Three patterns: (1)
一气〜 + verb = do something in one continuous burst (
一气呵成 finish in one go,
一气写完 write through in one sitting); (2)
串通一气 /
沆瀣一气 = collude as a single unit; (3) 〜
了一气 after a verb = did it for a (short) while. Don't confuse with
一口气 (in one breath), which is more physical.