scholarly journals On the similarities and differences between the products of oxidation of hydrocarbons under simulated atmospheric conditions and cool-flames

2020 ◽  
Author(s):  
Roland Benoit ◽  
Nesrine Belhadj ◽  
Maxence Lailliau ◽  
Philippe Dagaut
Keyword(s):  
Atmospheric Chemistry ◽  
High Resolution Mass Spectrometry ◽  
Direct Injection ◽  
Oxidation Products ◽  
Peroxy Radicals ◽  
Atmospheric Conditions ◽  
Combustion Chemistry ◽  
Stirred Reactor ◽  
Oxidation Of Hydrocarbons ◽  
Reacting Mixtures

Abstract. Whereas the kinetics of oxidation of limonene has been extensively studied and mechanisms for its oxidation by OH and/or ozone have been proposed, more studies are required for better understanding its oxidation pathways. The oxidation of limonene-oxygen-nitrogen mixtures was studied using a jet-stirred reactor at elevated temperature and atmospheric pressure. Samples of the reacting mixtures were collected and analyzed by high resolution mass spectrometry (Orbitrap) after direct injection or after separation by reverse-phase ultra-high-pressure liquid chromatography and soft ionization by (+/−) HESI and (+/−) APCI. The results indicate that among the 1138 detected products, many oxygenates found in earlier studies of limonene oxidation by OH and/or ozone are also produced under the present conditions. Other highly oxygenated products and oligomers were also detected in the present work. The results are discussed in terms of reaction pathways involving the initial formation of peroxy radicals, isomerization reactions yielding keto-hydroperoxides and other oxygenated intermediates and products up to C25H32O17. The possible occurrence of the Waddington mechanism and of the Korcek mechanism are also discussed. The present work demonstrates similarities between the oxidation products and oxidation pathways of limonene under simulated atmospheric conditions and in those encountered during the self-ignition of hydrocarbons at low temperatures, which should stimulate future interactions between communities of atmospheric chemistry and combustion chemistry to improve current chemical models.

scholarly journals Autoxidation of terpenes, a common pathway in tropospheric and low temperature combustion conditions: the case of limonene and α-pinene

2021 ◽  
Author(s):  
Roland Benoit ◽  
Nesrine Belhadj ◽  
Maxence Lailliau ◽  
Philippe Dagaut
Keyword(s):  
Mass Spectrometry ◽  
Low Temperature ◽  
Atmospheric Chemistry ◽  
Atmospheric Pressure ◽  
High Resolution Mass Spectrometry ◽  
Atmospheric Pressure Chemical Ionization ◽  
Oxidation Products ◽  
Low Temperature Combustion ◽  
Atmospheric Conditions ◽  
Temperature Combustion

Abstract. The oxidation of monoterpenes under atmospheric conditions has been the subject of numerous studies. They were motivated by the formation of oxidized organic molecules (OOM) which, due to their low vapor pressure, contribute to the formation of secondary organic aerosols (SOA). Among the different reaction mechanisms proposed for the formation of these oxidized chemical compounds, it appears that the autoxidation mechanism, involving successive events of H-migration and O2 addition, common to both low-temperature combustion and atmospheric conditions, is leading to the formation of highly oxidized molecules (HOM). In atmospheric chemistry, the importance of autoxidation compared to other oxidation pathways has been the topic of numerous studies. Conversely, in combustion, autoxidation under cool flame conditions is the main oxidation process commonly taken into account. An analysis of oxidation products detected in both conditions was performed, using the present combustion data and literature data from tropospheric oxidation studies, to investigate possible similarities in terms of observed chemical formulae of products. To carry out this study, we chose two terpenes, α-pinene and limonene (C10H16), among the most abundant biogenic components in the atmosphere, and considered in many previous studies. Also, these two isomers were selected for the diversity of their reaction sites (exo- and endo- carbon-carbon double bonds). We built an experimental database consisting of literature atmospheric oxidation data and presently obtained combustion data for the oxidation of the two selected terpenes. In order to probe the effects of the type of ionization used in mass spectrometry analyses on the detection of oxidation products, we used heated electrospray ionization (HESI) and atmospheric pressure chemical ionization (APCI), in positive and negative modes. The oxidation of limonene-oxygen-nitrogen and α-pinene-oxygen-nitrogen mixtures was performed using a jet-stirred reactor at elevated temperature (590 K), a residence time of 2 s, and atmospheric pressure. Samples of the reacting mixtures were collected in acetonitrile and analyzed by high-resolution mass spectrometry (Orbitrap Q-Exactive) after direct injection and soft ionization, i.e. (+/−) HESI and (+/−) APCI. This work shows a surprisingly similar set of chemical formulae of products, including oligomers, formed in cool flames and under simulated atmospheric conditions. Data analysis showed that a non-negligible subset of chemical formulae is common to all experiments independently of experimental parameters. Finally, this study indicates that more than 40 % of the detected chemical formulae in this full dataset can be ascribed to an autoxidation mechanism.

