Observations of OH and HO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; radicals over West Africa

Commane, R.; Floquet, C. F. A.; Ingham, T.; Stone, Daniel; Evans, M. J.; Heard, Dwayne E.

doi:10.5194/acp-10-8783-2010

Cited by 68 publications

(99 citation statements)

References 71 publications

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“…The calibration procedure has been described in detail by Commane et al (2010). Production of OH (and HO 2 ) is achieved through Reaction (R1) (and HO 2 through Reaction R2) by passing a turbulent flow of humidified ultra-high purity air (BTCA 178, BOC Special Gases) across a low pressure mercury vapour lamp to photolyse water vapour at λ = 184.9 nm.…”

Section: Calibration Of the Fage Detection Cellmentioning

confidence: 99%

“…The product F δt is determined by N 2 O actinometry (Commane et al, 2010), with F varied by changing the current supplied to the lamp, and δt controlled by the flow rate of the gas used in the calibration. The concentration of water vapour in the flow is determined by diverting a small known flow of the air to a dew point hygrometer (CR4, Buck Research Instruments), and was varied between 300 and 10 000 ppm during calibration experiments.…”

Section: Calibration Of the Fage Detection Cellmentioning

confidence: 99%

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Measurement of OH reactivity by laser flash photolysis coupled with laser-induced fluorescence spectroscopy

et al. 2016

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Abstract. OH reactivity (k OH ) is the total pseudo-first-order loss rate coefficient describing the removal of OH radicals to all sinks in the atmosphere, and is the inverse of the chemical lifetime of OH. Measurements of ambient OH reactivity can be used to discover the extent to which measured OH sinks contribute to the total OH loss rate. Thus, OH reactivity measurements enable determination of the comprehensiveness of measurements used in models to predict air quality and ozone production, and, in conjunction with measurements of OH radical concentrations, to assess our understanding of OH production rates. In this work, we describe the design and characterisation of an instrument to measure OH reactivity using laser flash photolysis coupled to laserinduced fluorescence (LFP-LIF) spectroscopy. The LFP-LIF technique produces OH radicals in isolation, and thus minimises potential interferences in OH reactivity measurements owing to the reaction of HO 2 with NO which can occur if HO 2 is co-produced with OH in the instrument. Capabilities of the instrument for ambient OH reactivity measurements are illustrated by data collected during field campaigns in London, UK, and York, UK. The instrumental limit of detection for k OH was determined to be 1.0 s −1 for the campaign in London and 0.4 s −1 for the campaign in York. The precision, determined by laboratory experiment, is typically < 1 s −1 for most ambient measurements of OH reactivity. Total uncertainty in ambient measurements of OH reactivity is ∼ 6 %. We also present the coupling and characterisation of the LFP-LIF instrument to an atmospheric chamber for measurements of OH reactivity during simulated experiments, and provide suggestions for future improvements to OH reactivity LFP-LIF instruments.

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Section: Calibration Of the Fage Detection Cellmentioning

confidence: 99%

Section: Calibration Of the Fage Detection Cellmentioning

confidence: 99%

Measurement of OH reactivity by laser flash photolysis coupled with laser-induced fluorescence spectroscopy

et al. 2016

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“…The instrument was calibrated twice weekly on average using photolysis of a known concentration of water vapour at 185 nm within a turbulent flow tube to generate OH and HO2, with the product of the photon flux at 185 nm and the water vapour 30 photolysis time measured using a chemical actinometer (Commane et al, 2010). For RO2, methane (BOC, CP grade, 99.5%) was added to the humidified air flow in sufficient quantity to rapidly convert OH to CH3O2.…”

Section: Calibrationmentioning

confidence: 99%

Understanding in situ ozone production in the summertime through radical observations and modelling studies during the Clean air for London project (ClearfLo)

Whalley¹,

Stone²,

Dunmore³

et al. 2017

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Abstract. Measurements of OH, HO2, RO2i (alkene and aromatic related RO2) and total RO2 radicals taken during the ClearfLo campaign in central London in the summer of 2012 are presented. A photostationary steady-state calculation of OH which considered measured OH reactivity as the OH sink term and the measured OH sources (of which HO2+NO reaction and HONO photolysis dominated) compared well with the observed levels of OH. Comparison with calculations from a detailed box model utilising the Master Chemical Mechanism v3.2, however, highlighted a substantial discrepancy between radical 20 observations under lower NOx conditions ([NO] < 1 ppbv) typically experienced during the afternoon hours, and indicated that the model was missing a significant peroxy radical sink; the model over-predicted HO2 by up to a factor of 10 at these times.Known radical termination steps, such as HO2 uptake on aerosols, were not sufficient to reconcile the model measurement discrepancies alone suggesting other missing termination processes. This missing sink was most evident when the air reaching the site had previously passed over central London to the east and when elevated temperatures were experienced and, hence, 25 contained higher concentrations of VOC. Uncertainties in the degradation mechanism at low NOx of complex biogenic and diesel related VOC species which were particularly elevated and dominated OH reactivity under these easterly flows, may account for some of the model measurement disagreement. Under higher [NO] (>3 ppbv) the box model increasingly underpredicted total [RO2]. The modelled and observed HO2 were in agreement, however, under elevated NO concentrations ranging from 7 -15 ppbv. 30The model uncertainty under low NO conditions leads to more ozone production predicted using modelled peroxy radical concentrations (~3 ppbv hr -1 ) versus ozone production from peroxy radicals measured (~1 ppbv hr -1 ). Conversely, ozone 2 production derived from the predicted peroxy radicals is up to an order of magnitude lower than from the observed peroxy radicals as [NO] increases beyond 7 ppbv due to the model under-prediction of RO2 under these conditions.

