The Differences of Atmospheric Air & Air Dissolved in Water

Composition

• Nitrogen is the most common gas in the atmosphere, making up 78 percent, while oxygen makes up 21 percent and argon makes up 1 percent. The rest of the atmosphere is other gases. Gases become less concentrated in higher parts of the atmosphere. The stratosphere has large concentrations of ozone molecules, which prevent some sun rays from reaching the Earth. In the exosphere, gases can escape the gravitational pull of the Earth and float into space.

  Nitrogen makes up 48 percent, oxygen makes up 36 percent and carbon dioxide makes up 15 percent of the ocean volume. Carbon dioxide only makes up 0.03 percent of the atmosphere. Carbon dioxide dissolves into water from the atmosphere and is produced as a byproduct of the consumption of organic matter.

Life

• Living organisms depend on the quantity of oxygen in the water, and concentrations that fall below 3 parts per million (ppm) can cause them to weaken. Concentrations below 2 ppm kill fish. As oxygen concentrations get lower, aerobic organisms die off and anaerobic organisms thrive. Many anaerobic organisms are pathogenic and produce toxins. For humans, concentrations of oxygen below 18 percent can lead to oxygen deficiency.

Water and Oxygen Cycle

• Oxygen in the atmosphere spreads out and some enters water. Plants add oxygen to the water, since they produce more oxygen than they need to generate energy. All the gases dissolve more in cold water. They dissolve less in salty water. Oxygen levels decline when there are too many fish.

  Water also enters the air, with water vapor mixing with air in the atmosphere. Most of the air is dry, but 1 percent of it is water vapor. Water vapor enters the atmosphere through evaporation. It returns to the Earth as dew, rain and snow. Warm air holds more water vapor than cold air. As water heats up, it rises and expands. As it cools, it falls and condenses, turning into clouds and eventually falling as rain and snow.

Nitrogen Cycle

• Nitrogen dissolves and passes through water. In the nitrogen cycle, nitrogen seeps into the soil and enters the groundwater. Some of the nitrogen is permanently buried in the ground, while bacteria fix other nitrogen molecules, turning them into ammonia. The nitrogen floats back up into the atmosphere as a gas.