scholarly journals Direct kinetic measurements and theoretical predictions of an isoprene-derived Criegee intermediate

2020 ◽  
Vol 117 (18) ◽  
pp. 9733-9740 ◽  
Author(s):  
Rebecca L. Caravan ◽  
Michael F. Vansco ◽  
Kendrew Au ◽  
M. Anwar H. Khan ◽  
Yu-Lin Li ◽  
...  
Keyword(s):  
Formic Acid ◽  
Transport Model ◽  
Thermal Conditions ◽  
Chem Phys ◽  
Kinetic Measurements ◽  
Atmospheric Species ◽  
Photoionization Mass Spectrometry ◽  
Criegee Intermediates ◽  
Atmospheric Processing ◽  
Theoretical Predictions

Isoprene has the highest emission into Earth’s atmosphere of any nonmethane hydrocarbon. Atmospheric processing of alkenes, including isoprene, via ozonolysis leads to the formation of zwitterionic reactive intermediates, known as Criegee intermediates (CIs). Direct studies have revealed that reactions involving simple CIs can significantly impact the tropospheric oxidizing capacity, enhance particulate formation, and degrade local air quality. Methyl vinyl ketone oxide (MVK-oxide) is a four-carbon, asymmetric, resonance-stabilized CI, produced with 21 to 23% yield from isoprene ozonolysis, yet its reactivity has not been directly studied. We present direct kinetic measurements of MVK-oxide reactions with key atmospheric species using absorption spectroscopy. Direct UV-Vis absorption spectra from two independent flow cell experiments overlap with the molecular beam UV-Vis-depletion spectra reported recently [M. F. Vansco, B. Marchetti, M. I. Lester, J. Chem. Phys. 149, 44309 (2018)] but suggest different conformer distributions under jet-cooled and thermal conditions. Comparison of the experimental lifetime herein with theory indicates only the syn-conformers are observed; anti-conformers are calculated to be removed much more rapidly via unimolecular decay. We observe experimentally and predict theoretically fast reaction of syn-MVK-oxide with SO2 and formic acid, similar to smaller alkyl-substituted CIs, and by contrast, slow removal in the presence of water. We determine products through complementary multiplexed photoionization mass spectrometry, observing SO3 and identifying organic hydroperoxide formation from reaction with SO2 and formic acid, respectively. The tropospheric implications of these reactions are evaluated using a global chemistry and transport model.

scholarly journals A large and ubiquitous source of atmospheric formic acid

2015 ◽  
Vol 15 (11) ◽  
pp. 6283-6304 ◽  
Author(s):  
D. B. Millet ◽  
M. Baasandorj ◽  
D. K. Farmer ◽  
J. A. Thornton ◽  
K. Baumann ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Formic Acid ◽  
Transport Model ◽  
Model Simulation ◽  
Vertical Gradient ◽  
Precipitation Chemistry ◽  
Chemical Production ◽  
Chemical Transport Model ◽  
Criegee Intermediates ◽  
Isoprene Oxidation

