Running a process at a lower temperature so that it results in smaller quantities of a toxic chemical being vaporized is an example of:

Running a process at a lower temperature to reduce the vaporization of toxic chemicals exemplifies moderation. This approach is aimed at controlling the conditions under which a process operates, with the specific intention of minimizing the release of harmful substances. By moderating the temperature, the process not only minimizes the risks associated with vapor formation but also often enhances safety in operational environments.

On the other hand, minimization typically refers to overall reduction of waste or by-products rather than adjusting specific variables like temperature. Substitution involves replacing a hazardous material with a less hazardous one, which doesn't apply here since the issue is about controlling vaporization. Simplification refers to reducing the complexity of a process which isn't the specific goal in this example. Therefore, moderation is the best fit as it directly addresses controlling hazardous emissions through temperature regulation.