the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Feb 2024
Surprisingly high levels and activity contributions of oxygenated volatile organic compounds on the southeast of the Tibetan Plateau
Abstract. Oxygenated volatile organic compounds (OVOCs) are reactive species and the primary precursors of free radicals; thus, OVOCs play important roles in tropospheric chemistry. @Tibet field campaigns 2021 discovered surprisingly high levels and activity contributions of OVOCs at Lulang, a site with high vegetation cover and strong solar ultraviolet radiation on the southeast of the Tibetan Plateau (TP). The 13 OVOCs detected accounted for 49 % of the total VOCs (TVOCs; average level of 11.7 ± 4.4 ppb), and the levels of these OVOCs exhibited typical diurnal variation, with high values in the daytime and a peak at approximately 12:00. OVOCs contributed 65 % and 63 % to VOC-kOH and the ozone formation potential, respectively, and thus had a strong influence on atmospheric chemical processes. Two independent methods were used to determine the contributions of various sources and revealed consistent conclusions regarding the importance of biological sources there. The source apportionment results obtained through positive matrix factorization indicated that sunlight-impacted and direct plant emission sources both related to plant sources contributed 47 % of the TVOCs and 65 % of the OVOCs. OVOC source fitting through the photochemical age parameterization method also indicated that biogenic sources made the largest contribution (67 %) to OVOCs and revealed a clear peak at noon. In addition, biomass burning sources were found to be closely related to the VOC background because biomass burning is highly prevalent across the whole TP; these sources made the second greatest contribution (33 %) to the TVOCs and contributed more than 23 % of OVOCs.
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RC1: 'Comment on egusphere-2024-262', Anonymous Referee #1, 03 Mar 2024
The manuscript, "Surprisingly high levels and activity contributions of oxygenated volatile organic compounds on the southeast of the Tibetan Plateau" based on the VOCs online observation experiment at the South-East Tibetan plateau Station for integrated observation and research of alpine environment in Lulang. It is 101 VOCs species were detected, including 13 OVOCs. The authors analyzed the contribution of OVOCs to VOCs concentration, OH• reactivity and OFP in the southeastern Tibetan Plateau. At the same time, PMF and PAP source analysis methods were combined to explain the maximum possible OVOCs contribution sources. However, there are doubts about the method used by the author to analyze OVOCs species by GS-MS/FID. The concentration of OVOCs obtained by GS-MS/FID method currently has a large uncertainty, so it is impossible to determine whether the conclusion obtained in this paper is correct. Therefore, the publication of this paper cannot be accepted, with deep regret.
Specific comments
- EPA TO15 and TO11A standard methods specify the analysis methods of NMHCs and carbonyl compounds in atmosphere respectively. When GS-MS/FID is used to analyze highly polar carbonyl compounds, there is a large uncertainty. The same adsorption column is used to detect OVOCs and other VOCs species, and the adsorption effect of the column adsorbed other VOCs is not good for polar OVOCs. Meanwhile, humidity and wall effect will make the GC-MS/FID method very susceptible to the detection of OVOCs species. Secondly, GS-MS/FID cannot detect formaldehyde, which accounts for a large proportion of OVOCs in daily detection. And the absence of formaldehyde may lead to the underestimation of the contribution of OVOCs to VOCs concentration and OFP, which has great limitations on the analysis of the nature of OVOCs species. Therefore, the current GC-MS/FID method for detecting OVOCs species is not reliable. The data thus obtained cannot lead to correct conclusions.
- In lines 72-76, when describing the situation around the observation site, the author mainly introduced the sites tens of kilometers away. This description does not seem to highlight the point, nor does it play a significant role in understanding the origin of OVOCs species at the Lulang It is suggested that the author consider the description here and make changes.
- Lines 160-173 describe the dominant species in no obvious order or logic, but the conclusion of the paragraph in line 173 states that OVOCs and alkenes have an important effect on the air of Lulang. It is suggested that OVOCs and other VOCs species should be explained in two parts based on the conclusion.