Abstract. Formic acid (HCOOH) is one of the most abundant acids in the atmosphere, with an important influence on precipitation chemistry and acidity. Here we employ a chemical transport model (GEOS-Chem CTM) to interpret recent airborne and ground-based measurements over the US Southeast in terms of the constraints they provide on HCOOH sources and sinks. Summertime boundary layer concentrations average several parts-per-billion, 2–3× larger than can be explained based on known production and loss pathways. This indicates one or more large missing HCOOH sources, and suggests either a key gap in current understanding of hydrocarbon oxidation or a large, unidentified, direct flux of HCOOH. Model-measurement comparisons implicate biogenic sources (e.g., isoprene oxidation) as the predominant HCOOH source. Resolving the unexplained boundary layer concentrations based (i) solely on isoprene oxidation would require a 3× increase in the model HCOOH yield, or (ii) solely on direct HCOOH emissions would require approximately a 25× increase in its biogenic flux. However, neither of these can explain the high HCOOH amounts seen in anthropogenic air masses and in the free troposphere. The overall indication is of a large biogenic source combined with ubiquitous chemical production of HCOOH across a range of precursors. Laboratory work is needed to better quantify the rates and mechanisms of carboxylic acid production from isoprene and other prevalent organics. Stabilized Criegee intermediates (SCIs) provide a large model source of HCOOH, while acetaldehyde tautomerization accounts for ~ 15% of the simulated global burden. Because carboxylic acids also react with SCIs and catalyze the reverse tautomerization reaction, HCOOH buffers against its own production by both of these pathways. Based on recent laboratory results, reaction between CH3O2 and OH could provide a major source of atmospheric HCOOH; however, including this chemistry degrades the model simulation of CH3OOH and NOx : CH3OOH. Developing better constraints on SCI and RO2 + OH chemistry is a high priority for future work. The model neither captures the large diurnal amplitude in HCOOH seen in surface air, nor its inverted vertical gradient at night. This implies a substantial bias in our current representation of deposition as modulated by boundary layer dynamics, and may indicate an HCOOH sink underestimate and thus an even larger missing source. A more robust treatment of surface deposition is a key need for improving simulations of HCOOH and related trace gases, and our understanding of their budgets.

scholarly journals A large and ubiquitous source of atmospheric formic acid

2015 ◽  
Vol 15 (4) ◽  
pp. 4537-4599 ◽  
Author(s):  
D. B. Millet ◽  
M. Baasandorj ◽  
D. K. Farmer ◽  
J. A. Thornton ◽  
K. Baumann ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Formic Acid ◽  
Transport Model ◽  
Model Simulation ◽  
Vertical Gradient ◽  
Precipitation Chemistry ◽  
Chemical Production ◽  
Chemical Transport Model ◽  
Criegee Intermediates ◽  
Isoprene Oxidation

Abstract. Formic acid (HCOOH) is one of the most abundant acids in the atmosphere, with an important influence on precipitation chemistry and acidity. Here we employ a chemical transport model (GEOS-Chem) to interpret recent airborne and ground-based measurements over the US Southeast in terms of the constraints they provide on HCOOH sources and sinks. Summertime boundary layer concentrations average several parts-per-billion, 2–3× larger than can be explained based on known production and loss pathways. This indicates one or more large missing HCOOH sources, and suggests either a key gap in current understanding of hydrocarbon oxidation or a large, unidentified, direct flux of HCOOH. Model-measurement comparisons implicate biogenic sources (e.g., isoprene oxidation) as the predominant HCOOH source. Resolving the unexplained boundary layer concentrations based: (i) solely on isoprene oxidation would require a 3× increase in the model HCOOH yield, or (ii) solely on direct HCOOH emissions would require approximately a 25× increase in its biogenic flux. However, neither of these can explain the high HCOOH amounts seen in anthropogenic air masses and in the free troposphere. The overall indication is of a large biogenic source combined with ubiquitous chemical production of HCOOH across a range of precursors. Laboratory work is needed to better quantify the rates and mechanisms of carboxylic acid production from isoprene and other prevalent organics. Stabilized Criegee intermediates (SCIs) provide a large model source of HCOOH, while acetaldehyde tautomerization accounts for ~ 15% of the simulated global burden. Because carboxylic acids also react with SCIs and catalyze the reverse tautomerization reaction, HCOOH buffers against its own production by both of these pathways. Based on recent laboratory results, reaction between CH3O2 and OH could provide a major source of atmospheric HCOOH; however, including this chemistry degrades the model simulation of CH3OOH and NOx:CH3OOH. Developing better constraints on SCI and RO2 + OH chemistry is a high priority for future work. The model does not capture the large diurnal amplitude in HCOOH seen in surface air, nor its inverted vertical gradient at night. This implies a substantial bias in our current representation of deposition as modulated by boundary layer dynamics, and may indicate an HCOOH sink underestimate and thus an even larger missing source. A more robust treatment of surface deposition is a key need for improving simulations of HCOOH and related trace gases, and our understanding of their budgets.

