the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Apr 2024
High Altitude Aerosol Chemical Characterization and Source Identification: Insights from the CALISHTO Campaign
Abstract. The Cloud-AerosoL InteractionS in the Helmos background TropOsphere (CALISHTO) campaign took place in autumn 2021 at the NCSR Demokritos background high-altitude Helmos Hellenic Atmospheric Aerosol & Climate Change station (HAC)2 to study the interactions between aerosols and clouds. The current study presents the chemical characterization of the Non-Refractory (NR) PM1 aerosol fraction using a Time-of-Flight Aerosol Chemical Speciation Monitor (ToF-ACSM). A comparative offline aerosol filter analysis by a High-Resolution Time-of-Flight Aerosol Mass Spectrometry (HR-ToF-AMS) showed consistent results regarding the species determined. Source apportionment applied on both datasets (ACSM-ToF and offline AMS analysis on filter extracts) yielded the same factors for the organic aerosol (one primary and two secondary factors). Additionally, the Positive Matrix Factorization (PMF) model was applied on the total PM1 fraction by the ToF-ACSM (including both organic and inorganic ions). Five different types were identified, including a primary organic factor, ammonium nitrate, ammonium sulphate, and two secondary organic aerosols; one more and one less oxidized. The prevailing atmospheric conditions at the station, i.e. cloud presence, influence from emissions from the Planetary Boundary Layer (PBL) and air mass origin were also incorporated in the study. The segregation between PBL and Free Troposphere (FT) conditions was made by combining data from remote sensing and in-situ measurement techniques. The types of air masses arriving at the site were grouped as continental, marine, dust and marine-dust based on back trajectories data. Significant temporal variability in the aerosol characteristics was observed throughout the campaign; in September, air masses from within the PBL were sampled most of the time, resulting in much higher mass concentrations compared to October and November when concentrations were reduced by a factor of 5. Both in-cloud and FT measurement periods resulted in much lower concentration levels, while similar composition was observed in PBL and FT conditions. We take advantage of using a recently developed “virtual filtering” technique to separate interstitial from activated aerosol sampled from a PM10 inlet during cloudy periods. This allows the determination of the chemical composition of the interstitial aerosol during in-cloud periods. Ammonium sulphate, the dominant PMF factor in all conditions, contributed more when air masses were arriving at (HAC)2 during Dust events, while higher secondary organic aerosol contribution was observed when air masses arrived from continental Europe.
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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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Preprint
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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
(1924 KB) - BibTeX
- EndNote
- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2024-737', Anonymous Referee #2, 17 Apr 2024
The manuscript by Zografou et al. describes measurements of aerosol composition collected at a high-altitude site and discusses aerosol-cloud interactions and differences between the boundary layer and free tropospheric aerosol. The manuscript is clear and relevant to the scientific community. I recommend for publication with the following minor revisions.
Specific Comments:
- Section 2: I don’t think the measurement duration is stated in the main text. Please include the dates (or at least number of days) in section 1 or 2.
- Section 3.1: It would be helpful to include the proportion of measurements collected in the FT versus in the BL. Additionally, what portion of the time has the collocated HALO measurements that were used for verification, and what portion was separated utilizing the thresholds described in section 3.
- I believe that more clarification is needed about the virtual filtering technique that is used. On line 360 it is stated that when Deff is < 13.5 µm, it is assumed that the composition reflects both the interstitial and residual, and when Deff is > 13.5 µm the composition reflects only the interstitial aerosol, however this still leaves me with some questions.
- Does this method account for the droplet size distribution at all. For example, if the Deff is slightly above the threshold, there are still likely to be some droplets smaller than 13.5µm. Will these still be sampled and categorized as interstitial?
- A description of the statistics of the duration of the cloud events is needed to provide confidence in these comparisons. How many cloud periods occurred, and what fraction of these were filtered as interstitial or activated. I might recommend including a time series of Deff in supplemental material - for example in conjunction with Figure S6.
- What are the main variables effecting the Deff at this site. Is there a possibility that the events with Deff above the filtering threshold are systematically different (in regards to sources and/or aerosol composition) than those with lower Deff.
