June 1986
A STUDY OF THE FORMATION AND TRANSPORT OF ACIDIC SPECIES BY
NON-PRECIPITATING CUMULUS CLOUDS DURING VENTEX-84
ATMOSPHERIC SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
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A STUDY OF THE FORMATION AND TRANSPORT OF ACIDIC SPECIES BY
NON-PRECIPITATING CUMULUS CLOUDS DURING VENTEX-84
by
A. J. Alkezweeny
Pacific Northwest Laboratory
Rich!and, WA 99352
InterAgency Agreement DW89930059
to the U.S. Department of Energy
Project Officer
Jason K.S. Ching
Meteoro.logy and Assessment Division
Atmospheric Sciences Research Division
Research Triangle Park, NC 27711
ATMOSPHERIC SCIENCES RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
RESEARCH TRIANGLE PARK, NORTH CAROLINA 27711
-------
NOTICE
The information in this document has been funded partly
by the United States Environmental Protection Agency
under Interagency Agreement DW89930059-01 to the United
States Department of Energy. It has been subject to the
Agency's peer and administrative review, and it has been
approved for publication as an EPA document.
1i
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ABSTRACT
A field experiment was conducted by Pacific Northwest Laboratory (PNL)
in Kentucky during the period July 8 to August 18, 1984 as part of the
VENTEX-84 field study to investigate the formation of sulfate and nitrate
aerosols and in the vertical transport of pollutants by non-precipitating
cumulus clouds. VENTEX is a research component of the National Acid Precip-
itation Assessment Program.
Analyses of data collected from DC-3 and Cessna 411 aircrafts and from
ground sampling show ratio of sulfate concentration to the total sulfur con-
centration (the sum of sulfate and sulfur dioxide) to be larger at the top of
clouds than at their bases. In-cloud oxidation rates were calculated to be
in excess of 100%/hr. The ratio of the total nitrate concentration (the sum
of nitric acid and nitrate aerosols) to the total sulfur concentration at
cloud tops, was higher than that at cloud bases on many days. This result
suggests that nitrate can form in the clouds but not as frequently as sulfate.
Ground concentrations of ammonia declined around midday followed by an increase
in the afternoon. Sulfur dioxide concentrations exhibit an opposite trend.
A case study of morning and afternoon soundings of ozone indicated vertical
transport of pollutants from the mixed layer to the cloud layer.
iii
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CONTENTS
Abstract i i i
Tabl es vi
Figures vi 1
Acknowledgements vi i i
Section
1. Introduction 1
2. Objectives 2
3. Scope 2
4. Previous Work 3
Cloud Chemistry 3
Vertical Transport 4
5. Field Experiment 5
Cloud Chemistry 7
Vertical Transport 8
6. Data Management 9
7. Results and Discussion 9
Cloud Chemistry 9
Vertical Transport 17
8. Field Study QA/QC Activity 20
9. Summary 30
References 31
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TABLES
Number Page
1 Comparison between the normalized concentrations of sulfur
aerosols measured at the cloud inflows (cloud bases) and
the outflows (cloud tops), indicating sulfate production.
Data from Alkezweeny and Hales (1981) 4
2 Techniques and detection limits for anion and cation
analyses 8
3 Data collected during VENTEX-84 by the PNL DC-3 aircraft
at bases, tops, and higher than cloud tops of non-
precipitating cumulus clouds. Altitudes are in thousands
of meters, and the3concentrat1on of S04, SO?, HNOo, and N03
are in nanomoles/m . Times are in eastern daylight time. . . 10
4 Ratios N/S and SO^ at cloud bases, B, and cloud tops, T,
where N is the concentration sum of nitric acid and
nitrate aerosols, and S is the sum of sulfate and sulfur
dioxide concentrations, k is the first order oxidation
rate of SO^ in clouds in %/minute. The ammonia and ozone
concentrations are in nonamoles/m and ppb respectively,
and the temperature, T, is in °C 11
5 Comparison between measured and simulated of SC^, NHj, and k.
Data from Nair et al. (1985) 14
6 Aircraft flight log during VENTEX-84 23
7 Instrument calibration methods and schedules 24
8 Accuracy and completeness of the measured parameters during
VENTEX-84 27
VI
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FIGURES
Number Page
1 Summary of VENTEX-84 activities 6
2 Ammonia concentrations measured on the ground near Kentucky
Center for Energy Research Laboratory in Lexington, KY.
August 12, 1984 15
3 Sulfur dioxide concentrations measured on the ground near
Kentucky Center for Energy Research Laboratory in Lexington,
KY. August 12, 1984 16
4 Cross sectional data of ozone, light scattering, relative
humidity, and temperature derived from the aircraft
penetrations, at constant altitude, through cloud tops
on the morning of July 13, 1984 18
5 The same as Figure 4 except the data were collected in
the afternoon 19
6 Ozone vertical profiles for the morning and afternoon of
July 13, 1984 21
7 Temperature vertical profiles for the morning and afternoon
of July 13, 1984 22
vn
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ACKNOWLEDGEMENTS
Several people contributed to the success of trhe field experiment .those
are: K.M. Busness, G.W. Dennis, J.L. Gregory, T. Heimbigner, D.W. Glover,
R.V. Hannigan, G.L. Laws, and A.C. Leslie, of PNL. The contributions of the
personnel from Argonne National Laboratory, Kentucky Center for Energy Research
Labratory, and Research Triangle Institute whose cooperation during the
VENTEX84 field study made it possible to perform an integrated variety of
measurement program of common goal. Credit also due to the members of the
National Weather Service, stationed at the Blue Grass airfield in Lexington,
KY who willingly supplied all the weather information requested and for their
competence in high quality forecasts. Special thanks to the Kentucky Energy
Cabinet and the Kentucky Center for Energy Research Laboratory for extending
their technical and logistical support during the entire period.
This research has been funded as part of the National Acid Precipitation
Assessment Program by an Interagency Agreement from the US Environmental
Protection Agency to the US Department of Energy (DW930059), Pacific Northwest
Laboratory (PNL) under a Related Services Agreement, Contract DE-AC06-76RLO
19830. PNL is operated for DOE BY Battalia Memorial Institute.
Although the information in this document has been funded wholly or in
part by the US Environmental Protection Agency, it does not necessarily
reflect the views of the Agency and no official endorsement should be inferred.
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INTRODUCTION
Satellite photographs show that, at any one time, approximately half of
the earth's surface is covered by clouds. However, it has been estimated
that less than one tenth of this cover can produce precipitation (McDonald
1958). This means that more than 90% of the cloud cover evaporates and may
form clouds at a later time. If we assume that the cloud cover thickness is
3.0 km and the liquid water content of the cloud is 0.5 g/m , then the average
2
liquid water over the earth's surface is 1.5 kg/m . Because the global average
precipitation is about 1 m/year (Sellers 1974), the average residence time of
liquid water is about 13 hours. However, the average lifetime of a cloud is
much shorter than that, approximately in the range of 30 minutes to 1 hour
(Pruppacher and Klett 1978). Therefore, the clouds must go through
approximately 13 to 26 cycles of condensation and evaporation before their
water reaches the ground. During cloud formation, atmospheric aerosols and
gases are incorporated in the cloud droplets and may undergo chemical and
physical changes before they are reemitted to the atmosphere. Possible changes
are the formation of new aerosol particles by the aqueous phase chemical
reaction, and the modification of the aerosol size distribution. These changes
do influence the rates of wet and dry removals of the pollutants from the
atmosphere and their impact on man.
