The rate constant is estimated from rate constants for 2,4-hexene-1,6-dial x isoprene / 1,3-butadiene. The rate constant used for 2,4-hexene-1,6-dial is 1.00e-17 cm[3] molec-1 s-1, based on the upper limit rate constant of Klotz et al (1995). Equal probability is assumed for reactions at the various positions, as shown above.

6-oxo 2,4-heptadienal

OH
Rate Constant = 7.51e-11 cm[3] molec-1 s-1

CH3C(O)CH=CH-CH=CHCHO + OH  H2O + CH3C(O)CH=CH-CH=CHC(O)·
                                      20%

CH3C(O)CH=CH-CH=CHCHO + OH  CH3C(O)CH=CH-CH(·)CH(CHO)OH
                                      40%

CH3C(O)CH=CH-CH=CHCHO + OH  CH3C(O)CH(OH)CH(·)CH=CHCHO
                                      40%

The rate constant and branching ratios estimated from estimated rate constants for reactions at various positions. Rate constant for abstraction from CHO assumed to be same as for analogous reaction of acrolein. Rate constant for addition to double bond assumed to be the same as the analogous reaction of 1,4-hexadiene-1,6-dial, derived as indicated above for 3-methyl-2-4-hexene-1,6-dial. The addition reactions shown are assumed to be the major processes, and equal probability for each is assumed.

O3
Rate Constant = 1.00e-17 cm[3] molec-1 s-1

CH3C(O)CH=CH-CH=CHCHO + O3  CH3C(O)CHO + HCOCH=CHCHOO[excited]
                                      25%

CH3C(O)CH=CH-CH=CHCHO + O3  HCOCH=CHCHO + CH3C(O)CHOO[excited]
                                      25%

CH3C(O)CH=CH-CH=CHCHO + O3  HCOCHO + CH3C(O)CH=CHCHOO[excited]
                                      25%

CH3C(O)CH=CH-CH=CHCHO + O3  CH3C(O)CH=CHCHO + HCOCHOO[excited]
                                      25%

The rate constant is assumed to be the same as that assigned for 3,4-hexene-1,6-dial, based on the upper limit data of Klotz et al (1995). Equal probability of reaction at the various positions is assumed.

3,5-octadien-2,7-dione

OH
Rate Constant = 6.02e-11 cm[3] molec-1 s-1

CH3C(O)CH=CH-CH=CHC(O)CH3 + OH  CH3C(O)CH=CH-CH(·)CH(OH)C(O)CH3
                                     100%

The rate constant for addition to the double bond is assumed to be the same as that derived for 2,4-hexadiene-1,6-dial, as indicated above for 3-methyl-2,4-hexene-1,6-dial. The reaction shown is assumed to be the major process.

O3
Rate Constant = 1.00e-17 cm[3] molec-1 s-1

CH3C(O)CH=CH-CH=CHC(O)CH3 + O3  CH3C(O)CHO + CH3C(O)CH=CHCHOO[excited]
                                      50%

CH3C(O)CH=CH-CH=CHC(O)CH3 + O3  CH3C(O)CH=CHCHO + CH3C(O)CHOO[excited]
                                      50%

The rate constant is assumed to be the same as that assigned for 3,4-hexene-1,6-dial, based on the upper limit data of Klotz et al (1995). Equal probability of reaction at the various positions is assumed.

Figure 4.	Action spectra for photodecompositions of 2-buene-1,4-dial, 4-oxo-2-penteneal and used for the model species AFG1 and AFG2.

Aromatic Ring Retaining Products
In addition to ring fragmentation, aromatics also react to form products where the aromatic ring is retained, such as phenols, cresols, aromatic aldehydes, and nitrophenols. Mechanisms for these species are included in the base mechanism, and are given in Table A-2 in Appendix A. The general methods used to represent these products are the same as employed in SAPRC-99, though rate constants and some mechanisms were updated. The various types of products that are represented, and changes relative to SAPRC-99, are summarized briefly below. Footnotes to Table A-2 document these reactions in more detail.
Phenols and Cresols. Although SAPRC-99 had a separate model species for phenol, in this mechanism the phenol and cresol model species are lumped together because representing phenol was found not to have a significant affect on model predictions for benzene, the only compound that forms phenol as a primary product in its reactions. The major atmospheric reactions of these compounds are with OH and NO3 radicals, with the latter generally being the more important sink under most conditions. Because very little was known about the mechanisms of these reactions at the time SAPRC-99 was developed, SAPRC-99 had very simplified and parameterized representations of these mechanisms, adjusted to fit results of a single o-cresol - NOx environmental chamber experiment. However, recently
Berndt and Boge (2003) and Olairu et al (2003) determined that the major products of the reactions of OH with these compounds were various dihydroxybenzenes, and Olariu et al (2000) obtained rate constants for these compounds indicating that they were very reactive. However, if it was assumed that these were the major products of the OH + cresol reaction then the mechanism could not simulate the results of the o-cresol - NOx chamber experiment. Because of this it was decided to defer updating the mechanism used for these compounds until more information is available, and the general parameterization used in SAPRC-99 for the reactions of the cresols was retained.  The rate constants were updated and the parameters in the mechanism were re-adjusted to fit the data for the current mechanism.
Nitrophenols. As with SAPRC-99, the nitrophenol model species (NPHE) is used to represent the products formed in the NO3 + cresol reactions. In SAPRC-99 it was assumed that the major reactions of nitrophenols were with OH and NO3 radicals, as was the case with cresols. However, recent data presented by Barnes (2006) and Bejan et al (2006) indicate that photolysis is a major loss process for nitrophenols, with some of the photolysis resulting in the formation of HONO, but most forming unspecified products. Evidence was not given for significant reaction of nitrophenols with NO3 radicals, though the possibility that it may occur at least to some extent cannot necessarily be ruled out. Based on this, the current mechanism includes photolysis as a major sink for nitrophenols, and assumes that its reaction with NO3 radicals is not significant.
Aromatic Aldehydes. Benzaldehyde and similar aromatic aldehydes may be formed when OH abstracts from methyl groups of methylbenzenes, and these continue to be represented using the benzaldehyde (BALD) model species. Its mechanism is the same as used in SAPRC-99, though the rate constants were updated. The mechanism incorporates updated absorption cross sections for its photolysis to unspecified products, but the overall photodecomposition rate was not changed.
Non-Alkylbenzene Aromatics
 The alkylbenzenes are not the only types of aromatics for which mechanisms were derived. Mechanism assignments were also made for styrenes, naphthalenes, tetralin, various halo- and nitro-benzenes, phthalates, and other aromatic-containing compounds. The derivation of the mechanisms for these compounds is summarized on Table 14, the rate constants are given in Table B-2 and Table B-4, and the mechanisms are given in Table B-2 in Appendix B. As indicted on Table B-4, some of these are based on the general procedures derived for the alkylbenzenes as discussed above, while others (e.g., styrenes, naphthalenes, tetralin, and the isocyanates) appear to have quite different mechanisms. In those cases mechanisms are derived based on considerations for the individual compounds (as with the styrenes), or parameterized mechanisms, that were adjusted to fit environmental chamber data, were used.
Other non-alkylbenzene aromatics are represented using the lumped molecule method based on mechanisms for aromatics for which mechanism assignments were made. These are discussed in the "Lumped Molecule Representation" section, below.
Reactions with Chlorine
Alkylbenzenes. The low rate constant for the reaction of chlorine atoms with benzene (1.3 x 10[-16] cm[3] molec-1 s-1, Sokolov et al, 1998), indicates that the only significant reactions of Cl with aromatics are abstractions off the aromatic ring. The rate constants for these reactions have been measured for some of the methylbenzenes (see Table 4) and can be estimated for other alkylbenzenes using the group-additivity parameters given on Table 3. The products formed are expected to be aromatic aldehydes that are represented using the benzaldehyde (BALD) model species if the reaction is on a methyl group, or primarily various aromatic ketones that are represented by the lumped higher ketone model species (PROD2), plus organic nitrates formed in the peroxy + NO reaction or hydroperoxides formed in the peroxy + HO2 reaction. These result from reactions of the same radicals formed when OH radicals react off the aromatic ring, and the mechanisms can be derived in the same way, except for the different branching ratios for the initial reactions at the various positions, where applicable.
Chlorine + alkylbenzene mechanisms were derived in this manner for all the alkylbenzenes that are used to derive parameters for the lumped model species ARO1 and ARO2, as discussed below. The rate constants and mechanisms so derived are given in Table B-7 in Appendix B.
Table 14.	Discussion of mechanisms for the non-alkylbenzene aromatic compounds that for which mechanistic assignments have been derived. The rate constants and additional documentation are given in Table B-4 and the reactions are given in Table B-2 in Appendix B.
Compound	Reacts With (reaction type)
Styrene	OH, O3, NO3, O[3]P (double bond reaction only)
   Mechanism as described by Carter et al (1999b) was used, except for some minor rate constants updates and the overall nitrate yield being increased from 13% to 18% to improve simulations of incremental reactivity data with styrene with the current mechanism. Results of model simulations of the chamber experiments with this compound are summarized on Table 23 in the Mechanism Evaluation Results section.
-Methyl styrene 	OH, O3, NO3, O[3]P (double bond addition only)
   Assumed to react analogously to the mechanism derived for styrene. The nitrate yield in the OH reaction was increased to correspond to the additional carbon.
Monochlorobenzene	OH (100% ring addition)
p-Dichlorobenzene 	OH (100% ring addition)
Hexafluorobenzene	OH (100% ring addition)
Nitrobenzene	OH (100% ring addition)
   The products formed in the reactions of these compounds are represented by those formed from in the reactions of OH with benzene. The appropriate measured rate constants for the compounds were used.
Benzotrifluoride 	OH (100% ring addition)
p-Trifluoromethyl-Cl-benzene 	OH (100% ring addition)
   The reaction is assumed to proceed only by addition of OH to the aromatic ring. The products formed are represented by those formed in the ring-addition reactions of toluene, as shown on Table 11. The nitrate yields in the reactions of the peroxy radicals are also assumed to be the same as used for toluene.
Benzyl Alcohol	OH (70% ring addition)
   The mechanism and environmental chamber data for this compound are discussed by Carter et al (2005a). The measured concentrations of benzaldehyde in the chamber experiments are consistent with a fraction reacted by abstraction from the -CH2OH of 30%, which is assumed in the mechanism. This is formed by O2 reacting with the BzCH(·)OH radical forming benzaldehyde + HO2 without NO to NO2 conversions or nitrate formation.  The products formed following the addition to the aromatic ring are assumed to be the same as used for ethylbenzene, as shown on Table 11. The nitrate yield factor derived for toluene is used for the peroxy reactions involved in the ring addition mechanism. Results of model simulations of the benzyl nitrate experiments are summarized on Table 23 in the Mechanism Evaluation Results section.
Methoxybenzene; Anisole	OH (93% ring addition)
m-Nitrotoluene	OH (60% ring addition)
   The fraction reacting by addition to the aromatic ring is estimated from the difference between the measured total OH rate constant and the rate constant for abstraction off the ring estimated using group-additivity methods as shown on Table 3. The products formed following ring addition are represented by those formed from ring addition to toluene, as shown on Table 11. The products formed from reaction off the ring are represented by the lumped higher oxygenated product PROD2 in the case of methoxybenzene and by the aromatic aldehyde species BALD in the case of m-nitrotoluene. The nitrate yield factor of toluene was assumed.
2-Phenoxyethanol; Ethylene glycol phenyl ether	OH (54% ring addition)
   The total rate constant was estimated by the sum of the estimated rate constants for addition to the aromatic ring and abstraction reactions off the aromatic ring. The latter was estimated using the group-additivity methods shown in Table 3, and the products formed were derived using the estimates and procedures incorporated in the mechanism generation system. The rate constant and products for the ring addition reaction were assumed to be the same as derived for methoxybenzene, as discussed above.
1,2-Diacetyl benzene 	OH (100% ring addition)
   100% ring addition is assumed  -  reaction on the methyl group is assumed to be relatively slow. The products formed are represented by those formed in the mechanism for OH ring addition to o-xylene, except that the nitrate yield factor for a C10 compound, shown on Figure 3,  was used.
Phthalic anhydride	OH (100% ring addition)
   The rate constant was assumed to be the same as the measured rate constant for 1,2-diacetyl benzene. The products formed are also represented by those formed in the mechanism for OH ring addition to o-xylene, except that the nitrate yield factor for a C8 compound, shown on Figure 3, was used.
Diethyl phthalate 	OH (71% ring addition)
Dibutyl phthalate 	OH (47% ring addition)
   The total rate constant was estimated by the sum of the estimated rate constants for addition to the aromatic ring and abstraction reactions off the aromatic ring. The latter was estimated using the group-additivity methods shown in Table 3, and the products formed were derived using the estimates and procedures incorporated in the mechanism generation system. The rate constant and products for the ring addition reaction were assumed to be the same as derived for 1,2-diacetylbenzene, as discussed above, except that the nitrate factors appropriate for the carbon numbers of the particulate compounds, shown on Figure 3, were used.
2-Ethylhexyl benzoate	OH (20% ring addition)
   The rate constant for reaction at the aromatic ring estimated to be the same as the total rate constant for acetophenone (as tabulated by Atkinson, 1989), assuming that ring addition is the major reaction for that compound. The mechanism for reaction at aromatic ring based on that of toluene. The rate constant and mechanism for reaction at groups off the aromatic ring based on those estimated for 2-ethyl hexyl acetate, since reaction at the acetate group is estimated to be negligible for that compound.
Naphthalene 	OH (parameterized)
Tetralin 	OH (parameterized)
2,3-Dimethyl naphthalene 	OH (parameterized)
   The details of the mechanisms for these compounds are still too uncertain to attempt to derive more explicit predictive mechanisms. The highly parameterized representations employed in SAPRC-99 (Carter, 2000a) are retained, though the values of the parameters were re-adjusted to fit the chamber data with the current mechanism. As discussed by Calvert (2002), the mechanisms for the reactions of these compounds are expected to be affected by total NO2 levels, since competitions apparently exist between reactions with O2 and NO2 for some of the intermediate radicals. In order to avoid introducing new model species into the mechanism to represent speculative and uncertain processes, this NOx dependence is in effect represented in SAPRC-99 and SAPRC-07 by using formation of lumped peroxyacetyl radicals (RCO3) in the parameterized mechanism.  Results of adjusted model simulations of the chamber data with these compounds are summarized on Table 23 in the Mechanism Evaluation Results section.
Methyl naphthalenes 	OH (parameterized)
   Estimated mechanism derived by averaging the parameters for naphthalene and 2,3-dimethylnaphthalene, as was the procedure used when deriving the mechanism for this compound for SAPRC-99.
Furan
2-Methyl furan
3-Methyl furan
2,5-Dimethyl furan
   As discussed in the Introduction, chamber experiments were carried out for several furans as part of this project because their initial reactions are expected to form unsaturated 1,4-dicarbonyls in high yield, which as discussed above are believed to be important photoreactive products formed in the oxidations of the aromatic hydrocarbons. The expected mechanism is as follows, using furan as the example:

