United States
Environmental Protection
Agency
Environmental Sciences
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S3-84-082 Sept. 1984
&EPA Project Summary
Reactivity/Volatility
Classification of Selected
Organic Chemicals:
Existing Data
Hanwant B. Singh, Helen M. Jaber, and John E. Davenport
This study deals with the classifica-
tion of 118 organic chemicals according
to their involvement in photochemical
smog formation. A three-tiered classifi-
cation system for these chemicals was
developed using all available informa-
tion on their chemical reactivity and
volatility, both major determinants of a
chemical's oxidant-forming ability. Al-
though the degree of photochemical in-
volvement of chemicals cannot be
rigorously compartmentalized into dis-
crete classes, a practical classification
system is considered useful from a con-
trol strategy viewpoint. Separate three-
tiered classification schemes of the
reactivity and volatility of these 118
chemicals were also developed. Smog
chamber data for low-reactivity organic
chemicals may not be directly applica-
ble to ambient conditions. In response
to extensive shortcomings in existing
information, a number of recommenda-
tions and theoretical/experimental pro-
tocols designed to bridge current infor-
mation gaps are presented.
This Project Summary was de-
veloped by EPA's Environmental Sci-
ences 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 or-
dering information at back).
Introduction
Current strategies to control photo-
chemical air pollution focus on decreas-
ing the emission of volatile organic
compounds (VOCs). VOCs contribute
significantly to the production of smog-
forming oxidants. A strategy based on
the control of such compounds that
manifest themselves strongly in smog
formation, rather than on indiscrimi-
nate control, clearly constitutes a
superior technical approach.
Three major factors determine the
ozone (O3)- or oxidant-forming ability of
an organic chemical:
• Ambient concentrations (or emis-
sions)
• The ability of the organic chemical
and its intermediate products to re-
main in the gas phase (volatility)
• The ability of the organic chemical
to oxidize in the atmosphere (typi-
cally, by reacting with hydroxyl
[OH] radical or O3) and the effi-
ciency of the oxidation products to
form 03 (reactivity).
This study deals with the reactivity/
volatility classification of 118 organic
chemicals (including isomers and mix-
tures) specified by the U.S. Environ-
mental Protection Agency (EPA). A
three-tiered classification system for
these chemicals was developed using
all available information on their chemi-
cal reactivity and volatility. As re-
quested by EPA, separate three-tiered
classification schemes of the reactivity
and volatility of these chemicals were
also developed. The three tiers of the
chemical classification system were
conceived as follows:
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• Class I: Compounds that are un-
reactive or nonvolatile and do not
contribute to smog formation.
• Class II: Compounds that are bor-
derline cases or for which insuffi-
cient information is available to
draw definitive conclusions.
• Class III: Compounds that are reac-
tive and volatile and contribute to
smog formation.
For cases where existing information
does not allow any definitive conclu-
sions, a research protocol to bridge
many of the shortcomings of the cur-
rent information needs to be de-
veloped. Note that the regulatory objec-
tive is to classify chemicals as those
that either "contribute to smog" or
those that "do not contribute to smog."
The middle category of chemicals
(Class II) was created as a practical
necessity when a compound could not
be placed in either of the other two
classes because of a lack of reliable in-
formation.
Results and Discussion
The reactivity of organic chemicals
(OCs) was assessed based on available
experimental and theoretical data.
Smog chamber data were available for
only about one-half the chemicals of in-
terest. Maximum O3 yield, OC depletion
rate, nitric oxide (NO), (or nitrogen
dioxide [NO2]) oxidation rate, and prod-
uct compositions and concentrations
were factors considered in the interpre-
tation of smog chamber data. When
smog chamber data were not available,
the photochemical potential of OCs was
determined based on their reactivity
with OH radical. Reactions with 03 or
NO3 and direct photolysis were con-
sidered when appropriate. When ex-
perimentally measured OH rate con-
stants were not available, an OH rate
constant estimation technique was em-
ployed. All the pertinent experimental
data and results based on theoretical
estimates are summarized in an appen-
dix to the final report. Based on our best
interpretation of available data, the fol-
lowing reactivity classification scheme
can be derived:
• Class I: Organics where direct
(smog chamber) data show 03 for-
mation significantly less than 0.12
ppm, and the chemical has a mea-
sured or calculated depletion rate
that is comparable to, or less than,
ethane.
• Class II: Direct evidence shows O3
formation near 0.12 ppm or deple-
tion rates are 1 to 5 times that of
ethane.
