The Importance of Peroxy Radical Hydrogen-Shift Reactions in Atmospheric Isoprene Oxidation

2019 ◽  
Vol 123 (4) ◽  
pp. 920-932 ◽  
Author(s):  
Kristian H. Møller ◽  
Kelvin H. Bates ◽  
Henrik G. Kjaergaard
Keyword(s):  
Peroxy Radical ◽  
Hydrogen Shift ◽  
Isoprene Oxidation

scholarly journals Cost-Effective Implementation of Multiconformer Transition State Theory for Peroxy Radical Hydrogen Shift Reactions

2016 ◽  
Vol 120 (51) ◽  
pp. 10072-10087 ◽  
Author(s):  
Kristian H. Møller ◽  
Rasmus V. Otkjær ◽  
Noora Hyttinen ◽  
Theo Kurtén ◽  
Henrik G. Kjaergaard
Keyword(s):  
Transition State ◽  
Transition State Theory ◽  
Peroxy Radical ◽  
Cost Effective ◽  
State Theory ◽  
Hydrogen Shift ◽  
Effective Implementation

scholarly journals Multigenerational Theoretical Study of Isoprene Peroxy Radical 1–5-Hydrogen Shift Reactions that Regenerate HOx Radicals and Produce Highly Oxidized Molecules

2018 ◽  
Vol 123 (4) ◽  
pp. 906-919 ◽  
Author(s):  
Ivan R. Piletic ◽  
Richard Howell ◽  
Libero J. Bartolotti ◽  
Tadeusz E. Kleindienst ◽  
Surender M. Kaushik ◽  
...  
Keyword(s):  
Theoretical Study ◽  
Peroxy Radical ◽  
Hydrogen Shift

scholarly journals Formaldehyde production from isoprene oxidation across NO<sub><i>x</i></sub> regimes

2016 ◽  
Vol 16 (4) ◽  
pp. 2597-2610 ◽  
Author(s):  
G. M. Wolfe ◽  
J. Kaiser ◽  
T. F. Hanisco ◽  
F. N. Keutsch ◽  
J. A. de Gouw ◽  
...  
Keyword(s):  
Transport Model ◽  
Model Simulation ◽  
Nonlinear Function ◽  
Peroxy Radical ◽  
Fold Increase ◽  
Oxidation Products ◽  
Box Model ◽  
Chemical Transport Model ◽  
Mixing Ratios ◽  
Isoprene Oxidation

Abstract. The chemical link between isoprene and formaldehyde (HCHO) is a strong, nonlinear function of NOx (i.e., NO + NO2). This relationship is a linchpin for top-down isoprene emission inventory verification from orbital HCHO column observations. It is also a benchmark for overall photochemical mechanism performance with regard to VOC oxidation. Using a comprehensive suite of airborne in situ observations over the southeast US, we quantify HCHO production across the urban–rural spectrum. Analysis of isoprene and its major first-generation oxidation products allows us to define both a "prompt" yield of HCHO (molecules of HCHO produced per molecule of freshly emitted isoprene) and the background HCHO mixing ratio (from oxidation of longer-lived hydrocarbons). Over the range of observed NOx values (roughly 0.1–2 ppbv), the prompt yield increases by a factor of 3 (from 0.3 to 0.9 ppbv ppbv−1), while background HCHO increases by a factor of 2 (from 1.6 to 3.3 ppbv). We apply the same method to evaluate the performance of both a global chemical transport model (AM3) and a measurement-constrained 0-D steady-state box model. Both models reproduce the NOx dependence of the prompt HCHO yield, illustrating that models with updated isoprene oxidation mechanisms can adequately capture the link between HCHO and recent isoprene emissions. On the other hand, both models underestimate background HCHO mixing ratios, suggesting missing HCHO precursors, inadequate representation of later-generation isoprene degradation and/or underestimated hydroxyl radical concentrations. Detailed process rates from the box model simulation demonstrate a 3-fold increase in HCHO production across the range of observed NOx values, driven by a 100 % increase in OH and a 40 % increase in branching of organic peroxy radical reactions to produce HCHO.

scholarly journals Glyoxal yield from isoprene oxidation and relation to formaldehyde: chemical mechanism, constraints from SENEX aircraft observations, and interpretation of OMI satellite data

2016 ◽  
Author(s):  
Christopher Chan Miller ◽  
Daniel J. Jacob ◽  
Eloise A. Marais ◽  
Karen Yu ◽  
Katherine R. Travis ◽  
...  
Keyword(s):  
Transport Model ◽  
Peroxy Radical ◽  
Satellite Observations ◽  
Chemical Mechanism ◽  
Chemical Transport Model ◽  
Formation Pathway ◽  
Isoprene Emission ◽  
Aircraft Observations ◽  
Isoprene Oxidation ◽  
Southeast Us

