1. PROPERTIES OF THE ATMOSPHERE

2. TEMPERATURE Temperature is the measure of the average kinetic energy of the particles in a material. Higher temperature means particles are moving faster. Temperature Scales Fahrenheit (used in United States) Celsius (used in the rest of the world) Kelvin (SI unit of temperature)

3. The Earths atmosphere, because air has weight, exerts pressure. Density of air decreases as altitude increases so pressure also decreases. AIR PRESSURE

4. PRESSURE-TEMPERATURE-DENSITY Air Pressure versus Temperature At the same density, warm air exerts more pressure than cooler air. Air Pressure and Density At the same temperature, more dense air exerts more pressure. Temperature and Density At the same pressure, warm air is less dense than cool air.

5. HUMIDITY Humidity is the amount of water vapor in the atmosphere at a given location. Two ways to express water vapor content: Relative Humidity Dew Point

6. RELATIVE HUMIDITY The amount of water in a volume of air relative to the amount of water vapor needed for that volume of air to reach saturation is called relative humidity.

7. The dew point is the temperature to which air must be cooled at constant pressure to reach saturation. When temperature falls to this level, dew begins to forms (condensation). If the dew point is nearly the same as the air temperature, then the relative humidity is high. DEW POINT

8. SAMPLE CALCULATION What is the relative humidity of 1 kg of air containing 20 g of water at 40 °C? There can be up to 50 g of water in a 40 °C sample. (20g/50g) x 100 = 40% relative humidity

9. CLASS ACTIVITIES Complete the Mini Lab on page 295 and answer the Analysis questions on your own sheet of paper. Complete the Problem-Solving Lab on page 294 and answer the Think Critically questions on the same sheet of paper.