- In lines 174-185, in the comparison between this experiment and other background sites or ordinary sites, the comparison logic is rather confused, and I can't see what the author wants to highlight at last. It is suggested that the author clarify the description logic, rearrange the content, and summarize the corresponding conclusion.
- In lines 303-315, after completing the fitting of photochemical aging parameters, the author only analyzed acetaldehyde and acetone, and did not mention other species. It is suggested that the author supplement the reasons why these two species were discussed separately, or supplement the analysis of other species.
Technical comments
- In Line 16 of the article, ";" in (TVOCs; average level of 11.7 ± 4.4 ppb) looks some strange. It is suggested that the author to change.
- There are some formatting problems in the illustrations of the article, such as the English font in the figures does not seem to use the New Roman font, and the scale lines of the picture frame sometimes face inward and sometimes face out, so it is suggested that the author should unify to make the graphics more beautiful. Secondly, the vertical axis label fonts of sub-figure 1 in Figure 4 overlap, so it is suggested that the author modify them.
- In the reference part of the article, the subscript format of "O3" should also be set. It is suggested that the author check and refer to all literatures and unify the format.
Citation: https://doi.org/10.5194/egusphere-2024-262-RC1 - AC1: 'Reply on RC1', Weili Lin, 07 Mar 2024
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RC2: 'Comment on egusphere-2024-262', Anonymous Referee #2, 11 Mar 2024
The authors of the manuscript, “Surprisingly high levels and activity contribution of oxygenated volatile organic compounds on the southeast of the Tibetan Plateau”, present observed characteristics of VOCs composition in a Tibet field campaign at Lulang, and investigate the sources of different VOC species using PMF and PAP approach. It is an interesting project, the outcome of which will definitely strengthen the understanding of atmospheric composition, especially in terms of OVOCs, in Tibetan Plateau. I appreciate the efforts the authors have made in conducting the in-situ measurements, analyzing the observational data, and performed the source apportionment. However, there are key questions need to be addressed before the manuscript become a qualified scientific article of Atmospheric Chemistry and Physics.
General comments:
1. The current Introduction provides very limited information on the innovation of the authors’ study. While VOCs are important air pollutants affecting atmospheric chemistry and human health, the authors are expected to provide more specific information on what makes their study a unique one, instead of spending most words in general introductions which are commonly knew. As the authors listed, there have been a few studies investigating OVOCs at different sites over the TP. What are the differences between their study and the previous ones? What innovative findings can they provide to advance the understanding of OVOCs at TP? Unfortunately, the audience cannot tell according to the authors’ descriptions. The VOC observations are so hard-won, and hopefully they can be well presented.
2. As the authors have mentioned, the PMF model includes a hypothesis that the composition profile of the studied air pollutants does not change in the air. As OVOCs are highly active, the PMF model may not be a quit suitable approach for source attribution of OVOCs. The authors suggest that they have introduced the initial mixing ratio to address this problem for a certain VOC species. Have this correction been applied to the concentrations of all the species included in the source apportionment? To what extent this mismatching problem can be fixed? The description is not clear so the related results presented by the authors are questionable from the perspective of audience. Even though the authors have obtained similar source attribution results from PMF and PAP methods, I still suggest them to consider whether the PMF part of discussion should be included in the manuscript if they cannot address the problem correctly.
3. As for the PAP method, the authors use another assumption that the OVOC emission is proportional to that of an inert tracer. There are observational evidence suggesting the correlation between the emissions of secondary organic VOCs with these inert traces (e.g., CO and benzene) from traditional sector (e.g., transportation) and volatile chemical products (e.g., pesticides, coatings, inks, cleaning agents). Do these emissions are important sources of VOCs over the region of the authors’ interest? Is there any observational evidence proving the rationality of this hypothesis in estimating OVOC emissions from other sectors? All the related queries should be addressed, otherwise the source attribution results cannot be logically convinced unfortunately.
