United States
Environmental Protection
Agency
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
EPA-600 3 79-002
January 1S79
Research and Development
xvEPA
Effects of Sulfuric
Acid Aerosols on
Vegetation
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.£
Protection Agency, have been grouped into nine series. These r
gories were established to facilitate further development and af
vironmental technology. Elimination of traditional grouping v\
planned to foster technology transfer and a maximum interface i
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 ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
cies, and materials. Problems are assessed for their long- and short-term influ-
ences. Investigations include formation, transport, and pathway studies to deter-
mine the fate of pollutants and their effects. This work provides the technical basis
for setting standards to minimize undesirable changes in living organisms in the
aquatic, terrestrial, and atmospheric environments.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/3-79-002
January 1979
EFFECTS OF SULFURIC ACID AEROSOLS ON VEGETATION
by
David S. Lang
Department of Plant Pathology
University of Minnesota
St. Paul, Minnesota 55108
Submitted by
S. V. Krupa
Principal Investigator
Air Pollution Laboratory
University of Minnesota
St. Paul, Minnesota
Grant No. R-804291
Project Officer
J. H. B. Garner
Health Effects Research Laboratory
Research Triangle Park, North Carolina 27711
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
HEALTH EFFECTS RESEARCH LABORATORY
RESEARCH TRIANGLE PARK, N.C. 27711
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DISCLAIMER
This report has been reviewed by the Health Effects Research
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 endorsement or recommendation for use.
ii
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FOREWORD
The many benefits of our modern, developing, industrial society are
accompanied by certain hazards. Careful assessment of the relative risk
of existing and new man-made environmental hazards is necessary for the
establishment of sound regulatory policy. These regulations serve to
enhance the quality of our environment in order to promote the public
health and welfare and the productive capacity of our Nation's population.
The Health Effects Research Laboratory, Research Triangle Park,
conducts a coordinated environmental health research program in toxicology,
epidemiology, and clinical studies using human volunteer subjects.
These studies address problems in air pollution, non-ionizing radiation,
environmental carcinogenesis and the toxicology of pesticides as well as
other chemical pollutants. The Laboratory participates in the develop-
ment and revision of air quality criteria documents on pollutants for
which national ambient air quality standards exist or are proposed,
provides the data for registration of new pesticides or proposed suspen-
sion of those already in use, conducts research on hazardous and toxic
materials, and is primarily responsible for providing the health basis
for non-ionizing radiation standards. Direct support to the regulatory
function of the Agency is provided in the form of expert testimony and
preparation of affidavits as well as expert advice to the Administrator
to assure the adequacy of health care and surveillance of persons having
suffered imminent and substantial endangerment of their health.
New technologies for controlling emissions of pollutants to the
atmosphere are always a welcome advance in the pursuit of a cleaner
environment through research. A thorough study of these new technologies
is in order, however, to assure that the net effect on public health is
beneficial. The Catalyst Research Program, in its investigation of the
automotive oxidation catalyst, provides a sound base upon which the EPA
can make a responsible assessment of the effect on public health of this
advanced emission control technology.
The following report assesses the effects of sulfuric acid aerosols
as generated by the catalysts on vegetation.
F. G. Hueter, Ph.D.
Director
Health Effects Research Laboratory
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ABSTRACT
A continuous flow system for exposing plants to submicron aerosols
of sulfuric acid has been developed and an operational model has been
constructed. Exposure chambers have been designed to allow simul-
taneous exposures of the same plant to aerosol and control environments.
All surfaces within the exposure system are composed of either Teflon
or stainless steel to minimize corrosion. Submicron acid aerosols are
mechanically generated and are distributed in size representative of
resident particulates found in the atmosphere. Plants have been found
to be injured by exposures to high concentrations of sulfuric acid
aerosol (100-200 ing/m^) for short times of 4-16 hours. Injury to
vegetation caused by sulfuric acid aerosol is similar to that caused
by gaseous fluoride and is characterized by marginal and tip necrosis
of foliage. This injury is distinctly different from that which .has
been attributed to acidic precipitation. Different plant species
vary greatly in sensitivity to sulfuric acid aerosol and injury to
sensitive species appears to be conditioned by biological as well as
physical factors. Results indicate that foliar sulfur accumulation
during exposure to sulfuric acid aerosol may be subject to substantial
temporal effects. The concentrations of sulfuric acid aerosol
required to produce acute vegetation effects are several orders of
magnitude higher than those, which have been reported for catalytic
emissions from automobiles. It is, therefore, unlikely that this new
source of atmospheric pollution will cause any significant acute
injury to vegetation. Potential problems associated with chronic
injury to vegetation from atmospheric sulfates remain unresolved.
iv
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TABLE OF CONTENTS
Page
ABSTRACT iv
TABLE OF CONTENTS v
LIST OF FIGURES viii
INTRODUCTION 1
SECTION I DESIGN AND CONSTRUCTION OF A SUBMICRON ACID
AEROSOL EXPOSURE SYSTEM FOR VEGETATION 6
GLASS HOUSE ENCLOSURE 6
1.1 Design and Construction 6
1.2 Heating and Cooling 6
1.3 Lighting ' 3
EXPOSURE CHAMBERS 8
2.1 Chamber Design and Construction g
2.2 Operation IQ
2.3 Flow Control 13
AEROSOL GENERATION 16
3.1 Equipment 15
3.2 Modifications 17
AEROSOL CHARACTERIZATION 18
J <•
4.1 Inertial Impact ion 18
4.2 Electrical Aerosol Analyzer 19
4.3 Mass Flow Calculations 22
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OPERATION OF EXPOSURE SYSTEM ....... 22
5.1 Design 22
5.2 Control and Measurement 24
5.3 Aerosol Removal 26
SECTION II. EFFECTS OF SULFURIC ACID AEROSOLS ON VEGETATION .... 27
MATERIALS AND METHODS 27
6.1 Growth and Maintenance of Plants^ 27
6.2 Growth Measurement: • 28
6.3 Sulfur Analysis 28
6.4 Scanning Electron Microscopy 28
6.5 Injury Evaluation 29
EXPOSURE CONDITIONS RELATED TO PLANT RESPONSE • • 29
7.1 Temperature : 30
7.2 Relative Humidity 30
7.3 A£e 30
7.4 Time - - • • 31
7.5 Light 31
7.6 Concentration 31
7.7 Stress 32
ACUTE PLANT RESPONSE TO SULFURIC ACID AEROSOLS • • 33
8.1 Macrosymptoms ,33
8.1-1 Bean 33
8.1-2 Poplar 34
8.1-3 Soybean 36
8.1-4 Ash and Birch 36
8.1-5 Corn and Wheat 36
vi
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JPa&iL
SUBTLE PLANT RESPONSES TO SULFURIC ACID AEROSOLS 38
9.1 Effect on Leaf Epidermis 38
9.2 Elemental Composition 42
9.3 Surface Particles 42
9.4 Changes in Foliar Sulfur Content 42
9.5 Change in Growth 49
9.6 Plant Reproductivity 49
AMMONIA NEUTRALIZATION OF SULFURIC ACID AEROSOL DURING
PLANT EXPOSURES 67
DISCUSSION 68
SUMMARY 76
LITERATURE CITED '78
vii
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LIST OF FIGURES
Page
Figure 1. Layout of greenhouse facility for exposing
plants to sulfuric acid aerosol 7
Figure 2. Temperature and relative humidity record
showing optimal environmental control in
greenhouse exposure faiclity 9
Figure 3. Construction detail of single exposure
chamber 11
Figures 4A and AB. Aerosol exposure chambers installed
in greenhouse 12
Figure 5. Mass flow nteasured through chamber vrithout
Teflon baffle . . . 14
Figure 6. Nass flow measured through chamber with Teflon
baffle installed 15
Figure 7. Typical aerosol size distribution in
exposure chamber ..... 20
Figure 8. Aerosol volume distribution measured
v/ithin exposure chambers 21
Figure 9. Flow chart showing logistic arrangnient
of components in system for exposing
vegetation f.o sulfuric acid aerosol 23
viii
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Page
Figure IDA. Humidifier equipped with stainless steel
plenum to provide moist air for maintaining
• chamber humidity. Figure 10B.. Inertial —
impactor inserted through port in chamber
for aerosol sampling 25
Figure 11A. Injury to trifoliolate leaf of pinto bean
caused by su.lfuric acid aerosol. Figure 11B.
Injury to primary leaf of pinto bean caused
by sulfuric acid aerosol 35
Figure 12A. Injury to soybean caused by exposure to sulfuric
acid aerosol. Figure 12B. Injury ta hybrid
poplar caused by exposure to sulfuric acid
aerosol 37
Figure 13;\. Injury to corn caused by exposure to sulfuric
acid aerosol. Figure 13B. Opposite branches
of hybrid poplar inserted through ports in control
chamber and aerosol chamber •"
Figure 14A. Scanning electron micrograph of non-exposed
leaf of pinto bean. Figure 14B. Scanning
electron micrograph of aerosol exposed leaf
of pinto bean ^0
Figure 15A. Scanning electron micrograph of healthy
stomate of pinto bean. Figure 1511. Scanning
electron micrograph of stomate exposed to
sulfuric acid aerosol 41
Ix
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Pagj!
Figure 16A. Scanning electron micrograph of leaf
surface of healthy pinto bean. Figure l&B.
Scanning electron micrograph of leaf
surface of pinto bean exposed to sulfuric
acid aerosol. Figure 16C. X-ray
microanalysis spectra of leaf surfaces of
pinto bean 43
Figure 17A. Cross section of pinto bean leaf exposed to
sulfuric acid aerosol. Figure 17B. X-ray
microanalysis spectra of leaf shown in 17A . . . ^
Figure ISA. Scanning electron micrograph of 5 um
particle found on surface cf leaf exposed
to sulfuric acid aerosol.