- I am slightly wary of figures 2 and 3. In figure 2, why does the interstitial box plot have error bars for 1SD, but no 25-75% area? Likewise, why does the activated box have neither. In figure 3, the organic FT has no 25-75 box.
- Section 4.4: two of the backtrajectories contain the label “dust”. Is there direct evidence that the aerosol actually contains dust particles (i.e. increase in TSP mass or evidence from the XRF measurements), or is this an assumption based on the back trajectory. As the focus of section 4.4 is on the submicron non-refractory aerosol composition, which is less likely to be directly impacted by dust, this nomenclature is slightly confusing as it seems probable that these periods are influenced by long range transport of pollutants. However, if there is evidence of these chemical differences being related to the presence of dust, this would be an important finding and should be more clearly stated.
Technical corrections:
Line 177: Missing parenthesis on citation
Line 332: The LWC threshold used for defining the cloud periods is not clearly stated.
Line 360: Whether a droplet activated also depends on aerosol composition as non-hygroscopic aerosol (i.e. most POA, eBC, etc) will not activate event with sufficient LWC or adequate aerosol size.
Citation: https://doi.org/10.5194/egusphere-2024-737-RC1 -
RC2: 'Comment on egusphere-2024-737', Anonymous Referee #1, 17 May 2024
The authors present a statistical analysis of chemical composition measured using a time of flight aerosol chemical speciation monitor at a mountain top site located in Greece. The analysis focuses on contrasting aerosol composition in the free troposphere and planetary boundary layer, and between cloud free, interstitial and activated aerosol. Positive matrix factorization is used to identify several factors contributing to the organic aerosol mass. I recommend the manuscript for publication after the following comments are addressed.
It would be helpful to more effectively summarize if the mass fractions of the different aerosol species - including the OA factors - vary between the PBL and the activated aerosol. It is probably buried somewhere in Figure 2, but it’s hard to quickly extract from the presentation. It wasn’t clear from the text to me what an 84 % activation rate really means.
It would seem to be important to better explain the in-cloud sampling technique, as it is new and not well characterized. Especially detailed discussion on how it differs from a traditional CVI inlet are critical to include. What is the precise cut size? How broad is the cut size? What are the transmission efficiencies of the transmitted cloud droplets? Is there an upper limit? Is there broad number closure (maybe even just with modeled CDNC since only the PVM was available) between CDNC passing through the inlet and measured residual aerosol number concentration? Perhaps these details are derived in the submitted papers, but it needs to be presented here as well.
The structure of the text could be improved. There seemed to be significant discussion of results with reference to Figures in the supplementary information. It would seem to me that many of these results should be promoted to the main text and/or discussion in the text referring to supplementary figures should be de-emphasized.
There are two Foskinis et al. papers in review. Please distinguish in the citations.
Citation: https://doi.org/10.5194/egusphere-2024-737-RC2 - AC1: 'Comment on egusphere-2024-737', Olga Zografou, 22 May 2024
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-737', Anonymous Referee #2, 17 Apr 2024
The manuscript by Zografou et al. describes measurements of aerosol composition collected at a high-altitude site and discusses aerosol-cloud interactions and differences between the boundary layer and free tropospheric aerosol. The manuscript is clear and relevant to the scientific community. I recommend for publication with the following minor revisions.
Specific Comments:
- Section 2: I don’t think the measurement duration is stated in the main text. Please include the dates (or at least number of days) in section 1 or 2.
- Section 3.1: It would be helpful to include the proportion of measurements collected in the FT versus in the BL. Additionally, what portion of the time has the collocated HALO measurements that were used for verification, and what portion was separated utilizing the thresholds described in section 3.
- I believe that more clarification is needed about the virtual filtering technique that is used. On line 360 it is stated that when Deff is < 13.5 µm, it is assumed that the composition reflects both the interstitial and residual, and when Deff is > 13.5 µm the composition reflects only the interstitial aerosol, however this still leaves me with some questions.
