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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 nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the INTERAGENCY ENERGY-ENVIRONMENT
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 sys-
tems. The goal of the Program is to assure the rapid development of domestic
energy supplies in an environmentally-compatible manner by providing the nec-
essary environmental data and control technology. Investigations include analy-
ses 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 environ-
mental issues.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/7-79-243
November 1979
CHARACTERIZATION OF VISIBILITY-REDUCING
AEROSOLS IN THE SOUTHWEST
Project VISTTA Progress Report No. 1
by
Edward S. Macias
California Institute of Technology
Consultant to MRI on leave from
Washington University - St. Louis
Donald L. Blumenthal
Jerry A. Anderson
Meteorology Research, Inc.
Bruce K. Cantrell
SRI International
Contract No. 68-02-2713
Project Officers
William E. Wilson, Jr., and Thomas Ellestad
Regional Field Studies Office
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
Laboratory, 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 endorse-
ment or recommendation for use.
11
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ABSTRACT
The atmospheric visibility-reducing aerosol in the Southwest has been
experimentally characterized in the Fall, 1977, with respect to particle
size, composition, and contribution to light scattering. Measurements
were taken within the mixing layer using the MRI instrumented Beech-
craft Queen Air aircraft. The aircraft was equipped to measure andre-
cord on magnetic tape the light-scattering coefficient, Aitken nuclei count,
size distribution, ozone, sulfur dioxide, nitrogen oxides, temperature,
dew point, turbulence, pressure (altitude), and navigational parameters.
Multistage impactor and size-fractionated filter samples were also col-
lected in order to determine aerosol elemental composition as a function
of size. Visual range estimates were obtained by viewing distant land-
marks and verified by optical photography.
111
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CONTENTS
Abstract iii
Figures vi
Tables viii
Acknowledgments ix
1. Introduction 1
Background 1
Objectives 3
Responsibilities 4
2. Summary and Conclusions 6
3. Future Plans and Recommendations 9
Recommendations for Future Experiments 9
Fall 1978 Experimental Design 12
4. Program Description 14
5. Summary of Results from Fall 1977 Experiments 19
Characterization of the Visibility-Reducing
Aerosol in the Southwest 19
Source Characterization 37
References 54
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FIGURES
Number Page
1 Map of Southwestern United States 2
2 Flight path of VISTTA regional flights on October 5 and 9, 1977 ... 20
3 Frequency distribution of the light-scatter ing coefficient
due to particles, bsp, measured in regional flights on October
5 and 9, 197', 22
4 Photograph of Navajo mountain at a distance of HO km from
the aircraft of October 5, 1977 23
5 Average size distribution of background Southwest aerosol
measured on the October 9, 1977, regional flight 24
6 Average size distribution of individual elemental species
determined from impactor samples collected on October 5
and 9 regional flights . 27
7 Size-fractioned mass balance of Southwest background aero-
sol measured on regional flights on October 5 and 9, 1977 30
8 Light scattering per unit volume of aerosol material as a
function of particle size, integrated over all wavelengths
for a. refractive index, m = 1. 5 34
9- Light scattering contribution as a function of size for the
Southwest region, October 9, 1977 36
10 Flight map of Arizona smelter flights:
a) October 1, 1977 38
b) October 2, 1977 38
c) October 4, 1977 38
11 Flight map of Mohave power plant flights on October 8, 1977 30,
12 Photograph of the San Manuel smelter plume 8 km downwind
of the plant looking normal to the plume 40
VI
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FIGURES (Continued)
Numbe r Page
13 Visual range calculations for the smelter and power plant
at several distances downwind compared to the background
visual range 44
14 Determination of SO2 conversion rate for the San Manuel
smelter on October 4, 1977 49
15 Qualitative indicators of SO2 conversion in plumes plotted vs.
distance from plant 50
16 Visual range through the San Manuel smelter plume with and
without SO2 conversion and through background only for two
downwind distances 51
VII
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TABLES
Number
1 Beechcraft Queen Air Instrumentation 13
2 Ground-Based Measurements, 1978 Experiments 14
3 VISTTA Field Program Summary - 1977 17
4 Average Parameters Measured during Regional Flights 19
5 Average Elemental Concentration of Aerosol in the
Southwest Region, October 5 and 9, 1977 26
6 Chemical Species Balance for the Southwest Region
October 5 and 9, 1977 29
7 Comparison of Aerosol Mass Determinations from
Volume and Composition Measurements 31
8 Southwest Regional Aerosol Enrichment Factors 32
9 Light Scattering Budget for the Southwest Region
October 9, 1977 35
10 Average Parameters Measured during Orbit Plume Flights 41
11 Plume Impact Data 43
12 Plume Excess Aerosol Elemental Concentration 45
13 Plume Excess Aerosol Enrichment Factors 46
14 Plume Accumulation Mode Integral Size Parameters 47
15 Plume Excess Visibility Budget 52
Vlll
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ACKNOWLEDGMENTS
This work has been supported by the Federal Interagency
Energy/Environment Research and Development program through
a contract with the EPA - ESRL Office of Regional Studies. We
appreciate the guidance provided by William Wilson, director of
the Office of Regional Studies, and the field support provided by
Tom Ellestad of EPA. The analysis herein was greatly enhanced
by consultation with and guidance from S. K. Friedlander and R.
Flagan of Caltech. We also appreciate the field support provided
by J. A. McDonald, the data processing support of J. Roebuck,
and the analysis support of J. Ogren and G. Markowski. Part of
the data analysis has been supported by the USEPA under Grant
No. R 802160 to Caltech.
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SECTION 1
INTRODUCTION
BACKGROUND
The southwestern United States desert and mountain areas, shown in
Figure 1, are generally characterized by very good visibility (100 km).
Until recent years, scenic vistas of natural landmarks and mountains with
a visual range of over 100 miles were common. These vistas have been
considered a major resource of the Southwest, and numerous national parks,
forests, and monuments have been created to preserve them. The tourism
resulting from the southwest scenery has played a major role in the economy
of the region.
As the population of the region has grown, there has been an apparent
reduction in the average visibility (Trijonis and Yuan, 1978). Residents of
the Southwest are concerned about this loss and point to various anthropo-
genic activities as the cause. This concern has led to the August, 1977,
amendments to the Clean Air Act, which contain a section stating, "as a
national goal the prevention of any future, and the remedying of any existing,
impairment of visibility in mandatory Class I Federal areas which impair-
ment results from man-made air pollution." Previously, however, com-
prehensive studies had not been performed to quantify and determine the
cause of the current problem or to provide the basis for a control strategy
to keep the problem from getting worse.
Visibility impairment in the atmosphere is due primarily to the pre-
sence of small particles which scatter and absorb light and, secondarily,
to NO2 which absorbs blue light (Charlson, Waggoner, and Thielke, 1978).
In the southwest, a regional decrease in visibility is likely due to the long-
range transport of aerosol or gaseous precursors into unpopulated pris-
tine areas. A second possible cause of regional visibility impairment may
be wind-blown dust. Both types of particle may be of anthropogenic origin.
Some of the varied activities which may contribute to the decline in visi-
bility are: increased population and the resulting increase in automotive
emissions; emissions from power plants; emissions from smelters; dis-
turbance of the topsoil and desert pavement due to agriculture, grazing,
and off-road vehicles; and mining activities.
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nit
COfffH (BELTERS
PCAIITS
Figure 1. Map of Southwestern United States,
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In addition to their scenic value, the mountain and desert regions
of the Southwest represent a major energy resource. Coal, oil, natural
gas, oil shale, uranium, and abundant sunlight are all found in the area.
The emerging national priority of developing domestic energy supplies
will accelerate the development of the Southwest's energy resources. If
not planned properly, this development could lead to greater visibility
impairment and loss of scenic resources.
Project VISTTA, * sponsored by the EPA Environmental Science Re-
search Laboratory in Research Triangle Park, North Carolina, has been
initiated to determine the sources of visibility reduction in the Southwest
and to help resolve the potential conflict between the congressional man-
date for improved visibility and the need for increased energy production.
The experimental approach of Project VISTTA is to characterize the
visibility-reducing species in the atmosphere, namely particulate matter
and NO2. To determine the relative contribution of the various anthropo-
genic activities to visibility degradation, and thus to develop control strat-
egies, the VISTTA project has concentrated on the study of the size distri-
bution and chemistry of the visibility-reducing aerosol in the region. This
defines the problem. At the same time, data have been collected to char-
acterize the emissions from some of the activities mentioned above, i.e.,
their size distribution and chemistry, and the transport and transforma-
tions these emissions undergo in the atmosphere. Knowing both the char-
acteristics of the atmospheric aerosol and of the emissions, the relative
contribution of each type of emission to the overall problem can be deter-
mined (Friedlander, 1977).
It has been estimated (Trijonis and Yuan, 1978) that in the southwest
region between 30 and 60 percent of the light extinction due to particles
is caused by sulfates. One of the sources of sulfur compounds in the at-
mosphere is the burning of sulfur-containing fuel for power generation.
As part of Project VISTTA, the EPA would like to quantify the contribu-
tion of the power industry to visibility impairment in the South-west.
