Direct Measurement of OH Radicals from Ozonolysis of Selected Alkenes:  A EUPHORE Simulation Chamber Study

2001 ◽  
Vol 35 (23) ◽  
pp. 4660-4667 ◽  
Author(s):  
Manfred Siese ◽  
Karl H. Becker ◽  
Klaus J. Brockmann ◽  
Harald Geiger ◽  
Andreas Hofzumahaus ◽  
...  
Keyword(s):  
Direct Measurement ◽  
Oh Radicals ◽  
Chamber Study ◽  
Simulation Chamber

Product study of the reaction of OH radicals with isoprene in the atmosphere simulation chamber SAPHIR

2006 ◽  
Vol 55 (2) ◽  
pp. 167-187 ◽  
Author(s):  
M. Karl ◽  
H.-P. Dorn ◽  
F. Holland ◽  
R. Koppmann ◽  
D. Poppe ◽  
...  
Keyword(s):  
Oh Radicals ◽  
Atmosphere Simulation Chamber ◽  
Product Study ◽  
Simulation Chamber

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

2020 ◽  
Author(s):  
Anna Novelli ◽  
Luc Vereecken ◽  
Birger Bohn ◽  
Hans-Peter Dorn ◽  
Georgios Gkatzelis ◽  
...  
Keyword(s):  
Oh Radicals ◽  
Oh Radical ◽  
Peroxy Radicals ◽  
Atmospheric Conditions ◽  
Unimolecular Reactions ◽  
Model Calculations ◽  
Hydrogen Shift ◽  
Wide Range ◽  
Regeneration Efficiency ◽  
Simulation Chamber

<p>Theoretical, laboratory and chamber studies have shown fast regeneration of hydroxyl radical (OH) in the photochemistry of isoprene largely due to previously disregarded unimolecular reactions which were previously thought not to be important under atmospheric conditions. Based on early field measurements, nearly complete regeneration was hypothesized for a wide range of tropospheric conditions, including areas such as the rainforest where slow regeneration of OH radicals is expected due to low concentrations of nitric oxide (NO). In this work the OH regeneration in the isoprene oxidation is directly quantified for the first time through experiments covering a wide range of atmospheric conditions (i.e. NO between 0.15 and 2 ppbv and temperature between 25 and 41°C) in the atmospheric simulation chamber SAPHIR. These conditions cover remote areas partially influenced by anthropogenic NO emissions, giving a regeneration efficiency of OH close to one, and areas like the Amazonian rainforest with very low NO, resulting in a surprisingly high regeneration efficiency of 0.5, i.e. a factor of 2 to 3 higher than explainable in the absence of unimolecular reactions. The measured radical concentrations were compared to model calculations and the best agreement was observed when at least 50% of the total loss of isoprene peroxy radicals conformers (weighted by their abundance) occurs via isomerization reactions for NO lower than 0.2 parts per billion (ppbv). For these levels of NO, up to 50% of the OH radicals are regenerated from the products of the 1,6 α-hydroxy-hydrogen shift (1,6-H shift) of Z-δ-RO<sub>2 </sub>radicals through photolysis of an unsaturated hydroperoxy aldehyde (HPALD) and/or through the fast aldehyde hydrogen shift (rate constant ~10 s<sup>-1</sup> at 300K) in di-hydroperoxy carbonyl peroxy radicals (di-HPCARP-RO<sub>2</sub>), depending on their relative yield. The agreement between all measured and modelled trace gases (hydroxyl, hydroperoxy and organic peroxy radicals, carbon monoxide and the sum of methyl vinyl ketone, methacrolein and hydroxyl hydroperoxides) is nearly independent on the adopted yield of HPALD and di-HPCARP-RO<sub>2</sub> as both degrade relatively fast (< 1 h), forming OH radical and CO among other products. Taking into consideration this and earlier isoprene studies, considerable uncertainties remain on the oxygenated products distribution, which affect radical levels and organic aerosol downwind of unpolluted isoprene dominated regions.</p>

scholarly journals OH regeneration from methacrolein oxidation investigated in the atmosphere simulation chamber SAPHIR

