Experimental Characterization of Particulate and Gaseous Emissions from Biomass Burning of Six Mediterranean Species and Litter

Round 1

Reviewer 1 Report

This manuscript has shown brilliant results on the characteristics of particulate and gaseous emissions from biomass burning in Meditteranean ecosystems.

However, it is necessary to add a further discussion regarding the results of trace elements obtained from this research. I wish the author could explain the differences between the trace elements detected in PM1, PM2.5, and PM10, but I can't find an adequate explanation of these differences.

This manuscript will have an extraordinary novelty if the author can explain this trace element phenomenon appropriately. 

Author Response

Response to Reviewer 1 Comments

Point 1: This manuscript has shown brilliant results on the characteristics of particulate and gaseous emissions from biomass burning in Meditteranean ecosystems.

However, it is necessary to add a further discussion regarding the results of trace elements obtained from this research. I wish the author could explain the differences between the trace elements detected in PM1, PM2.5, and PM10, but I can't find an adequate explanation of these differences.

This manuscript will have an extraordinary novelty if the author can explain this trace element phenomenon appropriately. 

Response 1: Dear Reviewer #1, thanks for your gratifying comment on the paper. We appreciate the constructive suggestions on adding a further discussion regarding the results of trace elements and we tried to ameliorate the work according to your comments.

As suggested, we integrated the discussion section with a large paragraph that handled in detail all trace elements found in the study. The additional text has been included within section 4.2 "Particles chemical composition" (new lines 660-699).

Reviewer 2 Report

The work is to be interesting, well structured in all its parts.
  But I wanted to make some comments to the authors

Line 90-91: what is meant by plant tissue?

Line 120-128: The different leaf morphology and consequent capacity of deposit and absorption in relation to the surface of the leaf blade were not taken into account in the choice of shrub and tree specimens.

Line 810-814: I do not agree with what is stated in this sentence. That is, being able to discern which particles are accumulated by trees and shrubs !!!!
In the conclusions paragraph some statements are not supported by the results and discussions paragraph, perhaps it should be reread!

The conclusions could be extended not only by referring to damage related to human health but also to air quality in the study area.

Author Response

Response to Reviewer 2 Comments

Point 1: The work is to be interesting, well structured in all its parts.
 But I wanted to make some comments to the authors

Response 1: Dear Reviewer #2, thanks for your general appreciation of our work. Below, we have answered all your comments in detail.

 

Point 2: Line 90-91: what is meant by plant tissue?

Response 2: Plant tissue refers to needles/leaves, branches, and needle/leaf litter as reported by the paper that we cited. For clarity, we integrate this information in the text (lines 90-91).

34. Pallozzi, E.; Lusini, I.; Cherubini, L.; Hajiaghayeva, R.A.; Ciccioli, P.; Calfapietra, C. Differences between a deciduous and a conifer tree species in gaseous and particulate emissions from biomass burning *. Environ. Pollut. 2018, 234, 457–467, doi:10.1016/j.envpol.2017.11.080.

 

Point 3: Line 120-128: The different leaf morphology and consequent capacity of deposit and absorption in relation to the surface of the leaf blade were not taken into account in the choice of shrub and tree specimens.

Response 3: Dear Reviewer #2, in our study, we sampled those species that well represented the local population. We sampled a coniferous (Pinus halepensis), broadleaf (Eucalyptus camaldulensis and Casuarina equisetifolia), and two shrubs (Juniperus oxycedrus and Pistacia lentiscus), thus considering different leaf morphology. Indeed, we did not consider the leaf morphology concerning the surface of the leaf blade but this was behind the purpose of our work. We were aimed to characterize particulate and gaseous emissions of Mediterranean species on a Protected Natural Reserve which is prone to fire, regardless of leaf morphology. Anyway, we are aware of the importance of leaf characteristics for the absorption and deposition of particles, especially since the findings of the study evidenced the characterizing presence of exogenous particles deposited on leaves and re-emitted during burning. Thus, this aspect could be certainly an interesting subject to examine in future work.

Point 4: Line 810-814: I do not agree with what is stated in this sentence. That is, being able to discern which particles are accumulated by trees and shrubs !!!!

Response 4: Dear Reviewer #2, we agree that, as it was presented, this conclusions section was not clear enough and could cause misunderstanding. The three bullet points you evidenced in the conclusions aimed to express and highlight the findings of our research and did not mean to be universal considerations.  

Thanks to your comment, we re-worded the sentences according to your considerations. Through the re-worded sentences we wanted to stress that differences evidenced between trees /shrubs/litter are strongly related to our study area:

“- The others higher vegetation types analyzed in our study, the tree species E. camaldulensis; C. equisetifolia and P. halepensis, are related to fine windblown particles: their canopies intercept PM10 and re-emit it during burning;

- Medium-high plants observed in our study, the 2 shrubs species P. lentiscus and J. oxycedrus are differentiated from other samples for the presence of resuspended particles from soil and/or roads;

- Litter samples evidenced a homogenous accumulation of different kinds of elements and markers, which characterize trees and shrubs in the study area.”