4. Given the shortcomings of the approaches that the authors have used in tracking the sources of VOCs, discussions on the uncertainty of their results should be necessary to show the audience the significance and representative of this study.
Specific comments:
L33: It would be better to use ‘both’ than ’whether’ in this sentence.
L34: ‘Activity’ is a countable noun, so it would be good to use plural here.
L54: Transport from south Asia is not ‘transcontinental’ transport.
L68-79: There are geographical information on so many different sites there. It would be good to show a map figure so that the audience can tell the relative location of these names more directly.
L77: Please add “LST” after the two time periods
L84: It would be good to include the name of each VOC species in Supporting Information so that the audience can get what VOC species are included in each group in this study.
L95: It would be good to introduce the approach briefly in the manuscript even though it has been used in other related works before.
L106-107: Please cite the related references here.
L128: Please explain how the emissions of OVOC and benzene can be obtained.
L152: It seems that the Lulang site is not an urban site according to the descriptions in Introduction section, but the observed CO and NOx still show distinct urban diurnal variations. The results are kind of confusing.
L156: It is hard to tell the diurnal variations of each VOC species in Figure1b, since it shows the accumulated concentrations. The authors may consider to use a more direct way to present this.
L174-196: I appreciate the efforts that the authors have made to compare their observations with literature studies. The results should be interesting. However, more innovative analysis should be conducted to make the manuscript more than an observational report. Unfortunately, the descriptions here are just another way to present Table S1. Questions (e.g., what cause the observed differences between this study and previous ones? Why the authors’ measurements matter a lot in VOC observational studies?) that the audience may be interested in are not mentioned at all.
L211: The authors suggest there is a surprisingly high levels of OVOCs observed at Lulang, however, the observed concentrations seem not that ‘surprising’ compared to literature studies in Figure 3. The authors would make more efforts in presenting why they think their findings are surprising. Otherwise, they may want to revise the misleading tile of the manuscript.
L271: Are there many emission from solvent sources in Lulang?
L296: Please explain how the mountain-valley can affect the VOC concentrations at Lulang.
Citation: https://doi.org/10.5194/egusphere-2024-262-RC2 - AC2: 'Reply on RC2', Weili Lin, 01 Apr 2024
-
RC3: 'Comment on egusphere-2024-262', Anonymous Referee #3, 18 Mar 2024
The manuscript titled "Surprisingly high levels and activity contributions of oxygenated volatile organic compounds on the southeast of the Tibetan Plateau" by Guo et al. reports findings from the @Tibet field campaigns 2021. The study focuses on oxygenated volatile organic compounds (OVOCs), which are significant for tropospheric chemistry due to their roles as precursors to free radicals. The research found high levels of OVOCs in Lulang, a region on the southeast of the Tibetan Plateau characterized by high vegetation cover and intense solar ultraviolet radiation. The study detected 13 OVOCs accounting for 49% of the total VOCs, with notable diurnal variation peaking at noon. These compounds contributed significantly to VOC reactivity and ozone formation potential. Source apportionment using positive matrix factorization and photochemical age parameterization methods indicated that biogenic sources, particularly plant emissions influenced by sunlight, were the primary contributors to the OVOC levels, with biomass burning also being a significant source.
The dataset may benefit the broad research community from the geographical uniqueness of the field site. However, the manuscript should clarify the key analyses of the manuscript to evaluate the scientific merit of the manuscript.
- I am not convinced the level of OVOC observed in this manuscript should be considered 'surprising.' surprising is an ill-defiled term for scientific literature. Using the term would be more acceptable if the presented results clearly contrasted with conventional wisdom, which is not the case for the presented dataset. I think OVOCs should be high in the studied area as it is far away from the major emission sources. I would recommend either the authors drop the term ‘surprising, or make a scientific argument if the observed OVOC levels are ‘surprising’
- Equation 3 appears too simplistic to account for real-world source distributions. Many other anthropogenic VOCs produce OVOCs other than benzene. The study should discuss how dominant benzene is as an OVOC source for justification. I understand isoprene is the most dominant BVOC on the global scale, but locally, it may not be the case. Without a proper justification, the underlying assumption cannot be prudently established.
