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 (NO x) enhances ozone, which is near source areas. The reactivity of AMP in the maximum incremental reactivity (MIR) scale, 0.25 gm O 3 / gm, is calculated to be slightly less than that of ethane, 0.28 gm O 3 / 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 NO 3 Radicals .............................................................................................................. 4 Reaction with Ozone ......................................................................................................................... 4 Reactions with HNO 3 ........................................................................................................................ 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............................................................................................................................................. 122

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 NO x 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, O 3 , NO 3 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 HNO 3 , 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):

CH 3 C(CH 3 )(NH 2)CH 2 OH + OH  H 2O + CH 3 C(CH 3 )(CH 2 OH)NH· (1) CH 3 C(CH 3 )(NH 2 )CH 2 OH + OH  H 2O + CH 3 C(CH 3 )(NH 2)CH(·)OH (2) CH 3 C(CH 3 )(NH 2)CH 2 OH + OH  H 2O + CH 3 C(CH 2 ·)(NH 2 )CH 2 OH (3) CH 3 C(CH 3 )(NH 2)CH 2 OH + OH  H 2 O + CH 3 C(CH 3 )(CH 2 O·)NH 2 (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 O 2 , forming HO 2 and the corresponding C=N compound, e.g.,
RCH 2NH· + O 2  HO 2 + RCH=NH (5) This is based on kinetic data obtained by Lindley et al (1979) for reactions of (CH 3 ) 2N· with O 2 , NO, and NO 2 , where the reaction with O 2 , forming HO 2 + CH 3 -N=CH 2 , is calculated to dominate under atmospheric conditions. This is a radical propagating reaction that promotes the formation of ozone.3

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, NO 2 , or HO 2 , e.g.,

CH 3 C(CH 3 )(CH 2OH)NH· + NO  CH 3 C(CH 3 )(CH 2OH)NHNO (6) CH 3 C(CH 3 )(CH 2 OH)NH· + NO 2  CH 3 C(CH 3 )(CH 2OH)NHNO 2 (7) CH 3 C(CH 3 )(CH 2 OH)NH· + HO 2  CH 3 C(CH 3 )(CH 2 OH)NH 2 + O 2 (8)
If NO x is present, which is required for O 3 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 NO x , 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 CH 2 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 O 2 forming HO 2 and the corresponding carbonyl compound, i.e.,

CH 3 C(CH 3 )(NH 2)CH(·)OH + O 2  CH 3 C(CH 3 )(CHO)NH 2 + HO 2 · (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):
CH 3 C(CH 2 ·)(NH 2)CH 2 OH + O 2  CH 3 C(CH 2 OO·)(NH 2)CH 2 OH (10)

CH 3 C(CH 2OO·)(NH 2)CH 2OH + NO  NO 2 + CH 3 C(CH 2 O·)(NH 2)CH 2 OH (11) CH 3 C(CH 2 OO·)(NH 2)CH 2OH + NO  CH 3 C(NH 2)(CH 2 OH)CH 2ONO 2 (12) CH 3 C(CH 2O·)(NH 2)CH 2OH + O 2  CH 3 C(CHO)(NH 2)CH 2 OH + HO 2 · (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 HO 2 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 NO 2 and CH 3 C(CH 3 )(CH 2OH)- NHNO 2 formation as discussed below, HO2 + RCHO + XN is used to represent formation of HO 2 and CH 3 C(CH 3 )(CHO)NH 2 , RO2C + xHO2 + xRCHO + XN is used to represent formation of HO 2 and CH 3 C(CHO)(NH 2)CH 2 OH following an NO to NO 2 conversion, and RO2XC + zRNO3 + XN is used to4

represent formation of CH 3 C(NH 2 )(CH 2 OH)CH 2 ONO 2 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 NO 2 to form relatively unreactive nitrogen-containing species such as nitrosamines. Its mechanism is as follows:
NRAD + NO 2  PROD2 + 2 XN (15) NRAD + HO 2  XN (16) Here, PROD2 + 2 XN is used to represent the nitramine CH 3 C(CH 3 )(CH 2 OH)NHNO 2 , 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 HO 2 is added to the mechanism to provide a sink for the radical intermediate in the absence of NO x , but this reaction is not important under conditions where O 3 formation is occurring.
Reaction with NO 3 Radicals The only kinetic data concerning the reactions of NO 3 radicals with amines is for N-methyl-2- pyrrolidinone (NMP), where a relatively high rate constant of 1.26 x 10 -13 cm 3 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 HNO 3 . 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 - CH 2 (N) or CH 3 (N) groups. The group rate constants for reactions at other amine groups, including NH and NH 2 , are estimated assuming that the ratios of rate constants for reactions at the various groups are the same for the NO 3 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 NO 3 radials with AMP is 5.9 x 10 -14 cm3 molec -1 s -1 , and that the mechanism is

