Temp (^oF) g H₂O/kg air

            14                                                                                                2

            41                                                                                                5

            50                                                                                                7

            59                                                                                                10           

            68                                                                                                14

            77                                                                                                20           

            86                                                                                                26.5

            95                                                                                                35

Air temp is 77^oF

1)  What is the capacity of the air mass

Use the chart above in order to figure this out:

                        Find 77^oF on the chart then go across to fine out how much water the air mass can

hold at that temperature…in this case it is 20 g H₂O/kg air

2)  If the air mass has 18 g H₂O/kg what is the relative humidity?

Relative humidity is a comparison of how much water the air mass has in it vs. how much water it can hold.  It is figured as a percentage.  To calculate this we divided how much water the air mass has by how much it can hold. To express it as a percentage we multiply our answer by 100.

amount of water in air mass:                             18 g H₂O/kg air   *100 = 90%

                        Maximum water air mass can hold at 77^oF:    20 g H₂O/kg air

Air temp is 41^oF

3)  What is the capacity of the air mass

Use the chart above in order to figure this out:

                        Find 41^oF on the chart then go across to fine out how much water the air mass can

hold at that temperature…in this case it is 5 g H₂O/kg air

4)  If the relative humidity is 22% how much water vapor is in the air mass?

This is similar to question 2 in the first example but in this case you are given the % and you have figured out how much water the air mass can hold from the first question (5 gH₂O/kg air).  Now we set up the equation with what we know and solve for the part that is missing:

amount of water in air mass:                              X g H₂O/kg air   *100 = 22%

                        Maximum water air mass can hold at 41^oF:    5 g H₂O/kg air

            We solve the equation for X (the amount of water in the air mass.

                        X g H₂O/kg air   =       22%

5 g H₂O/kg air           100%

X g H₂O/kg air   =      0 .22

5 g H₂O/kg air

                        X g H₂O/kg air   =  0.22 (5 g H₂O/kg air)

                        X= 1.1 g H₂O/kg air            

5) What is the dew point of an air mass that has 10gH₂O/kg

            Use the chart above in order to figure this out:

                        The Dew point is when the air mass is holding all the water it can at any particular temperature.  It is expressed as a temperature.  Therefore if the dew point is when the air mass can only hold what it has, we look to the chart to see at what temperature it can only hold 10gH₂O/kg air.  This turns out to be 59^oF

6)  An air mass has a relative humidity of 46% and a temperature of 68^oF. 

What is the capacity of the air mass and what is the absolute humidity (the amount of water in the air mass)?

The capacity is based on the temperature of the air mass. Use the table above and determine how much water the air mass can hold at 68_o. This would be 14g H₂O per kg of air. To determine what it actually has in it (i.e. the absolute humidity) you would set up the equation:

0.46= X Do the algebra and you have: (0.46)(14) = X (which is the absolute humidity)

14 X = 6.44 g H₂O per kg air

 7)  The absolute humidity of an air mass is 13gH₂O/kg air and the relative humidity is 37%.  What is the temperature of the air mass?

To determine the dew point, you need to know at what temperature the air mass can only hold the amount of water it has in it. This amount is given to you in the problem. The absolute humidity is what the air mass currently has in it. It is 13 g H₂O per kg air. Now use the chart above and determine at what tem. will this air mass only be able to hold this amount of water or reach 100% relative humidity. Since the value isn’t directly on the chart you would estimate it to be around 66^o-67^o since 14 grams = 68^o