I ordered 10m of GT2 timing belt for a printer I want to build, however, the chemical smell from the belt is completely unbearable, in the sense of it gives me the feeling it is destroying something in my nose (and my nose isn't even particularly good). I tried to leave the belt outside in my garage for about three weeks now, but the smell has gone only so much. I naively assume it is the chemical to make the belt soft and bendable, would that even be a health risk having the belt around me for more extended intervals of time? Can I make the smell go away, and what would be the best way to do so?
It's a garbage-quality belt, and it will probably continue outgassing at a steadily-decreasing rate for a very long time.
The fact that it has a strong chemical smell is pretty good evidence that it would not comply with regulations in civilized countries (such as REACH). I would recommend returning it or throwing it away and buying from a more reputable vendor. A large fraction of all cheap 3d printer parts these days are ridiculously far out of compliance with US/EU regs and basic common sense for contamination.
If you're hell-bent on using a crappy knock-off belt to save a few bucks, you could put it under vacuum to try to suck out the residual chemical gas faster. Just apply the vacuum very slowly / in stages (say over 10 minutes) so you don't get decompression blisters in the rubber. You shouldn't need a hard vacuum, dropping to 0.5-1 psia or 0.05 bar absolute for a day or two should help significantly. No guarantees though.