Importance of isomerization reactions for OH radical regeneration from the photo-oxidation of isoprene  investigated in the atmospheric simulation chamber SAPHIR

Novelli, Anna; Vereecken, Luc; Bohn, Birger; Dorn, Hans-Peter; Gkatzelis, Georgios I.; Hofzumahaus, A.; Holland, F.; Reimer, David; Rohrer, Franz; Rosanka, Simon; Taraborrelli, Domenico; Tillmann, Ralf; Wegener, Robert; Yu, Zeping; Kiendler‐Scharr, Astrid; Wahner, Andreas; Fuchs, Hendrik

doi:10.5194/acp-20-3333-2020

Cited by 64 publications

(99 citation statements)

References 88 publications

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“…A large correction is required to account for this effect. Novelli et al (2020) also point out that additional OH regeneration occurs by isomerization of isoprene peroxy radicals, which increases the non-photolytical regeneration rate to about 50 % of the OH loss rate. With a P d /(P hv +P d ) ratio of 0.5, the predicted decrease of the CMR transmission is still a factor of 1.5.…”

Section: Discussionmentioning

confidence: 92%

“…Here, OH reactivities up to 70 s -1 were reported (Sinha et al, 2008), while the dark OH production from the reaction of HO 2 with NO can be small compared to the total OH production rate. Novelli et al (2020) estimated the chemical regeneration of OH by Reaction R4 to be 10% in an isoprene emitting forest at 10 pptv NO, which according to the steady-state condition (Equation 20) would correspond to a P d /(P hv +P d ) ratio of 0.1. For such conditions, the kinetic model for the CMR predicts a decrease of the OH transmission by a factor of 2.5 -3 at k OH = 70 s -1 .…”

Section: Discussionmentioning

confidence: 99%

“…Similar good agreement was found in previous OH intercomparisons between the DOAS and FZJ-LIF, when the LIF instrument used wavelength modulation only and data 30 were corrected for the known ozone interference. These intercomparisons were performed in photochemical degradation experiments in SAPHIR for a wide range of VOCs and chemical conditions (Schlosser et al, 2007;Schlosser et al, 2009;Fuchs et al, 2012;Novelli et al, 2018;Rolletter et al, 2019;Novelli et al, 2020), and in a field campaign in relatively clean air in North East Germany (Hofzumahaus et al, 1998).…”

Section: Oh Measurement Comparisonmentioning

confidence: 99%

“…Theoretical (Peeters et al, 2009;da Silva et al, 2010;Peeters and Müller, 2010;Peeters et al, 2014;Wang et al, 2018;Møller et al, 2019) and experimental studies (Crounse et al, 2011;Berndt, 2012;Crounse et al, 2012;Wolfe et al, 2012;Fuchs et al, 2013;Fuchs et al, 2014;Teng et al, 2017;Berndt et al, 2019;Novelli et al, 2020) have 25 hypothesized and found significant regeneration of OH radicals from unimolecular reactions of organic peroxy radicals (RO 2 , R = organic group) originating from the oxidation of biogenic VOCs such as isoprene, methacrolein, and methyl vinyl ketone (MVK). Although the inclusion of these new reaction paths in atmospheric chemical models can increase the predicted concentration of OH considerably, for example by a factor of three over tropical forests (Novelli et al, 2020), it is often not enough to explain the high OH concentrations observed in field experiments in areas characterized by high 30 isoprene emissions (Stone et al, 2011;Lu et al, 2012;Stone et al, 2012;Fuchs et al, 2013;Lu et al, 2013;Feiner et al, 2016;Lew et al, 2020).…”

Section: Introductionmentioning

confidence: 99%

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Characterization of a chemical modulation reactor (CMR) for the measurement of atmospheric concentrations of hydroxyl radicals with a laser-induced fluorescence instrument

