Water Vapor and Saturation Pressure in Humid Air

The saturation pressure of water vapor in moist air varies with temperature

Saturation Pressure of Water Vapor

The maximum saturation pressure of the water vapor in moist air varies with the temperature of the air vapor mixture and can be expressed as:

p_ws = e^{(77.3450 + 0.0057 T - 7,235 / T)} / T^8.2 (1)

where

p_ws = water vapor saturation pressure (Pa)

e = the constant 2.718.......

T = temperature of the moist air (K)

Density of Water Vapor

The density of water vapor can be expressed as:

ρ_w = 0.0022 p_w / T (2)

where

p_w = partial pressure water vapor (Pa, N/m²)

ρ_w = density water vapor (kg/m³)

T = absolute dry bulb temperature (K)

Saturation pressure and density of water vapor for common temperatures:

vapor temperature saturation pressure diagram

Temperature		Saturation Pressure				Density
(^oC)	(^oF)	(Pa)	(mmHg)	(psia)	(inHg)	(kg/m³)	10^-3 (lb/ft³)
0	32	603	4.6	0.09	0.18	0.005	0.30
10	50	1212	9.2	0.18	0.36	0.009	0.59
20	68	2310	17.4	0.33	0.68	0.017	1.08
30	86	4195	31.7	0.61	1.24	0.030	1.90
40	104	7297	55.1	1.06	2.15	0.051	3.20
50	122	12210	92.2	1.8	3.60	0.083	5.19
60	140	19724	149	2.9	5.82	0.13	8.13
70	158	30866	233	4.5	9.11	0.20	12.3
80	176	46925	354	6.8	13.8	0.29	18.2
90	194	69485	525	10.1	20.5	0.42	26.3
100	212	100446	758	14.6	29.6	0.59	36.9
120	248	196849	1486	28.6	58.1	1.10	68.7
140	284	358137	2704	51.9	105.7	1.91	119
160	320	611728	4619	88.7	180.5	3.11	194
180	356	990022	7475	144	292.1	4.80	300
200	392	1529627	11549	222	451.2	7.11	444