1

ATMOSPHERIC OZONE REACTIVITY ESTIMATES FOR

2-AMINO-2-METHYL-1-PROPANOL

By

William P. L. Carter

Research Chemist Emeritus

College of Engineering Center for Environmental Research and Technology (CE-CERT) and

Air Pollution Research Center, University of California, Riverside CA 92521

September 26, 2012

Summary

Available information and estimates concerning the impacts of emissions of 2-amino-2-methyl-1-

propanol (AMP) on ground-level ozone are discussed. Until recently, the atmospheric ozone impacts of

AMP and other amines were difficult to estimate, and very high "upper limit" ozone reactivity estimates

were used in ozone reactivity scales. However, more recent data and estimates suggest that AMP reacts in

the atmosphere in such a way that it inhibits ground-level ozone formation under many conditions, and

only promotes ozone formation in environments where removing oxides of nitrogen (NOx) enhances

ozone, which is near source areas. The reactivity of AMP in the maximum incremental reactivity (MIR)

scale, 0.25 gm O3 / gm, is calculated to be slightly less than that of ethane, 0.28 gm O3 / gm ethane, the

compound the U.S. EPA has used as the standard to define "negligible" ozone reactivity for VOC

exemption purposes. This MIR value for AMP is an average over highly variable reactivities for the

individual scenarios used to derive the MIR scale, and is highly scenario-dependent. It is also likely that

the not all of the AMP introduced into the environment will be available for reaction in the gas phase to

promote ozone, which would mean that the magnitudes of the ozone impacts of AMP will be lower in real

ambient atmospheres than estimated in this work.

Contents

Introduction............................................................................................................................................. 2

Gas-Phase Atmospheric Reaction Mechanism ......................................................................................... 2

Reaction with OH radicals................................................................................................................. 2

Reaction with NO3 Radicals .............................................................................................................. 4

Reaction with Ozone ......................................................................................................................... 4

Reactions with HNO3 ........................................................................................................................ 4

Mechanism Evaluation...................................................................................................................... 5

Atmospheric Ozone Reactivity Estimates ................................................................................................ 6

Summary of Past and Current MIR Values ........................................................................................ 6

Reactivities of AMP Compared to Ethane.......................................................................................... 8

Uncertainties in Ozone Reactivity Estimates...................................................................................... 8

Conclusions........................................................................................................................................... 12

References............................................................................................................................................. 12
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Introduction

This paper will discuss current estimates of the ozone impacts of 2-amino-2-methyl-1-propanol

(AMP), a compound that is used in a number of consumer products. Available information and estimates

indicate that AMP either inhibits ozone formation or has relatively low positive impacts under many

conditions, despite the fact that previous estimates indicated that AMP has large positive impacts on

ozone formation because of its rapid rates of reaction in the atmosphere. This is because AMP is now

believed to react in such a way that it removes reactive radicals and NOx from the atmosphere. Given

below is a discussion of current estimates concerning the atmospheric reaction mechanisms of AMP that

affect ozone formation, and estimates of its ozone impacts in various reactivity scales, which have

changed over the years as new information became available.

Gas-Phase Atmospheric Reaction Mechanism

The atmospheric reaction mechanisms for AMP and other amines have been estimated by Carter

(2008) based on a review of available data and estimation methods and results of environmental chamber

experiments carried out with these compounds. These estimates are generally consistent with more recent

review of Ge et al (2011), which provides more information on the fate of many amines in the

atmosphere. This information as it relates to the gas-phase reactions AMP is reviewed here, but Carter

(2008) and Ge et al (2011) should be consulted for details and supporting data. Note that the data and

estimates of Carter (2008) resulted in a significant reduction in estimates of atmospheric ozone impacts of

AMP compared to previous estimates. The history of past estimates of ozone impacts of this and related

compounds is discussed separately below.

Amines might react in the atmosphere with OH radicals, O3, NO3 radicals, and all these

possibilities need to be considered when estimating their mechanisms for reactivity assessment. In

addition, unlike most other VOCs, amines are basic and might also be lost to some extent by reaction with

HNO3, forming non-volatile amine salts that may partition into aqueous aerosol, potentially reducing their

availability for ozone formation. Photolysis is not expected to be important based on available absorption

cross-section data for representative amines. These processes, and the expected subsequent reactions

where applicable, are discussed below.