- In the past decade, a substantial progress has made in the atmospheric isoprene oxidation processes, which illustrates the first-generation oxidation product yield (e.g. MVK and MACR) substantially varies as a function of the NO levels. The Equation (2) should be reconsidered to reflect the development.
Citation: https://doi.org/10.5194/egusphere-2024-262-RC3 - AC3: 'Reply on RC3', Weili Lin, 01 Apr 2024
Status: closed
-
RC1: 'Comment on egusphere-2024-262', Anonymous Referee #1, 03 Mar 2024
The manuscript, "Surprisingly high levels and activity contributions of oxygenated volatile organic compounds on the southeast of the Tibetan Plateau" based on the VOCs online observation experiment at the South-East Tibetan plateau Station for integrated observation and research of alpine environment in Lulang. It is 101 VOCs species were detected, including 13 OVOCs. The authors analyzed the contribution of OVOCs to VOCs concentration, OH• reactivity and OFP in the southeastern Tibetan Plateau. At the same time, PMF and PAP source analysis methods were combined to explain the maximum possible OVOCs contribution sources. However, there are doubts about the method used by the author to analyze OVOCs species by GS-MS/FID. The concentration of OVOCs obtained by GS-MS/FID method currently has a large uncertainty, so it is impossible to determine whether the conclusion obtained in this paper is correct. Therefore, the publication of this paper cannot be accepted, with deep regret.
Specific comments
- EPA TO15 and TO11A standard methods specify the analysis methods of NMHCs and carbonyl compounds in atmosphere respectively. When GS-MS/FID is used to analyze highly polar carbonyl compounds, there is a large uncertainty. The same adsorption column is used to detect OVOCs and other VOCs species, and the adsorption effect of the column adsorbed other VOCs is not good for polar OVOCs. Meanwhile, humidity and wall effect will make the GC-MS/FID method very susceptible to the detection of OVOCs species. Secondly, GS-MS/FID cannot detect formaldehyde, which accounts for a large proportion of OVOCs in daily detection. And the absence of formaldehyde may lead to the underestimation of the contribution of OVOCs to VOCs concentration and OFP, which has great limitations on the analysis of the nature of OVOCs species. Therefore, the current GC-MS/FID method for detecting OVOCs species is not reliable. The data thus obtained cannot lead to correct conclusions.
- In lines 72-76, when describing the situation around the observation site, the author mainly introduced the sites tens of kilometers away. This description does not seem to highlight the point, nor does it play a significant role in understanding the origin of OVOCs species at the Lulang It is suggested that the author consider the description here and make changes.
- Lines 160-173 describe the dominant species in no obvious order or logic, but the conclusion of the paragraph in line 173 states that OVOCs and alkenes have an important effect on the air of Lulang. It is suggested that OVOCs and other VOCs species should be explained in two parts based on the conclusion.
- In lines 174-185, in the comparison between this experiment and other background sites or ordinary sites, the comparison logic is rather confused, and I can't see what the author wants to highlight at last. It is suggested that the author clarify the description logic, rearrange the content, and summarize the corresponding conclusion.
- In lines 303-315, after completing the fitting of photochemical aging parameters, the author only analyzed acetaldehyde and acetone, and did not mention other species. It is suggested that the author supplement the reasons why these two species were discussed separately, or supplement the analysis of other species.
Technical comments
- In Line 16 of the article, ";" in (TVOCs; average level of 11.7 ± 4.4 ppb) looks some strange. It is suggested that the author to change.
