UPTAKE OF SULFURIC ACID MIST BY PLANT CANOPIES

- NOTICE This report was prepared as an account of work sponsored by the United States Government Neither the United States nor the United States Department or Energy, nor any of their employees, nor any of their contractors, subcontractors, or their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility Tor the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned rights

Final Report For Period Ju ly 1, 1977 - December 31 , 1978

James B. Wedding, Ph.D. Assoc ia te Professor

Aerosol Science Laboratory C iv i l Engineering Department

Colorado S t a t e Un ive r s i ty

January 1979

Prepared For The U.S. Department of Energy

Under Contract No. EE-77-S-02-4367

%

DISTRIBUTION OF THIS DOCUMENT IS UNLIMITED

V to

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER

Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

TABLE OF CONTENTS Page

ABSTRACT i i

1.0 INTRODUCTION 1

2.0 EXPERIMENTAL APPROACH 2 2.1 Testing Procedure 2 2.1.1 Particle Deposition Velocities 2 2.1.2 Physiological Exposure Chamber Studies 3 2.2 Plants 5 2. 3 The Environmental Wind Tunnel' 5 2.4 Plant Exposure Chamber 6 2.5 Canopy Configuration (deposition study) 6 2.6 Particle Injection Technique (deposition study) 8 2.7 Particle Generation Technique (deposition study) 8 2.8 Cloud Concentrations (deposition study) 10 2.9 Analysis Techniques (deposition study £ physiological

effects) .... 10 3.0 CONCLUSIONS 11 3.1 Particle Deposition Study 11 3.1.1 Fluid Mechanics 11 3.1.2 Effect of Species on Deposition 12 3.1.3 Effect of Growth Stage on Deposition 1 2 3.1.4 Effect of Velocity on Deposition 12 5.1.5 Effects of Canopy Location on Deposition ] 3 3.2 Physiological Effects Study 12 4.0 PUBLICATIONS RESULTING FROM THIS STUDY 14

L I

ABSTRACT

Wind tunnel studies and exposure chamber experiments were conducted in

the Aerosol Science Laboratory at Colorado State University. Full scale,

live plant canopies of 4-6 week old corn and soybeans were established in

a large wind tunnel. Monodisperse aerosols (l-15)Jm aerodynamic diameter)

were injected into the tunnel and deposition velocities were determined for

wind speeds of 183, 305 and 610 cm/sec. A minimum deposition velocity was

seen to occur at 5ym. (See appendix I publication pre-print).

Initially 4-6 week old soybean plants were exposed to hydrated sulfuric

acid mist droplets in a "gross effects" study. Unquantified topically

applied sulfuric acid mist was applied with a polydisperse atomizer at a

dosage of 1% and 10% volumetric concentration of acid to water. The 10%

solution produced severe necrotic lesions and large chlorotic regions on

the acropetal leaves. A heavy application of the 1% solution nroduced

similar effects but with a reduced number of necrotic lesions. A light appli­

cation had no visual effects on the plants even after 24 hours.

In addition, 4-6 week old corn and soybeans were placed in a glass

exposure chamber. Droplets of pure 18M sulfuric acid mist (1.7pm) were

injected into the chamber at a rate commensurate with the deposition velocity

results. Loading of 107particles/cm2 were realized during exposure periods

up to 10 hours per day extending to 14 days total fumigation periods. No

visible toxicity symptoms of damage resulted to the plants from these tests

conducted at background humidity levels of approximately 40 percent. Scanning

electron microscope observations of the 140 hour treated plants showed no

apparent damage due to the sulfuric acid mist treatment. (Sec appendix IT

for publication pre-print).

1.0 INTRODUCTION

The investigation of particle uptake or filtering by plant canopies

and their subsequent physiological/anatomical effects are not only of

academic interest or from a basic research point of view. The presence

in the atmosphere of nuisance dusts, topically applied sprays (insecticides)

and potentially deleterious particles, in particular sulfuric acid mists -

provides considerable application and interest in the dynamic filtering capa­

city of a greenbelt for aerosols. Results of this investigation are seen

in three areas.

The first aspect in which the results of this investigation can be

applied is in assessing the particle loading of plants and its resulting

physiological effect upon the plants. The economic impact of reduced yield

in cash crops, such as corn and soybeans incurred due to exposure to sulfuric

acid mists could be of substantial magnitude. The results of an investigation

such as the one being undertaken could help to predict such loss by deter­

mining if the mass loading realized is great enough to reduce plant yields.

Secondly, in areas of high particulate pollutant concentrations, plant

canopies may have some potential as a dynamic particle filter, thus reduc­

ing the ambient concentrations of harmful or undesirable airborne pollutants.

Finally, in the area of agricultural sprayi'ng, some knowledge will be

gained as to what optimum droplet size ranges should be used for maximum

canopy coverage and even distributions of spray within the canopy thus avoid­

ing loss of insecticides as well as potential insults to ecosystems.

Thus, such a study, dealing with particulate uptake or filtering by living

plant canopies, could provide valuable knowledge concerning basic physical

principals of particle and fluid mechanics as well as practical knowledge

immediately applicable to real world problems.

Canopy flows, as such, have been studied in considerable detail

through investigations of the absorption of gaseous'pollutants by plant

canopies, and the turbulent structure and fluid dynamics of flows over

and through plant canopies. Little work has been reported in the lit­

erature which investigates the uptake of filtering of particles by plant

canopies.

The purpose of this investigation was twofold. First was to identify

the functional form describing the uptake of aersolized particles by

leaf canopies and obtain values for deposition velocities as a function

of such variables as canopy density, plant surface characteristics, wind

velocity, particle size, and turbulence levels. It is entirely feasible

to develop a predictive model for topical loading as a function of known

environmental and physical parameters which can be related directly to

actual field canopies using the deposition velocity concept.

The second goal was to assess the effects of topically applied sulfuric

acid mist on the physiological processes of young plants. These two studies

coupled together provide the basis for a dose-response curve that can be

related to the atmosphere.

2.0 EXPERIMENTAL APPROACH

2.1 Testing Procedure (See Figure 1 for experimental configuration)

2.1.1 Particle Deposition Velocities

The wind tunnel velocity was adjusted to the desired value using a

pitot static probe and calibrated linear air flowmeter. The biplane grid

is positioned as shown in Figure 1. The aerosol generator was then engaged

to generate the desired particle size. Isokinetic samples were taken at

the inlet ports of the manifold system to determine the size and monodispersity

of the particles entering the wind tunnel. After the desired aerosol quality

Flow Straightener , Tubes

Screen

/ Biplane Grid to Generate Turbulance

Plant Rows

24

96" 4 2 '

Split ter Plate Transport Tubing 0 MC K r - 8 5 Line Source

Vibrat ing Or i f i ce Aerosol Generator

Nof to Scale

Figure 1. The Environmental Wind Tunnel

4

was achieved, the generator was disconnected from the manifold transport

system preventing the particles from entering the wind tunnel. Plants,

numbering thirty-six per canopy were placed in the canopy platform within

the wind tunnel. These plants arc not used for testing purposes, but arc

utilized for canopy flow simulation only. The aerosol generator was then

reconnected to the manifold transport tubes, allowing particles to be

injected into the wind tunnel. Isokinetic rake samples were taken at the

cross-sectional area 8" (20.32 cm) upstream of the canopy. The aerosol

generator was then disconnected from the manifold injectors once again.

The plants used for the rake tests were then removed from the canopy and

wind tunnel and replaced by the test plants. The aerosol generator was

then reconnected to the manifold injectors and the test conducted. After

the desired test period, the aerosol generator was once again disconnected

from the manifold injectors, and the test plants removed from the test site

for analysis. The simulation canopy was reinserted in the wind tunnel and

the aerosol generator reconnected to the manifold injectors. A final

isokinetic rake sample was taken. Rake samples were taken both before and

after the actual tests to ensure that the concentration of particles during

the test period was as uniform as possible.

2.1.2 Physiological-Exposure Chamber Studies

The qualitative, gross effects of sulfuric acid on the plants were

determined by a light spraying (one broad sweeping pass) of the foliage

of soybean plants with a hand-held polydisperse atomizer. Solutions used

were 1% and 10% volumetric concentrations of sulfuric acid mist and water.

