the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 16 Oct 2023
Chemical characterization of atmospheric aerosols at a high-altitude mountain site: a study of source apportionment
Elena Barbaro
Matteo Feltracco
Fabrizio De Blasi
Clara Turetta
Marta Radaelli
Warren Cairns
Giulio Cozzi
Giovanna Mazzi
Marco Casula
Jacopo Gabrieli
Carlo Barbante
Andrea Gambaro
Abstract. The study of aerosol in high mountain regions is essential because particulate matter can play a role in altering the energy balance of high mountain regions, and aerosols can accelerate glacier melting in high mountain areas by darkening the ice surface, reducing its reflectivity (albedo). Studying aerosols in high mountain areas provides insights into long-range transport of pollutants, atmospheric dynamics, and climate change impacts. These regions can serve as valuable observatories for studying atmospheric processes.
The main aim of this paper is to define the main sources of aerosol over an entire year of sampling at the Col Margherita Atmospheric Observatory (MRG 46° 22’ 0.059’’ N, 11° 47’ 30.911’’ E, 2543 m a.s.l.), a high-altitude background site in the Eastern Italian Alps. Here, we discuss the potential origins of more than one hundred chemical markers (major ions, water soluble organic compounds, trace elements, rare earth elements) using different approaches. Some diagnostic ratios were applied, but source apportionment using Positive Matrix Factorization was used to define the main inputs of PM10 collected at this high-altitude site. Moreover, a characterization of the air masses helped us to confirm the aerosol sources.
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Elena Barbaro et al.
Status: open (until 31 Dec 2023)
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RC1: 'Comment on egusphere-2023-2346', Anonymous Referee #1, 30 Nov 2023
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A review of the paper of authors:
Elena Barbaro, Matteo Feltracco, Fabrizio De Blasi, Clara Turetta, Marta Radaelli, Warren Cairns, Giulio Cozzi, Giovanna Mazzi, Marco Casula, Jacopo Gabrieli, Carlo Barbante, Andrea Gambaro
Chemical characterization of atmospheric aerosols at a high altitude mountain site: a study of source apportionmentSubmitted to ACP
The paper deals with analysis of one-year long dataset of very comprehensive chemical analysis results of PM10 samples at high altitude mountain sampling site at the Col Margherita Atmospheric Observatory. The authors obtained a unique dataset of 100 inorganic and organic chemical species based on analysis of 87 four-day samples using low volume samplers and a flow rate 38.3 l/min. Elemental analysis was provided using ICP-SFMS, water soluble compounds were analysed for inorganic ions, organic acids, monosaccharides, sugar alcohols, anhydrosugars, sucrose, amino acids, phenolic compounds and photooxidation products of α-pinen. Finally, the data were analysed using different statistical methods including PMF and air mass trajectory analysis. However, there are major issues that prevent to publish the manuscript in current state.
Major issues
Although, the reviewer cannot fully accept using balances with 0.1 mg resolution for gravimetry of samples taken using low volume sampler in such pristine environment despite four day samples, this is not a major objection.
More important is that except for elemental analysis no other method used is even named and at least some parameters of analysis should be mentioned not only references that are given here.
Second, based on average seasonal composition of Fig 2 and Fig 3 water soluble anions (mainly sulphates and nitrates) form important mass of PM10 mass and based on ionic balance Fig 3 they are compensated mainly as usual by NH4+ but in similar way by Ca2+. It is clear that in such case NH4+/ SO42- ratio cannot be used as a measure for nitrates formation, because large part of pH control is provided by Ca2+ and other cations, not only by NH4+. In this case, 96 hour sampling also prevent such conclusion as, due to long sampling, there is large probability that filter pass through high RH phase when part of aerosol become liquid and all redundant NH4+ will be removed from the solution into gas phase by Ca2+ and other cations especially when they are present as carbonates as the authors suppose. In the same time, free nitric acid can be captured on the filter if available in the air. Based on the above, the lines 230-245 should be removed.
