[qīng xīn]

pure and fresh air; crisp air
空氣清新

a fresh spring morning
清新的春天早晨

keep the classroom clean and sweet
保持教室整潔和空氣清新

The rain had cleared the air, and the grass smelt fresh and sweet.
雨水凈化了空氣， 青草聞起來清新芳香。