The length of time that a volcanic eruption impacts the climate is largely determined by

The length of time that a volcanic eruption impacts the climate is determined by the capacity of the volcano and how much material it will let out in the atmosphere. The smaller the volcano, with smaller capacity, the smaller effect it'll have on the climate and the duration of it's impact, and the space on which it'll have climatic impact. The bigger the volcano, with bigger capacity, the bigger the effect on the climate and the duration of it, and the bigger the space it will have climatic impact on.