Water-Vapor Capacity of Air

Any measure of water vapor in the air is referred to as humidity. The amount of water vapor

required for saturation is directly related to temperature. The mass of water vapor in a unit of air

compared to the remaining mass of dry air is referred to as the mixing ratio. Table 14.2 presents

the mixing ratios of saturated air (water vapor needed for saturation) at various temperatures. Use

the table to answer questions 1-3.

Table 14.2 Amount of water vapor needed to saturate

a kilogram of air at various temperatures, the saturation

mixing ratio.

a. 35°C:

b. 59°F:

TEMPERATURE

(°C)

-40

-30

-20

-10

c. 5°C:

d. -30°C:

0

5

10

15

20

25

30

35

40

(°F)

-40

-22

-4

14

32

41

50

59

68

77

86

95

104

WATER VAPOR

CONTENT AT

SATURATION (G/KG)

0.1

0.3

0.75

2

SONGS

3.5

5

7

10

14

20

26.5

35

1. To illustrate the relation between the amount of water vapor needed for saturation and

temperature, prepare a graph by plotting the data from Table 14.2 on Figure 14.5.

47

2. From Table 14.2 and/or Figure 14.5, what is the water vapor content at saturation of a kilogram

of air at each of the following temperatures?

grams/kilogram

grams/kilogram

grams/kilogram

grams/kilogram

3. From Table 14.2, raising the air temperature of a kilogram of air 10°C, from 10°C to 20°C,

(increases, decreases) the amount of water vapor needed for saturation by (3, 7) grams./nWater Vapor Content at Saturation (g/kg)

-40° -22° -4°

50

40

30

20

10

40°

-30°

-20°

Temperature (°F)

32° 50°

14°

10°

-10° 0°

Temperature (°C)

68°

20°

86° 104°

30°

40°