Figure 18B. X-ray microanalysis spectra
45
of particle shown in ISA . .
Figure 19. X-ray microanalysis spectra of particle!
found on surface of leaf exposed to sulfuric
acid aerosol ^6
Figure 20. Foliar sulfur accumulation in Bountiful bean ... 50
Figure 21. Foliar sulfur accumulation in soybean 51
Figure 22. Foliar sulfur accumulation in hybrid poplar ... 52
Figure 23. Foliar sulfur accumulation in green ash 53
Figure 24. Foliar sulfur accumulation in pinto bean 54
Figure 25. Sulfur accumulation in 7 clay old pinto bean
plants exposed to 250 mg/r.i sulfuric acid
aerosol for 3 hours 55
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Page
Figure 26. Sulfur accumulation in 9 day old pinto
bean plants exposed to 250 ing/m sulfuric
acid aerosol for 8 hours wiien 7 days old and
250 mg/m sulfuric acid aerosol for 8 hours
when 9 days old 56
Figure 27. Sulfur accumulation in 11 day old pinto bean
plants exposed to 250 mg/m sulfuric acid
aerosol for 8 hours when 7, 9 and 11 days old . . .
Figure. 23. Sulfur accumulation in 16 clay old pinto bean
•)
plants exposed to 175 mg/m" sulfuric acid
CO
aerosol for 7 hours
Figure 29. Sulfur accumulation in 26 day old pinto bean
plants exposed to 175 rag/nr sulfuric acid
cq
aerosol for 7 hours
Figure 30. Sulfur accumulation in 19 day old pinto bean
plants exposed to 175 mg/m sulfuric acid
aerosol for 5 hours
Figure 3.1. Sulfur accumulation in A3 day old pinto bean
plants exposed to 175 mg/m sulfuric acid aerosol
for 5 hours 61
Figure 32. Sulfur accumulation in pinto bean plants exposed
•} /-o
to 175 nig/nT sulfuric acid aerosol for 8 hours . .
Figure 33. Sulfur accumulation in pinto bean plants exposed
i r*\
to 390 m.'>,/nj sulfuric acid aerosol for 12 hours . .
xi
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Page
Figure 34. Relationship between growth and initial leaf
area of exposed and non-exposed trifoliolate
leaves of pinto bean 64
Figure 35. Growth of trifoliolate leaves of pinto bean
plants with similar initial leaf areas
exposed and not exposed to sulfuric acid
aerosol 65
figure 36. Sequential growth of primary leaves of pinto
bean plants at two week intervals exposed and
not exposed Co sulfuric acid aerosol
xii
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INTRODUCTION
Within the past 25 years much research has been directed toward
the study of abiotic diseases of plants. A substantial portion of
this research has been specifically concerned with air pollution and
its effect on vegetation. Although vegetation injury associated
with exposure to air pollution has been known since the nineteenth
century, carefully conducted studies which relate plant response to
defined experimental conditions have been relatively recent innovations
(20).
Scientists have discovered that plants are generally more
sensitive than animals to air pollution injury. It has also been
well documented that environmental conditions prior to, during, and
after exposure play an important, if not a critical role in determining
air pollutant injury to plants (31). Individual plant species have
been found to show significant variations in their sensitivity to air
pollutant injury, suggesting the possibility for genetic selections
tolerant to pollutant stress (31).
Using the information gathered in recent years governmental
regulatory agencies have been able to establish standards for pollutant
doses which will cause injury to vegetation and develop appropriate
control policies.
Specific air pollutants vary greatly in their relative effect
on vegetation. Relative effect of a particular pollutant is a
1
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function of three major parameters: chemical composition, concentration,
and duration of exposure. Of these, chemical composition and concen-
tration relations arc well defined for many specific pollutants.
Duration of exposure and its relative contribution related to varied
concentrations of individual pollutants is also well known for short
term or acute exposures of most major pollutants (17). However,
relatively little is known concerning the effect of complex pollutant
mixtures which regularly occur at low concentrations for extended
periods of time in the ambient environment (chronic exposures) (23).
As indicated, much work remains to be done in elucidating
traditional pollutant-plant interactions. Additionally, continual
revaluation and redefinition of previous studies relating to biological
effects is necessary to incorporate technological advancements in pol-
lutant characterization. Such a need has arisen from recent advance-
ments made in the understanding of atmospheric aerosols and their
relative contribution to total pollution effects on ecosystems (9).
The studies described in this thesis relate to a particular form
of aerosol pollution resulting from the oxidation of elemental sulfur
in fossil fuels during combustion processes. This research was
sponsored by a grant from the United States Environmental Protection
Agency Catalyst Research Program. Research sponsored under this
program was specifically concerned with the characterization and
definition of biological effects of sulfuric acid aerosol emissions
from automobiles equipped with catalytic converters (18). It has been
known for some time that elemental sulfur in fuel is oxidized
relatively more efficiently in catalyst equipped cars (.11). The
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SO-j ultimately formed reacts immediately with ambient water vapor
to form fine particles of concentrated sulfuric acid (6,30,33).
Sulfuric acid aerosol is highly reactive and may be neutralized by
ammonia or combine with metallic oxides to form salts (Charleston).
It is also produced via photo-oxidation of SC^ in the presence of
oxygen and nitrogen. This aerosol ranges in size from a few thou-
sandths of a micron to about 1 micron in diameter (32). Most of
these aerosols are respirable by animals and may be easily incorporated
in the. gaseous exchange processes of vegetation. The purpose of this
study was to define the relative effect of sulfuric acid aerosols on
vegetation.
Previous reports of laboratory and field studies on particulate-
induced vegetation injury have been primarily limited to the exposure
of plants to very large particles (13). Most of these studies have
dealt with specific kinds of dusts as they pertain to local field
problems (24). Few studies have been undertaken to determine the
effects of acid mists on vegetation. Where such studies have been
reported, the symptoms produced have resembled those expected if
small droplets of sulfuric acid were deposited on the leaf surfaces,
i.e., small necrotic pits scattered more or less uniformly over the
leaf surface rather than in specific patterns as are caused by sulfur
dioxide (8,26). According to Thomas (29) when leaves were exposed
to acid mist no injury occurred if the particles were smaller than
1 micron in diameter. Larger particles settled on the leaf but did
not wet dry surfaces. It was only whan the leaf surface was wet and
the droplets spread out that characteristic markings were developed.
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Thomas (29) stated that injury due to sulfuric acid mist has never
been observed in the field. However, Middleton ejt al. (20) reported
symptoms, which resembled those caused by acid mist, on vegetation
in the Los Angeles area.
Recent work in aerosol physics and atmospheric chemistry has
cast considerable doubt upon the credibility of past studies,
(which did not consider the specific effect of particle size).
Atmospheric particulars have been shown to exist in three modes
ranging from .015 to 30 micron particle size (34). Most particulate
sulfate is thought to be associated with the accumulation mode
(0.15 to 0.5 microns) since the other modes exist only transient
species (34). Questions concerning fine particulate sulfates have
not been considered in previous studies relating to vegetation effects
and have only recently (largely after 1970) been studied in relation
to animal effects.
Two objectives have been addressed in this study: (1) to design
and construct a system for exposing vegetation to fine acid aerosols
and (2) to define the effects of submicron sulfuric acid aerosols
on several diverse species of vegetation.
The acid aerosol-vegetation exposure system was designed to meet
two important criteria: (1) simultaneous exposure of different branches
of the same plant to aerosol and control environments and (2) genera-
tion and distribution of submicron sulfuric acid aerosol within a
closed exposure system essentially inert to the corrosive effects of
concentrated sulfuric acid. Simultaneous exposure of the same plant
to aerosol and control environments is an important criterion when
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one considers the significant variation in injury which can occur
between plants of the same species in response to pollutant stress
(31). In order that plant response in these controlled exposures be
comparable to the ambient environment it was necessary to insure that
a large amount of the aerosol produced be submicron in size.
We feel the approaches described here have the facility of being
applied toward the study of general aerosol problems. Altshuller (1)
and others have reported on the origin and transport of sulfate
aerosols and it is likely that the effects of long term chemical
loading of remote environments by atmospheric pollutants will become
an area of significant concern in the future. Whitby and others have
studied long distance pollutant transport mechanisms and conclude that
much of the transport occurs in the form of aerosol ranging in size
from 0.01 to 2 pm in diameter (34). Ultimately, the aerosol is carried
to the earth's surface by wet and dry deposition processes. It is hoped
that the application of the exposure system developed in the present
study could prove valuable in many studies relating to the effects of
aerosols on vegetation.
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SECTION I
DESIGN AND CONSTRUCTION OF A SUBMICRON ACID AEROSOL
EXPOSURE SYSTEM FOR VEGETATION
1. GLASS HOUSE ENCLOSURE
1.1 Design and Construction
f\
An aerosol exposure facility was developed in a 40 mz enclosed ,
space of a greenhouse. This area was located in the northwest corner
to allow natural lighting from 'the west, north and top. The south and
east faces were isolated from the rest of the greenhouse by constructing
a temporary wall of 5 cm by 10 cm wood supports spaced on .6 m centers
with 7.6 cm thick styrofoam panels. This design served to minimize .
solar radiation loading during the summer months, allow independent
heating and cooling, and isolate the area from normal greenhouse
particulate contaminants, insects and biotic pathogens. The principal
advantages of this location were the opportunity to use natural
photoperiods and provision of similar environments for plant growth
and exposure. The completed facility provided housing for two green-
house benches, six exposure chambers, space for instrument storage and
counter top work surface. Figure 1 shows the layout of this facility.
1.2 Heating and Cooling
Specific heating and cooling capacity was found to be necessary
to minimize daily cyclic temperature and humidity variation. Separate
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INSULATED WALL
GREEN
HOUSE
BENCH
NEUTRALIZATION
CHAMBER
GREEN
HOUSE
BENCH
CONTROL
CHAMBER
AEROSOL
CHAMBER
CONTROL
CHAMBER
Q Q <> Q Q-
CONTROL CEN-
TER LIGHTS.