Point 5: In the conclusions paragraph some statements are not supported by the results and discussions paragraph, perhaps it should be reread!

Response 5: We re-read the conclusions statements and, taking into account the improvements made following both Reviewers’ comments, we did not find statements not supported by results and discussion. We are confident that the improvements brought to the manuscript, after the review process, bridged this gap. Here below we report all the conclusions statements with the relative connections to results and/or discussion sections.  

“•           PM10 emissions from forest burning is related to species-specific characteristics of trees and shrubs but are also strongly influenced by local environment/regional conditions;” à some examples: A. saligna showed a peculiar KCl emission of particles; E. camaldulensis is strongly characterized by higher percentages of C-based particles; and P. halepensis showed the particular presence of S. Among other, the presence of iron particles together with oil refinery marker elements show the effect of local conditions. (Section 3.2; Figure 3 a,b,c). 

“•           A. saligna stands out for the highest number of particles emitted and remarkable values of KCl which is probably related to a plant protection mechanism from salinity;” à Figure 6 and Section 4.2 (third paragraph). We tried to interpret and discuss the KCl presence in A. saligna by comparing it with previous studies on the same genus.

“•           The others higher vegetation types analyzed in our study, the tree species E. camaldu-lensis; C. equisetifolia and P. halepensis, are related to fine windblown particles: their canopies intercept PM10 and re-emit it during burning;” à the sentence has been modified following Point 4. Section 3.2 together with Figure 6 (PCA) shows the differences between most of the tree species and shrubs species based on their exogenous components of particles. Road re-suspension technological particles (Cu / Zn/ Sb) were found only on shrubs. Wind-related components are mostly found on trees.

“•           Medium high plants observed in our study, the 2 shrubs species P. lentiscus and J. oxycedrus are differentiated from other samples for the presence of resuspended particles from soil and/or roads;” as above.

“•           Litter samples evidenced a homogenous accumulation of different kinds of elements and markers, which characterize trees and shrubs in the study area;” as above.

“•           Benzene and toluene are the dominant aromatic compounds emitted.”→ Table 2 and Figure 6d2, and relative descriptions in results.  

“• A. saligna (highest number of particles emitted and medium values for gaseous emissions); → Figure 2a and Table 2, and relative descriptions in results.

“• P. lentiscus (high density of particles; anthropogenic particles like Fe, Steel and Road group; highest emissions for all gaseous compounds).”→ Figures 2a and 6a,b,c; Table 2, and relative descriptions in results.

“• C. equisetifolia (high density of particles; technology-related particles, like Fe with Steel group although lowest emissions for gaseous compounds);” → Figures 2a and 6a,b,c; Table 2, and relative descriptions in results.

“• We also point out litter and P. lentiscus as strong contributors to greenhouse gas emissions in the atmosphere, considering their high emissions of CO₂.” → Figures 2a and 6d; Table 2, and relative descriptions in results.

Point 6: The conclusions could be extended not only by referring to damage related to human health but also to air quality in the study area.

Response 6: We thank Reviewer 2, an additional general mention of air quality is more appropriate than only the potential damage to human health. We re-worded the sentence as follows: “Finally, the species identified in our study with a stronger impact on local air quality and potentially more dangerous for human health when combusted are: …”

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Thank you for the revision. This manuscript now is getting better after you added discussions on your results of the trace elements. Its more sound now and should be more exciting to the readers.

However, you may want to add some expression for the last point of your conclusions. as for me all of the species studied here are subjected to be the emitter of CO2 if they are burnt. You may add some expressions such as 'stronger than another species(?) or other ones to show the higher level of litter and P. lenticus to CO2 emissions compare to other species that may contribute also to the GHG emissions if they are burnt. 

Author Response

Response to Reviewer 1 Comments

Point 1: Thank you for the revision. This manuscript now is getting better after you added discussions on your results of the trace elements. Its more sound now and should be more exciting to the readers.

However, you may want to add some expression for the last point of your conclusions. as for me all of the species studied here are subjected to be the emitter of CO2 if they are burnt. You may add some expressions such as 'stronger than another species(?) or other ones to show the higher level of litter and P. lenticus to CO2 emissions compare to other species that may contribute also to the GHG emissions if they are burnt.. 

Response 1: Dear Reviewer #1, as you suggested we modified the last statement in the conclusions section. This modification was needed and the last section was now improved in terms of consistency. Here below we report the new version: “We also point out litter and P. lentiscus as the strongest contributors to greenhouse gas emissions in the atmosphere if compared to all species ana-lysed, considering their significantly higher emissions of CO₂.”