Atmosphere Our atmosphere Earth’s atmosphere = the layer of gases that surround the planet Very thin layer, relative to size of planet Atmosphere: • • • • Absorbs solar radiation Burns up meteors Transports and recycles water and other chemicals Moderates climate Atmospheric composition 78% nitrogen 21% oxygen 1% argon traces of other permanent gases and variable small amounts of: water vapor carbon dioxide methane pollutants etc. Layers of the Atmosphere The atmosphere has four layers: Thermosphere Mesosphere Stratosphere Troposphere Layers of the Atmosphere The four layers of the atmosphere include: 1. the troposphere, where we live; 2. the stratosphere, which contains the ozone layer; 3. the mesosphere, where meteors burn; and 4. the thermosphere, where satellites orbit Earth. Layers of the Atmosphere The atmosphere is divided into layers based on temperature changes. 5.2 The exosphere and ionosphere Communication on Earth depends on satellites. Satellites transmit information used for television shows, radio broadcasts, data and photos used in weather reports, and long distance telephone calls. Atmospheric layers Atmosphere consists of several layers: • Troposphere = bottom layer, at Earth’s surface; 11 km high; temperature decreases with altitude • Stratosphere = next layer up (11–50 km); temperature increases with altitude; contains “ozone layer” • Mesosphere = third layer up (50–90 km); temperature decreases with altitude • Thermosphere = top layer (90–500 km); very thin air; mostly lightweight elements; very hot; ionic radiation Atmospheric layers Temperature and other characteristics vary with altitude. Ozone layer Tropopause marks boundary between troposphere and stratosphere. Layers don’t mix. Ozone layer Not really a layer, but a region of higher-than-normal ozone concentrations (which are still very low) ~17–30 km altitude Absorbs ultraviolet (UV) radiation from sun, protecting organisms on surface from radiation damage Atmospheric properties Atmospheric pressure = weight per unit area of air being pulled down by gravity (is less at higher altitudes) Relative humidity = ratio of water vapor air contains relative to how much it could contain at that temperature Temperature = air is warmed by the sun; temperature varies with altitude, location, time of day Pressure, density, and altitude Gravity pulls most air molecules close to Earth’s surface, so air density is greatest near the surface. Atmospheric pressure is the greatest near the surface because most molecules are above. The sun’s energy heats the atmosphere … and does so differentially at different latitudes. The sun and Earth’s tilt create seasons The sun drives weather in the troposphere Solar heating establishes convective circulation, circular currents in which warm air rises and cool air falls. Composition of Atmosphere (Mixture of gases, solids, and liquids) Early atmosphere was much different than today Volcanoes produced nitrogen and carbon dioxide, but little oxygen More than 2 billion years ago, early organisms began producing oxygen Eventually, oxygen formed an ozone layer that protected Earth from harmful rays Green plants and diverse life forms developed Atmospheric Gases (Mixture of gases, solids, and liquids) Nitrogen - 78% Oxygen - 21% Water Vapor – 0 to 4% Used for clouds and precipitation Carbon Dioxide - .037% Keeps Earth warm and is used by plants to make food Argon - .93% Traces of neon, helium, methane, krypton, xenon, hydrogen, and ozone Atmospheric Gases (Mixture of gases, solids, and liquids) Atmosphere is changing with the introduction of pollutants; increasing human energy use is increasing the amount of carbon dioxide Pollutants mix with oxygen and other chemicals to form smog Aerosols include solids such as dust, salt, and pollen Liquids include water droplets and droplets from volcanoes Lower Layers of Atmosphere Troposphere: lowest layer – extends up to 10km; contains 99% of the water vapor and 75% of the atmospheric gases The troposphere is the first layer above the surface and contains most clouds and half of the Earth's atmosphere. Weather occurs in this layer. Most of the layer’s heat is from Earth Temperature cools about 6.5 degrees Celsius per kilometer of altitude. Upper Layers of Atmosphere Mesosphere – extends from the top of the stratosphere to about 85 km above Earth Coldest layer with little ozone Meteors or rock fragments burn up in the mesosphere. Ionosphere here – layer of charged particles Upper Layers of Atmosphere Thermosphere – thickest atmospheric layer found between 85 km and 500 km above Earth’s surface The thermosphere is a layer with auroras, known for its high temperatures. Warms as it filters out X-rays and gamma rays from the Sun Ionosphere here, too – help carry radio waves. The Ionosphere (= Thermosphere) Above mesosphere; density so low the Space Shuttle and ISS orbit here, with little drag Temperature can be very high; 4,000F. But no significant heat because density is so low. Heated by ionization by UV from the sun, and the solar wind. Upper Layers of Atmosphere Exosphere - The atmosphere merges into space in the extremely thin exosphere. This is the upper limit of our atmosphere. Outer layer where space shuttle orbits. Atmospheric Pressure Molecules closer to the surface are more densely packed (at higher pressure) together than those higher in the atmosphere because of the mass of gases pressing down on them from higher in the atmosphere Temperature in atmospheric layers The troposphere is warmed primarily by the Earth’s surface; temperature decreases as altitude increases in this layer. Temperatures increase as altitude increases in the stratosphere, particularly in the upper portion – ozone Temperatures decrease with altitude in the mesosphere Thermosphere and exosphere are the first to receive Sun’s rays, so they are very hot The Ozone Layer About 19 km to 48 km above Earth in the stratosphere (90%) and troposphere (10%). Layer of 3-atom molecules that protects the Earth from the Sun’s harmful ultraviolet radiation Life depends on the ozone! Pollutants called chlorofluorocarbons (CFCs) are destroying the ozone CFCs are used in refrigerators, air conditioners, aerosol sprays, and foam packaging ~ if products leak, CFCs enter atmosphere Ozone layers has a large hole over Antarctica and a smaller one over the North Pole The Ozone Layer • Within the stratosphere, about 19 km to 48 km above your head, lies an atmospheric layer called the ozone layer. • Ozone is made of oxygen. • Although you cannot see the ozone layer, your life depends on it. The Ozone Layer • An ozone molecule is made up of three oxygen atoms bound together. • The ozone layer contains a high concentration of ozone and shields you from the Sun's harmful energy. • Ozone absorbs most of the ultraviolet radiation that enters the atmosphere. • Ultraviolet radiation is one of the many types of energy that come to Earth from the Sun. CFCs • Evidence exists that some air pollutants are destroying the ozone layer. • Blame has fallen on chlorofluorocarbons (CFCs), chemical compounds used in some refrigerators, air conditioners, and aerosol sprays, and in the production of some foam packaging. • When a chlorine atom from a chlorofluorocarbon molecule comes near a molecule of ozone, the ozone molecule breaks apart. • One of the oxygen atoms combines with the chlorine atom, and the rest form a regular, twoatom molecule. CFCs CFCs • These compounds don't absorb ultraviolet radiation the way ozone can. • In addition, the original chlorine atom can continue to break apart thousands of ozone molecules. • The result is that more ultraviolet radiation reaches Earth's surface. • Chlorofluorocarbon molecules destroy ozone. • By October, the ozone concentration reaches its lowest values and then begins to increase again. • By December, the ozone hole disappears. The Ozone Hole • The destruction of ozone molecules by CFCs seems to cause a seasonal reduction in ozone over Antarctica called the ozone hole. • Every year beginning in late August or early September the amount of ozone in the atmosphere over Antarctica begins to decrease.