OBJECTIVES
The objectives of Project VISTTA are as follows:
VISTTA is an acronym from Visibility Impairment due to Sulfur
Transport and Transformation in the Atmosphere
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1. To characterize the visibility-reducing aerosol in the Southwest
with respect to particle size, chemical composition as a function
of size, and spatial distribution. To meet this goal, measure-
ments will be taken on a regional scale (flight paths up to 1000
km) and at points near urban centers, power plants and smelters
in the region.
2. To characterize the emissions which are important in visibility
reduction from typical power plants and smelters in the region.
Both primary particulate emissions and gaseous aerosol precur-
sors will be taken into account.
3. To determine the detailed contributions to light scattering for the
Southwest region broken down by chemical composition and size
(light scattering budget).
4. To quantitatively assess the contributions of various sources,
both anthropogenic and natural, to the visibility-reducing aerosol.
Of particular interest is the contribution of emissions from power
plants.
The first experimental portion of Project VISTTA was aimed at the
first three objectives. This first study was a preliminary experiment, and
the data are rather limited. These results are summarized in Section 5 of
this report. In the later stages of the project, the fourth objective will be
more fully addressed. An outline of the future direction of the project is
given in Section 3 of this report.
RESPONSIBILITIES
Project VISTTA is a team project involving several groups. The
groups involved in the initial sampling period (October 1-10, 1977) and
subsequent analysis and their responsibilities are as follows :
Meteorology Research, Inc. (MRI) -- Project planning, design,
and coordination, aircraft sampling, and data analysis.
EPA - Environmental Science Research Lab (ESRL) at Research
Triangle Park -- Calibration of aircraft instruments.
University of California - Davis (UCD) -- Elemental Analysis of
samples from a specially designed UCD airborne impactor.
University of Washington (UW) -- Ground-based measurements of
size distribution, lignt scattering, and light absorption coefficients,
California Institute of Technology (CIT) -- Data analysis.
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The individuals involved in the
affiliations, and responsibilities are
Project Coordinator
Senior Data Analyst
Field Manager
Data Analysis
Data Analysis
Data Analysis
Impactor Design and
Sample Analysis
Sulfate Analysis
EPA Project Officer
MRI portion of the program, their
given below:
D. L. Blumenthal (MRI)
E. S. Macias (CIT, Consultant to
MRI on leave from Washington
University, St. Louis)
J. A. Anderson (MRI)
B. K. Cantrell (SRI International)
S. K. Friedlander (UCLA)
J. A. Ogren (MRI and UW)
D. L. Shadoan, T. Cahill (UCD)
J. D. Husar and Associates
W. E. Wilson (EPA)
T. Ellestad (EPA)
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SECTION 2
SUMMARY AND CONCLUSIONS
The atmospheric visibility-reducing aerosol in the Southwest has been
experimentally characterized with respect to particle size, composition,
and contribution to light scattering. Measurements were taken within
the mixing layer using the MRI instrumented Beechcraft Queen Air air-
craft. The aircraft was equipped to measure and record on magnetic tape
the light-scattering coefficient, Aitken nuclei count, size distribution,
ozone, sulfur dioxide, nitrogen oxides, temperature, dew point, turbu-
lence, pressure (altitude), and navigational parameters. Multistage
impactor and size-fractionated filter samples were also collected in order
to determine aerosol elemental composition as a function of size. Visual
range estimates were obtained by viewing distant landmarks and verified
by optical photography.
The multistage impactor was mounted in the nose of the aircraft. The
impactor stages had 50 percent collection efficiency for aerosol aero-
dynamic diameters of 4, 2, 1 and 0. 5 microns. Impactor samples were
collected on greased Mylar film. A Nuclepore final filter was used to
collect all particles not collected on the four impaction stages. The im-
pactor samples were analyzed by particle-induced X-ray emission. The
fine .particle samples from a TWOMASS two-stage filter sampler were
analyzed by flash vaporization - flame photometric detection.
The 1977 field program consisted of seven sampling days. The ex-
perimental data included flights of the region on three full days and parts
of one other, flights in the plume of a copper smelter (San Manuel smelter)
on three days, and flights in the plume of a coal-fired power plant (Mohave
power plant) on one day.
The regional flights were designed to characterize the visibility-re-
ducing aerosol within 500 m of the surface on flight paths over 250 km.
On two days, the total flight paths were over 1000 km. The visibility
along these paths was documented with a high-sensitivity nephelometer,
a camera, and visual range measurements from aircraft to prominent
landmarks.
A description of the 1978 field program and recommendations for future
studies are given.
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This study is the first of several similar studies. It should be con-
sidered as a pilot study and all results should be considered preliminary
and limited. The results of the Fall, 1977, study are summarized below:
1. On two regional flights over large parts of the Southwest, the
visibility-reducing aerosol was quite homogeneous throughout the entire
region, indicating that the visibility impairment was of regional extent.
2. The aerosol size distribution throughout the region on October 5
and 9, 1977, was bimodal, with a geometric volume mean size for the
fine particles of ~ 0.25 microns, which is slightly smaller than the con-
tinental background aerosol average mean size (0.3 microns). The
measured coarse particle mode volumetric mean size was ~ 5. 5 microns,
which is equal, within error, to the continental background.
3. The elemental size distribution from both regional and plume im-
pactor samples indicated that aluminum, calcium, and iron are present
predominantly in coarse particles; sulfur and titanium are present pre-
dominantly in fine particles; and silicon and potassium have substantial
concentrations in both modes.
4. Sulfur and silicon were found in nearly equal concentrations in
the Southwest background data and were the elements present in the highest
contrations in the fine particles (Dp^l/lm). The detailed aerosol mass
balance determined for the Southwest region showed that sulfur (expressed
as ammonium sulfate) and silicon (expressed as SiO2) amounted to ~ 50
percent and ~ 30 percent of the fine particle mass, respectively.
5. On the days sampled, a total of ~ 90 percent of the measured coarse
particle (D>l£lm) mass in the Southwest region was composed of elements
which were present in the same abundance relative to aluminum as in the
earth's crust. This indicates that the source of these particles is either
wind-blown dust or material with an elemental composition nearly that
of crustal material, such as flyash.
6. The light-scatter ing budget for Southwest background aerosol on
October 9, 1977, indicated that ~ 50 percent of the light scattering was due
to fine particles, ~ 40 percent was due to Rayleigh scattering from gases,
and ~ 4 was due to coarse particles. Considering only the light scattering
due to particles, ~ 90 percent is due to fine particles which are composed
mainly of sulfates [~ 50 percent as (NH^SO^] and silicon compounds
~ 30 percent as SiOg).
7. Mie scattering calculations of the light scattering coefficient due
to particles using the measured average regional size distribution were
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in good agreement with the values measured with a nephelometer. This
is a quantitative indication of the internal consistency of the size distri-
bution and bscat measurements which adds credibility to the calculated
light-scattering budget.
8. Plume excess fine particle aerosol, i.e., the point source
emission plume aerosol with the background subtracted, was composed
largely of sulfur and silicon compounds for both the smelter and power
plant plumes. The major elemental species in the plume excess coarse
particle aerosol were aluminum, silicon, potassium, calcium, and iron
in approximately crustal abundances in both plumes. These results indi-
cate that fine particle Si may be a good tracer for primary combustion
aerosol in smelter and power plant plumes.
9. A simple semi-quantitative calculation of visual plume impact is
described which compares the visual range with and without the plume
present. On October 4, 1977, the smelter plume caused an~90 percent
reduction of visual range relative to the background visual range (135 km)
at 8 km downwind from the plant. As far as 127 km downwind, increased
bscat and sulfate levels relative to background concentrations were observed
along with an ~ 40 percent reduction of visual range due to the smelter
plume.
10. Sulfate aerosol was formed in Southwest power plant and smelter
plumes. The measured SO2 conversion rate from the San Manuel copper
smelter on one morning between 0900 and 1230 (MST) was 0.7±0.2 per-
cent/hour between 60 and 127km downwind.
11. The plume excess visibility budget indicated that fine particle sul-
fur and silicon species contribute ~ 50 percent to the excess bscat in the
San Manuel smelter plume. In the Mohave power plant plume coarse
particles were the major contributors to the excess bscat, which may have
been at least partially due to measurement interferences from wind-blown
dust on the sampling day.
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SECTION 3
FUTURE PLANS AND RECOMMENDATIONS
RECOMMENDATIONS FOR FUTURE EXPERIMENTS
The initial exploratory experiments of Project VISTTA were produc-
tive. The characterization of the visibility-reducing aerosol with respect
to chemical composition! particle size, and spatial distribution in remote
areas and near sources was successful. However, these results indicate a
number of improvements and changes needed in future experiments in order
to meet the VISTTA goals described in the Introduction of this report.
The recommended improvements and changes are described below.
Some have been incorporated into the September 1978 VISTTA experiments
as described later in this section. In addition, Systems Applications, Inc.,
has suggested a number of measurements (SAI, 1978) to validate their visi-
bility models (Latimer et al. , 1978). Many of these measurements are
already part of the VISTTA experimental plan. Those additional measure-
ments which are compatible with the goals and measurements of the VISTTA
program are also included in the following discussion:
1. Total aerosol mass data for at least two size ranges are needed.
This is essential for both source identification and aerosol charac-
terization. Aerosol mass can be determined by gravimetric weigh-
ing, beta absorption, or use of a piezoelectric crystal.