   Model simulations of experiments with these compounds could therefore serve as a means to evaluate mechanisms for the individual unsaturated 1,4-dicarbonyls without the uncertainties involved with handling these highly reactive compounds directly. However, there was insufficient time and resources available to this project to complete the development of explicit mechanisms for aromatics and their ring-opening products, so the evaluation of mechanisms using experiments with these compounds will be completed in future projects. For this version of the mechanism, the unsaturated 1,4-dicarbonyls expected to be formed from these furans were represented using the same approach as used for the aromatic hydrocarbons, i.e., by the AFG1 and AFG2 model species with their relative yields adjusted to fit the chamber data. Results of adjusted model simulations of the chamber data with this compound are summarized on Table 23 in the Mechanism Evaluation Results section.
2,4-Toluene Di-isocyanate (TDI)	OH (parameterized)
   The details of the mechanism of this compound, which was found by Carter et al (1997d) to be a strong radical inhibitor, are unknown. The parameterized mechanism used by Carter et al (1997d) to fit the chamber data, which is retained in SAPRC-99, is still retained for SAPRC-07, though the parameters were re-adjusted to fit the data with the current base mechanism. Results of adjusted model simulations of the chamber data with this compound are summarized on Table 23 in the Mechanism Evaluation Results section.
Para Toluene Isocyanate (PTI)	OH (parameterized)
   This was experimentally studied by Carter et al (1999a) as a model compound from which to derive an estimated mechanism for MDI, which has too low a volatility to be studied experimentally. Like TDI, the mechanism for this compound is unknown and Carter et al (1999a) derived a highly parameterized mechanism to fit the chamber data. This was used in SAPRC-99 and is retained in SAPRC-07, but with the parameters re-adjusted to fit the data for the current mechanism. Results of adjusted model simulations of the chamber data with this compound are summarized on Table 23 in the Mechanism Evaluation Results section.
Methylene Diphenylene Diisocyanate (MDI)	OH (parameterized)
   The mechanism for this compound was derived from the PTI mechanism as discussed by Carter et al (1999a). Based on structural considerations, the rate constant is assumed to be twice that for PTI, but the same set of products is assumed to be formed.

Aromatic Products. Reactions of chlorine atoms with the -dicarbonyls and the aromatic ring-retaining products are included in the base chlorine mechanism, as shown in Table A-5 in Appendix A. Footnotes to that table document the sources of the rate constants and mechanisms that were used. Although the unsaturated dicarbonyls represented by AFG1-3 undoubtedly react relatively rapidly with chlorine atoms, these reactions are ignored in the base chlorine mechanisms. This is because it is expected that the other reactions would be more important sinks for these products under most atmospheric conditions, and their high reactivity would result in low concentrations that would make them unimportant as sinks for chlorine atoms. This is probably true for the -dicarbonyls as well, though their chlorine reactions are included.
Mechanisms for Amines
Amines react relatively rapidly with OH radicals, and are also expected to relatively rapidly with NO3, based on a relatively high rate constant for reaction of NO3 with 1-methyl-2-pyrrolidinone (Aschmann and Atkinson, 1999). Rate constant data of Tuazon et al (1994) suggests that the reaction with O3 may also be non-negligible for some amines. Mechanisms for all three of these types of reactions were derived, as discussed by Carter (2008a) and summarized below.
In the case of the OH and NO3 reactions, the reaction is assumed to proceed by H-atom abstraction from the amino group or from the group next to the amino group, forming HNO3 and the corresponding carbon- or nitrogen-centered radicals. Group-additivity parameters that can be used to estimate rates of these reactions are given in Table 3, above, and footnotes to that table indicate how these parameters were derived. Table 3c indicates that the group-additivity methods can estimate the rate constants to within 26% on the average.
The subsequent reactions of the carbon-centered radicals formed in these reactions can be derived using the mechanism generation system as employed for other compounds, except that estimates need to be made for reactions of -amino alkoxy radicals, e.g., RCH[O·]-NHR'. Although this is uncertain, to simplify the mechanism generation we assume that decompositions forming N-centered radicals, e.g., RCH[O·]-NHR'  RCHO + R'NH·, and estimate the relative rates of reactions for the competing routes based on estimates for other radicals considered to be similar. The applicable radicals and reactions assumed to dominate when generating mechanisms for amines in the current version of the mechanism are indicated on Table 15 These assumptions are uncertain, though alternative assumptions probably do not yield mechanisms with significantly different reactivities.
The subsequent reactions of the nitrogen-centered radicals formed after H-abstraction from NH2 or NH groups depends 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
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.
The subsequent reactions of the C=N products formed in this reaction are unknown and therefore this is an additional source of uncertainty in the mechanism. These are expected to be reasonably reactive compounds. For the current mechanism, they are represented by the generic reactive non-aldehyde oxygenated species PROD2. The appropriateness of this representation is highly uncertain.

Table 15.	Assignments made for alkoxy radical intermediates predicted to be formed in the photooxidation mechanisms of the amines.
Radical
Reaction Assumed to Dominate
·OCH2-NH2 + O2
HCO-NH2 + HO2·
CH3-NH-CH2O· + O2
CH3-NH-CHO + HO2·
.OCH2CH2-NH2
HCHO + .CH2-NH2
CH3CH(O·)NH2 + O2
CH3C(O)NH2 + HO2·
CH3-N(CH3)CH2O· + O2
CH3-N(CH3)CHO + HO2·
NH2CH(O·)CH2OH
HCO-NH2 + .CH2OH
CH3C(O·)(CH3)NH2
CH3C(O)NH2 + CH3·
CH3C(CH3)(CH2O·)NH2
HCHO + CH3C(·)(CH3)NH2
CH3-N(CH2O·)CH2CH2OH
CH3-N(CH2OH)CH2CH(·)OH
CH3C(CH2O·)(NH2)CH2OH + O2
CH3C(CHO)(NH2)CH2OH + HO2·
.OCH2CH2CH(NH2)CH2OH
NH2CH(CH2CH2OH)CH(·)OH
CH3-N(CH3)CH(O·)CH2OH
CH3-N(CH3)CHO + .CH2OH
CH3CH(O·)CH(NH2)CH2OH
CH3CHO + NH2CH(·)CH2OH
CH3CH2C(O·)(NH2)CH2OH
CH3CH2C(O)NH2 + .CH2OH
HOCH2CH2-NH-CH(O·)CH2OH
HCO-NH-CH2CH2OH + .CH2OH
CH3CH2-N(CH2CH3)CH2CH2O·
CH3CH2-N(CH2CH2OH)CH(·)CH3
CH3CH2-N(CH2CH3)CH(O·)CH3
CH3CH2-N(CH2CH2·)CH(CH3)OH
CH3CH2-N(CH2CH2O·)CH(CH3)OH
CH3CH(·)N(CH2CH2OH)CH(CH3)OH
CH3CH2-N(CH2CH2OH)CH(O·)CH3
CH3CH2-N(CH2CH(·)OH)CH(CH3)OH
CH3CH(O·)N(CH2CH2OH)CH(CH3)OH
CH3CH(OH)N(CH2CH(·)OH)CH(CH3)OH
HOCH2CH2-N(CH2CH2OH)CH(O·)CH2OH
HCO-N(CH2CH2OH)CH2CH2OH + .CH2OH
CH3CH(OH)CH2-N(CH2CH(CH3)OH)CH2-CH(CH2O·)OH
HCHO + CH3CH(OH)CH2-N(CH2CH(·)OH)CH2CH-(CH3)OH
CH3CH(OH)CH2-N(CH2CH(CH3)OH)-CH(O·)CH(CH3)OH
CH3CH(OH)CH2-N(CHO)CH2CH(CH3)OH + CH3CH(·)OH

