The Earth’s AtmosphereThe Earth’s Atmosphere

Earth’s AtmosphereEarth’s Atmosphere

Atmosphere is the gaseous layer that surrounds the earthAtmosphere is the gaseous layer that surrounds the earth

Is a mixture of gases that is naturally odorless, colourless, Is a mixture of gases that is naturally odorless, colourless, tasteless and formlesstasteless and formless

Air is blended so thoroughly that it behaves as if it were a Air is blended so thoroughly that it behaves as if it were a single gassingle gas

The AtmosphereThe Atmosphere

Air is held to the earth by the force of gravity:Air is held to the earth by the force of gravity:

The further away from the source of gravitational attraction The further away from the source of gravitational attraction (earth) the lower the attractional force(earth) the lower the attractional force

More air molecules are held closer to the earth than at More air molecules are held closer to the earth than at higher elevationshigher elevations

Atmosphere is more dense near the surface than at higher Atmosphere is more dense near the surface than at higher elevationselevations

The AtmosphereThe Atmosphere

No real “top” – atmosphere drifts off to nothingness above No real “top” – atmosphere drifts off to nothingness above about 100 kmabout 100 km

97% of the weight and 100% of the water vapor reside in 97% of the weight and 100% of the water vapor reside in the bottom 30 kmthe bottom 30 km

DensityDensity

The The densitydensity (mass per unit volume) of the atmosphere quickly (mass per unit volume) of the atmosphere quickly decreases with increasing elevation above sea leveldecreases with increasing elevation above sea level

Density of the atmos can be measured as it exerts its Density of the atmos can be measured as it exerts its weight as a pressure (force per unit area)weight as a pressure (force per unit area)

The pressure the atmos exerts on the surface is know as The pressure the atmos exerts on the surface is know as air pressureair pressure Air pressure at Air pressure at sea level = 1013 mbsea level = 1013 mb Air pressure at the top of the stratosphere (50km) = 0.78 mbAir pressure at the top of the stratosphere (50km) = 0.78 mb

Composition of the atmosphereComposition of the atmosphere

Proportion of Elements in Dry Air (by volume) Nitrogen – N2 78% Plants

Proportion of Elements in Dry Air (by volume) Nitrogen – N2 78% Plants Oxygen – O2 21% Animals

Together, Nitrogen and Oxygen account for99% of the atmosphere, by volume!

Proportion of Elements in Dry Air (by volume) Nitrogen – N2 78% Plants Oxygen – O2 21% Animals Argon – Ar 0.93% Inert Gas

93% of the remaining 1% is Argon, an inert gas!

Proportion of Elements in Dry Air (by volume) Nitrogen – N2 78% Plants Oxygen – O2 21% Animals Argon – Ar 0.93% Inert Gas Carbon Dioxide – CO2 0.0325% Plants

Proportion of Elements in Dry Air (by volume) Nitrogen – N2 78% Plants Oxygen – O2 21% Animals Argon – Ar 0.93% Inert Gas Carbon Dioxide – CO2 0.0325% Plants Neon – Ne 0.0005% Inert Gas

Proportion of Elements in Dry Air (by volume) Nitrogen – N2 78% Plants Oxygen – O2 21% Animals Argon – Ar 0.93% Inert Gas Carbon Dioxide – CO2 0.0325% Plants Neon – Ne 0.0005% Inert Gas Krypton – Kr 0.0001% Inert Gas

Proportion of Elements in Dry Air (by volume) Nitrogen – N2 78% Plants Oxygen – O2 21% Animals Argon – Ar 0.93% Inert Gas Carbon Dioxide – CO2 0.0325% Plants Neon – Ne 0.0005% Inert Gas Krypton – Kr 0.0001% Inert Gas Hydrogen – H2 0.00005% Helium – He <0.00001% Inert Gas Xenon – Xe <0.00001% Inert Gas Methane – CH4 <0.00001%

Water Vapor H2O 0 to 4% Ozone O3 0.0 to 0.0012% Chlorofluorcarbons – CFCs (e.g., Freon) Changing Concentrations of:

Ozone Carbon Dioxide Methane Water Vapor

The Atmosphere

ClimateChange!

