United States
Environmental Protection
Agency
Environmental Sciences
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S3-84-056 May 1984
&EPA Project Summary
Miniature Acid-Condensation
System: Design and Operation
James L Cheney
An extractive source sampling system
was designed and constructed. The
sampling system measures gaseous
sulfuric acid and sulfur dioxide in
combustion emissions. The miniature
acid condensation system (MACS)
includes a high-temperature quartz
probe and quartz-filter holder. The
temperatures of the probe and filter are
maintained at or above 520°F during
sampling with temperature controllers.
After removal of particles from the
source sample with a flat quartz filter,
the sulfuric acid is collected in a glass-
wool plug. The glass-plug temperature
is maintained at 140°F with a water
bath circulator. Subsequent midget
impingers containing hydrogen
peroxide collect sulfur dioxide.
Since there is no commercially-
available manual sampling system for
measuring gaseous sulfuric acid at the
present time, a prototype sampling
system must be constructed for making
such measurements. The purpose of
this work is to provide a guideline for
building such a sampling system. Also
included is a discussion of two sulfate
analytical methods, Barium-Thorin and
Ion Chromatography. In addition, a
brief discussion of sulfate analyses data
handling and the results of some source
emissions sampling are presented.
This Project Summary was developed
by EPA's Environmental Sciences Re-
search Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
Measuring sulfuric acid (H2SO4) as a
separate entity from particulate sulfate in
combustion source emissions requires
specific procedures. As the quantitative
determination of each relies on
measuring the sulfate ions, the two must
be separated prior to sample collection.
An acceptable method of separation is to
collect the particulate sulfate on a quartz
filter at a temperature near 520°F while
passing the gaseous H2SO4 through the
filter
Collecting the gaseous HrSO4 subse-
quent to particulate separation can be
difficult due to the possible oxidation of
sulfur dioxide (SO2) which is always
present in such gas streams. In addition
to an SO2 interference, collection
efficiency problems are also encountered
if attempts are made to collect the H2SO4
in impinger solutions For these reasons,
the H2S04 is usually collected in a
temperature-controlled condenser-type
device. The condenser will separate
H,SO4 from both SO? and moisture in the
gas stream if the temperature is below
the H2S04 dew point but above the water
dew point. For most combustion source
gases, the temperature of the condenser
is maintained at 140°F.
Two types of condensers currently are
used: the traditional Goksoyr-Ross type,
which consists of a water-jacketed spiral
tube with a backup frit and a simplified
type which consists of a water-jacketed
straight glass tube packed with Pyrex
glass wool The simplified glass-wool
plug was devised and evaluated in the
Environmental Sciences Research
Laboratory to overcome the high pressure
drops and frit recovery of sulfate that
persisted with the Goksoyr-Ross device.
As most source sampling that address-
es H2SO4 and particulate sulfate also
involves measurement of SO?, the
sampling system usually includes
impingers that contain 3% hydrogen
peroxide (H?02).
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Stack /
Gas Flow
Pump Housing
Rotameter, , I
Sample
Temperature-
Readout Meter
Figure 1.
Temperature Controller
The miniature acid condensation system.
Hot-water Bath
During the past few years ESRL's
Stationary Sources Emissions Research
Branch has conducted numerous source
emissions studies involving the
separation and measurement of gaseous
H2SO4 and paniculate sulfate. The
methods used for such sampling and
analysis have been continually updated.
One product of this research is the
Miniature Acid Condensation System
(MACS), a highly portable and easily
operable sampling system for gaseous
H?SO4 and SO,-..
While numerous systems of this type
have been constructed by various source
sampling groups, no such total system is
commercially available. Sampling for
gaseous H7SO4 in combustion source
emissions, therefore, currently must be
preceded by fabrication of a sampling
system. One purpose of this project report
is to provide guidelines for constructing
such a system. The report includes
drawings of system parts with suggested
dimensions, a listing of possible sources
for parts, and the approximate
construction cost. Also included is a
discussion of sampling train operation
and sample recovery. Topics covered
include the interpretation of results,
selective solvent recoveries, and
procedures for sulfate ion analysis by
barium-thorin titration and ion
chromatography.
Figure 1 depicts the MACS. The system
consists of a high-temperature probe and
filter holder, a temperature-controlled
glass-wool plug, a midget impinger
system and accompanying pump, a gas
meter, and electronic components.
The EPA author James L. Cheney (also the EPA contact) is with the Environmental
Sciences Research Laboratory, Research Triangle Park, NC 27711.
