It saw about 500 people evacuated from the terminal on Friday - some suffering with breathing difficulties - and the temporary closure of the transport hub.
The suspect was held on Saturday accused of "using a noxious substance to cause serious damage".
He has since been released on bail until late November.
The force said in a statement:  "The man, 25, was arrested at a residential address in east London and taken to a west London police station.
"He was arrested on suspicion of using a noxious substance to cause serious damage - an offence under section 113 of the Anti-Terrorism, Crime and Security Act 2001."
Two people were taken to hospital during the alert and 25 others were treated at the scene.
The airport's closure led to travel chaos as all flights were suspended, with several incoming flights being diverted to other airports.
A 25-year-old man has been arrested after a chemical alert that led to the evacuation of London City Airport.