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Chapter 13 Notes.docx

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Department
Environmental Science
Course
EESA01H3
Professor
,,
Semester
Fall

Description
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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