2. An improved impactor is needed to extend the size separation of par-
ticles down to approximately 0. 1 Jim in diameter. This increased
size resolution is needed for a more accurate determination of the
visibility budget, that is, the contributions of the various chemical
species to light scattering. The impactor used in the initial studies
has a 50 percent efficiency cutoff for the final stage of 0. 5/Ltm aero-
dynamic diameter which is near the peak of the curve of scattering
efficiency per unit mass versus particle size (Figure 8). Further-
more, the volume distribution in the Southwest, as described in
Section 3, peaks in the range of 0. 1 to 0. 3/im. Thus, data on chem-
ical composition as a function of size are most important in the
size range from 0.1 to 1.0/im. An eight-stage, low-pressure
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impactor with 50 percent efficiency cutoffs of 4. 0-, 2. 0-, 1. 0-,
0. 5-, 0. 26-, 0.11-, 0.076-, and 0. 05-jim aerodynamic diameter
which would be suitable for aerosol collection in VISTTA has been
developed by Hering, Flagan, and Friedlander at CIT (Hering et al. ,
1978). This instrument was tested in the MRI aircraft and on the
ground in the September 1978 VISTTA field program. Particles are
impacted on stainless steel strips for sulfate and nitrate analysis in
the present configuration, but it could be modified to accommodate
Mylar impaction surfaces needed for PIXE analysis.
3. Improved data on the concentration of the major chemical constitu-
ents--sulfate, nitrate, silicon, and carbon--are needed for aerosol
characterization. Wherever possible, more than one technique
should be used to determine the concentration of each element in order
to validate results. In the 1977 experiments, particulate sulfur was
measured by both PIXE and FV-FPD, but there were no redundant
measurements of other elements.
In future experiments, particulate nitrate in at least two size ranges
should be measured. Several methods are available which are sensitive
enough for use with relatively short aircraft sampling times, such as
ion chromatography (1C) (Mulik et al. , 1976) or flash vaporization and
gas phase chemiluminescence detection with an NOX monitor (Hering,
1978). The 1C analysis will also give sulfate concentration which
can be used as a determination of the chemical composition of the total
aerosol sulfur as determined by PIXE analysis of impactor samples.
Silicon was found to be a major constituent of fine particles in remote
areas in the 1977 VISTTA experiments using PIXE analysis of impac-
tor samples. In some cases, the silicon concentration exceeded the
sulfur concentration. However, the low energy of silicon x-rays
results in poor sensitivity. It is therefore necessary to measure
silicon by another, more sensitive technique to verify these results.
A sensitive method is flameless atomic absorption (AA), but we have
found no reference to its use for this purpose. A less sensitive al-
ternative is conventional flame AA (Moyers et al. , 1977).
Measurements of total carbon, soot carbon, and aerosol absorption
are needed for a complete characterization of the aerosol and for com-
pleting the Southwestern visibility budget. Carbon is a major consti-
tuent of fine particles near urban areas, with as much as 50 percent
of the carbon in the form of soot (Macias et al. , 1978b). In this form,
this constituent is the major contributor to particle absorption of light
and, therefore, is important to visibility reduction in urban areas
Rosen et al. , 1978). Diesel motor vehicles are a major source of fine
particle soot carbon (Pierson, 1978); coal combustion in a modern
power plant is thought to be a relatively minor source (Nolan, 1978).
10
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Measurements of particle absorption in the Southwest indicate that
the ratio of particle absorption to total extinction is 10 percent
in clean background areas in the Southwest and up to 50 percent in
urban areas (Weiss et al. , 1978). Total carbon can be measured by
inelastic proton scattering followed by gamma ray analysis of light
elements (GRALE) (Macias et al. , 1978b) or aerosol combustion with
detection of the evolved carbon dioxide or methane (Grosjean, 1975;
Huntzicker and Johnson, 1978; and Macias, 1978a). Soot carbon can
be measured by the GRALE technique after the volatile organic car-
bon compounds have been removed by heating. An alternate method
for estimating fine particle carbon measures the reflectance from a
white glass filter (Macias et al. , 1978b). Aerosol absorption can be
measured by the Integrating Plate Method, a technique based on the
transparency of a thin filter containing a small amount of aerosol
(Lin et al. , 1973).
4. More sensitive and extensive data of trace elements are needed for
source characterization studies. PIXE analysis for elements such as
silicon, sulfur, iron, etc. should be combined with neutron activa-
tion analysis for elements such as selenium, arsenic, antimony, etc. ,
seen in earlier studies (Ragaini and Gndov, 1977). Some of these
elements can be detected by both methods, which will act as a check
on the analysis technique,
5. Sampling should be carried out when the scattering due to particles
is greater than 40 x lO'^rrr1 in large parts of the region. Observa-
tions from aircraft indicate that occasionally areas of reduced visi-
bility ~1 00 km across exist in pristine areas of the Southwest sur-
rounded by areas of very good visibility (Beil, 1978). However, it
has been estimated by visual range observations that in pristine areas
of the Southwest these low visibility conditions exist only ~1 5 per-
cent of the time (Latimer et al. , 1978). Aircraft sampling under
these conditions would lead to an estimate of the spatial distribution
of the visibility-reducing aerosol. In addition, this -would result in
much more detailed elemental data and would greatly facilitate
source characterization studies.
6. Sampling should be carried out at different times of the year, par-
ticularly at times when the visibility impairment in the Southwest
is predicted to be greatest. Examination of seasonal visibility
patterns (Roberts et al. , 1975) shows that the lowest values of
visual range in the Southwest are observed in the summer months.
It has been suggested that, in the Southwest, stable conditions occur
most frequently in the winter, which should result in the greatest
plume visibility impairment (SAI, 1978). However, background
visual range is greatest during the winter.
11
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FALL 1978 EXPERIMENTAL DESIGN
The second set of field experiments in Project VISTTA was carried
out September 12-27, 1978. The instrumented MRI Beechcraft Queen Air
aircraft was again used for airborne sampling. This was augmented by
an expanded ground-based measurement program. The field measurements
were based in Farmington, New Mexico, during the first 10 days of the
program. Flights in the plume of the Four Corners Power Plant were
carried out during six days; regional sampling was performed on two days.
The last six days of the program were based in Tucson, Arizona, where
the aircraft Was flown in smelter and urban plumes and on flights through-
out the region.
The instrumentation used in the 1977 experiments was flown in the
aircraft (Table 1). However, a number of improvements, recommended
earlier in Section 4, -were made in this second experimental period. A
Washington University St. Louis aerosol charger (Husar, Macias, and
Dannevick, 1976) was added to the instrumentation package. This instru-
ment gives an on-line measurement which is most sensitive to particles
in the size range of 0. 01- to 0. 2- /im diameter (Sverdrup, 1977). A cy-
clone separator with backup filters was operated on most 1978 flights.
One filter was Teflon-coated glass used for ion chromatography analysis
of sulfate and nitrate. Occasionally a second backup Nuclepore filter was
used for determining aerosol absorption by the Integrating Plate Method.
A Caltech low-pressure impactor was installed on some of the flights in
place of the Nuclepore filter to determine the detailed sulfur size distri-
bution. The impactor stages were analyzed for sulfur using flash vapor-
ization followed by gas phase flame photometric detection (Roberts and
Friedlander, 1976). Fine particle aerosol mass was determined gravi-
metrically from the filters. The final filter from some of the UCD im-
pactor samples will be analyzed for trace elements by neutron activation
analysis. A few of the TWOMASS sampler fine particle filter samples
will be analyzed for carbon, sulfur, and nitrogen before FV - FPD sulfur
analysis.
Ground-based measurements were greatly expanded in the 1978
experiments. The measurements carried out in the Four Corners area
and at Mesa Verde National Park are outlined in Table 2. With this
more comprehensive set of aircraft and ground-based measurements,
it is expected that a more detailed characterization of the visibility-
reducing aerosol will be possible.
12
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TABLE 1. BEECHCRAFT QUEEN AIR INSTRUMENTATION
Measured Parameter
Instrument
Aerosols - Integral Size:
Light Scattering
Aitken Nuclei
Aerosols - Differential Size:
Particle Diameter -
0. 01 -1.0 |jm
0. 5 - 4. 0 |jm
2.0- 30. 0 (am
Aerosol Samples;
Two Stage Sampler
Multistage Impactor
Gases:
Ozone
Sulfur Dioxide
Nitrogen Oxides
Other:
Dew Point
Temperature
Turbulence
Altitude
Indicated Air Speed
Position - VOR
DME
Visual Range
MRI 1562 Nephelometer (modified by
UW for high sensitivity)
Environment One Condensation Nuclei
Monito r
TSI 3030 Electrical Aerosol Size
Analyzer (EAA)
Royco 218 Optical Particle Counter
(OPC)
Particle Measurement Systems Axial
Scattering Probe (ASP)
MRI TWOMASS Sampler
UCD Impactor System
REM 612 03
Meloy 285 Total Sulfur Monitor
Monitor Labs 8440 NO - NOX
Cambridge Systems 137
MRI Airborne Instrument Package
Aircraft Navigation System
Optical Photography
13
-------
TABLE 2. GROUND-BASED MEASUREMENTS, 1978 EXPERIMENTS
Parameter
Sampling Device/
Analysis Technique
Analysis
Responsibility
Four Corners Area;
Size Distribution
Light Scattering
Sulfate Size
Distribution
Nitrate Size
Distribution
Mass1
Sulfate2
Nitrate2
Carbon
NH3
Plume Optics
Wind Speed
Wind Direction
EAA, OPC
Nephelometer
LPI - FV/FPD
LPI - FV/
Chemiluminescence
Cyclone Separator with
Teflon Filter
1 Gravimetric Weighing
2 Ion Chromatography
CIT
CIT
CIT
CIT
CIT
ERT
TWOMASS Sampler/GRALE WU
Tandem Filter Rockwell Internat'l
Telephotometer
Pibal
EPA - LV
New Mexico Health
MRI
Mesa Verde National Park:
Size Distribution
Light Scattering
Aerosol Absorption
Silicon
EAA, OPC
Nephelometer
IPM
AA
UW
UW
UW
Univ. of Arizona
14
-------
SECTION 4
PROGRAM DESCRIPTION
The initial exploratory field program of Project VISTTA was carried
out October 1-10, 1977. This initial phase was designed to outline the ex-
tent and nature of the visibility impairment in the Southwest. The empha-
sis was placed on obtaining as complete a characterization of the aerosol
as possible in order to aid in planning a more optimal set of experiments
in the later stages of the VISTTA program.
