The Atmosphere and Weather
Atmosphere is the thin layer of gases that surrounds the earth.
o Provides us with oxygen, absorbs hazardous solar radiation, burns up incoming meteors,
transports and recycles water and nutrients, and moderates climates
o Consists of
78% nitrogen gas
21% oxygen gas
1% argon gas
o Some of which are permanent gases (remain at stable
concentrations) or variable gases (vary in concentration from
time to time)
Atmosphere chemical composition has changed over time.
Human activity is altering the quantities of some atmospheric gases
o Carbon Dioxide
o Methane
o Ozone
The Atmosphere is Layered
Is a thin coating about 1/100 of earths diameter, like the fuzzy skin of a peach.
Coating consists of four layers
o Trophosphere
Bottommost layer
Blankets earth surface
Provides with air we need to live
Air within troposphere responsible for the planets weather
Contains ¾ of the atmospheres mass, as air is denser near earth’s surface
Troposphereic air temperature declines 6’C for each km in altitude.
At the top of the troposphere, temperatures decline with altitude, marking a
boundary called tropopause (upper boundary of trophosphere, limits mixing
between troposphere and the stratosphere
o Stratosphere
extends from 11km and 50km above sea level
1000 times as dry and less dense then troposphere
Gases experience little vertical mixing, so when pollutants enter they stay for a
long time
Attains a max temperature of -3’C at its highest altitude, is colder in its lower
reaches
Because the ozone and oxygen absorb and scatter the suns ultraviolet
radiation so that much of the UV radiation penetrating the upper
stratosphere fails to reach the lower stratosphere Ozone layer contains most of the atmospheres minute amount of ozone from
17km to 30km above sea level
Reduces the amount of UV radiation that reaches the earths surface
UV light can damage living tissue and induce mutations in DNA
Its protective effects are vital for life on earth
o Mesosphere
Extends from 50km to 80km above sea level
Air pressure is low
Temperatures decrease with altitude, reaching their lowest point at the top of
the mesosphere.
o Thermosphere is the top layer and extends upward to an altitude of 500km
Atmospheric properties include temperature, pressure, and humidity
Differences in air masses allow movement in the lower atmosphere
o These properites include pressure, density, relative humidity and temperature
Gravity pulls down gas molecules toward earth’s surface
o Air is therefore more dense at the surface and less as altitude increases.
Atmospheric pressure is the force per unit area produced by a column of air, and also decreases
with altitude because at higher altitudes, fewer molecules are pulled down by gravety.
relative humidity is the ratio of water vapour a given volume of air contains to the maximum
amount it could contain at a given temperature.
o If relative humidity in June in Arizona is only 31%, this means the air contains less than a
third of the water vapour it possibly can at its temperature
o When humidity is high, the air is holding nearly as much water vapour as it can so sweat
evaporates slowly and the body cannot cool itelf efficiently.
Why humidity makes it feel hotter than it really is
Temperature on earth surface varies because sunr’s rays strike some areas more directly than
others.
o The side of a hill that is sheltered from wind or direct sunlight can have a totally
different weather pattern, or microclimate, from the side facing into the wind or
sunlight.
Solar Energy heats the atmosphere, helps create seasons, and causes air to circulate
(Title explains most of the paragraph)
Of all the solar energy that bombards the upper atmosphere, 70% is absorbed by the
atmosphere and planetary surface while the rest is reflected back into space.
The spatial relationship between the earth and sun determines how much solar radiation strikes
each point on earth’s surface.
o Sunlight is most intense when it shines overhead and is at a perpendicular angle to the
planets surface At this angle the sunlight passes through a minimum of energy absorbing
atmosphere and earths surface receives a maximum of solar energy per unit
surface area.
When solar energy approaches earths surface at an oblique angle it loses
intensity as it traverses a longer distance through the atmosphere, and is less
intense when reaching the surface.
Why intensity is highest near equator and weakest near poles
Because earth is tilted on its axis (imaginary line connecting the poles) by about 23’5 degrees.
The Northern and southern hemispheres each tilt toward the sun for half a year, resulting in the
change of seasons.
Air near earth’s surface tends to be warmer and moister than air at higher altitudes because
land and surface water absorb solar energy.
o These differences set into motion a process of convective circulation
Look this term up** it is complicated
The atmosphere drives weather and climate
Weather specifies atmospheric conditions over short time periods, typically days and within
relatively small geographic areas.
