HUMIDITY

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HUMIDITY
BY
SAMMY MAG
ADAM ERBS
JEREMY DOYLE
RYAN MACNEIL
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Who Discovered Humidity?
The first humidity measurements are attributed to
a German, Cardinal Nicholas in 1845.
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What is Humidity?

• Humidity is the measure of the amount of water
  vapor in the atmosphere.
• Low humidity means that evaporation can occur
• High humidity means that clouds and fog is more
  likely to form.

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• The term humidity is usually taken in daily
  language to refer to relative humidity. Relative
  humidity is defined as the amount of water vapor
  in a sample of air compared to the maximum amount
  of water vapor the air can hold at any specific
  temperature in a form of 0 to 100. Humidity may
  also be expressed as Absolute humidity and
  specific humidity. Relative humidity is an
  important metric used in forecasting weather.
  Humidity indicates the likelihood of
  precipitation, dew, or fog. High humidity makes
  people feel hotter outside in the summer because
  it reduces the effectiveness of sweating to cool
  the body by preventing the evaporation of
  perspiration from the skin. This effect is
  calculated in a heat index table. Warm water
  vapor has more thermal energy than cool water
  vapor and therefore more of it evaporates into
  warm air than into cold air.

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WHAT IS HUMIDITY MADE OF?

• A water molecule is 0.0001 micron in size
  Humidity is water vapor in a gas. Water vapor
  consists of individual water molecules moving
  independently and randomly of one another,
  suspended within gas. Individual water molecules
  are too small to see, as they are only one-ten
  thousandth of a micron in size. In comparison,
  some water droplets can be seen by the naked eye
  when they contain tens of thousands of water
  molecules bound together. The level of humidity
  in a gas is determined by temperature.

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Humidity and Plants

• Humidity is important to plants because it partly
  controls the moisture loss from the plant. The
  leaves of plants have tiny pores in them called
  stomata. Carbon dioxide enters the plants through
  these pores oxygen and water leave through them.
  
• The humidity inside a plant is close to 100. A
  plant growing in a dry room will lose moisture
  because water always moves from high to low
  humidity. When the difference in humidity is
  large, the loss of moisture from the plant is
  rapid and severe.
• Most houseplants prefer a humidity of about 60.
  Cacti, succulents and plants native to desert
  environments tolerate much lower humidity
  (30-35), but prefer not to drop below 20. House
  plants that are native to tropical rain forests
  require much higher humidity, 90 for example,
  and thus pose problems for most home owners.
  Plants that require a very high humidity are best
  grown in terrariums or closed containers where it
  is possible to regulate the humidity.
• Damage from excess humidity - Under very humid
  environments, fungal diseases can spread. This
  seldom happens during winter, but can be a
  problem in fall when the temperature is cool and
  the humidity is high. Mildew on plant leaves is
  an indication of excess humidity and lack of
  ventilation.
• Damage from dryness - Plants that prefer a more
  humid environment, but that are forced to grow in
  a dry environment will commonly suffer damage to
  younger leaves and to leaf tips. New leaves and
  leaf tips are the area of the plant with the most
  actively growing cells, and these cells are the
  most susceptible to dry air. Older leaves that
  are fully formed may be shed as a result of lack
  of humidity, but they will not be deformed or
  damaged by the dry air. Plants stressed in this
  way very frequently shed flower buds, or flowers
  die soon after opening.

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Temperature and Humidity combine to create hot
weather
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Humidity has a big affect on Southern Asia and
Africa
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What Causes Humidity

• The air that we breathe is made up of numerous
  gases, including water vapor. The term humidity
  generally refers to the amount of this water
  vapor in the atmosphere. Each atmospheric gas has
  its own vapor pressure, a measure of the number
  of molecules present at a given temperature. The
  vapor pressure of water thus measures the amount
  of water vapor in the air. The saturation vapor
  pressure is the vapor pressure when liquid water
  begins to condense. Relative humidity is
  determined by using the actual vapor pressure
  divided by the saturation vapor pressure

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References
www.images.google.ca, www.wikipedia.org , Nelson
text book, www.wildweather.com,
www.msc-smc.ec.gc.ca , www.theweathernetwork.com/