aki no asa ha kuuki ga hinyarisite kimotiii desu.

It is read:

あき の あさ は くうき が ひんやりして きもちいい です。

In normal writing, it would usually appear without spaces:

秋の朝は空気がひんやりして気持ちいいです。

A natural English gloss is something like:

Autumn mornings have cool air and feel pleasant.

秋の朝 means autumn mornings or a morning in autumn.

The particle の links nouns together. Here, it works a bit like of or like an apostrophe relationship in English:

• 秋 = autumn
• 朝 = morning
• 秋の朝 = autumn morning / morning of autumn

So の is showing that 朝 is being described by 秋.

This is a very common question.

In this sentence:

• 秋の朝は = As for autumn mornings, ...
• 空気が = the air is the thing that has the described quality

So:

• は marks the topic
• が marks the subject inside that topic

A literal breakdown is:

• 秋の朝は = regarding autumn mornings
• 空気がひんやりして = the air is cool/crisp
• 気持ちいいです = it feels pleasant

So the sentence is setting up autumn mornings as the topic, and then saying something about the air in those mornings.

Because 秋の朝 is not being used as a time marker here. It is the topic of the sentence.

Compare:

• 秋の朝は空気がひんやりして気持ちいいです。
  As for autumn mornings, the air is cool and pleasant.

• 秋の朝に散歩します。
  I take a walk on autumn mornings.

In the second example, に marks the time when an action happens. In your sentence, the speaker is talking generally about autumn mornings, so は makes more sense.

ひんやり is an adverb-like mimetic word, often grouped with Japanese sound-symbolic or sensation words.

It expresses a feeling like:

• pleasantly cold
• cool to the touch
• crisp

It often appears with する:

• ひんやりする = to feel cool / to be cool and refreshing

In your sentence, that becomes:

• ひんやりして = being cool, and...

So ひんやり is not a regular い-adjective like 寒い.

Because ひんやり usually works with する.

The base expression is:

• ひんやりする

Its て-form is:

• ひんやりして

That て-form links it to what comes next, just like and or being in English.

So:

• 空気がひんやりして気持ちいいです = The air is cool/crisp, and it feels nice

You generally would not say ひんやりです in the same way you say 静かです or きれいです.

The て-form in ひんやりして connects one description to another.

It links:

• 空気がひんやりして = the air is cool/crisp
• 気持ちいいです = it feels pleasant

So the flow is:

The air is cool, and as a result it feels nice.

In Japanese, the て-form often connects ideas in a smooth, natural way.

Both exist, but 気持ちいい is extremely common in everyday Japanese.

Historically and structurally, 気持ちがいい is the fuller form:

• 気持ちがいい = the feeling is good / it feels good

In casual, natural speech, this often becomes:

• 気持ちいい

So in your sentence, 気持ちいいです is completely normal and natural.

It means something like:

• pleasant
• comfortable
• feels nice

Here it refers to the overall sensation of the cool autumn air.

Not exactly in the personal, emotional sense that English I feel good sometimes has.

Here, 気持ちいい describes the experience as pleasant or comfortable.

So this sentence is closer to:

• The cool autumn morning air feels pleasant
• Autumn mornings are nice because the air is crisp

It is not mainly about someone’s mood. It is about the sensory feeling of the air and atmosphere.

Because です can be added after an い-adjective to make the sentence polite.

• plain: 気持ちいい
• polite: 気持ちいいです

Unlike nouns and な-adjectives, you do not remove the い.

So:

• 寒いです = polite
• おいしいです = polite
• 気持ちいいです = polite

This is standard modern Japanese.

A fairly literal breakdown is:

• 秋の朝は = as for autumn mornings
• 空気が = the air
• ひんやりして = is cool/crisp, and
• 気持ちいいです = feels pleasant

So a very literal rendering would be:

As for autumn mornings, the air is cool and it feels pleasant.

Natural English would usually smooth this out to something like:

Autumn mornings feel nice because the air is crisp.

Grammatically, it is directly describing 空気.

• 空気がひんやりして = the air is cool/crisp

But because that air is part of autumn mornings, the whole sentence ends up describing what autumn mornings are like overall.

So:

• direct description: the air
• overall topic: autumn mornings

No. Standard Japanese is normally written without spaces:

秋の朝は空気がひんやりして気持ちいいです。

The spaces in your version are probably just there to help learners see the parts more clearly.

That is very common in beginner materials, but it is not normal in everyday Japanese writing.

Yes, but the nuance changes a little.

• 涼しい means cool in a comfortable way
• ひんやりする gives a stronger sense of a crisp, slightly chilly feeling on the skin

So:

• 空気が涼しくて気持ちいいです。 = The air is cool and pleasant.

• 空気がひんやりして気持ちいいです。 = The air has that crisp, cool feeling, and it feels nice.

The original sentence gives a more sensory, vivid impression.

Usually, it sounds like a general statement about autumn mornings.

That is because:

• 秋の朝は with は often suggests a general topic
• there is no word showing a specific day, like 今日の or 今朝の

So the feeling is:

Autumn mornings are nice because the air is crisp.

If you wanted one specific morning, you might say something like:

• 今朝は空気がひんやりして気持ちいいです。 = This morning, the air is cool and feels nice.