Sections :

International Standard Atmosphere (ISA)

Sea Level Conditions

ISA Variation with Altitude

Variation due to Local Ground Conditions

Variation of Density due to Humidity

Variation of Density with Extremely High Altitude

Tabulated Data :

Table of Atmosphere Properties.

Software :

Atmosphere Properties Web Calculator

Atmosphere Properties Calculator (MS Windows Executable)

VARIATION IN DENSITY DUE TO HUMIDITY

The density of the air for a given level of humidity can be found by applying a correction factor to the above calculated perfect gas density.

$$ρ=ρ_{PG}K_h\text"       "ρ_{PG}=P/{RT}$$

The correction factor, Kh, can be found by using wet and dry bulb temperature measurements to predict relative humidity as shown in the table below. The relative humidity can be used to obtain the density correction factor from the following graph. Note that the density correction factor produced assumes approximately sea level pressure in the application of these formula.

Table: Relative Humidity (%) based on measured Temperature Difference

Relative Humidity (%)

Dry Bulb

Temperature Difference,oC TDRY - TWET

oC

1

2

3

4

5

6

7

8

9

10

11

12

81

64

46

29

13

2

84

68

52

37

22

7

4

85

71

57

43

29

16

6

86

73

60

48

35

24

11

8

87

75

63

51

40

29

19

8

10

88

77

66

55

44

34

24

15

6

12

89

78

68

58

48

39

29

21

12

14

90

79

70

60

51

42

34

26

18

10

16

90

81

71

63

54

46

38

30

23

15

8

18

91

82

73

65

57

49

41

34

27

20

14

7

20

91

83

74

66

59

51

44

37

31

24

18

12

22

92

83

76

68

61

54

47

40

34

28

22

17

24

92

84

77

69

62

56

49

43

37

31

26

20

26

92

85

78

71

64

58

51

46

40

34

29

24

28

93

85

78

72

65

59

53

48

42

37

32

27

30

93

86

79

73

67

61

55

50

44

39

35

30

32

93

86

80

74

68

62

57

51

46

41

37

32

34

93

87

81

75

69

63

58

53

48

43

39

35

36

94

87

81

75

70

64

59

54

50

45

41

37

Reference: "Handbook of Chemistry and Physics" Ed R.C.Weast, The Chemical Rubber Co., Ohio, 1964

Humidity Correction Factor.