During the warm season its very common to see non-precipitating cumulus
clouds covering a substantial portion of the visible sky. The National Weather
Service observational record for the period from 1978 to 1981 shows that these
clouds were present over Lexington, KY approximately 17 days in each month of
June, July, and August (Alkezweeny 1984). Plank (1969) reported that the
total volume of a typical sky cover over Florida peaks around midday.
Furthermore, the ratio of this volume to the volume of the boundary layer
below, calculated from his data, is between 0.3 and 0.4 for the time period
1100 to 1500^. Over Lexington, KY this ratio varies over a wider range from
one day to the other but the averaged value is in this given range. Since
the clear air first order transformation rate of sulfur dioxide to sulfate is
less than 5%/hour and also peaks around midday (Calvert and Stockwell 1983),
(a) All times reported in this report are in eastern daylight time.
1
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and as will be seen later that the in-cloud conversion rate can be much higher.
Therefore the presence of these clouds contributes significantly to the sulfate,
and possibly nitrate, levels in the atmosphere.
Since cumulus clouds form by convective activities that originated near
the surface, they transport pollutants to the cloud layer. Later in the
afternoon, when the clouds evaporate and vertical mixing is poor, a layer of
pollutants may exist and can be transported horizontally to other regions.
Distance transport is also possible if the clouds penetrate into the stable free
atmosphere above the mixed layer evaporate by mixing with the dry air and the
residue can be carried away by the wind which is generally high at those
elevations.
This report is the second in a series of reports that describes the VENTEX
field studies conducted near Lexington, KY. The first one was published by
Alkezweeny (1984). In this report, description of the experiment conducted
during the summer of 1984 (VENTEX-84), from July 8 to August 18, will be
presented, and samples of the data collected will be given. Possible uses of
the data and example of data manipulation will be illustrated.
OBJECTIVES
The principal objectives of this program are as follows:
• to determine the production of sulfate and nitrate aerosol particles by
non-precipitating cumulus clouds
• to investigate the vertical transport of pollutants caused by cumulus
convection
SCOPE
The basic scope of this project is to generate a large data base
comprehensive enough for the development and validation of a cloud chemistry
and vertical transport modules for the non-precipitating clouds. This will
be accomplished through field studies and data interpretation. Statistical
2
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analysis of the data will also be carried out to study the transformation and
transport.
PREVIOUS WORK
CLOUD CHEMISTRY
It has been established that dissolved sulfur dioxide can be oxidized to
form sulfate in liquid water. The rate of oxidations by ozone and hydrogen
peroxide have been measured (Maahs, 1983; Martin and Damschen, 1981). On the
other hand, observations of sulfate formation in natural clouds are very
limited. The first observation was reported by Alkezweeny and Hales (1981).
Using instrumented aircraft, Alkezweeny and Hales collected aerosol samples
at bases and tops of non-precipitating cumulus clouds and analyzed for sulfur
and trace metal content of the aerosols. Since in similar type of clouds the
majority of inflow and outflow are at cloud bases and tops respectively, a
comparison between aerosols measured in the two sites may be an indication of
aerosol formation. Furthermore, aerosols emerging from cloud tops are diluted
because of mixing with dry clean air above the mixed layer, therefore, the
concentration needs to be normalized by a conservative tracer (a tracer that
does not change chemically during its residence in clouds). The element Fe
and K were chosen and the normalized concentrations are given in Table 1. It
can be seen that the concentrations at cloud tops are higher than cloud bases.
The increases on July 17 are not significant and fall within the measurement
error, which indicates that sulfate did not form on this day, either because
of a lack of sulfur dioxide in the air entering the clouds or some other reason
such as a lack of oxidant. On the other hand, definite sulfate formation is
shown in the July 19 data; clearly the increases in the concentrations are much
larger than measurement errors. Unfortunately, they did not measure sulfur
dioxide needed in order to estimate the oxidation rate.
Sulfate formation has also been detected in wave clouds by Hegg and Hobbs
(1982). They found that the conversion rates of sulfur dioxide to sulfate to
be variable, and the rate can be as high as 300%/hr. When power plant plume
interacted with a cloud, Gilliani et al. (1983) estimated that the average rate
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was (12 + 6)% /hr for a midsummer day. Similarly, Eatough et al. (1984) deduced
an average rate of (25 + 4)% /hr when an oil-fired power plant plume passed
through a fog bank.
TABLE 1. Comparison between the normalized concentrations of sulfur aerosols
measured at the cloud inflows (cloud bases) and the outflows (cloud
tops), indicating sulfate production. Data are from Alkezweeny and
Hales (1981).
DATE POSITION S/Fe S/K
7/17/79
7/19/79
CLOUD BASES
CLOUD TOPS
CLOUD BASES
CLOUD TOPS
4.9 + 0.7
6.0 + 1.2
6.0 + 1.1
28.0 + 4.0
7.8 + 1.3
9.7 + 2.5
13.6 + 2.8
41.0 + 6.5
VERTICAL TRANSPORT
Experimental studies of the vertical transport by cumulus activities
started only a few years ago, and are mostly qualitative in nature. In one
experiment, Alkezweeny and Hales (1981) made a constant altitude sampling
flight above a field of non-precipitating cumulus clouds over Illinois and
detected boundary layer aerosols and trace gases when the aircraft passed
over a cloud. Ching et al. (1983) made several penetrations by instrumented
aircraft through cumulus clouds over southeastern Pennsylvania and measured
ozone concentrations 10 to 15 ppb higher than the concentrations outside the
clouds at the same elevation. Based on analysis of several vertical profiles
of Radon 222, an inert gas of continental ground origin, Liu et al. (1984)
estimated that 55% of the Radon 222 in summer was transported out of the mixed
layer. Isaacs et al. (1983) carried out preliminary analyses of their data
and estimated the rates of volume of subcloud air pumped through the cloud to
the total volume of the subcloud layer to be 50%/hr in the summer and 20%/hr
during other seasons. During VENTEX-83, SF6 tracer was released on two
occasions within the mixed layer, just below cloud bases, and on another
occasion at tops of a field of active clouds. Samples were taken both on and
above the ground (Alkezweeny 1984, Ching and Alkezweeny 1985). When all samples
were analyzed the following picture emerged: pollutants are carried upward
to the cloud layer by thermal plumes or cloud updrafts. The cloud layer
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consists of fair weather cumulus clouds, and towering clouds in various stages
of their growth. The towering clouds penetrate deep into the free atmosphere
and when they evaporate they leave the transported material aloft. The
detrainment occurs primarily at and above the cloud top. On the other hand,
the downdrafts associated with these clouds bring free tropospheric air into
the mixed layer and ultimately to the ground. Niewiadomski (1986) used a
three-dimensional cloud model to investigate the vertical transport of
pollutants by a field of non-precipitating cumulus clouds. Based on his
numerical simulation, he concluded that a field of relatively weak and sparse
cumuli can in one hour reduce the average boundary layer pollutant content
by 15%.
