the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 12 Dec 2022
Methodological advances to improve repeatability of SOA generation in environmental chambers
Abstract. Most laboratory atmospheric chamber studies probing the chemical and physical properties of secondary organic aerosol (SOA) perform such experiments with mixing ratios of volatile organic compounds (VOCs) well-above atmospheric relevance (≳50 ppbv). When performing ozonolysis of biogenic VOCs at mixing ratios of atmospheric relevance (≲10 ppbv), repeatability of replicate experiments is hindered by the limitations of conventional VOC injection techniques. To overcome these limitations, two novel components (stop/flow and split valves) were embedded in a conventional VOC injection setup, thereby permitting the use of higher VOC volumes of injection to attain low VOC mixing ratios, and the delivery of the VOC to the environmental chamber as a short, discrete pulse for subsequent reaction. Implementation of these novel VOC injection components has resulted in improvements in variability between replicate chamber experiments of up to a factor of 7 with respect to particle number, mass, and size distributions at both high and low VOC mixing ratios (50 and 10 ppbv, respectively). These improvements permit extension of quantitative measurements of SOA formation to VOC mixing ratios at or near atmospheric levels, where new particle formation (NPF) and SOA mass loading are typically within experimental variability.
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RC1: 'Comment on egusphere-2022-1249', Anonymous Referee #1, 20 Dec 2022
Flueckiger and Petrucci present a method to inject volatile organic compound (VOC) precursors into an atmospheric/environmental chamber (i.e., smog chamber) for studies, specifically secondary organic aerosol generation in this study. The authors conduct studies with and without this new delivery method. The new delivery method includes a split flow valve to flow a certain, known amount of carrier gas through a flask with evaporated precursor gas and another split valve that can change the amount of carrier gas introduced into the smog chamber. The authors argue this is necessary to allow for low mixing ratio injections (~10 parts per billion) and increased repeatability. Though this paper may be of interest to the AMT community, there are many concerns for the paper, as discussed below, that makes this study not ready for publication into AMT. Addressing the comments below will assist to strengthen the study and make it potentially suitable for AMT.
1) The introduction currently as written does not provide the necessary motivation for the current study and the majority of the references are not the appropriate references for the statements made in the introduction. For example, the Fischer et al. (2020) and Claflin et al. (2018) are chamber studies producing SOA and not ambient measurements of OA or SOA; therefore, they do not make any statements about the contributions of SOA to ambient aerosol. Also, the Claflin et al. (2018), being a laboratory study of one mechanism, does not have an direct discussion about how much VOC is emitted. The Xu et al. (2021) paper is a paper disucssing the impacts of human emissions on biogenic SOA formation and thus is not directly discussing the impacts of particulate matter/aerosol on climate change, air quality, and human health. Though Krechmer et al. (2020) is a study about chambers, other papers (reviews) or books (Seinfeld & Pandis, for example) would be better references concerning chambers. Other studies directly investigating the before mentioned areas would be beneficial. Further, there are other papers that have conducted smog chamber experiments at "atmospherically" relevant VOC concentrations -- Pathak et al., 2007; Li et al., 2017; Chen et al., 2018; Rolletter et al., 2019; Chen et al., 2022; Day et al., 2022; Liu et al., 2022, to name a few. A combination of how do these studies translate to the hypothesis of issues with reproducibility, how do their methods compare with the currently proposed study, and a more thorough literature search would benefit both the introduction and results/discussions.2) The authors are taking a very complicated problem, injecting precursors into a chamber, and over simplifying the problem, by looking at the number concentration of particles formed (see below for each step that needs to be quantified to understand reproducibility). The results being presented is too complex to understand the reproducibility of the injection method currently being proposed. Prior to formation of aerosol, the following aspects have not been addressed and would need to be carefully evaluated:
a) What is the loss of material from flask prior to injection of bag? What range of volatility does this new method work best for?
b) How much material is actually introduced into the bag? How quickly does the bag get well mixed with the material? E.g., measurements of the VOC precursor concentration in the bag from repeated injections would be valuable for this study. Looking at a-pinene in the bag for reproducibility with the number of different experiments discussed would be valuable as the first step of uncertainty. Further, looking at the amount of a-pinene in the bag would verify that the equations used are correct and there is minimal loss/uncertainty associated with the equations.
