Section 1 Characteristics of the Atmosphere

Earth Science Chapter 22 Section 1 – Characteristics of the Atmosphere E.Q.: What is the composition and characteristics of the Earth’s atmosphere? STANDARDS: SES1. Students will investigate the composition and formation of Earth systems, including the Earth’s relationship to the solar system. e. Identify the transformations and major reservoirs that make up the rock cycle, hydrologic cycle, carbon cycle, and other important geochemical cycles. SES6. Students will explain how life on Earth responds to and shapes Earth systems. c. Explain how geological and ecological processes interact through time to cycle matter and energy, and how human activity alters the rates of these processes (e.g., fossil fuel formation and combustion). Objectives • Describe the composition of Earth’s atmosphere. • Explain how two types of barometers work. • Identify the layers of the atmosphere. • Identify two effects of air pollution. COMPOSITION OF THE ATMOSPHERE atmosphere - a mixture of gases that surrounds a planet, such as Earth • The most abundant elements in air are the gases nitrogen, oxygen, and argon. • The two most abundant compounds in air are the gases

carbon dioxide, CO2, and water vapor, H2O. • In addition to containing gaseous elements and compounds, the atmosphere commonly carries various kinds of tiny solid particles, such as dust and pollen. Pete Turner/Stone Collection/Getty Images/Space Shuttle Images Objects that enter the Earth's atmosphere face a rough trip. Nitrogen in the Atmosphere • Nitrogen makes up about 78% of Earth’s atmosphere and is maintained through the nitrogen cycle. • Nitrogen is removed from the air mainly by the action of nitrogen-fixing bacteria. • Decay releases nitrogen back into the atmosphere.

Nitrogen is an enormously important element with a versatile chemistry. It is part

of every protein. Our air consists to 78% of N2. The chemical bond between the two atoms in the nitrogen molecule is the strongest bond between two atoms of

the same element. This makes N2 a very stable and inert gas. Ammonia, NH3, which itself is toxic, is the most important base material for the nitrogen chemistry and is one of the most produced chemicals in the world. From this, for example fertilizers and explosives are made. Oxygen in the Atmosphere • Oxygen makes up about 21% of Earth’s atmosphere. • Land and ocean plants produce large quantities of oxygen in a process called photosynthesis. • Animals, bacteria, and plants remove oxygen from the air as part of their life processes. Oxygen is the third most abundant element in the universe and makes up nearly 21% of the earth's atmosphere. Oxygen accounts for nearly half of the mass of the earth's crust, two thirds of the mass of the human body and nine tenths of the mass of water. Large amounts of oxygen can be extracted from liquefied air through a process known as fractional distillation. Oxygen can also be produced through the electrolysis of water or by heating potassium chlorate (KClO3). Water Vapor in the Atmosphere • As water evaporates from oceans, lakes, streams, and soil, it enters air as the invisible gas water vapor. • Plants and animals give off water vapor during transpiration, one of their processes. But as water vapor enters the atmosphere, it is removed by the processes of condensation and precipitation. • The percentage of water vapor in the atmosphere varies depending on factors such as time of day, location, and season. The primary greenhouse gases in the Earth's atmosphere are water vapour, carbon dioxide, methane, nitrous oxide, and ozone. Greenhouse gases greatly affect the temperature of the Earth; without them, Earth's surface would be on average about 33 °C (59 °F) colder than at present.

*Transpiration is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere. Transpiration is essentially evaporation of water from plant leaves. Studies have revealed that about 10 percent of the moisture found in the atmosphere is released by plants through transpiration. The remaining 90 percent is mainly supplied by evaporation from oceans, seas, and other bodies of water (lakes, rivers, streams). READING CHECK: Does transpiration increase the amount of water vapor in the atmosphere or decrease the amount of water vapor in the atmosphere? Transpiration increases the amount of water vapor in the atmosphere. Ozone in the Atmosphere ozone - a gas molecule that is made up of three oxygen atoms

• Ozone in the upper atmosphere forms the ozone layer, which absorbs harmful ultraviolet radiation from the sun. • Without the ozone layer, living organisms would be severely damaged by the sun’s ultraviolet rays. • Unfortunately, a number of human activities damage the ozone layer. Particulates in the Atmosphere • Particulates can be volcanic dust, ash from fires, microscopic organisms, or mineral particles lifted from soil by winds.

Strep throat is caused by group A beta-hemolytic streptococcus. • Pollen from plants and particles from meteors that have vaporized are also particulates. • Large, heavy particles remain in the atmosphere only briefly, but tiny particles can remain suspended in the atmosphere for months or years.

Dust storm in Phoenix, Arizona in 2011. ATMOSPHERIC PRESSURE atmospheric pressure - the force per unit area that is exerted on a surface by the weight of the atmosphere • 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. Gravitation, or gravity, is a natural phenomenon by which physical bodies attract with a force proportional to their masses. • Atmospheric pressure is exerted equally in all directions—up, down, and sideways. • 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.

