沼气 (沼氣) zhǎoqì

zhǎoqì noun marsh gas; swamp gas
Domain: Modern Chinese 现代汉语
Notes: A mixture of methaneand other gasses produced naturally in swamps (CC-CEDICT '沼氣'; Guoyu '沼氣'; Mathews 1931 '沼氣', p. 28; Wikipedia '沼氣')