Cho¹,

Hofzumahaus²,

Fuchs³

et al. 2020

Preprint

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Abstract. Precise and accurate hydroxyl radical (OH) measurements are essential to investigate how trace gases are oxidized and transformed in the troposphere and how secondary pollutants like ozone (O3) are formed. Laser induced fluorescence (LIF) is a widely used technique for the measurement of ambient OH radicals and was used for the majority of field campaigns and chamber experiments. Recently, most LIF instruments in use for atmospheric measurements of OH radicals introduced chemical modulation to separate the ambient OH radical concentration from possible interferences by chemically removing ambient OH radicals before they enter the detection cell. In this study, we describe the application, characterization, and validation of a chemical modulation reactor (CMR) applied to the Forschungszentrum Jülich LIF (FZJ-LIF) instrument in use at the atmospheric simulation chamber SAPHIR. Besides dedicated experiments in synthetic air, the new technique was extensively tested during the year-round Jülich Atmospheric Chemistry Project (JULIAC) campaign, in which ambient air was continuously flowed into the SAPHIR chamber. It allowed performing OH measurement comparisons with Differential Optical Absorption Spectroscopy (DOAS) and investigation of interferences in a large variety of chemical and meteorological conditions. A good agreement was obtained in the LIF DOAS intercomparison within instrumental accuracies (18 % for LIF, 6.5 % for DOAS) which confirms that the new chemical modulation system of the FZJ-LIF instrument is suitable for measurement of interference-free OH concentrations. Known interferences from O3 + H2O and the nitrate radical (NO3) were quantified with the CMR in synthetic air in the chamber and found to be 3.0 × 105 cm-3 and 0.6 × 105 cm-3, respectively, for typical ambient air condition (O3 = 50 ppbv, H2O = 1 %, NO3 = 10 pptv). The interferences measured in ambient air during the JULIAC campaign in summer season had the median diurnal variation of the interference with a maximum daytime value of 0.9 × 106 cm-3 and a minimum nighttime value of 0.4 × 106 cm-3. The highest interference of 2 × 106 cm-3 occurred in a heat wave from 22–29 August, when the air temperature and ozone increased to 40 °C and 100 ppbv, respectively. All observed interferences could be fully explained by the known O3 + H2O interference, which is routinely corrected in FZJ-LIF measurements when no chemical modulation is applied. No evidence for unexplained interference was found during the JULIAC campaign. A kinetic chemical model of the chemical modulation reactor was developed and applied to estimate the possible perturbation of the OH transmission and scavenging efficiency by reactive atmospheric trace gases. These can remove OH by gas phase reactions in the reactor, or produce OH by non-photolytical reactions, most importantly by the reaction of ambient HO2 with NO. The interfering processes become relevant at high atmospheric OH reactivities. For the conditions of the JULIAC campaign with OH reactivities below 20 s-1, the influence on the determination of ambient OH concentrations was small (on average: 2 %). However, in environments with high OH reactivities, such as in a rain forest or megacity, the expected perturbation in the currently used chemical modulation reactor could be large (more than a factor of 2) and would need careful analysis and correction. This implies that chemical modulation, which was developed to eliminate interferences in ambient OH measurements, itself can be subject to interferences that depend on ambient atmospheric conditions.

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Section: Discussionmentioning

confidence: 92%

Section: Discussionmentioning

confidence: 99%

Section: Oh Measurement Comparisonmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Characterization of a chemical modulation reactor (CMR) for the measurement of atmospheric concentrations of hydroxyl radicals with a laser-induced fluorescence instrument

Cho¹,

Hofzumahaus²,

Fuchs³

et al. 2020

Preprint

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“…These reactions play a role, for example, in the photooxidation of isoprene (e.g. Fuchs et al, 2013;Peeters et al, 2014;Novelli et al, 2020) and methacrolein (Crounse et al, 2012;Fuchs et al, 2014), where H-shift reactions in RO 2 species lead to decomposition into a radical (OH or HO 2 ) and a carbonyl compound. In general, rate coefficients of H-shift reactions are strongly enhanced by the presence of functional groups such as carbonyl groups, and can reach values in the order of 0.1 s -1 at room temperature (Crounse et al, 2013;Otkjaer et al, 2018).…”

Section: Photooxidation By Ohmentioning

confidence: 99%

Photooxidation of pinonaldehyde at ambient conditions investigated in the atmospheric simulation chamber SAPHIR

