the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Physicochemical and Temporal Characteristics of Individual Atmospheric Aerosol Particles in Urban Seoul during KORUS-AQ Campaign: Insights from Single-Particle Analysis
Hanjin Yoo
Hong Geng
Chul-Un Ro
Abstract. Single-particle analysis was conducted to characterize atmospheric aerosol particles collected at Olympic Park in Seoul, Korea as a part of the KORUS-AQ campaign which was carried out during May–June 2016. The KORUS-AQ campaign aimed to understand the temporal and spatial characteristics of atmospheric pollution on the Korean Peninsula through an international cooperative field study. A total of 8004 individual particles from 52 samples collected between 5/23–6/5, 2016, were investigated using a quantitative electron probe X-ray microanalysis (low-Z particle EPMA), resulting in the identification of seven major particle types. These included genuine and reacted mineral dust, sea-spray aerosols, secondary aerosol particles, heavy metal-containing particles, combustion particles, Fe-rich particles, and others (biogenic and humic-like substances (HULIS) particles). Distinctly different relative abundances of individual particle types were observed during five characteristic atmospheric situations, namely (a) a mild haze event influenced by local emissions and air mass stagnation, (b) a typical haze event affected by northwestern air masses with a high proportion of sulfate-containing particles, (c) a haze event with a combined influence of northwestern air masses and local emissions, (d) a clean period with low particulate matter concentrations and a blocking pattern, and (e) an event with an enhanced level of heavy metal-containing particles, with Zn, Mn, Ba, Cu, and Pb being the major species identified. Zn-containing particles were mostly released from local sources such as vehicle exhausts and waste incinerations, while Mn, Ba, and Cu-containing particles were attributed to metal-alloy plants or mining. The results suggest that the morphology and chemical compositions of atmospheric aerosol particles in urban area vary depending on their size, sources, and reaction or ageing status, and are affected by both local emissions and long-range air masses.
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Hanjin Yoo et al.
Status: open (until 18 Oct 2023)
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RC1: 'Comment on egusphere-2023-1787', Anonymous Referee #1, 15 Sep 2023
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Yoo et al. present a concise and well-written investigation of individual particles collected in Seoul as part of the KORUS-AQ campaign, with the goal of investigating the different particle types that might be found as a result of different atmospheric events. The authors furthermore specifically highlight the composition of particles in the supermicron size range. Some of the core findings aren’t particularly novel (e.g., from the abstract: “atmospheric aerosol 34 particles in urban area vary depending on their size, sources, and reaction or ageing status..”), and have been well known to the atmospheric community at large for some time. However, the authors don’t attempt to sell this as the novel aspect, and instead emphasize the need to establish these kinds of relationships for particle types that aren’t generally well characterized in a variety of environments (e.g., supermicron). The relatively high abundance of heavy metal particles that were observed is particularly interesting as well. I believe that this study will be publishable in ACP pending the addressment of several minor concerns listed below:
Page 4 Lines 120 – 123: Please use the HYSPLIT references that NOAA specifically requests (Stein et al; Rolph et al; https://www.ready.noaa.gov/HYSPLIT_traj.php).
Page 4 Lines 126 – 128: The vacuum conditions needed to analyze particles via SEM should be acknowledged, and caveats should be listed for how this affects the final particle characterization (e.g., bias against more volatile components).
Page 5 Line 149: The referred to particle classification scheme in the SI is somewhat unclear – the particle classification descriptions appear rather qualitative at times (e.g., ‘particles containing many heavy metals’) rather than a more precise, quantitative description (e.g., what quantitative abundance of which specific heavy metals do the authors use to assess a particle as one containing heavy metals?). As a result, it is somewhat difficult to get a true appreciation for how particle classification was done. Even if the authors are reproducing a previously published classification scheme, the precise information should be reproduced in the SI and if necessary, referenced accordingly.
Figure 3-4: Consider using a different color scheme that is more amenable to color-blindness.
Page 11 Lines 313 – 314: While the authors suppositions here may be true, they should caveat them by noting the extremely number of total particles that lead them to these observations.
Figure 4: Consider labeling what the various stages are in the figure, or alternatively, at least list it in the figure caption.
Page 14 Lines 369 – 370: Have the authors investigated the potential of biomass burning/wildfires specifically instead of just combustion in general? Consider the NASA fire map resource.