HEAT. COOL
CONTROL
CHAMBER
AEROSOL
CHAMBER
CONTROL
CHAMBER
AIR
CONDITIONER
HUMID-
IFIER
DRY
AIR
SOURCE
PP-O
\^/
AMMONIA
"SOURCE
AIR
COM-
PRESSOR
DL
EXH.
FAN
G
L
A
S
S
AEROSOL
GENERATOR
VARIABLE
RHEOSTAT
CONSTANT
FLOW AIR — 1
SAMPLER 1
*
ELECTRI
CAL SIZE
ANALY-
SER
GLASS
Figure 1. Layout of greenhouse facility for exposing plants to sulfuric
acid aerosol.
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steam heat controls, and a 4284 kg-c.al electric heater, coupled
with 6300 kg-cal air conditioner controlled by a centrally located
thermostat substantially reduced temperature and humidity variations.
Figure 2 shows optimal temperature and relative humidity control
achieved during fall and winter months. It was not possible to
maintain this degree of control during the summer months on days
when solar heat loading exceeded the cooling capacity of the air
conditioner. However, it was possible under most conditions to
maintain the daily temperature variation within +2° c.
1.3 Lighting
Fluorescent and ultraviolet enhancing fluorescent lamps controlled
by a timer switch maintained standard 16-hour photoperiods. Although
some plant species appeared to grow normally without supplementary
lighting, bean and soybean showed marked etiolation for all but a few
months of the year unless additional lighting was provided.
2. EXPOSURE CHAMBERS
2.1 Chamber Design and Construction
Original plans called for an all-glass exposure system to provide
an inert environment which would minimize the corrosive effects of
H^SO, and potential release of unknown substances which might have
complicated the assessment of vegetation effects. However, there
were some objections to the use of glass:
1) Cost increases involved made the system prohibitive
2) Delivery times on special order glass would have prevented
meeting the proposed schedule of investigation
3) One of the external reviewers of our research proposal
8
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TUESDAY WEDNESDAY THURSDAY FRIDAY SATURDAY SUNDAY
-6
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suggested that Teflon be used instead of glass.
For these reasons we designed a system consisting of clear
acrylic plastic support tubes 0.30 meters in diameter and 1.20
meters in length. The interior was lined with clear Teflon film
(0.076 mm thick) held in place by circumferential stainless steel
bands placed 0.20 meters apart through the length of each tube.
Each tube was fitted with machined Teflon ports 6.4 cm in diameter
through which plant branches could be inserted. Ports were machined
to match the internal radius of the tube and to project through the
tube. This provided a tight fitting at each port. Expanded poly-
ethylene foam plugs were slit to accommodate the plant branch and
covered with Teflon film on the interior surface. This allowed
branches to be "plugged" into the exposure chamber and maintained a
secure fitting between the plant and the chamber. A single exposure
chamber system is shown in Figure 3.
2.2 Operation
Figures 4A and B show several chambers arranged
for vegetation exposure. This system was efficient in that it allowed
two opposite branches of the same plant to be simultaneously but
separately exposed to the aerosol and the control environments.
In operation, each chamber was maintained under a slightly negative
pressure (.25 cm HOH) to prevent the escape of aerosol into the
ambient air. An exhaust blower, was connected via 5 cm diameter tubing
to each chamber. Exhaust aerosol was passed through a cylinder
(about cne meter in length and .15 meter in diameter) filled with
limestone chips to neutralize the sulfuric acid.
10
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VEGETATION EXPOSURE CHAMBER
Plug Diameter
6.4cm
Tellon
BJllle
Figure 3. Construction detail of single exposure chamber.
11
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Figures 4A and 4B. Aerosol exposure chambers installed
in greenhouse.
12
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Mass flov; in this system was balanced with a series of flow
meters, valves and a variable transformer connected to an exhaust
blower to control flow rates.
2.3 Flow Control
Initial exposures of vegetation to l^SO^ aerosol suggested
the presence of static areas within the chambers. Varied aerosol
concentrations were reflected by localized injury to vegetation in
certain chamber positions. Baffles were developed to improve turbu-
lent mixing within the chambers. The baffles were constructed of
Teflon sheet material 3 nun thick. Square Teflon stock 1.2 cm was
cut to 4 cm lengths and attached to circular sheet pieces 23 cm in
diameter at 90 degree intervals. Holes were drilled in the ends of
the square support brackets and fitted with a stainless steel spring
which was compressed with a Teflon piston made from A mm diameter
rod stock. The baffle assembly was then positioned in the chamber
approximately 15 cm from the aerosol inlet. This design facilitated
baffle removal during chamber cleaning and introduction of plants
into the chamber. The baffles improved mixing, as indexed by reduced
variation in symptoms. The relationship between mass flow within the
exposure system and pressure drop monitored in the chambers was also
improved with baffles.
Figures 5 and 6 show the relationship between velocity, pressure
drop and mass flow in chambers with and without baffles. Each point
represents the average of five velocity measurements at each location.
The similar curves shown in Figure 6 suggest a more accurate prediction
o£ mass flov; than those of Figure 5. .These curves were fitted to
4th order equations to provide exact fits of the observed data points.
13
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VELOCITY (cm/min)
120
110
100
90
•| 80
| 70
§ 60
o 50
u_
40
30
20
10
0
2182 3374
4319
5120
85.3 91.4
137
167
30 cm duct
5 cm duct
.25 .50 .75 1.0
PRESSURE DROP (cm/HOH)
Figure 5. Mass flow measured through chamber
without Teflon baffle.
14
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VELOCITY (cm/min)
•i 70-
tSI
« 60-
.25 .50 .75
PRESSURE DROP (cm HOH)
35.05
1.0
Figure 6. Mass flow measured through chamber
with Teflon baffle installed.
15
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The equations are as follows:
Chamber w/o baffle
5 cm duct
F = 250.6 P - 377.7 P2 + 370.7 P3 - 139.7 P4
30 cm duct
F = 587.4 P - 2010 P2 + 2851 P3 - 1300 P4
Chamber with baffle
5 cm duct
F = 107.9 P + 108.4 P2 - 458.7 P3 + 313.6 P4
30 cm duct
F = 311.5 P - 720.9 P2 + 705.6 P3 - 216.5 P4
Mass flow was calculated as the average of the two values
determined from the 5 and 30 cm ducts for the chamber with baffle
at a given pressure drop.
3. AEROSOL GENERATION
3.1 Equipment
Several methods were investigated for producing .submicron aerosols
of concentrated sulfuric acid. These included stabilized volatili-
zation of liquid sulfur trioxide and various types of aerosol
generators. The stabilized liquid SO volatilization, although widely
used, was not chosen for this project for three reasons. These were:
1) High output of H SO aerosol was not required in our
system
2) Liquid SOo is a hazardous material requiring elaborate
safety precautions
3) The costs incurred in meeting objective 2 could not be
satisfied by our current funding
16
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A specialized aerosol generator was therefore selected which met
our criteria for producing a substantial amount of particulate mass
in the submicron range while providing sufficient aerosol concentration.
The aerosol generator we used is commercially available (ERG
model 7330) and utilizes a three-stage system to produce the submicron
aerosol. A collison type nebulizer (19) produces a fine aerosol by
directing an atomization jet against a baffle, the finer aerosol
particles are carried by upxv-ard air flow to an inertial impaction
stage which removes particles larger than one micron, submicron
particles are then carried through a Krypton 85 charge neutralization
unit and into the exposure chamber., The generator is driven by
n
compressed dry air at 3.2 kg/cm . Inertial size separation and charge
neutralization minimize problems of condensation and liquid retention
in the aerosol space beyond the generator (7).
3.2 Modifications
Problems have been encountered with this system. Corrosion of
stainless steel components prior to the impaction stage of the generator
occurs if the system is not cleaned immediately after use. This is
due probably to the reaction of the acid aerosol with ambient humidity
resulting in a more dilute but more reactive sulfuric acid film on the
stainless steel surfaces. Careful monitoring of the system pressure
and the subsequent flow rates is required to assure experimental
reproducibility.
After a period of use it was determined necessary to replace the
stainless steel collison nebulizer portion of the generator.
Critical orifices in the stainless steel nebulizer were susceptible
17
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to corrosion by sulfuric acid. Aerosol distributions were shifted
to larger size particles. This was probably due to decreased jet
velocities through the larger corroded orifices and subsequent
decrease, in impaction efficiency on the nebulizer baffle.
A Teflon nebulizer was built to specifications similar to those
of the stainless steel unit. The Teflon nebulizer performed well
apart from construction problems associated with machining Teflon
to close tolerances. No significant change in aerosol size distribu-
tion was observed after prolonged use of the Teflon nebulizer.
This modification is necessary for use of this type of generator in
long term and/or intermittent HoSO^ aerosol production.
Most corrosion problems were associated with the nebulizer and
impaction stages of this generator. Fine particles passing through
the impactor produced very little corrosion. The neutralization stage
also mitigated corrosive affects by decreasing surface deposition and
particle agglomeration (15). There was no visible corrosion of
stainless steel components beyond the aerosol generator.
4. AEROSOL CHARACTERIZATION
4.1 Inertial Impaction
Several methods were used to define the character of the exposure
chamber aerosol. The principal method employed a seven stage
rectangular jet impactor operated at 20 liters per minute. Glass
fiber impaction surfaces were weighed immediately prior to sampling,
the impactor was assembled and placed in an insulated box before and
after use. Impaction discs were then reweighed and the percentage
mass collected per stage was plotted versus equivalent aerodynamic
18
-------
diameter on log-probability paper.. Figure 7 shows typical aerosol
size distributions for the two aerosol chambers. Note that these
aerosol distributions are similar with mass mean diameters of
0.64 ym - 0.56 ym and standard geometric deviations of 1.72 - 1.70.
