This is the 7154th most frequent Chinese word.
空气质量
Air quality.
In this sentence, '空气质量' is used as a noun referring to the state of the atmosphere's cleanliness or pollution level.
今天的空气质量很差，不适合进行户外运动。
Today's air quality is poor, not suitable for outdoor activities.
Here, '空气质量' serves as a subject to emphasize the importance of improving the cleanliness or conditions of the air.
空气质量的改善需要大家共同努力。
Improvement in air quality requires everyone's collective effort.
In this example, '空气质量' indicates a measure that influences personal decisions, connecting to indices or assessments of air cleanliness.