1. Unit 2: Surface Processes and the Hydrosphere Lesson 1: Characteristics and Significance of the Atmosphere ( Heath Earth Science – Pg. 480-487)

2. Today’s Objectives  Explain the characteristics and significance of the atmosphere, including:  Demonstrate and explain the relationships among air volume, density, pressure, and temperature  Describe the effects of the sun’s radiation on the atmosphere, including the greenhouse effect, conduction, convection, and radiation  Describe the structure of the atmosphere and the abundance of various substances in it  Predict the effects of changing the composition of the atmosphere (e.g., ozone depletion, adding water vapour, greenhouse gases, and pollutants)

3. The Atmosphere  The Earth is surrounded by a life-giving gaseous envelope called the Atmosphere  The atmosphere extends from the Earth’s surface to an altitude of a few hundred kilometers  The Atmosphere provides us with the air that we breath as well as protection from the Sun’s dangerous radiation  The atmosphere is also responsible for our weather and our climate

4. Bill Nye Video – The Atmosphere

5. Did you know?  If we could gather all of the gases that make up our atmosphere, and weigh them on a scale, the mass would be about 5 x 10 18 kg!

6. Layers of the Atmosphere  Our atmosphere has 4 main layers and a transitional layer that have varying characteristics:  Troposphere ~ 0-18 km above surface  Stratosphere ~ 18-50 km above surface  Mesosphere ~ 50-80 km above surface  Thermosphere ~ 80-500 km above surface  *Exosphere ~ 500~10,000 km above surface  *Exosphere is a transitional zone between atmosphere and outer space  A further sub-layer extends from about 65-500 km above surface known as the ionosphere

7. Layers of the Atmosphere The layers are based on temperature changes Each layer is separated by a zone called a “- pause” At each “-pause” the temperature remains relatively unchanged

8. Characteristics of Atmospheric Layers  Troposphere (0~18 km)  Thickness depends on latitude: at equator ~18km thick; at poles~8 km thick  Atmosphere is most dense in troposphere  The gases of the troposphere are essential to life on Earth  Earth’s weather occurs in the troposphere  Temperatures gradually decrease with altitude  Stratosphere (18~50 km)  Ozone layer found in stratosphere  Clear and dry  Strong steady winds  Steady weather conditions make stratosphere ideal for flights  Temperature steadily increases due to ozone absorption of sunlight

9. Characteristics of Atmospheric Layers  Mesosphere (50~80 km)  Steadily dropping temperature with increasing altitude due to lack of ozone  Thermosphere (80~500 km)  Steadily rising temperature with increasing altitude due to nitrogen and oxygen atoms absorbing solar energy  *Exosphere (500~10000 km)  Exosphere has very low density as distance from earth makes gravitational pull very weak  No clear boundary between exosphere and outer space

10. Ionosphere  Ionosphere (65~500 km)  Air is highly ionized  Ions formed when ultraviolet (UV) rays from the sun knock electrons off oxygen atoms  Stretches from lower mesosphere to top of thermosphere  These ions are responsible for reflecting radio waves, making broadcasting and cell phones possible  Also responsible for the aurora borealis and aurora australis, also known as the northern and southern lights

11. Practice  Topic Questions, pg. 483 #5, 6ab

12. Atmospheric composition  Our atmosphere is not just made of oxygen!  Atmospheric composition:

13. Atmospheric Composition  Air thins out quickly with increasing altitude  Composition remains the same by percentage to about 80 km  Above this altitude, gases form layers  Oxygen up to 1000 km  Helium up to 2400 km  Hydrogen above this gradually thinning out into space  Gas molecules at the bottom of the atmosphere are squeezed together by the gases above  As a result, 99% of atmospheric mass is within 32 km of Earth’s surface

14. Water Vapour, Ozone, and Dust  Water Vapour:  Air always contains some water vapour due to evaporation from oceans, and plants  Amount varies with location, season, and time of day  Most is near the surface, decreasing with height  Ozone:  Ozone is a form of oxygen gas, each molecule contains 3 oxygen atoms compared with 2 in oxygen gas  Ozone forms when UV rays from sun act on oxygen in upper atmosphere  Most concentrated at 10~50 km above surface to form ozone layer  Absorbs 99% of harmful UV rays  What are the consequences of ozone depletion?

15. Dust  Dust is another part of the air includes tiny grains of rock, dirt, pollen, salt crystals from sea spray, soot from fires, chemicals from factories, and bacteria  Dust helps form fog and rain: water vapour condenses around dust particles, forming tiny water droplets  *The Chinese government sometimes uses a method called “cloud seeding” before important holidays to reduce the chance of rain

16. Cloud Seeding

17. Ozone Depletion  Ozone thinning occurs from release of gases called chlorofluorocarbons (CFC’s) into the atmosphere  Used as coolants in air conditioners, cleaners, and foam products  Do not break apart easily; chlorine atoms break down ozone layer in presence of sunlight

18. Ozone Depletion The ozone layer decreased by as much as 50% with increased use of CFC’s in the 80’s and 90’s Most noticeable at the poles where cold weather allows clouds to form in the mesosphere: ice crystals in these clouds provide places for ozone destruction Global CFC policies have reduced this depletion, but ozone won’t fully recover until approx. 2050 at the earliest

19. Practice  Topic Questions, pg. 483 #3, 4

20. Heat Transfer in the Atmosphere  The sun provides most of the thermal (heat) energy in our atmosphere  This heat is transferred in 3 ways:  1) Radiation  Sun radiates energy in the form of waves  These short waves are seen as visible light  2) Conduction  Conduction occurs when heat is transferred from a hot object to a cooler object by physical contact  Ex. Air warms as it passes over the warm ocean

21. Heat Transfer in the Atmosphere  3) Convection  Most effective form of heat transfer in liquids and gases, therefor most effective in atmosphere  Molecules nearest heat source gain kinetic energy and move farther apart, becoming less dense  Cooler, more dense gas/liquid above sinks, forcing up the warmer, less dense gas/liquid – this flow is called a convection current  *If water were heated from the top, why wouldn’t convection occur?

22. Heat Transfer in the Atmosphere Transfer of warm or cold air by horizontal winds is called advection

23. Temperature Drops with Altitude  In the troposphere, the temperature drops about 1 ° C for every 160 meters gained in altitude  This is called the normal lapse rate  Why?  Most of suns radiation is absorbed by the earths surface  Heat is transferred to the air by conduction and carried aloft by convection  The rising air cools from expansion due to lower pressure  Lower pressure allows air molecules to move farther apart  As molecules move farther apart, they collide less often, so less energy is transferred  Less energy = lower temperatures

24. The Greenhouse Effect  The Earth’s surface radiates infrared waves  These waves warm the atmosphere because they are absorbed by water vapour and carbon dioxide in the air  These gases are known as “greenhouse gases”  Just like in a greenhouse, these gases allow the suns short wave UV radiation to enter, but trap the Earth’s long wave infrared radiation, thus heating the atmosphere  The greenhouse effect is necessary for life on earth, without it, our planet would be too cold  However, the burning of fossil fuels is constantly adding CO 2 to the air, increasing the greenhouse effect, and consequently raising temperatures  What are the consequences?

25. Earth’s Energy Budget

26. Practice  Topic Questions, pg. 486 #7-9

27. Air Pollution - Activity  Next class: we will measure the particulate air pollution in Shanghai  We will place several microscope slides with scotch tape attached to them in various locations around the school campus  We will leave these slides in place for several days, then view them under microscopes  We can count the number of particles on the tape per unit of area to determine the particulate air pollution