Given the task definition and input, reply with output. In this task, you are given a sentence and a question, you would be asked to create the answer which is contained in the sentence provided.

Sentence: Ash that enters the air naturally as a result of a volcano eruption is classified as a primary pollutant. Question: Ash that enters the air naturally as a result of a volcano eruption is classified as what kind of pollutant?
primary pollutant