Meaning-based. The second half also names a property of the element. Refers to 淡 “diluting”, the element that dilutes air
History of the character
Every form found in the sources, from the first missionary chemistry books of the 1850s to the current
standards. Hover a dot for the source. Simplified 氮, traditional 氮.
1849淡氣dànqì天文略論 Tiānwén Lüèlùn, Benjamin Hobson (合信)“diluting gas”: it dilutes the air
1868硝氣格物入門 Géwù Rùmén, W. A. P. Martin (丁韙良), Tongwen College
1870淡氣化學初階 Huàxué Chūjiē, John G. Kerr (嘉約翰) & Hé Liǎorán (何瞭然)
1871淡氣化學鑑原 Huàxué Jiànyuán, Xú Shòu (徐壽) & John Fryer (傅蘭雅), Jiangnan Arsenal
1871硝氣金石識別 Jīnshí Shíbié, D. J. MacGowan (瑪高溫) & Huà Héngfāng (華蘅芳)