ajër

Ajër is the colorless, odorless mixture of gases that forms Earth's atmosphere and surrounds the planet. It is essential for life, enabling respiration and playing a central role in weather, climate, and many industrial processes. In everyday terms, ajër refers to the air we breathe and the gaseous envelope that fills the space above the surface.

Dry ajër is composed mainly of nitrogen (about 78%) and oxygen (about 21%), with small amounts of argon, neon, helium, methane, krypton, hydrogen, and carbon dioxide making up the remainder. Water vapour is variable, depending on location and weather, and can range from nearly zero to several percent of ajër by volume. The exact composition can change with altitude and atmospheric conditions.

The atmosphere is structured into layers, with the troposphere closest to the surface where weather occurs, extending roughly 8 to 15 kilometers high depending on latitude. Above it lie the stratosphere, mesosphere, thermosphere, and exosphere. The troposphere contains most of the ajër’s water vapour and aerosols and is where temperature generally decreases with height, driving convection and wind. The stratosphere contains the ozone layer, which absorbs harmful ultraviolet radiation.

Human activities affect ajër through air quality and climate. Pollutants such as particulate matter, nitrogen oxides, sulfur dioxide, and ozone can impact health and ecosystems. Greenhouse gases, including carbon dioxide and methane, trap heat in the lower atmosphere and contribute to climate change.

Standard references describe ajër’s base conditions as about 101.3 kilopascals of pressure at 15 degrees Celsius, with air density near 1.225 kilograms per cubic meter at sea level.