the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 18 Dec 2023
Probabilistic hazard assessment of the gas emission of Mefite d’Ansanto, Southern Italy
Abstract. The emission of gas species dangerous for human health and life is a widespread source of hazard in various natural contexts. These mainly include volcanic areas but also non-volcanic geological contexts. A notable example of the latter occurrence is the Mefite d’Ansanto area in the Southern Apennines in Italy. Here, large emissions of carbon dioxide (CO2) occur at rates that make this the largest non-volcanic CO2 gas emission in Italy and probably of the Earth. Given the topography of the area, in certain meteorological conditions a cold gas stream forms in the valleys surrounding the emission zone, which proved to be potentially lethal for humans and animals in the past. In this study we present a gas hazard quantification study that considers the main specie, that is CO2, and the potential effect of the most dangerous, which is hydrogen sulphide (H2S). For these purposes we used VIGIL, a tool that manages the workflow of gas dispersion simulations specifically optimised for probabilistic hazard applications. Results are discussed and presented in form of maps of CO2 and H2S concentration and persistence at various exceedance probabilities considering the gas emission rates and their possible range of variation defined in previous studies.
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RC1: 'Comment on egusphere-2023-2867', Anonymous Referee #1, 14 Mar 2024
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The article “Probabilistic hazard assessment of the gas emission of Mefite d’Ansanto, Southern Italy” presents several gas dispersion simulations applied to previous recorded data and constitute a valuable approach to evaluate the hazard in this area that releases anomalous high CO2.
Diffuse degassing areas may occur both in volcanic and non-volcanic environments, as Mefite d’Ansanto and these approaches may be applied in several other degassing sites. The article well describes the tools and the methodologies used to perform the simulations, what is a positive aspect for further users. The article is in general well organized and the figure/tables are adequate.
I would suggest, however, a better clarification of the newness of the article, since it is not so clear. Is there any step of the analyses that is new in the current study or it is just the first time is applied in this degassing area? All these procedures integrating different tools (DISGAS, TWODEE-2, DIAGNO) were already applied before? This should be better clarified. Authors estimate probability maps not only for the CO2, but decided also to include the H2S. Was this approach already applied in other sites? Considering that CH4 may also be hazardous in certain concentrations and that the CH4 concentration in the emission is also high (Table 1 from the article), did authors consider to apply the methodology also to the CH4?
Chiodini et al. (2010) applied the TWODEE-2 code to the same dataset at Mefite. Authors should better discuss what are the major differences obtained between the two different studies especially when DISGAS is applied to similar wind conditions as the ones applied in the previous study.
Some more general comments:
Section 1. I suggest authors to review the references used for the CO2 thresholds and exposure time. Authors refer in one case to an Italian reference (Settimo et al., 2022) together with some studies that do not focus on these thresholds but use them based on other literature. I suggest one of the options: or authors include the references and add “and references therein”, or, in a better way, use more fundamental and specific literature on these thresholds, impacts and exposure time. Some recommendations are: Blong, 1984; Wong, 1996; IVHHN, NIOSH - https://stacks.cdc.gov/view/cdc/19367 (line 21 – page 1). I also suggest checking the references sequence in the text. Some of them do not appear with the chronological sequence.
Section 2. On the characterization of the area I suggest authors to better characterize the area including mention that the emissions are cold and the fluxes previously estimated by Rogie et al. (2000) and Chiodini et al. (2010). For instance, Rogie et al. (2000) report that CO2 concentrations > 30 vol.% were measured at an height higher than 2 m. This is an interesting aspect to recall in the discussion to compare with the results obtained in the current study.
