Speciation of OH reactivity above the canopy of an isoprene-dominated forest

Kaiser, Jennifer; Skog, Kate; Baumann, Karsten; Bertman, S. B.; Brown, Steven; Brune, William H.; Crounse, J. D.; Gouw, J. A. de; Edgerton, Eric S.; Feiner, P. A.; Goldstein, Allen H.; Koss, A.; Misztal, Pawel K.; Nguyen, Tran B.; Olson, K. F.; Clair, Jason M. St.; Teng, Alexander P.; Toma, Shino; Wennberg, P. O.; Wild, R. J.; Zhang, L.; Keutsch, Frank N.

doi:10.5194/acp-16-9349-2016

Cited by 65 publications

(77 citation statements)

References 44 publications

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“…A detailed analysis of the OH reactivity budget is provided by Kaiser et al (2016). The median diel variation presented here is slightly different from that presented by Kaiser et al because slightly different days are included in the median values.…”

Section: B Measured Oh Reactivitymentioning

confidence: 45%

Testing Atmospheric Oxidation in an Alabama Forest

Feiner

Brune

Miller

et al. 2016

Journal of the Atmospheric Sciences

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The chemical species emitted by forests create complex atmospheric oxidation chemistry and influence global atmospheric oxidation capacity and climate. The Southern Oxidant and Aerosol Study (SOAS) provided an opportunity to test the oxidation chemistry in a forest where isoprene is the dominant biogenic volatile organic compound. Hydroxyl (OH) and hydroperoxyl (HO 2 ) radicals were two of the hundreds of atmospheric chemical species measured, as was OH reactivity (the inverse of the OH lifetime). OH was measured by laser-induced fluorescence (LIF) and by taking the difference in signals without and with an OH scavenger that was added just outside the instrument's pinhole inlet. To test whether the chemistry at SOAS can be simulated by current model mechanisms, OH and HO 2 were evaluated with a box model using two chemical mechanisms: Master Chemical Mechanism, version 3.2 (MCMv3.2), augmented with explicit isoprene chemistry and MCMv3.3.1. Measured and modeled OH peak at about 10 6 cm 23 and agree well within combined uncertainties. Measured and modeled HO 2 peak at about 27 pptv and also agree well within combined uncertainties. Median OH reactivity cycled between about 11 s 21 at dawn and about 26 s 21 during midafternoon. A good test of the oxidation chemistry is the balance between OH production and loss rates using measurements; this balance was observed to within uncertainties. These SOAS results provide strong evidence that the current isoprene mechanisms are consistent with measured OH and HO 2 and, thus, capture significant aspects of the atmospheric oxidation chemistry in this isoprene-rich forest.

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Section: B Measured Oh Reactivitymentioning

confidence: 45%

Testing Atmospheric Oxidation in an Alabama Forest

Feiner

Brune

Miller

et al. 2016

Journal of the Atmospheric Sciences

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“…During the night, monoterpenes had a larger impact than isoprene due to their known temperature dependency (Kesselmeier and Staudt, 1999). α-Terpinene was the most reactive-to-OH BVOC also during nighttime; see Table 3.…”

Section: Calculated Oh Reactivity and Bvoc Influencementioning

confidence: 99%

“…Here, this is referred to as calculated OH reactivity, and comparisons between the calculated and the measured OH reactivity have showed that discrepancies in various environments exist (Di Carlo et al, 2004;Nölscher et al, 2016). The missing OH reactivity, namely the fraction of OH reactivity not explained by simultaneous measurements of reactive gases, has been associated with unmeasured compounds either primary emitted, secondary generated, or both (e.g., Sinha et al, 2010;Nölscher et al, 2012aNölscher et al, , 2013Edwards et al, 2013;Hansen et al, 2014;Kaiser et al, 2016).…”