The complete report, entitled "Miniature Acid-Condensation System: Design and
Operation, "f Order No. PB 84-182 823; Cost: $10.00, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, V'A 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
it US GOVERNMENT PRINTING OFFICE 1984 — 759-015/7711
Jnited States
nvironmental Protection
Vgency
Center for Environmental Research
Information
Cincinnati OH 45268
)fficial Business
'enalty for Private Use $300
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United States
Environmental Protection
Agency
Environmental Sciences
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S3-84-057 May 1984
SEPA Project Summary
Development of the
MESOPUFF II Dispersion Model
J. S. Scire, F. W. Lurmann, A. Bass, and S. R. Hanna
The development of the MESOPUFF
II regional-scale air quality simulation
model is described. MESOPUFF II is a
Lagrangian variable-trajectory puff-
superposition model that has been
designed to treat transport,
transformation, diffusion, and removal
processes of pollutants emitted from
multiple point and/or area sources at
transport distances beyond the range of
conventional straight-line Gaussian
model (i.e., beyond ~ 10-50 km).
The major features of this model and
enhancements over its predecessor,
MESOscale PUFF {MESOPUFF),
include the use of hourly surface
meteorological data, twice-daily
rawinsonde data, and hourly
precipitation data; separate wind fields
to represent flows within and above the
boundary layer; parameterization of
vertical dispersion in terms of micro-
meteorological turbulence variables;
transformation of sulfur dioxide (SO2)
to sulfate (SO4) and nitrogen oxides
(NOx) to nitrate (NO3 ); a resistance
model for dry deposition; time- and
space-varying wet removal; and a
computationally efficient puff-
sampling function. The scientific and
operational bases of the methods used
in the model are discussed. The
resultsfrom several model algorithms
also are compared against experimental
data.
This Project Summary was developed
by EPA's Environmental Sciences
Research Laboratory. Research
Triangle Park, NC, to announce key
findings of the research project that is
fully documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction
The regional and long-range transport
and transormation of sulfur oxides and
nitrogen oxides emitted from major point
sources have been of considerable
concern.There is a need for easily usable,
cost-efficient air-quality models that can
realistically treat the various physical
processes important on these scales. The
MESOscale PUFF (MESOPUFF) model
has been extensively modified to revise
and more realistically treat the transport,
vertical dispersion, chemical
transformation, and dry and wet removal
processes. The new model, designated
MESOPUFF II, is one element of an
integrated modeling package that
includes components for preprocessing
of meteorological data (READ56, MESO-
PUFF II) and for postprocessing of pre-
dicted concentrations (MESOFILE II).
Major Model Features
MESOPUFF II uses a puff-superposi-
tion approach to represent continuous
plumes. The pollutant material in each
puff is transported independently of that
in other puffs and is also subjected to
dispersion, chemical transformation, and
removal processes. Some of the general
features of the MESOPUFF II modeling
system are as follows:
(1) Hourly surface meteorological data,
twice-daily rawinsonde data, and
hourly precipitation data are read
from magnetic tapes.
(2) Wind fields to represent the mean
flow in the boundary layer and
above the boundary layer are
constructed, although several
options are given.
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(3) Boundary-layer structure is treated
in terms of micrometeorological
parameters that include the surface
friction velocity, mixing height,
convective velocity scale, and
Monin-Obhukov length.
(4) Space- and time-varying chemical
transformation can be performed
simultaneously for up to five pollu-
tant species, including sulfur diox-
ide (S02), sulfate (SO4=), nitrogen
oxides (NOx=NO+NO.->), nitric acid
(HN03), and nitrate (NO3 ).
(5) Dry deposition is prescribed by a
resistance model in the surface-
depletion mode, and the source-
depletion method is optional.
(6) Space- and time-varying wet
removal is parameterized according
to precipitation rate and scavenging
coefficients.
The meteorological data inputs
required by the preprocessors consist of
the routine twice-daily upper air sound-
ings, hourly surface meteorological
observations, and hourly precipitation
measurements reported by the National
Weather Service. The preprocessor pro-
grams have been designed to read the
standard-formatted meteorological data
tapes a vail able from the National Climatic
Center in Asheville, North Carolina
Wind fields for MESOPUFF II are con-
structed from the hourly surface wind
observations, as well as from the twice-
daily rawmsonde wind profile data The
surface station network data allow better
temporal and spatial resolution than do
the upper air sounding data, which
involve much larger distances and less
frequent measurements The wind fields
are constructed at two user-specified
levels--a lower level representing the
mean boundary-layer flow and an upper
level representing flow above the
boundary layer.
Boundary-layer structure is parameter-
ized in terms of micrometeorological
variables computed from the surface
station data and information about
surface characteristics (land use, or
roughness lengths) provided by the user
for each grid point. The surface friction
velocity, u*, the convective velocity scale,
w*, the Monin-Obukhov length, L, and
the boundary-layer height, zi, are
computed.
Chemical transformation rate express-
ions were developed from the results of
photochemical model simulations over a
wide range of environmental conditions.