The atomizer produced a mass mean aerodynamic diameter of 5ym with a geometric

standard deviation of 2.1. No attempt was made to quantify the application.

4(a)

Detailed quantitative tests were performed with the aid of the glass

walled chamber equipped with growth lamps. Six plants were exposed s simultaneously in the chamber for varying periods of time. (See figure 2)

Freshly generated aerosol produced by the vibrating orifice atomizer

shown was injected into the chamber with flow continuity achieved by the

four exhaust ports. Deposition of the small particles (1.7 ym) was

induced by Brownian motion in the near quiescent flow regime (injection

rate 12.75 m3/hr.) The fluid mechanics were designed purposely to in­

duce slow deposition rates thereby ensuring light particle loading over

long periods of time. These conditions were felt to be more representa­

tive of an actual atmosphere environment than excessively large does

over short periods of time. Exposure periods were from 4-10 hours a day

for up to 14 days. Dosage rates were compared to rates calculated from

depositions velocities as determined by Wedding (app. 1) in full-scale wind

tunnel tests on 4-6 week old soybean plants.

Quantative assessment of the particles on 1 cm of leaf surface area

realized in the tests were determined by first calibrating the chamber

using 1.91 UTI particles of sodium fluorescence equivalent in aerodynamic

diameter to the 1.7 sulfuric acid droplets. Sections of leaf exposed for

various time periods in the chamber were taken from plants and placed into

wash water. Subsequent analysis of the solution with the aid of a cali­

brated Turner Model III Fluorometer yielded the deposited mass. Careful

consideration was given to blanks of unexposed leaves to ensure zeroing out

of any residual background fluorescence.

Particle size and quality were affirmed by optical microscopy study

of the droplets deposited on glass slides placed at numerous locations

within the test chamber. The absence of moisture on the droplets when

5

they arrived at the plants were affirmed by scrutiny of the stain

diameters left on Kromekote cards placed at random locations throughout

the chamber.

A steady state concentration of acid droplets was created in the

test chamber before plants were inserted. This was achieved by running

the generator into an empty chamber for a period of seventy minutes prior

to the initiation of each test.

2.2 Plants

Two species of plants, corn and 'soybeans, were studied in the program.

These were chosen for a variety of reasons. Their leaf surface character­

istics were quite different. Soybeans are less pubescent than rough-

surfaced corn. The leaf morphology of the two species is quite different.

Corn, a monocot, has pointed leaves that are characteristically many times

longer than they are wide. Soybeans, a dicot, have leaves whose length

is of the same magnitude as their width. It was hoped that varying leaf

morphology would provide different types of canopy flow as well as exploring

the effects of leaf surface characteristics as deposition processes.

Two growth stages of each species were also tested to simulate differing

canopy densities and thus different flow characteristics.

Lastly, both soybeans and corn are crops which are widely utilized

food crops. Thus potential cytological damage could have serious economic

and social consequences.

2.3 The Environmental Wind Tunnel

The testing was done in the Environmental Wind Tunnel at Colorado

State University. The tunnel has a test section 52 ft. (15.85 m) in

length with an 8'xl2' (2.438 m x 3.658 m) cross-section. Three wind speeds

were utilized in the testing: 6, 10 and 20 ft/sec (1.83, 3.05, 6.1m/sec).

The turbulent intensity in the tunnel approaching the canopy test section

is varied from background levels to of the order of 8 percent, through the

use of a biplane grid constructed of 1.5" x 1.5" (3.81 cm x 3.81 cm)

6

aluminum bars placed in a square matrix on 9" (22.86 cm) centers.

2.4 Plant Exposure Chamber

The plants and exposure chamber are shown in Figure 2. Twelve

plants could be exposed simultaneously. The chamber was equipped with

growth lamps. The chamber inside dimensions were 120cm x 160cm x 160 cm.

2.5 Canopy Configuration (deposition study)

Two different canopy configurations were tested (see Figure 3).

In one test series a canopy of dimensions 48" x 67.5" (1.219 m x 1.71 m)

was utilized. Because it was subsequently determined by hot wire

anemometry that a canopy of this size would not allow the canony flow to

become fully developed, the canopy size was doubled by placing two

canopies of the above size in a longitutinal row. In each case, the row

spacing was 22-1/2" (57.15 cm) and the plant spacing was 7-1/2" (19.05 cm).

The canopy rows were formed in the shape of furrows made of styrofoam

in order to simulate field conditions found in the early growth stages

for corn. The canopy was placed on wooden supports at a height where the

troughs of the canopy surface were 36" (0.914 m) from the wind tunnel floor.

It was believed that the turbulence length and time scales of wind tunnel

boundary layer would not simulate those found in canopy flow in the atmos­

phere. Thus the canopy was placed outside of-the immediate influence of

the wind tunnel boundary layer. With the larger canopy configuration, it

was anticipated that the flow would be fully developed in the downstream

rows of the canopy or at least simulate the first few rows of a field near

a roadway. Since the canopy is only 4' (1.219 m) wide, when it is centered

In the wind tunnel there is a separation between the canopy and each wall

of 4' (1.219 m) to eliminate wall effects. The edge effects do remain

and the outer plant deposition results were discarded. The canopy size and

configuration was chosen in order that atmospheric conditions be as closely

simulated as possible.

r 100 cm

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Plant | | '~^s Locoiions | J*^ i 'x /

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Vitircit IIIQ Onl iCf Afro-.ol Genera lor

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2.6 Particle Injection Technique (deposition study)

The particle injection mechanism was designed to meet two objectives.

It was desired that the concentration of particulates approaching each

unit cross-sectional area presented by the canopy be uniform. In addition,

the mechanism was designed in order that wall losses in the injection

manifold would be minimized.

The result was a manifold shown in Figure 4. It was constructed of

essentially two rows of six circular ,3/4" OD inlet ports on 7-1/2"

(19.05cm) centers. The two rows were placed at a cross-section 8' up­

stream of the canopy leading edge. They were placed at a height of 36"

(0.914 m) and 48" (1.219 m) from the wind tunnel floor.

The two rows of inlet ports are then attached to the transport tubing

from the aerosol generator. A splitter plate is attached to the downstream

side of the transport tubing to break up vortices which are shed from the

main transport tube.

The overall manifold cross-stream length is 39" (0.991 m). Thus when

centered upstream in the wind tunnel 8' (2.438 m) from the leading edge

of the canopy, it presents a uniform concentration of particles to the

area presented by the plant canopy. Concentration measurements just up­

stream of the plant canopy confirm that the concentration is nearly

uniform.

2.7 Particle Generation Technique (deposition study)

The aerosols that were utilized in the deposition investigation were mono-

disperse solid uranine particles generated by a vibrating orifice aerosol

generator (Wedding, 1974) . The geometric standard deviation of such particles

is less than 1.06. The sizes of the particles utilized were 1.0, 5.0, 10.0

and 15.0 urn in diameter.

• »

Furrows

Potted Plants Inserted in Hol(

O o o o o o

's v~ - \

o o

• o o o

End View

o o o o o

o o o o o o

135 "

IZ'lz"

o o o o

11 %"

o o o o

m

7v;

48

Top V iew

Figure 3. Canopy Configuration

10

The particle quality was assessed by collecting the aerosol generator

output with millipore filters - type HA. They were then viewed optically

with a light microscope and sized using a moveable hairline graticular

eyepiece. A size distribution analysis of each sample is made to determine

the'particle size prior to each test to insure aerosols of monodispersc

nature were being utilized in the study.

2.8 Cloud Concentrations (deposition study)

It is desired that the concentration of particles at all points

approaching the canopy be known. The concentration cross-stream profiles

at a verticle cross section 8" (20.32 cm) upstream of the canopy leading

edge were obtained by taking samples with an isokinetic rake system. The

samples, collected on Gelman Type A-E glass fiber filters, were analyzed

with the aid of a calibrated fluorometer to determine the mass of uranine

or number of particles collected for the time period sampled. The pro­

files taken show that the concentration profiles just upstream of the

canopy were quite uniform over the cross-sectional area presented by the

canopy. A particle cloud concentration approaching the canopy can be

calculated. This was used to determine the amount of particles originally

available to the canopy for possible deposition. This value, in conjunc­

tion with particle flux to the canopy, was utilized in calculating deposi­

tion velocity to the leaf surfaces of the plants.