These values are comparable to ambient sulfate aerosols. Figure 8
shows a typical particle volume distribution, the shaded area was
estimated based on actual values shown by the vertical bars. When
SOo is introduced into the atmosphere and undergoes reaction with
ambient water vapor the l^SO^ particles formed grow and transition
from the nuclei to accumulation size modes occurs (5,32). jt ^s
reasonable to assume that particles in the accumulation mode (0.15 to
.5 vim diameter) will have the principal long range effect on vegetation
because of their residence time in the atmosphere. This is especially
pertinent when effects on remote environments are considered.
4.2 Electrical Aerosol Analyzer
A significant amount (about 25 percent) of the aerosol mass
produced by the aerosol generator was found to be below conventional
inertial impaction limits. Further characterization, therefore,
required the application of another device to assay these particles
(14). An electrical aerosol analyzer (EAA) was used to classify
fine particles from 0.02 to 1 urn in diameter (16). However, a problem
was encountered in using the EAA unit in the direct measurement of
chamber aerosol. At concentrations above about 5 mg/m^ the electro-
meter filter of the EAA became saturated and inoperative.
o
Concentrations greater than 5 mg/m were needed to induce acute
injury to vegetation. This problem necessitated the dilution of
19
-------
o
in
g
t:
10
20
30
40
50
60
70
80-
90
95
99
99.9-
AEROSOL /
CHAMBER 1A -. /
HMD = .64
og = 1.72
'
AEROSOL
CHAMBER 2A
MMD = .56
og = 1.70
/
/
/
/
/
/
/, L
10.0
1.0
.64 .56
EQUIVALENT AERODYNAMIC DIAMETER
Dp 50 Microns
.3
Figure 7. Typical aerosol size distribution
in exposure chambers.
20
-------
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1 iiiii
i i i 1 1 i
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1 1 1 1 1 1 1 1 1 1 1 1
80
70
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40 a
•o O
w
30
20 xw
o
10 °*
•3 -4 5 6 -8 I
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PARTICLE DIAMETER (microns)
Figure 8. Aerosol volume distribution measured within exposure
chambers.
-------
chamber aerosol prior to EAA characterization. Dilution introduced
a potentially significant variable. This problem is not expected to
occur during chronic exposures at concentrations of less than 100 ug/m
which could be monitored continuously and directed with the EAA.
4.3 Mass Flow Calculations
Aerosol mass per volume was calculated by measuring H^SO* mass
used and relating it to total air flow. It was necessary to make
HoSO^ mass measurement using gravinimetric procedures. Total I^SO^
mass per volume could be calculated on this basis and then compared
with that determined by summation of the masses on the impactor
stages. Significant quantities of ^SO^ were retained as thin films
on the aerosol generator components prior to the charge neutralizer
and could not be reproducibly recovered for volumetric assay.
5. OPERATION OF EXPOSURE SYSTEM
5.1 Design
Figure 9 shows the logistic arrangement of components in the
vegetation exposure system. Only two chambers are shown in this
diagram. In the actual system there were two aerosol chambers and
four control chambers connected in parallel in each position. This
may be visualized better in Figure 1. There are five processes
shown in Figure 9. These relate to aerosol generation, flow
amendment, flow control, flow measurement and aerosol removal.
Details of our aerosol generation methods have been discussed
in the previous section. Concentrated reagent grade sulfuric acid
was weighed' and placed in the nebulizer. Compressed dry air at 3.2 kg/
2 2
cm was used to drive the generator at 2.5 kg/cm . The aerosol was
22
-------
AEROSOL EXPOSURE SYSTEM FLOW CHART
COMPRESSED
DRY AIR
f \COMPRESSED
V. /AMMONIA
VELOCITY PORT
FLOVVVALVE
••p- VELOCITY PORT
FLOW VALVE
EXHAUST TO ATMOSPHERE
Figure 9. Flow chart showing logistic arrangement
of components in system for exposing vegetation to
sulfuric acid aerosol.
23
-------
carried to the chambers through 1.25 cm Teflon tubing.
Chamber aerosol was amended with either water vapor or ammonia
via a separate delivery system. Water saturated moist air was
evacuated from a stainless steel plenum attached to a commercial
humidifier and delivered to a distribution manifold. Figure 10A
shows the modified humidifier. Ammonia was also delivered to the
same distribution manifold, from a combination regulator - flow meter
attached to a compressed ammonia source. The distribution manifold
was connected to individual flow meters attached to each chamber.
5.2 Control and Measurement
Flow through the chambers was maintained by introducing the
aerosol and amendments under a slight positive pressure. Flexible
exhaust hoses were attached to the chambers by a short piece of
stainless steel pipe fitted with a butterfly type valve and a 64 cm
port through which an air velocity probe may be inserted. An exhaust
blower was attached to the exhaust hoses and regulated with a variable
power supply. Each chamber was fitted with a pressure drop gauge.
Individual chamber pressures were balanced by the variable speed
control and the butterfly valves in the exhaust lines. As discussed
in section 2.3 chamber pressure drop could then be correlated with
total mass flow.
Chamber aerosols were measured by inserting either the irapactor
(Figure 10B) or the sampling tube (EAA) through ports fitted to the
chambers, as discussed in section 2.2. Problems with simultaneous
characterization using inertial impaction and EAA were discussed
previously. Flow in the chambers was measured by inserting a hot wire
24
-------
ro
Figure IDA. Humidifier equipped with
stainless steel plenum to provide moist
air for maintaining chamber humidity.
Figure 10B. Inertial impactor in-
serted through port in chamber for
aerosol sampling.
-------
probe through ports in the chamber and through the exhaust control
valve and integrating the values obtained. Humidity within the system
was measured using an aspirated wet and dry bulb psychrometer. Room
humidity was monitored with a conventional hydrothermograph. A
thermocouple psychrometer was tested for use in this system but probe
design and calibration have not yet been perfected. The psychrometer has
twelve individual channels and has the advantage of providing a near
continuous record of humidity with the system. The principal
disadvantages are the limited humidity range where operation is pos-
sible and complications caused by air flow around the sensors.
5.3 Aerosol Removal
Aerosols were removed from the exposure chambers by exhausting
them through a stainless steel cylinder 100 cm by 15 cm filled with
limestone chips. This unit effectively removed aerosols and did not
introduce a large pressure drop in the aerosol exhaust line. Control
and aerosol exhaust lines were connected together after the limestone
filter and the filtered air was exhausted outside the greenhouse.
26
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SECTION II
EFFECTS OF SUBMICRON SULFURIC ACID AEROSOLS ON VEGETATION
6. MATERIALS AND METHODS
The principal materials and methods relating to this research
were covered in the preceding part of this thesis. These concerned
generation, distribution and characterization of the sulfuric acid
aerosols. Only those aspects relating to plant growth and study
will be considered here.
6.1 Growth and Maintenance of Plants
Plants were grown in steamed or unstearned soil mixtures con-
sisting of two parts soil and one part sand volume per volume. Most
plants were grown from seed in 10 cm square plastic pots with five
seeds per pot. After emergence plants were thinned to three plants
per pot removing nonuniform individuals. New foliage production was
forced on woody species by removal of old foliage, root pruning and
transplanting. Some woody species were regenerated by rooting stem
cuttings. When this was not possible plants were exposed only once
or as often as new foliage naturally developed.
Natural greenhouse lighting was supplemented with conventional
and ultraviolet-enhanced fluorescent lamps. Photoperiods were
maintained at 16 hours during the fall and winter. Plants were
placed in chambers and covered with black plastic to evaluate the
27
-------
effect of dark conditioning prior to exposure. During the summer, the
entire greenhouse was shaded by applying a 50% spray coating of white
shading compound to minimize solar heat loading.
6.2 Growth Measurement
Changes in plant growth after exposure were measured by carefully
placing individual leaves in a specially designed glass frame upon
which they could be traced. The same leaves were again traced after
varied growth periods. The respective changes in growth were then
quantified by measuring the area of the tracings using an area
integrating digitizer. This procedure is non-destructive and allows
the development of a continual growth record of individual leaves.
6.3 Sulfur Analysis
Foliar sulfur analyses were done by the Research Analytical
Laboratory at the University of Minnesota. Bulk foliage samples,
0.5 to 5 g fresh weight basis, were collected from paired areas of
individual chambers. Samples were air dried, ground and analyzed
using a nitric/perchloric acid digestion - barium chloride precipita-
tion procedure. Reproducibility is in the range of 10 to 15 percent
for this method. Results are reported as parts per million total
sulfur.
6.4 Scanning Electron Microscopy
Foliar samples were, also examined with a scanning electron
microscope. Leaf tissue was excised from healthy areas of control
plants and asymptomatic and necrotic areas of exposed plants.
Specimens were fixed in 5 percent glutaraldehyde and stored at 4°C for
72 hours. This was followed by 2-hour sequential dehydrations in
25, 50, 75 and 100 percent ethanol. Tissue was then dried using a
28
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critical point drier, sectioned and mounted in a silver mounting
compound. Mounts were then separated and those not intended for
X-ray analysis were gold coated. X-ray emission spectra were
obtained for those elements with greater atomic mass than sodium.
6.5 Injury Evaluation
Plants were rated according to the following scale, corresponding
to visible injury induced by sulfuric acid aerosol:
0 - no visible injury
1 - less than 1 percent necrotic leaf tissue
2 - less than 10 percent necrotic leaf tissue
3 - greater than 25 percent necrotic leaf tissue
Injury was determined from 24 to 48 hours after the exposure, when
the necrotic areas were clearly defined. Ratings were assigned
based on a qualitative evaluation of all exposed foliage.