FIELD EXPERIMENT
The VENTEX-84 field program was conducted near Lexington KY during the
period July 8 to August 18. The field activities involved several research
groups, and consisted of ground sampling and aircraft sampling in the clouds
and their environment. A summary of these activities is shown in Figure 1.
These groups are: Pacific Northwest Laboratory (PNL), Argonne National
Laboratory (ANL), Research Triangle Institute (RTI), and Kentucky Center for
Energy Research Laboratory (KCERL). Physical characteristics of clouds were
determined by RTI using a laser finder and photography. Basic boundary layer
parameters such as heat fluxes, height of the mixed layer top, vertical profiles
of temperature and relative humidity, and wind speed and direction at the
ground were obtained daily by ANL. KCERL provided logistical support and
carried out chemical analyses of exposed filters. The PNL contribution
consisted of two instrumented aircraft, ground sampling of aerosols and trace
gases, and releases of radiosondes. Details of the PNL activities will be
described below under subsections cloud chemistry and vertical transport.
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FIGURE 1. Aircraft flight paths to characterize the cloud environment.
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CLOUD CHEMISTRY
Samples of aerosols and trace gases were collected above the mixed layer
in cloud-free air (background samples), generally above 3,000 nra , at the cloud
inflow region (cloud bases) and cloud outflow region (cloud tops) using the
PNL DC-3 aircraft. The background samples were needed because when clouds
penetrate into the free atmosphere above, they mix with dry air and evaporate;
thus, the samples taken at the cloud outflow must be corrected for the
background concentrations. The aircraft flight routes consisted of a constant
altitude bow-tie path with one leg of the flight path passing over the VENTEX
ground sampling site (Figure 1). Several parameters were measured in real-time;
these are: 03, S02, NOX, aerosol light scattering, aerosol size distribution,
temperature, dew point temperature, altitude, turbulence in the inertial
subrange, and aircraft position. The aircraft was equipped with two high-volume
o
samplers. Each sampler used a filter pack that exposed 21.2 cm of the filter
area. One filter pack consisted of a Teflon® filter for the collection of
aerosols, followed by a cellulose filter impregnated with sodium chloride for
nitric acid collections, followed by another cellulose filter impregnated
with potassium carbonate and glycerine for sulfur dioxide collections. The
second filter pack employed a Teflon® filter, backed by a cellulose filter
treated with oxalic acid for the collection of ammonia gas.
As part of the surface-level sampling, two filter packs were used to
measure the chemical composition of aerosols and to monitor the concentrations
of sulfur dioxide and ammonia gas.
At the beginning of filter sampling an identical filter pack was handled
but not exposed and later analyzed in the same manner as the filter pack that
is being exposed in the high-volume sampler, so that filter blank and
contamination corrections can be made. Each exposed filter was placed inside
a 50 ml plastic syringe which contained distilled deionized water and left
for 24 hours, transferred to 60 ml plastic bottles, and analyzed. This filter
extraction technique was checked at PNL chemistry laboratory and found to be
more than 95% efficient in extracting water soluble compounds. The extracted
(a) All altitudes reported in this report are above sea level.
® Registered trademark of Du Pont de Nemours, E.I. & Co.
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solutions of the exposed and blank teflon filters were checked for conductivity
and pH, and then analyzed for anions and cations. Table 2 lists the methods
of analyses and the detection limits of the technique for each species. Nitric
acid and sulfur dioxide were determined as nitrate and sulfate ions by the
ion chromatography method. Ammonia was determined as ammonium ions by the
Automated Wet Chemistry (Colorimeter) technique.
VERTICAL TRANSPORT
The vertical transport was studied using two Instrumented aircraft, the
PNL DC-3 and Cessna 411. The DC-3 was outfitted with a gust probe and Inertial
navigation system for measurement of wind velocity and turbulence in real-time.
The data were made simultaneously with the cloud chemistry measurements
described above; thus, making it possible to determine fluxes of pollutants at
cloud bases and tops.
The Cessna 411 aircraft was instrumented to measure temperature, dewpoint
temperature, ozone, light scattering, altitude, and aircraft position. The
aircraft flew twice during the day and obtained the vertical profiles of these
species from an altitude of 600 to 3,600 m, two to three times per flight.
The aircraft also made several passes through cloud tops.
In support of the aircraft flights, wind speed and direction, temperature,
and relative humidity, were measured at midday by means of radiosonde.
Furthermore, vertical profiles of temperature, and dewpoint temperature were
also obtained twice a day by ANL from the releases of airsondes.
TABLE 2. Techniques and detection limits for anion and cation analyses
Species Technique Detection Limit
Cl 1C 0.14 /jrnol/1
NO, 1C 0.16 /iiiiol/1
S04 1C 0.31 junol/l
Na. 1C 0.22 fimol/1
NHt 1C 0.55 /zmol/1
K . . 1C 0.77 /iinol/1
CaTT DCP 0.75 /jmol/1
Mg DCP 0.21 1000} n
1C = Ion Chromatography
DCP = Direct Coupled Plasma Spectrophotometer
8
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DATA MANAGEMENT
The aircraft data were collected on magnetic tapes, strip chart recorder
and aircraft flight scientist notes. The DC-3 carried two data acquisition
systems, an HP-9920 computer-based system and a Particle Measuring DAS-64
system. The later one was used as a back up and recorded most of the real-time
parameters with the exception of the Gust Probe and the INS data. Both systems
record the data on 9-track tapes. The data acquisition onboard the Cessna 411
aircraft was also a computer-controlled system that recorded the data on
1/4-inch magnetic tape cartridges.
The data reduction process involves the merging of the data sets, along
with appropriate calibration information, to create a reduced data tape in
engineering units with all corrections for invalid or unwanted intervals edited
and data formatted. The reduced data tape is written in ASCII for ease of
interpretation and processing at various computer facilities. The tape also
contains a first file of header information that includes the flight dates,
tape recorded size, the order of parameters, and the format statement used to
write the parameters.
RESULTS AND DISCUSSION
In the following sections samples of the data collected will be presented
and discussed. Since the bulk of the data has not been examined any conclusion
drawn from these limited data should be viewed as highly tentative.
CLOUD CHEMISTRY
Table 3 shows the concentrations of sulfate, sulfur dioxide, nitric acid,
and nitrate measured at three altitudes each day. The lowest altitude was
chosen just below cloud bases, the intermediate altitude was at cloud tops,
and the higher altitude was much higher than cloud tops. The concentrations
of each species, at any altitude, varied from one day to another without any
particular trend or correlations among them. Nitric acid concentrations are
much higher than nitrate aerosol concentrations with the exception of one
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data point taken at cloud bases on July 31. In some cases the nitric acid
concentrations are higher than sulfate concentrations. For example, on August
4 the concentration of nitric acid is 22.9 nraoles/m compared to only 0.2
nmoles/m at cloud bases. There was a similar trend at the two other altitudes
and also on days August 8 and 12.