2.9 Analysis Techniques (deposition study f, physiological effects)

The analysis technique for the filters collected in rake samples

was as follows: The filters were placed singularly in a beaker with 25 ml

of distilled de-ionized water causing the deposited mass of uranine to

redissolve. The solution was analyzed in a calibrated Turner Fluorometer

Model #111. In this manner the mass of particles deposited on each filter

was determined.

• •

Manifold System

^ ^ ^ ^ ^ ^ ^

Drying Tube

Side View

lanifold System

o o j /

1

3 Dia.

|Q O O

Wind Tunnel Floor

^ ^ ^ ^ ^ J

® I'/,

18 %■ i i

3%"

O O

3/4 O.D.

Transport Tubing

Split ter Plate

S^^^?? Drying Tube

View from Downstream

Manifold Injection System

12

Similarly, in the technique for plant analysis, the plant leaves

were clipped and placed in large beakers. The uranine was then washed

from the leaves with varying amounts of distilled de-ionized water, depend­

ing on the leaf area of each plant. The solutions were analyzed in a

manner analagous to that of the rake sample filters. In both cases, blank

readings were substracted from the solution reading. Thus the mass per unit

area on each plant was determined. For the deposition study, the leaves of

each plant were dried and pressed and the area measured with the aid of a

planimeter.

In this manner a particle flux (mass per unit time per unit area)

to the canopy can be calculated from the rake samples; a particle flux to

each plant can be calculated; and a deposition velocity for the canopy/plant

can be determined.

3.0 CONCLUSIONS

3.1 Particle Deposition Study

During the study, the effects of particle size, approach flow turbulence,

species, growth stage and velocity on particle deposition were tested and

the results averaged. The data was consistent and presented as deposition

velocities for the great number of parameters as mentioned. The complete

set of results and figures are given by Montgomery* (1978). Sec appendix T

for pre-prints of paper delineating results and figures.

3.1.1 Fluid Mechanics

The flow for the canopies tested was within 15% of being fully developed

for freestream velocities of 198 and 305 cm/sec. There was some acceleration

around the canopy edges, leading edge, and trailing edge. This was

caused by a relatively high pressure region within and slightly behind

the canopy stands. The turbulent intensity was nearly constant

with height in a given canopy. The turbulent intensity increased

*M.S. Thesis, Civil Engineering Department, CSU

13

in regions of accelerating flow. Overall, the similation of actual

canopy flow was felt to be reasonable. • •

3.1.2 Effect of Species on Deposition

Soybeans generally captured a great deal more particles than did

corn. The effect of leaf shape and turbulence characteristics were

prominent but the principal"cause was leaf surface characteristics.

3.1.3 Effect of Growth Stage on Deposition

Deposition velocities for large growth stages were generally greater

than those for small growth stages. For corn it is believed this increase

is primarily caused by modifications of the flow caused by the area In­

crease and its effect on turbulence generation rather than the area

increase itself. Soybeans seemed to be controlled by both. Generally

growth stage had less effect on deposition velocity than did species.

3.1.4 Effect of Velocity on Deposition

Increasing freestream velocity generally decreased the deposition

velocity for particle sizes of 1 and 5 ym aerodynamic diameter. For

particles 10 and 15 ym, the effect of increasing freestream velocity

was a slight increase in deposition velocity.

Generally the deposition velocity decreases with increasing particle

diameter from 1 to 5 ym, increases with increasing particle diameter from

5 to 10 ym. It is believed that the decrease in deposition velocity

seen for particle diameter from 1 - 5 ym is caused by the increasing in­

fluence of canopy generated turbulence in causing deposition as the particle

size is decreased. This same effect is seen in pipe flow and flow over

flat plates except that less energy exists for inducing deposition in

these flows so the increase in deposition velocities is not seen until

14

the submission particle size range is reached.

3.1.5. Effects of Canopy Location on Deposition

Particles 1 and 5ym in diameter were deposited much more evenly

over all regions of the canopy. The larger particles tended to deposit

more efficiently in regions of accelerating flow, in particular near

the canopy outside edges and leading edge.

3.2 Physiological Effects Study

During the course of the study, the potential deleterious effects

of pure, 18M, unhydrated sulfuric acid mist deposited on plant leaves

was assessed for droplets representative of atmospheric sulfuric acid

mist. The detailed set of conclusions and results are presented in

appendix II.

1. Severe toxic symptoms were observed for 4-6 week old soybean pla

exposed to both "light and heavy" hydrated droplets of 1% and

10% solutions of sulfuric acid mist.

2. No apparent damage was observed for 4-6 week old soybean plants

exposed to realistic loadings of 1.7ym unhydrated sulfuric acid

mist droplets.

3. Further research is needed in this area. Controlled exposure

tests where moisture is added as an experimental parameter is

strongly suggested. Increased relative humidity and hydrated

droplets to provide an electrolyte pathway for physiological

effects to be realized appears to be a needed test condition.

15

0 PUBLICATIONS RESULTING FROM THIS STUDY

1 Wedding, J.B., Montgomery, M.M., "Deposition Velocities Monodisperse Dry Particles in Corn and Soybean Canopies," Submitted to International Journal of the Environment, Dec. 1978.

2 Wedding, J.B., Montgomery, M.M., "The Effects of Species, Growth Stage and Velocity on the Uptake of Particles by Corn and Soybean Canopies," To be submitted to Trans. ASAE, April, 1978.

3 Wedding, J.B., Ligotke, M., Hess, Dana F. "Effects of Sulfuric Acid Mist On Plant Canopies," Submitted to Environmental Science and Technology, November, 1978.

APPENDIX I

%

• DEPOSITION VELOCITIES FOR • ,

■ ' FULL-SCALE CORN.AND SOYBEAN

CANOPIES: A WIND TUNNEL SIMULATION

Prepared by .

■ James B. Wedding ■Associate Professor .Civil Engineering

■Colorado State University Fort Collins,-Colorado, 80523

Michael E. Montgomery Encotech, Inc.

P.O. Box 714, 434 St.-Street Schenectady, NY 12301

Submitted to-

International Journal of the Environment Dr. A.A-. Moghissi.

Editor In Chief P..0. Box 7166

Alexandria, VA . 22307

Submitted December,. 1978

Abstract

Deposition velocities have been determined for corn and soybeans

in the first 4-6 weeks of growth in a full-scale study of canopy flow

in a wind tunnel. Particles of 1, 5, 10 and 15 ym aerodynamic diameter

made of sodium fluorescein were injected into the Environmental Wind

Tunnel Facility at Colorado State University. Deposition velocities

were determined as a function of free stream velocity (185, 305 and

610 cm/sec) and approach flow turbulence intensity (- 1% and 8%). Plants

were arranged in realistic field configurations and hot-wire anemometer

studies confirmed that the fluid velocity profiles developed in the

wind tunnel were similar to the flow realized in canopies in actual

fields. An increase in velocity and turbulence intensity was found to

decrease the deposition velocities. A minimum deposition velocity was

observed at a particle diameter of 5 ym.

Introduction: Background and Purpose

The presence in the atmosphere of potentially deleterious aerosol

creates interest in the use of crops or trees as dynamic air filters.

Particles may arise from a variety of natural or anthropengic sources

such as wind erosion of soils, uranium mill tailings or nuclear waste

piles, the drift of aerially disseminated pesticides, sulfuric acid

mist emissions from stacks or automobiles, or accidential or purposeful

weapons explosion. In particular, the deposition of potentially harmful

particles onto croplands containing plants of economic importance could

have severe impact on potential yields. It has been shown by Wedding

(1975) that plant leaves are efficient collectors of aerosols with the

collection effectiveness a strong function of leaf surface character­

istics. Other researchers have investigated canopies as sinks for

2

gaseous contaminants, Hill (1971), Heck (1965, 1968), Jacobson (1966),

Rich (1970), Spedding (1969), Bennett (1975A, 1973B), Brandt (1962), or

other airborne particulate, Chamberlin (1970), Chadwick (1970), Langcr

(1965). Also numerous researchers have studied in detail the fluid

mechanics of canopy flow such as by Allen (196S) , Baynton (1964) ,

Bursinger (1974), Cionio (1965), Inoue (1963), Isobe (1964), Ito (1968),

Kawatani (1968), Legg (1975) to mention some.