7. EXPOSURE CONDITIONS RELATED TO PLAIT! RESPONSE
The principal objective of this research effort was to compare
the effects of sulfuric acid aerosols on several diverse plant species
under uniform exposure conditions. Additionally, temperature, relative
humidity, age and pollutant concentration were examined as variables in
relation to the response of specific species. Plant response was
evaluated both qualitatively and quantitatively. The quantitative
data is presented in the section dealing with sulfur accumulation.
Qualitative observations regarding the influence of traditional factors
affecting pollutant-plant interactions are discussed here. The objective
of this section is to indicate that there are presently unknown factors
involved in determining plant response to sulfuric acid aerosol and
29
-------
that traditional conditioning factors are not principally involved.
Detailed data regarding visible injury is not presented because
it was found to be highly variable and may be misleading. The
following comments are subjective evaluations based on at least 100
observations per factor. Rationale for varied response to sulfate
is discussed in a later section.
7.1 Temperature
Plants were exposed at temperatures ranging from 15° to 26°C.
Most exposures were conducted at 22 H- 2°C. Within this temperature
range there was no significant effect on symptom expression. Injury
to pinto bean ranged from less than 1 percent to greater than 25 per-
cent necrosis of exposed foliage. Similar plant responses with other
species were obtained over this temperature range with some mitigation
J
of symptom expression observed at the higher temperatures.
7.2 Relative Humidity
Most exposures were made at humidities, between 40 and 60 percent.
Symptom expression was essentially uniform within this range. Extreme
humidity changes altered responses. When conditions approached
saturation and free water condensed as droplets on the plant surface,
necrotic islands appeared at the point of droplet contact. Low
humidities which induced plant stress, possibly in conjunction with an
overall moisture deficit, reduced symptom development.
7.3 Age
Plant species examined did not appear to be significantly altered
in sensitivity with increased age. Injury to pinto bean expressed as
necrotic areas of exposed foliage ranged from less than 1 percent for
11 and 21 day old plants to greater than 25 percent for 12 day old
30
-------
plants. Seedlings of several species ranging in age from 1 to 8
weeks showed similar genotypic differences without apparent age
differences. However, pinto bean plants exposed at the time of
flowering showed somewhat more extensive injury than was observed on
younger plants. Primary leaves were generally more sensitive to
injury than were the trifoliolate leaves.
7.4 Time
Degree of symptom development and duration of exposure were not
well defined. Injury to pinto bean varied from less than 1 percent
to greater than 25 percent necrosis of exposed foliage during 4 hour
exposures. Injury appeared to reach a maximum for a given species
after a threshold time had been exceeded and then remained relatively
unchanged for the duration of the exposure. This critical time varied
between 2 and 8 hours. When injury occurred symptoms of water soaking
were often evident during exposure and necrosis was apparent 16 to 24
hours after exposure.
7.5 Light
Light and dark conditioning prior to exposure was not extensively
investigated. When plants were kept in the dark for 12 to 24 hours
and then exposed, after one hour in light, symptoms were similar to
a normal night-day regime. Plants were not exposed in complete
darkness. The lack of response to light may be due to the controlling
influence of a stable interstomatal CO^ concentration which was not
evaluated (22).
7 .6 Concentration
Throughout this study an attempt was made to correlate macro-
31
-------
symptom expression with the level of the factor inducing the
response. We have found that concentrations of sulfuric acid
3
aerosols below 10 mg/m will not induce injury during short term
(up to 12 hours) exposure in the species examined. Therefore, most
exposures were made at concentrations of about one order of magnitude
greater than this to characterize species sensitivity. A threshold
O
response for most species apparently occurs betxveen 10 and 100 mg/m
beyond which acute injury develops. Extremely high concentrations
3
of 300 mg/m induced necrosis which ranged from less than 1 percent
to greater than 25 percent of exposed pinto bean foliage. Much
additional work remains to be done to investigate chronic exposures
which would be analogous to the ambient environment. These studies
can only follox* the characterization of subtle plant responses which
can be substituted for visible symptoms.
7.7 Stress
Significant changes in plant metabolic and physiologic character
are known to occur which are non-specific responses to stress (25).
Responses xvhich mitigated symptom expression were observed during the
course of these studies. Specific studies to evaluate the effect of
stressing plants prior to exposure were not done. However, it was
noted that several factors could alter plant response if applied
before exposure. High temperatures, insecticide application,
attack by biotic pathogens, and moisture deficits appeared to reduce
injury from sulfuric acid aerosol.
32
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8. ACUTE PLANT RESPONSE TO SULFURIC ACID AEROSOL ON SELECTED SPECIES
8.1 Macrosymptoms
Previous reports of acid injury to vegetation have described
localized necrosis x^hich occurred at the point of droplet contact.
Symptoms of this type were induced by large diameter droplets of
acidic solutions deposited as rain or mist. The submicron acid
aerosols used in this study are 2 to 3 orders of magnitude smaller
than those previously reported and cause distinctly different
symptoms.
Acute exposure to submicron sulfuric acid aerosols causes a
marginal and tip necrosis of foliage which is similar to that caused
by gaseous fluoride (see Figures 11A-13A). All plant species studied
have shown a similar response which varies only in degree depending
upon sensitivity. Extent of injury has varied between 0 and 50 percent
necrosis of exposed foliage dependent upon exposure conditions and
species of plant.
The onset of symptoms caused by acute exposure to sulfuric acid
aerosol is relatively rapid. Water soaking is often apparent during
o
four hour exposures to concentrations of 100 mg/m . Necrosis of leaf
tips and margins is apparent after 12 to 16 hours and well defined
after 24 to 36 hours. The following susceptibility classification is
;
based on 8 hour exposures to sulfuric acid aerosol concentrations of
2
100 mg/m . Species are listed in order of decreasing sensitivity.
8.1-1 Bean-
Pinto bean (PhasGolus vulgaris L.) was the most studied and is one
of the bean cultivars most sensitive to injury when exposed to
33
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sulfuric acid aerosol. Bountiful bean was equally sensitive to this
pollutant. Both of these plants developed more severe symptoms
and showed injury earlier than other species exposed at the same
time. Navy bean was also found sensitive but to a lesser degree
than the other two bean cultivars. Injury to bean typically ranged
from 5 to 25 percent of the exposed foliage depending on exposure
conditions. Symptoms appeared first at the leaf edges and spread
inward. The primary leaves of bean were somewhat more sensitive
than were the trifoliolate leaves. However, symptoms were usually
apparent on most of the exposed foliage with most rapidly expanding
leaves showing the greatest degree of injury. Figures 11A and B
show trifoliolate leaves of pinto bean with symptoms typical of
sulfuric acid aerosol injury.
8..1-2 Poplar—
Hybrid poplar (Populus detoides Marsh, var.) was found more
sensitive than the other deciduous species to sulfuric acid aerosol
injury. The response of hybrid poplar varied from sensitive when
first exposed at midseason to moderately resistant after a second
flush of foliage was forced during midwinter. It is difficult to
attribute this change in response to any particular factor at this
time. There are several problems associated with the definition of
reproducible experimental methods for perennial plants. Forced
foliage production may also induce substantial physiological changes
which could be confounded by seasonal alterations. This rationale
makes the winter data questionable and we consider the sensitive
classification of tiiis species, based upon midsummer data, valid.
34
-------
Figure 11A. Injury to trifoliolate leaf of pinto bean
caused by sulfuric acid aerosol. Note: marginal and
tip necrosis.
Figure 11B. Injury to primary leaf of pinto bean caused
by sulfuric acid aerosol. Note: veinal necrosis near
leaf margin.
35
-------
Typical injury to hybrid poplar is shown in Figure 123.
8.1-3 Soybean-
Soybean (Glycine max [L.] Merr.) was found to be moderately
resistant to sulfuric acid aerosol injury. Some difference in
response among soybean cultivars was observed but all were more
resistant than was bean. In addition to necrosis of leaf tips and
margins, exposed soybeans of the cultivar Hodgson developed a cupped
leaf character somewhat resembling herbicide injury. Soybean seldom
developed necrosis which affected more than 5 percent of the
individual leaf area. Injury was usually restricted to a 1-2 mm
margin at the leaf edge. Typical symptoms oE sulfuric acid aerosol
i
injury on soybean are shown in Figure 12A.
8.1-4 Ash and Birch—
Green ash (Fraxinus pennsylvanica Marsh.) and birch (Betula
paperifera Marsh.) were more resistant than soybean to sulfuric acid
aerosol. Injury was usually restricted to leaf tips and seldom
exceeded one percent of the individual leaf area. Leaflets on ash
showed relatively uniform tip necrosis without apparent difference
due to age and position on the leaf. These species were exposed
only once per season per plant. Forced foliage production could not
be initiated as in the case of hybrid poplar. Different plants
exposed during different seasons showed similar symptom development.
8.1-5 Corn and Wheat—
Corn (Zea mays L.) and wheat (TrLticum aestivum L.) were the most
resistant species exposed to the sulfuric acid aerosols. Both
species showed some injury but it was usually restricted to a limited
36
-------
Figure 12A. Injury to soybean caused by exposure to sulfurlc
acid aerosol. Note: marginal necrosis of exposed leaf (right)
compared to control (left).
Figure 12B. Injury to hybrid poplar caused by exposure to
sulfuric acid aerosol. Note: marginal and tip necrosis of
exposed leaf (left) compared to control (right).
37
-------
margin of 1 mm or less at the leaf edge. Exposed and nonexposed
corn leaves are shown in Figure 13A. We do not yet know if this
could be considered a general response of the Gramineae compared to
broad leaf species. Both species appeared to grow normally after
exposure and individual leaf necrosis did not exceed one percent of
the individual leaf area. Corn and wheat were not examined for
subtle responses to sulfuric acid aerosol injury. Initial plant
exposures were made by inserting opposite plant branches through
.ports in the aerosol and control chambers as shown in Figure 13B.