The rate expressions include gas-phase
NOx oxidation, gas- and aqueous-phase
components of SO2 oxidation, and the
chemical equilibrium of the nitric acid,
ammonia, and ammonia nitrate system.
The parameterized transformation rates
depend on solar radiation, background
ozone concentration, and atmospheric
stability. The S02 oxidation rate is empir-
ically increased at high relative humidity
to account for aqueous-phase reactions.
In the case of NOx, the transformation
rate also depends on the NOx concentra-
tion.
The spatial and temporal variations of
dry deposition are treated by a resistance
model. The pollutant flux is proportional
to the inverse of a sum of resistances to
pollutant transfer through the
atmosphere to the surface. The
resistances depend on the characteristics
of the pollutant and the underlying
surface and atmospheric conditions.
MESOPUFF II contains options for the
commonly used source-depletion method
or for more realistic surface depletion,
where pollutants are removed only from a
surface layer in the three-layer mode.
Precipitation scavenging can be the
dominant pollutant removal mechanism
during precipitation periods MESOPUFF
II contains a scavenging ratioformulation
for wet removal. The scavenging ratio
depends on the type and rate of precipita-
tion (derived from hourly precipitation
measurements, if available) and the char-
acteristics of the particular pollutant.
In addition, improvements were
made in the method of summing the con-
tributions of individual puffs to the total
concentration at a receptor location. The
model uses an integrated form of the
puff-sampling function that eliminates
the problem of insufficient puff overlap
commonly encountered with puff-super-
position models. This development allows
continuous plumes to be more accurately
simulated with fewer puffs, thereby
saving computational time and reducing
computer storage requirements
MESOPUFF II Modeling System
The MESOPUFF II modeling package is
schematically illustrated in Figure 1. The
two meteorological preprocessor rou-
tines are READ56 and MESOPAC II.
READ56 processes the rawinsonde data,
and MESOPAC II reads the output file
created by READ56 and the standard-
formatted hourly surface meteorological
data and precipitation data. A single
output file is produced that includes all
the time- and space-interpolated fields of
meteorological variables required by
MESOPUFF II.
All source, receptor, and program-
control information is input by formatted-
card images. The control parameter
inputs determine which options are used
in the computations and what type of
output is produced.
The model was run for a two-day
period, to evaluate the SO2 to SOf
transformation mechanism and to
qualitatively demonstrate the behavior of
some other model algorithms. The modeled
period was taken from the August 1978
Tennessee Plume Study, which was
conducted near the Cumberland power
plant in northwestern Tennessee. The
two-day period (August 22-23) included
chemical measurements by aircraft
traverses through the plume at distances
of 18 km to 160 km and represented 2 to
10 hours of travel. The predicted
transformation rates were generally
close to the observed rates derived from
the pollutant measurements, especially
for the drier, sunny period on August 22.
During this period, SO2 oxidation was
probably dominated by gas-phase
reactions, whereas on the 23rd, when
plume-cloud interactions were observed,
the transformation rates were
underpredicted (values were two-thirds
the observed rates). The larger observed
values are attributed to greater
contributions by aqueous-phase
reactions.
Conclusions
The scientific and operational ap-
proaches to modification of the model are
completely described in the report. The
results of the model runs, including a
comparison of observed and predicted
transformation rates, the qualitative
behavior of plume growth, plume
fumigation, and dry deposition (surface
depletion) are also presented. A
companion report entitled "User's Guide
to the MESOPUFF II Model and related
Processor Programs" provides a brief
technical description of the methods and
a complete set of user instructions.
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{ ME SOP AC II
I Control Parameter
I Inputs
I READ56 Control
I Parameter Inputs
Twice-Dail
Rawinsonde
Data Files
(TDF5600
Format!
READ56 Upper Air
Preprocessor Program
Formatted
Twice Daily
Rawinsonde
Data Files
Hourly
Meteorologies
Data Files
(CD144
Format)
MESOPACII Meteorological
Preprocessor Program
Hourly
Ozone
Measurements
f MESOPUFFII
I Control Parameter
I Inputs
Meteorological
Variables
MESOPUFF II Dispersion Model
Concentration
Tables
Predicted
Concentration
f MESOFILEII
I Control Parameter
I Inputs
MESOFILE II
Postprocessor Program
^
,
/Direct Access\
f Concentration]
Files for
Plotting
figure 1. MESOPUFF II modeling package
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J. S. Scire, F. W. Lurmann. A. Bass, and S. P. Hanna are with Environmental
Research and Technology, Inc., Concord, MA 01742.
James M. Godowitch is the EPA Project Officer (see below).
The complete report, entitled "Development of the MESOPUFF II Dispersion
Model," (Order No. PB 84-183 753; Cost: $11.50, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
U.S. GOVERNMENT PRINTING OFFICE: 1984 — 759-015/771S
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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