The objective of this study' was to quantify deposition velocities

(V ) for full-scale canopy flows of two different growth stages of corn

(Zea Mays L.) and soybeans (Glycine Max L.) for particles of 1-15 ym

aerodynamic diameter at different flow velocities and approach flow

turbulence. The results presented herein will elucidate the effects of

particle size, turbulence in the flow appreaching the canopy, and free

stream velocity on deposition velocities for the small growth stages

studied for corn (28 cm) and soybeans (15 cm). A companion paper will

present the effects of variation of deposition velocity depending on

the plant species, location of a plant within the canopy and growth

stage.

Experimental Procedure

Wind Tunnel Tests

The Canopy and Wind Tunnel Facility

The plants utilized in the testing were live corn (Zea

Mays L.) and soybean (Glycine Max L.). The plants were quite dissimilar,

having different stem structure, leaf arrangement, leaf surface and

shape characteristics. They were chosen to allow observation of the

effect on deposition rates of these large differences in composition as

well as their recognized economic importance.

3

Plants of one species were placed in styrofoam holders, which were

shaped as furrows and rows. Referring to Fig. 1 the stands dimensions

were as follows: downstream length, 171.5 cm; cross-stream width,

121.9 cm; height to top of row, 76.2 cm; and height to bottom of furrow,

65.5 cm. The row 'spacing was 57.15 cm and the plant spacing was 19 cm.

This type of configuration was felt to be representative of actual field

furrows, especially irrigated fields. All tests reported employed two

such stands and hence each test utilized 56 plants in 6 rows of 6 pjants

each. The plants were oriented cross-stream to the wind tunnel flow.

The stands placed the canopy out of the effect of 'the wind tunnel floor

and walls.

The Wind Tunnel Facility employed for the testing is shown

schematically in Fig. 2 with the canopy configuration and particle in­

jection technique. The Facility is the Environmental Wind Tunnel at

Colorado State University, Fort Collins, Colorado. It is an open circuit

type having a working test section 17 m in length and 2.44 m high by

3.66 m in width.

The leading edge of the canopy was 2.43 m dounstream of the aerosol

injection point. Three mean wind speeds were utilized in the tests.

The mean wind speed was determined by using a calibrated Data Metrics

flowmeter. Mean velocity and turbulence intensity profiles with respect

to height and downstream position in the canopy were measured with a

calibrated TS1 anemometer, hot film probe and RMS voltmeter. The

measurements were taken to ensure that the velocity profile created by

the canopy configurations in the wind tunnel was indeed representative

of real world canopy flow. A biplane grid was used to vary the turbu­

lence intensity of the flow approaching the leading edge of the canopy.

4

It consisted of 3.8 cm x 3.8 cm aluminum bars placed in a square matrix

on 22.86 cm centers. The grid cross-section dimensions were 2.44 cm

in width by .83 cm in height.

Particle Generation, Characterization and Injection Techniques

The aerosols used in the testing were generated with a vibrating

orifice aerosol, generator. The aerosols consisted of solid sodium

fluorescein which allowed case of subsequent fluoroscopic analysis (sec

Sample Analysis). Four particle sizes tested had aerodynamic diameters

of 1, 5, 10, and 15 ym. The particle size and aerosol quality was

determined by taking samples of the freshly generated aerosol with a

sampling nozzle fitted with millipore filters type HA. The filter was

prepared for viewing with a transmission light microscope by placing a

small portion of the filter sample side down on a glass slide, adding

immersion oil followed by a cover slip. Aerosol size and consistency

was determined in this manner with the geometric standard deviation of

the aerosols less than or equal to 1.02 for all tests.

The aerosols were injected into the wind tunnel using the injection

manifold fastened to the wind tunnel floor as shown in Fig. 2. The

system was designed to minimize the transport loss of particles and to

deliver a temporally and spatially consistent particle cloud to the test

section. The aerosol entered the wind tunnel through two horizontal

rows of six 1.91 cm diameter inlet ports placed on 19.05 cm centers.

The two rows were at heights of 91 cm and 122 cm from the wind tunnel

floor. The manifold was centered in the wind tunnel and was 99.1 cm in

overall cross-stream width. Details or drawings of the system arc

available upon request.

5

The homogeneity of the aerosol cloud was determined prior to and

subsequent to each test with the aid of an isokinetic sampling manifold

equipped with 6 nozzles attached to absolute filters. The manifold was

108 cm in width with the nozzles spaced at equal intervals (IS cm) on

the same plane - see schematic in Fig. 2. If a variation in cloud

concentration between nozzles exceeding 10% was found, the data were

discarded and the test rerun.

Testing Procedure

The overall testing methodology was as follows. First a canopy of

either corn or soybeans was established in the wind tunnel. Hot-wire

anemomctry was used to determine if the velocity profiles were represen­

tative of the type of flow normally associated with canopies. None of

the plants in this initial canopy was used for deposition analysis.

Next the aerosol generator was started and the particles analyzed for

quality and size as previously discussed. The wind tunnel was then set

to the desired flow velocity of 183, 305, or 610 cm/sec. The sampling

manifold was then positioned in the upstream leading edge of the canopy.

The cloud concentration determined in this manner was scrutinized for

spatial consistency over the lateral and ve-rtical dimensions of the

canopy. If found to be consistent this value and the value determined

by a post test measurement were averaged and used as the denominator

in the deposition velocity (V ) calculation. Once these results were

confirmed along with consideration given to the canopy fluid velocity

profile, the injection manifold was covered to prevent contamination.

With the tunnel turned off, test plants were exchanged for the "dummy"

canopy used for determining the particle cloud concentration. Upon

6

completion of a test run the plants were removed from the tunnel and

carefully transported to the laboratory for immediate sample analysis.

Sample Analysis

All plants in the canopy, except those on the outer rows, were

immediately analyzed for flux data (mass/unit time-area) and ratioed to

the cloud concentration as measured with the isokinetic sampling mani­

fold to attain a deposition velocity. All leaves of each test plant

were placed singularly into beakers and distilled, deionized wash water

added. A four m£ aliquot of each sample solution was quantified in terms

of fluorescent content with the aid of a Turner Model 111 fluorometer.

The area of each leaf was measured with a pl.:aimcter Following analysis

and drying of the wetted surface. The time in the flux data was the

elapsed exposure time of each test.

Strong consideration was given to blanks prepared from nonexposed

controlled plant leaves to determine the background fluorescence that

existed in the test plants. Cuttings of numerous leaves of .equal area

to the tested plants were made to enable one to zero-out any reading

not arising from the deposited particles. Particles of solid sodium

fluorescein were used because the solvent was water and no damage to

the plant leaves resulted from the analysis procedure.

Results and Discussion

Fluid Mechanics

Hot wire anemometer measurements of mean velocity (u) and

turbulence intensity (vu' /u) (were vu' is the RMS of the fluctuating

component of velocity and u is the mean component--both in the direction

of flow) were made at numerous lateral and longitudinal positions as a

function of height. Also approach flow velocity profiles were taken

immediately downstream of the inlet manifold and up to the canopy.

These latter results will not be presented here (sec Montgomery 1978)

but revealed that the manifold injection system had essentially no effect

on the approach flow velocity profile leaving a nearly uniform velocity

profile at the leading edge of the canopy. These measurements did

reveal the anticipated retardation of flow upstream of the canopy and

some slight acceleration around the canopy itself. These measurements

provided the basis for discarding the plants on the outer rows for

deposition analysis.

Figure 3 is a typical plot of the local mean velocity profile for

corn (3a) and soybeans (3b) at 198 cm/sec at locations shown in Fig. 1

as PT1, PT3 and PT5. The code as given on the figure is interpreted as

velocity at the top of the canopy (u.) for relative plant heights (z/h)

where z is the vertical direction and h is the canopy mean height. The

code as given on the figure is interpreted as follous:

1C198 1st furrow, corn, 198 cm/sec

3S198 3rd furrow, soybeans, 198 cm/sec

These data show the velocity profiles for cprn have become nearly

invariant with downstream position and have the characteristic shape

of canopy flow such as given by Tan and Ling (1961) for mature corn.

The traces for soybeans indicate that the flow is slower in developing

but is still comparable to profiles published by Perrier (1971) for

mature soybeans.

