United States
Environmental Protection
Agency
Atmospheric Sciences
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S3-87/033 Dec. 1987
Project Summary
An Experimental and Modeling
Study of the Photochemical
Reactivity of Heatset
Printing Oils
William P. L Carter
A series of environmental chamber
experiments and computer model sim-
ulations were carried out to assess the
atmospheric ozone formation potential
of the respresentative heatset printing
oils Magie-47 and Magie-470 relative
to that of ethane. n-Pentadecane, a
representative major constituent of
these oils, was also studied. The results
showed that n-pentadecane and the
printing oils tend to slow down the
initial rate of ozone formation in NOx-
air irradiations, but they also caused
higher final ozone yields in some
surrogate-NOx-air experiments.
The results of these experiments
were used to test current models for
the reactivities of ethane and
n-pentadecane. The model predictions
fit the results of most of the experi-
ments within the experimental uncer-
tainty, though some discrepancies
were observed. It is unclear whether
the discrepancies are due to problems
with the mechanism or to experimental
difficulties.
The model was used to estimate the
reactivities of ethane and n-pentade-
cane for several idealized model sce-
narios representing urban air pollution
episodes. The predicted atmospheric
reactivities of n-pentadecane and the
printing oils relative to ethane were
found to be highly dependent on the
conditions of the model scenario. Thus,
decisions on whether regulation of
emissions of printing oils is beneficial
in reducing atmospheric ozone must
take into account the range of condi-
tions of the airsheds into which they
are emitted.
This Project Summary was devel-
oped by EPA's Atmospheric Sciences
Research Laboratory, Research Trian-
gle 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
Web-offset printing operations can
result in the emission of printing oils into
the atmosphere, and these vaporized oils
may undergo photochemical reaction
which contribute to the formation of
atmospheric ozone. Since ozone is a
major air quality problem in many urban
areas, the precursors to ozone formation
are subject to regulatory control under
State implementation plans. To deter-
mine whether controls of printing oil
emissions need to be included in such
plans, it is necessary to establish
whether the presence of these oils in the
atmosphere can contribute significantly
to ozone formation, i.e., to establish
whether these oils can be considered to
be "reactive" relative to ozone formation.
To be considered to be "reactive," an
organic compound or mixture must (1)
be sufficiently volatile so that it can react
in the gas phase, (2) react in the atmos-
phere sufficiently rapidly that its reac-
tions can be of significance, and (3) react
in such a manner that it contributes to
ozone formation. In many cases it is
obvious whether or not a compound or
mixture can be considered to be reactive
or unreactive. If a compound has a
negligible volatility or is essentially inert
in the atmosphere, it can be considered
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to be unreactive. If, however, relatively
low concentrations of a compound cause
significant ozone formation when irra-
diated in the presence of NO, in envir-
onmental chambers, then it is clearly
reactive. In cases when a compound or
mixture is either marginally volatile,
reacts in the atmosphere but does so
relatively slowly, or reacts in such a way
that it is not clear whether or not its
reactions enhance or suppress ozone
formation, then it is not immediately
obvious whether to classify this com-
pound or mixture as reactive or unreac-
tive. In these cases, the current regula-
tory policy is to use the reactivity of
ethane to define the borderline between
reactive and unreactive organic com-
pounds.
To obtain the data necessary to assess
whether heatset printing oils must be
considered to be reactive, Battelle,
Columbus, Laboratories had previously
studied volatility of representative print-
ing oils and their photochemical reactiv-
ity in environmental chamber irradia-
tions. The results of their study indicated
that the printing oils cannot be consid-
ered to be unreactive on the basis or
volatility, but the results of the environ-
mental chamber experiments were
ambiguous with regard to whether they
react in a manner which promotes ozone
formation. Some of the experiments
indicate that the printing oils studied are
somewhat more reactive than ethane,
while others indicated that they were
less reactive. A significant amount of this
uncertainty is due to problems in inter-
preting environmental chamber data
when used to study relatively unreactive
compounds, and because the conditions
of environmental chamber experients are
never exactly the same as those in the
ambient atmosphere. Previous studies
indicated that these differences become
highly significant when comparing rel-
atively unreactive substances such as
ethane and printing oils.
