This is the 1536th most frequent Korean word.
공기가
"공기가" means "air."
In this sentence, '공기가' ('air') is used as the subject of the sentence, described as clear, thereby influencing the conditions for walking outdoors.
공기가 맑아서 산책하기 좋다.
The air is clear, so it's good for walking.
Here, '공기가' ('air') again acts as the subject, emphasizing its temperature change that requires an appropriate action — wearing warm clothing.
공기가 차가워져서 따뜻한 옷을 입어야 해요.
The air has become cold, so you need to wear warm clothes.
'공기가' ('air') is referenced as a comparison subject, highlighting freshness relative to other locations.