Ammonia
From Memory Alpha, the free Star Trek reference.
Ammonia is a toxic gas compound with the formula NH3.
In 2365, the USS Enterprise-D investigated the planet Theta VIII and found the atmosphere composed of large concentrations of ammonia and other gases, and with wind speeds of up to 320 meters/second. Interesting weather phenomena included ammonia tornadoes. (TNG: "The Royale")
In early 2370, the Enterprise-D inspected the vessel USS Raman via an interface probe controlled by Geordi La Forge. The probe entered a hull breach in the aft section of the Raman and detected atmospheric gases inside the corridor – primarily methane and ammonia. (TNG: "Interface")