- There are some formatting problems in the illustrations of the article, such as the English font in the figures does not seem to use the New Roman font, and the scale lines of the picture frame sometimes face inward and sometimes face out, so it is suggested that the author should unify to make the graphics more beautiful. Secondly, the vertical axis label fonts of sub-figure 1 in Figure 4 overlap, so it is suggested that the author modify them.
- In the reference part of the article, the subscript format of "O3" should also be set. It is suggested that the author check and refer to all literatures and unify the format.
Citation: https://doi.org/10.5194/egusphere-2024-262-RC1 - AC1: 'Reply on RC1', Weili Lin, 07 Mar 2024
-
RC2: 'Comment on egusphere-2024-262', Anonymous Referee #2, 11 Mar 2024
The authors of the manuscript, “Surprisingly high levels and activity contribution of oxygenated volatile organic compounds on the southeast of the Tibetan Plateau”, present observed characteristics of VOCs composition in a Tibet field campaign at Lulang, and investigate the sources of different VOC species using PMF and PAP approach. It is an interesting project, the outcome of which will definitely strengthen the understanding of atmospheric composition, especially in terms of OVOCs, in Tibetan Plateau. I appreciate the efforts the authors have made in conducting the in-situ measurements, analyzing the observational data, and performed the source apportionment. However, there are key questions need to be addressed before the manuscript become a qualified scientific article of Atmospheric Chemistry and Physics.
General comments:
1. The current Introduction provides very limited information on the innovation of the authors’ study. While VOCs are important air pollutants affecting atmospheric chemistry and human health, the authors are expected to provide more specific information on what makes their study a unique one, instead of spending most words in general introductions which are commonly knew. As the authors listed, there have been a few studies investigating OVOCs at different sites over the TP. What are the differences between their study and the previous ones? What innovative findings can they provide to advance the understanding of OVOCs at TP? Unfortunately, the audience cannot tell according to the authors’ descriptions. The VOC observations are so hard-won, and hopefully they can be well presented.
2. As the authors have mentioned, the PMF model includes a hypothesis that the composition profile of the studied air pollutants does not change in the air. As OVOCs are highly active, the PMF model may not be a quit suitable approach for source attribution of OVOCs. The authors suggest that they have introduced the initial mixing ratio to address this problem for a certain VOC species. Have this correction been applied to the concentrations of all the species included in the source apportionment? To what extent this mismatching problem can be fixed? The description is not clear so the related results presented by the authors are questionable from the perspective of audience. Even though the authors have obtained similar source attribution results from PMF and PAP methods, I still suggest them to consider whether the PMF part of discussion should be included in the manuscript if they cannot address the problem correctly.
3. As for the PAP method, the authors use another assumption that the OVOC emission is proportional to that of an inert tracer. There are observational evidence suggesting the correlation between the emissions of secondary organic VOCs with these inert traces (e.g., CO and benzene) from traditional sector (e.g., transportation) and volatile chemical products (e.g., pesticides, coatings, inks, cleaning agents). Do these emissions are important sources of VOCs over the region of the authors’ interest? Is there any observational evidence proving the rationality of this hypothesis in estimating OVOC emissions from other sectors? All the related queries should be addressed, otherwise the source attribution results cannot be logically convinced unfortunately.
4. Given the shortcomings of the approaches that the authors have used in tracking the sources of VOCs, discussions on the uncertainty of their results should be necessary to show the audience the significance and representative of this study.
Specific comments:
L33: It would be better to use ‘both’ than ’whether’ in this sentence.
L34: ‘Activity’ is a countable noun, so it would be good to use plural here.
L54: Transport from south Asia is not ‘transcontinental’ transport.
L68-79: There are geographical information on so many different sites there. It would be good to show a map figure so that the audience can tell the relative location of these names more directly.
L77: Please add “LST” after the two time periods
L84: It would be good to include the name of each VOC species in Supporting Information so that the audience can get what VOC species are included in each group in this study.
