Learn Farsi: آلودگی هوا در این شهر کاهش یافته است. - Air pollution in this city has decreased.

In formal Farsi, یافتن acts as a light verb to form "inchoative" verbs—verbs that describe a process of changing state. While یافتن literally means "to find," when combined with the noun کاهش (reduction), the compound کاهش یافتن means "to undergo a reduction" or simply "to decrease."

Would I use کاهش یافتن in everyday spoken Farsi?

Generally, no. Compound verbs using یافتن are formal and are mostly found in news reports, academic articles, or formal speeches. In casual everyday conversation, you would use the much simpler کم شدن (kam shodan) to say that something decreased.

How do I change this verb if I want to say that someone actively decreased the pollution?

The light verb یافتن makes the compound intransitive (it describes a change happening to the subject itself). To make it transitive—meaning someone is actively doing the decreasing to an object—you swap یافتن for دادن (to give). For example, to say "The government decreased the pollution," you would use کاهش دادن.

Why use the present perfect tense (کاهش یافته است) here instead of the simple past (کاهش یافت)?

The present perfect is used here because the decrease in pollution has a direct, continuing result in the present—the air is currently cleaner. Using the simple past (کاهش یافت) would sound more like a finished historical event (e.g., it decreased last year, but maybe it went back up since).