Section 4. Tables 2 and 3 in my opinion need to be improved. Another column should be added in both tables to mention the maximum recommended exposure time for each of the thresholds. I would split the effects and the exposure times. Then, the last column would report the “tested exposure time in the current study”. Otherwise it seems that humans can be exposed to 10 vol.% during 1 hour (Table 1) and this is not true and could even be lethal. In fact, in Table 2 authors need to add that in this last threshold (100 000 = 10 vol.%) death can also be one of the effects. Same comment for the 500 ppm associated to the H2S. Still in what concerns Table 2, I suggest authors to use specific literature (NIOSH, Blong, Wong, as mentioned above, and complete the symptoms per threshold considered, since there is lack of symptoms in the table). The IDLH mentioned in the text (line 259, page 10) for the H2S also exists for the CO2 and should be mentioned (and added in the table). I suggest to review this section based on additional literature.
Section 5. The discussion and evaluation of the hazard considering different seasons is a very interesting contribution that should be applied in other degassing areas. Nevertheless, it is important that future studies attempt to couple seasonal degassing maps with the meteorological data associated with the different seasons. Several studies on degassing areas showed that CO2 is usually higher during winter comparing to summer, and for this reason the evaluation of this coupled (and eventually contradictory) effect will be very interesting. Is this the first study that reports these seasonal maps? If yes, this is not mentioned in the abstract and it should.
The are some general technical comments that I would like to call the attention, namely the need to control all the figures and tables that do not appear correctly in the text. This needs to be carefully checked:
- For instance, in line 29 – page 1, authors refer Figure 1, but this sentence refers to Figure 2b.
- Line 78, page 3 – the links to the webpages of NIOSH could be added as references (e.g. NIOSH, 2019), and then the links appear in the references list.
- Line 85, page 3 – authors should add the units also for the isotopes in the table.
- Figure 1 was redrawn from Chiodini et al. (2010). Looking at the literature, there are several geophysical studies (e.g. https://www.mdpi.com/1424-8220/23/3/1630; https://pubs.geoscienceworld.org/ssa/bssa/article-abstract/113/3/1102/620681/Hydrothermal-Seismic-Tremor-in-a-Wide-Frequency?redirectedFrom=fulltext) that were recently developed and I wonder if they could be used to improve the scheme showed. Authors should check. Anyway, remember that Figures 1 and 2 need to be checked as they are wrongly referenced in the text.
- Line 97, page 4 – check the chronological sequence of the references.
- Line 204, page 8 – when appears “figure 2” should appear “Figure 2”.
- Figure 2 – I think Figure 2 could be improved by inserting in Figure 2b a square with the location of Figure 2c.
- Line 221, page 9 – check what figure should be mentioned in the text. It does not refer to Figure 1.
- Line 245, page 9 – the number of the tables also need to be checked along the text. I believe that authors refer to “Table 2” and not “Table 1” as it is written.
- Table 3 – there is a reference missing in the first line.
- Line 285, page 13 – I think authors meant “winds blowing” instead of “finds blowing”. Check.
- Lines 294 and 295, page 14 – I could not see in the figure the statement “is also not negligible… along the main”. Maybe I misunderstood the sentence, but please check.
- Line 307, page 14 – Table 4 instead of Table 3.
- Line 318, page 14 –I wonder why authors decided to check the exceedance probability of 16%, and not any other percentage? What was the criteria?
- Line 382, page 21 – authors mention that certain concentrations of CO2 may be very dangerous for the human health, but I would even add for the “human life”, as in certain concentrations CO2 is lethal and it was even reported casualties in the area.
- Line 404, page 22 – “was evaluated” is repeated in the sentence.
Citation: https://doi.org/10.5194/egusphere-2023-2867-RC1 -
AC1: 'Reply on RC1', Fabio Dioguardi, 22 Mar 2024
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RC2: 'Reply on AC1', Anonymous Referee #1, 25 Mar 2024
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After reading the point to point answers, where authors state that they will implement the suggested corrections, I have not further comments. I am happy that the article is published after implementing the corrections.
Citation: https://doi.org/10.5194/egusphere-2023-2867-RC2
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RC2: 'Reply on AC1', Anonymous Referee #1, 25 Mar 2024
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