The longitudinal components of relative turbulence intensity were

measured at the same locations noted for mean velocity. The results of

these studies arc given in detail by Montgomery (1978). Briefly, typical

8

values for intensity for corn was 20%, nearly invariant with height and

constant with respect to downstream location for PT3 and PT5 at 198

cm/sec. These data compare favorably with 20% turbulence intensity

values published by Uchijima (1964). The traces for soybeans indicate

substantially higher values of 40% for intensity again independent of

height and also downstream positions for PT5 and PT5. These values

compare well with the 40% values of intensity published by Perrier (1971)

for mature soybeans.

These data supply good evidence that the fluid flow profiles of

these canopies arc indeed representative of real world canopy flow

noting that these tests were conducted on plants in the early stages of

growth (as noted by the heights given in Figs. 3a, 5b).

Particle Deposition

Data for deposition results are presented using the deposition

velocity concept and represent average values over all the plants in

the canopy. The effects of lateral and longitudinal plant position as

uell as species will not be addressed in this manuscript.

Effect of Approach Flow Turbulence

Initially to determine if turbulence has an effect on the behavior

of a particle, the product T • U (where x = particle character­

istic-time, which is the particle mass/particle drag and U = local

particle velocity) is compared to the scale of the turbulence in the

flow regime of the particle. In the case of decaying turbulence pro-/~~2 -duced by the biplane grid used in this study, the intensity (vu1 /u was

- 8%) and the macroscalc of the turbulence, L of the turbulence is

determined'by the bar size of the grid - 3.8 cm. For the particle

9

behavior to be affected by turbulence, the following expression must

be satisfied: tp • U . << L. Thus, one would expect the grid generated

turbulence to greatly affect the behavior of the 1 and 5 ym particles,

to a lesser degree the 10 ym particles and have little or no effect on

the 15 ym particle behavior. One may also note that increased turbulence

will cause greater particle motion and the turbulent perturbation

imparted to the particle will have a dual effect - that of increasing

the probability of bringing a particle closer to the surface as well as

moving it away.

For the present study, the effect of turbulence in the flow

approaching the canopy was studied with and without the biplane grid

in place for particles of 1 and 5 ym aerodynamic diameter. Figure 4

reveals the effect of increasing the approach flow turbulence from the

tunnel background of - 1% to 8% generated by the grid. In nearly all

cases the effect is seen to lower the deposition velocity. As this is

not necessarily what one might expect, the results may be explained as-

follows. As the local velocities and accelerations of a particle are .

increased by the turbulent motion, the fact that a small particle may

be brought closer to a surface may indicate a lesser probaoility of

collision with that surface as the particle will tend to follou the flow

around the potential deposition surface. For larger particles (10-15 ym)

the particle will tend to leave the fluid streamlines more easily and

deposition could be expected to increase.

Effect of Free Stream Velocity

Free stream velocities of 183, 305 and 610 cm/sec were used to

determine the effect of velocity on particle deposition rate for canopies

of corn and soybeans. Results arc given in Fig. 5. The biplane grid

10

was in place for all tests. For the smaller particles (1 and 5 ym)

whose behavior is not governed by inertial e.ffects, the results of

increasing velocity was to decrease the deposition velocity for the

soybeans. For the corn, the deposition velocity first decreased and

then increased due to the deposition induced by negative pressures exist­

ing on the downstream side of the corn leaves. For the larger particles,

inertial effects begin to dominate behavior and the increased velocity

caused higher deposition velocities in all cases.

Particle Size

The particle sizes utilized in these tests ranged from 1-15 ym

which allowed one to study deposition that was controlled purely by

turbulent diffusion (1 ym), some effects of inertia (5-10 ym), and

strongly inertially governed behavior (15 ym). Again three different

test velocities of 183, 305 and 610 cm/sec were employed.

It is of interest to compare the values of deposition velocities

for other turbulent flows to those for canopies. Figure 6 shows a plot

of deposition velocity vs. particle diameter for various researches and

flow geometries. Note two interesting comparisons. First, the greater

mass transfer realized in the highly turbulent, larger scale canopy flow

causes a minimum deposition velocity to occur at 5 ym with an increase

seen at the 1 ym size. The other curves showing similar trends show

the minimum at -1 ym and Sehmel (1974) has calculated the increase to

begin m 0.01 ym using a Brownian Diffusion model approach. Thus, it

would appear that the canopy deposition plot is shifted to the right

with respect to other turbulent flows where less energy exists in these

flows to influence particle deposition. The second item of interest to

11

note is the considerably higher free stream velocities used in the other studies which after -10 ym resulted in a leveling off of the deposition velocities.

Referring again to Fig. 6 and picking a representative deposition velocity for the small particles (lym*) of say 0.05 cm/sec and using published values for cloud concentrations of urban and rural aerosol of 1 yg/m (Stukel 1975) one can predict the anticipated loading of a given leaf surface area in the canopy. For example, a typical average surface

2 area for a soybean leaf may be -12 cm in the first 4-6 weeks of growth (where deleterious aerosols may have their greatest effect). In a two week period of time without rainfall, and assuming no recntrainment (to ' be addressed shortly), one realizes a value of 1.8 yg or -2 x 10 1 ym particles that could deposit on this particular leaf (note of course that numerous other sizes of aerosol exist for potential deposition as well). Whether or not this is important to potential losses in crop yield is not the purpose of this present paper. However, the data presented herein allows such calculations of loading to be made. An • '

ongoing study is assessing the impact of such loadings of sulfuric acid i mist on live corn and soybeans. I

A final point to consider in scrutinizing these data for credibility , is the use made of solid uranine particles. The choice was dictated by analysis procedures as well as the need to affirm a known particle size

*Note that this size is representative of sulfuric acid mist particles that are emitted from stack emission on 1975 and later cars (Whitby 1974). For example, gasoline typically contains .02% sulfur by weight, and a car burns four gallons (24 lb., 10.9 kg) of gasoline/hr. If the mean diameter is 1 ym, this corresponds to 10 particles/hr-car , emitted - certainly a substantial amount to cause potential damage to corn or soybean fields existing along a busy highway.

at the plant surface. However, the question of particle bounce or

reentrainment loss is a possibility that must be considered. A paper

by Forney (1974) discussed this issue and noted that a plot such as

Fig. 6 would level off and that a decrease in V would be seen with

further increase in particle inertia (i.e., either larger particles or

higher velocities). This change is seen slightly for the 15 ym

particles only at the higher test velocities of 305 and 610 cm/sec for

the soybeans. The soybeans did have a greater tendency to flutter

violently in the wind at these speeds.

Conclusions

1. The data presented herein was obtained for full-scale canopy

flow of corn and soybeans at an early stage of growth (4-6 weeks).

The velocity profiles as taken with hot-wire anemomctry indicate

that t>he values obtained for deposition velocities may be applied

with confidence to similar field geometries in the atmosphere.

2. It was shown that approach flow turbulence did have an effect on '

the behavior of 1 and 5 ym particles. The overall effect was to -

decrease the deposition velocity.

3. Increasing free stream velocity decreased the deposition velocities

of the 1 and 5 ym particles and increased the deposition velocities

for 10 and 15 ym particles.

4. The predominant effect on deposition velocity was particle size.

A minimum deposition velocity was seen to occur at the 5 ym

particle size with an order of magnitude increase in V at the

1 ym size. The data compare with other flow geometries if those

results are shifted to the right, i.e., the minimum deposition

13

velocities occur at larger particle sizes for the highly turbulent

flow regimes found in a canopy.

5. The hypothesis that canopies or single plants can act as efficient

dynamic filters for the planned removal of airborne matter has been

well substantiated. Calculations can now be quantified as to the

magnitude of anticipated loadings on corn and soybean canopies for

the ultimate goal of a dose response curve for plant yield. Model­

ing efforts could be applied to plant canopies paralleling the

filtration theory for fiber filters.

14

BIBLIOGRAPHY

Allen, L. H., Jr., "Turbulence and wind speed spectra within a Japanese larch plantation," Journal of Applied Meteorology, 7:73-78 (196S).

Baynton, H.- W. , W. G. Biggs, H. L. Hamilton, Jr., P. E. Sherr, and J. J. B. Worth, "Wind structure in and above a tropical forest," Journal of Applied Meteorology, 4:670-675 (1965). Bennett, J. B. and A. C. Hill, "Absorption of gaseous air pollutants by a standardized plant canopy," Journal of the Air Pollution Control Association, 24:205-206 (1975A).

