scholarly journals Dependence between the photochemical age of light aromatic hydrocarbons and the carbon isotope ratios of atmospheric nitrophenols

2019 ◽  
Vol 19 (8) ◽  
pp. 5495-5509
Author(s):  
Marina Saccon ◽  
Anna Kornilova ◽  
Lin Huang ◽  
Jochen Rudolph
Keyword(s):  
Carbon Isotope ◽  
Organic Compounds ◽  
Mechanistic Model ◽  
Isotope Effects ◽  
Isotope Ratios ◽  
Kinetic Isotope Effects ◽  
Laboratory Studies ◽  
Carbon Isotope Ratios ◽  
Kinetic Isotope ◽  
Volatile Organic

Abstract. Concepts were developed to establish relationships between the stable carbon isotope ratios of nitrophenols in the atmosphere and the photochemical processing of their precursors, light aromatic volatile organic compounds. These concepts were based on the assumption that nitrophenols are formed dominantly from the photo-oxidation of aromatic volatile organic compounds (VOCs). A mass balance model as well as various scenarios based on the proposed mechanism of nitrophenol formation were formulated and applied to derive the time-integrated exposure of the precursors to processing by OH radicals (∫[OH]dt) from ambient observations made between 2009 and 2012 in Toronto, Canada. The mechanistic model included the possibility of isotopic fractionation during intermediate steps, rather than only during the initial reaction step. This model takes kinetic isotope effects for the reaction of the precursor VOC with the hydroxyl radical and their respective rate constants into account, as well as carbon isotope ratio source signatures. While many of these values are known, there are some, such as the kinetic isotope effects of reactions of first- and second-generation products, which are unknown. These values were predicted in this study based on basic principles and published laboratory measurements of kinetic carbon isotope effects and were applied to the mechanistic model. Due to the uncertainty of the estimates based on general principles, three scenarios were used with different values for isotope effects that were not known from laboratory studies. Comparison of the dependence between nitrophenol carbon isotope ratios and ∫[OH]dt with published results of laboratory studies and ambient observations was used to narrow the range of plausible scenarios for the mechanistic model. The results also suggests that mass-balance-based models do not adequately describe the dependence between nitrophenol carbon isotope ratios and ∫[OH]dt.

scholarly journals Dependence between the Photochemical Age of Light Aromatic Hydrocarbons and the Carbon Isotope Ratios of Atmospheric Nitrophenols

2018 ◽  
Author(s):  
Marina Saccon ◽  
Anna Kornilova ◽  
Lin Huang ◽  
Jochen Rudolph
Keyword(s):  
Mass Balance ◽  
Carbon Isotope ◽  
Mechanistic Model ◽  
Isotope Effects ◽  
Isotope Ratios ◽  
Kinetic Isotope Effects ◽  
Oh Radicals ◽  
Laboratory Studies ◽  
Carbon Isotope Ratios ◽  
Kinetic Isotope

Abstract. Concepts were developed to establish relationships between the stable carbon isotope ratios of nitrophenols in the atmosphere and photochemical processing of their precursors, light aromatic volatile organic compounds. The concepts are based on the assumption that nitrophenols are formed dominantly from the photo-oxidation of aromatic VOC. A mass balance model as well as various scenarios based on the proposed mechanism of nitrophenol formation were formulated and applied to derive the time integrated exposure of the precursors to processing by OH-radicals (∫[OH]dt) from ambient observations taken between 2009 and 2012 in Toronto, Canada. The mechanistic model included the possibility of isotopic fractionation during intermediate steps, rather than during the initial reaction step alone. This model included knowledge of kinetic isotope effects of the precursor VOC with the hydroxyl radical and their respective rate constants, as well as isotope ratio source signatures. While many of these values are known, there were some, such as the kinetic isotope effects of reactions of the intermediate compounds, which were unknown. These values were predicted based on basic principles and published laboratory measurements of normal kinetic carbon isotope effects and were applied to the mechanistic models. Due to uncertainty of the estimates based on general principles three scenarios were used with different values for isotope effect that were not known from laboratory studies. Comparison of the dependence between nitrophenol carbon isotope ratios and ∫[OH]dt with published results of laboratory studies and ambient observations was used to narrow the range of plausible scenarios of the mechanistic model and to eliminate the mass balance based model as useful formulation of a the dependence between nitrophenol carbon isotope ratios and ∫[OH]dt.

scholarly journals Stable carbon isotope ratios of ambient aromatic volatile organic compounds

2016 ◽  
Vol 16 (18) ◽  
pp. 11755-11772 ◽  
Author(s):  
Anna Kornilova ◽  
Lin Huang ◽  
Marina Saccon ◽  
Jochen Rudolph
Keyword(s):  
Carbon Isotope ◽  
Organic Compounds ◽  
Stable Carbon Isotope ◽  
Isotope Ratios ◽  
Stable Carbon ◽  
Stable Carbon Isotope Ratios ◽  
Carbon Isotope Ratios ◽  
Volatile Organic ◽  
Photochemical Processing ◽  
Concentration Ratios

