposition Velocities Over a
Horizontal Smooth Surface. J. Colloid Interface. Sci., 37:891-906, 1971.
26. Sehmel, G.A. Particle Eddy Diffusivities and Deposition Velocities for
Isothermal Flow and Smooth Surfaces. Aerosol Science, 4:125-138, 1973.
27. Sehmel, G.A. and W.H. Hodgson. Particle and Gaseous Removal in the
Atmosphere by Dry Deposition. Battelle Pacific Northwest Laboratories,
Richland, WA 99352, BNWL-SA-4941, May 1974.
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TECHNICAL REPORT DATA
(Plecsc read Instructions on the reverse before completing)
i. REPORT NO.
EPA-600/7-77-021
3. RECIPIENT'S ACCESSI ON-NO.
4. TITLE AND SUBTITLE
SULFATES IN THE ATMOSPHERE
A Progress Report on Project MISTT
5. REPORT DATE
March 1977
6. PERFORMING ORGANIZATION CODE
AUTHOR(S)
W.E. Wilson, R.J. Charlson, R.B. Husar, K.T. Whitby
and D. Blumenthal
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Environmental Sciences Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
10. PROGRAM ELEMENT NO.
1NE625
11. CONTRACT/GRANT NO.
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
Interim
14. SPONSORING AGENCY CODE
EPA/600/09
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The size and sulfate content of atmospheric aerosols and the rate and
mechanisms for sulfate formation from sulfur dioxide in power plant plumes are
reviewed. Emphasis is given to results from the recent USEPA study, Project
MISTT (Midwest Interstate Sulfur Transformation and Transport). The rate of
conversion of sulfur dioxide to sulfate aerosol in power plant plumes is low near
the point of emission, but increases to several percent per hour as ambient air
mixes with the plume. Tall stacks reduce ground-level concentrations of sulfur
dioxide, resulting in a reduction of the amount removed by dry deposition. In
urban plumes, which are well-mixed to the ground near the source, sulfur dioxide
is removed more rapidly by dry deposition. Thus, tall stacks increase the
atmospheric residence time of sulfur dioxide, which leads to an increase in
atmospheric sulfur formation. These sulfate aerosols may be transported over
distances of several hundred kilometers and produce air pollution episodes far
from the pollution source.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
*Air pollution
'-Aerosols
*Sulfate
*Sulfur dioxide
*Sulfuric acid
Electric power plants
*Plumes
"Conversion
Project MISTT
13B
07D
07B
10B
21B
3. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
38
20. SECURITY CLASS (This page)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
30
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