the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 15 Mar 2024
Emissions of Methane from Coal, Thermal power plants and Wetlands and its implications on Atmospheric Methane across the South Asian Region
Abstract. Atmospheric methane (CH4) is a potent climate change agent responsible for a fraction of global warming. The present study investigated the spatial and temporal variability of atmospheric column-averaged (X) CH4 (XCH4) concentrations using Greenhouse gases Observing SATellite (GOSAT) and TROPOspheric Monitoring Instrument onboard the Sentienl-5 Precursor (S5P/TROPOMI) data from 2009 to 2022 over the South Asia region. During the study period, the long-term trends in XCH4 increased from 1700 ppb to 1950 ppb with an annual growth rate of 8.76 ppb year-1. Among all natural and anthropogenic sources of CH4, the rate of increase in XCH4 was higher over the Mundra thermal power station and Mundra ultra mega power plant at about 9.62 ppb year-1, followed by the coal site at about 8.76 ppb year-1 (Korba). With a growth rate of 8.61 ppb year-1, the Sundarbans natural wetland competes with coal sites, producing over 30 MT, indicating an equivalent anthropogenic source. For the 15 Indian Agroclimatic zones, significant high emissions of CH4 were observed over the Middle Gangetic Plains (MGP), Trans Gangetic Plains (TGP), Upper Gangetic Plains (UGP), East Coast Plains & Hills (ECPH), Lower Gangetic Plains (LGP) and East Gangetic Plains (EGP). Further, the bottom-up anthropogenic CH4 emissions data are mapped against the XCH4 concentrations and found high correlation in the Indo Gangetic Plains (IGP) region, indicating the hotspots of anthropogenic CH4. The present study highlighted the impact of natural and anthropogenic sources of XCH4 and quantified the spatio-temporal changes in XCH4 at each study site over the Indian region.
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RC1: 'Comment on egusphere-2024-405', Anonymous Referee #1, 27 Mar 2024
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The manuscript “Emissions of Methane from Coal, Thermal power plants and Wetlands and its Implications on Atmospheric Methane across the South Asian Region” investigates the spatial and temporal dynamics of atmospheric methane (CH4) concentrations over the South Asia region from 2009 to 2022, utilizing data from the Greenhouse gases Observing SATellite (GOSAT) and the TROPOspheric Monitoring Instrument onboard the Sentinel-5 Precursor (S5P/TROPOMI). The analysis identifies specific sources contributing to this increase, notably the Mundra thermal power station and Mundra ultra mega power plant, exhibiting higher rates of increase in XCH4 compared to other natural and anthropogenic sources. The study also highlights the significant methane emissions from the Sundarbans natural wetland, competing with coal sites in terms of emission rates, thus emphasizing its importance as an equivalent anthropogenic source. Furthermore, the investigation delves into the distribution of CH4 emissions across 15 Indian Agroclimatic zones; and employs bottom-up anthropogenic CH4 emissions data to map against XCH4 concentrations, revealing a high correlation in the Indo Gangetic Plains (IGP) region, thereby identifying key anthropogenic CH4 hotspots. Overall, the manuscript provides crucial insights into the impact of both natural and anthropogenic sources on XCH4 concentrations over the Indian region, quantifying spatio-temporal changes at each study site. The findings hold significance for understanding and addressing the complex dynamics of atmospheric methane, a potent climate change agent.
Atmospheric methane (CH4) is one of the high-potential greenhouse gases (GHG) that regulates the chemical reactions in the free troposphere and stratosphere.
Comment: Here, ‘regulates’ does not seem appropriate.
Comment: Could figures 1a, 1b, and 1c be merged into a single figure where all the sources are indicated with different shapes/colors?
Three heterogenic CH4 source regions
Comment: Are the entities depicted in the figure referred to as heterogenic source regions or individual sources? Coal fields and thermal power plants are primarily situated within the same region.
The Ministry of Environment, Forests and Climate Change (MoEF&CC), Government of India, has identified 75 Ramsar Wetland sites in India as of November 2022. These sites span a total area of 115 13,35,530 ha. Based on the high total geographical area coverage (Table 1), the top 10 places were determined for the current investigation. The size varies from 423000 ha (Sundarbans Wetland, West Bengal) to 18900 ha (Wular Lake, Jammu and Kashmir).