The above type of reaction cannot occur if the nitrogen-centered radical lacks an abstractable hydrogen in the -position, as is the case in radicals predicted to be formed in the reactions of t-butyl amine and 2-Amino-2-Methyl-1-Propanol (AMP). In this case, the only expected reactions of the nitrogen-centered radical is reaction with NO, NO2, or HO2, e.g.,
	(CH3)3CNH· + NO  (CH3)3CNHNO	(a)
	(CH3)3CNH· + NO2  (CH3)3CNHNO2	(b)
	(CH3)3CNH· + HO2  O2 + (CH3)3CNH2	(c)
If NOx is present, the major reaction is expected to be process (b), forming the nitramine, since the nitrosamine formed in process (a) is expected to undergo rapid photolysis back to NO and the radical, resulting in no net reaction. Since this is a radical inhibiting process, this mechanism predicts that t-butyl amine and AMP would be radical inhibitors, since reaction forming the N-centered radical is estimated to be the major initial reaction. This is consistent with the fact that these compounds are indeed found to be strong ozone and radical inhibitors in environmental chamber experiments (Carter, 2008a)
For implementation in the mechanism, the model species "NRAD" is used to represent the reactions of the N-centered radicals that lack abstractable hydrogens in the  position. This species is representing as reacting with NO2 to form a nitramine, with a rate constant estimated by assuming that it is the same as for the reaction of NO2 with the generic higher acyl peroxy radical species RCO3. The nitramine is approximately represented by PROD2 in the current mechanism, though the appropriateness of this representation is also highly uncertain. The reaction with NO, forming the nitrosoamine, is neglected because of the expected rapid photolysis of the nitrosoamine to reverse the reaction. In the absence of NOx, the NRAD is represented as reacting with HO2 to re-form the amine, with a rate constant assumed to be the same as used for the reaction of RCO3 with HO2. Because of the way the mechanism is implemented it is not practical to represent the amine formed in the reaction as the amine itself, so its subsequent reactions are therefore neglected. This is because the two amines represented to form NRAD are inhibitors, so representing them with reactive product model species such as PROD2 is inappropriate.
Methods for estimating rate constants and mechanisms for the reactions of O3 with amines were also derived. These are discussed in detail by Carter (2008a) and briefly summarized here. Based on the available rate constants of Tuazon et al (1994) and limited information concerning the products given by Tuazon et al (1994) and Murphy et al (2007), Carter (2008a) estimates that the initial reaction of O3 with amines is at the group next to the amino group, ultimately resulting in abstraction from  C-H bonds, forming OH radicals and the same types of radicals as formed in the OH reaction, e.g.,
	CH3NH2 + O3  [adduct?]  O2 + OH + ·CH2NH2
The available kinetic data for the methylamines and DMAE are fit by
	K(group,O3) = 10-42.97 - {5.84 k(group,OH)},
where k(group) refers to net H-atom abstraction at a group adjacent to the amino group and the rate constants are in cm[3] molec-1 s-1. This gives estimates for rate constants that agree with those of Tuazon et al (1994) to within a factor of two. This was also used as the basis for estimating relative rates of reaction at different positions secondary or tertiary amines that have non-equivalent substituents. The subsequent reactions of the radicals formed are derived as discussed above for the OH and NO3 mechanisms.
A significant uncertainty in terms of calculations of the atmospheric ozone impacts of the amines concerns the extent to which they react with gas-phase HNO3, forming the amine salt. If this reaction is sufficiently fast, and if most of the salt formed partitions to the vapor phase, then the amine would not be available to react in the gas phase and promote ozone formation. Although model simulations of the available environmental chamber experiments with amines are not sensitive to this reaction because the amount of HNO3 formed in the experiments is small compared to the amount of amine added, the atmospheric incremental reactivity simulations are very sensitive to this because of the amount of amine added is relatively small compared to the amount of HNO3 predicted to be formed (Carter, 2008a). The importance of this under atmospheric conditions is difficult to estimate because of uncertainties and variabilities concerning sources and sinks for HNO3 in the atmosphere. As discussed by Carter (2008a) in order to obtain upper limit magnitude estimates for the ozone impacts of the amines we assume that removal of the amines by reaction with HNO3 is negligible, but this is likely not to be the case in actual atmospheres.
Miscellaneous Assigned Mechanisms
There are several compounds for which mechanisms have been derived where the procedures discussed above could be employed. In those cases, mechanisms were derived based on considerations of the relevant reactions of the particular compounds, or, if the details of the reactions for the particular compound are sufficiently uncertain, parameterized mechanisms were derived and adjusted to fit available environmental. These compounds are listed in Table 16, along with a brief discussion of how
Table 16.	Discussion of mechanisms for miscellaneous compounds that were not derived using the procedures discussed previously in this report. The rate constants, reactions, and additional documentation are given in Table B-2, and Table B-4 through Table B-6 in Appendix B.
Compound	Reacts With
N-Methyl-2-Pyrrolidone 	OH, NO3
   Mechanism based on that originally developed by Carter et al (1996b), using the kinetic data of Aschmann and Atkinson (1999). The SAPRC-99 mechanism had an incorrect conversion of the original mechanism that did not incorporate all the NO to NO2 conversions in the OH and NO3 reactions, and compensated for this by reducing the overall nitrate yield to fit the chamber data. Once this was corrected, the chamber data are best fit using the nitrate yield originally derived by Carter et al (1996b). Note that the (presumably incorrect) SAPRC-99 mechanism fit some of the chamber data somewhat better than the original and the current updated mechanism, but is not as consistent with our current estimation of the chemistry. Results of model simulations of the chamber experiments with this compound are summarized on Table 23 in the Mechanism Evaluation Results section.
Dimethyl Sulfoxide 	OH, NO3
   Environmental chamber experiments and possible mechanisms for DMSO reactions were discussed by Carter et al (2000d). No mechanism that was entirely consistent with the available data was found, but the best fit "Mechanism C", as adopted for the ambient reactivity calculations given by Carter et al (2000d) is retained for this version of the mechanism. Results of model simulations of the chamber experiments with this compound are summarized on Table 23 in the Mechanism Evaluation Results section.
1,3-Butadiyne 	OH, NO3
   It is assumed that the primary reaction is OH or NO3 adding to terminal position, forming an allylic-stabilized radical. In the case of the OH reaction, the 1,2-unsaturated alpha-hydroxy radical reacts with O2 to form HO2 and 1,2-butadien-4-al, and in the case of the NO3 reaction the analogous compound reacts unimolecularly to form NO2 and the same aldehyde. The aldehyde is represented by RCHO, on the basis that this is probably not as bad an approximation as MACR. It is assumed that the reaction with O3 is slow.
Methyl Bromide	OH
Ethyl Bromide	OH
1,2-Dibromoethane	OH
n-Propyl Bromide	OH
n-Butyl Bromide	OH
   The mechanisms for these compounds are approximated by that of the corresponding chloride, but with the appropriate OH rate constant for the compound. This may somewhat overestimate the reactivity of the compounds, and may underestimate inhibition under low NOx conditions. This can be considered to be useful for upper-limit mechanism estimates, but will need to be refined for "best estimate" reactivity estimates. Results of model simulations of the chamber experiments with n-propyl bromide and n-butyl bromide, summarized on Table 23 in the Mechanism Evaluation Results section, are consistent with this assessment.
Hexamethyldisiloxane	OH
D4 Cyclosiloxane	OH
Hydroxymethyldisiloxane	OH
   Parameterized mechanisms adjusted to fit the incremental reactivity chamber data of Carter et al (1992) that were considered to be suitable for mechanism evaluation are employed. (Several runs had no assigned initial NO2 concentrations or non-standard run conditions, and were not used.) No chemically reasonable mechanism was found that was consistent with the data (Carter et al, 1992), so a highly simplified parameterized mechanism, which assumes an adjustable amount of radical loss and the remainder of the reaction forming HO2 after an NO to NO2 conversion, and assumes no reactive products formed, was used. Results of model simulations of the chamber experiments with these compounds are summarized on Table 23 in the Mechanism Evaluation Results section.
D5 Cyclosiloxane	OH
   Although reactivity chamber experiments were conducted for this compound (Carter et al, 1992), none of these runs were considered suitable for mechanism evaluation because of uncertainties concerning initial NOx concentrations. Qualitatively the results were similar to those for D4 cyclosiloxane in that large inhibition was assumed. The amount of inhibition used was assumed to be approximately the same as that derived for D4, since a similar mechanism is expected.
Acrylonitrile	OH
   The data of Hashimoto et al (1984) indicate that the products are formaldehyde and HCO-CN after an NO to NO2 conversion. HCO-CN is assumed to be relatively unreactive, which is supported by the concentration-time profiles reported by Hashimoto et al (1984). Reactions with NO3 and O3 are assumed to be relatively slow, though no data are available concerning these reactions.
Methyl nitrite 	OH, h
   The reaction with OH is assumed to proceed by abstraction from the methyl group, followed by decomposition to form NO and formaldehyde. The photolysis absorption cross sections are from Calvert and Pitts (1966). The major reaction pathway is photolysis, which is assumed to form methyl radicals and NO with unit quantum yields.
Chloropicrin	h
Carbon disulfide	OH, h
Methyl isothiocyanate	OH, h
EPTC (S-Ethyl dipropylthiocarbamate)	OH, NO3
Molinate	OH, NO3
Pebulate	OH, NO3
Thiobencarb	OH, NO3
   The mechanisms for these pesticide VOCs as given by Carter and Malkina (2007) are used without modifications other than adaptation to this version of the mechanism. Results of model simulations of the chamber experiments with these compounds are discussed in the Mechanism Evaluation Results section.
trans 1,3,3,3-Tetrafluoropropene 	OH
2,3,3,3-Tetrafluoropropene	OH
   The mechanisms derived for these compounds and evaluated against chamber data by Carter (2009a) and Carter (2009b), respectively, were used.
Ethyl methyl ketone oxime	OH
   An estimated mechanism was derived explicitly for this compound. About 24% of the reaction is assumed to occur at the methyl or CH2 groups, with the subsequent reactions estimated using the procedures in the mechanism generation system. The remainder of the reaction is assumed to be addition of OH to the C=N double bond, which is assumed to form primarily C2H2C(CH3)(OH)N(.)OH, which is assumed to react with O2 to form C2H5C(CH3)(OH)NO + HO2. The rate constant is estimated by the rate constant for OH + isobutene x the average of the ratio of the rate constants for CH2=NOH / Ethene and CH3CH=NOH / Propene, with abstractions from the methyl group subtracted off. The CH2=NOH and CH3CH=NOH rate constants are from the tabulation of Atkinson (1989). The C2H5C(CH3)(OH)NO is assumed to photolyze rapidly, forming NO + an alpha-hydroxy radical that reacts with O2 to form MEK and HO2. The absorption cross-sections and quantum yields are unknown, but photolysis is assumed to be relatively rapid, and estimated to be comparable to that of methyl nitrite.
Methyl iodide	OH, h
   The mechanism for this compound as given by Carter (2007) was used without modification. This mechanism, and the reactions of the inorganic iodine species formed in both the OH and photolysis reactions, are also included in Table B-2, with is available with the electronic version of this report. Results of model simulations of the chamber experiments with these compounds are discussed by Carter (2007) and summarized in the Mechanism Evaluation Results section.

the mechanisms were derived. The initial rate constants are given in Table B-4 and their reactions are given in Table B-2 in Appendix B, along with notes giving references for the rate constants and in some cases the mechanisms. The references cited can be consulted for additional information concerning the derivation of the mechanisms for these compounds.
Lumped Molecule Representations
A number of compounds or classes of compounds do not have explicit mechanistic assignments in the SAPRC-99 or SAPRC-07 mechanisms, but instead are represented by the "lumped molecule" approach for the purpose of estimating their reactivities or contributions to mixtures. In this approach, the impacts of a compound or class of compounds are assumed to be the same, on a per-molecule basis, as a compound or group of compounds for which a mechanism has been derived. This is used for compounds whose reactivities or impacts are of interest, but are either not considered to be sufficiently important to have an explicit mechanism derived, or whose mechanism is considered to be not significantly different from that for the compound representing it, or where the mechanistic difference with the representing compound is considered to be small compared to the uncertainty of the mechanism. It is also used for unspeciated mixtures of isomers, where a representative compound or group of compounds is used to estimate the impact of the mixture.
The SAPRC-07 lumped molecule representations are given in Table B-9 in Appendix B. In most cases the same representations are used in SAPRC-07 as implemented in SAPRC-99 (Carter, 2000a). The exceptions are primarily compounds or groups of compounds for which mechanisms have since been assigned, the representation of the higher alkylbenzenes, and the new detailed model species that have been added. The compounds or mixtures that were previously represented using the lumped molecule approach but now have mechanistic assignments are furan and lumped higher alkylbenzene species as discussed above in conjunction with the aromatics mechanisms. The new lumped aromatic model species is used to give a better lumped molecule representation for the higher aromatics that is more appropriate to their carbon numbers than by representing them using methylbenzenes or ethylbenzene, as was the case previously. In addition, a total of 31 new types of compounds that were not represented in SAPRC-99 are now represented in SAPRC-07 using the lumped molecule approach.
The lumped molecule assignments shown on Table B-9 are used to estimate the atmospheric reactivities of these compounds or mixtures, and are also used where applicable to derive the mechanisms for the lumped mechanisms in airshed models based on mixtures containing them, as discussed in the following section.
Lumped Mechanisms for Airshed Models
Airshed model applications require simulations of highly complex mixtures of large numbers of VOCs, and in most cases it is not necessary or practical to represent each of them separately. For such applications, models with lumped model species that represent reactions of a large number of species with similar reaction rates and mechanisms are generally employed. Even for VOC reactivity assessment it is only really necessary to separately represent the VOC whose reactivity is being assessed, with the reactions of most of the other VOCs present in the ambient simulation being represented using appropriate lumped model species. This is the approach used in the SAPRC-99 mechanism, and is retained for SAPRC-07. The lumping approach and recommended set of lumped model species is also unchanged in this version of the mechanism.
Adjustable Parameter Mechanisms
The SAPRC-99 mechanism has the option to vary the lumping approach in terms of the number of model species used and how they are lumped, and also to vary the mixture of compounds used to derive the parameters for the lumped model species, based on the emissions in model scenario or other considerations (Carter, 2000a,b; Adleman et al, 2005). This is referred to as the "adjustable parameter" mechanism for airshed models. This feature is retained in this version of the mechanism, with the procedures and software for adjustable parameter SAPRC-07 being the same as employed for SAPRC-99, as discussed by Carter (2000a) and Adleman et al (2005). The data files implementing the variable parameter version of SAPRC-07 will be made available at the Speciation Database website and the SAPRC mechanism website. The files will have the same format as those currently used to implement SAPRC-99.
Fixed Parameter Mechanism
In practice most model applications have used the "fixed parameter" version of SAPRC-99. This involves use of a fixed set of lumped model species, with the parameters for the adjustable parameter lumped species being derived using a pre-defined mixture. The updates to the fixed parameter mechanism for SAPRC-07 are documented in the remainder of this section.
The lumped model species and general lumping approach used in fixed parameter SAPRC-99 is the retained in SAPRC-99. The list of lumped and explicit model species used for representing various types of emitted VOCs is given in Table 17, and lumped model species added to the base mechanism for the fixed parameter mechanism are included in Table A-1 in Appendix A. These include the lumped model species that are added to the base mechanism whose parameter can be adjusted based on the emissions mixture being represented, the organic product model species already in the base mechanism that are also used to represent various types of primary emitted organics, and the model species for compounds that are explicitly represented. In all cases the lumped or explicit species represent the emitted compound on a mole-for-mole basis; there is no "reactivity weighting" in this version of the mechanism.

