Getting rid of hardware parts smell (GT2 timing belt)
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.