Humidity and Condensation

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Humidity and Condensation
Water is unique because it is the only substance
that commonly exists in all _____________________
_______ of matter. Depending upon temperature,
water can be a _____________, a
_________________ or a ________________.
Water is in a solid state at temperatures of
_______ or below, appearing as ice,
__________________, _____________________ and
ice crystals.
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Water is in a liquid state between _________ and
________________, present as _______________ and
cloud droplets.
At _________________ or above, water evaporates
and enters the atmosphere as ____________________
_____________, an invisible gas. The bubbles in
boiling water are an example of water vapor.
___________________ and _____________________
are liquid droplets, not gas.
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Although you can't see water vapor, sometimes you
can feel it. The more water vapor the air
contains, the more ________________________ the
air feels.
Water often changes state in the atmosphere.
Changing from one state to another requires
________________ to either be
___________________ or given off.
Condensation occurs when water vapor becomes a
________________- this creates ____________,
_______________ and clouds.
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The opposite of condensation is
____________________________. While
condensation ___________________ heat,
evaporation __________________ heat.
So condensation slows down the rate at which air
_______________. Evaporation, by contrast, is a
_______________ process. After you get out of
a swimming pool you may feel chilly, because
the water molecules on your skin are stealing
____________ from your body as they evaporate.
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Frost forms by _____________________ when water
vapor condenses as a solid. Snow often
disappears as much through ______________________
__ as by evaporation. Sublimation is when water
changes directly from a ______________ to a
___________, without becoming a liquid.
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The amount of water vapor present in the air
varies widely. The actual amount of water vapor
in the air at a given time and place is called
the ________________________________________.
It is expressed as the number of grams of water
vapor per ________________________________. On
a humid summer day, for example, the humidity
may be about ______________________ per kilogram.
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There is a limit to the amount of water vapor
that can be present in the air.
Imagine a fish tank with a glass lid. Some
water molecules have enough energy to escape
from the surface and become _____________________
_. Other water vapor molecules lose energy and
return to the liquid state though
_____________________.
When there is so much water vapor in the air that
the rate of condensation _________________ the
rate of evaporation, the air is
______________________.
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If any more water evaporates into saturated air,
an _______________________________ will
__________________. This explains why
_________________________ may form on the lid of
the fish tank. These drops confirm that as water
continues to _______________________, an equal
amount of water condenses from the
___________________________ air.
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The amount of water vapor present in saturated
air depends upon the ____________________________
_ of the air. The warmer the air, the
___________ water vapor it can contain. The
water vapor _____________________ of air roughly
doubles for every rise in air temperature of
about ___________
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Relative Humidity
When meteorologists refer to the relative
humidity, they are telling us how near the air
is to its ___________________ capacity for
holding water. Relative humidity compares the
___________________ amount of water vapor that
is present in air with the maximum amount of
water vapor that can be present at a given
__________________________________________________
.
It is usually stated as a ______________________.
Saturated air has a relative humidity of
______________ air that contains no water vapor
has a relative humidity of _____________
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To calculate the relative humidity of a kilogram
of air, _________________ its specific humidity
by its maximum capacity.
If the air holds 11 grams per kg of water vapor
and it can contain at most 22 grams per kg, then
it holds half of the water vapor it can contain.
Thus, its relative humidity is _______________.
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Measuring humidity
Humidity is typically measured with a
________________________ - an instrument that
works on the principle that evaporation causes
_______________.
A psychrometer consists of ________ thermometers.
One is a __________________ thermometer that
shows the air temperature. The other is a
______________________ thermometer that has a
water-soaked wick wrapped around its bulb.
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The wet-bulb thermometer usually has a
____________________ temperature because water
evaporating from the wick cools the wet bulb.
The drier the air, the ____________________ the
difference in the readings. If both the
wet-bulb and the dry-bulb thermometers read the
same, this shows that ______________________ is
evaporating from the wet bulb, and the air must
be ____________________________.
Relative humidity can be determined by using a
_____________________ along with a
__________________ like the one on the next page.

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Condensation
At night, the air _____________________________.
Its ability to contain water vapor
_________________________. The air becomes
___________________________. If the air
continues to cool past the point of saturation,
__________________________ occurs.
The water vapor may condense into droplets,
forming clouds or ____________. If the water
vapor condenses on a surface, such as grass,
it's called ____________.
The temperature at which saturation occurs and
condensation begins is called the
______________________.
Name ___________________________________________
____
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The dew point is a measure of the amount of
_____________________________ in the air. The
more water vapor the air contains, the
________________the air has to cool in order for
condensation to start, so the ___________________
____the dew point.
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Cooling and Condensation
Two conditions are necessary for water vapor to
condense.
1 - There must be ______________________ for
water vapor to condense onto and,
2 - Air must cool to or below its
________________________.
When fog or clouds form, the water vapor is
condensing on tiny particles called
___________________________________.
Condensation nuclei are usually substances such
as _________________, sulfate particles or
nitrate particles.
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The salts usually come from ___________________
evaporating. The sulfates and nitrates come
from natural sources and from the burning of
_______________________.
These particles are so small that one puff of
smoke contains _________________________ of
condensation nuclei.
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The cooling of the air occurs in the following
ways - _________________ with a colder
surface. - radiation of heat - mixing with colder
air - ____________________ as it rises
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Dew and frost form when moist air contacts a
colder surface. Fog forms when air cools
through contact and mixing.
Even when air is cooled below its dew point,
condensation into fog or clouds may not occur
if there are no __________________________________
________ available.
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Formation of Dew and Frost
When air cools to its dew point through
___________________________________________,
water vapor condenses directly onto that surface.

If the temperature is above ______, dew forms.
If the air temperature is below 0 C, the water
vapor becomes frost through _____________________
__. This type of frost is often called a
"killing frost" because it causes liquid in the
cells of some plants to _____________________.
As liquid water freezes, it expands, bursting
the cell walls and killing the plants.
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Formation of Fog
Fog forms when a cold surface cools the
________________________________ air above it.
As water vapor condenses in the air, tiny
droplets fill the air and form fog. Each
droplet is centered around a condensation
nucleus. The droplets are so tiny that they
fall slowly. The slightest air movement keeps
them ________________________________ in the air.
At very cold temperatures, the fog may consist
of tiny _______________________________.
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________________________________ Fog
- forms when the night sky is ____________________
_and the ground loses heat rapidly through
_____________________________. As the ground
cools, light winds mix the cooled bottom air
with the warmer air just above it. Eventually,
the whole _____________________cools to its dew
point.
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The radiation fog occurs at ground level and is
_____________________ than the air above it.
This arrangement of cold air beneath warm air is
called a ________________________________________
__________.
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Radiation fogs are common in _____________________
_________ near rivers or lakes. They are most
frequent in the __________________________ and in
winter. These fogs are thickest in the early
morning and are ________________________________"
by the later morning sunshine.
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_________________________________ Fog
- forms when warm, moist air _____________________
__________________________.
In the northern US and southern Canada, advection
fogs form when warm, moist _____________________
_______ winds blow over ______________-covered
ground.