But tiny grains of dust acted as 'condensation nuclei' to let droplets form.

但是微小的尘埃颗粒充当了“凝结核”，使液滴形成。

Dust particles, especially if coated by pollution, act as condensation nuclei for warm cloud formation and as efficient ice nuclei agents for cold cloud generation.

尘埃颗粒，尤其是被污染覆盖的尘埃颗粒， 充当暖云形成的凝结核和冷云生成的有效冰核剂。