happipitoisuus

Happipitoisuus (Finnish for oxygen concentration) denotes the amount of oxygen present in a given medium. It is a key parameter in biology, environmental science, medicine, and industry. The term encompasses dissolved oxygen in liquids, the oxygen fraction in air, and the oxygen content of blood.

In water, dissolved oxygen (DO) is typically measured in milligrams per liter (mg/L) or as percent saturation relative to equilibrium at a given temperature and pressure. At 20°C fresh water, saturation is about 9 mg/L, rising with cooler temperatures; salinity or altitude lowers solubility. DO is influenced by temperature, photosynthesis, respiration, mixing, and flow. Common measurement methods include Winkler titration, Clark-type electrochemical sensors, and optical oxygen sensors.

In air, oxygen makes up about 21% of the atmosphere by volume, with a partial pressure of about 160 mmHg at sea level. The delivered O2 to organisms depends on ventilation, diffusion, and circulation, and declines with altitude or extreme conditions.

In the human body and other animals, oxygen content refers to both dissolved O2 and oxygen bound to hemoglobin. The arterial oxygen content and saturation inform tissue oxygen supply and are monitored in clinical settings, especially in anesthesia and critical care.

Happipitoisuus is used to assess ecological health in rivers and lakes, optimize aquaculture and wastewater treatment, and guide medical decisions in contexts where oxygen availability is limiting.