| 11 Dec 2025
The Spatial and Temporal Distribution Patterns of XCH₄ in Iran: New Insights from TROPOMI Observations
Abstract. The unprecedented increase in methane concentration, as the second most important greenhouse gas after carbon dioxide, poses a serious challenge to climate change mitigation policies, while accurate and comprehensive monitoring remains insufficient in many countries, including Iran. This study investigates the spatial and temporal patterns of column-averaged methane in Iran using satellite-based observations from Tropospheric Monitoring Instrument on the Sentinel-5P satellite during 2019–2024 and compares them with data from the Emissions Database for Global Atmospheric Research database. On average, XCH₄ concentrations across Iran increased from 1872.6 ± 11.9 ppb in 2019 to 1918.6 ± 11.2 ppb in 2024, representing a +46.1 ± 16.4 ppb rise over six years. All uncertainty estimates represent standard deviations, with a mean value of 12.3 ppb. Statistical and spatial analyses, including Global Moran’s I (0.914–0.982, p < 0.01), Local Moran’s I, and the Getis-Ord Gi* hotspot analysis, confirmed that methane concentrations in Iran exhibit a significant clustering pattern. Hotspots were mainly observed in Class 1: Northern Agro-Hotspots (Gilan, Mazandaran, and Golestan), Class 2: Central Urban-Dense Hotspots, and Class 3: Southern Industrial-Fossil Hotspots, whereas Class 4: Low-Emission Provinces and Class 5: Very-Low-Emission Provinces exhibited lower concentrations with sparse hotspots, located mostly in western and eastern Iran. The highest seasonal averages were recorded in summer (1914.3 ± 13.1 ppb) and autumn (1910.5 ± 13.5 ppb). Comparison with EDGAR data indicates that several major emission sources are underestimated, and spatial overlaps with the observed hotspots did not exceed 5 % in any month. Satellite observations reveal discrepancies in hotspot locations and emission magnitudes, emphasizing that relying solely on modeled inventories may misrepresent methane emissions.
The Manuscript contains substantial research findings on the tropospheric methane concentration and hotspot identification. However, inclusion of some additional information would enhance the quality and clarity of the research as follows:
1. The process of hotspot identification was described in a very qualitative manner like using higher or lower values in Section 2.3.2. For better understanding and clarity the exact threshold values for differentiating the higher and lower values should be mentioned. A table representing the high and lower threshold values may be added.
2. Cite proper references for Global and Local Spatial Autocorrelation Analysis and hotspot analysis.
3. The validation between the two data source may be shown.
4. The research shows methane concentration over an entire country. Therefore, some reasons behind the high or low concentration should be included (with respect to hydro-meteorological variables, topographic variation, land use pattern etc. because these influence the methane concentration). Methane concentration pattern over different land use or topographic regime may be shown. The author can follow similar research if found suitable (https://doi.org/10.1007/s41324-025-00666-5).