Conversion Factors B-1
APPENDIX B: CONVERSION FACTORS
This section provides information on the conversion of water vapor pressure values to more com-
monly used terms, such as parts per million by volume, dew point, mg/L, and lb/mmft
3
.
Water Vapor Pressure and Temperature
Most tables used to express the concentration of water vapor are based on vapor pressure data of
liquid water and ice. The concentration of water vapor above the liquid or solid is known as the
water vapor pressure. Tables expressing the vapor pressure above ice and water at various tempera-
tures may be found in the International Critical Tables, chemical handbooks, or other engineering
handbooks.
water partial pressure (Pv) psia @ temperature
parts per million by volume = ————————————————————— x 10
6
total pressure (Pt) psia
At saturation pressures above 301 kPa absolute (45 psia), nonideal gas corrections are required.
Table B1: Saturation Vapor Pressure of Water Vapor in Millimeters of Mercury
with Respect to Water Above 0°C and with Respect to Ice Below 0°C
(Reproduced from the Smithsonian Meteorological Tables)
Temp 0 1 2 3 4 5 6 7 8 9
°C
– 70 0.0019 ------ ------ ------ ------ ------ ------ ------ ------ ------
– 60 0.0080 0.0070 0.0061 0.0053 0.0046 0.0040 0.0035 0.0030 0.0026 0.0022
– 50 0.0294 0.0260 0.0229 0.0202 0.0178 0.0156 0.137 .0120 0.0105 0.0092
– 40 0.0964 0.0859 0.0765 0.0680 0.0605 0.0537 0.0476 0.0421 0.0373 0.0329
– 30 0.2878 0.2591 0.2231 0.2094 0.1880 0.1686 0.1511 0.1352 0.1209 0.1080
– 20 0.7834 0.7115 0.6456 0.5854 0.5303 0.4800 0.4341 0.3923 0.3541 0.3194
– 10 1.9643 1.7979 1.6444 1.5029 1.3726 1.2525 1.1421 1.0406 0.9474 0.8618
– 0 4.5802 4.2199 3.8868 3.5775 3.2907 3.0248 2.7785 2.5505 2.3395 2.1445
0 4.5802 4.924 5.921 5.682 6.098 6.541 7.012 7.513 8.045 8.610
10 9.210 9.84 10.521 11.235 11.992 12.794 13.642 14.539 15.487 16.489
20 17.548 18.665 19.844 21.087 22.398 23.780 25.235 26.767 28.380 30.076
30 31.860 33.735 35.705 37.775 39.947 42.227 44.619 47.127 49.756 52.510
40 55.396 58.417 61.580 64.889 68.350 71.968 75.751 79.703 83.830 88.140
50 92.639 97.33 102.23 107.33 112.66 118.20 123.98 130.00 136.26 142.78
60 149.57 156.62 163.96 171.59 179.52 187.75 196.31 205.19 214.41 223.98
70 233.91 244.21 254.88 265.96 277.43 289.32 301.63 314.38 327.59 341.25
80 355.40 370.03 385.16 400.81 416.99 433.71 540.99 468.84 487.28 506.32
90 525.97 546.26 567.20 588.80 611.08 634.06 657.75 682.18 707.35 733.28
100 760.00
Absolute Humidity
The absolute humidity of water vapor in air or other gases is defined as the pressure of water vapor
or as the weight per volume of water vapor. It is expressed in various units such as grams per liter,
grams per cubic foot, or millimeters of mercury pressure.
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