TABLE 3. Data collected during VENTEX-84 by the PNL DC-3 aircraft at bases,
tops, and higher than tops of non-precipitating cumulus clouds.
Altitudes are in thousands of meters,3and the concentrations of S04,.
S02, HNOj, and N03 are in nanomoles/m . Times are in eastern daylight
time.
DATE ALTITUDE
TIME ON-OFF
1250-1335
1350-1450
1132-1230
1358-1443
1455-1555
1230-1330
1316-1346
1404-1504
1149-1249
1336-1421
1439-1539
1543-1643
1326-1412
1432-1532
1150-1250
S04
31.3
61.1
18.6
20.9
3.0
0.6
0.2
1.2
0.0
21.7
13.5
1.5
51.1
9.8
0.0
S0?
7.7
2.0
1.7
8.2
0.2
0.0
44.2
0.0
0.0
67.7
5.0
0.0
237.5
4.0
0.0
HNO?
20.7
20.3
8.9
2.1
4.1
2.3
22.9
6.3
4.1
54.2
35.7
20.5
76.5
33.1
0.0
N03
0.0
1.3
0.0
11.2
2.8
0.0
0.0
0.7
0.0
1.5
0.4
0.3
1.1
0.0
0.0
7/30 1.1
1.8
3.1
7/31 1.4
2.2
3.1
8/04 1.1
2.4
3.1
8/08 1.1
2.0
2.4
8/12 1.4
2.2
3.1
The in-cloud formation of sulfate and nitrate are examined by comparing
the concentrations at cloud tops against the concentrations measured at cloud
bases. However, before this comparison can be made we must recognize that
when cumulus clouds penetrate into the free atmosphere above the mixed layer,
they encounter dry and less polluted air of different chemical composition,
they mix with it, and evaporate. Thus the pollutants emerging from the clouds
will be diluted and chemically modified. In Table 4 the concentrations of
sulfate and total nitrate at cloud bases were divided by the total sulfur
(the sum of sulfate and sulfur dioxide), and the values at cloud tops were
first corrected for background values and then divided by the total sulfur at
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that altitude. The nitric acid and the nitrate aerosols were combined because
when ammonium nitrate and sulfuric acid dissolve in the droplet and the droplet
evaporates, an exchange of ions takes place resulting in the formation of nitric
acid and ammonium sulfate.
Table 4 includes the concentrations of ammonia and ozone, and outside air
temperature. Since these parameters were measured in real-time, their values
were averaged over filter collection time. The letters B and T refer to the
measurements locations, at cloud bases and cloud tops respectively.
Examining the data in Table 4, it can be seen that the ratio of sulfate
to the total sulfur at cloud tops is higher than that at cloud bases in all five
days, and the changes in the ratio is much larger than the estimated combined
errors in the measurements. This finding is in agreement with the VENTEX-83
results (Alkezweeny et al. 1984). In the case of total nitrate, three days
(August 4, 8, and 12) show in-cloud nitrate formation. The other two days no
production was detected. This is the first time that nitrate formation in
natural clouds has been observed.
TABLE 4. Ratios N/S and SO^/S at cloud bases, B, and cloud tops, T, where N
is the concentration sum of nitric acid and nitrate aerosols, and S
is the sum of sulfate and sulfur dioxide concentrations, k is the
first order oxidation rate of S02 in clouds,in %/minute. The ammonia
and ozone concentrations are in nanomoles/m and ppb respectively,
and the temperature, T is in °C.
DATE HEIGHT N/S SO/,/5 k NH, 0-
7/30
7/31
8/04
8/08
8/12
B
T
B
T
B
T
B
T
B
T
0
0
0
1
0
2
0
0
0
0
.53 +
.27 +
.46 +
.77 +
.52 +
.39 +
.62 +
.90 +
.27 +
.24 +
.07
.04
.01
.12
.07
.31
.08
.11
.03
.30
0.80
0.99
0.72
0.92
0.005
1.00
0.24
0.71
0.18
0.71
+ .02
+ .01
+ .03
+ .01
+ .00
+ .00
+ .03
+ .03
+ .02
+ .03
15.0
1.0
9.9
6.5
10.9
3.3
6.7
20.4
8.0
4
11
15
52
-5
.6
.7
.2
.3
.0
—
60
56
40
27
57
48
81
66
78
68
19.1
16.3
20.3
14.3
22.6
14.4
24.9
19.6
20.2
16.8
11
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The oxidation rate of sulfur dioxide in the cloud system can be estimated
in the following manner. Let the concentrations of sulfur dioxide and sulfate
be represented by X and Y respectively. Therefore the time rate of changes
in X and Y are:
dX/dt = -kX - KX (1)
dY/dt = kX - KY (2)
where k is the oxidation rate of S02, and K is the reduction rate due to
dilution and diffusion. Define a descriptor R such that:
R = X/(X+Y) (3)
Differentiating both sides of equation (3) with respect to t, and substituting
for the time derivatives from equations (1) and (2) results in the following
equation:
dR/dt = -kR (4)
k is influenced by many processes. It includes the reaction rate between S02
and the oxidizers, functions that take into account the transfer of the gases
from the air to the cloud droplets, and the concentrations of the oxidizers.
Temperature changes as droplets rise from cloud bases to cloud tops will affect
the value of k. For diagnostic analysis it is assumed that k is constant
with respect to t, X, and Y. Integrating equation (4) yields the following:
kt = In R0 - In R (5)
where RQ is the descriptor value at t = 0, at cloud bases.
In order to calculate k, the transport time t between cloud bases and
cloud tops is needed. Assuming an average updraft velocity of 1.0 m/s across
the cloud, the calculated values of k are shown in Table 4. The result shows
very fast conversion rates. It should be noted that even if the updraft
velocity is off by a factor of two or three the rate is still very high.
Furthermore, the calculated rate varies from one day to the other and does not
seem to correlate with any of the parameters listed in the table. Of course
what is missing from the data is a measurement of H202. This measurement was
not taken during VENTEX-84 but was made during VENTEX-85. Although the
VENTEX-85 data have not been analyzed, preliminary examination show that the
concentration of H202 is in the range of 1.0 to 6.0 ppb; certainly large enough
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to oxidize dissolved S02 in the cloud droplets. Furthermore, there is a strong
indication that ^2 was forming in the clouds. This was evident from vertical
profiles which show peaks in the concentrations at the cloud layer.
The high S02 oxidation rates calculated above are consistence with
VENTEX-83 results (Alkezweeny et al. 1984, c.f. Table 5) and those reported by
Hegg and Hobbs (1982) for wave clouds. Model simulation of non-precipitating
clouds by Seigneur and Saxena (1984) arrived at an oxidation rate on the order
of 100%/hr. Martin and Damschen (1981) used their laboratory measurement of
the aqueous oxidation of sulfur dioxide by hydrogen peroxide and calculated a
rate of 3.0 %/min. for clouds containing 0.3 g/m liquid and gas phase ^2^2
concentration of only 1.0 ppb.