Reaction with OH radicals

The rate constant for the gas-phase reaction of OH radicals with AMP has been measured to be

2.8 x 10-11 cm3 molec-1 s

-1 at ~300 K (Harris and Pitts, 1983), giving it a relatively short lifetime in the

atmosphere. The possible initial reactions are expected to be as follows (Carter, 2008):

CH3C(CH3)(NH2)CH2OH + OH  H2O + CH3C(CH3)(CH2OH)NH· (1)

CH3C(CH3)(NH2)CH2OH + OH  H2O + CH3C(CH3)(NH2)CH(·)OH (2)

CH3C(CH3)(NH2)CH2OH + OH  H2O + CH3C(CH2·)(NH2)CH2OH (3)

CH3C(CH3)(NH2)CH2OH + OH  H2O + CH3C(CH3)(CH2O·)NH2 (4)

The major reaction for AMP is estimated to be abstraction from the amino group (Reaction 1), which is

estimated to occur ~80% of the time based on structure-reactivity estimates (Carter, 2008, and references

therein). The subsequent reactions of the nitrogen-centered radicals formed in such reactions depend on

whether there is an abstractable hydrogen in the -position to the amine. If there is, then it is assumed that

the dominant reaction is abstraction of this hydrogen by O2, forming HO2 and the corresponding C=N

compound, e.g.,

RCH2NH· + O2  HO2 + RCH=NH (5)

This is based on kinetic data obtained by Lindley et al (1979) for reactions of (CH3)2N· with O2, NO, and

NO2, where the reaction with O2, forming HO2 + CH3-N=CH2, is calculated to dominate under

atmospheric conditions. This is a radical propagating reaction that promotes the formation of ozone.
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However, since AMP lacks such an  hydrogen such a reaction is not possible. In these cases, the only

expected reactions are those of the nitrogen-centered radical with NO, NO2, or HO2, e.g.,

CH3C(CH3)(CH2OH)NH· + NO  CH3C(CH3)(CH2OH)NHNO (6)

CH3C(CH3)(CH2OH)NH· + NO2  CH3C(CH3)(CH2OH)NHNO2 (7)

CH3C(CH3)(CH2OH)NH· + HO2  CH3C(CH3)(CH2OH)NH2 + O2 (8)

If NOx is present, which is required for O3 formation to occur, the major net sink reaction is expected to

be Reaction (7) forming the nitramine, since the nitrosamines formed in Reaction (6) are expected to

undergo rapid photolysis back to NO and the radical, resulting in no net reaction. Since nitramine

formation is a radical terminating process, this mechanism predicts that AMP would be a radical inhibitor,

since reaction forming the N-centered radical is estimated to be the major initial reaction. This is

consistent with the fact that AMP is found to be strong ozone and radical inhibitor in environmental

chamber experiments, as discussed in the Mechanism Evaluation Results section, below. Note that the

nitramine is estimated to be relatively unreactive, so its formation results in a sink for reactive NOx, at

least for the time scale of a 1-day pollution episode or an environmental chamber experiment. This also

has implications on AMP's ozone impacts, as discussed below.

The next most important route when OH radicals react with AMP is abstraction from the CH2

group adjacent to the alcohol, forming an -hydroxy carbon centered radicals. This is estimated to occur

about ~19% of the time based on structure-reactivity estimates. These radicals are believed to react

primarily with O2 forming HO2 and the corresponding carbonyl compound, i.e.,

CH3C(CH3)(NH2)CH(·)OH + O2  CH3C(CH3)(CHO)NH2 + HO2· (9)

This is a radical propagation that promotes the formation of ozone, but since it occurs only about 1/5 of

the time it is much less important than the termination reactions discussed above.

The other two possible reactions, abstraction from a methyl group (Reaction 4) or from the OH

group (Reaction 5) are estimated to occur less than 3% of the time, and are therefore not major factors

affecting their ozone reactivity. The subsequent reactions after Reaction 4 are estimated to be as follows,

based on the assumption that elimination of the amino group from alkoxy radicals is negligible (Carter,

2008):

CH3C(CH2·)(NH2)CH2OH + O2  CH3C(CH2OO·)(NH2)CH2OH (10)

CH3C(CH2OO·)(NH2)CH2OH + NO  NO2 + CH3C(CH2O·)(NH2)CH2OH (11)

CH3C(CH2OO·)(NH2)CH2OH + NO  CH3C(NH2)(CH2OH)CH2ONO2 (12)

CH3C(CH2O·)(NH2)CH2OH + O2  CH3C(CHO)(NH2)CH2OH + HO2· (13)

Note that nitrate formation (Reaction 12) is estimated to occur less than ~10% of the time relative to the

competing reaction (11), so most of the reaction involves radical propagation and HO2 formation through

Reactions 10, 11, and 13. Reaction (5) is estimated to occur less than 1% of the time (Carter, 2008), so its

occurrence and the subsequent reactions of the radicals formed are ignored.

In terms of model species used in the SAPRC-07 mechanism (Carter, 2010a), the overall process

for these reactions can be represented as follows:

OH + AMP  0.799 NRAD + 0.185 {HO2 + RCHO + XN} + 0.015 {RO2C + xHO2 +

xRCHO + XN} + 0.001 {RO2XC + zRNO3 + XN} + 0.016 yROOH (14)

See Carter (2010a) for a description of the model species and chemical operators used in the SAPRC-07

mechanism. Here NRAD is added to the mechanism to represent loss of NO2 and CH3C(CH3)(CH2OH)-

NHNO2 formation as discussed below, HO2 + RCHO + XN is used to represent formation of HO2 and

CH3C(CH3)(CHO)NH2, RO2C + xHO2 + xRCHO + XN is used to represent formation of HO2 and

CH3C(CHO)(NH2)CH2OH following an NO to NO2 conversion, and RO2XC + zRNO3 + XN is used to
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represent formation of CH3C(NH2)(CH2OH)CH2ONO2 following reaction of peroxy radicals with NO,

and XN represents unreactive nitrogen.