scholarly journals Rapid formation of isoprene photo-oxidation products observed in Amazonia

2009 ◽  
Vol 9 (3) ◽  
pp. 13629-13653 ◽  
Author(s):  
T. Karl ◽  
A. Guenther ◽  
A. Turnipseed ◽  
P. Artaxo ◽  
S. Martin
Keyword(s):  
Atmospheric Chemistry ◽  
Global Climate ◽  
Oxidative Capacity ◽  
Oxidation Products ◽  
Lower Atmosphere ◽  
Peroxy Radicals ◽  
Aerosol Formation ◽  
Photo Oxidation ◽  
Voc Oxidation ◽  
Rapid Formation

Abstract. Isoprene represents the single most important reactive hydrocarbon for atmospheric chemistry in the tropical atmosphere. It plays a central role in global and regional atmospheric chemistry and possible climate feedbacks. Photo-oxidation of primary hydrocarbons (e.g. isoprene) leads to the formation of oxygenated VOCs (OVOCs). The evolution of these intermediates affects the oxidative capacity of the atmosphere (by reacting with OH) and can contribute to secondary aerosol formation, a poorly understood process. An accurate and quantitative understanding of VOC oxidation processes is needed for model simulations of regional air quality and global climate. Based on field measurements conducted during the Amazonian aerosol characterization experiment (AMAZE-08) we show that the production of certain OVOCs (e.g. hydroxyacetone) from isoprene photo-oxidation in the lower atmosphere is significantly underpredicted by standard chemistry schemes. A recently suggested novel pathway for isoprene peroxy radicals could explain the observed discrepancy and reconcile the rapid formation of these VOCs. Furthermore, if generalized our observations suggest that prompt photochemical formation of OVOCs and other uncertainties in VOC oxidation schemes could result in substantial underestimates of modelled OH reactivity that could explain a major fraction of the missing OH sink over forests which has previously been attributed to a missing source of primary biogenic VOCs.

Photooxidation and ozonolysis of Δ3-carene and its oxidation product caronaldehyde in the atmospheric simulation chamber SAPHIR

2021 ◽  
Author(s):  
Luisa Hantschke ◽  
Anna Novelli ◽  
Birger Bohn ◽  
Changmin Cho ◽  
David Reimer ◽  
...  
Keyword(s):  
Oxidation Product ◽  
Boreal Forests ◽  
Oxidation Products ◽  
Organic Nitrate ◽  
Organic Nitrates ◽  
Peroxy Radicals ◽  
Atmospheric Conditions ◽  
Oxidation Reactions ◽  
Reaction Rate Constants ◽  
Simulation Chamber

<p>Of the total global annual monoterpene emissions, Δ<sup>3</sup>-carene contributes 4.5 %, making it the 7<sup>th</sup> most abundant monoterpene worldwide. As it is primarily emitted by pine trees, Δ<sup>3</sup>-carene can regionally gain in importance, for example in boreal forests and Mediterranean regions.  Oxidation products of monoterpenes such as organic nitrates and aldehydes are known to impact the formation of secondary pollutants such as ozone and particles, so understanding their atmospheric formation and fate is crucial.</p><p>The photooxidation and ozonolysis of Δ<sup>3</sup>-carene and the photooxidation and photolysis of its main daytime photooxidation product caronaldehyde were investigated in the atmospheric simulation chamber SAPHIR. Oxidation reactions were studied under atmospheric conditions with high (> 8 ppbv) and low (< 2 ppbv) NOx concentrations. Reaction rate constants of the reaction of Δ<sup>3</sup>-carene with OH and O<sub>3</sub>, and of the reaction of caronaldehyde with OH as well as photolysis frequencies of caronaldehyde were determined. Production and destruction rates of the sum of hydroxyl and peroxy radicals (ROx = OH+HO2+RO2) were analysed to determine if there were unaccounted production and loss processes of radicals in the oxidation of Δ<sup>3</sup>-carene. The yield of Δ<sup>3</sup>-carene’s oxidation product caronaldehyde was determined from measured timeseries from OH photooxidation and ozonolysis experiments. Additionally, the OH yield from ozonolysis of Δ<sup>3</sup>-carene was determined.</p><p>Organic nitrate (RONO<sub>2</sub>) yields of the reaction of RO<sub>2</sub> + NO, from RO<sub>2</sub> produced from the reactions of Δ<sup>3</sup>-carene and caronaldehyde with OH were determined by analyzing the reactive nitrogen species (NOy) in the chamber.</p>