The rates reported here are higher than those measured by Gillani et al.
(1983) and Eatough et al. (1984) for power plant plumes embedded in clouds.
Although these authors did not report any hydrogen peroxide measurements, it
can be assumed that in those studies the ^2 concentrations were very low.
Hydrogen peroxide vertical profile measurements during VENTEX-85 show that the
peroxide concentration drops almost to zero when a plume containing high
concentration oxide of nitrogen was encountered. This explanation is supported
by the measurement of Clark et al. (1984). They measured the chemical
composition of cloud water when a power plant plume was entirely trapped within
a shallow layer filled with stratocumulus clouds. When they compared their
measurements with the predictions of a reactive plume model they found the
rates of sulfur dioxide oxidation outside the plume to be substantially higher
than those within the plume. Since NOX concentration is much higher at the
plume center than at the plume edges, it follows that H202 concentration inside
the plume should be very low.
Measurements taken during the VENTEX-83 field study have been used in
model studies to simulate the chemistry system of the pollutants in a
non-precipitating cumulus cloud (Nair et al. 1985). Since H202 data were not
collected during that study, '^02 concentration of 1.0 and 5.0 ppb were assumed;
these concentration values are in the range of values measured near the clouds
during the VENTEX-85 field study. The model result and the experiment values
are given in Table 5 and are in reasonable agreement, considering the many
assumptions made about liquid water content, cloud droplet sizes, etc. In
13
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VENTEX-85 all the variables needed for this model simulation have been
measured. Therefore, the data can be used for cloud chemistry model validation.
TABLE 5. Comparison between measured and simulated of S02, NH3, and k. Data from
Nair et al. (1985)
S02 (nmoles/m3) NH3 (ug/m3) k(%/min.)
Expt.* Ippb** 5ppb** Expt.* Ippb** 5ppb** Expt. Ippb** 5ppb**
7/28 54.3 4 0.108 . .
5.1 15.00 5.1x10"^ 0.000 7.8x10 * 7.8x10"^ 5.0 4.1 28.0
8/02 14.7 0.375
0.1 0.89 0.079 0.011 0.019 0.020 36.0 27.0 51.0
8/08 78.2 0.080 . .
12.8 46.00 5.10 0.003 7.7x10"^ 4.1x10"* 2.0 4.2 21.0
8/19 202.0 0.230 .
0.9 155.00 57.00 0.016 6.4xlO~* 16.0 2.1 9.8
*First number measured at cloud bases, and the second number measured at cloud
tops.
**Assumed gas-phase fy^z concentration
Results of the ground measurements reveal interesting features. In general
the ammonia concentration profiles show a decline in concentration around midday
followed by an increase in the afternoon. A typical ammonia profile taken on
August 12 is given in Figure 2. On the other hand, the sulfur dioxide profiles
peak around noontime (Figure 3). The ammonia behavior is expected since its
sources are located on the ground. At night and early morning the ammonia is
emitted into and confined within a shallow layer that is capped by the nocturnal
temperature inversion. As the day progresses the inversion height rises and
the ammonia is mixed and distributed over a deeper layer. In the late afternoon
mixing is suppressed and therefore the concentration rises. More ammonia
measurements taken in 1983 at the same location on the ground and at several
elevations above the ground were reported by Alkezweeny et al. (1986). The
sulfur dioxide profile suggests that the main source of S02 was an elevated
plume. The weak or absence of vertical mixing during the afternoon, nighttime,
14
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and early morning keep the concentration low. However, at midday, when mixing
is at its best, the plume will be mixed to the ground and rise in the S02
concentration is expected.
VERTICAL TRANSPORT
Pollutant fluxes and other data collected by the PNL DC-3 aircraft
instrumentation have not been analyzed. Data collected by the PNL Cessna-411
aircraft instruments are partially analyzed; examples of the results will be
presented here. Figure 4 and 5 show the results of the aircraft constant
altitude penetrations through cloud tops on July 13, 1984 during the morning
and afternoon flights. Aircraft speed during penetrations was approximately
72 m/sec. An individual cloud is identified by the rise in the relative
humidity trace. Peak values vary from one cloud to the other because as the
cloud penetrates into the free atmosphere above the boundary layer, it mixes
with the dry air and starts to evaporate, thus the relative humidity drops
below saturation. The amount of reduction in the relative humidity, as detected
by the sensors, depends upon the aircraft location within the cloud.
The temperature inside the cloud is 1 to 3°C lower than the cloud
environment, at the same elevation, which is an indication of the cloud droplet
evaporation.
The figures show ozone concentrations and aerosol light scattering inside
the clouds are higher than that outside at the same elevation. The difference
in the ozone concentration is in the range of 5 to 15 ppb, which is comparable
with the 10 to 15 ppb measured by Ching et al. (1983) during their cloud
penetration experiment. Alkezweeny and Hales (1981) also detected boundary
layer ozone and other pollutants just above the visible cloud tops during
aircraft sampling over clouds that formed near Champaign, 111. It is
interesting to compare the ozone concentration baseline measured during the
morning and the afternoon flights. In the morning the concentration values
vary from about 49 to 53 ppb and in the afternoon the range is 52 to 60 ppb.
Since these measurements were taken above the mixed layer, the results suggest
an accumulation of ozone, and possibly other pollutants, in the cloud layer
(including the entrainment layer).
17
-------
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The vertical profiles of ozone, and temperature for the morning and
afternoon flights on July 13, 1984 are given in Figures 6 and 7. At 1130 the
top of the mixed layer was at about 1900 m. Cloud bases were estimated at
1800 m and most of the cloud tops were at 2000 m. By 1645 the top of the
mixed layer had risen to 2300 m, cloud bases to 2250 m, and cloud tops to
2500 m. Below the cloud layer the ozone concentration increased at all
altitudes by approximately 20 ppb over the five-hour period presumably as a
result of photochemical reaction expected to take place in polluted atmosphere.
The rate of increase, 4 ppb per hour, is comparable with the values of 5 to
10 ppb per hour reported by Alkezweeny et al. (1980) in polluted air over
Lake Michigan during the afternoon hours. Above about 2600 m the ozone
concentration was practically unchanged during this period, which suggests
that vertical transport, if any took place, did not reach above this altitude.
This is not surprising since ground and aircraft observers did not report any
towering cumulus clouds during the aircraft sampling. On the other hand, the
difference in the ozone concentrations measured at the beginning and the end
of this period increases steadily from the 2600 m level down to the top of the
mixed layer. Clearly, vertical transport was occurring, but was limited to the
cloud layer, and not above.