Sir Isaac Newton (1642-1727) was an English physicist, mathematician, astronomer, natural philosopher, alchemist, and theologian, who has been "considered by many to be the greatest and most influential scientist who ever lived. • Thus, atmospheric pressure decreases as altitude increases. • Atmospheric pressure also changes as a result of differences in temperature and in the amount of water vapor in the air. • In general, as temperature increase, atmospheric pressure at sea level decreases. • Similarly, air that contains a lot of water vapor is less dense than drier air because water vapor molecules have less mass than nitrogen or oxygen molecules do. • Barometric Pressure also known as atmospheric pressure is the same as Air Pressure. The pressure exerted by the atmoshpere at a given point. Air Pressure is the weight of the air pushing on Earth. It can change from place to place which causes air to move or circulate, flowing from areas of high pressure toward areas of low pressure. It's the same as atmospheric pressure. Air Pressure chances with the weather. In fact, its one of the most important factors in forecasting approaching weather and helps determine what the weather will be like. Example : Even though we do not always feel pressure changes, our bodies are able to detect fast changes. For example, when flying in a plane and increasing height quickly, our ears may "pop". This is due to low atmospheric pressure. Measuring Atmospheric Pressure • Meteorologists use three units for atmospheric pressure: atmospheres (atm), millimeters or inches of mercury, and millibars (mb). • Standard atmospheric pressure, or 1 atmosphere, is equal to 760 mm of mercury, or 1000 millibars. The average atmospheric pressure at sea level is 1 atm. • Meteorologists measure atmospheric pressure by using an instrument called a barometer. Mercurial Barometers • Atmospheric pressure presses on the liquid mercury in the well at the base of the barometer. • The height of the mercury inside the tube varies with the atmospheric pressure. • The greater the atmospheric pressure is, the higher the mercury rises.

Aneroid Barometers • Inside an aneroid barometer is a sealed metal container from which most of the air has been removed to form a partial vacuum. • Changes in atmospheric pressure cause the sides of the container to bed inward or bulge out. These changes move a pointer on a scale. • An aneroid barometer can also measure altitude above sea level.

READING CHECK: What is inside an aneroid barometer? An aneroid barometer contains a sealed metal container that has a partial vacuum. LAYERS OF THE ATMOSPHERE

• Earth’s atmosphere as a distinctive pattern of temperature changes with increasing altitude. • The temperature differences mainly result from how solar energy is absorbed as it moves through the atmosphere. • Scientists identify four main layers of the atmosphere based on these differences. The Troposphere troposphere - the lowest layer of the atmosphere, in which temperature drops at a constant rate as altitude increases; the part of the atmosphere where weather conditions exist • At an average altitude of 12 km, the temperature stops decreasing. This zone is called the tropopause and represents the upper boundary of the troposphere. The 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 • In the upper stratosphere, the temperature increases as altitude increases because air in the stratosphere is heated from above by absorption of solar radiation by ozone. The Mesosphere mesosphere - the coldest layer of the atmosphere, between the stratosphere and the thermosphere, in which the temperature decreases as altitude increases • The upper boundary of the mesosphere, called the mesopause, has an average temperature of nearly 90°C, which is the coldest temperature in the atmosphere. The Thermosphere thermosphere - the uppermost layer of the atmosphere, in which temperature increase as altitude increases; includes the ionosphere • The lower region of the thermosphere, at an altitude of 80 to 400 km, is commonly called the ionosphere. • Interactions between solar radiation and the ionosphere cause the phenomena known as auroras. An aurora (plural: aurorae or auroras) is a natural light display in the sky particularly in the high latitude (Arctic and Antarctic) regions, caused by the collision of energetic charged particles with atoms in the high altitude atmosphere (thermosphere). The charged particles originate in the magnetosphere and solar wind and, on Earth, are directed by the Earth's magnetic field into the atmosphere. • There are not enough data about temperature changes in the thermosphere to determine its upper boundary. • However, above the ionosphere is the region where Earth’s atmosphere blends into the almost complete vacuum of space. The diagram below shows the different layers of the atmosphere. READING CHECK: What is the lower region of the thermosphere called? The lower region of the thermosphere is called the ionosphere. Temperature Inversions • Any substance in the atmosphere and that is harmful to people, animals, plants, or property is called an air pollutant. • Today, the main source of air pollution is the burning of fossil fuels, such as coal and petroleum. • Certain weather conditions can make air pollution worse. • One such condition is a temperature inversion, the layer of warm air on top of cool air. • In some areas, topography may make air pollution even worse by keeping the polluted inversion layer from dispersing. • Under conditions in which air cannot circulate up and away from an area, trapped automobile exhaust can produce smog, a general term for air pollution that indicates a combination of smoke and fog.