"The air is very fresh" is a common way to express that the air is clean and pure. "Fresh" is an adjective used to describe something that is new, clean, or pure. It can also be used to describe something that is pleasing to the senses, such as a fresh breeze or a fresh scent.
来源：“fresh”这个词最早出现在古英语中，意思是“新鲜的”。在中古英语中，它还有“清新的”的意思。
例句:
The fresh air in the mountains always makes me feel better.
（山上的新鲜空气总是让我感觉更好。）
She opened the window to let in some fresh air.
（她打开窗户让新鲜空气进来。）
The smell of fresh flowers filled the room.
（新鲜花的香味充满了房间。）