Transmission is via air conditioning.
If there is any other gas or chemical which has this characteristic, I would be grateful to know. The building concerned is over 30 years old. The smell occurred about 2 years ago, stopped and is now recurring within one and a half hours of the air conditioning being put on. The reaction in some of those who detect it is strong, i.e. they feel sick and nervous. Also some people have unexplained coughing fits and one person has an unexplained dermatolgical complaint.