the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Oct 2023
Measurement report: Intra-annual Variability of Black/Brown Carbon and Its Interrelation with Meteorological Conditions over Gangtok, Sikkim
Abstract. Black carbon (BC) and brown carbon (BrC) have versatile nature, and they have apparent role in the climate variability and changes. As the anthropogenic activity is surging, the BC and BrC are also reportedly increasing. So, the monitoring of BC/BrC and observation of land use land cover changes (LULCC) at regional level are necessary for the various interconnected meteorological phenomenal changes. The current study investigates BC, BrC, CO2, BC from fossil fuels (BCff), BC from biomass burning (BCbb), LULCC, and their relationship to the corresponding meteorological conditions over Gangtok in Sikkim Himalayan region. The concentration of BC (BrC) 43.5 μg/m3 (32.0 μg/m3) is found to be highest during the March-2022 (April-2021). Surface pressure has been found to have a significant positive correlation with BC, BCff, BCbb and BrC. The boundary layer is calmer and more stable when the surface pressure is higher, which keeps contaminants deposited there. The wind, on the other hand, appears to represent the dispersion of pollutants with a strong negative correlation. The fact that all pollutants and precipitation have been shown to behave similarly points to moist scavenging of the pollutants. Despite the dense cloud cover, the area is not receiving convective precipitation, implying that orographic precipitation is occurring over the region. Most of Sikkim receives convective rain from May to September, indicating that the region has significant convective activity contributed from the Bay of Bengal during monsoon season. Furthermore, monsoon months have the lowest concentrations of BC, BCbb, BCff, and BrC, suggesting the potential of convective rain (as rain out scavenging) to remove most of the pollutants. Moreover, BC and BrC show positive radiative feedback.
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RC1: 'Comment on egusphere-2023-702', Anonymous Referee #1, 29 Oct 2023
This manuscript discussed about the Black carbon (BC) and Brown Carbon (BrC) variability based on measurements from March 2021 to March 2022 over Gangtok and their link with meteorological conditions obtained from satelitte observations. They discuss the inter-relationship between BC and BrC emissions and their potential impact on climate, with the co-emission of CO2 and the impact on temperature and the potential role of BC/BrC as cloud condensation nuclei. I don’t think the manuscript can be accepted as it is, the main reasons are addressed in the major comments.
Major comments:
- I addressed only a small part of the grammatical issues in my minor comments but the authors should seek the advise of an editor to revise the manuscript’s language accuracy.
- There is no mention of the mass absorption cross section used to estimate the mass concentration of BrC and considering the uncertainties around such value for BrC, it would be best to avoid using BrC mass concentrations and use BrC absorption coefficient at 370 nm instead.
- Also, it is hard to see the link between LULC 2000, 2010 and 2020 and how it impacts the BC/BrC emissions and climate with only the measurement from 2021 and 2022. It might be easier to just state that the growing urbanization of the region may be at least partially responsible for the level of BC/BrC and CO2 observed.
- There is a need for more references to support the different ideas mentioned in the discussion.
Minor Comments:
- Page 4 line 125: what does the author mean by “fragile forest covers” and “The Gangtok is a densely populated city”
- Page 6 equation 3: It is mentioned in the text “the negative log-log slope” so I would assume that a minus is missing in the actual equation.
- Section 3.1: The way all the equations are numbered and the reference to the supplement is very confusing.
- Page 6 Equation 1: The following writing is confusing “σBC + BrC(370 nm)” for the total absorption coefficient at 370, maybe write itσBC+BrC(370 nm).
- Page 6 Equation 2: Again, the way the equation is written is confusing. “σBC(λ) = β λ−𝐴𝐴𝐸BC” please rewrite the equation with “-AAEBC“ as an exponent to lambda.
- Page 6 Equation 4: You mention in the text “Equation (3.16) was employed to determine σBrC (370 nm) by substituting σBC(λ) at 370 nm, which was obtained using equation (3), into equation (3.13) (refer to supplementary methodology S1.1, S1.2, and figure 187 S2 for details). Shouldn’t equation (4) be “σBrC(370nm) = σBrC+BC(370nm) - β(370nm)-AAEBC”?
- Page 8 liness 244-245: “BC BCbb, BC BCff” Please remove extra BC and “apparently”.
- Page 8 lines 244-249: BCff peaks at 9am, CO2 at 10am and BrC/BCbb at 11am? What can you infer from these differences? Also, you mentioned that the same is observed for meteorological conditions? Can you be more precise because if their temporal variations were similar, it could mean that the meteorological conditions are driving the BC and BrC changes, which is not really the case here.
- Page 9 lines 260-262: “BrC is found the highest with maximum fluctuation during 10th January to 30th March that is pointing towards winter wood burning for the subsistence as similar observed BCbb.” Please rephrase
- Page 9 lines 262-267: What can you infer from the highest variations and concentrations of BC, BrC… and what could be the reasons behind such variation during March for BC and April for BrC ?
- Page 9 line 270: “The good significant” and line 272 “strong significant correlation” remove significant in both cases. Furthermore, aren’t BC and BCff and BCbb and BrC expected to correlate based on the way they are calculated?
- Page 9 lines 273-275: “A good significant positive correlation between CO2 and BC/BCff suggesting that fossil fuel burning is one of the causes of CO2 concentration or vis versa.” In figure 5, CO2 doesn’t seem correlated to anything else than himself.
- Page 9 lines 275-277: “Dewpoint temperature and CO2 has strong significant positive correlation coefficient suggesting to positive radiative forcing of the CO2.” Some reference would be welcome and can the correlation be considered strong with a correlation coefficient of 0.22?
