Evaluation of comprehensive monthly-gridded methane emissions from natural and anthropogenic sources in China

Highlights: • A monthly gridded CH₄ emission inventory from eight sources was developed. • We improved activity data and EFs with high spatial-temporal resolution. • Annual CH₄ emissions were 62 Tg, mostly from energy, livestock, and paddy fields. • CH₄ values peaked in July and August due to paddy fields, vegetation, and wetlands. • Inner Mongolia, Shanxi, Sichuan, Guizhou, and Hunan had the most emissions. The observed atmospheric methane (CH₄) concentration in China has grown rapidly in recent years, showing marked spatial-temporal variation. However, existing inventories, most of which are yearly, provincial, and incomplete, have failed to reflect the spatial variation and seasonal trends of CH₄ emissions. This study aims to develop a high-resolution (0.05° × 0.05°) monthly inventory of CH₄ emissions across China in 2015 from eight major natural and anthropogenic sources. The inventory evaluation of CH₄ emissions was based on the gridded activity data and high spatial-temporal resolution emission factors, which were estimated by their relationship with environmental factors in most source sectors. The results showed that the annual CH₄ emissions across China were 61.65 Tg, of which 85% was associated with anthropogenic emissions. Energy activities, livestock, and paddy fields were the largest contributors, accounting for 31% (19.06 Tg), 24% (15.01 Tg) and 19% (11.45 Tg) of the total emissions respectively, followed by vegetation (7%, 4.52 Tg), wetlands (7%, 4.20 Tg), wastewater (6%, 3.43 Tg), municipal solid waste, (4%, 2.59 Tg) and biomass burning (2%, 1.40 Tg). However, these proportions varied by month; paddy fields, vegetation, and wetlands emitted the most CH₄ in July and August with approximately 29%, 14%, and 8% of total emissions, respectively, and least in January and December with 0%, 2%, and 2%, respectively, leading to a CH₄ emissions peak in summer and a valley in winter. Moreover, the major contributing provinces of CH₄ emissions in China were Inner Mongolia, Shanxi, Sichuan, Guizhou, and Hunan, accounting for 33% of China's total emissions. The dominant emission sources were energy activities in Mongolia, Shanxi, and Guizhou; livestock in Sichuan; and paddy fields in Hunan. This improved inventory of CH₄ emissions can help understanding the spatial-temporal variation of CH₄ concentration in the atmosphere and formulating regional-seasonal-specific emission reduction policies.