2014 ◽  
Vol 14 (15) ◽  
pp. 7895-7908 ◽  
Author(s):  
H. Fuchs ◽  
I.-H. Acir ◽  
B. Bohn ◽  
T. Brauers ◽  
H.-P. Dorn ◽  
...  
Keyword(s):  
Reaction Pathway ◽  
Chemical Mechanism ◽  
Isomerization Reaction ◽  
Initial Reaction ◽  
Oh Radicals ◽  
Peroxy Radicals ◽  
Atmospheric Conditions ◽  
Model Calculations ◽  
Mixing Ratios ◽  
Simulation Chamber

Abstract. Hydroxyl radicals (OH) are the most important reagent for the oxidation of trace gases in the atmosphere. OH concentrations measured during recent field campaigns in isoprene-rich environments were unexpectedly large. A number of studies showed that unimolecular reactions of organic peroxy radicals (RO2) formed in the initial reaction step of isoprene with OH play an important role for the OH budget in the atmosphere at low mixing ratios of nitrogen monoxide (NO) of less than 100 pptv. It has also been suggested that similar reactions potentially play an important role for RO2 from other compounds. Here, we investigate the oxidation of methacrolein (MACR), one major oxidation product of isoprene, by OH in experiments in the simulation chamber SAPHIR under controlled atmospheric conditions. The experiments show that measured OH concentrations are approximately 50% larger than calculated by the Master Chemical Mechanism (MCM) for conditions of the experiments (NO mixing ratio of 90 pptv). The analysis of the OH budget reveals an OH source that is not accounted for in MCM, which is correlated with the production rate of RO2 radicals from MACR. In order to balance the measured OH destruction rate, 0.77 OH radicals (1σ error: ± 0.31) need to be additionally reformed from each reaction of OH with MACR. The strong correlation of the missing OH source with the production of RO2 radicals is consistent with the concept of OH formation from unimolecular isomerization and decomposition reactions of RO2. The comparison of observations with model calculations gives a lower limit of 0.03 s−1 for the reaction rate constant if the OH source is attributed to an isomerization reaction of MACR-1-OH-2-OO and MACR-2-OH-2-OO formed in the MACR + OH reaction as suggested in the literature (Crounse et al., 2012). This fast isomerization reaction would be a competitor to the reaction of this RO2 species with a minimum of 150 pptv NO. The isomerization reaction would be the dominant reaction pathway for this specific RO2 radical in forested regions, where NO mixing ratios are typically much smaller.

35 P 07 A simulation chamber study on the effects of atmospheric particles on mortars

1993 ◽  
Vol 24 ◽  
pp. S393-S394 ◽  
Author(s):  
G. Zappia ◽  
C. Sabbioni ◽  
G. Gobbi ◽  
M.G. Pauri
Keyword(s):  
Atmospheric Particles ◽  
Chamber Study ◽  
Simulation Chamber

scholarly journals Investigation of the oxidation of methyl vinyl ketone (MVK) by OH radicals in the atmospheric simulation chamber SAPHIR

2018 ◽  
Vol 18 (11) ◽  
pp. 8001-8016 ◽  
Author(s):  
Hendrik Fuchs ◽  
Sascha Albrecht ◽  
Ismail–Hakki Acir ◽  
Birger Bohn ◽  
Martin Breitenlechner ◽  
...  
Keyword(s):  
Quantum Chemical ◽  
Reaction Rate ◽  
Reaction Rate Constant ◽  
Oh Radicals ◽  
Methyl Vinyl ◽  
Product Yields ◽  
Reaction Channels ◽  
Ho2 Radical ◽  
Model Measurement ◽  
Simulation Chamber

