the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Mar 2024
Characterization of the new BATCH Teflon chamber and on-line analysis of isomeric multifunctional photooxidation products
Abstract. The photooxidation of volatile organic compounds (VOCs) in the troposphere has important implications for air quality, weather, and climate. A deeper understanding of the underlying mechanisms can be achieved by studying these reactions under controlled conditions and analyzing the emerging photooxidation products. This requires dedicated laboratory infrastructure as well as sensitive and selective analytical techniques. Here, we constructed a new 300 L indoor Teflon atmospheric simulation chamber as part of the Bayreuth ATmospheric simulation CHambers (BATCH) infrastructure. The chamber was irradiated by a bandpass-filtered solar simulator that enabled experiments with realistic photon fluxes and OH radical concentrations. It was coupled to a proton-transfer-reaction – time-of-flight – mass spectrometer (PTR-ToF-MS) and a solid phase microextraction – gas chromatography – mass spectrometry (SPME-GC-MS) system for the on-line analysis of the precursor VOC and its oxidation products in the gas phase. As part of the SPME-GC-MS method, multifunctional oxygenated compounds (carbonyls, alcohols, carboxylic acids) were derivatized with O-(2,3,4,5,6-Pentafluorobenzyl)-hydroxylamine (PFBHA) and N-trimethylsilyl-N-methyl trifluoroacetamide (MSTFA). We designed a permeation source for the on-line addition of internal standards to improve method reproducibility. The joint setup was tested and validated by studying the OH radical-induced photooxidation of toluene, one of the most abundant aromatic hydrocarbons in the atmosphere. For chamber characterization, we first derived the photolysis rates for several typical toluene products in the irradiated BATCH Teflon chamber (1.77×10−8 – 3.02×10−4 s−1). Additionally, wall loss rates were determined empirically (4.54×10−6 – 8.53×10−5 s−1), and then parameterized according to fundamental molecular properties. For the cresols and benzyl alcohol, we compiled a weighted calibration factor for the PTR-ToF-MS, taking into account isomer-specific sensitivities as well as the relative distribution as determined by the SPME-GC-MS. The weighted calibration improved the instrumental agreement to 15 %, whereas the PTR-ToF-MS overestimated the sum of the isomers by 25 % compared to the SPME-GC-MS concentrations when using the averaged calibration factor. Thus, the combined data set offered insight into both temporal trends and the isomeric composition. Finally, we conducted six toluene photooxidation experiments to evaluate the ring-retaining first generation products. Based on the loss-corrected concentrations, we derived formation yields for o-cresol (8.0±1.8 %), m-cresol (0.4±0.1 %), p-cresol (2.4±0.6 %), benzyl alcohol (0.5±0.1 %), and benzaldehyde (4.6±1.7 %) under NOx-free conditions at T = 298±1 K. These yields are consistent with previous studies and therefore serve as proof-of-concept for our applied methods.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-531', Anonymous Referee #1, 11 Apr 2024
- AC2: 'Reply on RC1', Finja Löher, 23 May 2024
-
RC2: 'Comment on egusphere-2024-531', Anonymous Referee #2, 16 Apr 2024
The paper “Characterization of the new BATCH Teflon chamber and on-line
analysis of isomeric multifunctional photooxidation products” by Finja Löher and coauthors
presents in detailed manner their new teflon batch reactor, using toluene oxidation by OH,
produced from photolysis of H2O2 via a sunlight-simulator for near-atmospheric oxidation
conditions, for characterization.
The group uses well-understood and suitable measurement techniques for characterization and
great care has been taken to ensure quantitative detection of major oxidation products and
distinguishing isomers by characterizing the analytical instruments (PTR-MS and SPME-GC-MS)
with authentic standards, added via a permeation tube.
From the described experiments, yields in agreement with literature data were calculated,
supporting that the reactor’s nonidealities (such as wall-losses) is well-understood after
characterizing. This paper is thus laying out the base for future interesting experiment at this teflon
batch reactor.
In view of the thoughtful experimental approach and clear description of the setup, I think that this
paper is well-suited for publication in AMT.
In the results section, some small parts could improve in clarity. I hope that addressing my minor
comments and questions will help improve the final revised publication in these points.
Some larger suggestions
General
I think, this paper and your (and your colleagues’) future work would benefit from stating, which of
the characterizations need to be performed regularly, before every experiment and which data can
be re-used from your publication as-is. I suggest to describe a “best-practice procedure” in this
paper, that you can refer to in the future.