Climate describes the pattern of atmospheric conditions found across large geographic regions
over long periods (seasons, years, mellennia)
‘Climate is what we expect; weather is what we get’
Air Masses Interact to produce weather
Weather can change quickly when air masses with different physical properties meet.
Boundary between air masses that differ in temxpperature and moisture is called a FRONT
The boundary along which a mass of warmer, moister air replaces mass of colder, drier air is
termed a warm front.
o Some of the warm, moist air behind a warm front rises over the cold air mass then cools
and condenses to form clouds that may produce a light rain (page 390)
A cold front is the boundary along which a colder, drier air mass displaces a warm, moister air
mass. The colder air, being denser, tends to wedge beneath warmer air
o The warmer air rises, expands and cools to form clouds that can produce thunderstord
o Once a cold front passes through, the sky clears and temperature and humidity drop.
Air masses may differ in atmospheric pressure
o A high-pressure system contains air that moves outward away from a centre of high
pressure as it descends.
Bring fair weather
o In a low-pressure system , air moves toward the low atmospheric pressure at the centre
of the system and spirals upward.
Air expands and cools and clouds and precipitation result
Air in the troposphere decreases in temperature as altitude increases. o Ocassionally, there is a layer of cool air beneath a layer of warmer air called
temperature inversion or thermal inversion
The cooler air at the bottom of the inversion layer is denser than the warmer air
so it doesn’t mix
One type of inversion occurs in mountain valleys where slopes block morning
sunlight, keeping ground level air within the valley shaded and cool.
Vertical mixing allows air pollution to be diluted upward but thermal inversions trap pollutants
near the ground.
Large-Scale Circulation Systems produce global climate patterns
At larger geographic scales, consecutive air currents contribute to broad climatical patterns.
Near the equator, solar radiation sets in motion a pair of convective cells known as Hadley cells
o Sunlight is most intense here
Surface air warms, rises and expands.
As it does so, it releases moisture producing the heavy rainfall that gives
rise to tropical rainforests near the equator.
o After releasing most of its moisture, this air diverges and moves
in currents heading north and south.
o The air in these currents cools and descend back to earth at
about 30’ Latitude north and south
Descending air has low relative humidity so these
regions are quite arid (like deserts)
Ferrel Cells and Polar Cells, lift air and create precipitation around 60’ latitude north and south
and cause air to descend at around 30’ latitude and the polar regions.
These three cells account for the latitudinal distribution of moisture across earths surface
o Warm wet climates near equator
o Arid climates and major deserts near 30’ latitude
o Moist temperate regions near 60’ latitude; and dry, cold conditions near the poles.
The three cells interact with the earths rotation to produce the global wind patterns
Earth rotates on its axis, and equator area spins faster than poles
*READ THE REST OF THIS.. PG 392… HARD TO UNDERSTAND
Outdoor Air Pollution
Air pollutants are gases and particulate material added to the atmosphere that can affect
climate or harm people or other organisms.
Air pollution is the release of air pollutants.
Gov’t is helping to diminish outdoor air pollution or ambient air pollution , in countries of the
developed world.
Natural Sources Can Pollute Natural processes produce a great deal of the worlds air pollution
Dust storms
Volcanic eruptions release large quantities of particulate matter
Major eruptions may blow matter into the stratosphere, where it can circle the globe and
remain aloft for months or years.
o Sulphur dioxide reacts with water & oxygen and condenses into fine droplets called
aerosols which reflect sunlight back into space and thereby cool the atmosphere and
surface.
Burning vegetation also pollutes the atmosphere with soot and gases
o Occur naturally and from human activity.
We create various types of outdoor air pollution
Arguably the greatest human induced air pollution problem today is our emission of greenhouse
gases that contribute to global climate change.
Once pollutants are in the atmosphere in sufficient concentrations they may do harm directly or
induce chemical reactions that produce harmful compounds
Primary pollutants are emitted into the troposphere in a form that can be directly harmful or
that can react to form harmful substances
Secondary pollutants include tropospheric ozone, sulphuric acid
CEPA identifies harmful airborne substances
The Canadian Environmental Protection Act (CEPA) provides a list of air pollutants that are
subject to legislative control and management
These pollutants differ widely in
o Chemical composition
o Chemical reactivity
o Emission sources
o Residence time(how long they remain in various reservoirs, including organisms)
o Persistence(how long they last before breaking down)
o Transportability (ability to be moved long or short distances)
o Impacts on natural and built environments
Environment Canada groups the pollutants of greatest concern in 4 categories
o
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