• Class III: Chemicals where direct
evidence of O3 formation in excess
of 0.12 ppm (initial conditions of
OC =s4 ppm and any OC:nitrogen
oxides [NOX] ratio) is available,
and/or measured, or calculated de-
pletion rates are larger than 5 times
that of ethane, or chemicals for di-
rect or indirect evidence on reactiv-
ity exists.
There are a number of exceptions to
such a reactivity classification scheme.
Typical examples are OCs such as per-
chloroethylene and carbon disulfide, for
which the smog chamber data conflict
with kinetic theory and are probably not
representative of atmospheric condi-
tions. Another exception is the group of
chemicals commonly called "inhib-
itors" (such as phenols, naphthalene,
aniline, and possibly cresols). Such
chemicals, although highly reactive,
may not produce significant 03. In as-
signing reactivity based on the above
guidelines, exceptions were kept in
mind.
A similar approach was used for the
volatility classification scheme. The ex-
perimental data, in this case, were
highly limited and often conflicting.
However, the presence of paniculate
matter and its composition had a pro-
found effect on the phase distribution
of OCs. For the purposes of this study,
we assumed a polluted atmosphere.
Low-volatility OCs appeared to favor
the gas phase in remote unpolluted at-
mospheres. Vapor pressure was judged
as one of the key physical properties in
establishing the aerosol/gas phase par-
titioning of OCs. When measurements
were not available, vapor pressures
were estimated from boiling-point data.
These are summarized in an appendix
to the final report. Although uncertain-
ties remain, OC volatility may be clas-
sified most conveniently as follows:
• Class I: Organics with clearly
greater percent occurrence in the
condensed phase (>75% con-
densed phase) under ambient con-
ditions (vapor pressure <1 x 10~8
atm).
• Class II: Organics with inter-
mediate phase distribution in am-
bient air (1 x 10~8 atm < vapor
pressure < 1 x 10~6 atm), and or-
ganics of uncertain phase distribu-
tion or those having insufficient lit-
erature information.
• Class III: Organics with clearly
greater percent distribution in the
gas phase (vapor pressure >1 x
10-6atm).
Based on the above criteria, each of the
118 chemicals was assigned an indi-
vidual "reactivity" and "volatility" class
and an "overall" chemical class based
on photochemical involvement (Table
1). For a description of the overall
chemical classes, see the scheme out-
lined in the Introduction.
Conclusions and
Recommendations
An important achievement of this
study is the compilation of available
reactivity and volatility information
within a single document. An inherent
limitation is the paucity of available
data on which to base assessments.
Even when data are available, there are
often significant inconsistencies among
the various studies performed. One
source of inconsistency is the incom-
pleteness of data. As an example, OCs
found to be quite unreactive at low
OC:NOX ratios (2:5), appear to be quite
reactive when this ratio is increased to
20 or more. In many cases, however,
the increased reactivity is simply a
smog chamber artifact that makes the
results unrepresentative of ambient
conditions. In addition, several classes
of compounds (such as organic acids)
have been insufficiently studied. Thus,
extreme caution and judgment are re-
quired to assess the reliability of a given
study.
Available volatility data are also very
sparse, and their interpretation is sub-
ject to some judgments as well. Be-
cause of the paucity of these data, we
have made several recommendations
to bridge the data gaps.
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Table 1. Reactivity /Volatility Classification of Selected Organic Chemicals
Classification
Chemical Name No.