Abstract. Glyoxal (CHOCHO) is produced in the atmosphere by oxidation of volatile organic compounds (VOCs). It is measurable from space by solar backscatter along with formaldehyde (HCHO), another oxidation product of VOCs. Isoprene emitted by vegetation is the dominant source of CHOCHO and HCHO in most of the world. We use aircraft observations of CHOCHO and HCHO from the SENEX campaign over the Southeast US in summer 2013 to better understand the time-dependent yields from isoprene oxidation, their dependences on nitrogen oxides (NOx ≡ NO + NO2), the behaviour of the CHOCHO-HCHO relationship, the quality of OMI satellite observations, and the implications for using satellite CHOCHO observations as constraints on isoprene emission. We simulate the SENEX and OMI observations with the GEOS-Chem chemical transport model featuring a new chemical mechanism for CHOCHO formation from isoprene. The mechanism includes prompt CHOCHO formation under low-NOx conditions following the isomerization of the isoprene peroxy radical (ISOPO2). The SENEX observations provide support for this prompt CHOCHO formation pathway, and are generally consistent with the GEOS-Chem mechanism. Boundary layer CHOCHO and HCHO are strongly correlated in the observations and the model, with some departure under low-NOx conditions due to prompt CHOCHO formation. SENEX vertical profiles indicate a free tropospheric CHOCHO background that is absent from the model. The OMI CHOCHO data provide some support for this free tropospheric background and show Southeast US enhancements consistent with the isoprene source but a factor of 2 too low. Part of this OMI bias is due to excessive surface reflectivities assumed in the retrieval. The OMI CHOCHO and HCHO seasonal data over the Southeast US are tightly correlated and provide redundant proxies of isoprene emission. Higher temporal resolution in future geostationary satellite observations may enable detection of the prompt CHOCHO production under low-NOx conditions apparent in the SENEX data.

scholarly journals Formaldehyde production from isoprene oxidation across NO<sub><i>x</i></sub> regimes

2015 ◽  
Vol 15 (21) ◽  
pp. 31587-31620 ◽  
Author(s):  
G. M. Wolfe ◽  
J. Kaiser ◽  
T. F. Hanisco ◽  
F. N. Keutsch ◽  
J. A. de Gouw ◽  
...  
Keyword(s):  
First Generation ◽  
Transport Model ◽  
Peroxy Radical ◽  
Oxidation Products ◽  
Peroxy Radicals ◽  
Chemical Transport Model ◽  
Mixing Ratios ◽  
Urban Rural ◽  
Isoprene Oxidation ◽  
Southeast Us

Abstract. The chemical link between isoprene and formaldehyde (HCHO) is a strong, non-linear function of NOx (= NO + NO2). This relationship is a linchpin for top-down isoprene emission inventory verification from orbital HCHO column observations. It is also a benchmark for overall mechanism performance with regard to VOC oxidation. Using a comprehensive suite of airborne in situ observations over the Southeast US, we quantify HCHO production across the urban-rural spectrum. Analysis of isoprene and its major first-generation oxidation products allows us to define both a "prompt" yield of HCHO (molecules of HCHO produced per molecule of freshly-emitted isoprene) and the background HCHO mixing ratio (from oxidation of longer-lived hydrocarbons). Over the range of observed NOx values (roughly 0.1–2 ppbv), the prompt yield increases by a factor of 3 (from 0.3 to 0.9 ppbv ppbv−1), while background HCHO increases by more than a factor of 2 (from 1.5 to 3.3 ppbv). We apply the same method to evaluate the performance of both a global chemical transport model (AM3) and a measurement-constrained 0-D chemical box model. Both models reproduce the NOx dependence of the prompt HCHO yield, illustrating that models with updated isoprene oxidation mechanisms can adequately capture the link between HCHO and recent isoprene emissions. On the other hand, both models under-estimate background HCHO mixing ratios, suggesting missing HCHO precursors, inadequate representation of later-generation isoprene degradation and/or under-estimated hydroxyl radical concentrations. Moreover, we find that the total organic peroxy radical production rate is essentially independent of NOx, as the increase in oxidizing capacity with NOx is largely balanced by a decrease in VOC reactivity. Thus, the observed NOx dependence of HCHO mainly reflects the changing fate of organic peroxy radicals.