Section: Introductionmentioning

confidence: 99%

Summertime OH reactivity from a receptor coastal site in the Mediterranean Basin

et al. 2017

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Abstract. Total hydroxyl radical (OH) reactivity, the total loss frequency of the hydroxyl radical in ambient air, provides the total loading of OH reactants in air. We measured the total OH reactivity for the first time during summertime at a coastal receptor site located in the western Mediterranean Basin. Measurements were performed at a temporary field site located in the northern cape of Corsica (France), during summer 2013 for the project CARBOSOR (CARBOn within continental pollution plumes: SOurces and Reactivity)-ChArMEx (Chemistry and Aerosols Mediterranean Experiment). Here, we compare the measured total OH reactivity with the OH reactivity calculated from the measured reactive gases. The difference between these two parameters is termed missing OH reactivity, i.e., the fraction of OH reactivity not explained by the measured compounds. The total OH reactivity at the site varied between the instrumental LoD (limit of detection = 3 s −1 ) to a maximum of 17 ± 6 s −1 (35 % uncertainty) and was 5 ± 4 s −1 (1σ SDstandard deviation) on average. It varied with air temperature exhibiting a diurnal profile comparable to the reactivity calculated from the concentration of the biogenic volatile organic compounds measured at the site. For part of the campaign, 56 % of OH reactivity was unexplained by the measured OH reactants (missing reactivity). We suggest that oxidation products of biogenic gas precursors were among the contributors to missing OH reactivity.

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“…Many studies have attempted to identify the missing sink: whilst some authors have attributed the missing reactivity to the presence of primary emissions that escaped detection (Holzinger et al, 2005;Kaiser et al, 2016;Sinha et al, 2010), others have pointed to the reactions of OH with short-lived oxidation intermediates (Hansen et al, 2014;Nakashima et al, 2014), which are notoriously challenging to measure in the field. Other studies still, including that by Nölscher et al (2016) in the Amazon rainforest, attributed the missing reactivity to both unidentified biogenic emissions and photooxidation products.…”

Section: Introductionmentioning

confidence: 99%

Global modelling of the total OH reactivity: investigations on the “missing” OH sink and its atmospheric implications

et al. 2018

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Abstract. The hydroxyl radical (OH) plays a crucial role in the chemistry of the atmosphere as it initiates the removal of most trace gases. A number of field campaigns have observed the presence of a "missing" OH sink in a variety of regions across the planet. A comparison of direct measurements of the OH loss frequency, also known as total OH reactivity (k OH ), with the sum of individual known OH sinks (obtained via the simultaneous detection of species such as volatile organic compounds and nitrogen oxides) indicates that, in some cases, up to 80 % of k OH is unaccounted for. In this work, the UM-UKCA chemistry-climate model was used to investigate the wider implications of the missing reactivity on the oxidising capacity of the atmosphere. Simulations of the present-day atmosphere were performed and the model was evaluated against an array of field measurements to verify that the known OH sinks were reproduced well, with a resulting good agreement found for most species. Following this, an additional sink was introduced to simulate the missing OH reactivity as an emission of a hypothetical molecule, X, which undergoes rapid reaction with OH. The magnitude and spatial distribution of this sink were underpinned by observations of the missing reactivity. Model runs showed that the missing reactivity accounted for on average 6 % of the total OH loss flux at the surface and up to 50 % in regions where emissions of the additional sink were high. The lifetime of the hydroxyl radical was reduced by 3 % in the boundary layer, whilst tropospheric methane lifetime increased by 2 % when the additional OH sink was included. As no OH recycling was introduced following the initial oxidation of X, these results can be interpreted as an upper limit of the effects of the missing reactivity on the oxidising capacity of the troposphere. The UM-UKCA simulations also allowed us to establish the atmospheric implications of the newly characterised reactions of peroxy radicals (RO 2 ) with OH. Whilst the effects of this chemistry on k OH were minor, the reaction of the simplest peroxy radical, CH 3 O 2 , with OH was found to be a major sink for CH 3 O 2 and source of HO 2 over remote regions at the surface and in the free troposphere. Inclusion of this reaction in the model increased tropospheric methane lifetime by up to 3 %, depending on its product branching. Simulations based on the latest kinetic and product information showed that this reaction cannot reconcile models with observations of atmospheric methanol, in contrast to recent suggestions.

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Speciation of OH reactivity above the canopy of an isoprene-dominated forest

Cited by 65 publications

References 44 publications

Testing Atmospheric Oxidation in an Alabama Forest

Testing Atmospheric Oxidation in an Alabama Forest

Summertime OH reactivity from a receptor coastal site in the Mediterranean Basin

Global modelling of the total OH reactivity: investigations on the “missing” OH sink and its atmospheric implications

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