From Steurmers GP interview 9/84; Q: "In the Air Tonight" has a really ghostly guitar throughout. How did you get that sound?
A: "I used chorus, Boss distortion and delay to get a very eerie, distant sound. And I bent the strings a lot. I had to use a volume pedal to bring it in and out, too... I have all my effects, then the volume pedal, then the amp"
No further elaboration on the specific model, he uses a "Boss Super Overdrive, Distortion" live, so, maybe one of those...?