geu sungan jeonghwa hwaldongi sijakdoeeossseupnida.

그 순간 literally means that moment, but in a sentence like this it usually works adverbially: at that moment or then.

Korean time expressions often appear without a particle when they are being used as adverbs of time. So:

• 그 순간 정화 활동이 시작되었습니다. = At that moment, the cleanup activity began.

You can also say 그 순간에, and that is grammatically fine, but leaving off 에 is very common and natural.

이 is the subject marker.

Here, 정화 활동이 means the cleanup activity is the thing that began. So the activity is the subject of 시작되었습니다.

• 정화 활동이 시작되었습니다. = The cleanup activity began.

If you changed it to 정화 활동은, the meaning would still be possible, but the nuance would shift more toward making 정화 activity the topic, as in As for the cleanup activity, it began.

정화 활동 is a noun phrase made of:

• 정화 = purification, cleanup, decontamination, cleansing
• 활동 = activity

Together, it means something like cleanup activity, purification activity, or decontamination efforts, depending on context.

It is written as two words because Korean often spaces nouns separately even when they function together like a compound in English. This is very normal.

Similar examples:

• 환경 보호 활동 = environmental protection activity
• 자원봉사 활동 = volunteer activity

So 정화 활동 being spaced is not strange.

This is a very common question.

• 시작하다 = to start, to begin
• 시작되다 = to be started, to begin, to get underway

In this sentence, 시작되었습니다 comes from 시작되다. It focuses on the event beginning rather than on a person actively starting it.

So:

• 정화 활동이 시작되었습니다. = The cleanup activity began.
• 누군가 정화 활동을 시작했습니다. = Someone started the cleanup activity.

Notice the difference:

• with 시작되다, the activity itself is the subject
• with 시작하다, a person or agent can be the subject, and the activity is often the object with 을/를

In formal writing and announcements, 시작되다 is very common.

It is related to a passive-like pattern, but it is often best learned simply as the verb 시작되다.

A literal analysis might suggest something like was started, but in actual Korean usage, 시작되다 very often just means to begin or to get started.

So in natural English, you usually translate it as:

• began
• started

not necessarily as:

• was started

So yes, it has a passive/backgrounded-agent flavor, but in practice it functions very naturally as begin.

Yes. It breaks down like this:

• 시작되- = verb stem of 시작되다
• -었- = past tense marker
• -습니다 = formal polite sentence ending

So:

• 시작되었습니다 = began / has begun in formal polite style

You may also see the contracted form:

• 시작됐습니다

That comes from 되었 becoming 됐 in contraction. Both are common, though 시작되었습니다 can feel slightly more formal or careful.

It is in the formal polite style, often called the -습니다 style.

This style is common in:

• news reports
• public announcements
• presentations
• formal narration
• official writing

Compare:

• 시작되었습니다 = formal polite
• 시작됐어요 / 시작되었어요 = standard polite
• 시작됐어 / 시작되었어 = casual

So this sentence sounds polite and somewhat formal.

Yes. Here are some natural alternatives:

• 그 순간 정화 활동이 시작됐어요.
  standard polite

• 그 순간 정화 활동이 시작됐어.
  casual

• 그 순간 정화 활동이 시작했어요.
  usually not correct for this meaning

That last one is important: if you want the activity itself to be the thing that began, 시작되다 is the better choice here.

If you use 시작하다, you would usually say something like:

• 그 순간 사람들이 정화 활동을 시작했어요.
  At that moment, people started the cleanup activity.

Because 정화 활동 is not the object here. It is the subject of 시작되다.

That is why you get:

• 정화 활동이 시작되었습니다.

If you use 시작하다 with a person doing the starting, then you often get an object:

• 사람들이 정화 활동을 시작했습니다.
  People started the cleanup activity.

So:

• 이/가 with 시작되다
• 을/를 often appears with 시작하다

This difference is very useful to notice.

Yes. Korean word order is flexible, especially with time expressions.

These are all possible:

• 그 순간 정화 활동이 시작되었습니다.
• 정화 활동이 그 순간 시작되었습니다.

The first version is more natural if you want to set the time first: At that moment...

Korean often puts time expressions near the beginning of the sentence, but moving them is possible if the sentence is still clear.

그 points to something already known from the context, so 그 순간 means that moment rather than just a moment.

Compare:

• 그 순간 = that moment
• 어느 순간 = at some moment / one moment
• 이 순간 = this moment
• 한 순간 = one moment / an instant

So 그 순간 usually refers back to a moment that has just been mentioned or is understood from the situation. It helps connect this sentence to what came before.