Pervasive Mist from Dementors Breeding

[Pat]

No: HPFGUIDX 137592

A chilly mist, which Fudge says is from dementors breeding (pg 14
US), is mentioned several times.  It's in London, and it's 
intermittent on the train ride to Hogwarts (pg 140 US). It's chilly 
when they go to Hogsmeade (pg 243 US), but I don't think we can tell 
if that's the from the dementors breeding, or just normal weather for 
October. 

Is it just chilly mist? Or does mist from breeding activity have 
anything to do with lovesick behavior in Tonks, and possibly others, 
too?

How do dementors breed? I don't believe we have been told in canon, 
have we? I had it in my head that they sucked the soul out of
someone, and that created a new dementor, but now I think that's from 
fan fiction.

I'm wondering if this mist is one of those things that turns out to
be significant later.