Subsequent studies with entire plants in the chamber gave similar
results.
9. SUBTLE PLANT RESPONSES TO SULFURIC ACID AEROSOLS
9.1 Effect on Leaf Epidermis
Several recent reports on pollutant-plant interaction have
described effects involving the degradation of cuticular waxes on the
leaf surface (26). Studies were conducted to ascertain the effect
of sulfuric acid aerosol on the cuticular layer. Pinto bean plants
3
were exposed to 100 mg/m of sulfuric acid aerosol and fixed for
SEM study. The leaf cuticle was found to be generally unaffected
except in areas where injury was macroscopically evident. Severe
injury was found in these areas. Figure 14 shows untreated (A) and
aerosol exposed (B) foliage. The epidermal cells and the guard
cells collapsed on the exposed foliage. Figure 15 shows a normal
stomate (A) and a stomate exposed to sulfuric acid aerosol (B). This
degree of injury is permanent and renders the affected tissue nonfunc-
tional. Although severe injury to the leaf is incurred, the cuticle
wax does not appear to be undergoing degradation. The acute collapse
38
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OJ
VO
Figure 13A. Injury to corn caused
by exposure to sulfuric acid aerosol.
Note: exposed leaf (left) compared
to control leaf (right).
Figure 13B. Opposite branches of
plant inserted through ports in control
chamber (left) and aerosol chamber
(right).
-------
Figure 1AA. Scanning electron micrograph of non-exposed
leaf of pinto bean. Note: condition of stomates and
cuticle.
Figure 1AB. Scanning electron micrograph of aerosol
exposed leaf of pinto bean. Note: collapsed epidermal
cells.
40
-------
Figure 15 A. Scanning electron micrograph of
healthy stcmate of pinto bean.
Figure 15 B. Scanning electron micrograph of
stomate exposed to sulfuric acid aerosol. Note:
collapsed guard cells.
41
-------
of epidermal cells can be better visualized in Figure 16 which
shows normal (A) and exposed (B) leaves.
9.2 Elemental Composition
Figure 16C shows the elemental distribution of the surfaces
shown in Figure 16A and B. The solid line represents the untreated
and the dotted line the exposed foliage. The similar elemental
composition indicates that sulfate is not being retained in the
cuticle. Figure 17A shows an aerosol exposed leaf in cross section.
The elemental composition of the surface (solid line) and interior
(dotted line) indicate the areas which are shown in Figure 17B.
Significantly more phosphorous and sulfur were found in the leaf
interior. This may indicate that aerosol sulfate is being accumulated
within the leaf.
9.3 Surface Particles
Efforts were made to assay the elemental composition of particles
found on the leaf surface. Figure ISA shows a large (5 pm) particle
which contains sulfur as a major constituent. Figure 18B shows the
elemental composition of the particle shown in Figure ISA. Figure 19
shows the elemental composition of another particle, which is probably
a silicate of aluminum, found near the particle in Figure ISA.
Varied particle compositions such as these were commonly found. A
predominance of sulfur particulates was not observed.
9.4 Changes in Foliar Sulfur Content
Several plant species were found to accumulate sulfur during 4 to
12 hour exposures to sulfuric acid aerosols ranging in concentration
3
from 100 to 200 mg/m . Sulfur uptake by plants did not appear to be
42
-------
Figure 16A. Scanning electron micro-
graph of leaf surface of healthy
pinto bean.
Figure 16B. Scanning electron micro-
graph of leaf surface of pinto bean
exposed to sulfuric acid aerosol.
Note: necrotic pit caused by drop-
let from sulfuric acid aerosol
condensation.
Figure 16C. X-ray microanalysis spectra of
leaf surfaces of pinto bean. Note: similar
elemental composition of surfaces exposed to
sulfuric acid aerosol (dotted line) and control
surface (solid line).
43
-------
Figure 17A. Cross section of pinto bean leaf exposed
to sulfuric acid aerosol. Note: epidermal surface
(solid triangle) and interior surface (dotted triangle)
Figure 17B. X-ray microanalysis spectra of leaf shown
in Figure 17A. Note: increased concentrations of sulfur
and phosphorous found in leaf interior (dotted line)
compared to exterior surface (solid line).
44
-------
Figure ISA. Scanning electron micrograph of
5 pm particle found on surface of leaf exposed
to sulfuric acid aerosol.
0_
00
150
100
50
AI
M9
Figure 18B. X-ray microanalysis spectra of
particle shown in Figure 18 A.
45
-------
2800
2400
2000
LU
Q_
1200
800
Figure 19. X-ray microanalysis spectra of particle
found on surface of leaf exposed to sulfuric acid
aerosol.
46
-------
as nuch a function of aerosol concentration and duration of exposure
as it did other unknown factors. Data on foliar sulfur content are
shown for several plant species in Figures 20-24. Figure 20 shows
sulfur accumulation in Bountiful bean on four different exposure
dates. Plants ranged from 15 to 30 days of age depending on the
specific exposure. On each occasion aerosol-treated plants had higher
foliar sulfur contents than untreated plants. As shown on the 7-27-77
exposure this amounted to more than a twofold increase from 2000
to 4180 ppn. Host species grown from seed and exposed at about the
same age showed an increase in background sulfur and a decrease in
total sulfur accumulated during exposure as the season progressed. The
reason for this is unknown. Figures 20-24 are comparable since the
plant species in question were simultaneously exposed on the designated
date. The season trend (showing decreased sulfur accumulation) is
apparent for all species except hybrid poplar which showed an
unusually high level of natural sulfur. Since exposure conditions
were not exactly reproduced on the dates shown in Figures 20-24
other factors may be influencing the seasonal trend.
Additional studies using pinto bean were done midwinter, 1977-78
in an attempt to better define the factors affecting sulfur accumula-
tion. Figure 24 shows pinto bean data comparable to that shown
in Figures 20-23. Figures 25-27 show the effect of sequential
sulfuric acid aerosol exposure on pinto bean at 48 hour intervals at
3
a concentration of 250 ing/m with 7, 9 and 11 day old plants,
respectively. Data arc presented for two control and two aerosol
chambers with two .subsurnplcs for each chamber. Adjacent bars of the
47
-------
same magnitude indicate insufficient foliage, was available for sub-
sampling. After the third exposure (Figure 27) the foliar sulfur
content of exposed foliage has approximately doubled. A response
of similar degree was achieved with one third this dose (concentration
X time) (3) during midsummer (see Figure 24).
Pinto bean plants of different ages were exposed for 5 and 7
o
hour periods to about 175 mg/m sulfuric acid aerosol. No apparent
differences in sulfur accumulation were found. These data are
presented in Figures 28-31 with the same subsampling format as
previously described. Figure 28 and 29 show foliar sulfur contents
for 16 and 26-day-old plants, respectively, exposed for 7 hours.
The values shown are within the limits of analytical error.
Figures 30 and 31 show the effect of 5-hour exposures on 19 and 43-
day-old plants. These data are also similar within the limits of
experimental error. A decreased response to increased aerosol
concentration x^as also noted during the midwinter studies. Figures
32 and 33 show the effect of more than doubling the aerosol dosage on
sulfur accumulation. Figure 32 shows the foliar sulfur content of
pinto bean plants exposed to 175 mg/m for 8 hours compared to control
plants. Figure 33 shows the results of 12-hour exposure with an
3
increased concentration of 390 mg/m . Differences in response are
not apparent.
These results indicate that there are substantial seasonal
differences in plant response to sulfuric acid aerosol stress. Plant
age, and aerosol concentration did not markedly influence plant response
during the midwinter studies yet similar plants accumulated large
amounts of sulfur during midsummer. Lack of predictable response to
48
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increased pollutant dosages may indicate that uptake of this pollutant
is not following simple diffusion processes, and that presently
unknovm factors may be controlling plant response.
9.5 Change in Growth
Changes in individual leaf area following exposure to sulfuric
acid aerosol were measured using a procedure described previously.
Figure 34 shows the growth of exposed and non-exposed trifoliolate
leaves of pinto bean as a function of initial leaf area. Young leaves
exposed to 175 mg/m for 7 hours showed a slight (P = .25) stimulation
in growth which decreased as the initial leaf area increased beyond
75 cm^. Growth of older trifoliolate leaves with similar initial
areas was essentially unchanged after the aerosol treatment (Figure 35).
Paired primary leaves of pinto bean of similar initial area
responded as did the paired trifoliolate leaves. Figure 36 shows
the growth response of the primary leaves over a 2-week period
following sequential exposures 1 week apart. Exposure to sulfuric
acid aerosol did not show consistent effects on primary leaf
development.
9.6 Plant Reproductivity
o
Pinto bean plants were exposed at time of flowering to 150 mg/m
of sulfuric. acid aerosol for 5 hours on two consecutive days. Visual
injury was apparent on foliage but not on flowers. Pollen viability
was not assessed and it was not possible to make an accurate assess-
ment of effect on yield. Since macroscopic effects on flowers were
riot observed and investigation of subtle effects on reproductivity
require longer term studies, more research needs to be done to define
this effect.
49
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SULFUR ACCUMULATION
IN BOUNTIFUL BEAN
10,000
9000
8000
9j 7000
u-
^ 6000
c/)
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Figure 20. Foliar sulfur accumulation in Bountiful bean.
Note: seasonal trend showing decreased sulfur accumulation.
50
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Figure 22. Foliar sulfur accumulation in hybrid poplar.
52
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Figure 23. Foliar sulfur accumulation in green ash.
53
-------
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Note: season trend showing decreased sulfur accumulation.
54
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bean plants exposed to 250 mg/m3 sulfuric acid
aerosol for 8 hours.
55
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plants exposed to 250 mg/m^ sulfuric acid aerosol for
8 hours when 7 days old and 250 mg/m3 sulfuric acid
aerosol for 8 hours when 9 days old.