- Page 9 lines 285-292: “However, cloud condensation nuclei formation and precipitation are prompted by aerosols (BC and BrC). Thereafter, BC and BrC have crucial role in precipitation mechanism.” Also, BC being mainly hydrophobic, how good would BC particles be as CCN and which conditions would be required to efficiently play such role?
- Page 10 lines 293-299: Most phrases here are poorly written and need serious revisions to convey the observations clearly.
- Page 10 lines 298-299: How do you explain that the scavenging seem to be only affecting BCbb and not BC or BCff?
- Page 10 line 300: “pattern” instead of “patten” and what does the relative humidity and temperature justify? This sentence is not clear.
- Page 10 line 308: “Figure 7 discusses” please rephrase.
- Page 10 lines 312-314: “approved” please use another verb and add reference regarding the important convective activity during the monsoon season in the Bay of Bengal.
- Page 10 lines 318-319: “supporting the convective rain (i.e., rain out scavenging) of all pollutants” do you mean scavenging of pollutant by convective rain here?
- Figure 2,3 and 4: Wouldn’t box plot be a better option than average and standard deviation? If the blox plot are hard to read maybe had the median in the Table S2 and S3.
- Figure 6: add the sampling site on, at least, one of the maps.
Supplementary information:
- Section 1.1: the notation is not consistent between the main text and the supplement (e.g. σBC(λ) and babs(λ)).
- Page 3: “ATN and BC relationship is given in figure (S7) for the daily data.” You are probably referring to figure S2 here.
- Page 3 Equation 3.4: instead of B(λ), do you mean BC(λ) = babs(λ) / σabs(λ)
- Page 4 equation 3.7 and 3.8: Shouldn’t “– aff” and “-abb” be exponent?
- Page 5 equation 3.12: Do you mean BCff?
- Page 6 Figure S2: Please correct the figure’s caption.
- Page 7 Figure S4: Please correct the figure “Total could cover” to “total cloud cover”
- Page 8 Figure S5: The BC and BrC data seem to still have zero did you estimate the limit of detection of the instrument? Should those points be included in the comparison?
Citation: https://doi.org/10.5194/egusphere-2023-702-RC1 -
AC1: 'Reply on RC1', Rakesh Kumar Ranjan, 04 Dec 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-702/egusphere-2023-702-AC1-supplement.pdf
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RC2: 'Comment on egusphere-2023-702', Anonymous Referee #2, 18 Nov 2023
This study analyzed the seasonal and annual variation of black carbon (BC) and brown carbon (BrC) in Gangtok, Sikkim. Authors characterized the sources of BC, and discussed how meteorological conditions affected BC based on correlation analysis. Although the topic of this paper suits for EGUsphere, most results are basic and the discussion is not enough, leading to limited scientific information. In addition, the manuscript is poorly written and the language should be improved. Therefore, I do not think this manuscript meets the requirements of EGUsphere. The questions are listed below:
Main:
The authors use the ERA-5 reanalysis data for meteorological analysis. How do authors consider the uncertainties of the data set?
Some results summarized in the abstract are not consistent with those analyzed in the paper. For instance, the authors mention when surface pressure is higher, the boundary layer is calmer, which results in the deposition of pollutants. In general, the deposition process leads to a decrease of pollutants. However, in the paper, the authors showed that higher surface pressure keeps the accumulation of pollutants, which is contradictory to the summary in the abstract. Please check these inconsistent contents.
The authors show many correlation efficiencies in the discussion section. Note that the correlation analysis indeed gives some evidences for what you observe, but they are not conclusive in this study. For example, the authors say ‘The good significant correlation between BC and BCff suggested that the major contribution of the BC is fossil fuel burning’. The good correlation between BC and BCff does not necessarily mean that fossil fuel burning is the major contributor to BC. The authors should also give the proportion of BCff in BC to support this point. Please check other similar discussions in this section.
Lines 273-275, the authors conclude that fossil fuel burning results in the increase of CO2 based on the good correlation between BC and BCff, and think that if the increase of CO2 is not caused by fossil fuel burning, BC and BCff have poor correlation. Please prove this point.
Lines 287-292, please give the evidence that the decrease of surface pressure is caused by the vertical rising of air parcels. Authors mention that BC and BrC play important roles in cloud formation, please provide the evidence.
Minor:
Line 177 and line 184, equations (3.15) and (3.16) are not contained in the supplementary information.
Line 244, Table S11 is not found in the supplementary information.
Line 248, it seems strange that the temperature increases during night time. Please explain why.
Line 263, ‘is’ should be changed to ‘are’
Line 270, delete ‘good’ or ‘significant’.
Citation: https://doi.org/10.5194/egusphere-2023-702-RC2 -
AC2: 'Reply on RC2', Rakesh Kumar Ranjan, 04 Dec 2023
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2023/egusphere-2023-702/egusphere-2023-702-AC2-supplement.pdf
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AC2: 'Reply on RC2', Rakesh Kumar Ranjan, 04 Dec 2023
Data sets
BC_Data_For_Sikkim Pramod Kumar, Khushboo Sharma, Ankita Malu, Rajeev Rajak, Aparna Gupta, Bidyutjyoti Baruah, Shailesh Kumar Yadav, Thupstan Angchuck, Jayant Sharma, Rakesh Kumar Ranjan, Anil Kumar Misra, and Nishchal Wanjari https://docs.google.com/spreadsheets/d/1N4F_fT68syY6n0UIfA6nzI5o-8LUWjyFfk5NpfquRyg/edit#gid=0
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