Table 17.	List of model species used in the lumped mechanism for airshed models for representing the various types of emitted VOCs.

   Name
Description
                            Amount in Base ROG [a]
Lumped model species added to the base mechanism. Parameters can optionally be adjusted based on mixture being represented.

ALK1
Alkanes and other non-aromatic compounds that react only with OH, and have kOH (OH radical rate constant at 300[o]K) between 1.36 and 3.41 x 10[-13] cm[3] molec-1 s-1.  (Primarily ethane)
                                     17.7

ALK2
Alkanes and other non-aromatic compounds that react only with OH, and have kOH between 3.41 x 10[-13] and 1.70 x 10[-12] cm[3] molec-1 s-1.  (Primarily propane)
                                     14.8

ALK3
Alkanes and other non-aromatic compounds that react only with OH, and have kOH between 1.70 and 3.41 x 10[-12] cm[3] molec-1 s-1.
                                     27.7

ALK4
Alkanes and other non-aromatic compounds that react only with OH, and have kOH between 3.41 and 6.81 x 10[-1][2] cm[3] molec-1 s-1.
                                     35.5

ALK5
Alkanes and other non-aromatic compounds that react only with OH, and have kOH greater than 6.81 x 10[-12] cm[3] molec-1 s-1.
                                     18.8

ARO1
Aromatics with kOH < 1.36 x 10[-11] cm[3] molec-1 s-1.
                                     12.9

ARO2
Aromatics with kOH > 1.36 x 10[-11] cm[3] molec-1 s-1..
                                     17.2

OLE1
Alkenes (other than ethene) with kOH < 4.77 x 10[-11] cm[3] molec-1 s-1.
                                     11.3

OLE2
Alkenes with kOH > 4.77 x 10[-11] cm[3] molec-1 s-1.
                                     12.5

TERP
Terpenes
                                      0.7
Lumped organic product model species that are already in the base mechanism that are also used to represent certain types of primary emitted VOCs. (Mechanisms are not adjustable)

RCHO
C3+ saturated aldehydes
                                      2.9

MEK
Ketones and other non-aldehyde oxygenated compounds with kOH between 5 x 10[-13] and 5 x 10[-12] cm[3] molec[-2] sec[-1].
                                      1.2

PROD2
Ketones and other non-aldehyde oxygenated compounds with greater than 5 x 10[-12] cm[3] molec[-2] sec[-1].

RCOOH
C3+ organic acids

MGLY
Methyl glyoxal and C3+ -dicarbonyl aldehydes

BACL
Biacetyl and other highly photoreactive compounds that are not otherwise represented.

CRES
Phenols and cresols

BALD
Aromatic aldehydes
                                      0.2

MACR
Acrolein and methacrolein

IPRD
Other unsaturated aldehydes

MVK
Unsaturated ketones

RNO3
Organic nitrates

Model species for explicitly represented product compounds that can also be emitted

HCHO
Formaldehyde
                                      8.3

CCHO
Acetaldehyde
                                      5.0

ACET
Acetone
                                      3.2

MEOH
Methanol

HCOOH
Formic acid

CCOOH
Acetic acid

GLY
Glyoxal

Model species for explicitly represented primary emitted VOCs.

CH4
Methane

ETHENE
Ethene
                                     14.1

ISOPRENE
Isoprene
                                      1.4

ACETYLEN
Acetylene
                                     10.2

BENZENE
Benzene (also used for halo- and nitro-benzenes)
                                      3.5
[a]	Relative amount in the base ROG mixture used to represent emissions from all sources, in units of ppb model species per ppmC of mixture. This mixture was used to derive the parameters for the adjustable parameter lumped model species as discussed in this section, and was also used in the reactivity assessment calculations discussed in the "Updated Reactivity Scales" section, below.

The mechanisms for the model species already in the base mechanism have been discussed previously, and are given in Table A-2 in Appendix A. The mechanisms for the lumped species added to the base mechanism fixed parameter SAPRC-07 are derived using the same standard mixtures as used to derive their parameters for parameter SAPRC-99. For the model species ALKn, AROn, and OLEn, the mechanisms are derived based on the mixture of alkanes, aromatics, and alkenes in base reactive organic gas (ROG) mixture used to represent anthropogenic emissions from all sources used when calculating the Carter (1994) reactivity scales. This is based on an analysis by Jeffries et al. (1989) of urban ambient air measurements made by Lonneman (1986). For the model species TERP, the mechanisms are derived based on the top 5 terpenes in the North American Biogenic Inventory from the Guenther et al (2000) NARSTO assessment.
The mixtures of compounds used to derive the parameters for the adjustable parameter model species for the fixed parameter mechanism are given in Table 18 and Table 19, and Table A-7 in Appendix A gives the mechanisms that were so derived. The latter includes the reactions that were added to the standard base mechanism and also the reactions of these model species with chlorine atoms that are included when the mechanism is used to represent chlorine chemistry. These are based on the mechanisms for the individual components given in Table B-2 and Table B-7 in Appendix B, with the weighting factors shown in Table 18 and Table 19. Note that because of the difficulties in generating complete mechanisms for the Cl + alkene reactions (discussed above), the terpene + Cl mechanism is based entirely on that derived for -pinene, and, as indicated in Table B-7 the mechanisms and rate constants for many of the alkenes were assumed to be the same as structurally similar compounds.
Note that the mixtures used to derive the parameters for the model species in the fixed parameter mechanism may be out of date and need to be updated. An update to the base ROG mixture used to derive
Table 18.	Compounds and weighting factors used to derive the parameters for the ALK and ARO model species in the fixed parameter mechanism for airshed models
Group and Compound
                                  Mole Fract.

Group and Compound
                                  Mole Fract.

Group and Compound
                                  Mole Fract.
ALK1

ALK5

ARO2

Ethane
                                     100%

2,4-Dimethyl Hexane
                                      12%

m-Xylene
                                      13%

n-Decane
                                      11%

p-Xylene
                                      13%
ALK2

3-Methyl Hexane
                                      11%

o-Xylene
                                      11%
Propane
                                     100%

2,3-Dimethyl Pentane
                                      7%

1,2,3-Trimethyl Benzene
                                      9%

2-Methyl Heptane
                                      6%

1,3,5-Trimethyl Benzene
                                      9%
ALK3

4-Methyl Heptane
                                      6%

1,2,4-C10 trisubstituted benzenes
                                      6%
n-Butane
                                      68%

2,4-Dimethyl Heptane
                                      5%

m-Ethyl Toluene
                                      5%
Isobutane
                                      30%

2,6-Dimethyl Octane
                                      5%

o-Ethyl Toluene
                                      5%
2,2-Dimethyl Butane
                                      2%

Methylcyclohexane
                                      4%

p-Ethyl Toluene
                                      5%

n-Nonane
                                      4%

1,2,4-Trimethyl Benzene
                                      5%
ALK4

n-Octane
                                      4%

1,2,3-C10 trisubstituted benzenes
                                      4%
Isopentane
                                      43%

Cyclohexane
                                      4%

1,3,5-C10 trisubstituted benzenes
                                      2%
n-Pentane
                                      17%

2-Methyl Nonane
                                      3%

m-C10 disubstituted benzenes
                                      2%
2-Methyl Pentane
                                      10%

2-Methyl Hexane
                                      3%

o-C10 disubstituted benzenes
                                      2%
3-Methylpentane
                                      7%

2-Methyl Octane
                                      3%

p-C10 disubstituted benzenes
                                      2%
2,4-Dimethyl Pentane
                                      5%

4-Methyl Octane
                                      3%

1-methyl-4-isopropylbenzene
                                      2%
Methylcyclopentane
                                      5%

n-Dodecane
                                      2%

m-C11 disubstituted benzenes
                                     0.4%
n-Hexane
                                      4%

4-Methyl Nonane
                                     1.4%

1,3,5-C12 trisubstituted benzenes
                                     0.3%
n-Heptane
                                      3%

Ethylcyclohexane
                                     1.1%

m-C12 disubstituted benzenes
                                     0.2%
2,3-Dimethyl Butane
                                      3%

n-Undecane
                                     1.0%

p-C12 disubstituted benzenes
                                     0.2%
Cyclopentane
                                      2%

3,6-Dimethyl Decane
                                     1.0%

1,2,4-C11 trisubstituted benzenes
                                     0.2%
   1,1-dimethylcyclopentane
                                     0.1%

2,6-Dimethyl Nonane
                                     0.5%

1,2,3-C11 trisubstituted benzenes
                                     0.2%

3-Methyl Undecane
                                     0.5%

1,3,5-C11 trisubstituted benzenes
                                     0.2%
ARO1

5-Methyl Undecane
                                     0.5%

1,2,4-C12 trisubstituted benzenes
                                     0.12%
Toluene
                                      75%

3-Methyl Decane
                                     0.2%

1,2,3-C12 trisubstituted benzenes
                                     0.12%
Ethyl Benzene
                                      10%

4-Methyl Decane
                                     0.2%

o-C11 disubstituted benzenes
                                     0.10%
C11 Monosubstituted Benzenes
                                      5%

1,2-dimethylcyclopentane
                                     0.12%

p-C11 disubstituted benzenes
                                     0.10%
n-Propyl Benzene
                                      4%

Ethyl Cyclopentane
                                     0.12%

o-C12 disubstituted benzenes
                                     0.06%
C10 Monosubstituted Benzenes
                                      3%

n-Tridecane
                                     0.09%

Isopropyl Benzene (cumene)
                                      2%

3,6-Dimethyl Undecane
                                     0.03%

t-Butyl Benzene
                                     0.7%

3-Methyl Dodecane
                                     0.02%

   C12 Monosubstituted Benzenes
                                     0.2%

5-Methyl Dodecane
                                     0.02%

Table 19.	Compounds and weighting factors used to derive the parameters for the OLE and TERP model species in the fixed parameter mechanism for airshed models
Group and Compound
                                 Mole Fraction

Group and Compound
                                Mole Fraction]
OLE1

OLE2

Propene
                                      29%

cis-2-Pentene
                                      14%
1-Hexene
                                      24%

trans-2-Pentene
                                      14%
1-Butene
                                      12%

trans-2-Butene
                                      11%
1-Pentene
                                      11%

Isobutene
                                      10%
1-Heptene
                                      11%

cis-2-Butene
                                      9%
1-Nonene
                                      5%

2-Methyl-1-Butene
                                      8%
3-Methyl-1-Butene
                                      3%

1,3-Butadiene
                                      6%
1-Octene
                                      2%

2-Methyl-2-Butene
                                      5%
1-Undecene
                                      2%

Cis-2-Hexene
                                      5%
1-Decene
                                     0.9%