scholarly journals Functionalized Hydroperoxide Formation from the Reaction of Methacrolein-Oxide, an Isoprene-Derived Criegee Intermediate, with Formic Acid: Experiment and Theory

Molecules ◽  
2021 ◽  
Vol 26 (10) ◽  
pp. 3058
Author(s):  
Michael F. Vansco ◽  
Kristen Zuraski ◽  
Frank A. F. Winiberg ◽  
Kendrew Au ◽  
Nisalak Trongsiriwat ◽  
...  
Keyword(s):  
Formic Acid ◽  
Appearance Energy ◽  
Electronic Structure Calculations ◽  
Methyl Vinyl ◽  
Photoionization Mass Spectrometry ◽  
Hydroperoxide Formation ◽  
Reaction Proceeds ◽  
Theoretical Predictions ◽  
Structure Calculations ◽  
Rapid Appearance

Methacrolein oxide (MACR-oxide) is a four-carbon, resonance-stabilized Criegee intermediate produced from isoprene ozonolysis, yet its reactivity is not well understood. This study identifies the functionalized hydroperoxide species, 1‑hydroperoxy-2-methylallyl formate (HPMAF), generated from the reaction of MACR-oxide with formic acid using multiplexed photoionization mass spectrometry (MPIMS, 298 K = 25 °C, 10 torr = 13.3 hPa). Electronic structure calculations indicate the reaction proceeds via an energetically favorable 1,4-addition mechanism. The formation of HPMAF is observed by the rapid appearance of a fragment ion at m/z 99, consistent with the proposed mechanism and characteristic loss of HO2 upon photoionization of functional hydroperoxides. The identification of HPMAF is confirmed by comparison of the appearance energy of the fragment ion with theoretical predictions of its photoionization threshold. The results are compared to analogous studies on the reaction of formic acid with methyl vinyl ketone oxide (MVK-oxide), the other four-carbon Criegee intermediate in isoprene ozonolysis.

scholarly journals Light Cluster Production in Central Symmetric Heavy-Ion Reactions from Fermi to Gev Energies

Symmetry ◽  
2021 ◽  
Vol 13 (8) ◽  
pp. 1406
Author(s):  
Rémi Bougault ◽  
Bernard Borderie ◽  
Abdelouahad Chbihi ◽  
Quentin Fable ◽  
John David Frankland ◽  
...  
Keyword(s):  
Equation Of State ◽  
Transport Model ◽  
Heavy Ion ◽  
Production Mechanism ◽  
State Information ◽  
Heavy Ion Reactions ◽  
Nuclear Equation Of State ◽  
Theoretical Predictions ◽  
Bombarding Energy ◽  
Deuteron Production

Correlations and clustering are of great importance in the study of the Nuclear Equation of State. Information on these items/aspects can be obtained using heavy-ion reactions which are described by dynamical theories. We propose a dataset that will be useful for improving the description of light cluster production in transport model approaches. The dataset combines published and new data and is presented in a form that allows direct comparison of the experiment with theoretical predictions. The dataset is ranging in bombarding energy from 32 to 1930 A MeV. In constructing this dataset, we put in evidence the existence of a change in the light cluster production mechanism that corresponds to a peak in deuteron production.

scholarly journals Importance of secondary sources in the atmospheric budgets of formic and acetic acids

2010 ◽  
Vol 10 (10) ◽  
pp. 24435-24497 ◽  
Author(s):  
F. Paulot ◽  
D. Wunch ◽  
J. D. Crounse ◽  
G. C. Toon ◽  
D. B. Millet ◽  
...  
Keyword(s):  
Formic Acid ◽  
Carboxylic Acids ◽  
Transport Model ◽  
Negative Temperature ◽  
Photochemical Oxidation ◽  
Secondary Source ◽  
Chemical Transport Model ◽  
Wet And Dry Deposition ◽  
Secondary Sources ◽  
Acetic Acids

