Atmosphere Composition What’s in the atmosphere?

Composition of the Atmosphere

Nitrogen Makes up ~78% of Earth’s atmosphere Maintained through nitrogen cycle-Nitrogen moves from air to soil, then to plants and animals, then back into the air. Bacteria in soil chemically change nitrogen from air into compounds that plants need to grow. Animals eat plants and nitrogen compounds returned to the soil through waste or decay of dead organism Decay releases nitrogen back into the atmosphere

Oxygen Makes up ~ 21% of Earth’s atmosphere Maintained through photosynthesis, in which plants produce large quantities of oxygen. Animals and bacteria use this oxygen for their life processes Forest fires, burning of fuels, and weathering of some rocks also remove oxygen from the air. Amount produced by plants is equal to the amount consumed by animal life processes.

Water Vapor Evaporation from oceans, lakes, streams, and soil causes invisible gas to form in air Plants and animals release water vapor in their life processes of transpiration or respiration Condensation and precipitation removes water vapor from the atmosphere

Water Vapor Percentage varies based on time of day, location, and season Dry air has less than 1% water vapor while moist air may have as much as 4% water vapor.

Ozone Made up of three atoms of oxygen (O3), while oxygen we breathe is made up of two atoms (O2) Ozone layer absorbs harmful UV radiation from the sun.

Ozone Without it, living organisms would be severely damaged by UV rays Human activities have damaged this layer, causing the layer to weaken. CFCs (compound called chlorofluorocarbons) were previously used in air conditioners and refrigerators. These, as well as, exhaust compounds like nitrogen oxide, break down ozone.

Particulates Tiny solid and liquid particles that exist in the atmosphere. Volcanic dust Ash from fires Microscopic organisms Mineral particles lifted from soil by winds Pollen from plants Particles from meteors Crystals of salt left from evaporation of ocean water

Particulates Large, heavy particles remain in the atmosphere for a short period of time while tiny particles can remain for months or years.

Air pressure The weight of the air/atmosphere above you causes air pressure.

Atmospheric Pressure Gravity holds the gases of the atmosphere near Earth’s surface. As a result, the air molecules are compressed together and exert force on Earth’s surface. Atmospheric pressure is exerted equally in all directions—up, down, and sideways.

Atmospheric Pressure, continued Earth’s gravity keeps 99% of the total mass of the atmosphere within 32 km of Earth’s surface. Because the pull of gravity is not as strong at higher altitudes, the air molecules are farther apart and exert less pressure on each other at higher altitudes. Thus, atmospheric pressure decreases as altitude increases.

Measuring Air Pressure Tool used to measure air pressure is a barometer. Air pressure pushes down on the surface of the mercury in the dish, causing the mercury in the tube to rise. The air pressure is greater on the barometer on the right, so the mercury is higher in the tube.