Citation: https://doi.org/10.5194/egusphere-2023-1787-RC1 -
AC1: 'Reply on RC1', Chul-Un Ro, 15 Sep 2023
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We appreciate the reviewer's thoughtful review, favorable evaluation, and valuable comments for our manuscript. All the minor comments and suggestions raised by the reviewer will be respected in the revised manuscript.
Citation: https://doi.org/10.5194/egusphere-2023-1787-AC1
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AC1: 'Reply on RC1', Chul-Un Ro, 15 Sep 2023
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RC2: 'Comment on egusphere-2023-1787', Anonymous Referee #2, 28 Sep 2023
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This study investigated physicochemical properties of individual particles during the KORUS-AQ campaign using a quantitative electron probe X-ray microanalysis. This study classified these individual particles into seven types and atmospheric situations into five types. This study showed relative abundances of different types of particles during five types of atmospheric situations. This study found that Zn-containing particles were mostly sourced from local vehicle exhausts and waste incinerations, while Mn, Ba, and Cu-containing particles were mainly attributed to metal-alloy plants or mining emissions. This study suggested that the morphology and chemical compositions of particles were affected by their sources and ageing processes. Although this study clearly expressed the results, some problems listed below need to be addressed before the manuscript could be published.
- L16: Please indicate the full name of ‘KORUS-AQ’.
- L117: The second sampling time (15:00 ~ 16:00) should be afternoon. I don't think it's appropriate for the authors to consider this period as an evening.
- L117-118: What is the range of sampling duration? The authors should show it.
- Section 3.1: The authors classified individual particles into seven types, but most of these seven types of particles are externally mixed. As we know, particles are usually internally mixed in aged air, especially during polluted periods. Many researchers have found this phenomenon in urban air using high-resolution TEM, such as internal mixing of carbonaceous and secondary inorganic aerosols (Adachi & Buseck, 2013; Li et al., 2021; Zhang et al., 2022). I suggest the authors to further consider the internal mixing of secondary aerosols and other particles (e.g., carbonaceous or metal-containing particles) to better evaluate the source of particles.
- Some data sources did not be indicated, such as ‘73.2% and 44.5%’ on L181, ‘71.0%’ on L189, and etc. A table may be appropriate.
- L272: ‘As’ is not a heavy metal element. Correspondingly, some results in section 3.1.5 and figures (e.g., Figure 3) need to be changed.
- L340: During period I, the air mass is more likely to be long-range transported based on backward trajectories in Figure S4a. How did the authors determine the period I as a local polluted event?
- L375-384: The sentence is repeated.
- L398-399: This result confuses me. Based on backward trajectories in Figure S4b, air masses at high altitudes (1000 m A.G.L) should be transported from northeastern China rather than that at low altitudes showed by the authors. Air masses at low altitudes are mainly from the local area.
Reference list:
Adachi, K., & Buseck, P. R. (2013). Changes of ns-soot mixing states and shapes in an urban area during CalNex. J. Geophys. Res.-Atmos., 118(9), 3723-3730. https://doi.org/10.1002/jgrd.50321
Li, W., Teng, X., Chen, X., Liu, L., Xu, L., Zhang, J., Wang, Y., Zhang, Y., Shi, Z., 2021. Organic Coating Reduces Hygroscopic Growth of Phase-Separated Aerosol Particles. Environmental Science & Technology 55 (24), 16339-16346.
Zhang, J., Wang, Y., Teng, X., Liu, L., Xu, Y., Ren, L., Shi, Z., Zhang, Y., Jiang, J., Liu, D., Hu, M., Shao, L., Chen, J., Martin, S.T., Zhang, X., Li, W., 2022. Liquid-liquid phase separation reduces radiative absorption by aged black carbon aerosols. Communications Earth & Environment 3 (1), 128.
Citation: https://doi.org/10.5194/egusphere-2023-1787-RC2 -
AC2: 'Reply on RC2', Chul-Un Ro, 03 Oct 2023
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Reply to Reviewer’s comments:
First of all, we thank the reviewer for the positive evaluation and valuable suggestions for our work.