Measurements were taken within the mixing layer (<500 m above
ground level) using the instrumented MRI Beechcraft Queen Air aircraft.
This twin-engine aircraft has minimum and maximum sampling speeds of
180 and 290 km/hr, respectively. With a full instrument complement, the
maximum sampling time is over four hours. The aircraft was equipped
to to continuously measure and record on magnetic tape light-scattering
coefficient, Aitken nuclei count, ozone, sulfur dioxide, nitrogen oxides,
temperature, dew point, turbulence, pressure (altitude), and navigational
parameters. Aerosol size distribution measurements were made over a
range of 0. 01 to 30^im. using three size-selective aerosol sensors. An
electrical aerosol analyzer and optical particle counter were used in con-
junction with an automated "grab bag" sampling system designed to col-
lect and hold a discrete static air sample for analysis (Blumenthal et al. ,
1978). An axial scattering probe was operated in the free stream near
the nose of the aircraft for particle size measurements in the range of
2 to 30pim. Multistage impactor and two-stage filter sampler samples
were also collected in order to determine the elemental composition as
a function of size. The details of the aircraft instrumentation are given
in Table 1. Visual range measurements were carried out by viewing dis-
tant landmarks and verified by optical photography.
Gas instrument calibration was carried out by personnel from the
EPA - ESRL. The nephelometer was calibrated with Freon-12 (bgcat =
235 x lO^rn"1 at 525 nm, sea level) and filter air (bscat = 1 5 x 1 O"6 nr1
at 525 nm, sea level). A gas phase titration was used to calibrate the C-3
and NO monitors. The SO2 monitor was calibrated with a permeation
tube.
15
-------
The multistage impactor, a Lundgren-type impactor specially mod-
ified for aircraft sampling by investigators at University of California at
Davis (UCD), was mounted in the nose assembly of the aircraft. The im-
pactor stages had 50 percent collection efficiency for particle diameters
of 4, 2, 1, and 0. 5j*m. Impactor samples were collected on greased My-
lar film. A Nuclepore final filter was used to collect all particles not col-
lected on the four impaction stages. The impactor samples were analyzed
by particle-induced X-ray emission (PIXE) (Cahill, 1975) at the Crocker
Nuclear Lab cyclotron at UCD. This analysis gives elemental concentra-
tion of elements with atomic numbers of 13 (Al) or greater.
The fine particle samples from the TWOMASS two-stage sampler
(Macias and Husar, 1976) were analyzed by flash vaporization-flame
photometric detection (Husar et al., 1975) by J. D. Husar and Associates
(St. Louis, MO).
The field program, summarized in Table 3, consisted of seven sam-
pling days. The experimental plan included flights of the region on three
full days and parts of one other, flights in the plume of a copper smelter
(San Manuel smelter) on three days, and flights in the plume of a coal-fired
power plant (Mohave power plant) on one day.
The regional flights were designed to characterize the visibility-
reducing aerosol on flight paths of over 300 km. On two days the total flight
paths were over 1000 km. All flights were within the mixing layer; how-
ever, occasional spirals were made to define the mixing layer structure.
The visibility along these paths was documented with a high-sensitivity
nephelometer, a camera, and with visual range measurements from the
aircraft to prominent landmarks. Ground measurements were made by
UW at Canyonlands National Park with a nephelometer and sampler for
aerosol absorption.
Smelter plume flights were carried out at several downwind distances
up to 127 km from the San Manuel smelter. Flights in the 1580 MW Mohave
power plant plume were performed at distances as far as 62 km downwind
of the plant.
The plume flight patterns were designed to provide a detailed char-
acterization of the plume at discrete distances downwind from the source.
At each distance horizontal traverses were made through the plume normal
to the plume axis at several elevations. Traverses were long enough to
include background air on either side of the plume. Vertical spirals were
also performed to help characterize the plume structure. In addition to
cross-sectional plume traverses, orbital flights within the plume of up to
16
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one hour were carried out at each distance to gather heavily loaded impac-
tor and filter samples. Orbits upwind of the source were flown to gather
background samples.
Single theodolite pilot balloon (pibal) releases were carried out at
various times on every sampling day to determine wind direction and speed
as a function of altitude in the sampling area.
18
-------
SECTION 5
SUMMARY OF RESULTS FROM
FALL 1977 EXPERIMENTS
CHARACTERIZATION OF THE VISIBILITY-REDUCING
AEROSOL IN THE SOUTHWEST
Spatial Distribution
The character of visibility-reducing aerosols in the Southwest
was determined in long regional flights in order to measure a regional
background. These flights were made between or upwind of large point
sources of pollutants, such as urban areas and power plants. All flights
were at a constant altitude to within ±25 m. On October 5, 1977, flights
were made between Flagstaff (AZ) - Tuba City (AZ) Island in the Sky -
Farmington (NM) - Grants (NM) Flagstaff, as shown in Figure 2. The
flights on October 9 followed the same 1080-km path in the reverse di-
rection. Shorter flights in the region (~260 km) were flown on October 8
and 10. On all days, the visibility and air quality were quite good (aver-
age visual range = 140 km). This resulted in very low values for all mea-
sured aerosol and gas parameters except ozone, which was present in
concentrations representative of clean air. Therefore, only data from
the longer flights on October 5 and 9 which have more meaningful aver-
ages, given in Table 4, are discussed in this report. The averages for
each day were determined by averaging over each segment of the flight
and then averaging the flight segment averages. The NO, NOX, and SO2
concentrations were below the sensitivity of the monitors throughout the
region. The bscat values, although quite low, were detectable with the
aircraft instrumentation. The light scattering coefficient values bscat,
given in Table 3, are from the nephelometer output with the contribution
of Rayleigh scattering of air molecules included.
TABLE 4. AVERAGE PARAMETERS MEASURED DURING REGIONAL
FLIGHTS
Date
10/5/77
10/9/77
Altitude
(MSL)
2428i23
2289A21
Flight
Length bscat SO2
(km) (xlO"6^!"1) (ppb)
1080 28i3a <1
1080 25±1
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The spatial distribution of the visibility-reducing aerosol is most
easily determined from the frequency distribution of the light-scattering
coefficient due to particles, bsp, as shown in Figure 3. These values are
determined from the 10-sec average nephelometer readings with the Ray-
leigh scattering contribution to the scattering coefficient at the flight al-
titude subtracted.
The average value of bsp on both sampling days was rather low, rang-
ing from (25 ±1) x 1 O^m'1 on October 9 to (28±3) x lO^rrf1 on October 5.
Although these values are low, they are above the minimum sensitivity of
the instrument [bs_ (min)~ 5 x 10"6m"1]. The Rayleigh scattering or clean
/i
air contribution at the sampling altitude (~11 x 10m) was, on the aver-
age, 42 percent of the total light scattering coefficient, during the very
clear days on which these regional flights were made. The average mea-
sured visual range in-Mesa Verde and other national parks in the region
in 1976 (Latimer et al. , 1976) was about equal to the average visual range
calculated from the scattering coefficient on the VISTTA sampling days
(~150 km). Therefore, the VISTTA data can be considered typical for the
region. The calculated visual range can be verified from photographs such
as shown in Figure 4. Navajo Mountain, which is at a distance of 11 0 km,
can be seen near the horizon in the photo. This photo was taken with a 50-
mm Nikon lens, Kodachrome 64 film, and a UV filter. The ground eleva-
tion is ~2000 m msl, the aircraft is at 2429 m msl, and the mountain top
is at 3166 m msl. The visual range calculated from bscat measured along
the sight path shown in Figure 4 was ~140 km.
The coefficient of variation of the bsp frequency distribution was 7
percent on October 9 and 18 percent on October 5 over the entire 1080-km
flight path, which indicates that the aerosol was homogeneous on both days.