56
-------
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Figure 28. Sulfur accumulation in 16 day old pinto
bean plants exposed to 175 mg/m3 sulfuric acid aerosol
for 7 hours.
58
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bean plants exposed to 175 mg/m3 sulfuric acid aerosol
for 7 hours.
59
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Figure 30. Sulfur accumulation in 19 day old pinto
bean plants exposed to 175 mg/m3 sulfuric acid aerosol
for 5 hours.
60
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Figure 31. Sulfur accumulation in 43 day old pinto
bean plants exposed to 175 mg/m3 sulfuric acid aerosol
for 5 hours.
61
-------
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plants exposed to 175 mg/m3 sulfuric acid
aerosol for 8 hours.
62
-------
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Figure 34. Relationship between growth and initial leaf
area of exposed (dashed line) and non-exposed (solid line)
trifoliolate leaves of pinto bean.
64
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Figure 35. Growth of trifoliolate leaves of pinto bean
plants with similar initial leaf areas exposed and not
exposed to sulfuric acid aerosol.
65
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LiJ
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Figure 36. Sequential growth of primary leaves of pinto
bean plants at two week intervals exposed and not exposed
to sulfuric acid aerosol.
66
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10. EFFECT OF AMMONIA NEUTRALIZATION OF SULFURIC ACID AEROSOL DUFFING
PLANT EXPOSURES
Pinto bean plants were exposed in groups of 25 to ambient air,
ammonia alone, sulfuric acid aerosol alone and ammonia plus sulfuric
acid aerosol. This experiment was done twice. Anhydrous ammonia was
metered to the aerosol chambers insufficient quantity to neutralize
150 mg/nr sulfuric acid aerosol. This concentration of ammonia was
much more injurious to vegetation than was 150 mg/m of sulfuric acid
aerosol. All plants exposed to ammonia alone wilted and died within
48 hours after exposure. Ammonia combined with sulfuric acid aerosol
substantially reduced injury to vegetation. Some injury from ammonia
was apparent on foliage when the ammonia concentration was in excess of
that required to neutralize the sulfuric acid aerosol in the chamber.
Injury was reduced such that no visible symptoms were produced on
plants exposed to ammonia with a slight excess of sulfuric acid
aerosol. Refinement of the technique for measuring and reacting
ammonia and sulfuric acid aerosol is necessary before quantitative
information can be gained. These results indicate, however, that
sulfuric acid aerosol and ammonia do react to form neutralization
products (6) which have less acute effect on vegetation than do
either ammonia or sulfuric acid aerosol alone.
67
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DISCUSSION
Acidic substances from the atmosphere have been widely implicated
in the production of adverse effects when deposited upon terrestrial
ecosystems (8,20,29). Most of the previous studies in this area
have related to the effects of acidic precipitation on foliage
(8,26). Since a significant part of the acidic material in the
atmosphere is now known to occur as aerosol (1), rather than as
precipitation droplets, additional studies vrere needed to assess
the effects of aerosols on vegetation. Sulfuric acid aerosol is
knoxm to be produced during the combustion of fossil fuels by the
oxidation of elemental sulfur and subsequent reaction with ambient
water vapor. Automobiles equipped with catalytic converters were
recently found to be new sources of this pollutant (11). This
project was thus implemented to address the environmental concerns
relating to the impact of sulfuric acid aerosol on vegetation.
It was necessary to develop a system for exposing plants to
sulfuric acid aerosols, to examine this problem, since previous
studies had not been done. The exposure system described here has
proven effective in meeting criteria relating to aerosol generation,
distribution, deposition, and removal for short term exposures of
less than 24 hours. Plants were found to respond to high aerosol
3
concentrations of 100 to 200 mg/m during short exposures of 4-16
hours. The results indicate that acute exposures of this kind to
sulfuric acid aerosol are injurious to vegetation and induce both
68
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macroscopic and subtle responses.
It was found necessary to study plant responses under these
conditions to produce symptoms characteristic of this form of
pollution so that other factors influencing injury could be assessed.
Visible injury from sulfuric acid aerosol resembles that caused by
gaseous fluoride. Subtle responses which have been observed include
foliar sulfur accumulation and the collapse of epidermal and
guard cells. Plants are not likely to develop any visible injury
from short term (4-16 hour) exposures to sulfuric acid aerosol at
concentrations which could be attributed to catalyst equipped cars
3 3
in the ambient environment (1 yg/m to 4 ug/m ). Concentrations
3
much higher than these (near 100 mg/m ) are required to produce
acute plant responses.
Predicting acute plant responses to sulfuric acid aerosol
appears to be complicated by factors under biological control. It
was not possible in these studies to accurately define plant
responses, either visible or subtle, in terms of physical factors
known to condition plant responses to other pollutants. Plants did
not show predictable changes in injury related to changes in
temperature. Nor was injury increased with increasing pollutant
concentration after a threshold concentration was reached. Similarly,
preliminary investigations of relative humidity and light influences
did not demonstrate predictable relationships.
These observations are not intended to suggest that physical
factors are not involved in conditioning plant responses to sulfuric
acid aerosol injury. It is probable that optimum temperatures,
69
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concentrations, humidities and lighting regimes exist which will,
when the plant is in a susceptible condition, yield maximal injury.
However, highly variable observations relating to plant responses
at different times to a constant level of a given physical factor has
led us to speculate that biological factors may be principally
involved. Several authors have provided rationale appropriate to
this conclusion.
Sulfate uptake and metabolism have been reviewed by Schiff and
Hodson (25). These authors have discussed several factors which we
did not resolve in this study. Of the major elements required by
organisms, sulfur is unusual in that it can be utilized as sulfate,
its most highly oxidized natural form. Most plants and animals are
capable of oxidizing reduced sulfur compounds to sulfate but sulfate
reduction reactions are primarily restricted to the plant kingdom.
Sulfate reduction is required during synthesis of many sulfur con-
taining amino acids and proteins. Organisms which can reduce sulfate
are capable of using sulfate as a sole source of sulfur. The
reduction process is expensive in terms of energy, requiring about
180 kcal/mole for reduction to the thiol level (25). For this
reason, highly evolved species may have lost this ability (25).
The ability of plants to metabolize sulfate brings into consider-
ation a number of factors which may complicate and interfere with
aerosol exposure studies. Varied plant responses to sulfate as
described in the results section may be a reflection of their effects.
Sulfate uptake seems to be accomplished by active transport mediated
by a carrier with enzyme properties (25,27). Transport is unidirectional
70
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from outside to inside the cell and is governed by pH, temperature,
sulfate concentration and available metabolic energy. Free internal
sulfate is also known to depress sulfate transport as is excess
endogenous sulfur, especially as cysteine and methionine (25,27).
Possibly the growth stimulation shown in Figure 34 for young leaves
exposed to sulfuric acid aerosol was due to the reflief (21) of an
initial endogenous sulfur deficit. Conversely, the growth inhibition
of older leaves may have been due to a net excess of endogenous
sulfur induced by sulfate accumulation . The foregoing considerations
make it apparent that plant responses to acute sulfate exposure may be
unpredictable, unless an intensive physiologic study is done concurrently.
Plant response to sulfuric acid aerosol is further regulated by
stomates. The basic mechanism of stomatal action is not yet understood
(10,22). What is know indicates that this action is also complicated
and may be unpredictable in many environments (2,14). It is currently
thought that stomates respond first to interstomatal carbon dioxide
concentration and only indirectly to other factors such as light which
subsequently influence carbon dioxide flux (22). Storaatal action is
known to be energy dependent. Each opening requires at least 0.5 erg
and is consequently controlled by uncoupling agents such as dinitro-
phenol and inhibitors of energy supply or high energy phosphate transport
such as sodium fluoride (22). Since sulfate activation to adenosine
3'-phosphate 5'-phosphosulfate (25) is thought to be necessary prior
to transport it is possible that the same factors which control
stomate closure and opening may prevent sulfate transport. Simultaneous
interference with these processes would be likely to cause substantial
71
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changes in plant response to sulfuric acid aerosol exposure.
Raschke has proposed a model for stomatal action based upon guard
cell turgor pressure controlled by metabolism of organic acids and trans-
port of inorganic ions (principally K+, H+ and C1-) . Malate is thought
to be the primary organic acid involved in this process. The direction
and magnitude of transport is dependent upon the pH of the cytoplasm
which in turn controls the concentration of malate. Carbon dioxide
t
serves as the substrate for acidity and the basis for osmotica produc-
tion. Other acids such as abscisic acid are known to enhance the
effect of carbon dioxide and act to expel H-f from the guard cells.
It seems probable that exposure to and uptake of other acidic species
could play a similar role and act to close stomates. These processes
are known to be actively controlled as was previously described.
A consideration of the complex interactions regulating sulfate
uptake and stomatal action can help explain the varied responses described
in the results section. Plants were found to be alternately sensitive
and insensitive to conventional factors controlling injury. Pollutant
concentration, temperature, duration of exposure and age of plants
did not appear to be fundamentally involved in determining plant
responses to sulfuric acid aerosols. Based on the foregoing discussion,
it is suggested that several additional factors may be involved in
conditioning plant response to sulfuric acid aerosol. These include
endogenous plant sulfur (especially as sulfate), plant energy status,
interstomatal carbon dioxide concentration, and stomatal diffusion
resistance. Quantification of these factors, in conjunction with
aerosol exposure, will require refinement of state of the art techniques
72
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in plant physiology for use during plant exposures. Application of
these techniques will be necessary to understand the observed seasonal
trends and will be essential to the development of reproducible studies
involving chronic exposures and subtle effects.
Most of the work reported here has involved the acute exposure of
plants to fine aerosols of sulfuric acid. Most plants were exposed to
o
sulfuric acid aerosol concentrations in the range of 100 to 200 mg/m .
.Exposures were for short times of less than 24 hours. These conditions were
not intended to be analogous to those found in the ambient environment.