FIELD STUDY QA/QC ACTIVITY
The field experiment QA/QC plan was developed as part of the design base
document, "VENTEX, Design and Operation Guide for the 1984 Field Study." The
v
plan specified operational, calibration, and data-handling procedures based
on ASD-36, the QA Project Plan for the Precipitation Scavenging Module
Development Project. This plan and the associated series of Quality Control
Descriptors (QCD'S), contain specific procedures for instrument and data
activities. This report describes procedures used, results, and deviations
from the field operations plan. The following is a summary of the QA/QC report
in the project file.
Both airborne and ground-based sampling were employed, with airborne
sampling performed by the two PNL aircraft, the Cessna 411 and the DC-3. The
20
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o
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40.0 50.0
13 JULY 1984
— time 1126-1143
time 1645-1700
60.0 70.0
OZONE, ppb
80.0 90.0
FIGURE 6. Ozone Vertical Profiles for the Morning and Afternoon of
July 13, 1984.
21
-------
§.
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13 JULY 1984
— time 1126-1143
time 1645-1700
10.0 20.0
TEMP, C
30.0
FIGURE 7. Temperature vertical profiled for the morning and afternoon of
July 13, 1984.
22
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Cessna 411 flew twice a day for a total of 75.4 hours; the DC-3 flew once a
day for a total of 66.2 hours. Table 6 shows the two aircraft flight times
and days.
TABLE 6. Aircraft flight log during VENTEX-84.
•
DATE DC-3 hrsrmin CESSNA 411 hrsimin
Flight 1Flight 2
7/11 1:55
7/12 2:40 2:20
7/13 1:30 2:40
7/18 2:30 3:10
7/19 2:35 3:30
7/24 0:40 3:10
7/25 2:00
7/28 3:50 2:35 1:10
7/29 5:25 4:20 1:30
7/30 5:00
7/31 5:10
8/04 5:00 2:25 2:30
8/05 5:50 2:50 2:05
8/06 5:50 2:25 2:00
8/08 5:20 2:30 2:00
8/09 0:25
8/10 3:00 2:10
8/12 5:50 2:55 2:15
8/13 5:30 2:45 2:00
8/14 2:05 2:10
8/15 5:20 2:05 2:05
8/16 3:05
CALIBRATIONS
The primary parameters, associated calibration methods, and schedule are
listed in Table 7. Calibration equipment employed in the field included a
CSI GPT (Gas Phase Titration) calibrator, AID permeation tube calibrator, flow
calibrator, cylinder SRM (Standard Reference Material) gases, FREON 12 and
various electronic measurement instruments.
1-Ozone: The Bendix Model 8002 ozone analyzer used in this program has
an internal ozone source for routine, daily operational checks. Operation in
the zero mode provides a check on the analyzer response to zero gas by passing
ambient air through a charcoal scrubber to destroy ozone. Zero and span checks
were conducted routinely during operation. The long-term stability of this
23
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unit, confirmed by extensive operating experience on an aircraft platform,
made daily multi-point calibration checks unnecessary. Primary calibrations
were performed with a CSI 1700 GPT calibrator referenced to a laboratory ozone
source. A zero check and four challenge concentrations in the range of 70 to
262 ppb were used. Variations in the instrument response were less than 10%
in the range of ambient concentration encountered.
TABLE 7. Instrument calibration methods and schedules.
PARAMETER METHOD SCHEDULE
Temperature NBS Reference Device 1,3
Dewpoint Temp. NBS Reference Device 1,3
Pressure NBS Reference Device 1,3
NOX Gas-phase titration 1,2,3,4
(SRM NO cylinder)
S02 SRM Permeation Tube 1,2,3,4
03 CSI calibration referenced 1,2,3,4
to UV photometer
bscat Freon 12 1,2,3,4
SF6 SF6 1,2,3
Turbulence Electronic 0,5
Hi-Vol Flow NBS Reference Device 0,5
Particle Size Aerosol Generator 1,3
(latex spheres)
Position (VLF/INS) Manufacturer Calibration 4
Wind (INS) Manufacturer Calibration 4
Air Motion (Gust Probe) Calibration weights & 5
Electronic
Schedule:
0 Primary calibration prior to field deployment
1 Primary calibration before field experiment
2 Primary calibration during field experiment
3 Primary calibration after field experiment
4 Zero and span checks on operating days
5 Primary calibration after return from field
2-Nitrogen Oxides: Quantitative detection of these species is derived
from the chemiluminescent reaction between nitric oxide and ozone. The
analyzers provide measurement of NO and oxidized nitrogen species which are
reduced to NO in a converter prior to entering the reaction chamber. The
primary analyzer was constructed at PNL for use in aircraft studies and has a
detection limit of less than 1 ppb. Zero checks of NOX analyzers were conducted
24
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frequently during each flight. Multi-point calibrations for NO and N02 were
performed prior to, during, and after the field experiment. This procedure
utilized a CSI 1700 6PT calibrator and cylinder SRM nitric oxide in nitrogen
to check the analyzer response and the NOX converter operation at zero and four
concentrations up to 50 ppb. Instrument response to the calibration standards
was determined to be within the 10% specified accuracy for the instrument.
Failure of the ozone generator in the NOX measurement system required
replacement by a lower output generator and resulted in some loss of sensitivity
for NOX measurements. Subsequent re-calibrations, however, indicated repeatable
response to calibration standard gas for the remainder of the experiment.
3-Sulfur Dioxide: A Meloy flame-photometric analyzer was used to measure
airborne concentrations of S02. Zero and span checks were performed prior
to, during, and after the field study, using a CSI 1700 calibrator and cylinder
of SRM S02. Instrument operation was less than optimal as a high baseline
could not be sufficiently reduced to permit operation on a high sensitivity
range, and the instrument had to be operated on the 0 to 100 ppb range.
Response to the calibration standard was within the specified 10% accuracy
for that range.
4-L1ght Scattering: An unheated integrating nephelometer, calibrated using
Freon 12, was used to measure total light scattering. Daily checks were made
using an internal calibration check, and full calibrations with Freon 12 were
performed before, during, and after the field study period.
5-Sulfur Hexafluoride: A real-time SF6 analyzer was installed on the
aircraft to detect movement of airborne releases of tracer. Calibrations
were performed using SRM cylinder sources of SFg gas which was expelled into
tedlar bags for sampling at low pressure.
5-Aerosol Size Distribution: Particle characterization instruments were
expected to provide qualitative information only and did not undergo rigorous
calibration. A TSI 3030 electrical mobility analyzer and an aerosol probe, a
PMS ASASP-100X, were operated onboard the DC-3.
6-Meteorological Parameters: Temperature, atmospheric pressure and
turbulence instruments were calibrated prior to and after the field study
25
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using NBS traceable instruments. These are reliable, stable sensors which
were determined to be within the desired calibration accuracies.
7-Inertial Navigation System/Gust Probe: The INS/gust probe hardware was
installed and interfaced to the data acquisition system just prior to the
field deployment. INS checkout and gust probe sensor calibration were performed
following the field study. Gust probe air vanes are equipped with strain
gauges which are calibrated by properly orienting the vanes and applying
calibration weights. A differential pressure sensor for monitoring longitudinal
airspeed is calibrated by means of an NBS referenced pressure gauge. Data
from both systems were recorded via the onboard data acquisition system in
the field and will be reduced using post-field calibration data.
