Около полудня на бульваре стало шумнее, чем утром.

Около means around / approximately / near, and when it refers to time or location, it normally takes the genitive case.

So:

• полдень = noon
• около полудня = around noon

This is a fixed grammar pattern:

• около часа = around one o’clock
• около дома = near the house
• около пяти минут = about five minutes

So полудня is genitive singular because около requires it.

Because this phrase answers the question where?, not to where?

• на бульваре = on the boulevard / at the boulevard → location
• на бульвар = onto the boulevard / to the boulevard → direction

After на, Russian uses:

• prepositional case for location: на бульваре
• accusative case for motion toward a place: на бульвар

Here the sentence describes what was happening there, so the location form на бульваре is needed.

Стало is the past tense of стать in an impersonal construction, and here it means it became / it got.

So:

• стало шумнее = it became noisier / it got noisier

There is no real subject like the boulevard doing the action. Russian often uses this kind of impersonal sentence to describe changes in weather, atmosphere, surroundings, or general conditions:

• Стало холодно. = It got cold.
• Стало темно. = It became dark.
• Стало шумнее. = It became noisier.

The form is neuter singular past tense because impersonal past-tense sentences usually use that form.

Шумнее is the simple comparative form of шумный / шумно and means noisier.

Russian often prefers these short comparative forms in everyday speech:

• громкий / громко → громче
• тихий / тихо → тише
• шумный / шумно → шумнее

So:

• стало шумнее = it got noisier

You could sometimes say более шумно, but шумнее is more natural and common here.

In this sentence, it works more like a predicative comparative, not like a normal adjective directly describing a noun.

It is not modifying a noun such as бульвар. The sentence does not mean a noisier boulevard. Instead, it means that the situation or environment became noisier.

So think of стало шумнее as a whole unit:

• стало шумнее = it became noisier

This is very common in Russian with words describing conditions:

• стало лучше = it got better
• стало хуже = it got worse
• стало тише = it got quieter

Чем is used after a comparative to mean than.

So:

• шумнее, чем утром = noisier than in the morning

This is the standard pattern:

• больше, чем... = more than...
• меньше, чем... = less than...
• лучше, чем... = better than...
• шумнее, чем... = noisier than...

So чем connects the two things being compared: around noon versus in the morning.

Утром is the instrumental form of утро, and Russian often uses this form by itself to mean in the morning.

This is a very common time expression:

• утром = in the morning
• днём = in the daytime / during the day
• вечером = in the evening
• ночью = at night

So чем утром literally means than in the morning.

You usually would not say в утро in this meaning. The bare instrumental form is the natural idiomatic choice.

Because Russian often allows impersonal sentences, especially when talking about general states, weather, surroundings, or changes in conditions.

In English, we often need a dummy subject like it:

• It got noisier.
• It became dark.

In Russian, that dummy subject is usually omitted:

• Стало шумнее.
• Стемнело.
• Похолодало.

So the sentence is complete without naming a subject. The meaning is understood from context: the environment on the boulevard became noisier.

Yes. Russian word order is flexible, and the sentence could be rearranged depending on emphasis.

The original:

• Около полудня на бульваре стало шумнее, чем утром.

This sounds natural and neutral: first the time, then the place, then what changed.

Other possible orders:

• На бульваре около полудня стало шумнее, чем утром.
• Шумнее, чем утром, на бульваре стало около полудня.

These versions are grammatical, but they shift emphasis or sound more literary or marked.

For a learner, the original order is a good standard model.

Yes, but the meaning changes slightly.

• около полудня = around noon
  This tells you the approximate time when it was noisier.

• к полудню = by noon / toward noon
  This suggests a gradual change leading up to noon.

Compare:

• Около полудня стало шумнее. = Around noon it got noisier.
• К полудню стало шумнее. = By noon it had become noisier / toward noon it got noisier.

So both can work, but около полудня is specifically about approximate clock time.

A useful way to break it down is:

• Около полудня = around noon
• на бульваре = on the boulevard
• стало шумнее = it got noisier
• чем утром = than in the morning

So the structure is:

time + place + change of state + comparison

This is a very common Russian pattern for describing changes in the environment:

• Вечером в городе стало тише, чем днём.
• Зимой в комнате стало холоднее, чем осенью.

Learning this pattern is very helpful because you can reuse it with many other words.