What
is Humidity?
The simple meaning of
humidity is ‘atmospheric moisture’ or ‘amount of water vapor in the atmosphere’.
Humidity is
the amount of water vapors present in the atmosphere (or air). Water vapors are
the gaseous state of water and are invisible.
Humidity can be measured by three ways that
are: absolute, relative and specific.
1. Absolute
humidity is the water content of air in the gram per cubic meter at
a given temperature.
2. Relative
humidity is expressed in percentage, and it measures the current
absolute humidity relative to
the maximum humidity for that temperature.
3. Specific
humidity is expressed as the ratio of the mass of the water vapors
to the total mass of moist air parcel.
What
is Absolute Humidity?
To
understand absolute humidity let’s assume you are standing in ground and you
collect some air. Now you check that air volume in your chemistry lab and get accurate
amount of water vapors in gram. If you collect 1 cubic meter of air volume and
it contains 30 gram water vapors than absolute humidity of that ground air is 30 grams
per cubic meter. So, now you answer this question i.e. what is absolute
humidity.
Absolute humidity (AH)
is defined as the total mass (in gram) of water vapor present in a given volume
(in cubic
meter) of air. Absolute Humidity changes
with changes in air temperature and pressure. Absolute humidity is the mass of
the water vapors( m H 2 O ) {\displaystyle
(m_{H_{2}O})} divided by the volume of the air and water vapor mixture.
AH
= m/V
Where,
AH = Absolute humidity,
m = mass of the water vapors( m H 2 O ) {\displaystyle (m_{H_{2}O})},
V = volume of the air and water
vapor mixture.
What
is Relative Humidity?
To
understand relative humidity let’s assume you are in a building where air
absolute humidity is 15 grams per cubic meter at 25 degree Celsius
temperature and at 25 degree Celsius temperature highest amount of water vapors
is 30 grams per cubic meter (saturated air with water vapors 15 grams
per cubic meter). So, now you can calculate relative humidity as follows:
Relative
humidity = (15 grams per cubic meter / 30 grams per cubic meter)x100
RH = 50%
So,
now you answer this question i.e. what is relative humidity.
Relative humidity (RH)
is defined as the
ratio of the partial pressure of water vapors to the equilibrium vapor pressure
of water at a given temperature. If temperature of the atmosphere is lower than
relative humidity is higher as cold air (air with low temperature) holds more
water vapors (moisture) but, If temperature of the atmosphere is higher than relative
humidity is lower as hot air (air with high temperature) holds less water
vapors (moisture).
What
is Specific Humidity?
To
understand specific humidity let’s assume you have an air parcel (air volume or
some amount of air) and this parcel contains 10 gram mass of water vapors and
total mass of air is 1 kg (including mass of all gases present in air and mass
of water vapors) than specific humidity is 10 gram per kilogram. So, now you
answer this question i.e. what is specific humidity.
Specific Humidity is defined as the ratio of the mass of water vapors in air to
the total mass of the mixture of air and water vapors.
Specific Humidity
= mass of water vapor/total mass of air
Difference
between Humidity and Relative Humidity
Before going to discuss
about “Difference between Humidity and Relative Humidity” we need to understand
that what is humidity and what is relative humidity. And to get answer of these
two questions just read above paragraph once again if you don’t understand.
Humidity is
the amount of water vapors present in the atmosphere (or air). Relative
humidity is expressed in percentage, and it measures the current absolute
humidity relative to the
maximum humidity for that temperature.