The model species NRAD is added to the mechanism to represent the formation of radicals that

reacts primarily with NO2 to form relatively unreactive nitrogen-containing species such as nitrosamines.

Its mechanism is as follows:

NRAD + NO2  PROD2 + 2 XN (15)

NRAD + HO2  XN (16)

Here, PROD2 + 2 XN is used to represent the nitramine CH3C(CH3)(CH2OH)NHNO2, where PROD2 is

the model species used in the model to represent moderately reactive products and the 2 XN represents

the fact that the nitramine contains two nitrogens that are relatively unreactive. The reaction with HO2 is

added to the mechanism to provide a sink for the radical intermediate in the absence of NOx, but this

reaction is not important under conditions where O3 formation is occurring.

Reaction with NO3 Radicals

The only kinetic data concerning the reactions of NO3 radicals with amines is for N-methyl-2-

pyrrolidinone (NMP), where a relatively high rate constant of 1.26 x 10-13 cm3 molec-1 s

-1 was measured

(Aschmann and Atkinson, 1999). This suggests that this reaction is also rapid for other amines. We

assume that this is an H-atom abstraction reaction, forming HNO3. For lack of other data, Carter (2008)

used the rate constant for NMP as the basis for estimating the group rate constants for reaction at the -

CH2(N) or CH3(N) groups. The group rate constants for reactions at other amine groups, including NH

and NH2, are estimated assuming that the ratios of rate constants for reactions at the various groups are

the same for the NO3 reaction as derived for the OH reaction. This is highly uncertain.

Based on these assumptions, Carter (2008) estimates that the rate constant for the reaction of NO3

radials with AMP is 5.9 x 10-14 cm3 molec-1 s

-1, and that the mechanism is

CH3C(CH3)(NH2)CH2OH + NO3  CH3C(CH3)(CH2OH)NH· + HNO3 (17)

where the CH3C(CH3)(CH2OH)NH· reacts to form the nitramine as discussed above. This is therefore

represented in the mechanism as

AMP + NO3  NRAD + HNO3, (18)

consistent with the treatment in the OH mechanism, discussed above. This is a relatively minor process

compared to the OH reaction, but is included in the mechanism for completeness.

Reaction with Ozone

There are no data available concerning the rate constant for the reactions of ozone with AMP,

though kinetic data are available for a few other amines as discussed by Carter (2008). The reaction of

methylamine with O3 is too slow to be important in atmospheric conditions, though the rate constants for

the other amines may be non-negligible. However, Ge et al (2011) estimate that reactions with O3 are

unimportant fates for amines in the atmosphere. Based on kinetic and mechanistic considerations Carter

(2008) estimates that the reaction at the N-H groups is probably not as important as reaction at hydrogen

atoms next to the amino groups. Since AMP lacks such hydrogen atoms, Carter (2008) estimated that the

reaction of AMP with O3 is negligible under atmospheric conditions. Although this is uncertain, it is

unlikely that the reaction with O3 would be an important fate of AMP compared to reactions with OH

radicals.

Reactions with HNO3

Amines are basic compounds that can react in the gas phase to form nitrate salts, which will make

them unavailable for participation in O3 formation but will enhance the formation of atmospheric particles

(Ge et al, 2011). The importance of this reaction depends on the thermodynamic stability of the amine
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nitrate salt, levels of HNO3, and other environmental conditions, and is difficult to estimate. This reaction

may occur to some extent but is probably not the major fate of amines under atmospheric conditions. The

environmental chamber experiments with AMP discussed by Carter (2008) indicate that AMP enhances

particle formation, but probably not to the extent that would be the case if salt formation were the

dominant process.

For the purpose of ozone reactivity estimates, we assume that the loss of AMP due to the

reactions with HNO3 is negligible. The reaction with HNO3 may be non-negligible under some

conditions, but if so the result would be that the magnitude of the impact of AMP on ozone would be

lower. Therefore, although the importance of this reaction is uncertain, neglecting it might result in an

overestimate in the role played by AMP in affecting atmospheric ozone concentration. Likewise the

neglect of partitioning to aqueous atmospheric aerosols and sorption to surfaces also may be nonnegligible and result in a lower magnitude atmospheric impact.

Mechanism Evaluation

Carter (2008) describes results of environmental chamber experiments designed to test the

predictive capabilities of the estimated mechanisms for AMP and several other representative amines.

These experiments, carried out in the UCR EPA environmental chamber (Carter et al, 2005) consisted of

"incremental reactivity" experiments where the effects of adding the amine on ozone formation and NO

oxidation rates to in irradiations of simplified ambient VOC surrogate - NOx mixtures were determined.

