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.

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.

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.

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.

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.

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.

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 ______________________.

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.

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 _______________.

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.

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.

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: _______________________________________________

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.

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.

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.

The cooling of the air occurs in the following ways:

- _________________ with a colder surface.

- radiation of heat

- mixing with colder air

- ____________________ as it rises

Even when air is cooled below its dew point, condensation into fog or

clouds may not occur if there are no __________________________________________ available.

Dew and frost form when moist air contacts a colder surface. Fog forms when air cools through contact and mixing.

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.

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 _______________________________.

________________________________ 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.

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

__________________________________________________.

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.

_________________________________ Fog

- forms when warm, moist air _______________________________________________.

In the northern US and southern Canada, advection fogs form when

warm, moist ____________________________ winds blow over ______________-covered ground.