Trans-2-Hexene
                                      5%

Trans-3-Heptene
                                      4%
TERP

Trans-4-Nonene
                                      2%
-Pinene
                                    38% [a]

Trans-4-Octene
                                      2%
-Pinene
                                      27%

Trans-5-Undecene
                                      2%
3-Carene
                                      17%

Trans-2-Heptene
                                      2%
Sabinene
                                      10%

Cyclohexene
                                      2%
d-Limonene
                                      9%

Trans-4-Decene
                                     0.7%

3,4-Diethyl-2-Hexene
                                     0.2%
                [a]	The TERP + chlorine mechanism is assumed to be the same as that derived for -pinene.

the ALK, ARO, and OLE parameters is almost certainly called for given changes in anthropogenic emissions since the mid 80's, and advances in analytical methods. However, deriving updated base ROG mixtures is beyond the scope of this project, and the CARB and the EPA were unable to provide recommendations for an updated mixture within the time frame of this project. Therefore, the same mixture is retained in this update for consistency with SAPRC-99. However, the mechanisms for the individual compounds given in Table B-2 in Appendix B could be used as the basis for deriving updated mechanisms for these lumped model species once updated base ROG or terpene compositions become available.
Emissions Assignments
An important part of implementing mechanisms into airshed models involves assigning individual chemical compounds and categories used in speciation profiles to lumped species in the mechanism. The general types of compounds assigned to the various model species in the fixed parameter version of SAPRC-07 are indicated in Table 17, and the assignments of lumped model species to the individual compounds or types of compounds for which mechanistic assignments are made are shown in Table B-11 in Appendix B. For compounds or groups of compounds that are represented using the lumped molecule method as shown on Table B-9, the lumped model assignments are derived from those that are assigned to the explicitly represented compounds that are used to represent them.
Emissions speciation profiles use a variety of types of chemical categories, many of which do not refer to individual compounds or chemical categories used in the SAPRC mechanism. Because of this, we have previously developed an emissions speciation database for the purpose of assigning chemical categories used in emissions profiles to model species in various mechanisms in a consistent manner. The mechanisms currently supported in the database include CB4, CB05, RADM2, as well as SAPRC-99 (Adelman et al, 2005; Carter, 2008b). This speciation database has been updated to support SAPRC-07 and the files needed to process emissions for the fixed-parameter version of SAPRC-07 are available at the speciation database project web site (Carter, 2008b).
Note that emissions assignments are different than lumped molecule representations. Lumped molecule representations involve representing the compound or categories by a detailed model species, of which there are over 700, while emissions assignments involve representing id by one of the ~30 lumped model species used in airshed models. Obviously lumped molecule assignments are less approximate and should be used for purposes of reactivity scale calculations or deriving optimum mechanistic parameters for mixtures, where maximum chemical detail is appropriate. Emissions assignments such shown on Table B-11 and given in the speciation database (Carter, 2008b) should be reserved for applications where using the more limited number of lumped model species is necessary and appropriate.
Mechanism Evaluation
The performance of the mechanism in simulating O3 formation, rates of NO oxidation, and other measures of reactivity was evaluated by conducting model simulations of over 2500 environmental chamber experiments carried out in 11 different environmental chambers at 4 different laboratories. The experiments included 682 single VOC experiments, consisting primarily of VOC - NOx or VOC - NOx experiments with added CO or alkane, 591 incremental reactivity experiments, and 973 experiments with mixtures, though approximately 2/3 of the mixture runs were replicate base case reactivity experiments of various types. These include not only the experiments used when evaluating the SAPRC-99 mechanism (Carter, 2000a), but also the more recent experiments carried out at out at our laboratories at CE-CERT through June, 2006, experiments carried out in the Tennessee Valley Authority (TVA) chamber that were used in the low NOx mechanism evaluation study of Carter (2004), and also earlier University of North Carolina (UNC) chamber experiments used in the SAPRC-90 and RADM-2 mechanism evaluations of Carter and Lurmann (1990, 1991) and in the isoprene mechanism evaluation of Carter and Atkinson (1996).
The chambers whose data were used for mechanism evaluation are summarized on Table 20, the types of experiments are summarized on Table 21, and the individual experiments are listed in Table C-1 in Appendix C. The input files, chamber data, and the computer programs used for the chamber simulations will be made available on the SAPRC mechanism web site. The results of the evaluation are given on Table C-1 and in the numerous figures in Appendix C, and are summarized below.
Note that the largest database of environmental chamber experiments used for mechanism evaluation for this project is from indoor chamber experiments carried out at the University of California at Riverside (UCR). These experiments serve as the primary basis for mechanism evaluation and any adjustments made to mechanisms for individual VOCs are based on simulations of UCR indoor chamber runs. However, simulations of the available experiments from the Tennessee Valley Authority (TVA) chamber a subset of the experiments carried out in the University of North Carolina (UNC) outdoor chamber were also carried out, and results are also shown for information purposes. We believe that the TVA chamber is reasonably well characterized for modeling, and the results of these simulations provide useful supporting information for mechanism evaluation. However, because of time and resource constraints we were unable to obtain and process the most complete and quality-assured set of UNC chamber data. The generally poor performance of the model in simulating the non-isoprene UNC experiments may reflect this. For this reason, the simulations of the UNC chamber experiments are shown for information only, and were not used as the primary basis for mechanism evaluation. A re-evaluation using an improved UNC chamber dataset may be appropriate, but was beyond the scope of this project.
The performance of the mechanism is measured primarily in terms of its ability to simulate O3 formation and NO oxidation. The effect of the compounds on overall OH radicals in the incremental reactivity experiments is also assessed. Although the model simulations of the experiments also give information on the ability of the mechanism to predict other chemical transformations, such as rates of consumption of reactants other than NO and formation of various products besides O3 that may have been measured, a comprehensive mechanism evaluation in this regard was beyond the scope of this project.
Table 20.	Summary of environmental chambers whose data were used for mechanism evaluation
ID
Brief description and references for additional information
        Chambers at the Statewide Air Pollution Research Center (SAPRC) or the College of Engineering Center for Environmental Research and Technology (CE-CERT) at the University of California at Riverside (UCR)
EC
A 5774-liter evacuable chamber constructed of Teflon-coated aluminum with Quartz end windows. Located at SAPRC. Xenon arc solar simulator light source. Most experiments at ~50% RH and around 300[o]K. Experiments carried out 1975 - 1984. See Carter et al (1995a) for description of chamber and experimental methods and Carter (2000a) for a discussion of the modeling methods used. This chamber is now primarily being used for mechanistic studies.
ITC
One semi-collapsible ~6400-liter reactor constructed of 2 mil FTP Teflon film held in a framework. Blacklight light source. Located at SAPRC. Most experiments at ~50% RH and around 300[o]K. Experiments carried out 1982 - 1986. See Carter et al (1995a) for description of chamber and experimental methods and Carter (2000a) for a discussion of the modeling methods used. This chamber is now primarily being used for mechanistic studies.
ETC
One semi-collapsible ~3000-liter reactor constructed of 2 mil FTP Teflon film held in a framework. Blacklight light source. Located at SAPRC. Most experiments used dry air and carried out around 300[o]K. Experiments carried out 1989 - 1993. See Carter et al (1995a) for description of chamber and experimental methods and Carter (2000a) for a discussion of the modeling methods used. This chamber no longer exists.
OTC
Two completely collapsible ~20,000-liter "pillow bag" reactors constructed of 2 mil FTP Teflon located outdoors. Located at the outdoor laboratory at SAPRC. Natural sunlight irradiation. Two irradiations carried out simultaneously, one in Side "A" and the other in Side "B". Experiments used dry air, with temperature varying with ambient conditions. Experiments carried out 1992 - 1993. See Carter et al (1995a,b) for description of chamber and experimental methods and Carter et al (1995b) and Carter (2000a) for a discussion of the modeling methods used. This chamber no longer exists.
DTC
Two semi-collapsible ~5000-liter reactors constructed of 2 mil FTP Teflon film held in a framework. Initially located at the outdoor laboratory building at SAPRC, but subsequently re-constructed at CE-CERT. Two irradiations carried out simultaneously, one in Side "A" and the other in Side "B". Blacklight light source. Most experiments used dry air at around 300[o]K. Experiments carried out 1993 - 1999. See Carter et al (1995a) for description of chamber and experimental methods and Carter (2000a) for a discussion of the modeling methods used. This chamber no longer exists.
XTC
One semi-collapsible ~5000-liter reactor constructed of 2 mil FTP Teflon film held in a framework. Xenon arc light source. Located the outdoor laboratory building at SAPRC. Experiments used dry air at around 300[o]K. Experiments carried out in 1993. See Carter et al (1995a) for description of chamber and experimental methods and Carter (2000a) for a discussion of the modeling methods used. This chamber no longer exists.
CTC (82)
Semi-collapsible ~5000-liter reactor constructed of 2 mil FTP Teflon film held in a framework. Xenon arc light source. Located at CE-CERT. Experiments used dry air at around 300[o]K. Experiments carried out in 1994 - 1995. See Carter et al (1995a) for description of chamber and experimental methods and Carter (2000a) for a discussion of the modeling methods used. This configuration is applicable to runs from 11 through 82.
CTC (83)
Two semi-collapsible ~2500-liter reactors constructed of 2 mil FTP Teflon film held in a framework. Xenon arc light source. Located at CE-CERT. Experiments used dry air at around 300[o]K. Experiments carried out in 1995 - 1999. This configuration is applicable to runs 83 and higher. See Carter et al (1995a) for description of chamber and experimental methods and Carter (2000a) for a discussion of the modeling methods used. This chamber no longer exists.
EPA
(Also referred to as the UCR EPA chamber.) Two ~90% collapsible ~100,000-liter reactors constructed of 2 mil FEP Teflon film held on a framework with a moveable top for positive pressure control. Located in a temperature-controlled "clean room" clean room enclosure flushed with purified air. Located at CE-CERT. Can use either an argon arc solar simulator light source or blacklights. Two irradiations carried out simultaneously, one in Side "A" and the other in Side "B". Although the temperature and humidity can be varied, all experiments in this evaluation were carried out with dry air at around 300[o]K. Experiments carried out from 2003 through present, but latest run in this evaluation was carried out in mid-2006. See Carter (2004) and Carter et al (2005b) for a description of the chamber and experimental methods and Carter (2004) for a discussion of the modeling methods used. Note that mechanism evaluation experiments in this chamber can be carried out under lower NOx conditions than the other chambers at UCR or the UNC outdoor chamber. This chamber is still in operation.
               Chamber at the Tennessee Valley Authority (TVA).
TVA
One 28,300-liter reactor constructed of 0.13 mm FEP Teflon film on a rigid frame located inside an enclosure flushed with purified air. Special procedures used to clean between experiments to permit experiments at lower concentrations. Light source consisted of blacklights and sunlamps. Experiments carried out at about 15% RH and the temperature varied from ~300-315[o]K.  Experiments carried out in 1993 - 1995. See Simonaitis and Bailey (1995) and Bailey et al  (1996) for a description of the chamber and experimental methods and Carter (2004) for a discussion of the modeling methods used. Note that mechanism evaluation experiments in this chamber were carried out under lower NOx conditions than in the other chambers except for UCR EPA, but the chamber experience high background formaldehyde levels that needed to be taken into account when modeling the experiments (Carter, 2004). This chamber no longer exists.
               Chamber at the University of North Carolina (UNC)
UNC
A very large dual reactor chamber consisting of 5 mil FEP Teflon film held on a rigid A-frame structure located outdoors. Natural sunlight light source. Located in a rural site in North Carolina with filtered but otherwise unpurified air used for experiments that were conducted at ambient temperature. Two irradiations carried out simultaneously, one in side "R" and the other in side "B". Experiments are designated by their run date and side (e.g., JN1279R). Most of the experiments used in this evaluation were carried out between 1978 and 1985, but a few isoprene experiments were carried out in 1992 and 1993. See Jeffries et al (1982, 1985a,b) for descriptions of the chamber and experimental methods and Carter and Lurmann (1990, 1991) for a discussion of the modeling methods used for the earlier experiments and Carter and Atkinson (1996) for the isoprene experiments. Note that this may not be a complete dataset or contain the best quality-assured data from this chamber. This chamber has since been rebuilt and is probably not the primary chamber now used at UNC.

Table 21.	Summary of types of experiments used for mechanism evaluation.