Abstract. Measurements of mixing ratios and stable carbon isotope ratios of aromatic volatile organic compounds (VOC) in the atmosphere were made in Toronto (Canada) in 2009 and 2010. Consistent with the kinetic isotope effect for reactions of aromatic VOC with the OH radical the observed stable carbon isotope ratios are on average significantly heavier than the isotope ratios of their emissions. The change of carbon isotope ratio between emission and observation is used to determine the extent of photochemical processing (photochemical age,  ∫ [OH]dt) of the different VOC. It is found that  ∫ [OH]dt of different VOC depends strongly on the VOC reactivity. This demonstrates that for this set of observations the assumption of a uniform  ∫ [OH]dt for VOC with different reactivity is not justified and that the observed values for  ∫ [OH]dt are the result of mixing of VOC from air masses with different values for  ∫ [OH]dt. Based on comparison between carbon isotope ratios and VOC concentration ratios it is also found that the varying influence of sources with different VOC emission ratios has a larger impact on VOC concentration ratios than photochemical processing. It is concluded that for this data set the use of VOC concentration ratios to determine  ∫ [OH]dt would result in values for  ∫ [OH]dt inconsistent with carbon isotope ratios and that the concept of a uniform  ∫ [OH]dt for an air mass has to be replaced by the concept of individual values of an average  ∫ [OH]dt for VOC with different reactivity.

scholarly journals Stable carbon isotope ratios of ambient volatile organic compounds

2016 ◽  
Author(s):  
Anna Kornilova ◽  
Lin Huang ◽  
Marina Saccon ◽  
Jochen Rudolph
Keyword(s):  
Carbon Isotope ◽  
Organic Compounds ◽  
Stable Carbon Isotope ◽  
Isotope Ratios ◽  
Stable Carbon ◽  
Stable Carbon Isotope Ratios ◽  
Carbon Isotope Ratios ◽  
Volatile Organic ◽  
Photochemical Processing ◽  
Concentration Ratios

Abstract. Measurements of mixing ratios and stable carbon isotope ratios of aromatic volatile organic compounds (VOC) in the atmosphere were made in Toronto (Canada) in 2009 and 2010. Consistent with the kinetic isotope effect for reactions of aromatic VOC with the OH-radical the observed stable carbon isotope ratios are on average significantly heavier than the isotope ratios of their emissions. The change of carbon isotope ratio between emission and observation is used to determine the extent of photochemical processing (photochemical age, ∫[OH]dt) of the different VOC. It is found that ∫[OH]dt of different VOC depends strongly on the VOC reactivity. This demonstrates that for this set of observations the assumption of a uniform ∫[OH]dt for VOC with different reactivity is not justified and that the observed values for ∫[OH]dt are the result of mixing of VOC from air masses with different values for ∫[OH]dt. Based on comparison between carbon isotope ratios and VOC concentration ratios it is also found that varying influence of sources with different VOC emission ratios has a larger impact on VOC concentration ratios than photochemical processing. It is concluded that for this data set the use of VOC concentration ratios to determine ∫[OH]dt would result in values for ∫[OH]dt inconsistent with carbon isotope ratios and that the concept of a uniform ∫[OH]dt for an air mass has to be replaced by the concept of individual values of an average ∫[OH]dt for VOC with different reactivity.

The photo-Wallach rearrangement. Heavy-atom kinetic isotope effects and mechanism

1986 ◽  
Vol 64 (6) ◽  
pp. 1108-1115 ◽  
Author(s):  
Henry J. Shine ◽  
Witold Subotkowski ◽  
Ewa Gruszecka
Keyword(s):  
Activation Barrier ◽  
Isotope Effects ◽  
Heavy Atom ◽  
Isotope Ratios ◽  
Kinetic Isotope Effects ◽  
Isotopic Ratios ◽  
Kinetic Isotope

The photo-rearrangement of mixtures of azoxybenzene 4 and, successively, [15N, 15N′]4, [18O]4, and [2-14C]4 were carried out. Kinetic isotope effects (KIE) were calculated from measurements of isotopic ratios in both recovered 4 and the product, 2-hydroxyazobenzene (6). Analogous rearrangement of mixtures of 2,2′-azoxynaphthalene (8) with [15N, 15N′]8 and [1,1′-13C2]8 were carried out and KIE were calculated from isotope ratios in the product. The results (particularly the lack of nitrogen KIE) collectively indicate that if an oxadiazole-like intermediate is involved in these rearrangements, an activation barrier exists in its formation rather than its decomposition.

Reactions of Muonium with simple biochemical solutes in water and micelles

1991 ◽  
Vol 69 (8) ◽  
pp. 1252-1258 ◽  
Author(s):  
Mary V. Barnabas ◽  
David C. Walker
Keyword(s):  
Reaction Mechanism ◽  
Organic Compounds ◽  
Rate Constants ◽  
Enhancement Factor ◽  
Isotope Effects ◽  
Ph Dependence ◽  
Kinetic Isotope Effects ◽  
Natural State ◽  
Sugar Phosphate ◽  
Kinetic Isotope

Rate constants are reported for the reaction of muonium atoms in water with some 36 organic compounds, many of interest in biology. These kM values range from < l05 to 7 × 1010 M−1 s−1, according to the type of reaction involved, with the sugar–phosphate backbones of nucleic acids being at the low end and their bases at the high end. They are compared with corresponding published H-atom data (kH), where possible, and show kinetic-isotope-effects ranging over five orders of magnitude. Since all kH data were obtained at pH = 1, while kM values refer to pH ~ 7 of the natural state, the pH-dependence of kM was examined in representative cases. The changes found result from protonation of the solute rather than a changed reactivity of Mu on being converted to MuH+. On localizing the solutes in the hydrophobic phase of dilute micelles, the reactivity of Mu was again measured (kM(mic)). The resulting "enhancement" factor was considered in terms of: the reaction mechanism, its dependence on microenvironment (solvation), and the concentrating effect of mutual confinement to small sections of a biphasal system. Key words: kinetic isotope effects, muonium, biochemicals, micelles.

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