c) What about wall losses of oxidized material? The authors are currently running experiments without any aerosol seed. Numerous studies have shown that low volatile gases readily partition to the chamber wall, impacting aerosol yields and reproducibility (e.g., the Krechmer et al., 2020 article cited in this paper as well as Liu et al., 2019, Comm. Chem. & references within the paper). The current study needs to conduct calculations of gas partition to the chamber (e.g., Krechmer et al., 2020) and determine how much of the low reproducibility may be due to reversible/irreversible partioning of gases.
d) With this competition of wall loss of SOA precursors to wall vs new particle formation, the "realistic" part that needs to be verified prior to showing particle number concentration showing minimal variation is that the partitioning of gases to aerosols is comparable to the ambient atmosphere.3) Other things that need to be discussed to understand reproducibility and applicability--
a) What is the temperature and relative humidity in the chamber? Both can impact new particle formation, particle growth, wall loss, etc.
b) What does the background of the chamber look like between injections?
c) In methods, the authors state only a-pinene is being used. Yet, in page 4, line 178, the authors state they used cis-3-hexen-1-ol. Why was this compound used here?
d) How does this study compare to other studies in regards to reproducibility for a-pinene + O3? How would this study change if it was conducted in a flow tube instead of a smog chamber?4) One other discussion point that would be good to include in the paper is why high concentrations are used. One reason is to push the partitioning of gases into aerosol (see point 2 above). Another is to ensure the concentrations of the intermediate species are high enough to measure (e.g., instrument analytical limitations). Limitations in using this method for understanding intermediates and mechanisms should be addressed and that this may be only useful in measuring total OA yields from one species.
Citation: https://doi.org/10.5194/egusphere-2022-1249-RC1 -
AC1: 'Reply on RC1', Giuseppe Petrucci, 03 Jan 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1249/egusphere-2022-1249-AC1-supplement.pdf
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AC1: 'Reply on RC1', Giuseppe Petrucci, 03 Jan 2023
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RC2: 'Comment on egusphere-2022-1249', Anonymous Referee #2, 04 Jan 2023
The manuscript by Flueckiger and Petrucci developed a new method of adding VOCs for smog chamber study. This method is expected to improve the reproducibility of the chamber experiments. However, the whole work just like the experiment results without deeply scientific. Some parts of this manuscript still need to be supplemented, and it does not meet the requirements of this journal at the current version. The specific comments are listed as follows.
- Page 1, Section Introduction. The scientific aspects of the need to study SOA formation at low VOCs concentrations should be mentioned in the Section Introduction, such as the fact that VOCs concentrations will affect the distribution of oxidation products and the oxidation state of SOA, as reported by previous studies conducted by Chen et al. (2019, 2022) and Alfarra et al. (2012).
- Page 2, Section 2.2. My biggest concern is that in order to verify the reliability of the improved method, a sufficient number of parameters of particle properties, including the physical and chemical properties, should be measured. In particular, the chemical properties should be carefully addressed, such as the formation of oxidation products and the oxidation state of SOA.
- Another of my concerns is whether this new method of adding VOCs affect the formation of gas phase products and the vapor wall loss, which is thought to be crucial to SOA formation, as reported by Zhang et al. (2014).
- Page 3, Section 2.4. Please check the Eq. (4). ξVOC should be VI?
- Page 4, Section 3.1. Why this compound of cis-3-hexen-1-ol (HXL) was chosen instead of the previously mentioned α-pinene?
- Page 5, Section 3.2. The calculation of RSD is based on the results obtained at the end of the reaction, right? However, this ignored the complex changes in time evolution during the reaction. Thus, more consideration of overall behavior of SOA formation is needed.
Chen, T.; Zhang, P.; Chu, B.; Ma, Q.; Ge, Y.; Liu, J.; He, H., Secondary organic aerosol formation from mixed volatile organic compounds: Effect of RO2 chemistry and precursor concentration. npj Clim Atmos Sci 2022, 5, (1), 95.
Chen, T.; Liu, Y.; Chu, B.; Liu, C.; Liu, J.; Ge, Y.; Ma, Q.; Ma, J.; He, H., Differences of the oxidation process and secondary organic aerosol formation at low and high precursor concentrations. J Environ Sci 2019, 79, 256-263.
Alfarra, M. R.; Hamilton, J. F.; Wyche, K. P.; Good, N.; Ward, M. W.; Carr, T.; Barley, M. H.; Monks, P. S.; Jenkin, M. E.; Lewis, A. C.; McFiggans, G. B., The effect of photochemical ageing and initial precursor concentration on the composition and hygroscopic properties of beta-caryophyllene secondary organic aerosol. Atmos Chem Phys 2012, 12, (14), 6417-6436.