Abstract. The photooxidation of methyl vinyl ketone (MVK) was investigated in the atmospheric simulation chamber SAPHIR for conditions at which organic peroxy radicals (RO2) mainly reacted with NO (“high NO” case) and for conditions at which other reaction channels could compete (“low NO” case). Measurements of trace gas concentrations were compared to calculated concentration time series applying the Master Chemical Mechanism (MCM version 3.3.1). Product yields of methylglyoxal and glycolaldehyde were determined from measurements. For the high NO case, the methylglyoxal yield was (19 ± 3) % and the glycolaldehyde yield was (65 ± 14) %, consistent with recent literature studies. For the low NO case, the methylglyoxal yield reduced to (5 ± 2) % because other RO2 reaction channels that do not form methylglyoxal became important. Consistent with literature data, the glycolaldehyde yield of (37 ± 9) % determined in the experiment was not reduced as much as implemented in the MCM, suggesting additional reaction channels producing glycolaldehyde. At the same time, direct quantification of OH radicals in the experiments shows the need for an enhanced OH radical production at low NO conditions similar to previous studies investigating the oxidation of the parent VOC isoprene and methacrolein, the second major oxidation product of isoprene. For MVK the model–measurement discrepancy was up to a factor of 2. Product yields and OH observations were consistent with assumptions of additional RO2 plus HO2 reaction channels as proposed in literature for the major RO2 species formed from the reaction of MVK with OH. However, this study shows that also HO2 radical concentrations are underestimated by the model, suggesting that additional OH is not directly produced from RO2 radical reactions, but indirectly via increased HO2. Quantum chemical calculations show that HO2 could be produced from a fast 1,4-H shift of the second most important MVK derived RO2 species (reaction rate constant 0.003 s−1). However, additional HO2 from this reaction was not sufficiently large to bring modelled HO2 radical concentrations into agreement with measurements due to the small yield of this RO2 species. An additional reaction channel of the major RO2 species with a reaction rate constant of (0.006 ± 0.004) s−1 would be required that produces concurrently HO2 radicals and glycolaldehyde to achieve model–measurement agreement. A unimolecular reaction similar to the 1,5-H shift reaction that was proposed in literature for RO2 radicals from MVK would not explain product yields for conditions of experiments in this study. A set of H-migration reactions for the main RO2 radicals were investigated by quantum chemical and theoretical kinetic methodologies, but did not reveal a contributing route to HO2 radicals or glycolaldehyde.

scholarly journals Investigation of the formaldehyde differential absorption cross section at high and low spectral resolution in the simulation chamber SAPHIR

2007 ◽  
Vol 7 (1) ◽  
pp. 2991-3012
Author(s):  
T. Brauers ◽  
J. Bossmeyer ◽  
H.-P. Dorn ◽  
E. Schlosser ◽  
R. Tillmann ◽  
...  
Keyword(s):  
High Resolution ◽  
Cross Section ◽  
Spectral Resolution ◽  
Absorption Cross Section ◽  
Broad Band ◽  
Oh Radicals ◽  
Absorption Cross ◽  
Chamber Volume ◽  
Path Lengths ◽  
Simulation Chamber

Abstract. The results from a simulation chamber study on the formaldehyde (HCHO) absorption cross section in the UV spectral region are presented. We performed 5 experiments at ambient HCHO concentrations with simultaneous measurements of two DOAS instruments in the atmosphere simulation chamber SAPHIR in Jülich. The two instruments differ in their spectral resolution, one working at 0.2 nm (broad-band, BB-DOAS), the other at 2.7 pm (high-resolution, HR-DOAS). Both instruments use dedicated multi reflection cells to achieve long light path lengths of 960 m and 2240 m, respectively, inside the chamber. During three experiments HCHO was injected into the clean chamber by thermolysis of well defined amounts of para-formaldehyde reaching mixing rations of 40 ppbV at maximum. The HCHO concentration calculated from the injection and the chamber volume agrees with the BB-DOAS measured value when the absorption cross section of Meller and Moortgat (2000) was used for data evaluation. In two further experiments we produced HCHO in-situ from the ozone + ethene reaction which was intended to provide an independent way of HCHO calibration through the measurements of ozone and ethene. However, we found an unexpected deviation from the current understanding of the ozone + ethene reaction when CO was added to suppress possible oxidation of ethene by OH radicals. The reaction of the Criegee intermediate with CO could to be 240 times slower than currently assumed. Based on the BB-DOAS measurements we could deduce a high-resolution cross section for HCHO which was not measured directly so far.

scholarly journals Direct Measurement of the Radiative Lifetime of Vibrationally Excited OH Radicals

2005 ◽  
Vol 95 (1) ◽  
Author(s):  
Sebastiaan van de Meerakker ◽  
Nicolas Vanhaecke ◽  
Mark van der Loo ◽  
Gerrit Groenenboom ◽  
Gerard Meijer
Keyword(s):  
Direct Measurement ◽  
Radiative Lifetime ◽  
Oh Radicals ◽  
Vibrationally Excited
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