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.