Zhang, X.; Cappa, C. D.; Jathar, S. H.; McVay, R. C.; Ensberg, J. J.; Kleeman, M. J.; Seinfeld, J. H., Influence of vapor wall loss in laboratory chambers on yields of secondary organic aerosol. Proc Natl Acad Sci USA 2014, 111, (16), 5802-5807.
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AC2: 'Reply on RC2', Giuseppe Petrucci, 05 Jan 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1249/egusphere-2022-1249-AC2-supplement.pdf
Status: closed
-
RC1: 'Comment on egusphere-2022-1249', Anonymous Referee #1, 20 Dec 2022
Flueckiger and Petrucci present a method to inject volatile organic compound (VOC) precursors into an atmospheric/environmental chamber (i.e., smog chamber) for studies, specifically secondary organic aerosol generation in this study. The authors conduct studies with and without this new delivery method. The new delivery method includes a split flow valve to flow a certain, known amount of carrier gas through a flask with evaporated precursor gas and another split valve that can change the amount of carrier gas introduced into the smog chamber. The authors argue this is necessary to allow for low mixing ratio injections (~10 parts per billion) and increased repeatability. Though this paper may be of interest to the AMT community, there are many concerns for the paper, as discussed below, that makes this study not ready for publication into AMT. Addressing the comments below will assist to strengthen the study and make it potentially suitable for AMT.
1) The introduction currently as written does not provide the necessary motivation for the current study and the majority of the references are not the appropriate references for the statements made in the introduction. For example, the Fischer et al. (2020) and Claflin et al. (2018) are chamber studies producing SOA and not ambient measurements of OA or SOA; therefore, they do not make any statements about the contributions of SOA to ambient aerosol. Also, the Claflin et al. (2018), being a laboratory study of one mechanism, does not have an direct discussion about how much VOC is emitted. The Xu et al. (2021) paper is a paper disucssing the impacts of human emissions on biogenic SOA formation and thus is not directly discussing the impacts of particulate matter/aerosol on climate change, air quality, and human health. Though Krechmer et al. (2020) is a study about chambers, other papers (reviews) or books (Seinfeld & Pandis, for example) would be better references concerning chambers. Other studies directly investigating the before mentioned areas would be beneficial. Further, there are other papers that have conducted smog chamber experiments at "atmospherically" relevant VOC concentrations -- Pathak et al., 2007; Li et al., 2017; Chen et al., 2018; Rolletter et al., 2019; Chen et al., 2022; Day et al., 2022; Liu et al., 2022, to name a few. A combination of how do these studies translate to the hypothesis of issues with reproducibility, how do their methods compare with the currently proposed study, and a more thorough literature search would benefit both the introduction and results/discussions.2) The authors are taking a very complicated problem, injecting precursors into a chamber, and over simplifying the problem, by looking at the number concentration of particles formed (see below for each step that needs to be quantified to understand reproducibility). The results being presented is too complex to understand the reproducibility of the injection method currently being proposed. Prior to formation of aerosol, the following aspects have not been addressed and would need to be carefully evaluated:
a) What is the loss of material from flask prior to injection of bag? What range of volatility does this new method work best for?
b) How much material is actually introduced into the bag? How quickly does the bag get well mixed with the material? E.g., measurements of the VOC precursor concentration in the bag from repeated injections would be valuable for this study. Looking at a-pinene in the bag for reproducibility with the number of different experiments discussed would be valuable as the first step of uncertainty. Further, looking at the amount of a-pinene in the bag would verify that the equations used are correct and there is minimal loss/uncertainty associated with the equations.
c) What about wall losses of oxidized material? The authors are currently running experiments without any aerosol seed. Numerous studies have shown that low volatile gases readily partition to the chamber wall, impacting aerosol yields and reproducibility (e.g., the Krechmer et al., 2020 article cited in this paper as well as Liu et al., 2019, Comm. Chem. & references within the paper). The current study needs to conduct calculations of gas partition to the chamber (e.g., Krechmer et al., 2020) and determine how much of the low reproducibility may be due to reversible/irreversible partioning of gases.
d) With this competition of wall loss of SOA precursors to wall vs new particle formation, the "realistic" part that needs to be verified prior to showing particle number concentration showing minimal variation is that the partitioning of gases to aerosols is comparable to the ambient atmosphere.3) Other things that need to be discussed to understand reproducibility and applicability--
a) What is the temperature and relative humidity in the chamber? Both can impact new particle formation, particle growth, wall loss, etc.
