the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Jun 2024
Atmospheric evolution of environmentally persistent free radicals in rural North China Plain: insights into water solubility and effects on PM2.5 oxidative potential
Abstract. Environmentally Persistent Free Radicals (EPFRs) represent a novel class of hazardous substances, posing risks to human health and the environment. In this study, we investigated the EPFRs in ambient fine, coarse, and total suspended particulate matter (PM2.5, PM10, TSP) in rural North China Plain, where local primary emissions of EPFRs were limited. We observed that the majority of EPFRs occurred in PM2.5. Moreover, distinct seasonal patterns and higher g-factors of EPFRs were found compared to those in urban environments, suggesting unique characteristics of EPFRs in rural areas. The source apportionment analyses revealed atmospheric oxidation as the largest contributor (33.6 %) to EPFRs. A large water-soluble fraction (35.2 %) of EPFRs was determined, potentially resulting from the formation of more oxidized EPFRs through atmospheric oxidation processes during long-range/regional transport. Additionally, significant positive correlations were observed between EPFRs and the oxidative potential of water-soluble PM2.5 measured by dithiothreitol-depletion and hydroxyl-generation assays, likely attributable to the water-soluble fractions of EPFRs. Overall, our findings reveal the prevalence of water-soluble EPFRs in rural areas and underscore atmospheric oxidation processes can modify their properties, such as increasing their water solubility. This evolution may alter their roles in contributing to the oxidative potential of PM2.5 and potentially also influence their impact on climate-related cloud chemistry.
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Notice on discussion status
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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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
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Supplement
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-1622', Anonymous Referee #1, 04 Jul 2024
The study examined the concentration, size distribution, and seasonal variations of EPFRs in the North China Plain region, as well as investigated their sources using PMF. It also explored the role of EPFR speciation in contributing to the oxidative potential of PM. I find this study very interesting and important. The authors have done a great job to discuss other studies comprehensively. I only have two comments as follows:
- The conclusion that the majority of EPFRs are present in PM2.5 is drawn from the fact that the average EPFRv in PM2.5 accounts for over 95.2% of those in PM10 and TSP. However, the box plots in Fig. 1 suggest that PM2.5 EPFRs may not make up such a high fraction. I recommend that the authors calculate the fraction of EPFRs in PM2.5 in PM10 or TSP for each sample and average it for discussion, for better representativeness.
- In Section 3.3.2 and Fig. 4, the associations of OP with various chemical species are discussed. The OP values are in mass-normalized activities, while the chemical species are in ambient concentrations in m3. It would be helpful for the authors to explain why volume-normalized OP data were not utilized for the association discussion, which makes more sense to me.
Citation: https://doi.org/10.5194/egusphere-2024-1622-RC1 -
AC1: 'Reply on RC1', Fobang Liu, 06 Aug 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1622/egusphere-2024-1622-AC1-supplement.pdf
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RC2: 'Comment on egusphere-2024-1622', Anonymous Referee #2, 31 Jul 2024
This study presents measurements of environmentally persistent free radicals (EPFRs) and oxidative potential (OP) of different size fractions of PM (PM2.5, PM10, TSP) collected over 1 year in a rural site in the North China Plane. The authors investigated the sources of EPFR using positive matrix factorisation and explored the role of solubility on EPFRs and their contribution to OP. Overall, the study is well written and presented, providing new insights into the sources contributing to EPFR, as well as the influence of EPFRs on OP, and the results are comprehensively compared to the literature. The findings in this study are novel and certainly within the scope of ACP. I recommend publication and only have a few minor comments.
- Line 57 - I am unclear as to the meaning of nonsolvent-extractable, please clarify.
- Were filters in this study all extracted and analysed at the end of the sampling campaign or were they systematically analysed during the measurement campaign? This is important to clarify given the broad range of lifetimes of EPFRs.
- References for the DTT protocol should be provided.
- Line 121 – Typo “The rest DTT...”