Important Roles Played by Trace GasesImportant Roles Played by Trace Gases

Carbon DioxideCarbon Dioxide An important absorber of outgoing terrestrial radiationAn important absorber of outgoing terrestrial radiation

It, along with water vapor, serve as the primary means It, along with water vapor, serve as the primary means of preventing rapid heat loss from the earth and of preventing rapid heat loss from the earth and atmosphere back into spaceatmosphere back into space

Important Roles Played by Trace GasesImportant Roles Played by Trace Gases

Water Vapor - An important absorber of outgoing terrestrial energy

Amounts vary from 0 to 4% depending on of evaporating water available and distance that source

This can cause tremendous differences in temperatures within the atmosphere

http://weather.unisys.com/satellite/sat_wv_us.html

Important Roles Played by Trace GasesImportant Roles Played by Trace Gases

Liquid Water – Causes clouds to form… this affects the amount of heat

absorbed by the earth and atmosphere

Can vary tremendously within the atmosphere

Insolation losses in the atmosphereInsolation losses in the atmosphereDust - Gas molecules, dust, and other particulates areimportant because they can cause the sun’s rays to be scattered or absorbed

Scattering - visible light rays to be turned aside in allpossible directions. Under clear sky conditions, scattering sends about 5% of the incoming solar radiation back to space.

Absorption - Solar rays strike gas molecules and dust, andtheir energy is absorbed and temperatures rise. This accounts for about a 15% decrease in solar radiation.

Both carbon dioxide and water vapor are capable of directlyabsorbing some wavelengths of solar radiation.

Electromagnetic RadiationElectromagnetic Radiation

Electromagnetic radiation can be:Electromagnetic radiation can be:

Absorbed Absorbed – – increases the energy content of the object, increases the energy content of the object, like a black car in the summerlike a black car in the summer

Reflected Reflected – – bounce the energy back toward the source, bounce the energy back toward the source, like a mirrorlike a mirror

TransmittedTransmitted – – pass through without absorption or pass through without absorption or reflection, like a pane of glassreflection, like a pane of glass

Electromagnetic RadiationElectromagnetic Radiation AlbedoAlbedo – percent of solar/shortwave radiation that is – percent of solar/shortwave radiation that is

reflected from a surface.reflected from a surface.

New snow:New snow: 80%80% Old Snow: Old Snow: 50%50%Clouds:Clouds: 50%50% Ice: Ice: 35%35%Dark, wet soil:Dark, wet soil: 5% 5% Light, dry soil: Light, dry soil: 40%40%Asphalt:Asphalt: 5% 5% Forest: Forest: 15%15%Grass:Grass: 20%20% Crops: Crops: 20%20%

Water – high incident angleWater – high incident angle 50%50%Water – low incident angleWater – low incident angle 5% 5%

Average albedo of the earth’s surface:Average albedo of the earth’s surface: 7%7%

Electromagnetic RadiationElectromagnetic Radiation

The atmosphere is generally transparent to The atmosphere is generally transparent to shortwave radiation and opaque to longwaveshortwave radiation and opaque to longwave

THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT

Vertical Distribution of the Atmosphere

The TroposphereThe Troposphere

Layer of the atmosphere in contact with the surfaceLayer of the atmosphere in contact with the surface Temperature decreases with height because the Temperature decreases with height because the

tropospheretroposphere is heated from below (atmosphere is is heated from below (atmosphere is generally transparent to shortwave radiation)generally transparent to shortwave radiation)

Layer that contains all weather and all cloudsLayer that contains all weather and all clouds Extends to about 12 to 15 km; actual height varies with Extends to about 12 to 15 km; actual height varies with

latitude and season (thicker as temperature increases)latitude and season (thicker as temperature increases) Much water vapor and dust – from interactions with Much water vapor and dust – from interactions with

the surfacethe surface

Contains about 80% of the mass of the atmosphereContains about 80% of the mass of the atmosphere

