\ I /
United States
Environmental Protection
Agency
Atmospheric Sciences
Research Laboratory
Research Triangle Park NC 27711 -
Research and Development
EPA/600/S3-85/012 Apr. 1985
SERA Project Summary
Methods for Simulating
Gas Phase S02 Oxidation in
Atmospheric Models
James F. Meagher and Kenneth J. Olszyna
Two different approaches are
presented for simulating gas phase
sulfur dioxide oxidation in at-
mospheric models. The first approach
was to develop an empirical relation-
ship based on rate data collected at
four coal-fired power plants during 11
separate studies. Cosine functions
were used to simulate annual and
diurnal variations in the oxidation rate
constant. The time variant rate con-
stant was superimposed on a con-
stant rate coefficient of 0.002 h'1 used
for nonsunlight hours. The model
predicts a maximum (solar noon) rate
constant of 0.0285 h'1 for mid-July.
The second approach was to
develop a kinetic model based on data
obtained from smog chamber ex-
periments using mixtures of sulfur
dioxide propene, butane, nitrogen ox-
ides, and water vapor. Sulfur dioxide
oxidation in the gas phase was found
to occur by two mechanisms. At low
HC/NOX values hydroxyl radical addi-
tion to sulfur dioxide predominates.
At high HC/NOX values, oxidation via
reaction with products of the ozone-
olefin reaction dominates. The
chamber data suggest that the HO-
SO2 reaction leads mainly to the pro-
duction of hydroperoxyl radical and
sulfuric acid. A previously proposed
mechanism for the reaction of sulfur
dioxide with Criegee intermediates
was found to provide an excellent fit
to the data at the high HC/NOX
values.
This Project Summary was
developed by EPA's Atmospheric
Sciences Research Laboratory,
Research Triangle Park, NC, to an-
nounce 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
In the past decade there has been an
intensive effort to determine the rate and
the mechanism of sulfur dioxide (S02) ox-
idation in the atmosphere. Although the
oxidation is believed to be a composite of
gas and liquid phase reactions, the majori-
ty of data available are applicable to the
gas phase only. Studies of droplet oxida-
tion have only just begun and the infor-
mation for chemical processes in cloud
systems is sparse. The mechanism and
models discussed in this report deal ex-
clusively with the gas phase oxidation of
SO2.
Mathematical models that simulate S02
to sulfate conversion in the atmosphere
fall into two general classes. The first,
empirical models, are based on ex-
perimental data with statistical averaging
to remove the inherent variability found in
field measurements. The rate is usually
assumed to be first order in S02. The sec-
ond, kinetic models, are based on a
chemical mechanism developed to
describe S02 oxidation in terms of
elementary reactions. Laboratory
measured rates of reactions are used in
mathematical expressions that describe
the time dependence of the major
species.
Empirical models represent average
conditions and thus can be expected to
fail in an event calculation. Kinetic
schemes borrow heavily from the
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smog/ozone models developed for urban
areas. The scheme may contain 50 to 150
individual reactions and might be ex-
pected to perform better for event
calculations. The price for this capability
is considerable. Model input requirements
can be staggering. A set of simultaneous
differential equations, one for each
species, must be solved at each time
step.
In this report various empirical and
kinetic schemes will be discussed. Al-
ternative schemes will be described.
These alternatives have been developed
using recent field and laboratory data,
much of which was not available to
previous modelers.
Empirical Model
A wide variety of schemes for the
parameterization of the S02 oxidation rate
constant has been developed in recent
years. Techniques vary from the use of
time invariant values for the rate constant
to ones that are allowed to vary diurnally
and seasonally. These procedures are
based loosely on field data and often
represent best fits to monitoring data.
Field studies funded by the U.S. En-
vironmental Protection Agency (EPA) be-
tween 1974 and 1979 have provided data
useful in developing parametric equations
relating S02 gas-phase oxidation and
meteorological variables. Wilson (1981),
for example, has analyzed the data from
12 power plant and smelter studies and
obtained a linear fit to the data (excluding
the VISTTA data from the Navajo Power
Plant):
SP/ST % = 3.66 (average solar radia-
tion, KW/m2 (time, h ) - 0.84 where the
left-hand side of the equation represents
the percentage sulfur in paniculate form.
This relationship is only useful if reliable
solar intensity data are available or can be
predicted.
A more elaborate scheme was proposed
by Gillani ef al. (1981) for dry conditions.
