Why is the government so interested in the air flow in major cities?

These devices have been popping up in major metropolitan areas. They measure the air quality. Mostly in places where there is a lot of pedestrian traffic. Tourist attractions, police stations, train and subway stations. Is this the prelude to the next disaster? One which I would presume would be man made. Another Anthrax attack? H1N1 virus?

cryptome.org...

reply to post by Jack Jouett


Weren't these devices put in place after 9/11 to detect a bio attack in the event that one happened? I remember hearing that a while ago.