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Kovacs, Thomas; Brune, William H.

doi:10.1023/a:1010614113786

Cited by 128 publications

(76 citation statements)

References 20 publications

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“…and k OH+X i is the corresponding bimolecular rate constant. The techniques used to determine k OH include the flow tube with sliding injector method pioneered by Brune and co-workers (Kovacs and Brune, 2001), a comparative rate method (Sinha et al, 2008) and a laser flash photolysis pumpprobe technique (Sadanaga et al, 2004). These techniques have been used in a variety of environments and the reader is referred to the overview of previous measurements provided by Lou et al (2010).…”

Section: K Whalley Et Al: Atmospheric Oh Reactivity In Central Lmentioning

confidence: 99%

Atmospheric OH reactivity in central London: observations, model predictions and estimates of in situ ozone production

et al. 2016

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Abstract. Near-continuous measurements of hydroxyl radical (OH) reactivity in the urban background atmosphere of central London during the summer of 2012 are presented. OH reactivity behaviour is seen to be broadly dependent on air mass origin, with the highest reactivity and the most pronounced diurnal profile observed when air had passed over central London to the east, prior to measurement. Averaged over the entire observation period of 26 days, OH reactivity peaked at ∼ 27 s −1 in the morning, with a minimum of ∼ 15 s −1 during the afternoon. A maximum OH reactivity of 116 s −1 was recorded on one day during morning rush hour. A detailed box model using the Master Chemical Mechanism was used to calculate OH reactivity, and was constrained with an extended measurement data set of volatile organic compounds (VOCs) derived from a gas chromatography flame ionisation detector (GC-FID) and a twodimensional GC instrument which included heavier molecular weight (up to C 12 ) aliphatic VOCs, oxygenated VOCs and the biogenic VOCs α-pinene and limonene. Comparison was made between observed OH reactivity and modelled OH reactivity using (i) a standard suite of VOC measurements (C 2 -C 8 hydrocarbons and a small selection of oxygenated VOCs) and (ii) a more comprehensive inventory including species up to C 12 . Modelled reactivities were lower than those measured (by 33 %) when only the reactivity of the standard VOC suite was considered. The difference between measured and modelled reactivity was improved, to within 15 %, if the reactivity of the higher VOCs ( C 9 ) was also considered, with the reactivity of the biogenic compounds of α-pinene and limonene and their oxidation products almost entirely responsible for this improvement. Further improvements in the model's ability to reproduce OH reactivity (to within 6 %) could be achieved if the reactivity and degradation mechanism of unassigned two-dimensional GC peaks were estimated. Neglecting the contribution of the higher VOCs ( C 9 ) (particularly α-pinene and limonene) and model-generated intermediates increases the modelled OH concentrations by 41 %, and the magnitude of in situ ozone production calculated from the production of RO 2 was significantly lower (60 %). This work highlights that any future ozone abatement strategies should consider the role that biogenic emissions play alongside anthropogenic emissions in influencing London's air quality.

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Section: K Whalley Et Al: Atmospheric Oh Reactivity In Central Lmentioning

confidence: 99%

Atmospheric OH reactivity in central London: observations, model predictions and estimates of in situ ozone production

et al. 2016

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“…Several methods to measure OH reactivity have been developed since the first measurements were made by Penn State University (PSU) (Kovacs and Brune, 2001). The different methods fall into two categories.…”

Section: Introductionmentioning

confidence: 99%

“…In the instrument developed by Kovacs and Brune (2001), the decay of OH is measured in a flow tube through which ambient air is drawn by the direct detection of OH using laser-induced fluorescence. OH is continuously produced by water photolysis.…”

Section: Introductionmentioning

confidence: 99%

Comparison of OH reactivity measurements in the atmospheric simulation chamber SAPHIR

Fuchs¹,

Novelli²,

Rolletter³

et al. 2017

Atmos. Meas. Tech.

