Vesihöyry

Vesihöyry is the gaseous state of water. The Finnish term covers water vapor in general and is sometimes distinguished from steam, which is formed when water boils. Vesihöyry occurs in the atmosphere as humidity and is produced whenever water evaporates or sublimates.

Physically, vesihöyry is a colorless, odorless gas composed of H2O molecules. Its density depends strongly on temperature and pressure; at a given temperature it is far less dense than liquid water and lighter than dry air, so it tends to rise in air. It is a greenhouse gas and contributes to the natural greenhouse effect.

Formation and phase changes: Vesihöyry forms when liquid water or ice gains enough energy to overcome intermolecular forces. Evaporation can occur at any temperature at the surface; boiling occurs at the boiling point. Condensation converts it back to liquid water, releasing latent heat.

In meteorology and climate, water vapor is central to humidity, dew point, and cloud formation; relative humidity measures how close the air is to saturation. Its concentration varies with temperature and weather, and it has a short atmospheric lifetime compared to most other greenhouse gases. It amplifies warming via feedback.

Applications and safety: Vesihöyry is essential in power generation (steam turbines), heating, sterilization, and industrial processes. Hot steam can cause severe burns; condensation causes fog and energy losses. In everyday life, humidity affects comfort, storage, and agricultural crops.