They were designed to produce acute plant responses (necrosis and vn.lt)
which could then be related to subtle plant responses (pollutant
accumulation and growth). Correlation of acute and subtle plant
response to pollution is necessary to predict when significant injury
will occur from chronic exposures. Whitby (34 has reported atmospheric
sulfate concentrations of 80 vig/m-* under highly polluted conditions.
This value is two to three orders of magnitude less than the concentra-
tion we have found necessary to induce acute injury to vegetation and
is 10 to 100 times larger than that which could be. attributed to
automobiles equipped with catalytic converters. Additionally, the
relative effects of hydrogen and sulfate ions deposited as acid or
neutralized salt aerosol (12) were not evaluated. It is likely that
under most ambient conditions plants will be exposed to mixtures of
pollutants includins aerosols, oxidants and oxides of sulfur and
nitrogen. Investigations of these multivariable interactions are
needed.
There is presently a need to extend these results to include chronic
73 :
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plant responses Co sulfuric acid aerosol at concentrations which
occur in the environment. Chronic exposure studies will require increased
stability of the exposure system and are additionally complicated by
the observation tliat injury appears to be conditioned by biological
as well as physical factors.
The exposure system should be modified somewhat for continuous
operation during chronic exposure studies. The compressed air cylinders,
while providing an excellent degree of air contaminant control, could
be replaced with a compressor system fitted with appropriate pollutant
filters and air dryers. Additionally, the problem of changing cylinders
during long term exposures would be eliminated. The aerosol generator
equipped with the Teflon nebulizer modification and perhaps a Teflon
irapaction stage should provide good service during continuous operation.
The principal problem associated with long term plant exposures
relates to the changing responses of growing plants and presents a paradox
of sorts. The objective addressed in designing this system was to develop
a reasonably closed exposure system in which physical variables could
be controlled. This becomes increasingly difficult as the duration of
the exposure is increased. It may also be anticipated that more changes
in the biological variables which condition response to pollutant stress
will occur in proportion to the length of time the plants are in an
exposure chamber. This increased variability in plant response is
superimposed upon a decrease in degree of response at lower pollutant
concentrations. The researcher is thus confronted with a paradox:
more variability in frequency of response and a decrease in the
intensity of the response which is to be measured. These aspects of
74
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chronic plant exposure call for an additional degree of refinement
in the exposure system. Refinement may be accomplished in part, by
operating the system as a reactor in which incoming and outgoing
pollutant concentrations are known, and uptake can be thereby predicted,
Such a system has been described by Hugo Rogers (PhD Thesis North
Carolina State University 1975).
Much work remains to be done to resolve these questions. It is
apparent that sulfate loading of the atmosphere from fossil fuel
combustion with subsequent deposition on terrestrial ecosystems will
continue into the predictable future (9). The ultimate fate and
effect of sulfate on ecosystems is a question is demand of an answer.
If plants are found to accumulate sulfate in excess of their ability
to utilize sulfate, a decline in the productivity of photosynthetic
systems may be anticipated with significant subsequent effects on the
health and welfare of mankind.
75
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SUMMARY
1. A continuous flow system for exposing vegetation to submicron
sulfuric acid aerosols has been designed and constructed. All
surfaces within the exposure system which are in contact with sulfuric
acid aerosols are composed of either Teflon or stainless steel and
are essentially inert to sulfuric acid corrosion.
2. Exposure chambers were designed to allow simultaneous exposure
of different branches of the same plant to aerosol and control
environments to minimize variation associated with individual plant
differences.
3. Submicron sulfuric acid aerosols are mechanically produced
using a nebulization-impaction-neutralization process. Typical
aerosol distributions have a mass mean diameter of about 0.5 ura and
a standard geometric deviation near 1.7.
4. Plants are injured during acute exposures to sulfuric acid
aerosols. However, the aerosol concentrations required to produce
visible injury are several orders of magnitude higher than those
which have been attributed to sulfate in the ambient environment.
5. All plant species exposed to sulfuric acid aerosols have shown
the same characteristic injury to leaf margins and tips.
76 '
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6. This is the first report of this form of injury attributable
to acidic pollutants.
7. Plants vary in susceptibility to sulfuric acid aerosol injury.
8. Plant responses to sulfuric acid aerosol have not followed
proportional relations to pollutant dose (concentration X time).
9. Lack of proportional dosage relations suggests that active
rather than passive mechanisms may be controlling plant response to
this pollutant.
10. Simultaneous exposure of plants to ammonia and sulfuric acid
aerosol in stoichiometric quantities appears to decrease visible
injury normally associated with exposure to sulfuric acid aerosol
alone.
77
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LITERATURE CITED
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of sulfur dioxide to sulfates in the U.S. J. Air Poll. Control
Assoc. 26:4.
2. Barrs, H. D. 1971. Cyclic variation in storaatal aperature
transpiration, and leaf water potential under constant
environmental conditions. Ann. Rev. Plant Physiol. 22:223-36.
3. Benedict, H. M., D. D. Davis and A. S. Heagle. 1974. Dose
response of vegetation to minor pollutants. Proc. Ann. Air
Poll. Control Assoc. Denver, Col. #74-229.
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effects of low concentrations of sulfur dioxide on stomatal
behavior in Vicia faba. NewPhytol. 72:1299-1306.
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8. Dochinger, L. S. and T. A. Selica. 1975. Acidic precipitation
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9. Fennelly, P. F. 1976. The origin and influence of atmospheric
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2 ~~~
Phytol. 73:299-307.
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18. Maugh, T. H. 1977. Sulfuric acid from cars: A problem that
never materialized. Science 193:280.
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performance, and application. Aerosol Science 4:235-243.
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i
to vegetation from polluted atmospheres. J. Air Poll. Control
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23. Reinert, R. A., A. S. Heagle and W. W. Heck. 1975. Plant
responses to pollutant combinations. Responses of Plants to Air
Pollution. J. B. Mudd and T. T. Kozlowski (ed.) Academic Press,
New York. p. 159-175.
24. Ricks, G. R. and R. J. H. Williams. 1974. Effects of atmos-
pheric pollution on deciduous woodland part 2: Effects of
particulate matter upon stomatal diffusion resistance in leaves
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Ann. Rev. Plant Physiol. 24:381-414.
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27. Smith, I. K. 1976. Characterization of sulfate transport in
cultured tobacco cells. Plant Physiol. 58:358-362.
28. Smith, R., R. G. DePena, and J. Heicklen. 1975. Kinetics of
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oxidation of SC>2 in moist C^-No mixtures. J. Colloid and
Interface Sci. 53:202-213.
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(ed.) McGraw-Hill. New York, p 9-16.
30. Thomas, M. D. 1962. Sulfur dioxide, sulfuric acid aerosol and
visibility in Los Angeles. Inter. J. Air and Water Poll.
6:443-454.
31. U.S. Department of Health Education and Welfare. 1970. Air
Quality Criteria for Photochemical Oxidants. National Air
Pollution Control Administration, Washington, D. C.
32. Willeke, K. and K. T. Whitby. 1975. Atmospheric aerosols size
distribution interpretation. J. Air Poll. Control Assoc.
25:529-534.
33. Wilson, W. E., L. L. Spiller, T. G. Ellestad, P. J. Lamother,
T. G. Dzubay, R. K. Stevens, E. D. Macias, R. A. Fletcher,
J. D. Husar, R. B. Husar, K. T. Whitby, D. B. Kittelson,
B. K. Cantrell. 1977. General Ilotors sulfate disperson
experiments: Summary of EPA measurements. J. Air Poll. Control
Assoc. 27:1
34. Whitby, K. T. 1970. The physical characteristics of sulfur
aerosols. Atmospheric Environment. 12:135-159.
81 ~
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TECHNICAL REPORT DATA
(Mease read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-79-002
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
EFFECTS OF SULFURIC ACID AEROSOLS ON VEGETATION
5. REPORT DATE
January 1979
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
David S. Lang
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Department of Plant Pathology
University of Minnesota
St. Paul, Minnesota 55108
10. PROGRAM ELEMENT NO.
1AA601
11. CONTRACT/GRANT NO.
R-804291
12. SPONSORING AGENCY NAME AND ADDRESS
Health Effects Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
TT-> flnol o ParV N.r.. 97711
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA 600/11
15. SUPPLEMENTARY NOTES
Principal Investigator
S. V. Krupa
16. ABSTRACT
A continuous flow system for exposing plants to submicron aerosols of sulfuric
acid has been developed and an operational model has been constructed. Exposure
chambers have been designed to allow simultaneous exposures of the same plant to
aerosol and control environments. All surfaces within the exposure system are
composed of either Teflon or stainless steel to minimize corrosion. Submicron
acid aerosols are mechanically generated and are distributed in size representative
of resident particulates found in the atmosphere. Plants have been found to be
injured by exposures to high concentrations of sulfuric acid aerosol (100-200
mg/m3) for short times of 4-16 hours. Injury to vegetation caused by sulfuric
acid aerosol is similar to that caused by gaseous fluoride and is characterized by
marginal and tip necrosis of foliage. This injury is distinctly different from
that which has been attributed to acidic precipitation. Different plant species
vary greatly in sensitivity to sulfuric acid aerosol and injury to sensitive
species appears to be conditioned by biological as well as physical factors.
Results indicate that foliar sulfur accumulation during exposure to sulfuric acid
aerosol may be subject to substantial temporal effects. The concentrations of
sulfuric acid aerosol required to produce acute vegetation effects are several
orders of magnitude higher than those which have been reported for catalytic
emissions from automobiles.
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
sulfuric acid
vegetation
air pollution
aerosols
04 A
06 C
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (This Report)
UNCLASSIFIED
21. NO. OF PAGES
94
20. SECURITY CLASS (This page)
UNCTASSTyTFTi
22. PRICE
EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION is OBSOLETE
82
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