- Line 122-126. The authors state that 2-OHTA production is proportional to OH formation, however Gonzalez et al (2018) demonstrated that the yield of the 2-OHTA from the terephthalate-OH reaction is around 31%, and thus calculated OH concentrations need to be corrected concerning the yield of 2-OHTA . Have the author’s considered this when calculation OPOH? Ref: https://doi.org/10.1080/00032719.2018.1431246
- Regarding the correlation of OP to components (Section 3.3.2, Figure 4), mass normalised OP values were used, but were these correlated with mass normalised components (e.g. Fe ug-1)? This should be clarified. It also seems strange that correlation analysis between EPFR and components is not presented in the main manuscript in Figure 4, given a lot of the manuscript focus is on EPFRs.
Citation: https://doi.org/10.5194/egusphere-2024-1622-RC2 -
AC2: 'Reply on RC2', Fobang Liu, 06 Aug 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1622/egusphere-2024-1622-AC2-supplement.pdf
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-1622', Anonymous Referee #1, 04 Jul 2024
The study examined the concentration, size distribution, and seasonal variations of EPFRs in the North China Plain region, as well as investigated their sources using PMF. It also explored the role of EPFR speciation in contributing to the oxidative potential of PM. I find this study very interesting and important. The authors have done a great job to discuss other studies comprehensively. I only have two comments as follows:
- The conclusion that the majority of EPFRs are present in PM2.5 is drawn from the fact that the average EPFRv in PM2.5 accounts for over 95.2% of those in PM10 and TSP. However, the box plots in Fig. 1 suggest that PM2.5 EPFRs may not make up such a high fraction. I recommend that the authors calculate the fraction of EPFRs in PM2.5 in PM10 or TSP for each sample and average it for discussion, for better representativeness.
- In Section 3.3.2 and Fig. 4, the associations of OP with various chemical species are discussed. The OP values are in mass-normalized activities, while the chemical species are in ambient concentrations in m3. It would be helpful for the authors to explain why volume-normalized OP data were not utilized for the association discussion, which makes more sense to me.
Citation: https://doi.org/10.5194/egusphere-2024-1622-RC1 -
AC1: 'Reply on RC1', Fobang Liu, 06 Aug 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1622/egusphere-2024-1622-AC1-supplement.pdf
-
RC2: 'Comment on egusphere-2024-1622', Anonymous Referee #2, 31 Jul 2024
This study presents measurements of environmentally persistent free radicals (EPFRs) and oxidative potential (OP) of different size fractions of PM (PM2.5, PM10, TSP) collected over 1 year in a rural site in the North China Plane. The authors investigated the sources of EPFR using positive matrix factorisation and explored the role of solubility on EPFRs and their contribution to OP. Overall, the study is well written and presented, providing new insights into the sources contributing to EPFR, as well as the influence of EPFRs on OP, and the results are comprehensively compared to the literature. The findings in this study are novel and certainly within the scope of ACP. I recommend publication and only have a few minor comments.
- Line 57 - I am unclear as to the meaning of nonsolvent-extractable, please clarify.
- Were filters in this study all extracted and analysed at the end of the sampling campaign or were they systematically analysed during the measurement campaign? This is important to clarify given the broad range of lifetimes of EPFRs.
- References for the DTT protocol should be provided.
- Line 121 – Typo “The rest DTT...”
- Line 122-126. The authors state that 2-OHTA production is proportional to OH formation, however Gonzalez et al (2018) demonstrated that the yield of the 2-OHTA from the terephthalate-OH reaction is around 31%, and thus calculated OH concentrations need to be corrected concerning the yield of 2-OHTA . Have the author’s considered this when calculation OPOH? Ref: https://doi.org/10.1080/00032719.2018.1431246
- Regarding the correlation of OP to components (Section 3.3.2, Figure 4), mass normalised OP values were used, but were these correlated with mass normalised components (e.g. Fe ug-1)? This should be clarified. It also seems strange that correlation analysis between EPFR and components is not presented in the main manuscript in Figure 4, given a lot of the manuscript focus is on EPFRs.
Citation: https://doi.org/10.5194/egusphere-2024-1622-RC2 -
AC2: 'Reply on RC2', Fobang Liu, 06 Aug 2024
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2024/egusphere-2024-1622/egusphere-2024-1622-AC2-supplement.pdf
Peer review completion
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Xu Yang
Shuqi Yang
Yuling Yang
Yanan Wang
Jingjing Li
Mingyu Zhao
Zhao Wang
Kai Wang
Chi He
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(2615 KB) - Metadata XML
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Supplement
(2257 KB) - BibTeX
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- Final revised paper