b) What does the background of the chamber look like between injections?
c) In methods, the authors state only a-pinene is being used. Yet, in page 4, line 178, the authors state they used cis-3-hexen-1-ol. Why was this compound used here?
d) How does this study compare to other studies in regards to reproducibility for a-pinene + O3? How would this study change if it was conducted in a flow tube instead of a smog chamber?4) One other discussion point that would be good to include in the paper is why high concentrations are used. One reason is to push the partitioning of gases into aerosol (see point 2 above). Another is to ensure the concentrations of the intermediate species are high enough to measure (e.g., instrument analytical limitations). Limitations in using this method for understanding intermediates and mechanisms should be addressed and that this may be only useful in measuring total OA yields from one species.
Citation: https://doi.org/10.5194/egusphere-2022-1249-RC1 -
AC1: 'Reply on RC1', Giuseppe Petrucci, 03 Jan 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1249/egusphere-2022-1249-AC1-supplement.pdf
-
AC1: 'Reply on RC1', Giuseppe Petrucci, 03 Jan 2023
-
RC2: 'Comment on egusphere-2022-1249', Anonymous Referee #2, 04 Jan 2023
The manuscript by Flueckiger and Petrucci developed a new method of adding VOCs for smog chamber study. This method is expected to improve the reproducibility of the chamber experiments. However, the whole work just like the experiment results without deeply scientific. Some parts of this manuscript still need to be supplemented, and it does not meet the requirements of this journal at the current version. The specific comments are listed as follows.
- Page 1, Section Introduction. The scientific aspects of the need to study SOA formation at low VOCs concentrations should be mentioned in the Section Introduction, such as the fact that VOCs concentrations will affect the distribution of oxidation products and the oxidation state of SOA, as reported by previous studies conducted by Chen et al. (2019, 2022) and Alfarra et al. (2012).
- Page 2, Section 2.2. My biggest concern is that in order to verify the reliability of the improved method, a sufficient number of parameters of particle properties, including the physical and chemical properties, should be measured. In particular, the chemical properties should be carefully addressed, such as the formation of oxidation products and the oxidation state of SOA.
- Another of my concerns is whether this new method of adding VOCs affect the formation of gas phase products and the vapor wall loss, which is thought to be crucial to SOA formation, as reported by Zhang et al. (2014).
- Page 3, Section 2.4. Please check the Eq. (4). ξVOC should be VI?
- Page 4, Section 3.1. Why this compound of cis-3-hexen-1-ol (HXL) was chosen instead of the previously mentioned α-pinene?
- Page 5, Section 3.2. The calculation of RSD is based on the results obtained at the end of the reaction, right? However, this ignored the complex changes in time evolution during the reaction. Thus, more consideration of overall behavior of SOA formation is needed.
Chen, T.; Zhang, P.; Chu, B.; Ma, Q.; Ge, Y.; Liu, J.; He, H., Secondary organic aerosol formation from mixed volatile organic compounds: Effect of RO2 chemistry and precursor concentration. npj Clim Atmos Sci 2022, 5, (1), 95.
Chen, T.; Liu, Y.; Chu, B.; Liu, C.; Liu, J.; Ge, Y.; Ma, Q.; Ma, J.; He, H., Differences of the oxidation process and secondary organic aerosol formation at low and high precursor concentrations. J Environ Sci 2019, 79, 256-263.
Alfarra, M. R.; Hamilton, J. F.; Wyche, K. P.; Good, N.; Ward, M. W.; Carr, T.; Barley, M. H.; Monks, P. S.; Jenkin, M. E.; Lewis, A. C.; McFiggans, G. B., The effect of photochemical ageing and initial precursor concentration on the composition and hygroscopic properties of beta-caryophyllene secondary organic aerosol. Atmos Chem Phys 2012, 12, (14), 6417-6436.
Zhang, X.; Cappa, C. D.; Jathar, S. H.; McVay, R. C.; Ensberg, J. J.; Kleeman, M. J.; Seinfeld, J. H., Influence of vapor wall loss in laboratory chambers on yields of secondary organic aerosol. Proc Natl Acad Sci USA 2014, 111, (16), 5802-5807.
-
AC2: 'Reply on RC2', Giuseppe Petrucci, 05 Jan 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-1249/egusphere-2022-1249-AC2-supplement.pdf
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