This method has been employed extensively to evaluate mechanisms for a wide variety of other VOCs

(Carter, 2010a and references therein), and is particularly useful for radical inhibitors where single VOC -

NOx chamber irradiations do not provide useful data.

In addition to AMP, Carter (2008) describes results of similar experiments with ethanolamine,

and single experiments were carried out with isopropyl and t-butyl amine. The differences in the results

with these compounds were significant, but were consistent with predictions of the estimated

mechanisms. AMP was found to inhibit rates of NO oxidation, O3 formation, and OH radical levels under

all the experimental conditions employed. This indicates that AMP has both radical and NOx sinks in its

mechanism, consistent with the predictions of our estimated mechanism discussed above. On the other

hand, ethanolamine was found to enhance rates of NO oxidation and O3 formation in experiments with

relatively high NOx/VOC ratios and have relatively little effects on OH radical levels, though it tended to

somewhat decrease final O3 yields in experiments with low NOx/VOC ratios. This indicates that

ethanolamine does not have significant radical sinks in its mechanism and that its NOx sinks are

significantly less than is the case for AMP. The results of the single experiment with t-butyl amine were

similar to those for the comparable experiment with AMP, while the results of the isopropylamine

experiment were similar to the comparable experiment with ethanolamine.

The results of the chamber experiments, and the reactivity differences between the four amines

studied, were qualitatively consistent with the mechanisms estimated by Carter (2008), including the

estimated AMP mechanism discussed above. The differences between the compounds are attributed to the

fact that AMP and t-butyl amine both lack  hydrogens and therefore form radicals that are expected to

react primarily to form nitramines in a radical and NOx sink process, while ethanolamine and isopropyl

amine have such hydrogens and are predicted to react primarily via radical propagation steps that cause

less removal of NOx from the system.

The mechanism evaluation described by Carter (2008) is not as quantitative as one would like

because no satisfactory method to monitor the amounts of amines injected into the gas phase was

available, and the reactivity data in the experiments with all four amines studied, including AMP, suggest

that the amounts of amine actually available for gas-phase reaction in these experiments was considerably

less than the calculated amounts based on the volume of liquid injected. This is attributed to absorption or

losses of the amines on the walls or the injection line. It is not due to condensation of the amines onto

particles at the start of the experiment because measurable particle matter (PM) formation did not occur
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until after the irradiations began. However, the fact that the estimated mechanisms correctly predicted the

general reactivity characteristics, and the reactivity differences among the compounds studied, tends to

support the mechanisms estimated by Carter (2008), including the AMP mechanism discussed in this

paper.

Atmospheric Ozone Reactivity Estimates

The ozone impacts of a VOC depend on the environment where it is emitted as well as on its

atmospheric reaction mechanism, and both need to be specified if a quantitative ozone reactivity number

is desired. Probably the most important environmental characteristic that affects ozone reactivity is the

availability of NOx, since NOx is required for O3 to be formed. VOCs have zero impact on O3 in the

absence of NOx, and have the highest impacts on O3 when NOx is abundant. Carter (1994) developed

various reactivity scales to represent various conditions of NOx availability, and these scales are still used

today, though with updated gas-phase mechanisms (Carter, 2000, 2002, 2010a,b). These include the

maximum incremental reactivity (MIR) scale representing relatively high NOx conditions where O3 is

most sensitive to changes in VOC emissions, the maximum ozone incremental reactivity (MOIR) scale

representing lower NOx conditions that are optimum for maximum O3 formation, and the equal benefit

incremental reactivity (EBIR) scale representing even lower NOx conditions where controlling NOx and

controlling VOCs have equal relative effects on reducing ozone. Reactivities can be calculated for even

lower NOx conditions than EBIR, but they are of less interest because O3 is more sensitive to NOx than

VOCs under such conditions.

The California Air Resources Board (CARB) adopted the MIR scale for use for reactivity-based

regulations because this reflects environments where VOC control is most relevant to reducing O3

formation, and use of MIR for VOC regulations complements the use of NOx control to reduce O3 under

the lower NOx conditions that are not well represented by the MIR scale (CARB 1993). However, it is

appropriate to look at the reactivity of the compound under the full range of NOx conditions when making

comprehensive assessments of atmospheric impacts.

Before discussing the current reactivity estimates for AMP, it is useful to review past MIR values

because they have undergone significant changes. The current and past MIR values are discussed in the

following section. The current reactivity values for AMP are given for the full range of scenarios and NOx

conditions for which reactivity scales were derived.

Summary of Past and Current MIR Values

Table 1 summarizes the past and current estimates for the MIR values for AMP. As with other

amines, the MIR estimates for AMP underwent significant changes over the years. Prior to the

mechanism estimates and chamber experiments described by Carter (2008) the atmospheric reaction

mechanisms for amines were considered to be highly uncertain and no estimated mechanisms were

available for calculating reactivity values. In order to derive at least approximate values for upper limit

reactivity estimation purposes, "placeholder" mechanisms were derived for amines based on their known

or estimated rate constants and assuming a mechanism with minimal radical and NOx sinks and forming

reactive products. In addition "upper limit" MIR (ULMIR) values were derived using the procedures

developed by Carter (2000), and the ULMIR value for AMP, ≤15.08 gm O3/gm AMP, was used by the

CARB at the time (2002).