scholarly journals OH and HO<sub>2</sub> radical chemistry in a midlatitude forest: Measurements and model comparisons

2019 ◽  
Author(s):  
Michelle L. Lew ◽  
Pamela S. Rickly ◽  
Brandon P. Bottorff ◽  
Sofia Sklaveniti ◽  
Thierry Léonardis ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Global Climate ◽  
Oxidation Products ◽  
Chemical Mechanism ◽  
Ozone Production ◽  
Peroxy Radicals ◽  
Mixing Ratios ◽  
Photolysis Rates ◽  
Model Predictions ◽  
Ho2 Radical

Abstract. Reactions of the hydroxyl (OH) and peroxy radicals (HO2 and RO2) play a central role in the chemistry of the atmosphere. In addition to controlling the lifetimes of many trace gases important to issues of global climate change, OH radical reactions initiate the oxidation of volatile organic compounds (VOCs) which can lead to the production of ozone and secondary organic aerosols in the atmosphere. Previous measurements of these radicals in forest environments characterized by high mixing ratios of isoprene and low mixing ratios of nitrogen oxides (NOx) have shown serious discrepancies with modeled concentrations. These results bring into question our understanding of the atmospheric chemistry of isoprene and other biogenic VOCs under low NOx conditions. During the summer of 2015, OH and HO2 radical concentrations as well as total OH reactivity were measured using Laser-Induced Fluorescence - Fluorescence Assay by Gas Expansion (LIF-FAGE) techniques as part of the Indiana Radical, Reactivity and Ozone Production Intercomparison (IRRONIC). This campaign took place in a forested area near the Indiana University, Bloomington campus characterized by high mixing ratios of isoprene and low mixing ratios of NOx. Supporting measurements of photolysis rates, VOCs, NOx, and other species were used to constrain a zero-dimensional box model based on the Regional Atmospheric Chemistry Mechanism (RACM2) and the Master Chemical Mechanism (MCM). Using an OH chemical scavenger technique, the study revealed the presence of an interference with the LIF-FAGE measurements of OH that increased with both ambient concentrations of ozone and temperature. Subtraction of the interference resulted in measured OH concentrations that were in better agreement with model predictions, although the model still underestimated the measured concentrations, likely due to an underestimation of the concentration of NO at this site. Measurements of HO2 radical concentrations during the campaign included a fraction of isoprene-based peroxy radicals (HO2* = HO2 + αRO2) and were found to agree with model predictions. On average, the measured reactivity was consistent with that calculated from measured OH sinks to within 20 %, with modeled oxidation products accounting for the missing reactivity, although significant missing reactivity (approximately 40 % of the total measured reactivity) was observed on some days.

scholarly journals Rapid formation of isoprene photo-oxidation products observed in Amazonia

2009 ◽  
Vol 9 (20) ◽  
pp. 7753-7767 ◽  
Author(s):  
T. Karl ◽  
A. Guenther ◽  
A. Turnipseed ◽  
G. Tyndall ◽  
P. Artaxo ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Global Climate ◽  
Field Measurements ◽  
Oxidative Capacity ◽  
Oxidation Products ◽  
Lower Atmosphere ◽  
Peroxy Radicals ◽  
Aerosol Formation ◽  
Photo Oxidation ◽  
Voc Oxidation

