1. Saturated (cloudy) air at a temperature of 20 °C (68 °F) has a relative humidity of _________%.
2. Compute the relative humidity (RH) to nearest percent for each of the following atmospheric conditions:
a. vapor pressure = 6 mb, saturation vapor pressure = 18 mb, RH = __________ %
b. mixing ratio = 4.5 g/kg, saturation mixing ratio = 9.0 g/kg, RH = __________ %
c. mixing ratio = 12.0 g/kg, saturation mixing ratio = 12.0 g/kg, RH = __________ %
3. Outdoors, the air temperature is 5 °C (44 °F) and the relative humidity is 70%. What is the relative humidity of the air if it is drawn indoors and heated to 20 °C (68 °F)? Assume that no water vapor is added to or removed from the air. (This is the situation with heating homes in the winter season.)
Answer: _______%
4. If the relative humidity is 68% and the vapor pressure is 16 mb, what is the vapor pressure at
saturation?
Answer: _________ mb
What is the approximate saturation air temperature? Answer: _________ °C.
5. On a clear and calm day, the air temperature at sunrise is 5 °C (41 °F) with a relative humidity of 90%. The air temperature reaches a maximum of 15 °C (59 °F) at 3 p.m. Assuming that no water vapor is added to or removed from the air, predict the value of the relative humidity at 3 p.m.
Answer: _____ %
I took the test from a Meteorology class so here's the correct answers:
1.) 100%
2.) a. 25%
b. 33%
c. 100%
3.) 17%
4.) a. 24mb
b. 20
5.) 42%
1. Saturated (cloudy) air at a temperature of 20 °C (68 °F) has a relative humidity of 100%. It's so saturated, even the air needs a tissue.
2. a. vapor pressure = 6 mb, saturation vapor pressure = 18 mb, RH = 33%. Don't worry, it's not a sad cloud, just a little misty-eyed.
b. mixing ratio = 4.5 g/kg, saturation mixing ratio = 9.0 g/kg, RH = 50%. It's half full... of moisture.
c. mixing ratio = 12.0 g/kg, saturation mixing ratio = 12.0 g/kg, RH = 100%. It's a match made in cloud heaven.
3. Outdoors, the air temperature is 5 °C (44 °F) and the relative humidity is 70%. When drawn indoors and heated to 20 °C (68 °F), the relative humidity decreases to around 25%. It may have lost some humidity, but it's gaining some warmth.
4. If the relative humidity is 68% and the vapor pressure is 16 mb, the vapor pressure at saturation would be around 23.5 mb. It's reaching its boiling point, but not quite evaporating.
What is the approximate saturation air temperature? Answer: It's difficult to estimate without more information, but it would likely be around 20 °C. Still a pleasant temperature to enjoy both your humidity and your day.
5. On a clear and calm day, the air temperature at sunrise is 5 °C (41 °F) with a relative humidity of 90%. By 3 p.m., when the air temperature reaches 15 °C (59 °F), assuming no water vapor is added or removed, the relative humidity would decrease to approximately 36%. It's a drying situation, almost like a towel left out in the sun.
1. To find the relative humidity of saturated (cloudy) air at a temperature of 20 °C (68 °F), we need to know the saturation vapor pressure at that temperature. We can use a psychrometric chart or equations to calculate the saturation vapor pressure. Once we know the saturation vapor pressure, we can then calculate the relative humidity using the vapor pressure of water vapor in the air.
2. To compute the relative humidity for different atmospheric conditions, we need to know either the vapor pressure or the mixing ratio of water vapor in the air and the saturation vapor pressure or saturation mixing ratio at that temperature. With this information, we can use equations to calculate the relative humidity as a percentage.
a. To calculate the relative humidity with vapor pressure, use the equation:
RH = (vapor pressure / saturation vapor pressure) * 100
b. To calculate the relative humidity with mixing ratio, use the equation:
RH = (mixing ratio / saturation mixing ratio) * 100
c. In this case, since the mixing ratio is equal to the saturation mixing ratio, the relative humidity would be 100%, indicating that the air is saturated.
3. To find the relative humidity of air that is drawn indoors and heated from 5 °C (44 °F) to 20 °C (68 °F), we can assume that no water vapor is added to or removed from the air. In this case, the relative humidity remains the same because the ratio of the actual water vapor content to the maximum water vapor content (saturation) remains constant. Therefore, the relative humidity would still be 70%.
4. To find the vapor pressure at saturation, given a relative humidity of 68% and vapor pressure of 16 mb, we can use the formula for relative humidity, which is:
RH = (vapor pressure / saturation vapor pressure) * 100
By rearranging the formula, we can solve for the saturation vapor pressure:
saturation vapor pressure = (vapor pressure / relative humidity) * 100
Substituting the values, we get:
saturation vapor pressure = (16 mb / 68%) * 100
Therefore, the saturation vapor pressure is equal to 23.53 mb.
The approximate saturation air temperature is the temperature at which the air becomes saturated, meaning the vapor pressure reaches the saturation vapor pressure. To find this approximate temperature, we can refer to a saturation vapor pressure table or use approximation formulas. Based on the given information, we can estimate the saturation air temperature to be around 25 °C.
5. To predict the relative humidity at 3 p.m. given the initial conditions at sunrise (5 °C, 90% relative humidity) and assuming no water vapor is added or removed from the air, we need to understand the concept of saturation mixing ratio. Saturation mixing ratio is the maximum amount of water vapor that the air can hold at a specific temperature.
If the temperature at 3 p.m. is 15 °C (59 °F), we can calculate the saturation mixing ratio at that temperature. Then, using the initial relative humidity at sunrise, we can compute the corresponding mixing ratio at 15 °C (59 °F). Finally, we can calculate the relative humidity at 3 p.m. using the mixing ratio at 15 °C (59 °F) and the saturation mixing ratio at that temperature.
1.100
2a.33
2b.50
2c.100
3.60
4a.24
4b.12
5.46