At the time that the SAPRC-07 mechanism was first developed and reported there were no

reactivity values given for amines because the work of Carter (2008) was still in progress, and although it

was clear that the previous values were incorrect, the new amine mechanisms were not yet developed.

The Carter (2008) report used the current mechanism for AMP as described in this paper, but the reported

MIR value given for AMP in that report was in error because the portion of the mechanism giving the

reactions of the NRAD model species was accidentally excluded. This resulted in the mechanism not

representing the loss of NO2 in the reaction forming the nitramine product. This error was subsequently
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Table 1. Summary of past and current MIR estimates and upper limit values for 2-amino-2-

methyl-1-propanol.

Date MIR (gm O3

/ gm VOC) Discussion

SAPRC-99 Mechanism

5/8/2000 Not listed Not on list for the listing given with the latest version of the SAPRC-99

documentation report (Carter, 2000). Also not on listings for previous

versions of MIR scale using SAPRC mechanisms (e.g., Carter, 1994).

10/26/2002 4.75  0.77 Provided to the CARB as an estimated MIR for this compound (Carter,

2002). Estimates based on measured OH rate constants and assuming a

simplified "placeholder" mechanism assuming that relatively reactive

products (represented by formaldehyde and propionaldehyde model species)

are formed. Considered a reasonable upper limit. Values shown are the

average and standard deviation for the 39 city-specific MIR scenarios.

10/26/2002  15.08 Provided to the CARB as an upper limit MIR estimate for this compound

(Carter, 2002). Derived using the "Upper Limit MIR" estimation method

described in Appendix D of the SAPRC-99 documentation report (Carter,

2000). This is based on assuming that compound reacts completely and that

it has the maximum ozone impact based on those calculated for other

compounds. This is intended to be an absolute upper limit for regulatory

applications where use of upper limit values are appropriate. This upper

limit value was adopted by the CARB for consumer product regulations

SAPRC-07 Mechanism

8/21/2007 Not Listed Not on the list for the version of the SAPRC-07 report submitted and

approved by the CARB (Carter, 2007) because the project to update

mechanisms for amines was still underway when the report was due. It was

clear at this point that the previous values were incorrect but the mechanism

was still being developed so no new values were available.

2/19/08 -2.68 This was the value given on the report of Carter (2008) documenting the

chamber experiments and new mechanisms for the amines. However, this

calculation was not valid because it failed to include the reactions of the

NRAD model species. This error resulted in the loss of NO2 associated with

the formation of the nitramine not being represented. Although this NOx

loss process results in lower (more negative) reactivities under low NOx

conditions (e.g., EBIR), it causes higher reactivities under MIR conditions

because O3 is suppressed by NOx under MIR conditions. The associated

MOIR and EBIR values were -0.8 and -0.3, respectively.

1/28/10 0.25  0.57 This is the current, corrected value given provided to the CARB on this date

(Carter, 2010a,b). Values shown are the average and standard deviation for

the 39 city-specific scenarios shown in Table 2. It is derived using the same

mechanism as discussed here and given by Carter (2008), which includes

the loss of NO2 involved with nitramine formation. The associated MOIR

and EBIR values are -0.19 and -1.03, respectively.
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discovered and corrected, and the corrected reactivity values are included in the updated version of the

SAPRC-07 reactivity scale that was submitted to the CARB (Carter, 2010b). These corrected values are

also in the updated version of the SAPRC-07 documentation report at the SAPRC mechanism website

(Carter, 2010a). Including this NO2 loss process resulted in significantly lower (more negative)

reactivities under low NOx conditions such as those used for the EBIR scale (the EBIR value changed

from -0.3 to -1.03 gm O3 /gm AMP), but resulted in significantly higher reactivities in the MIR scale,

causing the MIR to go from -2.7 to +0.25 gm O3 /gm AMP. This is because O3 is strongly inhibited by

NOx under MIR conditions, so reducing NOx will increase O3 under those conditions.

Reactivities of AMP Compared to Ethane

The incremental reactivities for AMP calculated for the various city-specific scenarios used to

derive the MIR, MOIR, EBIR and base case reactivity scales (Carter, 2010a) are tabulated on Table 2 and

plotted against the reactive organic gas (ROG) / NOx ratio in Figure 1. Incremental reactivities for ethane,

the compound used by the EPA to determine negligible reactivity for exemptions (Dimitriades, 1999) are

also shown. The "averaged conditions" scenario reactivities on Table 2 are given for MIR, MOIR, and

EBIR conditions, but are given as a continuous function of the ROG/NOx ratio on Figure 1.