- Does this method account for the droplet size distribution at all. For example, if the Deff is slightly above the threshold, there are still likely to be some droplets smaller than 13.5µm. Will these still be sampled and categorized as interstitial?
- A description of the statistics of the duration of the cloud events is needed to provide confidence in these comparisons. How many cloud periods occurred, and what fraction of these were filtered as interstitial or activated. I might recommend including a time series of Deff in supplemental material - for example in conjunction with Figure S6.
- What are the main variables effecting the Deff at this site. Is there a possibility that the events with Deff above the filtering threshold are systematically different (in regards to sources and/or aerosol composition) than those with lower Deff.
- I am slightly wary of figures 2 and 3. In figure 2, why does the interstitial box plot have error bars for 1SD, but no 25-75% area? Likewise, why does the activated box have neither. In figure 3, the organic FT has no 25-75 box.
- Section 4.4: two of the backtrajectories contain the label “dust”. Is there direct evidence that the aerosol actually contains dust particles (i.e. increase in TSP mass or evidence from the XRF measurements), or is this an assumption based on the back trajectory. As the focus of section 4.4 is on the submicron non-refractory aerosol composition, which is less likely to be directly impacted by dust, this nomenclature is slightly confusing as it seems probable that these periods are influenced by long range transport of pollutants. However, if there is evidence of these chemical differences being related to the presence of dust, this would be an important finding and should be more clearly stated.
Technical corrections:
Line 177: Missing parenthesis on citation
Line 332: The LWC threshold used for defining the cloud periods is not clearly stated.
Line 360: Whether a droplet activated also depends on aerosol composition as non-hygroscopic aerosol (i.e. most POA, eBC, etc) will not activate event with sufficient LWC or adequate aerosol size.
Citation: https://doi.org/10.5194/egusphere-2024-737-RC1 -
RC2: 'Comment on egusphere-2024-737', Anonymous Referee #1, 17 May 2024
The authors present a statistical analysis of chemical composition measured using a time of flight aerosol chemical speciation monitor at a mountain top site located in Greece. The analysis focuses on contrasting aerosol composition in the free troposphere and planetary boundary layer, and between cloud free, interstitial and activated aerosol. Positive matrix factorization is used to identify several factors contributing to the organic aerosol mass. I recommend the manuscript for publication after the following comments are addressed.
It would be helpful to more effectively summarize if the mass fractions of the different aerosol species - including the OA factors - vary between the PBL and the activated aerosol. It is probably buried somewhere in Figure 2, but it’s hard to quickly extract from the presentation. It wasn’t clear from the text to me what an 84 % activation rate really means.
It would seem to be important to better explain the in-cloud sampling technique, as it is new and not well characterized. Especially detailed discussion on how it differs from a traditional CVI inlet are critical to include. What is the precise cut size? How broad is the cut size? What are the transmission efficiencies of the transmitted cloud droplets? Is there an upper limit? Is there broad number closure (maybe even just with modeled CDNC since only the PVM was available) between CDNC passing through the inlet and measured residual aerosol number concentration? Perhaps these details are derived in the submitted papers, but it needs to be presented here as well.
The structure of the text could be improved. There seemed to be significant discussion of results with reference to Figures in the supplementary information. It would seem to me that many of these results should be promoted to the main text and/or discussion in the text referring to supplementary figures should be de-emphasized.
There are two Foskinis et al. papers in review. Please distinguish in the citations.
Citation: https://doi.org/10.5194/egusphere-2024-737-RC2 - AC1: 'Comment on egusphere-2024-737', Olga Zografou, 22 May 2024
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Cited
Olga Zografou
Maria Gini
Prodromos Fetfatzis
Konstantinos Granakis
Romanos Foskinis
Manousos Ioannis Manousakas
Fotios Tsopelas
Evangelia Diapouli
Eleni Dovrou
Christina N. Vasilakopoulou
Alexandros Papayannis
Spyros N. Pandis
Athanasios Nenes
Konstantinos Eleftheriadis
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(1324 KB) - Metadata XML
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Supplement
(1924 KB) - BibTeX
- EndNote
- Final revised paper