Reply [to “Comment on ‘The measurement of tropospheric OH radicals by laser‐induced fluorescence spectroscopy during the POPCORN field campaign’ by Hofzumahaus et al. and ‘Intercomparison of tropospheric OH radical measurements by multiple folded long‐path laser absorption and laser induced fluorescence’ by Brauers et al.”]

Hofzumahaus, A.; Brauers, T.; Aschmutat, U.; Brandenburger, Uwe; Dorn, Hans-Peter; Hausmann, Martin; Heßling, Martin; Holland, F.; Plaß-Dülmer, C.; Sedlaček, Marko; Weber, Miriam; Ehhalt, D. H.

doi:10.1029/97gl02947

Cited by 65 publications

(35 citation statements)

References 10 publications

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“…In this equation, φ OH+H is the quantum yield of OH from water photolysis and σ H 2 O is the absorption cross section of water (7.14 × 10 −20 cm −2 molecule −1 ; Cantrell et al, 1997;Hofzumahaus et al, 1997;Creasey et al, 2000). The product of the photon flux (F ) and the photolysis time (t) can be determined from oxygen actinometry, as the photolysis of oxygen at 185 nm leads to the production of ozone (Reactions R6 and R7;Okabe, 1978):…”

Section: Instrument Calibration For Oh and Homentioning

confidence: 99%

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Measurement of interferences associated with the detection of the hydroperoxy radical in the atmosphere using laser-induced fluorescence

2018

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Abstract.One technique used to measure concentrations of the hydroperoxy radical (HO 2 ) in the atmosphere involves chemically converting it to OH by addition of NO and subsequent detection of OH. However, some organic peroxy radicals (RO 2 ) can also be rapidly converted to HO 2 (and subsequently OH) in the presence of NO, interfering with measurements of ambient HO 2 radical concentrations. This interference must be characterized for each instrument to determine to what extent various RO 2 radicals interfere with measurements of HO 2 and to assess the impact of this interference on past measurements. The efficiency of RO 2 -to-HO 2 conversion for the Indiana University laser-induced fluorescencefluorescence assay by gas expansion (IU-FAGE) instrument was measured for a variety of RO 2 radicals. Known quantities of OH and HO 2 radicals were produced from the photolysis of water vapor at 184.9 nm, and RO 2 radicals were produced by the reaction of several volatile organic compounds (VOCs) with OH. The conversion efficiency of RO 2 radicals to HO 2 was measured when NO was added to the sampling cell for conditions employed during several previous field campaigns. For these conditions, approximately 80 % of alkene-derived RO 2 radicals and 20 % of alkane-derived RO 2 radicals were converted to HO 2 . Based on these measurements, interferences from various RO 2 radicals contributed to approximately 35 % of the measured HO 2 signal during the Mexico City Metropolitan Area (MCMA) 2006 campaign (MCMA-2006), where the measured VOCs consisted of a mixture of saturated and unsaturated species. However, this interference can contribute more significantly to the measured HO 2 signal in forested environments dominated by unsaturated biogenic emissions such as isoprene.

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Section: Instrument Calibration For Oh and Homentioning

confidence: 99%

“…The lineshape depends on the operating conditions of the lamp as a result of line reversal and potential fluorescence of the fused silica envelope (Cantrell et al, 1997;Hofzumahaus et al, 1997;Lanzendorf et al, 1997).…”

Section: Instrument Calibration For Oh and Homentioning

confidence: 99%

Measurement of interferences associated with the detection of the hydroperoxy radical in the atmosphere using laser-induced fluorescence

2018

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“…(7), was corrected by a profile factor, which accounts for the variation in axial velocity across the laminar flow in the calibration tube, defined as [O 3 ] excess /[O 3 ] centre , which was determined experimentally to be 1.94±0.07. Several studies have shown that the effective absorption cross section of O 2 at 185 nm depends on the individual photolysis lamp used (and its operating conditions) and the O 2 column through which the radiation propagates (Cantrell et al, 1997;Creasey et al, 2000;Hofzumahaus et al, 1997) and as a result σ 184.9 nm(O 2 ) was measured for the actual lamp and operating conditions used in the field calibrations. OH and HO 2 calibrations were carried out daily during the NAMBLEX campaign.…”

Section: Calibrationmentioning

confidence: 99%

Concentrations of OH and HO2 radicals during NAMBLEX: measurements and steady state analysis

