E ARTH S CIENCE Name: ____________
W ATER IN THE A TMOSPHERE Period: Date:
25
30
35
40
5
10
15
20
To illustrate the relation between water vapor capacity and air temperature, prepare a graph by plotting the following data:
Temperature
ºC
Water Vapor per kg of Air
(g/kg)
The Affect of Temperature on
Water Vapor Capacity
-40
-30
0.1
0.3
50
-20
-10
0.75
2
40
0 3.5
30
5
7
10
14
20
26.5
35
47
20
10
0
-40 -30 -20 -10 0 10
20 30 40
Analyze the data table and graph to complete the following statements and answer the following questions.
Whenever two words are given in parentheses, circle the correct word or number from each pair .
1)
Raising the air temperature of a kilogram of air 5ºC, from 10ºC to 15ºC,
(increases, decreases) its water vapor capacity by (3, 6) grams. However, raising the temperature from 35ºC to 40ºC (increases, decreases) the capacity by (8, 12) grams.
2) What is the relationship between the water vapor capacity of air and the temperature of the air? Use a complete response and be as specific as possible.
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Measuring Humidity
Relative humidity is the most common measurement used to describe water vapor in the air. In general, it expresses how close the air is to reaching its water vapor capacity. Relative humidity is the ratio of the air’s water vapor content (amount actually in the air) to its water vapor capacity at a given temperature, expressed as a percent. The general formula is
Relative Humidity (%) = Water vapor content
Water vapor capacity
* 100%
For example, from the table, the water vapor capacity of a kilogram of air at 25ºC would be 20 grams per kilogram.
If the actual amount of water vapor in the air was 5 grams per kilogram (the water vapor content), the relative humidity of the air would be calculated as follows:
Relative Humidity (%) = 5 g/kg * 100% = 25%
20 g/kg

3) Use data from the table and the formula for relative humidity to determine the relative humidity for each of the following situations of identical temperature.
4) Based on these results, if the temperature of air remains constant, adding water vapor will (raise, lower) the relative humidity, while removing water vapor will (raise, lower) the relative humidity.
Air Temp
(ºC)
15
Water Vapor
Content (g/kg)
Water Vapor
Capacity (g/kg)
2
15
15
5
7
Relative
Humidity (%)
5) Use data from the table and the formula for relative humidity to determine the relative humidity for each of the following situations of identical water vapor content.
6) Based on these results, if the amount of water vapor in the air remains constant, cooling the air will (raise, lower) the relative humidity, while warming the air will
(raise, lower) the relative humidity.
Air Temp
(ºC)
25
15
5
Water Vapor
Content (g/kg)
5
5
5
Water Vapor
Capacity (g/kg)
Relative
Humidity (%)
7) In the winter, air is heated in homes. What effect does heating the air have on the relative humidity inside the home? What can be done to lessen this effect? (Hint: Obviously, heating the air increases temperature. What does it do to the water vapor content in the air and the water vapor capacity of the air?)
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8) Explain why a cool basement is humid (damp) in the summer. (Hint: Although it sounds different, this is almost the same question as the previous heating question.)
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9) Write brief statements describing each of the two ways that the relative humidity of air can be changed. Both should be phrased as a relationship. To be different, these relationships can’t just be the same thing phrased oppositely. (Hint: Look at the equation for relative humidity)
1. ________________________________________________________________________________________
2. ________________________________________________________________________________________
One of the misconceptions concerning relative humidity is that it alone gives an accurate indication of the amount of water vapor in the air. For example, on a winter day if you hear on the radio that the relative humidity is 90 percent, can you conclude that the air contains more moisture than on a summer day which records a 40 percent relative humidity? Find the answer as part of question 10.
10) Use data from the table to determine the water vapor content for each of the following situations. As you do the calculations, keep in mind the definition
(equation) of relative humidity.
Summer
Air Temperature = 25ºC
Capacity = ______g/kg
Relative Humidity = 40%
Content = ______g/kg
Winter
Air Temperature = 5ºC
Capacity = ______g/kg
Relative Humidity = 90%
Content = ______g/kg
11) Explain why relative humidity does not give an accurate indication of the amount of water vapor in the air.
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