Vertical Distribution of the AtmosphereVertical Distribution of the Atmosphere

The TropopauseThe Tropopause

Small, isothermal layer above the troposphereSmall, isothermal layer above the troposphere

IsothermalIsothermal – no temperature change with height – no temperature change with height

About 12 to 15 km in height – actual height varies with About 12 to 15 km in height – actual height varies with latitude and seasonlatitude and season

Vertical Distribution of the AtmosphereVertical Distribution of the Atmosphere

The StratosphereThe Stratosphere

Layer of the atmosphere above the troposphereLayer of the atmosphere above the troposphere Temperature increases with height because of Temperature increases with height because of

absorption of ultraviolet light by ozone (Oabsorption of ultraviolet light by ozone (O33)) Extends up to about 50 km in heightExtends up to about 50 km in height Little exchange of air between troposphere and Little exchange of air between troposphere and

stratosphere – little dust or water vaporstratosphere – little dust or water vapor

Stable air layer – little vertical motions because of the Stable air layer – little vertical motions because of the increasing temperature with height -- increasing temperature with height -- inversioninversion

Vertical Distribution of the AtmosphereVertical Distribution of the Atmosphere

The StratopauseThe Stratopause

Small, Small, isothermalisothermal layer above the stratosphere layer above the stratosphere Isothermal – no temperature change with Isothermal – no temperature change with

heightheight

About 50 km in heightAbout 50 km in height

Vertical Distribution of the AtmosphereVertical Distribution of the Atmosphere

The MesosphereThe Mesosphere

Layer of the atmosphere above the stratosphereLayer of the atmosphere above the stratosphere

Temperature decreases with height because of a lack Temperature decreases with height because of a lack of contact with the ground and a lack of ozoneof contact with the ground and a lack of ozone

Extends up to about 80 km in heightExtends up to about 80 km in height

Vertical Distribution of the AtmosphereVertical Distribution of the Atmosphere

The MesopauseThe Mesopause

Small, isothermal layer above the mesosphereSmall, isothermal layer above the mesosphere

Isothermal Isothermal – no temperature change with height– no temperature change with height

About 80 km in heightAbout 80 km in height

Vertical Distribution of the AtmosphereVertical Distribution of the Atmosphere

The ThermosphereThe Thermosphere

Layer of the atmosphere above the mesosphereLayer of the atmosphere above the mesosphere Temperature increases with height because of energy Temperature increases with height because of energy

from gamma and x-ray absorption due to the earth’s from gamma and x-ray absorption due to the earth’s magnetic field (van Allen radiation belt)magnetic field (van Allen radiation belt)

Density of air at this altitude is very thin and the Density of air at this altitude is very thin and the thermosphere holds little heatthermosphere holds little heat

Thermosphere essentially drifts off to nothingness Thermosphere essentially drifts off to nothingness above about 120 kmabove about 120 km

Lapse Rates:Lapse Rates:

Temperature decreases with increasing altitude within the Temperature decreases with increasing altitude within the troposphere at an average rate of 6.4 C/kmtroposphere at an average rate of 6.4 C/km

6.4 C/km = Normal Lapse Rate6.4 C/km = Normal Lapse Rate

The actual decrease in temp, or actual lapse rate may vary The actual decrease in temp, or actual lapse rate may vary considerably from the normal lapse: considerably from the normal lapse: environmental lapse environmental lapse raterate

PollutionPollution

The atmosphere is made up of two zones based in function: The atmosphere is made up of two zones based in function: to remove harmful wavelengths of solar radiation and charged to remove harmful wavelengths of solar radiation and charged

particlesparticles

IonosphereIonosphere

Extends throughout the Extends throughout the thermopause and into thermopause and into underlying mesosphereunderlying mesosphere

Absorbs cosmic rays, gamma Absorbs cosmic rays, gamma rays, x-rays, and shorter rays, x-rays, and shorter wavelengths of UV radwavelengths of UV rad