In principle, computer model simula-
tions, where the chemical mechanisms
used in the model is tested by comparing
its predictions against the available
environmental chamber data, can be
employed to predict reactivities under
atmospheric conditions. In this way the
computer model is used as a means of
correcting for chamber effects and
making extrapolations from conditions of
environmental chamber experiments to
those in urban airshed. However, for this
procedure to be appropriate as a basis
for control decisions, it is necessary that
the model employed be consistent with
our current understanding of atmos-
pheric chemistry and the atmospheric
reactions of the major constituents of the
printing oils, which consist primarily of
saturated hydrocarbons with an average
molecular weight corresponding to that
of n-pentadecane (n-CisHaz).
High molecular weight alkanes are
expected to be reactive in the sense that
they have relatively high rate constants
for reaction with hydroxyl radicals (the
primary mode of reaction of saturated
compounds in the atmosphere), but they
also react in a manner which removes
radicals and NO, from the system. This
latter characteristic tends to reduce their
reactivity, and may even make them
ozone inhibitors under some conditions.
Computer model simulations could indi-
cate whether this is so under atmos-
pheric conditions, provided the mecha-
nism is adequately characterized and
tested. However, the available chamber
data were not sufficient to establish the
reliability of computer models for the
purpose of predicting the reactivities of
high molecular weight alkanes under
atmospheric conditions.
Because of this need for further studies
concerning the atmospheric reactivity of
the printing oils, the EPA contracted to
the Statewide Air Pollution Research
Center (SAPRC) of the University of
California at Riverside to carry out
additional environmental chamber
experiments to provide additional data
needed for model testing, and to use
these data as a basis for evaluating their
atmospheric reactivities. This Project
Summary summarizes the results of that
study.
Experimental
The experiments were carried out in
the SAPRC 6400-liter indoor Teflon
chamber (ITC), which uses blacklamps as
the light source. The experiments con-
sisted of NO,-air irradiations of the
representative printing oils Magie-47
and Magie-470, of ethane, and of the
representative printing oil constituent
n-pentadecane, both by themselves (with
trace amounts of propene present in
order to test the effects of their reactions
on radical levels), and when added to a
standard "mini-surrogate"-NOIl-air mix-
ture. This "mini-surrogate" consisted of
four hydrocarbons (n-butane, propene,
frans-2-butene, and m-xylene) designed
to be a simplified representative of the
mixture of organics emitted into polluted
urban areas. The experiments also
included an appropriate array of control
and characterization runs necessary for
the data to be sufficiently well charac-
terized for model testing. A total of 33
environmental chamber irradiations
were carried out, and detailed tabula-
tions of the data obtained are available
from the author in computer readable
format.
Computer Model Calculations
Computer model simulations were
carried out as part of this study to
determine whether our current under-
standing or estimates of the atmospheric
reactions of n-pentadecane (the repre-
sentative printing oil constituent), and of
ethane are consistent with our experi-
mental results, and to estimate the
relative reactivities of these compounds
under conditions of idealized ambient
pollution scenarios. The chemical mech-
anism used for the N0,-air reactions of
ethane and the surrogate components
was that recently developed and tested
by us under USE PA funding. That
mechanism did not include the reactions
of n-pentadecane, and these had to be
estimated as part of this study.
Although prior to this experimental
study there have been no data available
concerning the atmospheric reactions of
n-pentadecane, estimates can be made
based on extrapolating our knowledge of
the atmospheric reactions of lower
alkanes. However, there is a major
uncertainty concerning the overall or-
ganic nitrate yield in the n-pentadecane
reactions, and two alternative mecha-
nisms, designated model "A" and model
"B", were employed in an attempt to
bracket the range of uncertainty. Model
"A" is based on assuming relatively high
nitrate yields consistent with theoretical
estimates, and model "B" is based on
assuming lower nitrate yields suggested
by our previous modeling of Ce-Ca n-
alkane-NOx-air experiments.