scholarly journals Stereoselectivity in Atmospheric Autoxidation

2020 ◽  
Author(s):  
Kristian H. Møller ◽  
Eric Praske ◽  
Lu Xu ◽  
John D. Crounse ◽  
Kelvin H. Bates ◽  
...  
Keyword(s):  
Transport Model ◽  
Theoretical Calculations ◽  
Peroxy Radical ◽  
Rate Coefficients ◽  
Large Set ◽  
Atmospheric Conditions ◽  
Hydrogen Shift ◽  
The Difference ◽  
Shift Reaction ◽  
High Level

&lt;p&gt;The importance of peroxy radical hydrogen shift reactions in the atmosphere has gained acceptance in recent years. Recent theoretical calculations have suggested that these can be stereoselective i.e. that different stereoisomers react with significantly different rate coefficients. Combining experiments (GC-CIMS) with high-level calculations (MC-TST), we show that two hydroxy peroxy radical diastereomers formed in the oxidation of crotonaldehyde have rate coefficients for their peroxy radical hydrogen shift reactions that differ by more than a factor of 10. The difference is large enough that under urban atmospheric conditions, one diastereomer would react primarily by the unimolecular H-shift, while the other would react mainly by bimolecular reactions leading to diastreomeric enhancement of the products.&lt;/p&gt;&lt;p&gt;For a large set of peroxy radical hydrogen shift reactions in the oxidation of isoprene, the stereospecific rate coefficients are calculated to assess the global importance of this phenomenon in the atmosphere. &amp;#160;These calculated rate coefficients are implemented into the global chemistry-transport model GEOS-Chem to model the effect. Results show that more than 30 % of all isoprene molecules emitted undergo a minimum of one peroxy radical hydrogen shift reaction during its oxidation. Furthermore, the results show that the different diastereomers may react with rate coefficients differing by up to almost a factor of 1000, highlighting how important it is to account for this phenomenon.&lt;/p&gt;

scholarly journals Glyoxal yield from isoprene oxidation and relation to formaldehyde: chemical mechanism, constraints from SENEX aircraft observations, and interpretation of OMI satellite data

2017 ◽  
Vol 17 (14) ◽  
pp. 8725-8738 ◽  
Author(s):  
Christopher Chan Miller ◽  
Daniel J. Jacob ◽  
Eloise A. Marais ◽  
Karen Yu ◽  
Katherine R. Travis ◽  
...  
Keyword(s):  
Transport Model ◽  
Peroxy Radical ◽  
Satellite Observations ◽  
Chemical Mechanism ◽  
Chemical Transport Model ◽  
Formation Pathway ◽  
Earth Observing System ◽  
Aircraft Observations ◽  
Isoprene Oxidation ◽  
Southeast Us

Abstract. Glyoxal (CHOCHO) is produced in the atmosphere by the oxidation of volatile organic compounds (VOCs). Like formaldehyde (HCHO), another VOC oxidation product, it is measurable from space by solar backscatter. Isoprene emitted by vegetation is the dominant source of CHOCHO and HCHO in most of the world. We use aircraft observations of CHOCHO and HCHO from the SENEX campaign over the southeast US in summer 2013 to better understand the CHOCHO time-dependent yield from isoprene oxidation, its dependence on nitrogen oxides (NOx  ≡  NO + NO2), the behavior of the CHOCHO–HCHO relationship, the quality of OMI CHOCHO satellite observations, and the implications for using CHOCHO observations from space as constraints on isoprene emissions. We simulate the SENEX and OMI observations with the Goddard Earth Observing System chemical transport model (GEOS-Chem) featuring a new chemical mechanism for CHOCHO formation from isoprene. The mechanism includes prompt CHOCHO formation under low-NOx conditions following the isomerization of the isoprene peroxy radical (ISOPO2). The SENEX observations provide support for this prompt CHOCHO formation pathway, and are generally consistent with the GEOS-Chem mechanism. Boundary layer CHOCHO and HCHO are strongly correlated in the observations and the model, with some departure under low-NOx conditions due to prompt CHOCHO formation. SENEX vertical profiles indicate a free-tropospheric CHOCHO background that is absent from the model. The OMI CHOCHO data provide some support for this free-tropospheric background and show southeast US enhancements consistent with the isoprene source but a factor of 2 too low. Part of this OMI bias is due to excessive surface reflectivities assumed in the retrieval. The OMI CHOCHO and HCHO seasonal data over the southeast US are tightly correlated and provide redundant proxies of isoprene emissions. Higher temporal resolution in future geostationary satellite observations may enable detection of the prompt CHOCHO production under low-NOx conditions apparent in the SENEX data.

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