Based on analysis of two sets of field
measurements taken in 1976, the authors
obtained the following relationship:
(k,)d = (0.03 ± 0.01)(R.H.[03]0
where (k,)d = dry atmospheric rate con-
stant (% h'1)
R = solar radiation (kW/m2)
H = mixing height (m)
[03] = background ozone con-
centration (ppm)
The parameterization is based on a very
limited data base and requires more input
parameters than other techniques.
Perhaps the most obvious feature of
field measurements for S02 oxidation rate
constants is the variability of the data.
Measured rate constants range from 0.0
to greater than 0.1 h"1, sometimes at the
same location within a period of a few
days. There are, however, several features
of the data that provide reason for op-
timism. The most striking of these are the
diurnal and seasonal trends.
Diurnal Variations
The diurnal variation in the measured
S02 rate constant has been reported by
Husar et al. (1978), Forrest ef al. (1981),
Gillani et al. (op. cit. 1981), and Bailey et
al. (1982). The maximum rate constant
(0.02 - 0.08 rr1) was observed for
measurements made near solar noon.
Nighttime values are generally less than
0.005 h'1 with intermediate values in the
morning and late afternoon.
All of the studies cited above occurred
during the summertime and early fall.
There is a limited data base for wintertime
studies. Meagher et al. (1978) reported no
systematic change (diurnal trend) in a
Tennessee Valley Authority (TVA) study
during the winter of 1975-76. This marked
difference between summer and winter
measurements leads to a discussion of
seasonal trends.
Seasonal Variations
Altshuller (1979) used model estimates
of clean tropospheric hydroxyl (HO),
hydroperoxyl (H02), and methylperoxyl
(CH302) radical concentrations to
calculate the seasonal dependence of the
homogeneous S02 oxidation rate. The
bulk of the oxidation was due to the
hydroxyl radical reaction.
Meagher, et al. (1983) used data col-
lected during eight plume studies at four
coal-fired power plants to demonstrate
similar annual trends. The average rates
calculated varied from a winter low of 1.5
x 10~3 h"1 to a summer high of 1.3 x
10"2 h'1; this variation was similar to that
predicted by Altshuller's model.
Model Description
Conceptual development. An alternative
parameterization scheme for estimating
the atmospheric S02 oxidation rate is
presented here. It is intended that this
technique complement those described
previously and be used when the amount
of reliable input data are limited.
The model developed is based loosely
on the diurnal and annual variation in
clear-sky, solar intensity. The basic
assumption is that the rate constant can
be separated into a constant value and a
component that is allowed to vary diurnal-
ly and annually.
t,i) = k0
fA(i)
where k(t,i) = diurnally and annually vary-
ing rate constant
t = time of day (solar)
i = Julian date
k0 = time invariant component
of the rate constant
km* = maximum value the time
variant portion of the rate
constant may attain
fA (12 + 0.5 Td)
For a time dependent rate constant the
average value (k) during any period of the
solar day (tj --- > t2) is given by
t2
* = (t2 - t,)-1 J k(t,)dt
t,
Substituting the proposed functionality
for k(t)i and integrating we obtain a rela-
tionship between k~ and sine functions of
Td, t2, and t, . This equation is of the form i
-------
R = ko + Mmax) • g(t,,t2). Values for
g(t,,t2) have been calculated for each of
the plume measurement data bases.
Estimates of Mi)™* have been obtained
for each study by plotting R against
g(t,,t2) and performing a least squares fit
while forcing the line through 0.002 h'1 at
g(ti,tz) = 0. The objective of the model is
to reproduce average situations rather
than events; thus, a single outlier was
removed from each data set to prevent it
from unduly biasing the fit.
Annual function If All The annual variation
in the daily maximum rate constant,
kCOmax, was determined from the expres-
sion
M1U, = 0.5
[cos (2* (\ - inv»)/365) + 1]
where im>x
occurs
Julian date on which kn
The seasonal trend previously described
by Meagher ef al. (op. tit. 1983), is based
on morning rate measurements. The
mean solar time for each of these is 8.4
± 0.9 a.m. The rate constant was
calculated for each of the five diurnal
studies.
The annual maximum time variant rate
constant at solar noon Ik™*) and the date
of that maximum (inuJ were adjusted to
obtain the best fit to the data. The best fit
was obtained for k,™, = 0.0265 rr1 and
imax = 192.5. Therefore, the maximum
rate constant of 0.0285 rr1 is predicted for
mid-July, 20 days after the summer
solstice.
