空气变得更清新了可以用英语表达为"the air has become fresher"。
来源：这句话来源于英语中"fresh"一词，该词有"新鲜的"的意思，所以"the air has become fresher"表示空气变得更新鲜了。
一些例句及其中文翻译:
The air has become fresher since the factory closed down. 由于工厂停产了，空气变得更新鲜了。
I can breathe easier now that the air has become fresher. 由于空气变得更新鲜了，我可以更轻松地呼吸了。
The mountain air is always fresher than the city air. 山上的空气总是比城市空气新鲜。