Eighth Grade Science Notes

Grading Procedure: 30% Tests, 30% Projects, 30% Labs, 10% Quizzes

Chapter 15 Notes

Topic: The Air Around You                                                                 Date: __________

AIM: state how the atmosphere is important to living things.

Earth’s atmosphere contains gases, including oxygen, that living things need to carry out their life processes.

AIM: identify the gases that are present in the atmosphere.

Nitrogen (78%)

Oxygen (21%)

Other gases (1%) These other gases include argon, carbon dioxide, neon, helium, methane, krypton, hydrogen and water vapor.

Topic: Air Quality                                                                         Date: __________

AIM: name the main sources of air pollution.

Most air pollution is the result of burning coal, oil, gasoline, and diesel fuel.

AIM: explain how photochemical smog forms.

Photochemical smog is the brown haze that forms in cities when sunlight interacts with chemicals in the air. When fossil fuels are burned, some of the hydrocarbons and the nitrogen that they contain are released into the atmosphere. The nitrogen combines with oxygen and forms nitrogen oxides at high temperatures. The nitrogen oxides, the hydrocarbons, other chemicals in the air, and the sunlight combine to form ozone and other chemicals which can cause difficulties breathing and harm living and nonliving things.

AIM: explain how acid rain forms.

Acid rain is any type of precipitation (rain, snow, sleet, or hail) that has more acid than usual. Burning coal releases sulfur into the air. The sulfur combines with oxygen in the atmosphere to form sulfur oxides. These sulfur oxides combine with water to form sulfuric acid. Burning oil releases nitrogen into the air. As discussed in the previous AIM, when nitrogen and oxygen combine at high temperature they form nitrogen oxides. These combine with water to form nitric acid. When either the sulfuric acid or the nitric acid becomes part of the water cycle, acid rain occurs. If the rain becomes too acidic, it can kill plants and animals that depend on it. In more severe cases, acid rain can burn buildings and statues.

Topic: Air Pressure                                                                                   Date: __________
AIM: identify some properties of air.

Air has mass, density, and pressure.

AIM: name some instruments that are used to measure air pressure.

The instruments used to measure air pressure are mercury barometers and aneroid barometers. A mercury barometer is made of a glass tube and a dish of mercury. The glass tube has (nearly) no air in it. The air from the atmosphere presses down on the mercury in the dish. As air pressure increases, the mercury rises in the tube. As air pressure decreases, the mercury falls in the tube. An aneroid barometer uses an airless metal tube to measure air pressure. When the pressure increases, the tube is pushed inward. When the air pressure decreases, the tube expands outward. Air pressure is measured in inches of mercury (how far the mercury has traveled up the tube of a mercury barometer) for common (unscientific) use. For scientific purposes, air pressure is measure in millibars.

Problem Solving: One inch of mercury is 33.87 millibars. What is the air pressure in millibars at 28 inches? _____ 29 inches? _____ 30 inches? _____

What is the air pressure in inches if it is 987 millibars?_____ 995 millibars?_____ 1032? _____

AIM: explain how increasing altitude affects air pressure and density.

As altitude increases, air pressure and density decrease. Put another way, the higher you go above sea level, the farther apart the air molecules are and the less they are pressing down on objects. The reverse is also true; As altitude decreases, ___________________________________________________________________________________________________________________________________________________________.

Put another way, the closer you are to sea level, the closer together air molecules are and the more they are pressing down on you.

Topic: Layers of the Atmosphere                                                      Date: __________
AIM: describe the characteristics of the main layers of the atmosphere.

There are four main layers of the atmosphere: the troposphere, the stratosphere, the mesosphere, and the thermosphere. The layers of the atmosphere are divided according to changes in temperature.

The lowest level of the atmosphere is the troposphere. This is where conditions change the most. For every kilometer increase in altitude, there is a 6.5 degree Celsius decrease in temperature.On average the troposphere is 12 km high. It is shorter at the poles (about 9 km high) and taller at the equator (about 16 km high). On average, what is the temperature difference between the bottom of the troposphere (sea level) and the top of the troposphere (12 km high)? __________ The troposphere is the thinnest layer of the atmosphere, but it is the most massive. It is where the weather (storms) occurs.

Above the troposphere is the stratosphere. It reaches from the top of the troposphere (about 12 km) to 50 kilometers high. It is cold at the bottom (about -60 degrees Celsius) and warm at the top. Air pressure decreases as you go higher in the stratosphere. The stratosphere contains the ozone layer (it is at the top of the stratosphere) which protects living things on Earth from harmful ultraviolet (UV) rays emitted by the sun.

The next layer of the atmosphere is the mesosphere. It is 30 km thick. It starts 50 km above sea level and ends 80 km above sea level. Recall that the stratosphere warms as altitude increases. Scientists mark the end of the stratosphere and the beginning of the mesosphere as the place where the temperature drops. The mesosphere is very cold.  The mesosphere protects living things on Earth from space objects. Most objects that fall to Earth from space are destroyed in the mesosphere.

The top layer of the atmosphere is the thermosphere. The thermosphere is the hottest layer of the atmosphere because it is the first layer to get energy from the sun. Most of the energy is absorbed in the thermosphere. It is divided into the ionosphere (80 km to 550 km) and the exosphere (550 km and above). The ionosphere is where radio signals are bounced from. The exosphere is where television and phone signals are bounced from.