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“…Experimental conditions are discussed in detail by Whalley et al (2013), and are provided only briefly here. Interference testing was conducted using the FAGE calibration setup described by Commane et al (2010), in which equal amounts of OH and HO 2 are produced by passing a known flow (∼ 50 dm 3 min −1 ) of humidified ultra-high purity air (BTCA 178, BOC Special Gases) across a low pressure mercury lamp of known actinic flux: H 2 O + hν(λ = 184.9 nm) → H + OH,…”

Section: Model Treatment Of Potential Ro 2 Interferences In Ho 2 Measmentioning

confidence: 99%

Radical chemistry at night: comparisons between observed and modelled HOx, NO3 and N2O5 during the RONOCO project

et al. 2014

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Abstract. The RONOCO (ROle of Nighttime chemistry in controlling the Oxidising Capacity of the AtmOsphere) aircraft campaign during July 2010 and January 2011 made observations of OH, HO 2 , NO 3 , N 2 O 5 and a number of supporting measurements at night over the UK, and reflects the first simultaneous airborne measurements of these species. We compare the observed concentrations of these short-lived species with those calculated by a box model constrained by the concentrations of the longer lived species using a detailed chemical scheme. OH concentrations were below the limit of detection, consistent with model predictions. The model systematically underpredicts HO 2 by ∼ 200 % and overpredicts NO 3 and N 2 O 5 by around 80 and 50 %, respectively. Cycling between NO 3 and N 2 O 5 is fast and thus we define the NO 3x (NO 3x = NO 3 + N 2 O 5 ) family. Production of NO 3x is overwhelmingly dominated by the reaction of NO 2 with O 3 , whereas its loss is dominated by aerosol uptake of N 2 O 5 , with NO 3 + VOCs (volatile organic compounds) and NO 3 + RO 2 playing smaller roles. The production of HO x and RO x radicals is mainly due to the reaction of NO 3 with VOCs. The loss of these radicals occurs through a combination of HO 2 + RO 2 reactions, heterogeneous processes and production of HNO 3 from OH + NO 2 , with radical propagation primarily achieved through reactions of NO 3 with peroxy radicals. Thus NO 3 at night plays a similar role to both OH and NO during the day in that it both initiates RO x radical production and acts to propagate the tropospheric oxidation chain. Model sensitivity to the N 2 O 5 aerosol uptake coefficient (γ N 2 O 5 ) is discussed and we find that a value of γ N 2 O 5 = 0.05 improves model simulations for NO 3 and N 2 O 5 , but that these improvements are at the expense of model success for HO 2 . Improvements to model simulations for HO 2 , NO 3 and N 2 O 5 can be realised simultaneously on inclusion of additional unsaturated volatile organic compounds, however the nature of these compounds is extremely uncertain.

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Observations of OH and HO<sub>2</sub> radicals over West Africa

Cited by 68 publications

References 71 publications

Measurement of OH reactivity by laser flash photolysis coupled with laser-induced fluorescence spectroscopy

Measurement of OH reactivity by laser flash photolysis coupled with laser-induced fluorescence spectroscopy

Understanding in situ ozone production in the summertime through radical observations and modelling studies during the Clean air for London project (ClearfLo)

Radical chemistry at night: comparisons between observed and modelled HO<sub>x</sub>, NO<sub>3</sub> and N<sub>2</sub>O<sub>5</sub> during the RONOCO project

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Observations of OH and HO&lt;sub&gt;2&lt;/sub&gt; radicals over West Africa

Cited by 68 publications

References 71 publications

Measurement of OH reactivity by laser flash photolysis coupled with laser-induced fluorescence spectroscopy

Measurement of OH reactivity by laser flash photolysis coupled with laser-induced fluorescence spectroscopy

Understanding in situ ozone production in the summertime through radical observations and modelling studies during the Clean air for London project (ClearfLo)

Radical chemistry at night: comparisons between observed and modelled HO&lt;sub&gt;x&lt;/sub&gt;, NO&lt;sub&gt;3&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt; during the RONOCO project

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Observations of OH and HO<sub>2</sub> radicals over West Africa

Radical chemistry at night: comparisons between observed and modelled HO<sub>x</sub>, NO<sub>3</sub> and N<sub>2</sub>O<sub>5</sub> during the RONOCO project