尾气
wěi qì · HSK 7
exhaust
🚗💨 尾气 = 尾 tail + 气 gas = tail-gas, the waste gas from a car tailpipe
尾 means tail and 气 means gas or air, so 尾气 is literally the gas out the tail end of an engine: exhaust fumes and emissions. The same 气 shows up in 空气 (air) and 气体 (gas).
气 — steam/vapor radical 气
Originally a pictograph of rising vapor or clouds drifting in the sky, depicting curling streams of air. The character came to mean breath, air, and by extension vital energy or 'qi.' The simplified form 气 keeps the original outline; the traditional 氣 added 米 (rice) to suggest steam rising from cooking grain.