Results
One run each was carried out in which
ethane, n-pentadecane, Magie-47, or
Magie-470 were irradiated in NO,-air
mixtures without other added reactants
besides propene and n-butane tracers
(10 ppb each) added to monitor radical
levels. In all cases the addition of the test
substance tended to suppress radical
levels, but the suppression of radical
levels was significantly greater for
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n-pentadecane and the printing oils than
it was for ethane. In particular,
n-pentadecane, Magie-47, and Magie-
470 suppressed radicals by factors of
~50, —40, and —25 more than ethane,
respectively. The model simulations fit
the ethane runs to within the range of
uncertainty caused by the variability of
the chamber radical source. The exper-
imental results of the n-pentadecane run
fell somewhat between the predictions
of the two n-pentadecane mechanisms
(models "A" and "B"), while the results
of the Magie-47 run were well simulated
by the more reactive model "B", and both
models underpredicted the reactivity
observed in the run with Magie-470.
Most of the experiments consisted of
runs where either ethane, n-penta-
decane or one of the printing oils were
added to a standard "mini-surrogate"-
NO» mixture, and of control runs where
the standard surrogate-NOx mixture was
irradiated with no test compound added.
The results of these experiments were
analyzed to determine the "incremental
reactivities" of the test compounds,
defined as the change (in ppm) in the
1 -, 2-, 3-, or 6-hour ozone yields caused
by the addition of a test compound to the
standard surrogate-NOx mixture, divided
by the ppmC of the test compound added.
The incremental reactivities of ethane in
these experiments were found to be 2
to 5 ppb ozone per ppmC ethane added,
in good agreement with model predic-
tions. The incremental reactivities of n-
pentadecane and the printing oils are
shown, as a function of amount of
compound added and irradiation time, in
Figure 1, where they can be compared
with predictions using the two n-
pentadecane mechanisms.
It can be seen that under some con-
ditions the addition of n-pentadecane or
the printing oils inhibit ozone, and in
others they enhance it, with the effect
depending significantly on both reaction
time and the amount of test compound
added. The predictions of the models
agree qualitatively with the experimen-
tally determined incremental reactivities,
with the more reactive n-pentadecane
model "B" being more consistent with
most results, though there are discrepan-
cies. However, given our current limited
knowledge of the details of the atmos-
pheric photooxidation reactions of the
higher alkanes and the products formed,
and the experimental difficulties in
obtaining precise measures of reactivity
for relatively unreactive compounds, the
performance of the model in simulating
these results is probably as good as can
reasonably be expected at the present
time.
To provide an indication of the model
predictions of the relative reactivities of
ethane and the printing oils (as repre-
sented by the two n-pentadecane mech-
anisms) for conditions more representa-
tive of polluted urban atmospheres than
can be attained with environmental
chamber experiments, model simula-
tions of incremental reactivities were
i
= n-Pentadecane
carried out using several idealized
airshed model scenarios. The specific
quantities calculated were the "limiting
incremental reactivities," defined as the
difference in the maximum A([03HNO]>
in the simulations with and without the
added test compound, divided by the
amount (on a mole carbon basis) of test
organic added, at the limit as the amount
of test compound that goes to zero. The
airshed scenarios were based on three
different model formulations of emission
schedules, transport, dilution, and back-
1 = n-Magie-47
= n-Magie-470
0.04
T=60
T=120
-0.12
Added Compound (PPMC)
Figure 1. Plots of experimental and calculated incremental reactivities of n-pentadecane
and the printing oils Magie-47 and Magie-470 against amounts of test substance
added in the ITC "mini-surrogate"-NO,-air experiments. 0 = Experimental. (See
above for symbols for different types of runs.) = Model calculations of
incremental reactivities for the times shown. The lower fines were calculated
using n-pentadecane Model A, and the upper lines were calculated using Model
B.
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ground conditions, with the "EKMA-1 "
and "EKMA-3" scenarios being based on
city-specific EKMA defaults for low and
high dilution conditions, respectively,
and the "MD" scenario being an ideal-
ized representation of a multi-day pol-
lution episode in the California South
Coast Air Basin. Two different surrogate
mixtures, "Surg-4", and "Surg-8",
which differ in complexity but are similar
in overall reactivity, were employed to
represent base case ROG emissions in
these scenarios. For comparison pur-
poses, reactivities were also calculated
for the conditions of our indoor Teflon
chamber (ITC) experiments. For each
scenario, incremental reactivities were
calculated for a ra nge of ROG/NO. ratios.