DATA HANDLING
It is essential that instrument data are carefully tracked through the
total path from instrument to computer data reduction process. Pre-flight,
in-flight, and post-flight checks were used to ensure correct operation and
data logging.. A pre-flight checklist documents several physical checks to be
performed, such as power connections, signal connections to the data acquisition
system and chart recorders, sample inlet connections, and inventory of required
onboard supplies. An in-flight checklist supports examination of instruments
for expected operations, with both instrument front panel observations and
display of each parameter as received by the data acquisition system, checks
for correct operation of instrumentation power conversion and distribution
system, chart recorder checks, sample and reagent flow checks, etc.
The DC-3 aircraft acquisition system is a newly installed HP 9920 computer
based system which includes an analog-to-digital conversion subsystem, a serial
digital interface to the INS and a magnetic tape transport for data recording
on 9-track tape. Since the system is programmable, programs can be loaded in
the field to permit examination of the data tapes acquired as well as to run
the acquisition process, to provide on-the-spot assessment of instrument and
data system performance. Calibrated chart recorders were used for checkup
and for in-flight indication of experiment progress.
A Particle Measuring Systems probe and acquisition system was also carried
on the DC-3 aircraft. Since this system also has analog signal input
26
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capability, several primary parameters were recorded redundantly for backup
f
purposes as well as data quality comparison.
A computer-controlled data acquisition system was used onboard the Cessna
411 aircraft, which recorded data onto 1/4-inch magnetic tape cartridges. This
system was also capable of providing field examination of recorded data.
Calibrated chart recorders were used to provide backup of primary parameters.
Thirty-one data tapes were acquired during the DC-3 aircraft flights and
30 tapes were recorded on the Cessna 411 aircraft. Backup copies of the raw
data tapes were made upon returning to PNL, to be used in the data reduction
process. All but 2 of the 30 Cessna tapes were reduced, resulting in estimated
data completeness inventory of about 93%. The DC-3 data tapes have not been
reduced, only backed up, but with redundant system recording, we expect
virtually complete data recovery for all parameters except the inertial
navigation system and gust probe data. The INS/gust probe data have gaps as
a result of hardware and software problems in the operation of the new data
acquisition system. Estimated data recovery for these parameters is 70% to
75%. Table 8 indicates instrument response time, calibration accuracies and
estimated data completeness for the aircraft data.
TABLE 8. Accuracy and completeness of the measured parameters during VENTEX-84
Instrument
Response 12 3
Parameter Time . Accuracy Accuracy Completeness
Temperature 2 sec 1°C 1°C 95%
Dewpoint Temp. 0.5 sec/°C 1°C 1°C 93%
Pressure 1 sec 10% 10% 95%
NOX 3 sec 10% 10% 95%
SOo 30 sec 10% 10% 95%
Ozone 5 sec 10% 10% 95%
bscat 2 sec 10% 10% 95%
Hi-Vol flow — 10% 10% 95%
Position — 10% 10% 70%
Wind — 10% 10% (?)
Air motion — 10% 10% 70%
1 Specified accuracy.
2 Calibration accuracy.
3 Estimated data completeness.
27
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FILTER COLLECTIONS
A primary set of data for this study was obtained from the two high-volume
air samplers operated on the DC-3 aircraft; other high-volume samplers were
used on the ground. In the aircraft, filter packs were removed from sealed
bags and inserted into the high-volume samplers immediately prior to exposure.
Upon completion of the sample collection, the filter packs were returned to
plastic bags where they remained until transported to the chemistry laboratory
no later than the following day. Each filter was marked with a unique
identifier and essential information was noted on a collection record as the
sample was acquired (ID, time, altitude, volume, sample ID). For each flight,
additional filter packs were unsealed and re-bagged to serve as blanks. After
disassembly of the packs in the chemistry laboratory, the filters were placed
in sterile syringes and leached into solution for analysis. Sample ID and
log sheets followed the samples through the analysis and reporting process.
Similar procedure was also followed for samples collected on the ground. A
total of 37 filter sets were exposed onboard the DC-3 aircraft. Each set
consisted of 2 filter packs holding 5 filters. Additionally, 11 sets were
handled, but not exposed, to serve as blanks for background correction. On
the ground, the number of filters exposed are: 93 for ammonia, 90 for sulfur
dioxide filters, 93 for aerosols, and 38 blanks.
Laboratory space for the duration of the field study was provided by the
Kentucky Center for Energy Research Laboratory, located north of Lexington,
KY. This facility was used as a filter-handling area in which aircraft and
surface filter packs were prepared for sampling use and also were unpacked
and extracted in preparation for analysis. Filter preparation, particularly
those with oxalic acid treatment for capturing ammonia, were completed the
day prior or the same day as a planned flight to prevent aging effects and
maintain uniform filter collection characteristics.
DEVIATION AND PROBLEMS NOTED
As with any field program, a few difficulties were encountered which
affected planned performance. In preparation for the study, a nose boom was
constructed for the DC-3 aircraft for mounting of the gust probe components.
Problems encountered by the fabricator in securing FAA certification for the
28
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boom resulted 1n a 2 week delay in getting the aircraft to field site, and even
then, it was necessary to place the aircraft in the FAA experimental category
designation.
Immediately prior to deployment to the field site, the dewpoint sensor for
the DC-3 aircraft was determined inoperational, thus, no dewpoint temperature
measurements were made with this aircraft. An operating dewpoint sensor was
onboard the Cessna 411 aircraft which was used during the aircraft sampling.
Early in the flight series, the ozone generator for the NOX monitor failed
and had to be replaced with a unit of lower generation capacity. This resulted
in some loss of sensitivity for NOX measurements. As discussed earlier,
precalibration results verified acceptable operation.
A high baseline level in the Meloy S02 analyzer could not be corrected and
also resulted in loss of sensitivity as the instrument had to be operated on
a less sensitive range than desirable.
Similarly, baseline problems with the real-time SF6 analyzer made tracer
detection difficult. The few tracer releases that were made were not
successful.
Problems also occurred with the data acquisition systems on both aircraft.
As discussed earlier, the new DC-3 aircraft computer, INS and gust probe systems
were newly installed prior to departure to field site. Difficulties were
encountered in intermittent failures in the serial data interface to the INS,
but data were recorded for most flights. Hardware/software problems were
experienced with the magnetic tape recording system resulting in considerable
difficulty in maintaining a continuous acquisition and recording process.
For most flights, there were frequent short time interruptions in recording.
Also, due to limited time with the system prior to departure to the field site,
on-site analysis of the recorded data was not attempted. Dump programs were
used to ensure that data was being correctly recorded on a daily bases.
The microprocessor acquisition system on the Cessna 411 aircraft also
experienced intermittent failures. Fortunately, these were physical
interconnect problems which were generally corrected prior to the aircraft
takeoff. Two tape cartridges recorded on this system were found to be
defective; one with loss of data and one which internally jammed in-flight.