Bennett, J. B., A. C. Hill, and D. M. Gates, "A model for gaseous pollutant sorption by leaves," Journal of the M r Pollution Control Association, 25:957-962 (1975B).

Brandt, C. S., "Effects of air pollution on plants," in Air Pollution, A. C. Stern, editor, Academic Press, New York, 255-281, (1962).

Businger, J. A., "Aerodynamics of vegetated surfaces," Department of Aerosol Science, University of Washington, Seattle, Washington (1974).

Chadwick, R. C. and A. C. Chamberlain, "Field loss of radio-nucledes from grass," Atmospheric Environment, 4:51-56 (1970).

Chamberlain, A. C , "Interception and retention of radioactive aerosols by vegetation, "Atmospheric Environment,4:57-78 (1970).

Cionco, R. M., "A mathematical model for air flow in a vegetative canopy," Journal of Applied Meteorology, 4:517-522 (1965).

Forney, L. J. and L. A. Spielman, "Deposition of coarse aerosols from turbulent flow," Aerosol Science Vol. 5, pp. 257-271 (1974).

Heck, W. W. , J. A. Dunning, and I. J. llmdawl, "Interactions of environmental factors on the sensitivity of plants to air pollution, Journal of the Air Pollution Control Association, 15:511-515 (1975).

lleck, W. W., "Factors influencing expression of oxidant damage to plants," Annual Revision Phytopath, 6:165-1SS (196S) .

Hill, A. C , "A special purpose plant environmental chamber for air pollution studies," Journal of the Air Pollution Control Association, 17:745-748 (1967).

Hill, A. C , "Vegetation: a sink for atmospheric pollutants," Journal of the Air Pollution Control Association, 21:541-346 (1971).

15

15. Inoue, E., "On the turbulent structure of airflow within crop canopies," Journal of the Meteorological Society of Japan, 41:317-525 (1965).

16. Isobe, S., "Zero-plane displacement in relation to extinction of momentum flux in crops," Bulletin of the National Institute of Agricultural Sciences, Series A, 11:1-16 (1964).

17. Ito, S., "Inner and outer velocity distributions through tall simulated vegetation, "Technical Report CER67-68JEC61, Colorado State University, Fort Collins, Colorado (1968).

18. Jacobson, J. S., L. H. Weinstein, D. C. McCune, and A. E. Hitchcock, "The accumulation of fluorine by plants," Journal of the Air Pollution Control Association, 16:412-416 (1966).

19. Kawatani, T., and R. N. Meroney, "The structure of canopy flow field," Technical Report CER67-6STK66, Colorado State University, Fort Collins, Colorado (1968).

20. Langer, G., "Particle deposition and reentrainment from coniferous trees," Kolloid-Z. A. Polym. 204:119-124 (1965).

21. Lcgg, B. J., and I. F. Long, "Turbulent diffusion within a wheat canopy," Quarterly Journal of the Royal Meteorological Society 101:597-628 (1975).

22. Montgomery, M. L., M.S. Thesis, "Uptake of aerosols by plant canopies," Civil Engineering Dept., Colorado State University, Fort Collins (1978).

23. Perrier, E. R., J. M. Robertson, R. J. Millington, and D. B. Peters, "Spatial and temporal variation of wind above and within-a soybean canopy," Agricultural Meteorology, pp. 421-442 (1971).

24. Rich, S., P. E. Waggoner, and H. Tomlinson, "Ozone uptake by bean leaves," Science 169:79-80 (1970).

25. Sehmel, G. A. and W. H. Hodgson, "Predicted dry deposition velocities," Pacific Northwest Laboratories, Washington, BNWL-SA-S125 (1974).

26. Spedding, D. J., "Uptake of sulphur dioxide by barley leaves at low sulphur dioxide concentrations," Nature, 224:1229-1250 (1969).

27. Stukel, J. J., R. L. Solomon and J. L. Hudson, "A model for the dispersion of particulate of gaseous pollutants from a network of streets and highways," Atmospheric Environment Vol. 9 (1975).

28. Tan, H. S. and S. C. Ling, "A study of atmospheric turbulence and canopy flow," in The Energy Budget at the Earth's Surface, Part II USDA Production Research Report #72, pp. 13-25 (1963).

16

29. Uchijima, Z., and J. L. Wright, "An experimental study of airflow in a corn plant-air layer," Bulletin of the National Institute of Agricultural Science, Series A, No. 11, pp. 19-65 (1964).

30. Wedding, J. B., R. W. Carlson, J. J. Stukel, and F. A. Bazzaz, "Aerosol deposition on plant leaves," Environmental Science and Technology, 9:151-153 (1975).

31. Whitby, K. T., R. E. Charlson, W. E. Wilson, and R. K. Stevens, "The size of suspended particle matter in air," Science, Vol. 185, March 15, 1975.

LIST OF FIGURE CAPTIONS

1. Canopy configuration used in wind tunnel tests.

2. Environmental Wind Tunnel schematic.

3a. Velocity profile for corn in wind tunnel canopy flow.

3b. Velocity profile for soybeans in wind tunnel canopy flow.

4. Effect of approach flow turbulence on deposition velocity for corn

and soybean canopies for a range of particle sizes.

5. Effect of free stream velocity on deposition velocity for corn and

soybean canopies for a range of particle size.

6. Effect of particle size on deposition velocity for corn and soybean

canopies at various free stream velocities.

f

Dimensions in cm

FLOW FURROWS

TOP VIEW

-N,

AIR FLOW

A

r INLET TO TEST SECTION

^ MANIFOLD INJECT l Of J SYSTEM

ISOKINETIC -SAMPLING MANIFOLD

■0.61

1

-Bl-PLANE GRID

FLOW STRAIGTENERJ

V

3.66

•TWO CANOPY STANDS

•AEROSOL INJECTION

Dimansions in m e t e r s

FLO W METER

V

VACUUM PUMP

"o 6'

.Or

0.8

0.6

0.4

0.2

(cm/sec) h(crri) C ! C6 192.1 8 3^.88 D 3C6 BZ.'cT 3b.83 A 5C6 77.18 33.34

uyd

I.Or

OX

0.6

h

0.4

0.2

uh (cm/scc) h(cm)

O IS5 a 7 : f

A 5S6

106.04 24.75 fil.toO r"4.02 53.04 22.96

°ou J_ I

0.2 0.4 _ 0.6 u

0.8 .0

U h

Key " 1 , 1 8 3 = \j±m P a r t i c l e S i ze @ 183 c m / s e c

o c> to c CJ

o o o > c: o

o ex a

>

D Corn O Soy

Grid Bar S i z G = 3 .8 cm

5, 183

0

G r i d f u_\z' |°/c U I Z )

y u ' ( z r u ( z )

J

•0.2 G r i d - 8 %

0 ' r -

o O) I/)

o 10 tr

0

I0~J< 0

v-\ \ i^i / i o a Com

o Soy

Noto! Numbers Signify D0 ( a i n ) ,

Each Point is the Averag.-i of 2 9 P lants

six V - c > — - x ^ \ ^ o

o U » ( cm/sec ) • I O " 2

Liu Q Agarwal Pipe - U,-o= 10 G m/soc 10=I 27cm o

Chamberlain Grass U^cm/sec)

O 10

Sshmel -P ipe - Uco= 4 m / s e c ID= 7.|4 c r n

Dp (,um)

-\

f

p

APPENDIX I I

t

\

DRAFT

EFFECTS OF SULFURIC ACID MIST ON PLANT CANOPIES

Submitted to:

Environmental Science and Technology 1155 16th St., N.W. Washington, D.C. 20036

Proposed by:

James B. Wedding Associate Professor of Civil Engineering Colorado State University Fort Collins, Colorado 80523

Michael Ligotke Civil Engineering Department Colorado State University Fort Collins, Colorado 80523

F. Dana Hess Assistant Professor of Botany and

Plant Pathology Purdue University W. Lafayette, Indiana- 74907

ABSTRACT

Soybean plants 4-6 weeks old were exposed to sulfuric acid mist

droplets. The plants were grown under greenhouse conditions. Initially,

gross effects of unquantified topically applied sulfuric acid mist were

obtained by spraying plants with a dosage of one percent and ten percent

(by volume with water) acid with a polydisperse atomizer (- 5 ym mean

diameter, geometric standard deviation - 2.5). The ten percent solution

produced severe necrotic lesions and large chlorotic regions on the

acropetal leaves. A heavy application of the one percent solution

produced similar effects but with a reduced number of necrotic lesions.