Designation
Mixture irradiated or description

Radical Source Characterization

CO - NOx
CO - NOx

C4 - NOx
n-Butane - NOx
NOx Offgasing characterization

CO - Air
CO - Air

HCHO - CO - Air
Formaldehyde - CO - Air

ACETALD - Air
Acetaldehyde - Air
VOC Mechanism Evaluation

VOC - NOx
VOC - NOx

VOC - CO - NOx
VOC - NOx with added CO

VOC - C4 - Air
VOC - air with added n-butane

VOC - C4 - NOx
VOC - NOx with added n-butane

VOC - C2 - NOx
VOC - NOx with added ethane

VOC - O3
VOC + O3 (also includes control experiment in the other reactor without the VOC)

IR
Incremental reactivity experiment. Type of base case indicated
Standard surrogate - NOx experiments used in recent UCR experiments for mechanism evaluation

Surg-8
Standard 8-component "full surrogate" consisting of n-butane, n-octane, ethene, propene, trans-2-butene, toluene, m-xylene and formaldehyde (e.g., Carter et al, 1995c; Carter, 2002)

Surg-7
Standard 8-component "full surrogate", above, but without formaldehyde (e.g. Carter and Malkina, 2005, 2007, Carter et al, 2005a)

Surg-3
Standard mini-surrogate consisting of ethene, n-hexane, and m-xylene (e.g., Carter et al, 1993, 1995c).

Surg-NA
Standard 8-componene "full surrogate" but without aromatics and formaldehyde (unpublished results from this laboratory).

Surg-E
Ethene surrogate consisting of ethene alone (e.g., Carter et al, 1995c).

Surg-x
Miscellaneous 3- or 4-componene surrogates (e.g., Carter et al, 1993, Carter and Malkina, 2002)
Types of surrogate or incremental reactivity base case experiments

MIR1
Low ROG/NOx, MIR-like conditions. NOx 300-500 ppb (e.g., Carter et al, 1993, 1995c)

MIR2
Low ROG/NOx, MIR-like conditions, NOx < 100 ppb (e.g., Carter, 2002; Carter and Malkina, 2005, 2007, Carter et al, 2005a)

LN1
Lower NOx, e.g., MOIR/2. NOx >100 ppb (e.g., Carter et al, 1993, 1995c)

LN2
Lower NOx,, e.g. MOIR/2 conditions, NOx < 50 ppb (e.g., Carter, 2002; Carter and Malkina, 2005, 2007, Carter et al, 2005a)

vary
Non-standard ROG/NOx. Conditions varied
Older UCR and UNC and TVA surrogate and mixture - NOx experiments

ITCsrg-4
Experiments in the ITC chamber (primarily) using a 4-component surrogate, primarily for the early incremental reactivity study of Carter and Atkinson (1987). Surrogate consisted of propene, n-butane, trans-2-butene, and m-xylene.

ITCsrg-4R
Based on ITCsrg-4, but with propene removed. Used in the study of Carter and Atkinson (1987).

ECsrg-7
A surrogate mixture of seven hydrocarbons used in several runs in the SAPRC EC (Pitts et al, 1979). Consisted of n-butane, 2,3-dimethyl butane, ethene, propene, trans-2-butene, toluene, m-xylene

MDsrg-8
A surrogate mixture of 8 hydrocarbons used in the "multi-day effects" study of Carter et al (1984). Consisted of n-butane, n-pentane, isooctane, ethene, propene, isobutene, toluene, and m-xylene

TVAsrg-1
A complex surrogate mixture of alkanes, alkenes, and aromatics used in the TVA chamber (Simonaitis and Bailey, 1995; Bailey et al, 1996).

TVAsrg-2
A complex surrogate mixture of alkanes, alkenes, and aromatics used in the TVA chamber (Simonaitis and Bailey, 1995; Bailey et al, 1996).

UNCsrg-3
A simple surrogate of propene, n-butane and an aromatic used in the UNC chamber (Jeffries et al, 1982, 1985a).

SynUrb
A complex "synthetic urban" VOC mixture used in the UNC chamber (Jeffries et al, 1985a)

SynAuto
A synthetic auto exhaust VOC mixture used in the UNC chamber (Jeffries et al, 1985b)

UNCsrg-x
Miscellaneous surrogates used in the UNC chamber (Jeffries et al, 1982, 1985a).
Simple mixtures (incomplete surrogates)

Mix-A
Mixture of alkanes

Mix-E
Mixture of alkenes

Mix-AE
Mixture of alkanes and alkenes

Mix-AO
Mixtures of alkanes and oxygenates (generally aldehydes)

Mix-EO
Mixture of alkenes and oxygenates

Mix-RO
Mixtures of aromatics and oxygenates (generally aldehydes)

Mix-AR
Mixtures of alkanes and aromatics

Mix-ER
Mixtures of alkenes and aromatics
Light Source Designations used in run listing

A
Arc light (Xenon or Argon arc) solar simulator

Bl
Blacklights

Bs
Mixture of blacklights and sunlamps

S
Solar light

This would be a major effort because of the considerable amount of variation from experiment to experiment in terms of measurements of other species that were made, and the highly variable and uncertain quality of much of the measurements (e.g., see Carter et al, 1995a for a discussion of the measurement data for the earlier UCR chamber experiments). However, evaluations of model performance in simulating individual oxidation products was often used when developing mechanisms for individual VOCs when relevant data were available, and in general the mechanisms for these compounds retain the product yield predictions so developed when updated for this version.
Methods
The procedures used when evaluating the mechanism against the chamber data were the same as employed in previous evaluations of the SAPRC-90 (Carter and Lurmann, 1990, 1991) and SAPRC-99 (Carter, 2000a, 2004; Carter and Malkina, 2007) mechanisms. Briefly, evaluations of mechanisms using chamber data require an appropriate representation of the conditions of the chamber experiments that affect the simulation results. These include initial reactant concentrations, physical conditions such as temperature and dilution, light intensity and spectrum, and the major wall effects such as the chamber radical source, O3 decays, NOx offgasing, etc. These considerations are discussed in detail elsewhere (e.g., Carter et al, 1982; Carter and Lurmann, 1990, 1991; Carter et al, 1995a,b, 1997a; Carter, 2000a and references therein), and that discussion will not be duplicated here.
The parameters in the chamber effects model used when modeling the experiments for this mechanism evaluation are given in Table 22. Except for the parameters used to model the chamber-dependent radical source and NOx offgasing, which have to be adjusted for each mechanism, the input data used in modeling the chamber experiments were the same as used in previous studies. The reports describing the methods used to derive the input data, and giving the chamber effects characterization parameters employed, are given in footnotes to Table 20. As indicated above, the input data files will be made available at the SAPRC mechanism web site.
The most important and variable chamber background effect is the "chamber radical source" first noted by Carter et al (1982) and background NOx offgasing. The former causes enhanced NO oxidation and O3 formation experiments, such as CO - NOx or alkane - NOx irradiations with no significant radical sources in the gas-phase mechanism, while the latter causes O3 formation in experiments where NOx has not been added. Both of these effects are attributed to offgasing of HONO, which have been observed experimentally in the SAPHIR outdoor chamber in Germany (Brauers et al, 2003, Rohrer et al, 2004) to occur at rates similar to the radial source and NOx offgasing rates derived for the UCR EPA chamber (Carter et al, 2005b). The magnitudes of the radical source and NOx offgasing effects are larger in the older chambers (Carter and Lurmann, 1990, 1991; Carter et al, 1995a, 2005b; Carter, 2000a), but they are still generally comparable to each other, consistent with the assumption that both are due to the same process. This is represented in the chamber model by the parameter RN, which is the rate of HONO offgasing relative to the light intensity as measured by the NO2 photolysis rate.
Since HONO has not been measured directly in any of the chambers used for mechanism evaluation for the conditions relevant to the experiments, the HONO offgasing rate parameter has to be determined by adjusting the parameter so the model calculations can simulate results of the appropriate characterization experiments. The most sensitive experiments are the CO - NOx and alkane (primarily n-butane) - NOx experiments used for radical source characterization, and modeling these experiments is the primary method used to derive the RN parameters used when modeling the mechanism evaluation runs. The best fit parameters depend to some extent on the chemical mechanism used, particularly the rate constant for the OH + NO2 reaction, which is the main radical terminating reaction in the characterization experiments. Since this rate constant changed in SAPRC-07 compared to SAPRC-99, the set of RN parameters used in the mechanism evaluation also changed.
The RN parameters that were used when modeling the chamber experiments for this mechanism evaluation are given on Table 22. They were derived to minimize biases in simulations of the radical source characterization experiments, as indicated on Table 21 and Table C-1 in Appendix C. For this purpose, experiments were grouped into "characterization sets" that were assumed to have similar chamber effects parameters. As discussed by Carter et al (1995a) and Carter (2002), for some chambers the conditions affecting radical sources and NOx offgasing appeared to change from time to time due to changes in reactors, exposure to reactants, etc., and assignments to characterization sets are used to take this into account. The characterization sets associated with the individual experiments are included with the run listing in Table C-1.

Table 22.	Chamber wall effect and background characterization parameters used in the environmental chamber model simulations for mechanism evaluation.
Cham.
                                    Set(s)
                                     Value
Discussion

RN-I (ppb)
Ratio of the rate of wall + h -> HONO to the NO2 photolysis rate.
EPA
                                       2
                                    0.0075
Average of values that gave best fits to n-butane - NOx and CO - NOx, radical source characterization and CO - air NOx offgasing characterization experiments carried out in this chamber. Note that for Set 3 the best fit RN-I values depended on the reactor.

                                      3A
                                    0.0165

                                      3B
                                    0.0115

                                       4
                                    0.0055

                                       5
                                    0.0110

                                       6
                                    0.0150

                                       7
                                    0.0100

ITC
                                      All
                                    0.0475
Average of value of RS-I that gave best fits to n-butane - NOx radical source characterization chamber experiments carried out in this chamber.
ETC
                                      2-3
                                     0.04
Same procedure as above
DTC
                                       1
                                     0.058
Same procedure as above

                                       3
                                     0.210

                                       4
                                     0.300

                                      10
                                     0.055

                                      11
                                     0.092

                                      12
                                     0.310

                                      13
                                     0.170

                                      14
                                     0.095

                                      15
                                     0.063

                                      16
                                     0.240

                                      17
                                     0.083

                                      18
                                     0.074

XTC
                                      All
                                     0.085
Same procedure as above
CTC
                                       1
                                     0.06
Same procedure as above

                                      2,3
                                     0.10

                                      4-8
                                     0.095

                                       9
                                     0.115

                                      10
                                     0.08

OTC

                       7.2e+9 exp(-9712/T) 0.063 @ 300K
Based on Arrhenius plots of values of RS-I that give fits to n-butane - NOx chamber experiments carried out in this chamber for the average temperatures of the experiments.
EC
                                       1
                                     0.235
Based on the NO2 dependence radical source derived by Carter et al (1982), adjusted to reduce biases in simulations of n-butane - NOx experiments carried out in this chamber using this mechanism.  The NO2-dependent radical source term, RS-S, was reduced by an equal factor.
TVA
                                      All
                                     0.008
Estimated value. Could not be determined by modeling radical source characterization because of the large formaldehyde offgasing. See Carter (2004).
UNC
                                      All
                      4.0e+14 exp(-12581/T) 0.248 @ 300K
Based on Arrhenius plots of values of RS-I that give fits to the few available alkane - NOx chamber experiments carried out in this chamber for the average temperatures of the experiments. Older experiments modeled by Carter and Lurmann (1990, 1991) were used.
RS-S (unitless)
Ratio of the rate of NO2 + hv -> 0.5 HONO + 0.5 wall NOx to the NO2 photolysis rate.
EC
                                       1
                                    0.0017
Based on the NO2 dependence radical source derived by Carter et al (1982), adjusted downward by 20% to reduce biases in simulations of n-butane - NOx experiments carried out in this chamber.  The NO2-independent radical source term, RN-I, was reduced by an equal factor.
All others
                                       0
Any dependence of apparent radical source on initial NOx levels in Teflon bag chambers was found to be much less than the run-to-run variability.
HONO-I (ppb)

Initial HONO in experiment, assumed to be independent of other reactants unless indicated.
EPA
                                      All
                                     0.05
Value that usually gives best fits to model simulations of results of n-butane - NOx and CO - NOx experiments in this chamber.
ITC
                                      All
                                      1.7
Average of initial HONO value that gave best fits to n-butane - NOx chamber experiments carried out in this chamber. The RN-I parameter was optimized at the same time. The best fit initial HONO values appear to be approximately independent of the initial NO2.
ITC
                                      All
                                      1.7
Similar procedure as above.
TVA
                                      All
                                      0.5
Similar procedure as above.
DTC
                                       1
                               0.001 x [NO2]init
Similar procedure as above, except for this chamber the best fit initial HONO appeared to be correlated with the initial NO2 concentrations.

