Understanding Relative Humidity and Dew Point in Air Masses

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Homework Help Overview

The discussion revolves around understanding the concepts of relative humidity, dew point, and water vapor density in air masses, particularly at varying temperatures. The original poster presents a scenario involving an air mass at 90 degrees F with a specific amount of vapor, seeking to calculate relative humidity and dew point, and to analyze changes in water vapor as temperature changes.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • Participants explore how to calculate relative humidity by comparing the amount of water vapor to the saturated vapor density at given temperatures. Questions arise regarding the dew point and how to determine it based on vapor density and temperature. There is also discussion about the expected loss of water vapor when the temperature drops.

Discussion Status

Some participants have provided guidance on calculating relative humidity and dew point, suggesting methods involving the ideal gas equation and vapor pressure tables. Multiple interpretations of the problem are being explored, particularly regarding the calculations needed for different temperatures.

Contextual Notes

Participants note the need for specific vapor density values at different temperatures, which may not be readily available, and reference external resources for further information. There is an acknowledgment of the complexity involved in determining these values accurately.

Esoteric
An air mass is at 90 degrees F. It contains 20 grams of vapor/m^3. What is the relative humidity of this air mass?

What would the relative humidity of this air mass be if its temperature were increased to 100 degrees F?

What is the dew point of this air mass?

The temperature is now expected to drop to 50 degrees F. How much water vapor (g/m^3) do you expect the air mass to lose?
 
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guess not.
 
Esoteric said:
An air mass is at 90 degrees F. It contains 20 grams of vapor/m^3. What is the relative humidity of this air mass?

What would the relative humidity of this air mass be if its temperature were increased to 100 degrees F?
What is the saturated vapour density of water at 90 degrees F in g/m^3? Divide 20 by that number and you will have the relative humidity. To work the density out from the vapour pressure, if you can't find it on a table, you will have to use the ideal gas equation.

What is the dew point of this air mass?
The dew point is the temperature at which 20 g/m^3 is the saturated vapour density of water. Work out what this is in terms of pressure and just go down the graph of vapour pressure vs. temperature to find this temperature.

The temperature is now expected to drop to 50 degrees F. How much water vapor (g/m^3) do you expect the air mass to lose?
Find the saturated vapour density of water at 50F and subtract that from 20 g/m^3. That is the amount of mass/m^3 of water that will precipitate out.

AM
 
Last edited:
thanks a lot Gamma and Mason.
 

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