1. Atmosphere Composition
What’s in the atmosphere?

2. Composition of the Atmosphere

3. 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

4. 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.

6. 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

7. 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.

8. 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.

9. 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.

10. 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

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

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

13. 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.

14. 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.

16. 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.