Abstract. Isoprene represents the single most important reactive hydrocarbon for atmospheric chemistry in the tropical atmosphere. It plays a central role in global and regional atmospheric chemistry and possible climate feedbacks. Photo-oxidation of primary hydrocarbons (e.g. isoprene) leads to the formation of oxygenated VOCs (OVOCs). The evolution of these intermediates affects the oxidative capacity of the atmosphere (by reacting with OH) and can contribute to secondary aerosol formation, a poorly understood process. An accurate and quantitative understanding of VOC oxidation processes is needed for model simulations of regional air quality and global climate. Based on field measurements conducted during the Amazonian Aerosol Characterization Experiment (AMAZE-08) we show that the production of certain OVOCs (e.g. hydroxyacetone) from isoprene photo-oxidation in the lower atmosphere is significantly underpredicted by standard chemistry schemes. Recently reported fast secondary production could explain 50% of the observed discrepancy with the remaining part possibly produced via a novel primary production channel, which has been proposed theoretically. The observations of OVOCs are also used to test a recently proposed HOx recycling mechanism via degradation of isoprene peroxy radicals. If generalized our observations suggest that prompt photochemical formation of OVOCs and other uncertainties in VOC oxidation schemes could result in uncertainties of modelled OH reactivity, potentially explaining a fraction of the missing OH sink over forests which has previously been largely attributed to a missing source of primary biogenic VOCs.

scholarly journals Atmospheric photooxidation and ozonolysis of Δ<sup>3</sup>-carene and 3-caronaldehyde: rate constants and product yields

2021 ◽  
Vol 21 (16) ◽  
pp. 12665-12685
Author(s):  
Luisa Hantschke ◽  
Anna Novelli ◽  
Birger Bohn ◽  
Changmin Cho ◽  
David Reimer ◽  
...  
Keyword(s):  
Rate Constants ◽  
Oxidation Products ◽  
Organic Nitrate ◽  
Effective Quantum Yield ◽  
Peroxy Radicals ◽  
Atmospheric Conditions ◽  
Mixing Ratios ◽  
Photolysis Frequency ◽  
First Time ◽  
Good Agreement

Abstract. The oxidation of Δ3-carene and one of its main oxidation products, caronaldehyde, by the OH radical and O3 was investigated in the atmospheric simulation chamber SAPHIR under atmospheric conditions for NOx mixing ratios below 2 ppbv. Within this study, the rate constants of the reaction of Δ3-carene with OH and O3 and of the reaction of caronaldehyde with OH were determined to be (8.0±0.5)×10-11 cm3 s−1 at 304 K, (4.4±0.2)×10-17 cm3 s−1 at 300 K and (4.6±1.6)×10-11 cm3 s−1 at 300 K, in agreement with previously published values. The yields of caronaldehyde from the reaction of OH and ozone with Δ3-carene were determined to be 0.30±0.05 and 0.06±0.02, respectively. Both values are in reasonably good agreement with reported literature values. An organic nitrate (RONO2) yield from the reaction of NO with RO2 derived from Δ3-carene of 0.25±0.04 was determined from the analysis of the reactive nitrogen species (NOy) in the SAPHIR chamber. The RONO2 yield of the reaction of NO with RO2 derived from the reaction of caronaldehyde with OH was found to be 0.10±0.02. The organic nitrate yields of Δ3-carene and caronaldehyde oxidation with OH are reported here for the first time in the gas phase. An OH yield of 0.65±0.10 was determined from the ozonolysis of Δ3-carene. Calculations of production and destruction rates of the sum of hydroxyl and peroxy radicals (ROx=OH+HO2+RO2) demonstrated that there were no unaccounted production or loss processes of radicals in the oxidation of Δ3-carene for conditions of the chamber experiments. In an OH-free experiment with added OH scavenger, the photolysis frequency of caronaldehyde was obtained from its photolytical decay. The experimental photolysis frequency was a factor of 7 higher than the value calculated from the measured solar actinic flux density, an absorption cross section from the literature and an assumed effective quantum yield of unity for photodissociation.

scholarly journals Atmospheric photooxidation and ozonolysis of Δ<sup>3</sup>-carene and 3-caronaldehyde: Rate constants and product yields

2021 ◽  
Author(s):  
Luisa Lamberta Hantschke ◽  
Anna Novelli ◽  
Birger Bohn ◽  
Changmin Cho ◽  
David Reimer ◽  
...  
Keyword(s):  
Rate Constants ◽  
Reactive Nitrogen Species ◽  
Oxidation Products ◽  
Organic Nitrate ◽  
Effective Quantum Yield ◽  
Peroxy Radicals ◽  
Atmospheric Conditions ◽  
Mixing Ratios ◽  
Photolysis Frequency ◽  
First Time