Abstract. We present a detailed budget of formic and acetic acids, two of the most abundant trace gases in the atmosphere. Our bottom-up estimate of the global source of formic and acetic acids are ~1200 and ~1400 Gmol/yr, dominated by photochemical oxidation of biogenic volatile organic compounds, in particular isoprene. Their sinks are dominated by wet and dry deposition. We use the GEOS-Chem chemical transport model to evaluate this budget against an extensive suite of measurements from ground, ship and satellite-based Fourier transform spectrometers, as well as from several aircraft campaigns over North America. The model captures the seasonality of formic and acetic acids well but generally underestimates their concentration, particularly in the Northern midlatitudes. We infer that the source of both carboxylic acids may be up to 50% greater than our estimate and report evidence for a long-lived missing secondary source of carboxylic acids that may be associated with the aging of organic aerosols. Vertical profiles of formic acid in the upper troposphere support a negative temperature dependence of the reaction between formic acid and the hydroxyl radical as suggested by several theoretical studies.

scholarly journals Kinetic studies of C1 and C2 Criegee intermediates with SO2 using laser flash photolysis coupled with photoionization mass spectrometry and time resolved UV absorption spectroscopy

2018 ◽  
Vol 20 (34) ◽  
pp. 22218-22227 ◽  
Author(s):  
N. U. M. Howes ◽  
Z. S. Mir ◽  
M. A. Blitz ◽  
S. Hardman ◽  
T. R. Lewis ◽  
...  
Keyword(s):  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Kinetic Studies ◽  
Laser Flash ◽  
Major Product ◽  
Time Resolved ◽  
Photoionization Mass Spectrometry ◽  
Criegee Intermediates ◽  
Wide Range ◽  
Kinetics Of

Kinetics of CH2OO + SO2 confirmed over a wide range of [SO2]. Acetaldehyde observed as a major product of the reaction of CH3CHOO + SO2.

scholarly journals Электрохимическое окисление муравьиной кислоты на поверхности анодно-модифицированного сплава Ag15Pd

2020 ◽  
Vol 22 (2) ◽  
pp. 204-210
Author(s):  
Евгения Валерьевна Бедова ◽  
Евгения Андреевна Тонких ◽  
Олег Александрович Козадеров
Keyword(s):  
New York ◽  
Fuel Cells ◽  
Formic Acid ◽  
Formic Acid Oxidation ◽  
Chem Phys ◽  
Acid Oxidation ◽  
Power Sources ◽  
Transient Techniques ◽  
Pore Size Distributions ◽  
Nanoporous Metals