Size Distribution
The average size distribution of background Southwest aerosol mea-
sured on the aircraft during the October 9 regional flight is shown in Fig-
ure 5. The distribution is bimodal. Reduction of the aerosol size distri-
bution data was accomplished using reduction procedures described by
Cantrell and Whitby, 1978. The size distribution data were collected every
five minutes during the entire flight. All measured size distributions were
averaged before extracting integral parameters using a lognormal approxi-
mation technique. There is some question about altitude effects on these in-
struments, which may lead to errors in the size distribution measurements.
However, we do not think these errors are large enough to alter the conclu-
sions of this report. We are presently looking into the magnitude of this
21
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Figure 4. Photograph of Navajo mountain at a distance of
110 km from the aircraft of October 5, 1977. The
visual range calculated from measured bscat values
along the sight path was ~140 km.
23
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flow rate effect. The fine particle or accumulation mode had a geometric
volume mean size, D_ , of 0. 25jim and a geometric standard deviation, Og,
of 2.0. The coarse mode geometric volume mean size is 5. 5pm, with a 0"
of 2. 2. The volume concentration of particles is 2.6 mVcm3 and 2. 5
mVcrr^for the fine and coarse modes, respectively. The accumulation
mode mean size is slightly smaller than the continental average of 0.
described by Whitby (1978). However, the coarse particle mean size is
the same as the continental average of 6 jzm, within experimental error,
expected for particles from similar sources such as windblown dust.
Elemental Composition
The elemental composition of the visibility-reducing aerosol in the
Southwest was determined from impactor and filter samples collected on
regional flights October 5 and 9, 1977. As discussed previously, the aer-
osol was quite homogeneous throughout the region during this sampling,
making a regional average meaningful. The elemental concentrations
divided into fine particles (Dp £l /am) and coarse particles (Dp 21 /im) aver-
aged for all samples collected on October 5 and 9 are given in Table 5.
The rationale for the separation at 1 pm is based on the high scattering ef-
ficiency for particles with diameters less than 1 ^im. Furthermore, parti-
cles in each of these size ranges generally have different chemical compo-
sition. All other elements not listed were below the minimum detectable
limits. The elemental concentration of fine particle sulfur was measured
by FV-FPD analysis of TWOMASS samples. All other data are from PIXE
analysis of impactor samples. There was some discrepancy between the
sulfur concentration values from the two techniques with the PIXE values
being generally higher than the FV-FPD results. The explanation of this
discrepancy is made more difficult because different samplers as well as
different analysis techniques were used. In the second VISTTA study in
Fall, 1978, additional samplers and sulfur analysis methods were used to
get a more detailed understanding of this discrepancy and to obtain more
reliable sulfur concentration values. In this report, the FV-FPD results
were used in order to obtain preliminary conservative sulfur values. The
detailed explanation of this problem will be given in a later VISTTA report.
The coarse particle fraction is dominated by crustal elements such as
silicon, aluminum, calcium, and iron. Sulfur, silicon, and potassium
are predominant elemental species in the fine particles.
The size distribution of individual elemental species determined from
regional impactor samples collected on the October 5 and 9 regional flights
is shown in Figure 6. Aluminum, calcium, and iron all show very similar
size distributions, with the highest concentration of each element in parti-
cles with diameters greater than 4fim. The concentration on the final fil-
25
-------
ter (DpSO. 5^m) was below the minimum detectable limit for all these ele-
ments. Silicon has a size distribution similar to aluminum down to Ijim;
below that diameter the concentration of silicon increases. The concen-
tration of small particle silicon (DpSO. 5^m) is nearly equal to the large
particle value (Dp>4jzm). These data indicate that silicon is a major con-
tributor to the fine particle mass and, as discussed in a later section of
this report, to visibility reduction. This is an unexpected but quite impor-
tant result of this work. From the source characterization determined in
this work, fine particle silicon is likely to be the result of condensation of
volatile silicon emitted from high-temperature combustion sources. It is
important to verify the presence of small particle silicon by further chem-
ical measurements.
TABLE 5. AVERAGE ELEMENTAL, CONCENTRATION OF AEROSOL
IN THE SOUTHWEST REGION, OCTOBER 5 AND 9, 1977
Fine Particles1" Coarse Particles0
Element' fcg/m3)
Al
Si
S
Cl
K
Ca
Ti
V
Cr
Fe
Zn
Zr
Pd
Ba
Pt
Pb
0.01
0.72
D.68
0.11
0.21
0. 03
0.08
0.04
_
0. 004
0. 03
-
0.02
0.10
0.07
0.09
0.28
1.12
0.06
0.01
0.09
0.24
0.01
0.01
0.01
0.16
0.003
0.02
0. 01
0.01
0.01
0.004
*The following elements were detected in only a few samples and, there-
fore, it is not possible to determine a meaningful average concentration:
Fine Particles - Cu, Mn, Ni, Rb, Co, Hg, Mo.
Coarse Particles - Cu, Mn, Se, Ni, Rb, Co, Mo, Br.
Fine particle (Dp £ 1pm) concentrations were determined from the sum
of impactor stage 4 and the final filter. Sulfur values were determined
from TWOMASS samples.
"Coarse particle (Dp ii^im) concentrations were determined Irom the
sum on impactor stages 1, 2, and 3.
26
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Particulate sulfur is concentrated mainly in small oarticles
(Dp £ 0. 5/im). This is reasonable considering that SOi" i-s a large frac-
tion of the accumulation mode which peaks at 0. 25/^m. Titanium and
potassium show slightly increased concentration for small partricles,
but the variations with size are not dramatic.
Chemical Composition
The total aerosol mass was not measured, but it can be estimated
from the measured elemental concentrations, and the oxygen concentra-
tion estimated with assumptions of the chemical form of the measured
elements. The sulfur can be expressed as sulfate because the FV-FPD
method is specific for water-soluble sulfate (Husar et al. , 1975). It is
also assumed that ammonium is the only ion associated with the sulfate.
Other elements are assumed to exist as oxides. This leads to the mass
balance listed in Table 6 and Figure 7. The mass estimates may be low
due to unmeasured elements, particularly those with Z < 13. The total
mass in each size range can also be estimated from the aerosol volume
determined by integrating each mode in the differential size distribution
and by estimating the aerosol density from the chemical composition. A
comparison of these two approaches, given in Table 7 indicates that the
elemental mass balance accounts for ~93 percent and ~64 percent of the
fine and coarse particle mass derived from volume, respectively. The
assumptions of chemical form, although somewhat arbitrary, lead to a
conservative estimate of the total mass. For example, iron has been as-
sumed to be present exclusively as Fe2O3 when in reality it is likely that
FeO is present as well. This is the case for crustal material (Mason,
1966). Comparison of fine particle mass and bsp allows a further check
on the mass estimate. Extensive measurements in the western United
States indicate that the fine particle mass /bsp ratio is normally 0.32 to
0. 3i g/m2 (Waggoner, 1978). The ratio for the VISTTA regional data is
0. 34 g/m2, -which is a further indication that the fine particle mass esti-
mate is reasonable.
The total measured aerosol mass in both size ranges (9. 23/ig/m3)
determined from the sum of the concentration of each compound is lower
than the average total suspended particulate value (~20pig/m3) measured
in several National Parks in the region (Trijonis and Yuan, 1978). It
appears from, volume and bscat measurements that this discrepancy is not
primarily due to fine particle mass estimates. It is more likely that the
coarse particle mass estimate is low due to unmeasured constituents.
Furthermore, coarse particles may be diminished due to settling at 300
to 500 m above the ground where the samples were collected.
28
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29
-------
so:
COARSE PARTICLES.
MASS =4.0
SiO,
61%
FINE PARTICLES .
MASS = 5.3 4/g/mJ
39%
SiO,
A10, CaO,
78-404/1
Figure 7. Size-fractioned mass balance of Southwest background aerosol mea-
sured on regional flights on October 5 and 9, 1977. The concentration
of individual compounds was determined from the measured elemental
concentration and assumed chemical form. The total aerosol mass in
each size fraction was determined from the sum of the individual chem-
ical components. Comparison with aerosol volume measurements indi-
cates that the mass estimated from composition measurements repre-
sents 93% and 64% of the fine and coarse particle mass, respectively.
30
-------
f
NATIONS
CEMENTS
§5
I?
w 3
H 5
W *
Q Z
S2
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< KH
^ CO
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. Compos it
erosol
o J5
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ID sO
-------
Probably the most important species unaccounted for are nitrates,
carbon compounds, and water. The average annual concentration of ni-
trate in the nonurban Southwest region was about 20 percent of the sulfate
value in the early 1970's as measured in Grand Canyon and other remote
Southwestern national parks by the National Air Surveillance Network
(Latimer et al. , 1978). These values may be subject to error due to arti-
fact sulfate and nitrate effects on filters. Very few data exist on the con-
centration of carbon in Southwest ambient aerosols, but it is a significant
component of eastern urban aerosols (Lewis and Macias, 1978).
Enrichment Factors^
The predominant species in the coarse particles are elements found
in high concentration in soil and crustal material. Elemental enrichment
factors, given in Table 8, help to characterize the source of these particles.