Rolletter¹,

Blocquet²,

Kaminski³

et al. 2020

Preprint

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Abstract. The photooxidation of pinonaldehyde, one product of the &#945;-pinene degradation, was investigated in the atmospheric simulation chamber SAPHIR under natural sunlight at low NO concentrations (<&#8201;0.2&#8201;ppbv) with and without an added hydroxyl radical (OH) scavenger. With scavenger, pinonaldehyde was exclusively removed by photolysis, whereas without scavenger, the degradation was dominated by reaction with OH. In both cases, the observed rate of pinonaldehyde consumption was faster than predicted by an explicit chemical model, the Master Chemical Mechanism (MCM version 3.3.1). In the case with OH scavenger, the observed photolytic decay can be reproduced by the model, if an experimentally determined photolysis frequency is used instead of the parameterization in the MCM. A good fit is obtained, when the photolysis frequency is calculated from the measured solar actinic flux spectrum, absorption cross-sections published by Hallquist et al. (1997), and an effective quantum yield of 0.9. The resulting photolysis frequency is 3.5 times faster than the parameterization in the MCM. When pinonaldehyde is mainly removed by reaction with OH, the observed OH and hydroperoxy radical (HO2) concentrations are underestimated in the model by a factor of 2. Using measured HO2 as a model constraint brings modeled and measured OH concentrations into agreement. This suggests that the chemical mechanism includes all relevant OH producing reactions, but is missing a source for HO2. The missing HO2 source strength of (0.8 to 1.5)&#8201;ppbv&#8201;h&#8722;1 is similar to the rate of the pinonaldehyde consumption of up to 2.5&#8201;ppbv&#8201;h&#8722;1. When the model is constrained by HO2 concentrations and the experimentally derived photolysis frequency, the pinonaldehyde decay is well represented. The photolysis of pinonaldehyde yields 0.18&#8201;&#177;&#8201;0.20 formaldehyde molecules at NO concentrations of less than 200&#8201;pptv, but no significant acetone formation is observed. When pinonaldehyde is also oxidized by OH under low NO conditions (maximum 80&#8201;pptv), yields of acetone and formaldehyde increase over the course of the experiment from 0.2 to 0.3 and from 0.15 to 0.45, respectively. Fantechi et al. (2002) proposed a degradation mechanism based on quantum-chemical calculations, which is considerably more complex than the MCM scheme and contains additional reaction pathways and products. Implementing these modifications results in a closure of the model-measurement discrepancy for the products acetone and formaldehyde, when pinonaldehyde is degraded only by photolysis. In contrast, the underprediction of formed acetone and formaldehyde is worsened compared to model results by the MCM, when pinonaldehyde is mainly degraded in the reaction with OH. This shows that the current mechanisms lack acetone and formaldehyde sources for low NO conditions like in these experiments. Implementing the modifications suggested by Fantechi et al. (2002) does not improve the model-measurement agreement of OH and HO2.

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A Multiconformational Transition State Theory Approach to OH Tropospheric Degradation of Fluorotelomer Aldehydes

Viegas

2023

ChemPhysChem

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Experimental work on the OH‐initiated oxidation reactions of fluorotelomer aldehydes (FTALs) strongly suggests that the respective rate coefficients do not depend on the size of the CxF2x+1 fluoroalkyl chain. FTALs hence represent a challenging test to our multiconformer transition state theory (MC‐TST) protocol based on constrained transition state randomization (CTSR), since the calculated rate coefficients should not show significant variations with increasing values of . In this work we apply the MC‐TST/CTSR protocol to the cases and calculate both rate coefficients at 298.15 K with a value of cm3 molecule−1 s−1, practically coincident with the recommended experimental value of kexp= cm3 molecule−1 s−1. We also show that the use of tunneling corrections based on improved semiclassical TST is critical in obtaining Arrhenius‐Kooij curves with a correct behavior at lower temperatures.

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Importance of isomerization reactions for OH radical regeneration from the photo-oxidation of isoprene investigated in the atmospheric simulation chamber SAPHIR

Cited by 64 publications

References 88 publications

Characterization of a chemical modulation reactor (CMR) for the measurement of atmospheric concentrations of hydroxyl radicals with a laser-induced fluorescence instrument

Characterization of a chemical modulation reactor (CMR) for the measurement of atmospheric concentrations of hydroxyl radicals with a laser-induced fluorescence instrument

Photooxidation of pinonaldehyde at ambient conditions investigated in the atmospheric simulation chamber SAPHIR

A Multiconformational Transition State Theory Approach to OH Tropospheric Degradation of Fluorotelomer Aldehydes

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