Model results. A combination of the diur-
nal and seasonal functions provides the
following equation for the pseudo first
order rate constant.
k(i,t,Td) = 0.002 + 0.006625
[cos (2 T (\ - 192.5)7365)+ 1]
. [cos(2 T (t - 12)/Td) + 1]
where k(i,t,Td) is in units of Ir1
A linear regression analysis of all 1.03 in-
dividual measurements from the data base
indicates that this simple model accounts
for 56% of the observed variation.
Model Limitations
The model proposed is intended to
represent average situations. It should not
be expected to exhibit significant skill in
reproducing individual events such as
daily values. All the field measurements of
S02 oxidation have been made in rural
areas; past experience has shown that ur-
ban areas with their local emissions can
significantly alter the observed rate con-
tent. Thus, extrapolation of these data to
urban conditions must be done with cau-
tion.
Kinetic Models
Many of the limitations inherent in em-
pirical models can be avoided through the
use of detailed kinetic schemes. As the
name implies, this approach presupposes
an understanding of the operative
mechanisms and requires rate data for all
elementary and composite reactions mak-
ing up the mechanisms.
Calvert and Stockwell (1984) reviewed
available data on, gas phase oxidation of
S02 in the atmosphere. They concluded
that hydroxyl radical addition was the
most important reaction in the oxidation
process. At higher HC/NOX values and
pollutant concentrations another
mechanism becomes equally important.
This mechanism is poorly understood but
involves the products of the ozone-alkene
reaction. Models that are used for rural
assessment could probably ignore the
contribution of the ozone-alkene
mechanism without significantly affecting
the predictions of atmospheric sulfate pro-
duction. However, in an urban environ-
ment, both mechanisms should be
included.
HO + S02. Most modelers have assumed
that S02 is an HO chain terminator and
have summarized the oxidation by
S02 + HO
H2S04
If the reaction is chain terminating, then
model calculations predict a high degree
of nonlinearity between S02 and sulfate
concentrations. Also, this assumption
leads modelers to conclude that a reduc-
tion in S02 would lead to an increase in
nitrate concentrations.
Recently, the S02 + HO reaction has
been studied by photolyzing mixtures of
nitrous acid (HONO) in the presence of
S02, NO, N02, H20, and CO. Extrapola-
tion of the data to atmospheric conditions
leads one to conclude the reaction can be
summarized in one equation thusly:
HO + S02 + (02, H20) ---- >
H2S04 + H02
and is, therefore, not chain terminating.
TVA conducted smog chamber ex-
periments to evaluate the mechanistic op-
tions for S02 oxidation. Chamber runs
were performed at constant initial NOX
and hydrocarbon concentrations with
variable amounts of S02 (0 to 6.4 ppm).
Runs were conducted at low and
moderate humidities (5% and 40% at
25°C). The overall effect of S02 on the
NO to N02 conversion and the formation
of ozone was to slightly accelerate the
conversion process and to increase the 03
peak concentration. The HO steady state
concentration decreased during the runs.
Comparison between the dry and wet ex-
periments reconfirms the observation of
other investigators that water vapor
enhances the photochemical activity in
these systems.
The HO concentrations for each experi-
ment were used to calculate the sulfate
formation rate using the rate coefficient
recommended by Atkinson and Lloyd
(1984) (1.39 x 103 ppm-1 min'' at 350°K,
1 atm). These values were compared with
values calculated by monitoring the rate
of aerosol volume increase. The agree-
ment between the two methods indicates
that under these conditions, HO addition
to S02 can account for all measured
sulfate.
Discussion
Two extreme mechanistic approaches
have been used to explain sulfate produc-
tion following HO addition to S02. The
first mechanism tested in this study was
the simple HO chain termination. The
reduction in HO steady-state concentra-
tion predicted by this mechanism severely
inhibited photochemical reactivity
resulting in an extreme underestimation of
ozone formation and very slow NO to N02
conversion. In this study, reaction with
S02 represents a significant sink for HO
radicals (about 35% using 1.5 ppm S02).
Atkinson ef al. (1982) had successfully
modeled Miller's experiments using the
termination mechanism because, in that
case, the S02 + HO > H2S04
reaction represented only a 2% loss of
HO radicals.