UV part of the bandpass-filtered solar simulator spectrum (section 4.1.1)
As you measure ozone, you could use the photolysis of ozone alone in the chamber to double-
check the scaling of the old UV-spectrum. Currently, the scaling of the old dataset is motivated by
the comparison with the new dataset at higher wavelength, but it is not clearly tested, if the simple
scaling of the old data is correct.
Wall losses (section 4.1.2):
Since your chamber can be temperature-controlled over a large temperature-range, I suggest to
test wall losses at different temperatures (shift of vapor pressure – this would be nice to set into
relation with existing parametrizations), but also at different humidities (effect of hygroscopicity can
play a role here)
Also, since your measured wall losses seem to not level off, I would also suggest to test the
maximal wall loss rate with sulfuric acid.
Please find below some small comments, mainly to improve clarity:
ll. 120- … : Please give a temperature range for which given toluene + OH reaction rate and
abstraction/addition channel ratio are valid
Table S1:
table S1 also needs the name of the species (at least in the table description), not just the short
form, as these short forms were not introduced yet. Not in the main text until this point, nor in the SI
l. 230: here I wondered, how long is one experiment roughly? Information on this comes much later
in the manuscript, but would be interesting already at a much earlier stage, e.g. here.
l. 265: “SIM” has not been explained yetll. 339/340:
does that mean, the PTR-MS was calibrated only once, due to the complication of focusing on the
oxygenated species?
While it makes a lot of sense to calibrate these species individually, I suggest to use gas-standards
with e.g. a set of hydrocarbons, ketones, siloxanes (…) to allow for more frequent calibrations to
monitor variations in its transmission curve.
l. 370: many teflon chambers are operated continuously under pressure to avoid contamination
from outside. Did you determine the effectiveness of cleaning your chamber both with just flushing
under pressure vs with evacuation? (same: L 400 → emptying it to 30% of its original volume). I
wonder, what the impact of small leaks would be here. Did you perform leak tests, e.g. by spraying
acetone outside the teflon chamber and monitoring it inside?
L 379 ff. – not completely clear to me. Is the toluene flushed with the N2 (15mins, 5slpm) into the
larger teflon batch chamber or was the N2 flushing used to clean the toluene flask before toluene
was injected? In the latter case, how is the toluene entering the batch chamber?
fig. 3 – I suggest to add long names with the short forms in brackets in the figure description
l. 480 – You mention that the reactions with NO3 and O3 are negligible due to their small reaction
rates. This is slightly confusing, as I thought the experiments were Nox-free and you did not
mention that you actively added O3, so are the experiments not O3 and NO3-free?
Fig. 4: the legend could be improved for more clarity. There are e.g. multiple grey lines in different
shades of gray, but only 1 line in the legend. Alternatively, decreasing the visibility of the error-
minima and maxima traces and just using shading might help
l. 523: how did you find the OH concentration? Was it measured via the toluene decay?
L. 525: that’s good! But I believe, this needs to be checked before future experiments after NOx
has been added, again.
Fig. 7: “relative response” is not clear from the figure or figure description (only after reading the
text). It is not described, in relation to what the signals are shown. Please add units for more clarity.
Fig. 8: please add the shortforms (e.g. PHE-d6) in the figure caption
Fig. 11: instead of “final concentration”, maybe call it total produced concentration or similar?
And mark it in the plot as a horizontal bar with uncertainties (cause the loss rates also have
uncertainties)
Fig. 12: please just write mixing ratio instead of the new shortform “MR”
fig. S6.4: is m your calibration factor? Y-axis unit missing…Citation: https://doi.org/10.5194/egusphere-2024-531-RC2 - AC1: 'Reply on RC2', Finja Löher, 23 May 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-531', Anonymous Referee #1, 11 Apr 2024
- AC2: 'Reply on RC1', Finja Löher, 23 May 2024
-
RC2: 'Comment on egusphere-2024-531', Anonymous Referee #2, 16 Apr 2024
The paper “Characterization of the new BATCH Teflon chamber and on-line
analysis of isomeric multifunctional photooxidation products” by Finja Löher and coauthors
presents in detailed manner their new teflon batch reactor, using toluene oxidation by OH,
produced from photolysis of H2O2 via a sunlight-simulator for near-atmospheric oxidation
conditions, for characterization.
The group uses well-understood and suitable measurement techniques for characterization and
great care has been taken to ensure quantitative detection of major oxidation products and
distinguishing isomers by characterizing the analytical instruments (PTR-MS and SPME-GC-MS)
with authentic standards, added via a permeation tube.
