Learn Farsi: برای کاهش آلودگی، خیابان بسته خواهد شد. - To reduce pollution, the street will be closed.

The future passive combines the past participle of your main verb with the future tense of شدن (to become). Here, the past participle of بستن (to close) is بسته. The future tense of شدن for a third-person singular subject like the street is خواهد شد. Together they make بسته خواهد شد (it will be closed).

Why does the Farsi sentence say برای کاهش instead of using a verb for "to reduce"?

In Farsi, expressing purpose is often done with a noun rather than an infinitive verb. While English says "to reduce pollution," Farsi literally says "for the reduction of pollution." کاهش is the noun form meaning "reduction" or "decrease."

Is there a hidden sound connecting کاهش and آلودگی?

Yes, there is an invisible ezafe (an "-e" sound) linking the two nouns. It is pronounced "kāhesh-e ālūdagī" which means "reduction of pollution." The ezafe acts like the English word "of" in this context.

How would the verb change if the sentence were active, like "The police will close the street"?

In the active voice, you would not use شدن or the past participle بسته. Instead, you would use the future form of the main verb itself. It would look like پلیس خیابان را خواهد بست (the police will close the street), using the auxiliary خواهد and the short infinitive بست.