To get you thinking This is our atmosphere. All life on Earth exists within this tiny protective blanket. Why is the atmosphere important to us? What do you think it does for us? Chapter 11: Atmosphere Atmospheric Composition Atmosphere a mixture of gases that surrounds the Earth Protects the Earth s surface from the sun s radiation Regulates the temperature of Earth s surface Permanent atmospheric gases Earth s atmosphere has changed greatly over the course of time. Conditions would not have supported life as we know it The early atmosphere consisted of Helium Hydrogen Methane Ammonia Permanent atmospheric gases 99% of the atmosphere is composed of Nitrogen (N 2 ) 78% Oxygen (O 2 ) 21% The remaining 1% is composed of Argon 0.93% Carbon Dioxide 0.038% Water Vapor 0.0 4.0% Trace Gases 0.01% 1
Variable atmospheric gases The concentrations of some atmospheric gases are not as constant over time as the concentrations of nitrogen and oxygen. Water Vapor The amount of water vapor in the atmosphere can vary greatly over time and from one place to another Varies with the seasons Altitude Properties of earth s surface beneath the air Carbon dioxide Measurements of carbon dioxide has increased from approximately 0.028% to it current level of 0.038% over the past 150 years. Primarily due to the burning of fossil fuels Carbon dioxide is cycled between the atmosphere, the oceans and living organisms Ozone Ozone gas molecule that is made up of three oxygen molecules Forms the ozone layer in the atmosphere and absorbs harmful ultraviolet radiation from the sun. The maximum concentration of ozone in this layer is only 0.0012% Ozone concentration varies seasonally at higher latitudes Typically occurs in spring CFCs, or chlorofluorocarbons, which were previously used in Freon and aerosols breakdown ozone and have caused parts of the ozone layer to weaken. Ozone hole over Antarctica 2
Atmospheric particles Particulates tiny solid particles that are in the atmosphere such as dust, microscopic organisms and pollen Four common sources of particulates include: Volcanoes Tornadoes and wind storms Plants (pollen) Oceans (sea spray) Atmospheric Layers The atmosphere is classified into five different layers. Troposphere Stratosphere Mesosphere Thermosphere Exosphere Troposphere Troposphere the layer of the atmosphere that is closest to Earth s surface Temperature decreases as altitude increases because air in this layer is heated from below by thermal energy that radiates from the Earth s surface. Temperature decreases at a rate of 6.5 o C per kilometer of altitude Temperatures in the upper troposphere can be as low as 60 o C All weather conditions exist in the troposphere. The troposphere ends at the tropopause. Section 1: Characteristics of the Atmosphere Tropopause Tropopause the upper boundary of the troposphere where temperature stops decreasing; usually at an average altitude of 12 km. 3
Stratosphere Stratosphere the layer of the atmosphere that lies between the troposphere and the mesosphere and in which temperature increases as altitude increases; contains the ozone layer Temperature increases as altitude increases because air in the stratosphere is heated from above by absorption of solar radiation by ozone. Stratopause the upper boundary of the stratosphere where the temperature reaches 0 o ; usually at an altitude of about 50 km. About 99.9% of the mass of Earth s atmosphere is below the stratopause Mesosphere Mesosphere the coldest layer of the atmosphere, between the stratosphere and thermosphere, in which temperature decreases as altitude increases. Located between 50 km to 85 km above Earth s surface Very little solar radiation is absorbed in the mesosphere Mesopause the upper boundary of the mesosphere where the average temperature is 90 o C, which is the coldest temperature of the atmosphere. Thermosphere Thermosphere the layer of the atmosphere between the mesosphere and exosphere, in which temperature increases as altitude increases; includes the ionosphere Temperature increases as altitude increases because nitrogen and oxygen atoms absorb solar radiation. Temperatures in the thermosphere can exceed 2000 o C Ionosphere the lower region of the thermosphere, which is made of electrically charged particles Auroras occur in the ionosphere 4
Exosphere Exosphere the outermost layer of Earth s atmosphere Extends from about 600 km to 10,000 km above Earth s surface Transitional region between Earth s atmosphere and outer space Exosphere Mesopause Stratopause Tropopause 5
Energy Transfer in the Atmosphere Radiation the transfer of thermal energy by electromagnetic waves Thermal energy is transferred from the sun to Earth this way. Energy that reaches Earth is absorbed and reflected by Earth s atmosphere and Earth s surface. Absorption and reflection Most of the solar energy reaches Earth is in the form of visible light and infrared waves. 30% of solar radiation is reflected into space by Earth s surface, the atmosphere, or clouds 20% is absorbed by the atmosphere and clouds 50% is absorbed directly or indirectly by Earth s surface Keeps Earth s surface warm Rate of absorption Depends on the physical characteristics of the area and the amount of solar radiation it receives Water heats and cools more slowly than land Darker objects absorb energy faster than light colored objects Conduction Conduction the transfer of thermal energy between objects when their atoms or molecules collide Occurs more easily in solids and liquids Air is a poor conductor of thermal energy In the atmosphere, conduction occurs between Earth s surface and the lowest part of the atmosphere. 6
Convection Convection the transfer of thermal energy by the movement of heated material from one place to another More dense cool material sinks Less dense warm material rises In the atmosphere, convection occurs between warmer and cooler air. Main mechanism for energy transfer in the atmosphere End of Section 1 7