A light application had no visual effect on the plants after 24 hours.

Subsequent detailed quantitative studies were performed using a

flow through exposure chamber equipped with a vibrating orifice aerosol

generator and growth lamps. Plants were exposed to 1.7 ym aerodynamic

diameter IS M sulfuric acid. Exposure times were up to 10 hours a day 7 extending to 14 days total fumigation period. Loading up to 10

particles/leaf were achieved after the full 140 hours. Background

humidity was - 40 percent. No visible toxicity symptoms of damage

resulted to the plants from the tests. Scanning electron microscope

observations of the 140-hour treated plants showed no apparent damage

due to the sulfuric acid treatment.

Introduction

The goal of the study was to assess both qualitatively and

quantitatively the effects of pure sulfuric acid mist on 4-6 week old

soybean plants. The investigation was performed qualitatively using a

hand held polydisperse atomizer and plants were lightly dusted with both

1% and 10% solutions. Quantitative results were obtained with a glass

exposure chamber equipped with growth lamps. 1.7 ym sulfuric acid

droplets were generated using a vibrating orifice type atomizer (11)

and exposure periods were up to 10 hours a day extending to 14 continuous

days of exposure.

Background

Ln the early 1970's it was reported that the installation of an

oxidation catalyst in automobile exhaust systems increased the amount of

particulate material emitted (1, 2). The chemical nature of the parti­

culate emission was published by Pierson, Hammerle and Kummer in 1974 (3) .

They found that "at a 60 mph road load a monolithic oxidation catalyst

converts almost half of the S02 into S03, the bulk of which is emitted

from the tailpipe as sulfuric acid." Forty percent of the particle mass

was found to be sulfuric acid. The rest of the particulate matter was

determined to be water that was associated with the sulfuric acid, a

substance known to be hygroscopic. If the catalyst was removed from the

exhaust system, the amount of sulfuric acid was reduced by 90%.

There have been no in-depth quantitative measurements of

environmental influences of sulfuric acid emitted from automobiles

equipped with a catalytic exhaust system. There have, however, been

studies of the effects of sulfuric acid originating from other forms of

pollution. Scientists in Europe have reported that over the past several

years rain at some locations in Europe has increased acidity (acid

rain). One of the strong acids that is causing this decrease in the pH

of rain is sulfuric acid (4). The impact on the ecosystem is unknown;

however, such things as increases in leaching of nutrients from plants

and soils, and changes in metabolism in plants and other organisms (4)

have been proposed. Recently, the effect of simulated acidic rain on

greenhouse and field grown herbaceous vegetation was investigated (4) . i

Dilute sulfuric acid (pH range - 2.2 to 3.4) was applied for durations

of from 1 minute to 9 hours. The application was repeated daily for up »

to 4 days.' Foliar injury to plants occurred after the 1 minute treat­

ment if the pH of the treatment solution was below 2.6. For the 9 hour

treatment, injury occurred if the pH was 3.4 or below. The most common l

type of injury observed in this study was necrotic lesions on the foliage r

of treated plants, which is sometimes called leaf spotting (6). Other

symptoms of sulfuric acid injury have also been reported. Tomiya et al.

(7) treated plants with dilute sulfuric acid and found that the sulfur

content of the plant tissue significantly increased, the chlorophyll

content and number of chloroplasts decreased, and the water content of- r

leaf tissue decreased as the sulfuric acid concentration increased. At i

concentrations of 0.1% sulfuric acid, there was a disruption of tissue ,

in the spongy mesophyll and palisade layers of the leaf.

The purpose of the research being reported is to determine if

simulated sulfuric acid particle emissions from catalyst equipped exhaust

systems are capable of inducing damage to the important agronomic crops

of corn and soybeans. The significance of this study is that, to date,

no qualitative or quantitative data has been collected with regards to

the potential environmental impact of the sulfuric acid particles emitted '

from automobiles equipped with catalytic exhaust systems.

Experimental Procedure

Plant Growth and Care

Five corn (Zea mays L.) or soybean (Glycine max L. Merr.) seeds

were planted in five inch diameter styrofoam pots (Tufflite Plastics

Inc., Ballston Spa, New York, 12020) using a stream sterilized mixture

of loam soil, peat and sand (1:1:1). The plants were grown under green­

house conditions with an average day:night temperature regime of 25 C

and 20 C respectively. Supplemental lighting was provided by fluorescent

lamps (cool-white) in order to obtain a sixteen hour photoperiod. While

growing, the plants received twice weekly supplemental applications of

nutrients (S). After emergence from the soil the plants were thinned to

one uniform plant per pot. Both control plants and test plants were

transported to the exposure chamber. After the test plants were sub­

jected to the acid fumigation, they were returned to the greenhouse

along with the control plants. All plants were watered an equal amount

on a daily basis.

Fumigation of Plants with Sulfuric Acid

The qualitative, gross effects of sulfuric acid on the plants were

determined by a light spraying (one broad sweeping pass) of the foliage

of soybean plants with a hand-held polydisperse atomizer. Solu­

tions used were 1% and 10% volumetric concentrations of sulfuric acid

mist and water. The atomizer produced a mass mean aerodynamic diameter

of 5ym with a geometric standard deviation of 2.1. No attempt was made

to quantify the application.

Detailed quantitative tests were performed with the aid of the

glass walled chamber equipped with growth lamps shown in Figure I. Six

plants were exposed at a time in the chamber for varying periods of

I 8 0 cm

1 6 4 cm

f "

t"

i ^ :

^ _ . L -Plant I Locations |

rV! • i , i i

x, !

I v .

- * - - - ■

ld= 7± +T

°l_n f°

^ j

"Grow'n Lamps

i r ^ © o o Vibrat ing Orif ice Aerosol

Genera lor

Figure 1. Glass-walled exposure chamber.

Freshly generated aerosol produced by the vibrating orifice atomizer

shown was injected into the chamber with flow continuity achieved by the

four exhaust ports. Deposition of the small particles (1.67ym) was

induced by Brownian motion in the near quiescent flow regime (injection 3

rate 12.75 m /hr). The fluid mechanics were designed purposely to in­duce slow deposition rates thereby ensuring light particle loading over long periods of time. These conditions were felt to be more representa­tive of an actual atmosphere environment than excessively large doses over short periods of time. Exposure periods were from 4-10 hours a day for up to 14 days. Dosage rates were compared to rates calculated from depositions velocities as determined by Wedding (9 ) in full-scale wind tunnel tests on 4-6 week old soybean plants.

2 Qualitative assessment of the particles 1 cm of leaf surface area

realized in the tests were determined by first calibrating the chamber

using 1.91ym particles of sodium fluorescence equivalent in aerodynamic

diameter to the 1.67 sulfuric acid droplets. Sections of leaf exposed

for various time periods in the chamber were taken from plants and

placed into wash water. Subsequent analysis of the solution with the

aid of a calibrated Turner Model III Fluorometer yielded the deposited

mass. Careful consideration was given to blanks of unexposed leaves to

ensure zeroing out of any residual background fluorescence.

Particle size and quality were affirmed by optical microscopy study

of the droplets deposited on glass slides placed al numerous locations

within the test chamber. The absence of moisture on the droplets when

they arrived at the plants was affirmed by scrutiny of the stain

diameters left on Kromekote cards placed at random locations throughout

the chamber.

A steady state concentration of acid droplets was created in the

test chamber before plants were inserted. This was achieved by running

the generator into an empty chamber for a period of seventy minutes

prior to the initiation of each test.

Evaluation of Results from Plant Exposure

Gross Qualitative Study

Significant symptoms of toxicity were noted when the plants were

exposed to the hydrated sulfuric acid droplets produced by the hand.

held polydisperse atomizer.