These factors are calculated as follows:
Enrichment Factor (EF) =
(X/A1) Aerosol
(X/A1) Crust
TABLE 8. SOUTHWEST REGIONAL AEROSOL ENRICHMENT FACTORS
Element
Enrichment Factor
Fine Particles Coarse Particles
Al
Fe
Si
K
Ca
Ti
S
Cl
V
Cr
Zn
Zr
Pd
Ba
Pt
Pb
1.0 ) Crustal 1
0. 7 /Abundance 0
21 ^ 1
66 \ 1
7
IxlO2
2xl04
7xl03
2xl03
_
4xl03
_
2xl07
2xl03
6xl07
1
0
67
Enriched 23
Relative 29
to Crust 1 3
35
3
7
3
88
6 x 1 O4 J
° ^\
Q
. 2 Crustal
. 0 f Abundance
Q
.7 _J
^\
\
Enriched
> Relative
xlO5 to Crust
xlO5 1
y
32
-------
Aluminum was chosen as the reference element because its major source
is likely to be soil. However, aluminum is also present in flyash from
coal combustion (Lyon, 1977). Crustal abundances were taken from Mason
(1976). Enrichment factors >1 indicate an enrichment of that element
relative to crustal abundances; values <1 indicate a depletion relative
to crust. Because of the uncertainty in the data, EF values between 0. 5
and 2 indicate no significant difference from crustal abundance. It can be
seen from Table 8, that Si, K, Ca, Ti, V, and Fe are all near the crustal
abundance in the coarse particles relative to At. These elements repre-
sent 93 percent of the measured coarse particle mass. The other coarse
particle species are enriched, indicating an anthropogenic source. This
analysis is complicated by the fact that many of these elements are pre-
sent in coal flyash with abundances similar to crustal material.
All fine particle species except iron are enriched relative to the
crust (normalized to aluminum) with enrichment factors ranging from 7
to 2 x 107. The enriched fine particle species represent 99.5 percent of
the measured fine particle mass, which indicates that the vast majority
of fine particles are not due to wind-blown dust of crustal origin.
Light Scattering Budget
The detailed contributions to light scattering as a function of par-
ticle size can be determined from Mie calculations (Mie, 1908) of the
light scattering efficiency and the measured particle size distribution.
The sum of the calculated bsp over all particle sizes can be compared to
the measured light scattering coefficient from the integrating nephelo-
meter. Mie scattering calculations combined with particle size and com-
position measurements permit the determination of the individual contri-
bution to visibility reduction for particles of a given composition and size
(light scattering budget). This approach can also serve as a test of the
consistency of the various measurements. Ensor et al. (1972) have de-
scribed the calculations used in this work in an earlier paper. The fol-
lowing expression was evaluated in the scattering coefficient calculation:
bscat ~
where G is the light scattering per unit volume of aerosol. The quantity
G, calculated using Mie scattering functions, is plotted in Figure 8 as a
function of particle size for a refractive index m = 1. 54 and a standard
solar radiation distribution at sea level. It can be seen from the figure
that particles with diameters between 0.1 and 1 jim have the greatest scat-
tering efficiency.
33
-------
Figure 8. Light s;. i-; ^ring per unit volume of aerosol material
as a function of particle size, integrated over all
wavelengths for a refractive index, m = 1.5. The
incident radiation is assumed to have the standard
distribution of solar radiation at sea level (Bolz,
R, E. , and Tuve, G. E. (Eds.), 1970, Handbook of
Tables /or Applied Engineering Science, Chemical
Rubber Co. Cleveland, Ohio, p. 159.) The limits
of integration on wavelength were 0. 36 to 0. 680jjm.
The limits of visible light are approximately 0. 350
toO.TOO^m. (Friedlander, 1977)
34
-------
The contributions to the light scattering coefficient as a function of
particle size for the average Southwest regional aerosol (October 9, 1977)
calculated from the average regional aerosol size distribution are given
in Figure 9. A refractive index, m = 1.54, was used in this calculation,
which is slightly lower than the mass-weighted values of 1. 57 and 1.65
for fine and coarse particles, respectively, calculated from aerosol com-
position measurements. The calculation was done for light of 525 nm
wavelength. The sum over all calculated contributions yields
]£bsp = (16±2) x I0-6m-1 ,
which agrees well with the average value of light scattering due to parti-
cles measured with the integrating nephelometer (with the contribution of
Rayleigh scattering due to gases removed) of bsp(measured) = 14±1 xlO"6m"
The visibility budget for the Southwest background aerosol on Octo-
ber 9, 1977, determined from the Mie calculations, indicates that 52 per-
cent of the light scattering was due to fine particles (Dp sl^im), 44 per-
cent was due to Rayleigh scattering from gases, and 4 percent was due to
coarse particles. Considering only the light scattering due to particles,
93 percent is due to fine particles. The detailed visibility budget, sum-
marized in Table 9, was constructed using the results of the fine particle
mass balance and assumes that sulfur and silicon compounds have the
same size distribution as the total fine particle aerosol. This is reason-
able, since these compounds represent 82 percent of the measured fine
particle mass.
TABLE 9. LIGHT SCATTERING BUDGET FOR THE SOUTHWEST REGION
OCTOBER 9, 1977 (Visual Range ~160 km)
Component
Dp (Aim)
scat
Contribution
to Total bscat
(percent)
Air Molecules
(NH4)2S04 a
SiO2b
Other Compounds
Coarse Paricles
(Given in Table 5)
0.
0.
0.
1.
1
1
1
0
to
to
to
to
1.
1.
1.
20.
0
0
0
0
11
7
4
2
1
25 XlO^m-1
44
28
16
8
4
100
aAssumes that all fine particle sulfate exists as ammonium sulfate.
Assumes that all fine particle silicon exists as SiO2.
35
-------
E
I
TO «
I «
.£ TO
tJ
-------
The ratio of fine particle sulfate mass to the total bsp value for the
Southwest region measured on October 9, 1977, is 0.15 g(SO4=)/m2. A
similar calculation for the fine particle SiO2 mass / bsp ratio yields
0.11 g(SiO2)/m2. Perhaps a more interesting calculation is the ratio
of fine particle sulfate or SiO2 mass to the contribution of that species to
bsp, as determined in the visibility budget. This ratio is 0.4 g/m2 for
for both fine particle sulfate and SiO2. * This calculation assumes that
sulfur and silicon have the same size distribution.
SOURCE CHARACTERIZATION
In order to characterize the emissions from specific sources in the
region, measurements were made in plumes from the San Manuel copper
smelter on October 1, 2, and 4, 1977, and the Mohave power plant Octo-
ber 8, 1977. The flight paths on these days are shown in Figures 10 and
11. Separate orbital flights in the plume and in the background, as well
as plume traverses, were carried out at each distance downwind of the
source as outlined in Table 2. Analog gas and aerosol parameters mea-
sured during these flights averaged over each flight segment are summa-
rized in Table 10. Data from October 1 have not been included in Table 10
or in any subsequent data analysis because of the poor spatial resolution
of the plume on that day. A photo of the San Manuel smelter plume 8 km
downwind of the plant looking normal to the plume is shown in Figure 12.
The plume is easily visible and well defined against the sky and mountains.
To help evaluate the data presented in this section on source char-
acterization it is instructive to compare the emission rates of the San
Manuel smelter and Mohave power plant. In 1975 the Mohave power plant
emitted an estimated average of 66 tons/days of SOX and 77 tons/day of NOX
(Marians and Trijonis, 1978). In 1977 the San Manuel smelter emitted 557
tons per day of sulfur, expressed as SO2 (Larson and Billings, 1978).
The inverse of this ratio, i.e., the contribution of SO4~ or
SiO2 to bgp divided by the fine particle SO4~ or SiO2 mass is
2. 5 x 10-^m
for SO4 and for SiC2.
37
-------
u
O .
O
4->
o
rj-j
o
!I
0>
QD
38
-------
Figure 11. Flight map of Mohave power plant flights
on October 8, 1977.
39
-------
Figure 12. Photograph of the San Manuel smelter plume
8 km downwind of the plant looking normal to
the plume.
40
-------
in
H
ffi
O
H
H
(4
CQ
O
O
D
Q
Q
H
w
2
w
C4
w
H
W
H
O
W
SMELTER
J
H
D
2
"S
i^
2
5
XfcL
O n
2
^-.
f~\ r^
23
3"
^"*
0N5
^
4J C
m i
J3 O
^H
o r* o m co
CO O CO CO ON Tf O
rO T3
00 CO O £ O I- £
CO vD QJO vD CO yj
CQ «
r^ r^
CO -^
*^^
0 0
'ER PLANT
£
0
PH
W
>
v£)
CO
00 ^H O
-H
M Tl QS
m co .
0
CO CO CO
CO -4
U -H «
^4 ^N v^
in \o co
m co co
r-4 ^H CO
-H -H -ti
O O Tj4
r^ r- co
vO "^ ON
CO CO "g
CO vO >-(
«
£
00
o
t4
e
o
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C
0)
g
CO
a
0)
o
n
41
-------
Plume Impact
The impact of a plume on visibility can be estimated by comparing
the visual range with the plume present to the visual range through the
background without the plume. The parameters used in this semi-quanti-
tative calculation are shown in the schematic diagram below.
OBSERVER
PLUME
BACKGROUND
BLACK OBJECT
78-*::
The subscripts p and b indicate plume and background parameters, re-
spectively. The light scattering coefficient in the plume, b , includes
the background contribution.