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Abstract. Hydroxyl (OH) radical reactivity (k OH ) has been measured for 18 years with different measurement techniques. In order to compare the performances of instruments deployed in the field, two campaigns were conducted performing experiments in the atmospheric simulation chamber SAPHIR at Forschungszentrum Jülich in October 2015 and April 2016. Chemical conditions were chosen either to be representative of the atmosphere or to test potential limitations of instruments. All types of instruments that are currently used for atmospheric measurements were used in one of the two campaigns. The results of these campaigns demonstrate that OH reactivity can be accurately measured for a wide range of atmospherically relevant chemical conditions (e.g. water vapour, nitrogen oxides, various organic compounds) by all instruments. The precision of the measurements (limit of detection < 1 s −1 at a time resolution of 30 s to a few minutes) is higher for instruments directly detecting hydroxyl radicals, whereas the indirect comparative reactivPublished by Copernicus Publications on behalf of the European Geosciences Union. H. Fuchs et al.: OH reactivity comparison in SAPHIRity method (CRM) has a higher limit of detection of 2 s −1 at a time resolution of 10 to 15 min. The performances of the instruments were systematically tested by stepwise increasing, for example, the concentrations of carbon monoxide (CO), water vapour or nitric oxide (NO). In further experiments, mixtures of organic reactants were injected into the chamber to simulate urban and forested environments. Overall, the results show that the instruments are capable of measuring OH reactivity in the presence of CO, alkanes, alkenes and aromatic compounds. The transmission efficiency in Teflon inlet lines could have introduced systematic errors in measurements for low-volatile organic compounds in some instruments. CRM instruments exhibited a larger scatter in the data compared to the other instruments. The largest differences to reference measurements or to calculated reactivity were observed by CRM instruments in the presence of terpenes and oxygenated organic compounds (mixing ratio of OH reactants were up to 10 ppbv). In some of these experiments, only a small fraction of the reactivity is detected. The accuracy of CRM measurements is most likely limited by the corrections that need to be applied to account for known effects of, for example, deviations from pseudo first-order conditions, nitrogen oxides or water vapour on the measurement. Methods used to derive these corrections vary among the different CRM instruments. Measurements taken with a flowtube instrument combined with the direct detection of OH by chemical ionisation mass spectrometry (CIMS) show limitations in cases of high reactivity and high NO concentrations but were accurate for low reactivity (< 15 s −1 ) and low NO (< 5 ppbv) conditions.

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“…Over the last two decades, techniques capable of measuring the total OH reactivity directly, without the need to quantify individual sinks, have become available: these rely either on direct measurements of the OH decay rate (Di Carlo et al, 2004;25 Ingham et al, 2009;Kovacs and Brune, 2001) or on the comparative reactivity method (Sinha et al, 2008). A review (Yang et al, 2016) recently described these techniques in detail, whilst the various instruments developed for direct measurements of kOH have been the subject of an extensive intercomparison (Fuchs et al, 2017).…”

Section: Introductionmentioning

confidence: 99%

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

Ferracci¹,

Heimann²,

Abraham³

et al. 2018

Preprint

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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. Comparison of direct measurements of the OH loss frequency, also known as total OH reactivity (kOH), with the 10 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 kOH 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 15 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, while tropospheric methane lifetime increased by 20 2 % when the additional OH sink was included. The UM-UKCA simulations also allowed us to establish the atmospheric implications of the newly characterised reactions of peroxy radicals (RO2) with OH. While the effects of this chemistry on kOH were minor, the reaction of the simplest peroxy radical, CH3O2, with OH was found to be a major sink for CH3O2 and source of HO2 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 25 product information showed that this reaction cannot reconcile models with observations of atmospheric methanol, in contrast to recent suggestions.Atmos. Chem. Phys. Discuss., https://doi

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Cited by 128 publications

References 20 publications

Atmospheric OH reactivity in central London: observations, model predictions and estimates of in situ ozone production

Atmospheric OH reactivity in central London: observations, model predictions and estimates of in situ ozone production

Comparison of OH reactivity measurements in the atmospheric simulation chamber SAPHIR

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

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