"Atmospheric Inversion" just means that the air below is trapped, and cannot dissipate above, because of clouds, high vs low pressure turned around, or whatever....thereby trapping whatever pollution, smells, etc. might be hanging low to the earth.

I do not believe that is the cause of such a large-scale "stink" that is being described, but I guess it's possible. It's also a perfectly good "cover story" for the press!