The calculated reactivities of ethane
were found to be always positive, and
to depend primarily on the amount of
dilution occurring in the scenario, being
highest in the highest dilution "EKMA-3"
scenario, and the lowest in the no-
dilution "ITC" scenario. The reactivity of
ethane also depends on the ROG/NOX
ratio, being the highest for ratios slightly
less than those most favorable for ozone
formation. The maximum reactivity of
ethane was calculated to be somewhat
higher when the Surg-8 mixture is used
for the base case ROG surrogate, and
was also calcualted to increase with the
number of days in the multi-day
simulation.
The calculated reactivities for
n-pentadecane were found to be much
more variable and dependent on the
conditions of the scenario than was the
case with ethane. Regardless of which
of the two n-pentadecane mechanisms
was employed, n-pentadecane was
predicted to inhibit ozone under some
conditions, and to be somewhat more
reactive than ethane under others. This
is shown in Table 1, which gives' the
ratios of the reactivities calculated for the
two n-pentadecane mechanisms, rela-
tive to those calculated for ethane, for
the conditions of the various scenarios.
It can be seen that the calculated
reactivities of n-pentadecane relative to
ethane are highly dependent on the
ROC/NO* ratio, the n-pentadecane
mechanism assumed, and the nature of
the scenario and the base case ROG
mixture, in approximately that order of
importantce. The relative reactivities are
the highest under the conditions most
favorable to ozone formation, tending to
become negative both at low and at high
ROG/NOx ratios, due respectively to the
Table 1.
HOG/NO*
Ratios of Calculated Incremental Reactivities for n-Pentadecane to Those for Ethane
for the Airshed and ITC Scenarios
n-Pentadecane Reactivity/Ethane Reactivity
ITC
Surg-4
EKMA-1
Surg-4
Surg-8
EKMA-3
Surg-8
MD. Surg-8
Day 1 Day 2
n-Pentadecane Model "A "
4
8
12
16
40
-12.6
-10.8
-8.3
-7.3
-2.8
-6.4
-4.0
-2.7
-4.5
-14.1
-0.7
0.5
-0.5
-2.5
-13.3
0.8
1.2
0.0
-1.6
-10.4
-1.0
-0.8
0.3
-0.7
-11.4
0.5
1.2
0.9
-0.2
-9.3
n-Pentadecane Model "B"
4
a
12
16
40
-4.9
-3.3
-1.3
-0.2
2.6
-1.5
-0.1
0.9
-0.1
-5.2
1.7
2.2
1.7
0.8
-4.8
2.1
2.2
1.6
0.8
-3.8
1.6
1.3
1.9
1.6
-3.8
2.3
2.2
2.0
1.6
-3.2
radical termination and the NO, removal
characteristics of the n-pentadecane
photooxidation mechanism.
Conclusions
The currently available experimental
data and theoretical estimates and
calculations suggest that, with respect
to atmospheric ozone formation, it is
more probable than not that under some
conditions the printing oils are more
reactive than ethane. On the other hand,
it is also clear that under other conditions
the printing oils will inhibit ozone
formation. Although in theory airshed
model calculations could be used to
estimate the reactivities of the printing
oils for specific airsheds, the extreme
sensitivity of the predicted reactivities to
the conditions of the airshed into which
they are emitted, combined with the
uncertainties in the photooxidation
mechanisms for their major constituents,
makes such estimates subject to consid-
erable uncertainty. Until more is known
about the details of the atmospehric
photooxidation mechanisms of the
higher alkanes and other components of
the printing oils, and how their reactiv-
ities depend on the conditions of the
airsheds where they are emitted, it will
not be possible to make definitive con-
clusions as to whether the printing oils
should be judged to be reactive for
regulatory purposes.
Finally, it should be recognized that
this study addressed only the effects of
emissions of the printing oils on ozone
formation. The emissions of these oils
could have other impacts on air quality,
such as aerosol formation, formation of
toxic products, etc., which should also
be taken into account in making any
decisions on whether to regulate the
emissions of these oils. A discussion of
these aspects is beyond the scope of this
study, but obviously they should not be
ignored.
William P. L. Carter is with the Statewide Air Pollution Research Center,
University of California, Riverside, CA 92521.
Joseph J. Bufalini is the EPA Project Officer (see below).
The complete report, entitled "An Experimental and Modeling Study of the
Photochemical Reactivity of Heatset Printing Oils," fOrder No. PB 88-113
253/AS; Cost: $19.95, 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
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