A better agreement between ex-
perimental data and model results was ob-
tained when a simplified version of the
reaction
HO + SO2 > H2SO« + H02 (1)
proposed by Calvert and Stockwell was
used. This model qualitatively predicts the
main chemical changes observed, i.e., ac-
celerated NO to N02 conversion, en-
hanced O3 formation, and the depression
of the HO steady state concentration with
added S02. The experimental data show
that at the beginning of the experiment
the HO concentration is insensitive to ad-
ded S02 probably because H02 produced
in the above reaction probably regener-
ates HO by reacting with NO. The model
predicts this observation. Near the end of
the experiment the lack of NO inhibits the
H02 to HO conversion and the HO
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steady-state concentration decreases. This
mechanism, however, does overestimate
the ozone formation increase caused by
S02 addition.
It is apparent that the assumption of an
HO chain propagation mechanism is a
better approximation to the experimental
data than that provided by termination.
However, the data suggest addition ter-
mination routes are needed. Several reac-
tions, which may occur in this system,
were proposed:
S02 + HO > HS03 (2)
AH = - 37 kcal • moM
HS03 + 02 > HS05 (3)
AH = - 16 kcal • mol'1
HS05 + NO > HSO, + N02(4)
AH = -25 kcal • mol'1
HS04 + H02 > H2S04 + 02 (5)
AH = - 61 kcal • mol'1
It was assumed that reactions (3) and
(4) are very fast (k3 and kj are greater
than 1 x 10* ppnr1 min"1). The rate coef-
ficient ks was estimated to be in the range
of 103 - 106 pprrr1 min"1. The addition of
these reactions to the model enhanced
the fit to the 03 data in the early stages of
the experiments, but little improvement
was noted in the prediction of the 03
maximum.
The overestimation of the 03 maximum
suggests the presence of additional reac-
tion(s) that consume 03 or its precursors.
A simple reaction that satisfies this re-
quirement is
HSO« + 03 > HS05 + 02 (6)
AH = - 23 kcal > mor1
By adjusting the ratios k,/k2 and kg/kg,
good agreement was obtained between
model prediction and experimental data.
All rate coefficients used for the simula-
tions are listed in the Project Report.
Because this project was intended to
develop the capability to predict ambient
sulfate levels, it is of interest to compare
model predictions with observed values.
The data also allow a comparison be-
tween the wet and dry experiments, i.e.,
high and low relative humidity. At low
S02 concentrations (< 1.0 ppm) when the
consumption of HO by S02 is small
(<10%) the approximation of linearity
(perfect hydroxyl propagation} between
S02 and sulfate formation is valid. As the
S02 concentration increased to about 5
ppm, significant deviation (factors of 2 to
3) from linearity were observed.
The chemical mechanism proposed in
this report indicates that 98.5% of the
time the H0-S02 reaction leads to H02
formation. This is consistent with the
conclusions of Calvert and Stockwell (op.
cit. 1984) that S02 termination of the HO
radical may not be important in the free
atmosphere. It must be emphasized that,
although the observed HO termination is a
small fraction of the total reaction, it
significantly affects the temporal behavior
and maximum levels of secondary
pollutants.
Alkene + O3 + SO*
Although the S02 + OH addition reac-
tion can explain the bulk of the field
measurements of S02 oxidation rate, the
mechanism cannot explain nighttime S02
oxidation, the very high rates observed
near urban areas, or the formation of
organosulfur compounds.
An additional pathway to sulfate forma-
tion that has been suggested by several
authors involves S02 oxidation in the
presence of ozone and olefinic hydrocar-
bons. The mechanism of this reaction is
not well understood at all. The general
opinion is that the S02 oxidation occurs
via reaction with a product from the
ozone-olefin reaction. A reasonable
mechanism proposed by Calvert et al.
(1978) to explain the observed S02 oxida-
tion in this system is
R'HC = CHR + 03 > Molozonide (7)
Molozonide > R'CHO +
[RHCOO]*
(8)
[RHCOO]* > Products (9)
[RHCOO]* + M > RHCOO + (10)
M
Thermalized Criegee intermediate
The thermalized Criegee intermediate
can then react with S02 to produce S03
which hydrolyzes to H2S04 or with H2O to
undergo rearrangement to a carboxylic
acid.
RHCOO + S02 >
(11)
H20
RCHO + S03 > H2SO,
RHCOO + H20 > (12)
RCOOH + H20
The Criegee intermediate can also react
with other atmospheric constituents as
follows:
RHCOO + NO >RCHO + N02 (13)
RHCOO+ NO2 >RCHO + NO2 (14)
RHCOO + CO > Products (15)
RHCOO + RCHO >0zonides (16)
Martinez and Herron (1981) also pro-
posed an addition reaction between S02
and the Criegee intermediate to produce
an organosulfur intermediate collisionally
stabilized to a heterocyclic organosulfur
species.