                                      3,4
                               0.004 x [NO2]init

                                     10,18
                               0.008 x [NO2]init

                                     11,14
                               0.006 x [NO2]init

                                     12,16
                               0.005 x [NO2]init

                                      13
                               0.009 x [NO2]init

                                      15
                               0.007 x [NO2]init

                                      17
                               0.003 x [NO2]init

XTC
                                      All
                               0.012 x [NO2]init
Similar procedure as above
CTC
                                      All
                               0.008 x [NO2]init
Similar procedure as above
EC
                                      All
                               0.07 x [NO2]init
Similar procedure as above
ETC, OTC, UNC
                                       0
For most (though not all) characterization runs in these chambers the data are simulated best if the effect of any initial HONO is small compared to other chamber radical sources, o
E-NO2/K1 (ppb)
Ratio of rate of NO2 offgasing from the walls to the NO2 photolysis rate.
EC
                                       1
                                     0.10
Adjusted to fit O3 formation in acetaldehyde/air run EC-253.
All Teflon Film Chambers
                                       0
The NOx offgasing caused by representing the radical source by HONO offgasing appears to be sufficient for accounting for NOx offgasing effects in most cases. RN-I parameters adjusted to fit experiments sensitive to the radical source are consistent with NOx offgasing rates adjusted to fit pure air or aldehyde - air runs, to within the uncertainty and variability.
K(NO2W) (min[-1])
Rate of unimolecular loss (or hydrolysis) of NO2 to the walls.
All Teflon Film Chambers
                                    1.6e-4
Based on dark NO2 decay and HONO formation measured in the ETC by Pitts et al. (1984).  Assumed to be the same in all Teflon bag chambers, regardless of volume.
EC
                                       1
                                    2.8e-4
Based on dark NO2 decay and HONO formation measured in the EC by Pitts et al. (1984).
UNC
                                      All
                                    5.0e-5
Value used by Carter and Lurmann (1990, 1991) was not updated.
YHONO
Yield of HONO in the unimolecular reaction (hydrolysis) of NO2 on the walls.
All Teflon Film Chambers
                                      0.2
Based on dark NO2 decay and HONO formation measured in the ETC by Pitts et al. (1984).  Assumed to be the same in all Teflon bag chambers, regardless of volume.
EC
                                       1
                                      0.5
Based on dark NO2 decay and HONO formation measured in the EC by Pitts et al. (1984).
E-ALD/K1 (ppb)
Ratio of rate of formaldehyde offgasing from the walls to the NO2 photolysis rate.
EPA
                                      All
                                     0.01
Gives best fits to formaldehyde data in most pure air irradiations and other experiments where formaldehyde should not otherwise be present.
TVA

                    0.045 + other sources (see discussion)
This chamber had significant wall offgasing of formaldehyde and assuming a constant offgasing rate did not give best fits to the data. The additional process required to fit the data, derived by Simonaitis et al (1997) and used by Carter (2004), are as follows:
Walls + h  WALLVOC; rate = NO2 photolysis rate x 0.135 ppb
WALLVOC + OH  HO2 + 0.2 HCHO; k = 2 x 10[4] ppm-1 min-1
All other chambers
                                       0
Simulations of characterization experiments do not require assuming formaldehyde offgasing. Formaldehyde measurements not sufficiently sensitive to determine formaldehyde offgasing.
K(O3W) (min[-1])
Unimolecular loss rate of O3 to the walls.
EPA
                                      All
                                    1.08e-4
Based on results of O3 decays carried out in this chamber
ITC, ETC, DTC, XTC
                                    1.5e-4
Based on results of O3 decay in Teflon bag chambers experiments as discussed by Carter et al (1995a).
CTC
                                      All
                                    8.5e-5
Based on results of O3 decay experiments in this chamber
OTC
                                      All
                                    1.67e-4
Similar procedure as above
EC
                                      All
                                    1.1e-3
Similar procedure as above
TVA
                                      All
                                    7.0e-4
Similar procedure as above
UNC
                                      All
                                    1.43e-4
Similar procedure as above
k(N26I) (min[-1])

Rate constant for N2O5 -> 2 Wall-NOx.  This represents the humidity-independent portion of the wall loss of N2O5, or the intercept of plots of rates of N2O5 loss against humidity.
All Teflon Bag Chambers
                                    2.8e-3
Based on N2O5 decay rate measurements made by Tuazon et al (1983) for the ETC. Assumed to be independent of chamber size (Carter et al, 1995a).
EC
                                       1
                                    4.7e-3
Based on N2O5 decay rate measurements made by Tuazon et al (1983) for the EC. See also Carter et al (1995a).
k(N26S) (ppm[-1] min[-1])
Rate constant for N2O5 + H2O -> 2 Wall-NOx.  This represents the humidity dependent portion of the wall loss of N2O5, or the slope of plots of rates of N2O5 loss against humidity. Note that this is in addition to the N2O5 hydrolysis reaction in the gas-phase mechanism.
All Teflon Bag Chambers
                                    1.1e-6
Based on N2O5 decay rate measurements made by Tuazon et al (1983) for the ETC. Assumed to be independent of chamber size (Carter et al, 1995a).
EC
                                       1
                                    1.8e-6
Based on N2O5 decay rate measurements made by Tuazon et al (1983) for the EC. See also Carter et al (1995a).
EPA
                                      All
                                       0
Assumed to be negligible compared to the homogeneous process already in the base mechanism
UNC
                                      All
                                    2.0e-8
Value used by Carter and Lurmann (1990, 1991) was not updated.
k(XSHC) (min[-1])
Rate constant for OH -> HO2.  This represents the effects of reaction of OH with reactive VOCs in the background air or offgassed from the chamber walls. This parameter does not significantly affect model simulations of experiments other than pure air runs.
All Teflon Bag Chambers
                                      250
Estimated from modeling several pure air in the ITC (Carter et al, 1996d), and also consistent with simulations of pure air runs in the ETC (Carter et al, 1997a).
EC
                                       1
                                       0
Assumed to be negligible because the EC is generally evacuated overnight between experiments (Carter et al, 1995a).
EPA, TVA
                                       0
Assumed to be negligible because steps are taken to reduce background effects for low concentration experiments.
UNC

                                      750
Value used by Carter and Lurmann (1990, 1991) was not updated.
H2O (ppm)

Default water vapor concentration for runs where no humidity data are available.
EPA
                                      All
                                    3.4e+2
The EPA chamber experiments used for mechanism evaluation to date were not humidified. This is the expected upper limit water concentration.
ITC
                                      All
                                    2.0e+4
This corresponds to ~50% RH at 303K, which is the condition for most experiments in this chamber.
DTC
                                       4
                                    2.0e+4
This corresponds to ~50% RH at 303K, which is the condition for experiments in this characterization set. (The other DTC experiments are not humidified)
EC
                                       1
                                    2.0e+4
This corresponds to ~50% RH at 303K, which is the condition for most experiments in this chamber. Humidity data are available for most EC runs, so the default is usually not used.
TVA, UNC
                                 (no default)
The water concentration is specified in the input files for all experiments.
All Other Chambers or char. sets.
                                    1.0e+3
Experiments in these chambers were carried out using dried purified air. The limited humidity data for such runs indicate that the humidity was less than 5%, probably no more than ~2.5%, and possibly much less than that. The default value corresponds to ~2.5 - 3% RH for the conditions of most experiments.
Dilution rate (min-1)
Default rate of dilution in the experiment (used for most experiments if no dilution specified for the experiment)
EPA
                                      All
                                       0
Dilution expected to be small because of the design of the chamber
ITC
                                      All
                                       0
Dilution not well characterized but assumed to be small.
ETC
                                      All
                                    8.0e-5
Based on CO dark decays or other dilution characterization data.
DTC
                                       1
                                    5.3e-5
Similar procedure as above

                                      3,4
                                    1.8e-4

                                     10-18
                                    5.3e-5

XTC
                                      All
                                    2.7e-5
Similar procedure as above
CTC
                                      All
                                    6.7e-5
Similar procedure as above
OTC
                                      All
                                    6.7e-5
Similar procedure as above
EC
                                      All
                                    2.0e-4
Similar procedure as above
TVA

                                 (no default)
Dilution specified in input files for each experiment
UNC
                                      All
                                    2.0e-4
Value used by Carter and Lurmann (1990, 1991) was not updated.