Comment: Reference for the aforementioned statement.
In the present study, the atmospheric CH4 was obtained from 2009 to 2020….
Comment: As previously stated and indicated in Figure 2, data up to 2022 was utilized for the current study.
Comment: There is no mention of gridding of level 2 data, if any has been applied. Have all the datasets been gridded to the same resolution?
Comment: In Figure 3, regarding the TROPOMI data from 2019 to 2022, is it averaged over this period or does it represent all the observations?
There are data gaps in Tropomi, which are assumed to occur during the monsoon season. However, these gaps are absent in GOSAT. Are you employing any data-filling method for the GOSAT data?
Figures 5a-c shows the monthly time series of XCH4 over the specific sources of CH4 dotted in the Indian region during 2009 to 2020.
Comment: dotted?
The seasonal cycle (peak and trough) of XCH4 is strongly associated with the vegetation during the active phase of cultivation and reduced photochemical reaction by the hydroxyl radicals, respectively.
Comment: could you provide a reference for the statement? Considering wetlands and coal as the largest emitter of CH4, how is the seasonal cycle associated with this?
A seasonal maximum of XCH4 was observed over Coal and Thermal power plants from September to October and a minimum in pre-monsoon (March-May).
Comment: Are you associating this cycle with rice cultivation?
Comment: There is a typo in Figure 7, indi. Does the spatial distribution represent the mean of all the years?
Comment: The descriptions of Figures 7 and 8 do not match their respective figures. Additionally, the description of Figure 8 appears before that of Figure 7.
Significant high emissions of CH4, as shown in Figure 7c
Comment: Figure 7c is missing.
Additional Suggestions
Emissions from EDGAR only verify the anthropogenic emissions, but there is a significant wetland source situated over India that requires verification with the appropriate inventory.
Additionally, previous studies have demonstrated the limitations of satellite data during the monsoon season and the biases associated with global inventories such as EDGAR, over the Indian region. Therefore, it would be appropriate to study the uncertainty associated with the emissions and XCH4 from their respective datasets.
There are extensive studies of XCH4 over India from satellites have been conducted by Mottungan et al. However, the authors have not reffered them in their study.
Citation: https://doi.org/10.5194/egusphere-2024-405-RC1 -
RC2: 'Comment on egusphere-2024-405', Anonymous Referee #2, 23 Apr 2024
reply
The current manuscript titled “Emissions of Methane from Coal, Thermal power plants and Wetlands and its implications on Atmospheric Methane across the South Asian Region” by Mahalakshmi et al., carried out a detailed study on atmospheric column CH4 using the satellite data and bottom-up emission inventory data. This work is well executed and importantly carried out an extensive analysis over different source type of methane which is an important approach. The content is well-written and structured. The study looked into the effects of changes Emissions of Methane from Coal, Thermal power plants and Wetlands and its implications on Atmospheric Methane across the South Asian Region. Author (s) could use potentially the S5P/TROPOMI observations to map the point level sources. The present study has many important points in which it highlights the emission source versus concentrations in the IGP region. Also they carried out methane emissions variability in the agroclimatic zones.
Therefore, I believe this paper may be accepted with the following minor corrections.
- In the title capitalisation of every letter of the word may not be required.
- 205: Is there any references supporting this statement “higher concentrations of CH4 were observed in the Indo-Gangetic Plain (IGP) and northwest (NW) areas of India, southeast of China, and NW of China. Southern China and north China are marked with wetlands and rice paddy fields, which are the primary sources of CH4”
- Figures 5c adjust the x axis scale accordingly with the Fig. 5(a) and (b)
- There is a typo in the caption of Figure 7, indi. “Figure 7. S5P/TROPOMI XCH4 gridded to 0.05° × 0.05° over Indi and XCH4 over wetland, coal, and thermal power plant sites with a radius of 100 km”
- Significant high emissions of CH4, as shown in Figure 7c, but there is no Figure 7c it is missing.
- Figures 7 and 8 are described differently than their respective figures. Furthermore, the description of Figure 8 comes before that of Figure 7.
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