Hydrogen sulfide evolution from asphalt or heavy fuel oil may be reduced or eliminated using an additive to act as a scavenger. Zinc, in conjunction with an additional metal selected from Fe, Mn, Co, Ni, Cr, Zr, when present in the form of nano-particles of an oxide, borate or carboxylate is an effective component is preventing or mitigating the evolution of hydrogen sulfide. The nano-particles may be used neat or as a dispersion. These metals may also be complexed and used in the form of a solution. Molybdenum, when used with one or both of Fe and Zn is also a useful in any of these forms for the same purpose.