Third, source apportionment needs substantial improvement. The matrix itself is already well below recommended threshold ratio between number of lines to number of columns that is 3:1. This could be improved by removing several apparently quite correlated crustal related species. The method used for selection of number of factors is not referenced and it is not clear if any of the used chemical species was set “weak” or “bad”. Moreover, it is quite clear on the base of presented solution, that uncertainty matrix is not constructed properly, the whole solution is driven by elemental composition and major species among water soluble ions, amino acids, PDαP, PC or sugar-like compounds are modelled quite badly (Table S1). Most probably the errors of elemental composition are set much lower in comparison to rest of the data, harmonisation of uncertainties is needed. Finally, for PMF solution the major Saharan dust event having almost one order higher concentrations than any other datapoint must be removed from the dataset as it is another driving force that distorts the solution.Minor comments
Line 58 and many other cases: chemical formulas should be typed properly e.g. NH4+ instead of NH4+
Lines 74-75: preheating of filters seems at edge, ACTRIS recommendation is 3 hours at 800°C, 4h at 400°C may not be enough, but especially for elemental carbon that is not measured here.
Line 75: At this first occasion it is not clear if 96 h means that each sample was sampled for 96 h or any shorter time every 4th day. Please correct.
Lines 125: the sentence: “ The elevation of the site was considered the elevation of site (2543 m a.s.l)…” should be corrected
Line 133: Concentrations are given at µg/m3. It should be stated clearly whether volumes are real one or standard volumes.
Line 380 – ssCa is used here as reference element for marine enrichment factors. However, it is not clear at all how ssCa was calculated and if it is even possible when a lot of calcium carbonate is probably present that become soluble in acidic environment on the filter as mentioned above.
Line 384-385 – LREE, MREE and HREE are not defined before)
Fig 9 – it is difficult to find blue point due to very small data points
Fig 9 and Fig 10 – bigger legend and number font is needed, it is difficult to read it.
Conclusions should be corrected after major revisions.Citation: https://doi.org/10.5194/egusphere-2023-2346-RC1 -
RC2: 'Comment on egusphere-2023-2346', Anonymous Referee #2, 05 Dec 2023
reply
This study presents a thorough discussion on the chemical composition of PM10 at Col Margherita. The datasets and analysis are robust and provide valuable insights for high-altitude background sites. The source apportionment results are interesting, as mass trajectories from different regions have distinct chemical characteristics. The manuscript can be further improved in the following aspects:
- The abstract only included the meaning of the study and the method. The main conclusions were not mentioned.
- It seems only ~30 compounds were used in the PMF analysis, despite that ~100 is measured. What’s the reason? What would happen like if all the measured species are included?
- Figure 13, the PMF results only show contributions from primary sources and are mostly transported from other regions, are there secondary sources or background aerosols?
- Section 3.2 provides too many details and some may not be relevant to the main conclusions of the manuscript, these parts can go to the supplementary information. For instance, Figure 7-11 provides too many information on the trace elements and it distract the readers a lot.
- Line 468, the traffic/refinery and oil combustion process are not recognized in PMF. Please discuss the reasons.
Other minor comments:
- Line 57-62 was duplicated with Line 165-173.
- Line 94: what instrument is used to analyze the organic compounds?
- The definition of periods are obscure, please define in the method which month are regarded as “spring”, ”summer”, “autumn”, “winter”, ”the seasons without snow cover”, “the snow season”, “the cold period”.
- Figure 2, what is “CA”, why it increases in Spring and Summer?
- Line 161-162 please give a brief preview here of what might be missing in December and January, and mention the exact section that discuss this in detail. It’s hard for the readers to search for the clues in the long discussion part.
- Line 173, please give a brief ratio of the concentration measured by the two methods.
- Line 266-268 The logic here is hard to understand. Authors say that the two acids are from α-pinene, then they say its poorly understood? And the following examples in Line 268-230 should provide specific conclusions of the two studies.
Elena Barbaro et al.
Elena Barbaro et al.
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