Absorption changes atoms to Absorption changes atoms to +ve charged ions ~ ionosphere+ve charged ions ~ ionosphere

OzonosphereOzonosphere

ozone layer that is within the ozone layer that is within the stratosphere that contains Ostratosphere that contains O33

Highly reactive to oxygen Highly reactive to oxygen moleculesmolecules

Ozone is harmful to living Ozone is harmful to living creatures when present near the creatures when present near the surfacesurface

Is necessary as absorbs harmful Is necessary as absorbs harmful wavelengths of UV rad and wavelengths of UV rad and reradiates it as safer LW radreradiates it as safer LW rad

Ozone DepletionOzone Depletion

CFC’s- ChloroflurocarbonsCFC’s- Chloroflurocarbons

-became widely used in the 1920s for industry-became widely used in the 1920s for industry-valuable as propellants for aerosol sprays and as refrigerants-valuable as propellants for aerosol sprays and as refrigerants-also used in industry as solvents and foaming agents-also used in industry as solvents and foaming agents

Good for industry as were not flammableGood for industry as were not flammable Cannot be broken down by atmospheric processes near the earth’s Cannot be broken down by atmospheric processes near the earth’s

surfacesurface Not water soluble and do not break down by biologic processesNot water soluble and do not break down by biologic processes Can be broken down by UV radiation within the stratosphereCan be broken down by UV radiation within the stratosphere

-CFC’s migrate to the stratosphere over time-CFC’s migrate to the stratosphere over time

Breakdown of CFCs from UV radiationBreakdown of CFCs from UV radiation

Separates single Cl atoms or chlorine monoxide (ClO) Separates single Cl atoms or chlorine monoxide (ClO) molecules from the CFC componentsmolecules from the CFC components

Ozone is an unstable molecule (OOzone is an unstable molecule (O22 or O or O33)) Chlorine is a catalyst for the destruction of ozoneChlorine is a catalyst for the destruction of ozone

One Cl atom can decompose 100,000 ozone moleculesOne Cl atom can decompose 100,000 ozone molecules Cl atoms have a residence time within the ozone layer of 40-100yrs.Cl atoms have a residence time within the ozone layer of 40-100yrs.

Example of ozone breakdown……Example of ozone breakdown……

1970s1970s – noticed depletion in levels of ozone, studies into the – noticed depletion in levels of ozone, studies into the effect of chemicals on ozone depletioneffect of chemicals on ozone depletion

19781978 – US banned CFC’s in aerosols but was still used in – US banned CFC’s in aerosols but was still used in refrigerants and polyurethane foamrefrigerants and polyurethane foam

1981 1981 – banned CFC products still allowed to be exported– banned CFC products still allowed to be exported19851985 – British Ant Survey reported ozone hole over Antarctica – British Ant Survey reported ozone hole over Antarctica19871987 – peak in CFC sales since aerosol ban (1.32 million – peak in CFC sales since aerosol ban (1.32 million

tons)tons)1990 (1992 & 1997)1990 (1992 & 1997) – Montreal Protocol to reduce use of – Montreal Protocol to reduce use of

CFC’s globallyCFC’s globally19981998 – production of CFC’s declined to 1/4 – production of CFC’s declined to 1/4thth that of the 1987 that of the 1987

peakpeak

PollutionPollution

Air Pollution – Air Pollution – an unwanted substance injected into the an unwanted substance injected into the atmosphere from the earth’s surface by either natural or atmosphere from the earth’s surface by either natural or human activitieshuman activities Come as aerosols, gases or particulatesCome as aerosols, gases or particulates

Aerosols – Aerosols – small bits of matter in the air that move freely with normal air small bits of matter in the air that move freely with normal air movementsmovements

Gases –Gases – molecular compounds mixed together to form air molecular compounds mixed together to form air

Particulates –Particulates – larger, heavier particles that sooner or later fall back to the larger, heavier particles that sooner or later fall back to the surface (haze, smoke, dust)surface (haze, smoke, dust)

