# Change in the Atmosphere with Altitude

## Air pressure changes with altitude.

Air is all around us, but we cannot see it. Gravity from the Earth pulls air down - this is called air pressure. We don't feel this pressure because our bodies push an equal amount of pressure outward. This graph shows how air density and air pressure changes with altitude (the distance above sea level). Barometers are used to measure air pressure in milibars.

This graph shows how air pressure changes with altitude (the distance above sea level) as one moves upward in the atmosphere. The density of air is computed based on the mass of air molecules, divided by the volume of air. Density and pressure change similarly with height.

### Which of the following statements about the graph are true?

Air pressure is higher at lower altitudes.
Air density is higher at lower altitudes.
There is more space between air molecules at higher altitudes.
There is less oxygen to breathe at the top of a high mountain than there is at sea level.

## Temperature changes with altitude

The atmosphere is divided into different layers depending on how temperature changes. Take a look at the graph below to see how temperature changes with altitude.

### Which of the following statements about the graph are true?

If you follow the temperature line in the graph above from the surface of the Earth to the top of the atmosphere, moving to your left represents a decrease in temperature, to your right represents an increase in temperature, and straight up represents a constant temperature.
Temperature increases as you gain altitude in the stratosphere and the thermosphere.
Temperature decreases as you gain altitude in the troposphere and mesosphere.
Air temperature varies in complicated ways with altitude.

## Near the Earth's surface, air gets cooler the higher you climb.

As you climb a mountain, you can expect the air temperature to decrease by 6.5° C for every 1000 meters you gain. This is called the standard (average) lapse rate.

If air temperature is 27° C at sea level as shown, you can expect it to be around 1° C at air altitude of 4000 meters because of the lapse rate.

### Plan an Expedition

You are going to climb Mount Audubon in Colorado today!

When you leave your house at 2000 meters, the air temperature is 15° C. What is the temperature likely to be at the 4000 meter summit?