* Comment #4: Section 3.1: The authors classified individual particles into seven types, but most of these seven types of particles are externally mixed. As we know, particles are usually internally mixed in aged air, especially during polluted periods. Many researchers have found this phenomenon in urban air using high-resolution TEM, such as internal mixing of carbonaceous and secondary inorganic aerosols (Adachi & Buseck, 2013; Li et al., 2021; Zhang et al., 2022). I suggest the authors to further consider the internal mixing of secondary aerosols and other particles (e.g., carbonaceous or metal-containing particles) to better evaluate the source of particles.
Response: Thank you for your valuable comment. We agree that individual particles, particularly in aged air, can be characterized more in detail by investigating their internal mixing, and we are grateful for the references the reviewer provided. The significance of internally mixed particles in pinpointing pollution sources and understanding their health and climate implications is well recognized by us, too. However, given the extensive dataset of over 8,000 particles in this study, our primary objective was to delve deeply into the physicochemical and temporal characteristics of these particles, relating them to atmospheric conditions and transport pathways. To reflect the importance of internal mixing and to clarify our intent, we will modify Section 3.1 in the final version, ensuring the inclusion of reviewer’s valuable comments and suggested references.
* Comment #6: L272: ‘As’ is not a heavy metal element. Correspondingly, some results in section 3.1.5 and figures (e.g., Figure 3) need to be changed.
Response: The term "heavy metal" has been somewhat ambiguously used, and its definition can vary based on the context. As the reviewer points out, ‘As (arsenic)’ is, by strict chemical classification, a metalloid, which means it possesses properties intermediate between metals and nonmetals. Nonetheless, the term "heavy metal" in environmental and toxicological contexts often encompasses both toxic metals and certain metalloids, like arsenic. This classification is informed not only by the element's strict chemical classification but also by its practical implications related to density and toxicity. Specifically, arsenic has a significant density (5.7 g/cm3) and notable toxicological effects on organisms, as highlighted in studies such as Tian et al., 2015 (in the manuscript), and following references.
Nies. D. H., Microbial heavy-metal resistance, Appl. Microbiol. Biotechnol., 51, 730-750, 1999.
Li et al., The preferential accumulation of heavy metals in different tissues following frequent respiratory exposure to PM2.5 in rats, Sci. Rep., 2015, DOI: 10.1038/srep16936.
Mc Neill et al., Large global variations in measured airborne metal concentrations driven by anthropogenic sources, Sci. Rep., 2020, doi.org/10.1038/s41598-020-78789-y.
* Comment #7: L340: During period I, the air mass is more likely to be long-range transported based on backward trajectories in Figure S4a. How did the authors determine the period I as a local polluted event?
Response: As shown in Fig. S4a, the majority of the airmass on that day came mainly via Korea's inland regions, indicating a strong influence of local emissions. The PM concentration shown in Fig. S3 also exhibit relatively higher value than clean period (6/1-6/3). Moreover, the ratio of SOA to secondary aerosol particles was observed to be approximately 2.5 times higher on that day. This observation aligns with findings from Nault et al. (2019), Kim et al. (2018a), and Kim et al. (2018b), which indicated that the primary sources of SOA in Korea are local emissions. Studies from the KORUS-AQ campaign, conducted during the same timeframe, further suggest that air masses experienced stagnation under persistent high pressure. This stagnation likely resulted in local emissions becoming the predominant contributors (Kim et al., 2018b; Peterson et al., 2019; Heim et al., 2020).
* Comment #9: L398-399: This result confuses me. Based on backward trajectories in Figure S4b, air masses at high altitudes (1000 m A.G.L) should be transported from northeastern China rather than that at low altitudes showed by the authors. Air masses at low altitudes are mainly from the local area.
Response: The reviewer correctly observed that the air mass at a high altitude (1000 m A.G.L) displayed in Fig. S4b originates from northeastern China. Nevertheless, the air masses at lower altitudes (250 m and 500 m A.G.L) directly reached Korea via the Shandong Peninsula and the Yellow Sea. The duration for which low-altitude air masses spent over the Korean inland before reaching the sampling site was shorter than 3 hours. The spatial coverage and transit time of the air masses over Korean terrain shown in Fig. S4b were considerably smaller and shorter compared to their journey during periods of local pollution as shown in Fig. S4a.
* Comments #1, #2, #3, #5, and #8, which suggest the modifications in the text and figures, will be respected in the final version.
Citation: https://doi.org/10.5194/egusphere-2023-1787-AC2
Hanjin Yoo et al.
Hanjin Yoo et al.
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