夜间天空发灰代表西面空气水汽充沛，将要下雨。

A gray sky at night means that the western air is filled with moisture and it will likely rain soon.

youdao

第二阶段是由近地面微气象条件决定的水分凝结过程，所吸收水量受空气水汽压、地面温度和地表可利用能量的影响。

The second is the process of water condensation determined by air vapor, soil surface temperature and the available energy of soil.

youdao

他呼出的水汽悬浮在他面前的空气中。

His breath was hanging in the air before him.

《柯林斯英汉双解大词典》