Temperature Inversion-Honors
In some cities, the weather report often warns of high air-pollution levels. People are asked not to drive
unless it is absolutely necessary, and wood fires and barbeques are forbidden. A frequent reason for high
levels of air pollution near the ground is a temperature inversion in the atmosphere. On most days, the
temperature of air in the atmosphere is cooler higher up in altitude. This is because most of the sun’s
energy is converted to infrared terrestrial radiation that in turn warms the atmosphere. The warm air
expands, rises and cools. Sometimes, however, the temperature of air actually increases with altitude.
The situation of having warm air on top of cooler air is referred to as a temperature inversion, because
the temperature profile of the atmosphere is “inverted” from its usual state. These inversions can be
caused by exceptionally cold ground level temperatures in narrow valleys resulting in stagnant, nonmixing air that traps air pollution in the lower cool layer.
Purpose/Objective: How does density change with altitude in normal air and in a temperature inversion?
Which conditions produce a temperature inversion and how does it trap pollution?
Procedure:
1. Absolute Zero is the temperature at which molecules stop moving. Absolute temperature uses the
Kelvin scale (00K = -273.150C). Determine the absolute temperatures by converting from Celsius to
Kelvin. For both sets of data. 0K = _____0C + 273.15
2. Density is inversely proportional to temperature; that is to say the more dense an item is the colder it is.
Therefore the (density) x (absolute temp.) at height h = (density) x (absolute temp.) at ground level
Dh x Th = Dg x Tg
This relationship can be rearranged to solve for an unknown density of air at a known absolute
temperature when compared to ground level air if we assume a density of 1 kg/m3 at ground level.
Calculate the density of air at increasing heights using the following equation for both sets of data.
Density h = density(ground) x absolute temp (K)
Absolute temp at height h
OR
Dh = _ Dg x Tg __
Th
3. Plot Data Set A. Label height on the x axis, Temp on the left y, and density on the right y. Repeat for
Data Set B on another graph.
Data:
Data Set A
Height
(m)
0
100
200
300
400
500
600
700
Temperature
(Degrees C)
20.0
19.5
18.7
18.0
17.5
16.9
16.0
15.5
Absolute
Temperature
(K)
293.15
Data Set B
Density
(kg/m3)
Temperature
(Degrees C)
Absolute
Temperature
(K)
Density
(kg/m3)
20.0
19.3
18.8
18.0
19.0
19.5
19.4
18.8
Analysis:
Analyze each graph. Identify the patterns, cite data as evidence, and infer the cause of the
pattern.
Temperature Inversion Lab-Honors
Follow-up Questions
1. How might a temperature inversion alter the normal flow of a convection current?
2. At what altitude would you expect to find the greatest concentrations of pollutants during the
inversion graphed in Set B? Explain why.
3. Los Angeles has the reputation as being very smoggy. In fact, the native locals – the Chumash
– name for the area translates to “the valley of the smoke”. What is it about the geography of the
LA basin that results in a lot of smog, even when populations are small?
http://commons.wikimedia.org/wiki/File:Los Angeles Basin JPLLandsat.jpg
Temperature Inversion Lab-Honors
Follow-up Questions
1. How might a temperature inversion alter the normal flow of a convection current?
2. At what altitude would you expect to find the greatest concentrations of pollutants during the
inversion graphed in Set B? Explain why.
3. Los Angeles has the reputation as being very smoggy. In fact, the native locals – the Chumash
– name for the area translates to “the valley of the smoke”. What is it about the geography of the
LA basin that results in a lot of smog, even when populations are small?
http://commons.wikimedia.org/wiki/File:Los Angeles Basin JPLLandsat.jpg