It can be seen that the ozone impact of AMP for the scenarios depends significantly on the

ROG/NOx ratio, being positive (ozone forming) and becoming greater than that of ethane at the high NOx,

low ROG/NOx ratios, and becoming significantly negative (ozone inhibiting) as the ROG/NOx ratio

increases (NOx becomes lower). The incremental reactivity for ethane also depends on the ROG/NOx

ratio, but to a much lesser extent than AMP, and it is always positive (ozone forming). The highest

incremental reactivity for AMP in the averaged conditions scenarios is under MIR conditions, and it is

calculated to decrease at both lower and higher ROG/NOx ratios. The reactivities for AMP does not

exceed that of ethane for any of the averaged conditions scenarios, but it does for some, though not all, of

the city-specific MIR scenarios. The incremental reactivity of AMP in the MIR city-specific scenarios are

highly variable, and still depend on the ROG/NOx ratio, even though they were adjusted to give MIR

conditions for the scenarios (see the circled "x"'s on Figure 1). Although the average MIR for AMP in the

city-specific scenarios is close to that for ethane, the scatter of reactivities in the city-specific MIR

scenarios is relatively large, with AMP reactivities in the individual MIR scenarios ranging from -0.8 to

1.5. This is a much larger scatter than observed for most other VOCs, though AMP is not unique in this

regard (see city-specific reactivity tabulation data provided by Carter, 2012). The average ratio of AMP’s

to ethane’s reactivity for the MIR scenarios is 0.4  2.3, which is somewhat lower than the ratio of the

MIRs for averaged conditions, which is 0.9, both indicating a lower average MIR for AMP than ethane,

though not outside the scatter of the data. The reactivities of AMP are lower than ethane in almost all

scenarios with lower NOx levels than MIR conditions.

Uncertainties in Ozone Reactivity Estimates

Ozone reactivity estimates depend on models for the mechanisms of the atmospheric reactions of

the compounds, models for the airshed conditions used, methods used to derive ozone reactivity scales

from values for the individual scenarios, and the availability of the compounds to undergo gas-phase

reactions in the atmosphere when they are introduced into the environment. All of these have nonnegligible uncertainties that need to be considered when assessing the implications of the ozone impact

estimates discussed here.

Chemical Mechanism Uncertainty. The uncertainties in the atmospheric reaction mechanisms

whereby amines affect ozone formation appear to be much less than was the case prior to the study of

Carter (2008), but the mechanism uncertainty is still non-negligible. The environmental chamber

experiments provided a qualitative test of the ability of the mechanism to predict ozone formation, and

the general trends in terms of effects of molecular structure and environmental chamber reaction

conditions are consistent with model predictions. However, the evaluation against chamber data was not

quantitative because it was not possible to quantitatively inject or measure the amines into the gas phase,
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Table 2. Summary of incremental reactivities calculated for ethane and AMP for the various cityspecific scenarios used for calculating the MIR and other reactivity scales.

Scenario

AMP Reactivity (gm O3/gm VOC) Ethane Reactivity (gm O3/gm VOC)