CH 3 C(CH 3 )(NH 2)CH 2 OH + NO 3  CH 3 C(CH 3 )(CH 2 OH)NH· + HNO 3 (17)
where the CH 3 C(CH 3 )(CH 2 OH)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 O 3 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 O 3 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 O 3 is negligible under atmospheric conditions. Although this is uncertain, it is unlikely that the reaction with O 3 would be an important fate of AMP compared to reactions with OH radicals.
Reactions with HNO 3 Amines are basic compounds that can react in the gas phase to form nitrate salts, which will make them unavailable for participation in O 3 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 amine5

nitrate salt, levels of HNO 3 , 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 HNO 3 is negligible. The reaction with HNO 3 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 theneglect 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 - NO x 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 - NO x 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, O 3 formation, and OH radical levels under all the experimental conditions employed. This indicates that AMP has both radical and NO x 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 O 3 formation in experiments with relatively high NO x/VOC ratios and have relatively little effects on OH radical levels, though it tended to somewhat decrease final O 3 yields in experiments with low NO x/VOC ratios. This indicates that ethanolamine does not have significant radical sinks in its mechanism and that its NO x 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 NO x 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 NO x 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 occur6

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 NO x , since NO x is required for O 3 to be formed. VOCs have zero impact on O 3 in the absence of NO x , and have the highest impacts on O 3 when NO x is abundant. Carter (1994) developed various reactivity scales to represent various conditions of NO x 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 NO x conditions where O 3 is most sensitive to changes in VOC emissions, the maximum ozone incremental reactivity (MOIR) scale representing lower NO x conditions that are optimum for maximum O 3 formation, and the equal benefit incremental reactivity (EBIR) scale representing even lower NO x conditions where controlling NO x and controlling VOCs have equal relative effects on reducing ozone. Reactivities can be calculated for even lower NO x conditions than EBIR, but they are of less interest because O 3 is more sensitive to NO x 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 O 3 formation, and use of MIR for VOC regulations complements the use of NO x control to reduce O 3 under the lower NO x 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 NO x 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 NO x 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 NO x sinks and forming reactive products. In addition "upper limit" MIR (ULMIR) values were derived using the procedures deve l op e d b y C arter (2 0 0 0 ) , and t he ULMIR value f

or AMP , ≤ 1 5

. 0 8 gm O 3/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 NO 2 in the reaction forming the nitramine product. This error was subsequently7

Table 1. Summary of past and current MIR estimates and upper limit values for 2-amino-2-

methyl-1-propanol.

Date MIR (gm O 3

/ 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 NO 2 associated with the formation of the nitramine not being represented. Although this NO x loss process results in lower (more negative) reactivities under low NO x conditions (e.g., EBIR), it causes higher reactivities under MIR conditions because O 3 is suppressed by NO x 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 NO 2 involved with nitramine formation. The associated MOIR and EBIR values are -0.19 and -1.03, respectively.8

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 NO 2 loss process resulted in significantly lower (more negative) reactivities under low NO x conditions such as those used for the EBIR scale (the EBIR value changed from -0.3 to -1.03 gm O 3 /gm AMP), but resulted in significantly higher reactivities in the MIR scale, causing the MIR to go from -2.7 to +0.25 gm O 3 /gm AMP. This is because O 3 is strongly inhibited by NO x under MIR conditions, so reducing NO x will increase O 3 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) / NO x 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/NO x ratio on Figure 1. It can be seen that the ozone impact of AMP for the scenarios depends significantly on the ROG/NO x ratio, being positive (ozone forming) and becoming greater than that of ethane at the high NO x , low ROG/NO x ratios, and becoming significantly negative (ozone inhibiting) as the ROG/NO x ratio increases (NO x becomes lower). The incremental reactivity for ethane also depends on the ROG/NO x 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/NO x 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/NO x 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 NO x 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-phasereactions 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,9

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 O 3/gm VOC) Ethane Reactivity (gm O 3/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

- 0.1 0

- 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 0.1 1 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

- 1.0 3 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 0.1 2 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 0.1910 -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)IncrementalReactivity(gmO3/gmVOC) 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 /

NO x 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 NO x 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 MIRand 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 HNO 3 , 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 NO x , high ROG/NO x conditions and positive (promoting ozone) under the higher NO x , lower ROG/NO x 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 O 3 / 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 O 3 / 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 NO x 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 NO x 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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