Abstract. The oxidation of Δ3-carene and one of its main oxidation products, caronaldehyde, by the OH radical and O3 was investigated in the atmospheric simulation chamber SAPHIR under atmospheric conditions for NOx mixing ratios below 2 ppbv. Within this study, the rate constants of the reaction of Δ3-carene with OH and O3, and of the reaction of caronaldehyde with OH were determined to be (8.0 ± 0.5) × 10−11 cm3 s−1 at 304 K, (4.4 ± 0.2) × 10−17 cm3 s−1 at 300 K and (4.6 ± 1.6) × 10−11 cm3 s−1 at 300 K, respectively, in agreement with previously published values. The yields of caronaldehyde from the reaction of OH and ozone with Δ3-carene were determined to be (0.30 ± 0.05) and (0.06 ± 0.02), respectively. Both values are in reasonably well agreement with reported literature values. An organic nitrate (RONO2) yield from the reaction of NO with RO2 derived from Δ3-carene of (0.25 ± 0.04) was determined from the analysis of the reactive nitrogen species (NOy) in the SAPHIR chamber. The RONO2 yield of the reaction of NO with RO2 derived from the reaction of caronaldehyde with OH was found to be (0.10 ± 0.02). The organic nitrate yields of Δ3-carene and caronaldehyde oxidation with OH are reported here for the first time in the gas phase. An OH yield of (0.65 ± 0.10) was determined from the ozonolysis of Δ3-carene. Calculations of production and destruction rates of the sum of hydroxyl and peroxy radicals (ROx = OH+HO2+RO2) demonstrated that there were no unaccounted production or loss processes of radicals in the oxidation of Δ3-carene for conditions of the the chamber experiments. In an OH free experiment with added OH scavenger, the photolysis frequency of caronaldehyde was obtained from its photolytical decay. The experimental photolysis frequency was a factor of 7 higher than the value calculated from the measured solar acintic flux density, an absorption cross section from the literature and an assumed effective quantum yield of unity for photodissociation.

Mechanisms of Reactions of the RO Radicals

2015 ◽  
Author(s):  
Jack G. Calvert ◽  
John J. Orlando ◽  
William R. Stockwell ◽  
Timothy J. Wallington
Keyword(s):  
Carbonyl Compound ◽  
Atmospheric Chemistry ◽  
Carbon Chain ◽  
Oxidation Products ◽  
Rate Coefficients ◽  
Radical Reactions ◽  
Atmospheric Conditions ◽  
Alkoxy Radical ◽  
Unimolecular Decomposition ◽  
Alkoxy Radicals

The atmospheric chemistry of alkoxy radicals determines the first-generation oxidation products of organic compounds in the atmosphere. There are three competing fates for alkoxy radicals: reaction with molecular oxygen (O2), isomerization, and decomposition (Atkinson and Arey, 2003b; Devolder, 2003; Orlando et al., 2003b; Calvert et al., 2008). Reaction with O2 preserves the carbon chain of the parent alkane and results in the production of a carbonyl compound and HO2. Unimolecular decomposition usually results in the formation of an alkyl radical and a carbonyl compound with a shortening of the carbon chain. Unimolecular isomerization usually leads to multifunctional oxidation products (e.g., 1,4-hydroxycarbonyls and 1,4-hydroxynitrates) and a preservation of the carbon chain. These potentially competing pathways are illustrated in Figure VI-A-1 for the 2-pentoxy radical: Absolute rate coefficients for these processes have been obtained for only a few of the smaller alkoxy radicals. For example, rate coefficients have been firmly established only over a range of temperatures for reaction of a subset of the C1–C6 alkoxy radicals with O2; dissociation rate coefficients have only been directly measured for ethoxy, 2-propoxy, 2-butoxy, and tert-butoxy radicals (Balla et al., 1985; Blitz et al., 1999; Caralp et al., 1999; Devolder et al., 1999; Fittschen et al., 1999, 2000; Falgayrac et al., 2004); and no direct measurement of isomerization rates have been reported to date. A large portion of the database describing the atmospheric behavior of alkoxy radicals has been built up primarily from two sources: (1) environmental chamber experiments, where end-product distributions observed under atmospheric conditions have been used to infer relative rates of competing alkoxy radical reactions (e.g., Carter et al., 1976; Cox et al., 1981; Niki et al., 1981a; Eberhard et al., 1995; Aschmann et al., 1997; Orlando et al., 2000a; Cassanelli et al., 2006); and (2) from theoretical methodologies that lend themselves well to the study of unimolecular processes (e.g., Somnitz and Zellner, 2000a, 2000b, 2000c; Mereau et al., 2000a, 2000b; Fittschen et al., 2000; Lin and Ho, 2002; Mereau et al., 2003; Davis and Francisco, 2011). An overview of these three classes of competing alkoxy radical reactions (reaction with O2, unimolecular decomposition, and isomerization) is given in this section.