M
RHCOO + S02 --- > (17)
0 — -S = 0
This species can then react with water to
produce sulfuric acid:
0-0
RCH
RCHO+H2SO«
(18)
To simplify the kinetic treatment of
aerosol production in these systems, we
propose an empirical representation of the
formation process thusly:
X0 Ox (19)
RCH 0 S = 0 >
S(IV) aerosol
A steady-state treatment -of the in-
termediates in this mechanism yields the
following rate law for S02 oxidation:
-d[S02]/dt = k7[03][HC].A.B (I)
where k7 = rate coefficient for the ozone-
alkene reaction
A = MMl/kg + k10tM]; frac-
tional yield of the thermal-
ized Criegee intermediate
B = k17[S02]/k,7[S02] + k,2[H20]
+ k,3[NO] + k,4[N02]; frac-
tion of Criegee intermediates
that react with S02
The rate law for sulfuric acid formation
becomes:
d[H2S04]/dt = k7[O3][HC]A.B-C (II)
where k;, A and B are defined above and
C = k18[H20]/(kie[H20] + k,9);
fraction of the S02-Criegee
adduct intermediates that
are hydrolyzed to H2S04.
Conversely, the production of the S(IV)
aerosols can be described by
d[S(IV)]/dt = k7[03][HC]A • B • D (III)
where D = ki9/(ki8 [H2O] = ki9); fraction
of the S02-Criegee adduct
intermediates that produce
S(IV) aerosol
The equation for H2S04 production rate
states that the S02 oxidation to sulfuric
acid is a function of six terms. The im-
portance of this nonhydroxyl pathway is (
-------
difficult to assess due to the paucity of
experimental data.
The results of chamber runs conducted
at TVA indicated that all of the S02-
Criegee adduct intermediates hydrolized
to sulfuric acid. Under dry conditions (~
5% RH) the results were in qualitative
agreement with Equations I and II. The
competition between H20 and paniculate
formation for the adduct species (term D
in Equation III) predicts an increase in
S(IV) aerosol formation. The dry experi-
ment was repeated with measurements
for total aerosol volume and analysis of
the aerosols produced for both total sulfur
content and sulfate content. The sulfate is
found to be approximately 25 to 50% of
the total sulfur. The results suggest that
both sulfate and nonsulfate aerosols are
produced in an S02-NO-alkene system.
Laboratory experiments during this
study confirmed an earlier observation by
Eatough et al. (1981) that S(IV) aerosols
formed in an 03-alkene-S02 system spon-
taneously convert to S(VI) aerosols over a
period of days or weeks. Since most am-
bient air filter samples are usually not
analyzed for several weeks after being
taken, one would not expect to observe
S(IV) aerosols in these samples.
Kinetic Mechanism-SO2
Oxidation
A summary of the mechanism and a
listing of the rate parameter requirements
for modeling SO2 oxidation are presented
in the Project Report. The entire chemical
mechanism, which draws extensively on
the work of Atkinson et al. (op. cit. 1982)
is also listed there. The mechanism in-
volves 33 individual species and 69 reac-
tions and is obviously too large to be in-
cluded here. The reactions and rate data
presented must be combined with a free
radical photochemical scheme describing
atmospheric HC-NOX reactions. Several
such schemes are available (see reference
list in Project Report) and can be modified
to accommodate this mechanism.
The mechanism is suitable for both
rural and urban situations because it has
been tested over a broad HC/NOX range.
The hydroxyl radical mechanism will
dominate at low values of HC/NOX with
the Criegee mechanism becoming more
important at the higher values. From
modeling and chamber data we conclude
that, although the relative importance of
the two mechanisms shifts dramatically as
the HC concentrations inprease from 0.5
(to 3.0 ppm C, the effect on sulfate pro-
duction is small.
Conclusions and
Recommendations
Two options are provided in the Project
Report for simulating S02 chemistry in at-
mospheric models. Both are intended for
gas-phase oxidation and do not address
cloud or precipitation chemistry. The op-
tion selected depends, to a large extent,
on available input data.
The empirical model provides a simple
alternative to the complex kinetic models.
The S02 rate coefficient predictions are
based on field measurements solely. This
model is intended to represent the
average situation. It should not be ex-
pected to reproduce individual events.
