# GEOG1200 Saint Mary’s Module2 Humidity Assignment This is an geology assignment associated with humidity. One of its objectives is to understand use of sat

GEOG1200 Saint Mary’s Module2 Humidity Assignment This is an geology assignment associated with humidity. One of its objectives is to understand use of saturation curve graph. Another objective is to learn about how relative humidity s measured using a sling psychrometer. The third objective is to study the concept of humidity. There are total of 5 sections in this assignment. And you can just accomplish this assignment step by step. If you need more information, you can ask me to provide. I will appreciate your help. SAINT MARY’S UNIVERSITY
GEOG 1200
DEPARTMENT OF GEOGRAPHY
FUNDAMENTALS OF PHYSICAL GEOGRAPHY
Module 2: HUMIDITY
Objectives
1.
To study the concept of humidity.
2.
To understand use of the saturation curve graph.
3.
Learn about how relative humidity is measured using a sling psychrometer.
Section 1: Understanding Humidity
Terminology
Air can hold up to a certain amount of water vapour (water in a gaseous state) but the amount varies depending on the
temperature. Humidity is a general term that refers to the amount of moisture in air. Some other important terms to
know when dealing with moisture in the atmosphere are:
Specific Humidity (SH): the actual quantity of water vapour in the air, in grams per kilogram (g/kg).
Maximum Specific Humidity (MSH): the maximum quantity of water vapour that could be held in the air at a given
temperature (g/kg). If the air is unsaturated, the SH is less than the MSH.
Relative Humidity (RH): the ratio of SH to MSH, expressed as a percentage:
Equation 1:
Specific Humidity
RH (%) = ———————————-Maximum Specific Humidity
x
100
Dew-Point Temperature (DT): the temperature at which air saturation and condensation occur for a given value of
specific humidity. Condensation is the change of water from a gaseous state to a liquid state.
Saturation Curve: a graph (on a separate sheet) showing the relationship between air saturation and temperature.
Once the saturation point is reached, the RH is 100% and no more water vapour can be evaporated into the air.
Example
For reference, an example using the Saturation Curve Graph is given. Follow the example of how to correctly read the
graph.
a.
A sample of air is collected and determined to lie at Point X on the graph.
b.
The air temperature is 30C.
c.
The SH is 10.0g/kg (grams of water vapour per kilogram of air).
d.
What is the MSH?
e.
What is the RH, rounded to the nearest %?
f.
What is the DT?
1
Air Temperature
(C)
X
30
Specific Humidity
(g / kg)
10
Maximum Spec.
Humidity
(g / kg)
Relative
Humidity
(%)
Dew-Point
Temperature (C)
27.5
36
12.5
2
Section 2: Using the Saturation Curve Graph

Recall from the previous section that relative humidity is the ratio between specific humidity and maximum specific
humidity expressed as a percentage.

It is possible for the specific humidity to be lower than or equal to, but not higher than, the maximum specific
humidity. A point on the graph can only lie on or below the line.

A series of values will be used to demonstrate the relationships between temperature and humidity of air.

In this example, the temperature of the air changes, forcing changes in the relative humidity values. A starting
point was selected with an air temperature of 20C and a specific humidity of 10 g / kg.
Air Temperature
(C)
Specific Humidity
(g / kg)
A
20
10
B
13
10
C
0
4
D
10
4
Maximum Spec.
Humidity
(g / kg)
Relative
Humidity
(%)
Dew-Point
Temperature (C)
Use the Saturation Curve Graph to complete the table (above or attached).
Section 3: Measuring Relative Humidity with a Sling Psychrometer
Background

A device for measuring relative humidity is called a sling psychrometer.

The paragraphs below describe the sling psychrometer and its operation – For the on-line course you will not be
using the instrument, however you will learn about it .
The Sling Psychrometer

The sling psychrometer contains two thermometers housed in a plastic casing attached to a handle.

The casing is designed to be spun around the handle, vigourously.

The upper thermometer is a standard mercury thermometer with a Celcius temperature scale – this is the dry-bulb
thermometer it measures the air temperature.

The lower thermometer is similar, except it is covered by a wick at the far end- this is the wet-bulb thermometer. If
the wick is dry, unscrew the plastic cap and add water to the reservoir.