Показано, что фазовое превращение палладия в собственную фазу при селективном растворении сплава Ag15Pd протекает в режиме мгновенной нуклеации и лимитируется поверхностной диффузией ад-атомов Pd к растущему трехмерному зародышу новой фазы. С применением нестационарных электрохимических методов установлены кинетические закономерности процесса электроокисления муравьиной кислоты на сплаве Ag15Pd, подвергнутом предварительному селективному растворению. Найдено, что процесс анодной деструкции НСООН в кислом сульфатном растворе протекает с более высокой скоростью на анодно-модифицированном сплаве Ag15Pd, поверхность которого морфологически развита и обогащена палладием в результате потенциостатическогоселективного растворения при закритических условиях поляризации. Процесс электроокисления НСООН является нестационарным, протекает в смешанно-кинетическом режиме и ускоряется с ростом анодного потенциала. С применением метода хроноамперометрии найдены кинетические токи анодного окисления муравьиной кислоты. Обнаружена корреляция между значением электрического заряда, пропущенного при предварительной анодной модификации сплава Ag15Pd и скоростью кинетической стадии электроокисления НСООН.         ЛИТЕРАТУРА 1. Бедова Е. В., Козадеров О. А. Кинетика электроокисления муравьиной кислоты на анодно-модифицированных серебряно-палладиевых сплавах. Электрохимическая энергетика. 2018;18(3): 141–154. DOI: https://doi.org/10.18500/1608-4039-2018-18-3-141-1542. Маршаков И. К, Введенский А. В., Кондрашин В. Ю., Боков Г. А. Анодное растворение и селективная коррозия сплавов. Воронеж: Изд-во Воронеж. гос. ун-та; 1988. 208 с.3. Encyclopedia of electrochemistry. Vol. 4. Corrosion and oxide fi lms. Eds. A. J. Bard, M. Stratmann, G. S. Frankel. Weinheim (Germany): Wiley-VCH; 2003. 755 p.4. Landolt D. Corrosion and Surface Chemistry of Metals. EPFL Press; 2007. 632 c.5. Кеше Г. Коррозия металлов. Физико-химические принципы и актуальные проблемы. М.: Металлургия; 1984. 400 с.6. Маршаков И. К. Термодинамика и коррозия сплавов. Воронеж: Изд-во Воронеж. гос. ун-та; 1983. 168 с.7. Козадеров О. А. Массоперенос, фазообразование и морфологическая нестабильность поверхностного слоя при селективном растворении гомогенных металлических сплавов: дис. ... докт. хим. наук. Воронеж; 2016. 361 с. Режим доступа: http://www.science.vsu.ru/disserinfo&cand=28978. Зарцын И. Д., Введенский А. В., Маршаков И. К. О неравновесности поверхностного слояпри анодном растворении гомогенных сплавов Электрохимия. 1994;30(4): 544–565. Режим доступа:https://www.elibrary.ru/item.asp?id=238281399. Зарцын И. Д., Введенский А. В., Маршаков И. К. О превращениях благородной компоненты при селективном растворении гомогенного сплава в активном состоянии. Защита металлов.1991;27(1): 3–12. Режим доступа: https://www.elibrary.ru/item.asp?id=2395144310. Зарцын И. Д., Введенский А. В., Маршаков И. К. Термодинамика неравновесных фазовыхпревращений при селективном растворении гомогенных бинарных сплавов Защита металлов.1991;27(6): 883–891. Режим доступа: https://www.elibrary.ru/item.asp?id=1271261511. Козадеров О. А., Введенский А. В. Массоперенос и фазообразование при анодном селективномрастворении гомогенных сплавов. Воронеж: Научная книга; 2014. 288 с.12. Liu W. B., Zhang S. C., Li N., Zheng J. W., An S. S., Xing Y. L. A general dealloying strategy tonanoporous intermetallics, nanoporous metals with bimodal, and unimodal pore size distributions Corro-sion Science. 2012;58: 133–138. DOI:  https://doi.org/10.1016/j.corsci.2012.01.02313. Hakamada M., Chino Y., Mabuchi M. Nanoporous surface fabricated on metal sheets by alloying/dealloying technique. Materials Letters. 2010;64(21):2341–2343. DOI: https://doi.org/10.1016/j.matlet.2010.07.04614. Weissmüller J., Newman R. C., Jin Hai-Jun, Hodge A. M. Nanoporous metals by alloy corrosion:Formation and mechanical properties. MRS Bull. 2009;34(8): 577–586. DOI: https://doi.org/10.1557/mrs2009.15715. Erlebacher J., Aziz M. J., Karma A., Dimitrov N., Sieradzki K. Evolution of nanoporosity in dealloying.Nature. 2001;410(6827): 450–453. DOI: https://doi.org/10.1038/3506852916. Wang Y., Wu B., Gao Y., Tang Y., Lu T., Xing W., Liu Ch. Kinetic study of formic acid oxidation on carbonsupported Pd electrocatalyst. Journal of Power Sources. 2009;192(2): 372–375. DOI: https://doi.org/10.1016/j.jpowsour.2009.03.02917. Rice C., Ha S., Masel R.I., Waszczuk P., Wieckowski A., Barnard T. Direct formic acid fuel cells. J.Power Sources. 2002;111(1): 83–89. DOI: https://doi.org/10.1016/S0378-7753(02)00271-918. Rice C. A., Wieckowski A. Electrocatalysis of formic acid oxidation. In: Shao M. (eds.) Electrocatalysisin Fuel Cells. Lecture Notes in Energy. London: Springer; 2013:9. 43–67. DOI: https://doi.org/10.1007/978-1-4471-4911-819. Jiang K., Zhang H., Zou Sh., Cai W. Electrocatalysis of formic acid on palladium and platinumsurfaces: from fundamental mechanisms to fuel cell applications. Phys. Chem. Chem. Phys. 2014;16. 20360–20376. DOI: https://doi.org/10.1039/C4CP03151B20. Хансен М., Андерко К. Структуры двойных сплавов: Справочник. М.: Металлургиздат; 1962;1.608 с.21. Исаев В. А. Электрохимическое фазообразование. Екатеринбург: УрО РАН; 2007. 123 с.22. MacDonald D. D. Transient techniques is electrochemistry. New York; London: Plenum Press; 1977.329 p. DOI: https://doi.org/10.1007/978-1-4613-4145-1