et al. 2006

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Abstract. OH and HO 2 concentrations were measured simultaneously at the Mace Head Atmospheric Research Station in the summer of 2002 during the NAMBLEX (North Atlantic Marine Boundary Layer EXperiment) field campaign. OH was measured by laser-induced fluorescence employing the FAGE (Fluorescence Assay by Gas Expansion) technique, with a mean daytime detection limit of 2.7×10 5 molecule cm −3 (5 min acquisition period; signal-tonoise ratio = 1). HO 2 was detected as OH following its chemical conversion through addition of NO, with a mean detection limit of 4.4×10 6 molecule cm −3 . The diurnal variation of OH was measured on 24 days, and that of HO 2 on 17 days. The local solar noon OH concentrations ranged between (3-8)×10 6 molecule cm −3 , with a 24 h mean concentration of 9.1×10 5 molecule cm −3 . The local solar noon HO 2 concentrations were (0.9-2.1)×10 8 molecule cm −3 (3.5-8.2 pptv), with a 24 h mean concentration of 4.2×10 7 molecule cm −3 (1.6 pptv). HO 2 radicals in the range (2-3)×10 7 molecule cm −3 were observed at night. During NAMBLEX, a comprehensive suite of supporting measurements enabled a detailed study of the behaviour of HO x radicals under primarily clean marine conditions. Steady state expressions are used to calculate OH and HO 2 concentrations and to evaluate the effect of different free-radical sources and sinks. The diurnally averaged calculated to measured OH ratio was 1.04±0.36, but the ratio displays a distinct diurnal variation, being less than 1 during the early morning and late afternoon/evening, and greater than 1 in the middle of the day. For HO 2 there was an overprediction, with the agreement between calculated and measured concentrations improved by including reaction with measured IO and BrO radicals and uptake to aerosols. Increasing the concentration of IO radicals included in the calculations to above that measured by a DOAS instrument with an absorption path located mainly Correspondence to: D. E. Heard (d.e.heard@leeds.ac.uk) over the ocean, reflecting the domination of the inter-tidal region as an iodine source at Mace Head, led to further improvement. The results are compared with previous measurements at Mace Head, and elsewhere in the remote marine boundary layer.

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“…The instrumental reproducibility (precision) based upon calibration was 6%. The uncertainty (accuracy) of the measurements, which had been determined during an intercalibration experiment to AE20% (see also Hofzumahaus et al, 1997), must now be considered as 100%À20%, since Mihele and Hastie (1998) reported the radical ampli®cation to depend on moisture. From March to the beginning of May the temperatures were below freezing so that the error from disregarding the dependence on water vapour might then be small.…”

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confidence: 99%

The role of bromine and chlorine chemistry for arctic ozone depletion events in Ny-Ålesund and comparison with model calculations

1999

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Abstract. During the Arctic Tropospheric Ozone Chemistry (ARCTOC) campaigns at Ny-A Ê lesund, Spitsbergen, the role of halogens in the depletion of boundary layer ozone was investigated. In spring 1995 and 1996 up to 30 ppt bromine monoxide were found whenever ozone decreased from normal levels of about 40 ppb. Those main trace gases and others were speci®cally followed in the UV-VIS spectral region by dierential optical absorption spectroscopy (DOAS) along light paths running between 20 and 475 m a.s.l.. The daily variation of peroxy radicals closely followed the ozone photolysis rate J(O 3 (O 1 D)) in the absence of ozone depletion most of the time. However, during low ozone events this close correlation was no longer found because the measurement of radicals by chemical ampli®cation (CA) turned out to be sensitive to peroxy radicals and ClO x . Large CA signals at night can sometimes de®nitely be assigned to ClO x and reached up to 2 ppt. Total bromine and iodine were both stripped quantitatively from air by active charcoal traps and measured after neutron activation of the samples. Total bromine increased from background levels of about 15 ppt to a maximum of 90 ppt during an event of complete ozone depletion. For the spring season a strong source of bromine is identi®ed in the pack ice region according to back trajectories. Though biogenic emission sources cannot be completely ruled out, a primary activation of halogenides by various oxidants seems to initiate an ecient autocatalytic process, mainly driven by ozone and light, on ice and perhaps on aerosols. Halogenides residing on pack ice surfaces are continuously oxidised by hypohalogenous acids releasing bromine and chlorine into the air. During transport and especially above open water this air mixes with upper layer pristine air. As large quantities of bromine, often in the form of BrO, have been observed at polar sunrise also around Antarctica, its release seems to be a natural phenomenon. The source strength of bromine from halogen activation on the pack ice, as based on the measured inorganic bromine levels, averages about 1012 Br-atoms m À2 s À1 during sunlit periods in Arctic spring. The total source strength of inorganic bromine from sunlit polar regions may therefore amount to 30 kt y À1 .

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Cited by 65 publications

References 10 publications

Measurement of interferences associated with the detection of the hydroperoxy radical in the atmosphere using laser-induced fluorescence

Measurement of interferences associated with the detection of the hydroperoxy radical in the atmosphere using laser-induced fluorescence

Concentrations of OH and HO<sub>2</sub> radicals during NAMBLEX: measurements and steady state analysis

The role of bromine and chlorine chemistry for arctic ozone depletion events in Ny-Ålesund and comparison with model calculations

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Cited by 65 publications

References 10 publications

Measurement of interferences associated with the detection of the hydroperoxy radical in the atmosphere using laser-induced fluorescence

Measurement of interferences associated with the detection of the hydroperoxy radical in the atmosphere using laser-induced fluorescence

Concentrations of OH and HO&lt;sub&gt;2&lt;/sub&gt; radicals during NAMBLEX: measurements and steady state analysis

The role of bromine and chlorine chemistry for arctic ozone depletion events in Ny-Ålesund and comparison with model calculations

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Concentrations of OH and HO<sub>2</sub> radicals during NAMBLEX: measurements and steady state analysis