From the described experiments, yields in agreement with literature data were calculated,
supporting that the reactor’s nonidealities (such as wall-losses) is well-understood after
characterizing. This paper is thus laying out the base for future interesting experiment at this teflon
batch reactor.
In view of the thoughtful experimental approach and clear description of the setup, I think that this
paper is well-suited for publication in AMT.
In the results section, some small parts could improve in clarity. I hope that addressing my minor
comments and questions will help improve the final revised publication in these points.
Some larger suggestions
General
I think, this paper and your (and your colleagues’) future work would benefit from stating, which of
the characterizations need to be performed regularly, before every experiment and which data can
be re-used from your publication as-is. I suggest to describe a “best-practice procedure” in this
paper, that you can refer to in the future.
UV part of the bandpass-filtered solar simulator spectrum (section 4.1.1)
As you measure ozone, you could use the photolysis of ozone alone in the chamber to double-
check the scaling of the old UV-spectrum. Currently, the scaling of the old dataset is motivated by
the comparison with the new dataset at higher wavelength, but it is not clearly tested, if the simple
scaling of the old data is correct.
Wall losses (section 4.1.2):
Since your chamber can be temperature-controlled over a large temperature-range, I suggest to
test wall losses at different temperatures (shift of vapor pressure – this would be nice to set into
relation with existing parametrizations), but also at different humidities (effect of hygroscopicity can
play a role here)
Also, since your measured wall losses seem to not level off, I would also suggest to test the
maximal wall loss rate with sulfuric acid.
Please find below some small comments, mainly to improve clarity:
ll. 120- … : Please give a temperature range for which given toluene + OH reaction rate and
abstraction/addition channel ratio are valid
Table S1:
table S1 also needs the name of the species (at least in the table description), not just the short
form, as these short forms were not introduced yet. Not in the main text until this point, nor in the SI
l. 230: here I wondered, how long is one experiment roughly? Information on this comes much later
in the manuscript, but would be interesting already at a much earlier stage, e.g. here.
l. 265: “SIM” has not been explained yetll. 339/340:
does that mean, the PTR-MS was calibrated only once, due to the complication of focusing on the
oxygenated species?
While it makes a lot of sense to calibrate these species individually, I suggest to use gas-standards
with e.g. a set of hydrocarbons, ketones, siloxanes (…) to allow for more frequent calibrations to
monitor variations in its transmission curve.
l. 370: many teflon chambers are operated continuously under pressure to avoid contamination
from outside. Did you determine the effectiveness of cleaning your chamber both with just flushing
under pressure vs with evacuation? (same: L 400 → emptying it to 30% of its original volume). I
wonder, what the impact of small leaks would be here. Did you perform leak tests, e.g. by spraying
acetone outside the teflon chamber and monitoring it inside?
L 379 ff. – not completely clear to me. Is the toluene flushed with the N2 (15mins, 5slpm) into the
larger teflon batch chamber or was the N2 flushing used to clean the toluene flask before toluene
was injected? In the latter case, how is the toluene entering the batch chamber?
fig. 3 – I suggest to add long names with the short forms in brackets in the figure description
l. 480 – You mention that the reactions with NO3 and O3 are negligible due to their small reaction
rates. This is slightly confusing, as I thought the experiments were Nox-free and you did not
mention that you actively added O3, so are the experiments not O3 and NO3-free?
Fig. 4: the legend could be improved for more clarity. There are e.g. multiple grey lines in different
shades of gray, but only 1 line in the legend. Alternatively, decreasing the visibility of the error-
minima and maxima traces and just using shading might help
l. 523: how did you find the OH concentration? Was it measured via the toluene decay?
L. 525: that’s good! But I believe, this needs to be checked before future experiments after NOx
has been added, again.
Fig. 7: “relative response” is not clear from the figure or figure description (only after reading the
text). It is not described, in relation to what the signals are shown. Please add units for more clarity.
Fig. 8: please add the shortforms (e.g. PHE-d6) in the figure caption
Fig. 11: instead of “final concentration”, maybe call it total produced concentration or similar?
And mark it in the plot as a horizontal bar with uncertainties (cause the loss rates also have
uncertainties)
Fig. 12: please just write mixing ratio instead of the new shortform “MR”
fig. S6.4: is m your calibration factor? Y-axis unit missing…Citation: https://doi.org/10.5194/egusphere-2024-531-RC2 - AC1: 'Reply on RC2', Finja Löher, 23 May 2024
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Esther Borrás
Amalia Muñoz
Anke Christine Nölscher
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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