Today,the filters clean the air in planes.

VOA: special.2009.07.14

The air is crisp and clean, unlike this room.

不像这屋子里，外面的空气新鲜又清静。

I want to 实战 - SpeakingMax英语口语达人

She says that the goods and services provided by nature - like clean air, rain or fertile soils - should not be taken for granted.

VOA: standard.2010.02.24

"China has reduced extreme poverty through economic growth, but until very recently has overlooked the growing inequalities in health and health determinants like access to clean air,water, and sanitation."

VOA: standard.2010.04.07