A heavy application of the 10% sulfuric acid solution resulted in

severe damage within 2.5 hours after treatment. The foliage was twisted

and definite lesions were forming around individual sulfuric acid drop­

lets. Another characteristic response was that plants were flaccid when

compared to control soybean plants. Twenty-four hours after the treat­

ment, the plants had regained their trugidity; however, numerous necrotic

lesions were present on the leaves. Lesions were not observed on the

stems of treated plants. In this experiment, the lesions did not increase

in size as time from application to observation was increased beyond 24

hours. This would indicate that toxic concentrations of sulfuric acid

were not translocated. This lack of increase in lesion size may have

been due to the acidity being neutralized by the buffering capacity of

the cytoplasm in individual cells. Another explanation is that death

of the tissue in contact with the sulfuric acid was instantaneous, thus

preventing translocation to other living tissues.

Where a light application of a 10% solution of sulfuric acid was

appliced to soybean plants, younger leaves (acropetal leaves) were more

affected by the treatment than were the older leaves (basipetal leaves) .

As with the heavy application, the plants appeared flaccid 2.5 hours

after treatment. Twenty-four hours after treatment the turgidity of the

plants was regained. The toxic symptoms of this treatment were large

chlorotic regions on the acropetal leaves, which would indicate that

some translocation had taken place prior to tissue damage. This region

was not limited to any one area of the leaf. Small lesions observed in

the 10% heavy application were not observed on these plants. This would

suggest that the heavy applicati6n of sulfuric acid had caused death by

acid burning of the tissue, while the light application of sulfuric acid

was causing death by a physiological disorder, which may or may not be

related to the pH effect of the sulfuric acid.

When the sulfuric acid concentration applied to the soybean plants

was reduced to 1%, the effect of a heavy application was similar to the

heavy 10% application; however, the number of necrotic lesions per leaf

was significantly reduced. Some leaf curling was noted 2.5 hours after

treatment; however, no lesions were noted (Figure 2-1). Twenty-four hours

after treatment, the young expanding leaves were curled and many small.

necrotic lesions were apparent on the leaves (Figure 2-2). These lesions

were most abundant near the margins of the leaves. As was observed for

the heavy application of the 10% concentration, there did not appear to

be any translocation of the sulfuric acid. A light application of 1%

sulfuric acid had no visual effect on the plants at the 2.5 or 24-hour

observation period.

One month after treatment with a heavy application of 1% sulfuric

acid the small lesions were still apparent. In addition, the leaves

were chlorotic and appeared to be undergoing a general senescence

(Figure 2-1). It is important to note that the plant tissue formed after

Figure 2. Plants Treated with Polydispersion Mixture of Sulfuric and Mist and Water. 2-1. Plants created with heavy application of 1% solution -

2.5 hours after treatment 2-2. Plants treated with heavy application of 1% solution -

24 hours after treatment 2-3 Plants treated with heavy application of 1% solution -

30 days after treatment 2-4 Plants treated with heavy application of 10% solution -

2.5 hours after treatment

9

the sulfuric acid treatment appeared normal. This normal regrowth

indicates that the sulfuric acid was not translocated in toxic concen­

trations, but rather damage was restricted to areas where the chemical

came in direct contact with living epidermal tissues of the plants.

Quantitative Study, Glass Exposure Chamber

The plant loadings plotted as droplets of sulfuric acid mist/cm

of leaf surface vs. exposure time (hrs) is given in Figure 3. Note

that the loadings become large after long exposure periods but the

deposition' rates are low. To determine if the rates are realistic to

expect for plants existing in the atmosphere, one refers to work by

Wedding and Montgomery (9). Deposition velocities are published for

4-6 week old corn and soybean plants in a full-scale wind tunnel test.

A depsotion velocity for a -2 ym particle diameter at a representative

average free stream velocity of 183 cm/sec (4 mph) is .02 cm/sec.

Applying published values for ambient cloud concentration of aerosols 3

of lmg/m (10) (which is conservative but not unreasonable to antici­pate for the concentrations of sulfuric acid mist droplets existing alongside a roadway) one can calculate the predicted loading of a given leaf in a canopy. The resulting flux would then be given as

-2 2 0.432 x 10 part/cm sec.

The slope of Figure 3 yields a value of 0.68 droplets/cm sec.

Thus, the cliambcr deposition rate is -150 times the projected atmospheric

rate. Note, however, that value of 1 nig/in could easily be higher for

crops existing adjacent to an interstate or downwind of a cool fixed

power plant equipped with a scrubber. This accelerated deposition rate

was established to shorten the time frame from a test to no longer than

a two-week period of time and still realize a significant loading level.

4 5 6 Exposure Time (hours)

Figure 3. Droplet deposition on soybean leaves realized in chamber shown in Figure 1.

For the total 140 hour exposure time and an average leaf surface of 2 7

-40 m particle loadings up to -10 particles/leaf were realized.

The experiments conducted in the exposure chamber did not result in

any visual toxicity symptoms on the test plants. In addition, growth of

the treated plants was not different from the control plants when

measurements were taken at selected intervals after treatment all

measurements were recorded photographically. Scanning electron micro-

slope observations of treated (lu hours per day for two weeks) and

control soybean leaf surfaces showed no apparent damage "due to the sul­

furic acid treatment.

There are several possible reasons for not observing damage in

plants exposed to the pure sulfuric acid particles. First, the sulfuric

acid load may have been below the threshold amount needed to induce

measureable damage to the plant species tested. Secondly, the sulfuric

acid particles were in a dehydrated state upon contacting the leaf sur­

face and remained dehydrated due to the low relative humidity at the

test site. This dehydrated state may have prevented sulfuric acid

interaction with the plant surface. Thirdly, the particles of sulfuric

acid may have been of the size where most did not directly contact the

plant surface, but rather remained supported on projections of the

cuticle. It seems reasonable to anticipate that some of the droplets

did in fact penetrate to the leaf surface and some immediate local

damage should have occurred.

LITERATURE CITED

1. Moran, J. B., 0. J. Manary, R. 11. Fay, and M. J. Baldwin (1971). Development of particulate emission control techniques for spark-ignition engines. EPA Air Programs Publication APTD-0949.

2. Gentel, J. E., 0. J. Manary, and J. C. Valenta (1973). Characterization of particulates and other non-regulated emissions from mobile sources and the effect of exhaust emissions control devices on these emissions. EPA Air Programs Publication APTD-1567.

3. Pierson, W. R., R. H. Hammerle, and J. T. Kummer (1974). Sulfuric acid aerosol emissions from catalyst-equipped engines. SAE Paper 750095.

4. Likens, G. ?.., F. II. Borman, and N. M. Johnson (1972). Acid rain. Environment 14:33-40.

5. Jacobson, J. S. and P. Van Leuken (1977). Effects of acidic precipitation on vegetation. Proceedings, 4th International Clean Air Congress, Tokyo, 4:124-127.

6. Middlcton, J. T. (1966). Plant damage: An indication of the presence and distribution of air pollution. Bulletin, World Health Organization (Geneva) 34:477-4S0.

7. Tomiya, K., S. Tanida, K. Aonuma, M. Takahashi, A. Kawana, and M. Doi (1975). The effects of sulfate ion in rain water on trees. On the response of trees sprayed with very dilute sulfuric acid, Part 2. Proceedings, Japan Forestry Society 86:449-451.

8. Hoagland, D. R. and R. I. Anion (1950). The water culture method for growing plants without soil. California Agricultural Experi­ment Service Circular No. 547.

9. Wedding, J. B. and M. E. Montgomery (1978). Deposition velocities for full-scale corn and soybean canopies: A wind tunnel simulation. Accepted by Journal of Aerosol Science, October.

10. Stukel, J. J., R. L. Solomon, and J. L. Hudson (1975). A model for the dispersion of particulate or gaseous pollutants from a network of streets and highways. Atmospheric Environment, Vol. 9.

11. Wedding, J. B. (1975). Operational characteristics of the vibrating orifice aerosol generator. Environmental Science and Technology, Vol. 9, No. 7, July. p. 673.

Conclusions and Recommendations

Severe toxic symptoms were observed for 4-6 week old soybean plants

exposed to both "light and heavy" hydrated droplets of 1% and 10%

.solutions of sulfuric acid mist.

No apparent damage was observed for 4-6 wjeek old soybean plants

exposed to realistic loadings of 1.7ym nonhydrated sulfuric acid

mist droplets.

Further research is needed in this area. Controlled exposure tests

where moisture is added as an experimental parameter is strongly

suggested. Increased relative humidity and hydrated droplets to

provide an electrolyte pathway for physiological effects to be

realized appears to be a needed test condition.