Argonite was a substance. Seventeen parts per million was within safety margins for Deep Space 9's air supply.
In 2373, Julian Bashir told Benjamin Sisko he was concerned with how much argonite was seeping into the station's air supply. (DS9: "Doctor Bashir, I Presume")
Argonite is trademarked mix of argon and nitrogen and owned by Ginge-Kerr.