29
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Only one sampling mission was cancelled as a result of aircraft problems.
An August 14 flight had to be scrubbed when a defective fuel boost pump was
discovered on the DC-3 aircraft left engine. Repairs were completed in time
for flight the following day. Other scheduled aircraft maintenance was
performed as planned.
SUMMARY
Preliminary results show that the ratio of sulfate concentration to the
total sulfur concentration (the sum of sulfate and sulfur dioxide) at top of
clouds is much higher than that measured at their bases. The in-cloud oxidation
rates were calculated to be in excess of 100%/hr. This required an assumed
averaged updraft velocity of 1.0 m/sec. The ratio of the total nitrate
concentration (the sum of nitric acid and nitrate aerosols) to the total sulfur
concentration at cloud tops, was higher than that at cloud bases on many days.
This result suggests that nitrate can form in the clouds but not as frequently
as sulfate.
The ammonia concentrations measured on the ground show a decline around
midday followed by recovery in the afternoon. On the other hand, the sulfur
dioxide concentrations show an opposite trend for the one day that was examined,
August 12, 1984.
The vertical profiles of ozone measured during the morning and afternoon
of July 13, 1984 indicated that pollutants from the mixed layer have been
transported vertically to the cloud layer. No transport above the layer was
detected on this day. It should be noted that no towering cumulus clouds
were observed during the aircraft sampling.
30
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REFERENCES
Alkezweeny, A. J., W. E. Davis, and R. C. Easter. 1980. "Comparison of Ozone
in Polluted and Clean Air Masses Over Lake Michigan." In Proceedings of
the International Ozone Symposium, August 4-9, 1980, Boulder,
Colorado. Vol. 1, ed. Julius London.
Alkezweeny, A. J. and J. M. Hales. 1981. "The Impact of Non-Precipitating
Clouds on the Transport and Formation of Acid Aerosols." Paper presented
at the Annual Meeting of the American Chemical Society, August 1981, New
York, New York.
Alkezweeny, A. J. 1984. Non-Precipitating Cumulus Cloud Study. PNL-5283,
Pacific Northwest Laboratory, Richland, Washington.
Alkezweeny, A. J., K. M. Busness, and D. W. Koppenaal. 1984. "Contribution
of Non-Precipitating Clouds to Acid Deposition." Paper presented at the
Fourth Joint Conference on Application of Air Pollution Meteorology,
October 1984, Portland, Oregon.
Alkezweeny, A. J., G. L. Laws, and W. Jones. 1986. "Aircraft and Ground
Measurements of Ammonia in Kentucky." Atmos. Environ., 20:357.
Ching, J. K. S., J. F. Clarke, J. M. Irwin, and J. M. Godowitch. 1983.
"Relevance of the Mixed Layer Scaling for Daytime Dispersion Based on RAPS
and Other Field Programs." Atmos. Environ., 17:859.
Ching, J. K. S., and A. J. Alkezweeny. 1985. "Vertical Transport by Cumulus
Clouds." Paper presented at the 7th Symposium on Turbulence and Diffusion
of the AMS, November 12-15, 1985.
Clark, P. A., I. S. Fletcher, A. S. Kallend, W. J. McElroy, A. R. W. Marsh,
and A. H. Webb. 1984. "Observations of Cloud Chemistry During Long-Range
Transport of Power Plant Plumes." Atmos. Environ., 18:1849.
Calvert, J. G. and W. R. Stockwell. 1983. "Acid Generation in the Troposphere
by Gas-Phase Chemistry." Environ. Sci. Tech., 17:428A.
Eatough, D. J., R. J. Arthur, N. L. Eatough, M. W. Hill, N. F. Mangelson,
B. E. Richter, L. D. Hansen, and J. A. Cooper. 1984. "Rapid Conversion
of S02(g) to Sulfate in a Fog Bank." Environ. Sci. Tech.. 18:855.
Gillani, N. V., J. A. Colby, and W. E. Wilson. 1983. "Gas-to-Particle
Conversion of Sulfur in Power Plant Plumes-Ill. Parameterization of
Plume-Cloud Interactions." Atmos. Environ., 17:1753.
Hegg, D. A. and P. V. Hobbs. 1982. "Measurements of Sulfur Production in
Natural Clouds." Atmos. Environ., 16:2663.
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Isaac, G. A., P. I. Joe and P. W. Summers. 1983. "The Vertical Transport and
Redistribution of Pollutants by Clouds." Transaction of the APCA Specialty
Meeting on the Meteorology of Acid Deposition, ed. P. J. Samson, p. 496.
Hartford, Connecticut.
Liu, S. C., J. R. McAfee and R. J. Cicerone. 1984. "Radon 222 and Tropospheric
Vertical Transport." J. Geophys. Res., 89:7291.
Maahs, H. 6. 1983. "Measurements of the Oxidation Rate of Sulfur(IV) by
Ozone in Aqueous Solution and Their Relevance to S02 Conversion in Nonurban
Tropospheric Clouds." Atmos. Environ., 17:341.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
2.
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
A STUDY OF THE FORMATION AND TRANSPORT OF ACIDIC
SPECIES BY NON-PRECIPITATING CUMULUS CLOUDS DURING VENTEX
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5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
A.J. Alkezweeny
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME ANO ADDRESS
Pacific Northwest Laboratory
Rich!and, WA 99352
10. PROGRAM ELEMENT NO.
CCVNIA/01-3095 (FY-86)
11. CONTRACT/GRANT NO.
DW 89930059
12. SPONSORING AGENCY NAME AND ADDRESS
Atmospheric Science Research Laboratory—RTF, NC
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
EPA/600/09
IS. SUPPLEMENTARY NOTES
16. ABSTRACT
A field experiment was conducted by Pacific Northwest Laboratory (PNL) in
Kentucky during the period July 8 to August 18, 1984 as part of the VENTEX-84 field
study to investigate the formation of sulfate and nitrate aerosols and in the
vertical transport of pollutants by non-precipitating cumulus clouds. VENTEX is a
research component of the National Acid Precipitation Assessment Program.
Analyses of data collected from DC-3 and Cessna 411 aircrafts and from ground
sampling show ratio of sulfate concentration to the total sulfur concentration (the
sum of sulfate and sulfur dioxide) to be larger at the top of clouds than at their
bases. In-cloud oxidation rates were calculated to be in excess of 100%/hr. The
ratio of the total nitrate concentration (the sum of nitric acid and nitrate aero-
sols) to the total sulfur concentration at cloud tops, was higher than that at
cloud bases on many days. This result suggests that nitrate can form in the clouds
but not as frequently as sulfate. Ground concentrations of ammonia declined around
midday followed by an increase in the afternoon. Sulfur dioxide concentrations
exhibit an opposite trend. A case study of morning and afternoon soundings of ozone
indicated vertical transport of pollutants from the mixed layer to the cloud layer.
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b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Croup
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RELEASE TO PUBLIC
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20. SECURITY CLASS (Thispage/
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (R«». 4-77) PREVIOUS EDITION is OBSOLETE
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