The difference between the dry bulb and wet bulb temperatures is called the wet-bulb depression (or depression of
the wet bulb).
How the Sling Psychrometer Works

When the psychrometer is spun, evaporation causes the wet-bulb temperature to be lowered.
3

The amount of evaporation from the wick is related to the relative humidity (RH). The amount of evaporation is
determined by the amount of water vapour already in the air (the specific humidity) compared to the maximum
amount of water vapour that can be held at that temperature (maximum specific humidity).

If the RH is high, there will be relatively little evaporation and the dry and wet bulb temperatures will be close to
each other.

If the RH is low, there will be relatively more evaporation and the dry and wet bulb temperatures will be further
apart.
Using the Psychrometer

To use, spin the psychrometer vigourously for 30-40 seconds.

Read off the two temperatures to the nearest half degree and calculate the wet-bulb depression.

On a separate sheet is a chart that will tell you the relative humidity for the air temperature you measure (dry-bulb
temperature) and the corresponding wet-bulb depression.

Read the chart down to the dry-bulb temperature you recorded, and across to the wet-bulb depression to obtain
the relative humidity value.

For example, if you measured a dry-bulb temperature of 34C and a wet-bulb temperature of 24.5C, the wet-bulb
depression is 9.5C and the relative humidity is 46%. Use the chart to confirm how this value of relative humidity is
obtained.

On the chart, if the exact dry-bulb temperature you recorded is missing, you must interpolate between given
values.
Before Moving On

It is essential to understand the information provided to this point before moving on. Three points that
frequently require emphasis or clarification are:
o
Dry-bulb temperature on the psychrometer measures the air temperature.
o
Wet-bulb temperature is not the same as wet-bulb depression.
o
Wet bulb depression is the difference between dry-bulb and wet-bulb temperatures. (That is, how much
lower, or “depressed”, is the temperature of the wet-bulb compared to the dry-bulb?)
Section 4: Practice Exercises Using Given Sling Psychrometer Values
Work out the relative humidity assuming the following temperatures were measured off a sling psychrometer:
Dry-Bulb Temperature
(C)
Wet-Bulb Temperature
(C)
30
26
5
2
45
27.5
Wet-Bulb Depression
(C)
Relative Humidity
(%)
4
9.5
4.5
4
Section 5: Relative Humidity Measurements

I completed these measures for the class using the sling psychrometer to measure the relative humidity in three
locations on the campus:
1.
In room B205
2.
In the lobby of the Atrium, near the entrance to the library
3.
Outside, well away from any buildings or building entrances

Spaces are provided below to about the humidity conditions (using the relative humidity results and the saturation
curve graph).

Equation 1 – used to calculate RH when SH and MSH are known – can be rearranged into Equation 1a to calculate
SH, if RH and MSH are known.
Equation 1:
RH = (SH / MSH) x 100
Equation 1a:
SH = (RH / 100) x MSH
Make sure you include appropriate units for all values on p. 4 and 5.
Location 1: In Room B205
Dry-Bulb Temperature
_20.5 C ______________ Wet-Bulb Temperature
16.0 C _______
Location 2: In the lobby of the Atrium
Dry-Bulb Temperature
_19.5 C
Wet-Bulb Temperature
__18.5 C ______________
Location 3: Outside, away from buildings
Dry-Bulb Temperature
6 C ________________
Wet-Bulb Temperature
__2 C ______________
Location 1: In Room B205
Wet-Bulb Depression
Relative Humidity
________________
________________
Maximum specific humidity for this air temperature
________________
Specific humidity (SH = [RH / 100] x MSH)
________________
Dew-point temperature
________________
Location 2: In the Atrium, on the second floor beside the green living wall
Wet-Bulb Depression
Relative Humidity
________________
________________
Maximum specific humidity for this air temperature
________________
Specific humidity (SH = [RH / 100] x MSH)
________________
Dew-point temperature
________________
5
Location 3: Outside, away from buildings
Wet-Bulb Depression
Relative Humidity
________________
________________
Maximum specific humidity for this air temperature
________________
Specific humidity (SH = [RH / 100] x MSH)
________________
Dew-point temperature
________________
For each of the three locations, plot your values of specific humidity vs. air temperature on the Saturation Curve graph.

At which location is the relative humidity highest?
________________

Which location has the greatest amount of water vapour in the air?
________________

Is it possible for the highest relative humidity and the greatest amount of water vapour in the air to have occurred
at different locations?
6