Dew

Dew forms when water vapour in the air condenses directly onto cooler solid surfaces — stones, grass blades, plant leaves — rather than onto dust or smoke particles floating in the air above the ground. The key distinction is the surface: the moisture settles on objects, not on nuclei suspended in the atmosphere.

The ideal conditions for dew formation are:

• Clear sky — allows the ground to cool rapidly by radiating heat away at night
• Calm air — still conditions keep the cooled air near the surface in contact with the objects, so condensation can occur
• High relative humidity — the air is already close to saturation, so only slight cooling is needed
• Cold and long nights — prolonged cooling brings the surface temperature down enough for condensation …