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Dräger sampling tubes and systems - 20351 A

1.3 Water Vapor and Humidity

Water vapor in the atmosphere is commonly called humidity. There are many sources forit, after all the surface of the earth consists of two thirds water. Humans also "produce" water vapor as a metabolic product with each breath that is exhaled. The maximum water vapor content of the air depends on temperature, i. e. the figures ofrelative humidity are always to be considered in reference to temperature. To convert relative humidity into absolute humidity as a function of temperature, the above diagram orthe following formula can be used. Using a pocket calculator a conversion can be done:Y = 3.84
D-1219-2009 Water Content [mg/L]

0102030405002550 75100 Temperature [ °C]

â‹… 10
-6 â‹… Ï‘
4 + 2.93 â‹… 10
-5 â‹… Ï‘
3 + 0.014 â‹… Ï‘
2 + 0.29 â‹… Ï‘ + 4.98With y = maximum absolute humidity in mg H
2 O / L and Ï‘ = temperature in °C. This formula is valid for the temperature range of 0 to 100 °C.Example: The absolute humidity at t = 25 °C is needed. Using the formula the result is y= 22.94 mg H
2 O / L. The result indicates that at 25 °C the maximum absolute humidity is22.94 mg/L; that corresponds to a relative humidity of 100 % at the same temperature.Similarly, every other absolute humidity at this temperature can be calculated, e. g. 50 %relative humidity at 25 °C equals 11.47 mg H
2 O / L etc. If the relative humidity and the corresponding temperature are known, the absolute humidity can be calculated using theabove formula.