Characteristics of the Atmosphere 7 th Grade Science Mr. Bombick

Outline 1.Composition 2.Properties 3.Organization 4.Involvement with Biosphere 5.Pollutants

Composition of Dry Air Air Component % of Dry Air Nitrogen78 Oxygen21 Other (CO 2, H 2 O, Noble Gases, H 2, Methane, Particulates 1

Components of Air  Nitrogen-Each nitrogen molecule contains two nitrogen atoms; usually biologically inert  Oxygen-Most oxygen molecules contain two oxygen atoms; critical for animal life; involved in combustion processes; ozone is a harmful oxygen molecule that contains three oxygen atoms (generated by lightning and human sources)

Components of Air (cont.)  Carbon Dioxide-Each molecule of carbon dioxide has one atom of carbon and two atoms of oxygen; absorbed by plant photosynthesis; released by human sources  Water Vapor-Each water molecule contains one oxygen atom and two hydrogen atoms; wide variations in amount of water vapor depending on the type of climate; critical to formation of clouds; basis of precipitation

Components of Air (cont.)  Other Gases-Hydrogen (one molecule of hydrogen contains two atoms of hydrogen); Noble gases (argon, neon, krypton); methane released from biological and human sources  Particulates-solid particles from biological and chemical sources

Properties of the Atmosphere  Density-measurement of the amount of mass in a given volume of air  Pressure-The amount of force of air due to weight of a column of air pushing down on an area

Measurement of Air Pressure  Can be measured using a barometer (can be a mercury or aneroid barometer)  Units of air pressure are given as “inches of mercury” or in millibars (National Weather Service uses millibars)  Inches of mercury refers to the height of a mercury column caused by air pressure  Millibars are related to inches to mercury (one inch of mercury equals millibars

Air Pressure and Altitude  Air pressure decreases with increasing altitude  Air pressure is greatest at sea level  For air pressure to exist there has to be air

Air Pressure and Density  Increasing altitude results in lower air density  Gas molecules get farther apart with increasing altitude (due to less pressure)

Layers of the Atmosphere  Troposphere (0 to 12 km)  Stratosphere (12 to 50 km)  Mesosphere (50 to 80 km)  Thermosphere (Above 80 km) composed of Ionosphere and Exosphere

Troposphere  Closest layer to the earth  Conditions of this layer are the most variable  Layer where weather occurs  Contains almost all the mass of the atmosphere  This layer is thickest above the equator and thinnest at the poles

Stratosphere  Extends from top of troposphere to approximately 50 km above Earth’s surface  Upper stratosphere is warmer relative to the lower stratosphere because of an ozone layer absorbing solar radiation  Ozone layer is important in shielding Earth from harmful solar UV (ultraviolet) radiation

Mesosphere  Begins 50 km above Earth to 80 km above Earth  Upper mesosphere is colder than coldest region of stratosphere  Region of atmosphere that protects Earth’s surface from being hit by most meteoroids (meteors that have entered Earth’s atmosphere)

Thermosphere  Region of atmosphere 80 km and above Earth’s surface  Very low density atmosphere  Thermal energy of gases are very high 1800 o C however, temperatures would be very low because of sparse density of gas molecules to interact with thermometer or other objects

Thermosphere (cont.)  Thermosphere is composed of two layers, the ionosphere and the exosphere  Ionosphere starts at 80 km above Earth and extends to about 400 km above Earth  Ionosphere is the layer responsible for the auroras (Northern and Southern lights)  Ionosphere also reflects AM and short wave radio waves back to Earth’s surface  Exosphere begins at 400 km above Earth and extends for thousands of kilometers above Earth’s surface

The End of Atmosphere Characteristics