scholarly journals WOMBAT v1.0: A fully Bayesian global flux-inversion framework

2021 ◽  
Author(s):  
Andrew Zammit-Mangion ◽  
Michael Bertolacci ◽  
Jenny Fisher ◽  
Ann Stavert ◽  
Matthew L. Rigby ◽  
...  
Keyword(s):  
Transport Model ◽  
Atmospheric Transport ◽  
Trace Gases ◽  
Chem Phys ◽  
Remotely Sensed Data ◽  
Bayesian Hierarchical ◽  
Correlated Error ◽  
Out Of Sample ◽  
Fully Bayesian ◽  
Observing System Simulation Experiment

Abstract. WOMBAT (the WOllongong Methodology for Bayesian Assimilation of Trace-gases) is a fully Bayesian hierarchical statistical framework for flux inversion of trace gases from flask, in situ, and remotely sensed data. WOMBAT extends the conventional Bayesian-synthesis framework through the consideration of a correlated error term, the capacity for online bias correction, and the provision of uncertainty quantification on all unknowns that appear in the Bayesian statistical model. We show, in an observing system simulation experiment (OSSE), that these extensions are crucial when the data are indeed biased and have errors that are spatio-temporally correlated. Using the GEOS-Chem atmospheric transport model, we show that WOMBAT is able to obtain posterior means and variances on non-fossil-fuel CO2 fluxes from Orbiting Carbon Observatory-2 (OCO-2) data that are comparable to those from the Model Intercomparison Project (MIP) reported in Crowell et al. (2019, Atmos. Chem. Phys., vol. 19). We also find that WOMBAT's predictions of out-of-sample retrievals obtained from the Total Column Carbon Observing Network are, for the most part, more accurate than those made by the MIP participants.

scholarly journals Global emission estimates and radiative impact of C<sub>4</sub>F<sub>10</sub>, C<sub>5</sub>F<sub>12</sub>, C<sub>6</sub>F<sub>14</sub>, C<sub>7</sub>F<sub>16</sub> and C<sub>8</sub>F<sub>18</sub>

2012 ◽  
Vol 12 (5) ◽  
pp. 12987-13014 ◽  
Author(s):  
D. J. Ivy ◽  
M. Rigby ◽  
M. Baasandorj ◽  
J. B. Burkholder ◽  
R. G. Prinn
Keyword(s):  
Molecular Weight ◽  
High Molecular Weight ◽  
Transport Model ◽  
Emission Rates ◽  
Chemical Transport Model ◽  
Bottom Up ◽  
Radiative Efficiency ◽  
Atmospheric Species ◽  
Global Emission ◽  
Atmospheric Observations