The kinetic model provides much more
insight into the complex chemical reac-
tions governing SO2 oxidation in the at-
mosphere. When coupled with a com-
prehensive free radical photochemical
model, the recommended scheme should
reproduce observed sulfate formation over
a wide range of NOX and HC concentra-
tions. This scheme is more appropriate to
assessments requiring estimates for fine
temporal and spatial scales.
References
1. Altshuller, A. P. Model predictions of
the rates of homogeneous oxidation
of sulfur dioxide to sulfate in the at-
mosphere. Atmos. Environ. 13,
1653-1661 (1979).
2. Atkinson, R., and A. C. Lloyd.
Evaluation of kinetic and mechanistic
data for modeling of photochemical
smog. J. Phys. Chem. Ref. Data (in
press) (1984).
3. Atkinson, R., A. C. Lloyd, and L.
Winges. An updated chemical
mechanism for hydrocar-
bons/NOX/S02 photooxidation suit-
able for inclusion in atmospheric sim-
ulation models. Atmos. Environ. 16,
1341-1355 (1982).
4. Bailey, E. M., R. W. Garber, J. F.
Meagher, R. J. Bonanno, and L.
Stockburger. Atmospheric oxidation
of flue gases from a partially sulfur
dioxide-scrubbed power plant: Study
II. TVA Report No. ONR/ARP-82/4
(1982).
5. Calvert, J. G., F. Su, J. W. Bot-
tenheim, and 0. P. Strausz.
Mechanism of homogeneous oxida-
tion of sulfur dioxide in the
troposphere. Atmos. Environ. 12,
197-226 (1978).
6. Calvert, J. G. and J. R. Stockwell.
Mechanism and rates of gas-phase
oxidations of sulfur dioxide and
nitrogen oxides in the atmosphere. In:
Acid Precipitation Series—Volume 3,
S02, NO, and NO2 Oxidation
Mechanisms: Atmospheric Considera-
tions. John I. Teasley, Series Editor,
Ann Arbor Press (1984).
7. Eatough, D. J., M. L. Lee, D. W.
Later, B. E. Richter, N. L. Eatough,
and L. D. Hansen. Dimethyl sulfate in
paniculate matter from coal- and oil-
fired power plants. Environ. Sci.
Tech. 15, 1502-1510 (1981).
8. Forrest, J., R. W. Garber, and L.
Newman. Conversion rates in power
plant plumes based on filter pack
data: The coal-fired Cumberland
plume. Atmos. Environ. 15, 2273-2282
(1981).
9. Gillani, N. V., S. Kohli, and W. E.
Wilson, Jr. Gas to particle conversion
of sulfur in power plant plumes—I.
Parameterization of the conversion
rate for dry, moderately polluted am-
bient conditions. Atmos. Environ. 15,
2293-2313 (1981).
10. Husar, R. B., D. E. Patterson, J. D.
Husar, N. V. Gillani, and W. E.
Wilson, Jr. Sulfur budget of a power
plant plume. Atmos. Environ. 12,
549-568 (1978).
11. Martinez, R. I. and J. T. Herron. Gas
phase reaction of S02 with a Criegee
intermediate in the presence of water
vapor. J. Environ. Sci. Health,
A16(6), 623-636 (1981).
12. Meagher, J. F., E. M. Bailey, and M.
Luria. The seasonal variation of the
atmospheric S0a to SOf conversion
rate. J. Geophys. Res. 88, 1525-1527
(1983).
13. Meagher, J. F., L. Stockburger, E.
M. Bailey, and 0. Huff. The oxidation
of sulfur dioxide to sulfate aerosols in
the plume of a coal-fired power plant.
Atmos. Environ. 12, 2197-2203 (1978).
14. Wilson, W. E., Jr. Sulfate formation
in point source plumes: A review of
recent field studies. Atmos. Environ.
15, 2573-2581 (1981).
*U.S.Government Printing Office: 1985 — 559-111/10823
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James F. Meagher and Kenneth J. Olszyna are with the Tennessee Valley
Authority, Muscle Shoals, AL 35660.
H. M. Barnes is the EPA Project Officer (see below).
The complete report, entitled "Methods for Simuilating Gas Phase SOz Oxidation
in A tmospheric Models," (Order No. PB 85-173 110/AS; 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:
Atmospheric Sciences Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
0000329 PS
U S ENVJR PROTECTION AGENCY
REGION 5 LI8RARY
230 S DEARB6RN STREET
CHICAGO IL
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