The visual range, V, is defined as "the distance, under daylight
conditions, at which the apparent contrast between a specified type of
target and its background becomes just equal to the threshold contrast
of an observer" (Huschke, 1959). For the following analysis, the target
and background are a black object viewed against the horizon sky, and
the threshold contrast of a typical observer, 0. 02, is used (Middleton,
1952). In this case, the visual range is given by
-In 0. 02 _ 3.9
°ext ""fext »
where bext is the average extinction coefficient along the sight path. This
equation assumes uniform illumination along the sight path, and neglects
multiple scattering.
The following calculations assume that the contribution of absorp-
tion to extinction is small, so that the equation for visual range can be
rewritten as V bscat = 3.9. For the case depicted above of a plume im-
bedded in background air, the corresponding equation is
Xpbp + Xbbb = 3.9, where bb and bp are the average scattering coef-
ficients in the background and plume, respectively, and Xp is the mea-
sured plume width. The quantity Xpbp, termed the optical depth of the
plume (Tp), is the integral of scattering across the plume, i.e.,
42
-------
Tp = /bp(x)dx.
The visual range looking through the plume was calculated using the equation
V = XT
3.9 - T
*b =
The values for Xp, bp, and b^ were determined from measurements at the
the lowest altitude at which plume traverses were made. The plume opac-
ity is defined in terms of the plume optical depth as 1 - exp(-T).
The visual range and plume optics calculations are summarized
in Table 11 and Figure 13. The visual range through the copper smelter
plume is reduced at 8 km downwind of the stack from 135 km in the back-
ground to 1 3 km with the plume present (90 percent reduction). The visi-
bility reduction decreases further downwind of the plant. At 60 km down-
wind, the visual range is 82 km with the plume present (39 percent visi-
bility reduction relative to the background). The visibility reduction
with the plume present is nearly equal at 60 and 127 km downwind of the
smelter. The power plant plume exhibits quite different visual behavior.
TABLE 11. PLUME IMPACT DATA
Visual Range
Downwind
San Manuel
Smelter
Mohave
Power Plant
Distance
(km)
8
32a
60
127
32
60
Plume
Width
(km)
16
20
25
54
8
27
Plume
Optical
Depth
4.9
2.8
2.2
3.1
0.66
1.92
Plume
Opacity
0.99
0.94
0.89
0.95
0.48
0.85
With
Plume
(km)
12
54
82
78
98
82
Back-
ground
135
135
135
135
110
110
Visual
Range
Reduc-
tion due
to Plume
(%)
90
60
39
42
11
25
aPlume width at 32 km downwind interpolated from measurements at
8 and 60 km downwind.
43
-------
DISTANCE
DOWNWIND, km
8
32
60
127
BACKGROUND
32
60
BACKGROUND
PLUME IMPACT
SMELTER
;- :
^^^^§i^^^^:iSs^^^
POWER
X"x'x"X'X'X'x'"X'X-X*X*l'X*X-X'X'x"X***i
*X* X vX'XvX*X*X X v.%
;!^^^^^^^^^^^^
PLANT
X'X'X- *X*X*X*X*X *; ;X* ">
50 100
VISUAL RANGE, km
150
76-;::
Figure 13. Visual range calculations for the smelter and
power plant at several distances downwind
compared to the background visual range.
44
-------
The reduction of the background visual range is less at 32 km than at 60
km downwind (11 percent versus 25 percent, respectively). However,
the power plant plume was measured under meteorological conditions
which varied during the day, resulting in erratic plume behavior. The
difference in the reduction of the background visual range between these
plumes may be the result of greater emissions released from the smel-
ter stack and of greater dispersion of the Mohave plume on October 8.
Elemental Composition in Plumes
The elemental composition of the plume excess aerosol, i.e., the
plume aerosol with the background subtracted, was determined from the
analysis of samples collected in orbital plume flights. The background
concentrations were determined in orbital flights upwind of the plume.
The aerosol elemental composition for the San Manuel smelter plume at
60 km downwind and the Mohave power plant at 32 km downwind are given
in Table 12.
TABLE 12. PLUME EXCESS* AEROSOL ELEMENTAL CONCENTRATION
San Manuel Smelter
60 km downwind (10/4/77)
Fine Coarse
Particles*5 Particlesc
Element3
Mohave Power Plant
32 km downwind (10/8/77)
Fine Coarse
Particles Particles
(mg/m3)
Al
Si
S
K
Ca
Ti
Mn
Cr
Fe
Cu
Ni
Se
Pb
<0. 01
1.08
2.29
0.43
-
0.02
_
0. 20
0. 02
.
_
0.26
-
1.91
6.12
_
0.60
1.58
0.03
0.02
0.06
1.02
0.06
-
-
-
0.05 1.46
0.34 3.67
0.30
0.25
1.16
0.04
.
0.05
0.55
.
0.20 0.01
-
0.03
aMolybdenum was detected in concentrations above background but at
the minimum detectable limit in the Mohave power plant plume.
"Fine particle (Dp fil^m) concentrations were determined from the
sum of impactor stage 4 and the final filter. Sulfur values were de-
termined from TWOMASS samples.
cCoarse particle (EL zl/im) concentrations were determined from the
sum of impactor stages 1, 2, and 3.
* - Plume excess values were determined by subtracting background
concentrations from plume concentrations of each element.
45
-------
The largest plume excess elemental constituents of the fine particle
aerosol in both plumes are sulfur and silicon. Silicon, aluminum, cal-
cium, and iron are major constituents of the plume excess coarse parti-
cles. These data indicate that coal-fired power plants and copper smel-
ters in the Southwest may be major sources of the fine particle silicon as
as well as sulfur, the two major consitutents of the Southwest visibility-
reducing aerosol.
Plume excess aerosol enrichment factors for the San Manuel smel-
ter and Mohave power plant are given in Table 13. Coarse particle Si,
K, Ca, Ti, and Fe in both plumes and coarse particle Mn in the smelter
plume are present in crustal abundances relative to Al. Thus, the crus-
tal abundances of these elements in Southwest background coarse particles
may be an indication that the source of these particles is crustal weather-
ing or flyash. Plume excess coarse particle Cr, Ni, Cu, and Pb are all
enriched relative to crustal abundances. All plume excess fine particle
species are enriched relative to the crust except for fine particle Si in the
Mohave plume.
The size distribution of plume excess elemental constituents shows
many similarities with the regional data. Aluminum, calcium, and iron all
exhibit the highest concentrations for particles with diameters >4pim. Sili-
con has a size distribution similar to aluminum down to 1pm but increases
below that diameter. Sulfur is mainly concentrated in fine particles.
TABLE 13. PLUME EXCESS AEROSOL ENRICHMENT FACTORS
San Manuel Smelter Mohave Power Plant
60 km downwind (10/4/77) 32km downwind (10/8/77)
Element Fine Coarse Fine Coarse
Particles Particles Particles Particles
Elements in crustal abundances in coarse particles, enriched in fine particles
Al
Si
K
Ca
Ti
Mn
Fe
1.0
32
IxlO2
-
37
-
3
1.0
0.9
1.0
2
0.3
0.9
0.9
1.0
2
.
.
-
.
-
1.0
0.7
0.5
2
0.5
-
0.6
Elements enriched in both size fractions
S 7xl04 - 2xl03
Cr 2x1 0< 26 - 28
Ni - - 4x1 O3 7
Cu - 46
Se 4xl07
Pb - - - 128
46
-------
The total aerosol mass was not measured but can be estimated from
the elemental concentrations and mean aerosol volume as described pre-
viously. A comparison of these two approaches shows that in the San
Manuel smelter on October 4, 1977, at 62 km downwind, 100 percent of
the plume excess fine particle mass determined from plume excess aer-
osol volume (assuming a mass weighted density of 2 g/cm2) can be ac-
counted for from the measured constituents. The coarse particle volume
was not measured in this plume. Approximately 73 percent of the plume
excess fine particle mass is siilfate (expressed as ammonium sulfate),
and 17 percent is silicon (expressed as SiO2). In the Mohave power plant
plume on October 8, 1977, only about 50 percent of the fine particle mass
determined from aerosol volume can be accounted for by the measured
constituents. Of this 50 percent at 32 km downwind, plume excess sulfate
[expressed as (NH4)2SO4] accounts for 52 percent of the mass inferred from
measured aerosol composition and plume excess fine particle silicon (ex-
pressed as SiO2) accounts for 31 percent. A summary of accumulation
mode aerosol integral size parameters is given in Table 14.
TABLE 14. PLUME ACCUMULATION MODE INTEGRAL
SIZE PARAMETERS
Downwind Accumulation Mode Accumulation Mode
Distance Volume, Va Mean Size, Da
(km) _ (^tm3/ cm3) _ (ptm)
San Manuel Smelter (10/4/77)
60 9.9 0.18 2.0
127 12.9 0.14 1.9
Background 3.5 0.24 2.2
Mohave Power Plant (10/8/77)
32 5.0 0.23 2.1
62 4.7 0.19 2.1
Background 2. 8 0. 20 2. 1
Sulfur Transformation
The conversion of SO2 to particulate sulfate in plumes can be esti-
mated from the measurements of gaseous SO2, particulate sulfate, light
scattering coefficient, and mean accumulation mode volume. A number
of methods to determine SO2 conversion rates in power plant plumes have
47
-------
been used in the past (Wilson, 1978). The approach used here compares
the fraction of particulate sulfur of the total sulfur, SD/Sj, to plume age,
estimated from analysis of winds aloft. Plume excess sulfur values with
background subtracted were used in this calculation. The SO2 conversion
rate measured in the San Manuel smelter plume on October 4, 1977, from
0900 to 1230 MST was measured to be 0. 7±0. 2 percent/hour between 60
127 km downwind from the plant (Figure 14). This calculation assumes no
SO2 deposition between measurements. However, even as much as 20 per-
cent SO2 deposition would not lower the conversion rate below the stated
uncertainty. The SO2 conversion rate was not calculated for the Mohave
power plant plume because of poor plume resolution and erratic wind be
havior encountered on October 8, 1977.