MIR MOIR EBIR Base MIR MOIR EBIR Base

Averaged Conditions 0.26 -0.20 -1.10 0.28 0.20 0.14

City-Specific Average 0.25

0.57

-0.19

0.41

-1.03

0.33

-0.66

0.53

0.28

0.07

0.20

0.06

0.14

0.04

0.17

0.04

Atlanta, GA 0.49 -0.23 -1.04 -0.91 0.26 0.19 0.14 0.14

Austin, TX 0.75 0.03 -1.04 -1.44 0.30 0.22 0.16 0.14

Baltimore, MD 0.06 -0.06 -1.00 0.07 0.27 0.19 0.14 0.21

Baton Rouge, LA -0.34 -0.67 -1.18 -0.80 0.21 0.14 0.09 0.12

Birmingham, AL 0.75 0.32 -0.51 -0.76 0.37 0.26 0.20 0.18

Boston, MA 1.00 0.24 -0.53 -0.52 0.30 0.22 0.16 0.16

Charlotte, NC 1.52 0.60 -0.04 -1.63 0.33 0.26 0.22 0.13

Chicago, IL -0.40 -0.47 -1.15 -1.49 0.25 0.16 0.11 0.09

Cincinnati, OH 0.76 0.29 -0.95 -0.13 0.32 0.25 0.18 0.22

Cleveland, OH 0.12 -0.46 -1.30 -0.46 0.23 0.17 0.11 0.17

Dallas, TX 0.01 -0.39 -1.12 0.00 0.25 0.18 0.12 0.24

Denver, CO -0.36 -0.91 -1.82 -0.61 0.19 0.13 0.09 0.15

Detroit, MI 0.43 0.14 -0.89 -0.17 0.31 0.22 0.16 0.20

El Paso, TX -0.40 -0.96 -1.66 -0.85 0.20 0.14 0.10 0.15

Hartford, CT 1.01 0.38 -0.71 -1.16 0.35 0.27 0.20 0.18

Houston, TX 0.13 -0.10 -0.87 -0.13 0.29 0.20 0.14 0.19

Indianapolis, IN 0.04 -0.52 -1.45 -0.65 0.30 0.21 0.15 0.20

Jacksonville, FL 0.15 -0.49 -1.21 -1.33 0.28 0.18 0.13 0.12

Kansas City, MO 1.16 0.49 -0.88 -0.44 0.37 0.28 0.20 0.22

Lake Charles, LA -0.60 -0.54 -1.00 -1.11 0.32 0.18 0.12 0.11

Los Angeles, CA -0.66 -0.66 -0.97 -0.64 0.15 0.08 0.06 0.09

Louisville, KY 0.88 0.09 -0.87 -0.24 0.36 0.27 0.19 0.24

Memphis, TN 0.51 0.03 -0.80 -0.57 0.36 0.22 0.16 0.17

Miami, FL 0.71 -0.10 -0.92 -2.13 0.31 0.22 0.16 0.11

Nashville, TN 1.10 0.46 -0.56 -1.57 0.48 0.33 0.24 0.18

New York, NY -0.37 -0.53 -0.99 -0.79 0.17 0.09 0.07 0.08

Philadelphia, PA 0.07 -0.20 -1.00 -0.24 0.28 0.19 0.13 0.18

Phoenix, AZ 0.04 -0.27 -1.51 -0.27 0.27 0.20 0.14 0.20

Portland, OR 0.68 -0.17 -1.01 -0.92 0.32 0.23 0.17 0.18

Richmond, VA 0.22 0.09 -1.05 -0.14 0.29 0.21 0.15 0.20

Sacramento, CA 0.13 -0.28 -1.22 -0.54 0.33 0.22 0.16 0.20

St Louis, MO -0.23 -0.43 -1.33 -0.28 0.22 0.15 0.11 0.17

Salt Lake City, UT 0.75 0.08 -1.18 -1.03 0.30 0.24 0.17 0.18

San Antonio, TX 0.44 -0.25 -0.99 0.01 0.27 0.20 0.15 0.22

San Diego, CA -0.84 -0.96 -1.41 -1.00 0.15 0.10 0.07 0.10

San Francisco, CA -0.64 -0.80 -1.16 -0.54 0.12 0.07 0.05 0.09

Tampa, FL -0.11 -0.54 -1.13 -0.33 0.27 0.17 0.12 0.20

Tulsa, OK 0.58 0.11 -0.86 0.03 0.28 0.22 0.15 0.21

Washington, DC 0.33 0.07 -0.71 -0.15 0.30 0.21 0.16 0.19
10

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

1 2 3 4 5 6 7 8 9 10 11 12 13

Reactive Organic Gas / NOx Ratio (Mole C / Mole N)

Incre

m

ental R

e

activity (gm

O3 / gm

V

O

C)

Averaged Conditions City Specific

Ethane Ethane

AMP AMP

MIR Scenario

Ozone Inhibiting

Ozone Enhancing

Figure 1. Plots of incremental reactivities of AMP and ethane against the reactive organic gas /

NOx ratio for the averaged conditions and city-specific scenarios. The scenarios used to

derive the MIR values are circled.

and the amounts that made it into the gas phase, as opposed to being lost on surfaces or injection lines,

had to be adjusted from run to run to obtain satisfactory fits to the results of the individual experiment.

The adjustment factors (gas phase concentration that fit the data / calculated amount injected if all the

injected liquid made it to the chamber in the gas phase) varied from ~5% to ~50% for the AMP

experiments, with no apparent dependence on the type of experiment conducted (Carter, 2008).

Therefore, although the data can test whether the model correctly predicts ozone or radical inhibition or

effects, they must be considered to be qualitative at best.

Uncertainties in Appropriate Reactivity Quantification Method. The effect of VOCs on ozone

formation varies widely depending on the environment where the VOC is emitted, and quantifications of

ozone impacts require some method to derive a single reactivity measure from the multiple impacts. The

MIR scale has been considered to be an appropriate basis for a regulatory reactivity scale because it

reflects conditions where ozone formation is most sensitive to changes in VOC emissions (Carter, 1994;

CARB, 1993). However, MIR scales reflect only highly urban areas and are only a small fraction of total

of areas throughout the U.S. where ozone standards are exceeded. As discussed elsewhere (see Hales,

2007 and references therein), other methods can be used to derive single scales from varying ozone

impacts, including those that weigh impacts on all regions, or that weigh impacts on all regions but weigh

regions where VOCs have the greatest effects more heavily, or weighing impacts by population exposed.

Considering the impacts for all conditions may be more appropriate than just looking at MIR when

making comprehensive ozone impact assessments.
11

This is a particularly important issue in the case of AMP because of the relatively large variability

of its reactivity depending on scenario conditions, as indicated on Figure 1. It is calculated to have

positive ozone impacts in at least some scenarios under MIR conditions, but generally negative impacts

under the lower NOx conditions that represent most of the regional environment. If a quantification other

than MIR is used, then AMP may well be judged to be an inhibitor, while if MIR or a similar scale is used

its reactivity relative to ethane may be quite sensitive the set of scenarios used. In this case, uncertainties

in scenario conditions, discussed below, become important.

