It seems to be a problem that's pretty persistent. It's the scent of animal fats going rancid. This is almost certainly not from the dumpster itself but from residues and other bits and pieces on the pavement around the dumpster.

My suspicion is that this is a result of the combined input of all of the food-selling businesses in that block of buildings. All are good, and McKinnon's is pretty great, but yeah, the smell is really trying.