Note that, as discussed by Carter (2002) and Carter et al (2005b), the UCR EPA and the TVA chambers have much lower apparent NOx offgasing rates than the older chambers, because these chambers were designed for conducting experiments at lower pollutant concentrations. Runs in these chambers were generally carried out at lower pollutant levels than in the other chambers, and the concentrations are generally more representative of ambient conditions. However, the TVA chamber had very high background levels of formaldehyde (Carter, 2002), so of these two chambers the UCR EPA chamber has the lowest overall background effects.
Although most of the mechanism evaluation is based on simulations of environmental chamber experiments, we will also present results of simulations of the "direct reactivity" experiments developed by Carter and Malkina (2002). These consist of plug flow experiments where the effect of adding the VOC to HONO - air irradiations is determined. In the absence of added VOCs, the HONO - air plug flow irradiations results in the formation of NO, which is measured. If a VOC is added to the mixture, the OH radicals formed in the photolysis of HONO become peroxy radicals that convert the NO to NO2, and, if the amount of added VOC is sufficient to consume all the NO, causes O3 to be formed. The change in NO consumption and O3 formation, relative to the no-VOC case, for the limit of zero added VOC is the measure of direct reactivity that is used. Model calculations carried out by Carter and Malkina (2002) show that this measurement is sensitive to the rate constant for the reactions of the VOC and the number of NO to NO2 conversions caused when it reacts, but is not sensitive to indirect reactivity effects such as effects of VOCs on radical or NOx levels. They showed that the results were generally consistent with the predictions of the SAPRC-99 mechanism except for benzene and toluene, where the direct reactivities were significantly overpredicted.
The methods used to simulate the direct reactivity experiments for this evaluation were the same as described by Carter and Malkina (2002) for SAPRC-99.
Data Presented
The results of the model simulations of the various types of experiments are given primarily in various plots and tables in Appendix C, and a few representative results are presented in conjunction with the discussion below. In most cases, results are given for SAPRC-99 as well as this version of the mechanism, so the changes caused by the mechanism update can be assessed. As indicated above, the performance of the mechanism is measured primarily in terms of its ability to simulate O3 formation and NO oxidation, though the effect of the compounds on overall OH radicals in the incremental reactivity experiments is also assessed.
The amount of O3 formed and NO oxidized in the experiments is measured by the quantity ([O3]-[NO]), which is calculated by [O3]t - [NO]t - ([O3]0 - [NO]0), where [O3]0, [NO]0, [O3]t, and [NO]t are the initial and time=t concentrations of ozone, and NO, respectively. As discussed previously (e.g., Carter and Atkinson, 1987; Carter and Lurmann, 1990, 1991), this gives a measure of the ability of the model to simulate the chemical processes that cause ozone formation that gives a useful measure even where ozone is suppressed by the presence of excess NO. The ability of the mechanism to simulate this quantity in the experiments is measured by its "model error", which is calculated as
	([O3]-[NO]) model error = {([O3]-[NO])model - ([O3]-[NO])experimental} / ([O3]-[NO])experimental.
These values are calculated for each hour of the experiments, with the experimental values being derived by linear interpolation if no measurement were made exactly on the hour. Table C-1 in Appendix C gives the model errors for the second hour and the sixth hour (or final hour if the experiment was less than 6 hours) for all the experiments, and distributions of these values are shown for various types of experiments as discussed below.
Because of the very large number of VOC - NOx and mixture - NOx experiments used in the evaluation, in most cases experimental and calculated concentration time plots are not shown for individual experiments, and only distributions of model errors are presented. The model error results for the different types of experiments are shown in various figures in Table C-1 and in the discussion of the results below. These figures show how the average model errors vary with time during the experiments, which give information on the model performance in terms of simulating rates of NO oxidation and O3 formation, as well as simulating final O3 yields. These figures also show distribution plots of model errors for hour 2 and final ([O3]-[NO]). These show the degree of run-to-run variability of model performance in simulating these quantities. Results for comparable types of experiments are shown together, but because of the large number of types of experiments, a relatively large number of plots is needed.
As indicated in Table 20, a large number of mechanism evaluation experiments consisted of incremental reactivity experiments, and a different method was used to present the results for these experiments. Incremental reactivity experiments consist of simultaneous (or alternating) irradiations of a "base case" reactive organic gas (ROG) - NOx mixture providing a simplified model of ambient chemical conditions, and irradiations of the same mixture with a test compound or mixture added. In this case the measures of model performance of interest concern the ability of the mechanism to predict the effects of the compound on the experiment. However, it is also important to see how well the model simulates the base case experiment as well, because if it performs poorly it may introduce errors in the simulations of the effects of adding the test compound if the chemical conditions influencing these effects are not correctly simulated.
Because of the relatively limited number of incremental reactivity experiments for any given compound combined with the additional considerations involved in assessing model performance for such experiments, the presentation of the evaluation results for the incremental reactivity experiments in Appendix C give plots for each experiment. These include experimental and calculated time plots of ([O3]-[NO])Base, ([O3]-[NO])Test, and IR ([O3]-[NO]), where ([O3]-[NO])Base and ([O3]-[NO])Test are the ([O3]-[NO]) in the base case and the added test VOC experiments, respectively, and
	IR ([O3]-[NO]) = {([O3]-[NO])Test - ([O3]-[NO])Base} / amount of test VOC added
where ([O3]-[NO])Base and ([O3]-[NO])Test are the ([O3]-[NO]) in the base case and the added test VOC experiments, respectively. The IR ([O3]-[NO]) values are given in molar units (e.g., ppm ([O3]-[NO]) / ppm VOC added) if the test VOC is a single compound, or in mole carbon units if the test VOC is a complex mixture such as a petroleum distillate. Each figure includes plots for experiments with a single compound or group of similar compounds.
Note that in the incremental reactivity experiments carried out in the ETC, the base case experiments were not carried out at the same time as the added test VOC experiments, but were carried out separately. This is because this is a single reactor chamber that does not permit simultaneous injections and irradiations of common reactants. For those experiments, the base case results for a given added test VOC experiment were interpolated or derived using correlations between initial reactant concentrations and other characterization results in the base case experiment. Therefore, in the plots of the ([O3]-[NO]) data, the figures only show the model calculations for the base case experiment, not the experimental data.
The figures with the evaluation results for the incremental reactivity experiments also show plots of the experimental and calculated effects of the VOC on the integrated OH radical levels. This is useful for mechanism evaluation because an important factor affecting a VOC's incremental reactivity is its effect on overall radical levels, which affects O3 formation caused by the reactions of other VOCs that are present. For radical inhibiting VOCs such as higher alkanes, the reduced O3 formation caused by the effect of the VOCs on the reactions of the other compounds present counter-acts the direct O3 formation caused by the compound's own reactions, resulting in a low net incremental reactivity for ([O3]-[NO]). However, for such compounds the effects on integrated OH levels, or IntOH are quite large, indicating that the compound indeed is having a large effect on the chemistry of the system.
 The IntOH levels in the experiments are calculated from the rates of consumption of the most reactive VOC in the base case mixture that reacts only with OH radicals (usually m-xylene but sometimes n-octane or 1,3,5-trimethylbenzene) (Carter et al, 1993). The effect of the test VOC on this quantity is measured by
	IR IntOH = {IntOHTest - InOHBase} / amount of test VOC added
where IntOHBase and IntOHTest are the IntOH values derived from the base case and the added test VOC experiments, respectively. They are given in units of ppt-minute per ppm of test VOC added if the test VOC is a compound, or ppt-minute per ppmC of test VOC if it is a complex mixture.
Results
Results for Chamber Characterization Experiments
The results of the simulations of the radical source and NOx offgasing characterization experiments are shown on Figure 5 and Figure 6, respectively. These show distribution of model errors for both the SAPRC-99 and SAPRC-07 mechanisms as described above. It can be seen that there is relatively large variation from run to run, indicating the variability of the chamber effects related to radical source and NOx offgasing. The average biases for the radical source characterization runs are generally small being within 25%, as would be expected since the radical source parameters were adjusted to minimize the biases. Except for the single CTC experiment, the biases for the NOx offgasing characterization runs are also not large compared to the variability, despite the fact that, except for the TVA chamber where the large formaldehyde offgasing makes runs insensitive to the chamber radical source, the NOx offgasing parameters were adjusted based on the radical source characterization runs. This is consistent with the expectation that they are both due to the same effect.
From the perspective of mechanism evaluation it is important to realize that these radical source and NOx offgasing characterization experiments are, by design, particularly sensitive to these variable chamber effects. The experiments used for mechanisms evaluation, discussed in the following section, are much less sensitive to these effects, and variabilities in radical source or NOx offgasing should not be important sources of variability in the simulations of these experiments. However, it is important that these chamber effects not be a source of bias in the simulations of the mechanism evaluation runs, so it is important that appropriate values of the parameters representing these effects be used.
Results for Mechanism Evaluation Experiments
The performance of the SAPRC-07 mechanism in simulating NO oxidation and O3 formation in the mechanism evaluation experiments is given in Table C-1 and in the various figures in Appendix C. The ability of the mechanism to simulate effects of the added test compounds on integrated OH levels in the incremental reactivity experiments is also shown in the figures for those experiments. For comparison purposes, results for SAPRC-99 are also shown on the figures, except for those few compounds that are not represented in SAPRC-99. The results for various types of experiments are summarized below.
Overall Performance in Simulating Entire Dataset
Figure 7 shows the distributions and averages of model errors in the SAPRC-07 and SAPRC-99 simulations of NO oxidized and O3 formation in the entire set of mechanism evaluation chamber experiments modeled for this project. It can be seen that both mechanisms have essentially no bias in simulating ([O3]-[NO]) after the first hour of the experiment, though they both tend to slightly overpredict NO oxidation rates in the first hour. The same is true for the SAPRC-99 simulations of the mixture experiments. On the other hand, the updated mechanism has a small positive average bias in simulating the mixture experiments, averaging about 20% for the first hour (only slightly greater than that for SAPRC-99), going down to about 6% by the end of the run. However, this bias is small compared to the overall variability of the fits, which are within 30% for most experiments for both mechanisms. Therefore, this slight positive bias for the updated mechanism in simulating the mixture runs may not be significant.
The reason for the slight positive bias in the simulations of ([O3]-[NO]) in the mixture runs, if significant, is uncertain. The results for the single compounds or individual mixtures do not clearly indicate a cause in terms of particular compounds or types of compounds. It is considered unlikely that the slightly increased positive bias is due to problems with chamber characterization, since the most important chamber characterization parameters, regarding radical sources and NOx offgasing, were re-adjusted for this version of the mechanism, and the other parameters were the same as used for SAPRC-99.
Indeed, if anything, Figure 5 and Figure 6 suggest that the parameters used with updated mechanism may be slightly biased towards being too unreactive in this regard. Of the rate constant updates made to the base mechanism, potentially the most important is the increase in the OH + NO2 reaction, which is a major radical termination process that is important in essentially all experiments. But the increase, by itself, should cause slower NO oxidation and O3 formation, which is opposite of the direction seen. On the other hand, if parameters in the mechanisms for the individual VOCs are adjusted to compensate for this change, it might cause increased reactivity in simulations of experiments that are more sensitive to these parameters than the OH + NO2 rate constant. As indicated below, some uncertain mechanistic parameters (primarily nitrate yields in peroxy + NO reactions or yields of photoreactive aromatic products) had to be re-adjusted for the updated mechanism to fit results of reactivity and single VOC - NOx experiments. This may need to be investigated.
Evaluation Experiments for Individual VOCs
The major mechanism evaluation dataset consisted of the >1200 experiments carried out to evaluate mechanisms of almost 130 individual compounds and mixtures. These compounds or mixtures are listed on Table 23, along with an indication of the number and types of experiments for each, and references to the figure or figures in Appendix C where the results of the evaluation are presented. Table 23 also indicates whether any uncertain parameters were adjusted in the mechanisms as a result of this evaluation, and gives codes and comments concerning the overall quality of the fits, which are described

Figure 5.	Distribution of ([O3]-[NO]) model errors for the radical source characterization experiments.

Figure 6.	Distribution of O3 model errors for the NOx offgasing characterization experiments

Figure 7.	Distributions of ([O3]-[NO]) model errors for all of the single VOC - NOx and mixture - NOx experiments used in the mechanism evaluation.

Table 23.	Summary of mechanism evaluation results using chamber experiments for individual compounds and mixtures.
Compound or Mixture
                                 No. Runs [a]
                                 Fig. No. [b]
                                O3-NO Fits [c]
                                    Adj [d]
                                   Note [e]

                                    Single
                                     Rct'y
                                    Single
                                     Rct'y
                                     Rate
                                      Max

                Single Compounds (or simple isomeric mixtures)
Carbon monoxide

                                      13

                                       1
                                      ok
                                      ok

Ethane

                                       7

                                       2
                                      ok
                                      ok

Propane

                                       3

                                       2
                                      ok

N-Butane

                                      10

                                       3
                                      ok
                                      ok

N-Hexane

                                       3

                                       4
                                      ok
                                      ok

N-Octane

                                      13

                                       5
                                      ok
                                      ok

N-Dodecane

                                       9

                                       6
                                      ok
                                      +1

N-Tetradecane

                                       8

                                       7
                                      ok
                                      +1

N-Pentadecane

                                       2

                                       8
                                      ok
                                      +1

N-C16

                                       5

                                       8
                                      ok
                                      +1

Isobutane

                                       4

                                       9
                                      ok

2,2,4-Trimethyl pentane

                                       2

                                       9
                                      ok

                                       1
2,6-Dimethyl octane

                                       5

                                       9
                                      ok
                                      ok

2-Methyl nonane

                                       5

                                      10
                                      ok
                                      +1

3,4-Diethyl hexane

                                       6

                                      10
                                      ok
                                      +1

Cyclohexane

                                       6

                                      11
                                      ok
                                      ok

Hexyl cyclohexane

                                       6

                                      11
                                      ok
                                      ok

Octyl cyclohexane

                                       7

                                      12
                                      ok
                                      ok

Ethene
                                      49
                                       4
                                      13
                                      14
                                      ok
                                      ok
                                      Or

Propene
                                      190
                                      10
                                      15
                                      16
                                      ok
                                      ok
                                      Or

1-Butene
                                       6

                                      17

                                      ok
                                      ok
                                      Or

1-Hexene
                                       3

                                      17

                                      -2
                                      -2
                                      Or

Isobutene
                                       2
                                       3
                                      18
                                      19
                                      ok

Trans-2-butene
                                       6
                                       9
                                      18
                                      19
                                      ok
                                      ok

Isoprene
                                      28
                                      10
                                      20
                                      21
                                      ok
                                      ok

3-carene
                                       4

                                      22

                                      -1
                                      -1

-Pinene
                                       6
                                       4
                                      22
                                      23
                                      ok
                                      ok
                                    Or, yN

-Pinene
                                       6
                                       2
                                      22
                                      23
                                      ok
                                     note
                                    Or, yN
                                       2
d-Limonene
                                       7
                                     3 [f]
                                      22
                                      23
                                      ok
                                      ok

Sabinene
                                       3

                                      22

                                      ok
                                      ok

Cyclohexene

                                       1

                                      24
                                      ok
                                      ok

Styrene

                                       6

                                      25
                                      ok
                                      ok

Benzene
                                       9
                                       4
                                      25
                                      27
                                     note
                                      ok
                                      yP
                                      3,4
Toluene
                                      60
                                       6
                                      28
                                      30
                                     note
                                      ok
                                      yP
                                     4,5,6
Ethyl benzene
                                       8
                                       3
                                      29
                                      30
                                      ok
                                      ok
                                      yP

m-Xylene
                                      66
                                      17
                                      31