Abstract. Global emission estimates based on new atmospheric observations are presented for the acylic high molecular weight perfluorocarbons (PFCs): decafluorobutane (C4F10), dodecafluoropentane (C5F12), tetradecafluorohexane (C6F14), hexadecafluoroheptane (C7F16) and octadecafluorooctane (C8F18). Emissions are estimated using a 3-dimensional chemical transport model and an inverse method that includes a growth constraint on emissions. The observations used in the inversion are based on newly measured archived air samples that cover a 39-yr period, from 1973 to 2011, and include 36 Northern Hemispheric and 46 Southern Hemispheric samples (Ivy et al., 2012). The derived emission estimates show that global emission rates were largest in the 1980s and 1990s for C4F10 and C5F12, and in the 1990s for C6F14,C7F16 and C8F18. After a subsequent decline, emissions have remained relatively stable, within 20%, for the last 5 yr. Bottom-up emission estimates are available from the Emission Database for Global Atmospheric Research version 4.2 (EDGARv4.2) for C4F10, C5F12, C6F14 and C7F16, and inventories of C4F10, C5F12 andC6F14 are reported to the United Nations' Framework Convention on Climate Change (UNFCCC) by Annex 1 countries that have ratified the Kyoto Protocol. The atmospheric measurement based emission estimates are 20 times larger than EDGARv4.2 for C4F10 and over three orders of magnitude for C5F12. The derived emission estimates for C6F14 largely agree with the bottom-up estimates from EDGARv4.2. Moreover, the C7F16 emission estimates are comparable to those of EDGARv4.2 at their peak in the 1990s, albeit significant underestimation for the other time periods. There are no bottom-up emission estimates for C8F18, thus the emission rates reported here are the first for C8F18. The reported inventories for C4F10, C5F12 and C6F14 to UNFCCC are five to ten times lower than those estimated in this study. In addition, we present measured infrared absorption spectra for C7F16 and C8F18, and estimate their radiative efficiencies and global warming potentials (GWPs). We find that C8F18's radiative efficiency is similar to trifluoromethyl sulfur pentafluoride's (SF5CF3) at 0.57 W m−2 ppb−1, which is the highest radiative efficiency of any measured atmospheric species. Using the 100-yr time horizon GWPs, the high molecular weight perfluorocarbons studied here contributed up to 15.4% of the total PFC emissions in CO2 equivalents in 1997 and 6% of the total PFC emissions in 2009.

scholarly journals Kinetics of dimethyl sulfide (DMS) reactions with isoprene-derived Criegee intermediates studied with direct UV absorption

2020 ◽  
Author(s):  
Mei-Tsan Kuo ◽  
Isabelle Weber ◽  
Christa Fittschen ◽  
Jim Jr-Min Lin
Keyword(s):  
Atmospheric Chemistry ◽  
Dimethyl Sulfide ◽  
Relative Rate ◽  
Chem Phys ◽  
High Reactivity ◽  
Rate Coefficients ◽  
Visible Absorption ◽  
Criegee Intermediates ◽  
The Individual ◽  
Kinetics Of

Abstract. Criegee intermediates (CIs) are formed in the ozonolysis of unsaturated hydrocarbons and play a role in atmospheric chemistry as a non-photolytic OH source or a strong oxidant. Using a relative rate method in an ozonolysis experiment, Newland et al. [Atmos. Chem. Phys., 15, 9521–9536, 2015] reported high reactivity of isoprene-derived Criegee intermediates towards dimethyl sulfide (DMS) relative to that towards SO2 with the ratio of the rate coefficients kDMS+CI / kSO2+CI = 3.5 ± 1.8. Here we reinvestigated the kinetics of DMS reactions with two major Criegee intermediates formed in isoprene ozonolysis, CH2OO and methyl vinyl ketone oxide (MVKO). The individual CI was prepared following reported photolytic method with suitable (diiodo) precursors in the presence of O2. The concentration of CH2OO or MVKO was monitored directly in real time through their intense UV-visible absorption. Our results indicate the reactions of DMS with CH2OO and MVKO are both very slow; the upper limits of the rate coefficients are 4 orders of magnitude smaller than that reported by Newland et al. These results suggest that the ozonolysis experiment could be complicated such that interpretation should be careful and these CIs would not oxidize atmospheric DMS at any substantial level.

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