The original Tear Gas is still attached where it was.
Visitor would be attached to your card effectively counting as a Tear Gas.
That seems like an odd solution. Visitor from the Spheres doesn't get discarded like other event cards when it mimics their effects. Why should it share in their fate this time? Also, from the FAQ:
If a card copies another card’s text
or effect and the text includes self-
references (i.e. the card’s title) is it
replaced by the card’s title that is
copying the effect?
Copying a character’s text box does
just that. All examples of a card’s name
remain unaltered, and as such refers to
cards of that name only.