This single measurement of the SO2> SO4= conversion rate should
not be considered typical without many additional measurements under a
variety of conditions. It is interesting to note, however, that this value
is within the range of conversion rates measured in plants in the midwest
(Husar et al. , 1978).
A number of other parameters can be used as qualitative indicators
of SO2 conversion, such as plume excess bsp/Sg, SD/Sg, and mean accu-
mulation mode volume (Va)/Sg ratios and accumulation mode aerosol size,
Dy. These indicators are shown graphically in Figure 15 as a function of
distance downwind from the plant for the San Manuel smelter and Mohave
power plant plumes on October 4, 1977, and October 8, 1977, respectively.
The three plume excess parameter ratios all increase downwind in both
plumes, indicating that sulfur aerosol is being formed. The mean accu-
mulation mode size decreases downwind from both plants which also in-
dicates fresh aerosol is being formed.
One method of assessing the effect of sulfur transformation on
visib;lity is to determine the improvement of visual range if no SO2 was
converted to sulfate. This can be estimated for the San Manuel smelter
at 20 and 32 km downwind on October 2, 1977, assuming that the bsp/SO2
ratio remains constant beyond 8 km downwind. The visual range with the
plume present is then calculated using bscat and assuming no conversion,
as described previously. This approach will slightly overestimate the
effect of aerosol dilution (and therefore visual range) due to loss of SO2
from the plume because of deposition and transformation. The results of
this calculation are shown in Figure 16. At 32 km downwind from the
smelter on October 2 the visual range would increase by nearly a factor
of two if no SO2 were converted to sulfate. At 60 km downwind the visual
range would be increased by 36 percent if there were no conversion.
Thus sulfur transformation has a large effect on visibility impairment
within at least 60 km of the shelter.
48
-------
15
10
o:
a:
Q-
O
z
o
t
(_>
s
SM MANUEL SMELTER
OCTOBER 4, 1977
0.7 %/hr
\x
X
4.1
x
-©-
2.5
I
I
5 10
PLUME AGE, hours
15
76-424/1
Figure 14. Determination of SO2 conversion rate for the San Manuel
smelter on October 4, 1977, from the fraction of particu-
late sulfur vs. plume age.
49
-------
SAN MANUEL SMELTER
10/4/77
MOHAVE POWER PLANT
10/8/77
0.2
0.1
o -o
0.5
0.25
£
0.2
0.1
I
60 127 32
DISTANCE FROM PLANT, km
62
0.2
0.1
20
10
0.5
0.2
0.1
78-423
Figure 15. Qualitative indicators of SO2 conversion in plumes
plotted vs. distance from plant.
50
-------
SAN MANUEL SMELTER
10/2/77
PLUME (Measured)
PLUME (No Conversion,
Scaled to S02)
BACKGROUND ONLY
(Measured)
150
60
DISTANCE DOWNWIND, km
Figure 16. Visual range through San Manuel smelter plume
with and without SO^ conversion and through back
ground only for two downwind distances.
51
-------
Light Scattering Budget in Plumes
The detailed contributions to visibility impairment as a function of
particle size due to a smelter and power plant plume can be determined
using Mie calculations and measured plume excess aerosol size distribu-
tions in an analogous manner to the treatment of regional data. However,
there are several problems with the plume data. During the San Manuel
smelter plume flights only the fine particle size distribution was measured
(Dp £l pm). During the Mohave power plant flights on October 8, 1977, the
entire size distribution was measured, but wind-blown dust was occasion-
ally mixing into the plume. Therefore, the plume visibility budgets must
be considered as much more tentative than the regional visibility budget.
In the San Manuel smelter plume at 62 km downwind on October 4,
1977, the plume excess bsp value synthesized from only the measured fine
particle size distribution (D_ sl/jm), using Mie scattering functions, was
Ibsp = 56 x lO"6^!'1 . This is 59 percent of measured value:
bsp (measured) = 95 x lO^rrf1 . The detailed fine particle visibility bud-
get given in Table 15 was determined from chemical composition and size
distribution, using Mie scattering calculations. Sulfate [assumed to be in
the chemical form of (NH4)2SO4] accounted for 43 percent of the total bsp in
the smelter plume of 10/4/77; SiC2 accounted for 10 percent.
TABLE 15. PLUME EXCESS VISIBILITY BUDGET
Component 1
Dp b.
(^m) (x 10'" m'
SAN MANUEL SMELTER (62 km downwind)
(NH4)2S04
SiO2
Other Compounds
Coarse Particles
0. 1 to 1.0
0. 1 to 1.0
0.1 to 1.0
1.0 to 20.0
MOHAVE POWER PLANT (32 km downwind)
(NH4)2SO4
SiO,
Other Compounds
Coarse Particles1
0.1 to 1.0
0.1 to 1.0
0.1 to 1.0
1.0 to 20.0
Contribution
to total bsp
-1 ) (percent)
10/4/77
41
9.5
5.5
39
95 xlO-fcm-'
10/8/77
3
2
1
21
27 x!0-6m-'
43
10
6
41
100
11
7
4
78
100
1 Assumes that all fine particle sulfate exists as ammonium sulfate.
b Assumes that all fine particle silicon exists as SiO2.
'Determined from b.cat(total) - b.cat(fine particles).
52
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The Mohave power plant plume excess bsp calculation on October 8,
1977, at 32 km downwind was EbSD(calc) = 27xlO'6m'1 , while the
/ i "
measured value was 18x10" m . This difference may be due to the loss
of large particles in the nephelometer sampling line.
Calculations of the light scattering budget for the Mohave power plant
are complicated by the fact that aerosol composition calculations account for
only about fifty percent of the fine particle aerosol mass as estimated
from aerosol volume measurements. Therefore, the estimated contribu-
tions of individual chemical special to bsp may be somewhat high. The
visibility budget for the Mohave power plant plume at 32 km downwind on
October 8, 1977, is quite different from the smelter results. Coarse
particles account for 78 percent of the calculated bsp. This high value
is at least partially due to wind-blown dust mixing into the power plant
plume at the time of the measurement. Fine particle ammonium sulfate
accounted for 11 percent of bsp (bsp [ (NH4)2SO4 ] - 3 x lO^rrr1). Fine
particle silicon accounted for 7 percent of bsp in the Mohave plant.
53
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Raleigh, North Carolina. October 19-22, 1976.
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W. E. Wilson, Jr. Sulfur Budget of a Power Plant Plume. Atmos.
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57
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing]
1. REPORT NO.
EPA-600/7-79-243
4. TITLE AND SUBTITLE
CHARACTERIZATION OF VISIBILITY-REDUCING AEROSOLS IN
THE SOUTHWEST
Project VISTTA Progress Report No. 1
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
E.S. Macias, D.L. Blumenthal, J.A. Anderson and
B.K. Cantrell
8. PERFORMING ORGANIZATION REPORT NO.
MRI 78IR-1585
3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
November 1979
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Meteorology Research, Inc.
Box 637, 464 West Woodbury Rd.
Altadena, CA 91001
1O. PROGRAM ELEMENT NO.
1NE625 EA-13 (FY-77)
11. CONTRACT/GRANT NO.
68-02-2713
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, N.C. 27711
13. TYPE OF REPORT AND PERIOD COVERED
Final 10/1/77 - 10/10/77
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT
The atmospheric visibility-reducing aerosol in the Southwest has been ex-
perimentally characterized with respect to particle size, composition, and contri-
bution to light scattering. Measurements were taken within the mixing layer using
the MRI instrumented Beechcraft Queen Air aircraft. The aircraft was equipped to
measure and record on magnetic tape the light-scattering coefficient, Aitken nuclei
count, size distribution, ozone, sulfur dioxide, nitrogen oxides, temperature, dew
point, turbulence, pressure (altitude), and navigational parameters. Multistage
impactor and size-fractionated filter samples were also collected in order to de-
termine aerosol elemental composition as a function of size. Visual range estimates
were obtained by viewing distant landmarks and verified by optical photography.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS
c. COS AT I Field/Group
*Air pollution
*Aerosols
*Sulfur oxides
Visibility
*Light scattering
*Plumes
*Measurement aircraft
Project VISTTA
Southwest
13B
07D
07B
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19 SECURITY CLASS (This Report)
IINCLASSIEIED
21 NO. OF PAGES
68
20 SECURITY CLASS (This page!
UNCLASSIFIED
22. PRICE
2220-1 (Rev. 4-77) PREVIOUS E.CIT'CN SOBSOL.FTE
58
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