L95: It would be good to introduce the approach briefly in the manuscript even though it has been used in other related works before.
L106-107: Please cite the related references here.
L128: Please explain how the emissions of OVOC and benzene can be obtained.
L152: It seems that the Lulang site is not an urban site according to the descriptions in Introduction section, but the observed CO and NOx still show distinct urban diurnal variations. The results are kind of confusing.
L156: It is hard to tell the diurnal variations of each VOC species in Figure1b, since it shows the accumulated concentrations. The authors may consider to use a more direct way to present this.
L174-196: I appreciate the efforts that the authors have made to compare their observations with literature studies. The results should be interesting. However, more innovative analysis should be conducted to make the manuscript more than an observational report. Unfortunately, the descriptions here are just another way to present Table S1. Questions (e.g., what cause the observed differences between this study and previous ones? Why the authors’ measurements matter a lot in VOC observational studies?) that the audience may be interested in are not mentioned at all.
L211: The authors suggest there is a surprisingly high levels of OVOCs observed at Lulang, however, the observed concentrations seem not that ‘surprising’ compared to literature studies in Figure 3. The authors would make more efforts in presenting why they think their findings are surprising. Otherwise, they may want to revise the misleading tile of the manuscript.
L271: Are there many emission from solvent sources in Lulang?
L296: Please explain how the mountain-valley can affect the VOC concentrations at Lulang.
Citation: https://doi.org/10.5194/egusphere-2024-262-RC2 - AC2: 'Reply on RC2', Weili Lin, 01 Apr 2024
-
RC3: 'Comment on egusphere-2024-262', Anonymous Referee #3, 18 Mar 2024
The manuscript titled "Surprisingly high levels and activity contributions of oxygenated volatile organic compounds on the southeast of the Tibetan Plateau" by Guo et al. reports findings from the @Tibet field campaigns 2021. The study focuses on oxygenated volatile organic compounds (OVOCs), which are significant for tropospheric chemistry due to their roles as precursors to free radicals. The research found high levels of OVOCs in Lulang, a region on the southeast of the Tibetan Plateau characterized by high vegetation cover and intense solar ultraviolet radiation. The study detected 13 OVOCs accounting for 49% of the total VOCs, with notable diurnal variation peaking at noon. These compounds contributed significantly to VOC reactivity and ozone formation potential. Source apportionment using positive matrix factorization and photochemical age parameterization methods indicated that biogenic sources, particularly plant emissions influenced by sunlight, were the primary contributors to the OVOC levels, with biomass burning also being a significant source.
The dataset may benefit the broad research community from the geographical uniqueness of the field site. However, the manuscript should clarify the key analyses of the manuscript to evaluate the scientific merit of the manuscript.
- I am not convinced the level of OVOC observed in this manuscript should be considered 'surprising.' surprising is an ill-defiled term for scientific literature. Using the term would be more acceptable if the presented results clearly contrasted with conventional wisdom, which is not the case for the presented dataset. I think OVOCs should be high in the studied area as it is far away from the major emission sources. I would recommend either the authors drop the term ‘surprising, or make a scientific argument if the observed OVOC levels are ‘surprising’
- Equation 3 appears too simplistic to account for real-world source distributions. Many other anthropogenic VOCs produce OVOCs other than benzene. The study should discuss how dominant benzene is as an OVOC source for justification. I understand isoprene is the most dominant BVOC on the global scale, but locally, it may not be the case. Without a proper justification, the underlying assumption cannot be prudently established.
- In the past decade, a substantial progress has made in the atmospheric isoprene oxidation processes, which illustrates the first-generation oxidation product yield (e.g. MVK and MACR) substantially varies as a function of the NO levels. The Equation (2) should be reconsidered to reflect the development.
Citation: https://doi.org/10.5194/egusphere-2024-262-RC3 - AC3: 'Reply on RC3', Weili Lin, 01 Apr 2024
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