scholarly journals <i>α</i>-Pinene Nitrates: synthesis, yields and atmospheric chemistry

2011 ◽  
Vol 11 (2) ◽  
pp. 6845-6874
Author(s):  
S. X. Ma ◽  
J. D. Rindelaub ◽  
K. M. McAvey ◽  
P. D. Gagare ◽  
B. A. Nault ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Organic Aerosol ◽  
Reaction Chamber ◽  
Oxidation Products ◽  
Ozone Production ◽  
Organic Nitrate ◽  
Peroxy Radicals ◽  
Nitrate Precursor ◽  
Volatile Organic ◽  
Major Oxidation

Abstract. The biogenic volatile organic compound α-pinene is one of the dominant monoterpenes emitted to the Earth's atmosphere at an estimated rate of ~50 Tg yr−1. Its atmospheric oxidation products in the presence of NO can lead to ozone production, as well as production of secondary organic aerosol (SOA). The major oxidation pathway of α-pinene is reaction with OH, which in the presence of NO can form either α-pinene nitrates or convert NO to NO2, which can photolyze to form ozone. In this work, we successfully synthesized four α-pinene hydroxy nitrates through three different routes, and have identified the 4 individual isomers in α-pinene/OH/NO reaction chamber experiments. From the experiments, we determined their individual production yields, estimated the total RONO2 yield, and calculated the relative branching ratios of the nitrate precursor peroxy radicals (RO2). The combined yield of the four α-pinene nitrates was found to be 13.0 (±0.7) % at atmospheric pressure and 296 K, and the total organic nitrate yield was estimated to be 0.19 (+0.10/−0.06). We also determined the OH rate constants for two of the isomers, and have calculated their overall atmospheric lifetimes, which range between 22 and 38 h.

scholarly journals <i>α</i>-Pinene nitrates: synthesis, yields and atmospheric chemistry

2011 ◽  
Vol 11 (13) ◽  
pp. 6337-6347 ◽  
Author(s):  
S. X. Ma ◽  
J. D. Rindelaub ◽  
K. M. McAvey ◽  
P. D. Gagare ◽  
B. A. Nault ◽  
...  
Keyword(s):  
Atmospheric Chemistry ◽  
Organic Aerosol ◽  
Reaction Chamber ◽  
Oxidation Products ◽  
Ozone Production ◽  
Organic Nitrate ◽  
Peroxy Radicals ◽  
Nitrate Precursor ◽  
Volatile Organic ◽  
Major Oxidation

Abstract. The biogenic volatile organic compound α-pinene is one of the dominant monoterpenes emitted to the Earth's atmosphere at an estimated rate of ~50 Tg C yr−1. Its atmospheric oxidation products in the presence of NO can lead to ozone production, as well as production of secondary organic aerosol (SOA). The major oxidation pathway of α-pinene is reaction with OH, which in the presence of NO can form either α-pinene nitrates or convert NO to NO2, which can photolyze to form ozone. In this work, we successfully synthesized four α-pinene hydroxy nitrates through three different routes, and have identified these 4 individual isomers in α-pinene/OH/NO reaction chamber experiments. From the experiments, we determined their individual production yields, estimated the total RONO2 yield, and calculated the relative branching ratios of the nitrate precursor peroxy radicals (RO2). The combined yield of the four α-pinene nitrates was found to be 0.130 (±0.035) at atmospheric pressure and 296 K, and the total organic nitrate yield was estimated to be 0.19 (+0.10/−0.06). We also determined the OH rate constants for two of the isomers, and have calculated their overall atmospheric lifetimes, which range between 22 and 38 h.

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