Sources of Air PollutionSources of Air Pollution

NaturalNatural – produce great quantities of pollutants than human – produce great quantities of pollutants than human sourcessources

Volcanoes, forest fires, plants, soil, and oceanVolcanoes, forest fires, plants, soil, and ocean Produce NOx, CO, HCx and CO2Produce NOx, CO, HCx and CO2

Anthropogenic Anthropogenic – although less than natural sources, humans – although less than natural sources, humans have yet to adapt to anthropogenic pollution as for naturalhave yet to adapt to anthropogenic pollution as for natural

Sources include every day activities by large numbers of people (cars!)Sources include every day activities by large numbers of people (cars!) Industrial burning of fossil fuels and ore smeltingIndustrial burning of fossil fuels and ore smelting

Carbon Monoxide - Carbon Monoxide - consists of one carbon and one oxygen consists of one carbon and one oxygen atomatom

incomplete combustion of fossil fuelsincomplete combustion of fossil fuels 90% produced by natural sources (decay of carbon 90% produced by natural sources (decay of carbon

sources – wood)sources – wood) 10% anthropogenic, mainly cars10% anthropogenic, mainly cars

Source of CO for individuals is first and second hand tobacco and Source of CO for individuals is first and second hand tobacco and smokesmoke

Photochemical Smog – Photochemical Smog – interactions of sunlight and interactions of sunlight and combustion products in automobile exhaust (NOx and combustion products in automobile exhaust (NOx and VOC’s)VOC’s) Result of increased automobile usage over the past centuryResult of increased automobile usage over the past century

Smog –Smog – combination of smoke and fog combination of smoke and fog Aerosols and gas pollutants in urban areasAerosols and gas pollutants in urban areas Lets in light but can obscure objects in the skyLets in light but can obscure objects in the sky Irritates eyes and throat – difficult to breatheIrritates eyes and throat – difficult to breathe Corrodes structures over timeCorrodes structures over time

Acid Precipitation – Acid Precipitation – atmospheric acids brought to the surface atmospheric acids brought to the surface by precipitation (rain, snow) or by dry dustby precipitation (rain, snow) or by dry dust Major source of SOx from industrial emissionsMajor source of SOx from industrial emissions

Acid rainAcid rain = rain/snow polluted with SO2 or NO2 = rain/snow polluted with SO2 or NO2 Acid dustAcid dust = sulfuric and nitric nuclei cling to dust particles = sulfuric and nitric nuclei cling to dust particles

Fall to earth and coat surfaceFall to earth and coat surface Increase the acidity of soil with wetIncrease the acidity of soil with wet Accumulate with snow and melt in spring as surge of acid waterAccumulate with snow and melt in spring as surge of acid water

Haze – Haze – humid air causes a film of water to attach to aerosol humid air causes a film of water to attach to aerosol particles making them large enough to scatter light and particles making them large enough to scatter light and reduce visibilityreduce visibility Natural and anthropogenic sourcesNatural and anthropogenic sources Soil dust, salt crystals, pollen, smokeSoil dust, salt crystals, pollen, smoke

Natural Factors Affecting PollutionNatural Factors Affecting Pollution

Wind – Wind – move pollutants from one area to anothermove pollutants from one area to another

Pollution DomePollution Dome – dome of pollution over an urban area under calm, – dome of pollution over an urban area under calm, stable atmospheric conditionsstable atmospheric conditions

Pollution PlumePollution Plume – plume of pollution originating over an urban area – plume of pollution originating over an urban area that is transported downwind from its urban sourcethat is transported downwind from its urban source

But it’s not all bad!But it’s not all bad!

Clean Air Act (1970) – Clean Air Act (1970) – lead to decrease in pollutants and lead to decrease in pollutants and increase in human healthincrease in human health Decrease in cancer ratesDecrease in cancer rates Less acid rainLess acid rain 206,000 fewer deaths from air pollution in 1990206,000 fewer deaths from air pollution in 1990