Uncertainties in Scenario Conditions. Regardless of how the reactivity scale is derived, some

model must be used to represent ambient conditions when calculating VOC reactivity scales. The MIR

and other reactivity scales derived by Carter (1994, 2000, 2002, 2010a,b) are based on 39 single-day cityspecific box model scenarios originally developed by Baugues (1990) to represent various ozone nonattainment areas throughout the United States. Although the chemical mechanisms have been updated a

number of times since the MIR and other Carter reactivity scales were first developed (Carter, 1994), the

scenarios have never been updated, despite the fact that they are not well documented and clearly out of

date. In some cases, AMP here, propylene carbonate (Carter 1996, 2010b, 2012) and carbon disulfide

(Carter and Malkina, 2007, Carter, 2010b, 2012) the MIR value obtained for some of the 39 scenarios

exceeds that of the ethane standard while on average the MIR value is less than or the same as that of the

standard. This variability over the different scenarios creates the possibility that a change in the scenarios

would result in a change of the relative ratio of the MIR of the VOC to the standard. Updating the

scenarios has been given relatively low priority compared to mechanism updates until recently, but a

project to update the scenarios for ozone reactivity assessment is now part of the CARB's 2012-13 annual

research plan (CARB, 2012). There is a scientific consensus that at some point in the future the box

models will be replaced by 3-D models that are considered to be superior for representing ambient

conditions, though use of such models is still not practical for deriving reactivities for the large numbers

of compounds in present scales. Limited studies with selected compounds have shown that for most

compounds the relative reactivities calculated using 3-D models are not greatly different than those in the

MIR scale if consistent methodologies and mechanisms are used. However, this may not be the case for

compounds where the ozone impacts are as sensitive to airshed conditions as appears to the case for

AMP.

Availability Uncertainty. In order for a compound to promote ozone formation, it must be emitted

into the atmosphere in the gas phase, and it must remain there long enough to undergo the gas-phase

reactions that affect ozone. If the compound is deposited onto surfaces or the aqueous phase or is

consumed by condensed phase reactions and is not re-emitted back to the gas-phase, then it will not react

to form ozone and the magnitude of its ozone impact will be less than calculated in current reactivity

scales. As discussed above, the evaluation against chamber data indicated that the amounts of AMP and

other amines that reacted in the gas phase in the chamber experiments was consistently less than the

amount of material injected, with the ratio of apparently reacted amine to injected amine varying

considerably from experiment to experiment. This is despite the fact that every attempt is made to

minimize surface losses of injected materials, such as heading injection lines, using long flushing times,

etc. Such surface losses are expected to be even more variable in ambient environments, where the

surfaces are more varied and no attempts are made to minimize surface losses. How much AMP is

available will depend on the environment and exactly how the AMP is emitted, and is difficult to predict.

There is in addition the possibility of salt formation by reaction with HNO3, or partitioning into aqueous

atmospheric aerosols, which will further reduce the availability of the amine for ozone formation to an

unknown extent that is highly dependent on the environment. Therefore, since some fraction of the

emitted AMP might not participate in ozone formation, the magnitudes of the reactivity estimates shown

on Table 2 and Figure 1, whether positive or negative, must be considered to be upper limits.
12

Conclusions

The atmospheric ozone reactivity of AMP is calculated to be highly dependent on ambient

conditions, being negative (inhibiting ozone) under relatively low NOx, high ROG/NOx conditions and

positive (promoting ozone) under the higher NOx, lower ROG/NOx conditions used to derive maximum

incremental reactivity (MIR) scale. The reactivity of AMP in the MIR scale is also quite dependent on

scenario conditions, ranging from -0.8 to +1.5 grams O3 / gram AMP depending on which of the 39 cityspecific MIR scenarios are used, with an average of 0.25  0.57. By comparison, the reactivity of ethane

in the MIR scale ranges from 0.12 to 0.48 grams O3 / gram ethane, with an average of 0.28  0.07.

Therefore, the average MIR for AMP is somewhat less than that for ethane, though the difference is well

within the scatter of the data. The average MIR for AMP may well be higher than that for ethane had a

different set of scenarios been used, though it might be significantly lower had a reactivity quantification

method that gives more weight to lower NOx scenarios been used.

The reactivity estimates for AMP have changed quite significantly over the years because of the

uncertainties in its atmospheric chemical mechanism. Uncertainties in the mechanism still remain, in part

because of experimental difficulties in working with and analyzing this compound in the gas phase,

though its ozone inhibiting characteristics under low NOx conditions has been verified by the available

chamber experiments. Because of this, chemical mechanism uncertainty is probably not as important in

uncertainty in the reactivity quantification of AMP as the uncertainty due to variability of its reactivity

with scenario conditions, or the uncertainty due to availability issues. The ozone impacts calculated in this

work were based on assuming 100% availability for reaction in the gas phase, but this was not observed

in the environmental chamber experiments with AMP, so it is not likely to be the case in real

atmospheres. For this reason, the magnitudes of the ozone impacts of AMP, whether negative or positive,

are likely to be lower than shown in this work.

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