PROPERTIES OF THE ATMOSPHERE

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)

• The Earth’s atmosphere, because air has weight, exerts pressure.

• Density of air decreases as altitude increases so pressure also decreases.

AIR PRESSURE

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.

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

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.

• 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

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

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.