Acetic acid
Acetic anhydride
Acetaldehyde
Acetone
Acetone cyanohydrin
Acetonitrile
Acetylene
Aery lie Acid
Acrylonitrile
Adipic acid
Aniline
Benzene
Bisphenol-A
1,3-Butadiene
n-Butane
i-Butane
Butenes
Isobutylene
n-Butanol
2-Butoxyethanol
n-Butyl acetate
s-Butyl acetate
t-Butyl alcohol
Carbon disulfide
Carbon tetrachloride
Chloroform
Monochlorobenzene
p-Dichlorobenzene
Dichloropropene (1,3 and 1,2)
Cumene
Cyclohexane
Cyclohexanol
Cyclohexanone
Diethylene glycol
Di-(2-ethylhexyl) phthalate
Diisodecyl phthalate
Dimethyl terephthalate
Epichlorohydrin
Ethane
Ethanol a mine (mono)
Ethanol amine (di)
Ethanol amine (tri)
Ethyl acetate
Ethyl alcohol
Ethyl benzene
Ethyl chloride
2-Ethoxyhexanol
Ethylene
Ethylene dibromide
Ethylene dichloride
Ethyl ether
Ethylene glycol
Ethylene oxide
2-Ethyl hexanol
Fluorocarbon 11
Fluorocarbon 12
Fluorocarbon 22
Fluorocarbon 113
Fluorocarbon 114
Formaldehyde
Glycerine
Hexamethylenetetramine
Heptenes
1,6-Hexane diamine
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17A-C
18
19
20
21
22
23
24
25
26
27
28
29A-B
30
31
32
33
34
35
36
37
38
39
40A
40B
40C
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
Reactivity
III
If
III
III
If
1
I
llf
III
llf
II'
II
llf
III
III
III
III
III
III
III
III
III
III
II
1
1
II
1
llf
III
III
llf
III
llf
llf
llf
llf
III5
1
llf
llf
llf
III
III
III
IIs
llf
III
Is
I
III
llf
1
llf
1
1
1
1
1
III
If
llf
III
llf
Volatility
III
III
III
III
III
III
III
III
III
III
III
III
1"
III
III
III
III
III
III
III
III
III
III
III
III
III
III
III
III
III
III
III
III
III
1
1
III"
III
III
III
1
II
III
III
III
III
III
III
III
III
III
III
III
III
III
III
III
III
III
III
II
II"
III
III"
Overall
III
II
III
III
II
1
1
III
III
III
II
II
1
III
III
III
III
III
III
III
III
III
III
II
1
1
II
1
III
III
III
III
III
III
1
1
III
III
1
III
1
II
III
III
III
II
III
III
1
1
III
III
1
III
1
I
1
1
1
III
II
II
III
III
-------
Table 1. (Continued)
Chemical Name
Hydrogen cyanide
Isodecyl alcohol
Isoprene
Isopropyl alcohol
n-Propyl alcohol
Maleic anhydride
Methanol
Methyl chloride
Methylene chloride
Methyl ethyl ketone
Methyl isobutyl ketone
Methyl methacrylate
Solvent naphtha
Naphthalene
Nitrobenzene
n-Octyl-n-decylphthalate
Nonylphenol (ethoxylated)
Perchloroethylene
Phenol
Phosgene
Phthalic anhydride
Propane
Propylene
Propylene glycol
Propylene oxide
Styrene
Jerephthalic acid
Terephthalic acid (dimethyl ester)
Jetraprop ylene
Toluene
Toluene diisocynate
1, 1, 1- Trichloroethane
Trichloroethylene
Triethy/ene glycol
Vinyl acetate monomer
Vinyl chloride monomer
m-and mixed Xylenes
o-Xylene
p-Xylene
Dimethyl succinate
Dimethyl glutarate
Dimethyl adipate
2-methoxy ethanol
Ethylene glycol monomethyl ether
Ethylene glycol monoethyl ether
Diisoamyl ketone
Propylene glycol methyl ether
Dipropylene glycol methyl ether
o,m,p Cresols
No.
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90,37
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
1 1 1A-C
Reactivity
Is
ur
III
III
IIIs
ll/f
HI
Is
1
III
III
III
III
II"
1
ur
///r
r
ir
/f
nr
HI
in
ur
//s
in
HI*
HI
ur
HI
ur
i
in
mf
in
in
in
HI
in
i//f
nr
ur
mf
nr
///'
nr
///'
nr
in5
Classification
Volatility
III
II
III
III
III
III
III
III
III
III
III
III
III"
III
III
I
II"
III
III
HI
II
III
III
III
III
III
III
III"
III"
III
III
III
III
III
III
III
III
III
III
III"
III"
III"
III"
III
III
II"
III
III
III
Overall
1
II
III
III
III
III
III
1
1
III
III
III
III
II
I
I
II
1
II
1
II
III
III
III
II
III
III
III
III
III
III
I
III
III
III
III
III
III
III
III
III
III
III
III
III
II
III
III
III
rNo smog chamber or measured hydroxyl radical rate constant data were available.
"Exception requiring special interpretation of data (see text).
"Vaporpressure was estimated.
!No smog chamber data were available.
"No vapor pressure estimate was possible.
-------
Hanwant B. Singh, Helen M. Jaber, and John E. Davenport are with SRI
International, Menlo Park, CA 94025.
Basil Dimitriades is the EPA Project Officer (see below).
The complete report, entitled "Reactivity/Volatility Classification of Selected
Organic Chemicals: Existing Data." (Order No. PB 84-232 883; Cost: $ 17.50,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA22161
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: 1984/759-102/10690
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