The Earth s Atmosphere

Transcription

1 The Earth s Atmosphere

2 Earth s Atmosphere Atmosphere is the gaseous layer that surrounds the earth Is a mixture of gases that is naturally odorless, colourless, tasteless and formless Air is blended so thoroughly that it behaves as if it were a single gas

3 The Atmosphere Air is held to the earth by the force of gravity: The further away from the source of gravitational attraction (earth) the lower the attractional force More air molecules are held closer to the earth than at higher elevations Atmosphere is more dense near the surface than at higher elevations

4 The Atmosphere No real top atmosphere drifts off to nothingness above about 100 km 97% of the weight and 100% of the water vapor reside in the bottom 30 km

5 Density The density (mass per unit volume) of the atmosphere quickly decreases with increasing elevation above sea level Density of the atmos can be measured as it exerts its weight as a pressure (force per unit area) The pressure the atmos exerts on the surface is know as air pressure Air pressure at sea level = 1013 mb Air pressure at the top of the stratosphere (50km) = 0.78 mb

6 Composition of the atmosphere

7 Proportion of Elements in Dry Air (by volume) Nitrogen N 2 78% Plants

8 Proportion of Elements in Dry Air (by volume) Nitrogen N 2 78% Plants Oxygen O 2 21% Animals Together, Nitrogen and Oxygen account for 99% of the atmosphere, by volume!

9 Proportion of Elements in Dry Air (by volume) Nitrogen N 2 78% Plants Oxygen O 2 21% Animals Argon Ar 0.93% Inert Gas 93% of the remaining 1% is Argon, an inert gas!

10 Proportion of Elements in Dry Air (by volume) Nitrogen N 2 78% Plants Oxygen O 2 21% Animals Argon Ar 0.93% Inert Gas Carbon Dioxide CO % Plants

11 Proportion of Elements in Dry Air (by volume) Nitrogen N 2 78% Plants Oxygen O 2 21% Animals Argon Ar 0.93% Inert Gas Carbon Dioxide CO % Plants Neon Ne % Inert Gas

12 Proportion of Elements in Dry Air (by volume) Nitrogen N 2 78% Plants Oxygen O 2 21% Animals Argon Ar 0.93% Inert Gas Carbon Dioxide CO % Plants Neon Ne % Inert Gas Krypton Kr % Inert Gas

13 Proportion of Elements in Dry Air (by volume) Nitrogen N 2 78% Plants Oxygen O 2 21% Animals Argon Ar 0.93% Inert Gas Carbon Dioxide CO % Plants Neon Ne % Inert Gas Krypton Kr % Inert Gas Hydrogen H % Helium He < % Inert Gas Xenon Xe < % Inert Gas Methane CH 4 < %

14 Water Vapor H 2 O 0 to 4% Ozone O to % Chlorofluorcarbons CFCs (e.g., Freon) Changing Concentrations of: Ozone Carbon Dioxide Methane Water Vapor The Atmosphere Climate Change!

15 Important Roles Played by Trace Gases Carbon Dioxide An important absorber of outgoing terrestrial radiation It, along with water vapor, serve as the primary means of preventing rapid heat loss from the earth and atmosphere back into space

16 Important 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

17 Important 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

18 Insolation losses in the atmosphere Dust - Gas molecules, dust, and other particulates are important because they can cause the sun s rays to be scattered or absorbed Scattering - visible light rays to be turned aside in all possible 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, and their 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 directly absorbing some wavelengths of solar radiation.

19 Electromagnetic Radiation Electromagnetic radiation can be: Absorbed increases the energy content of the object, like a black car in the summer Reflected bounce the energy back toward the source, like a mirror Transmitted pass through without absorption or reflection, like a pane of glass

20 Electromagnetic Radiation Albedo percent of solar/shortwave radiation that is reflected from a surface. New snow: 80% Old Snow: 50% Clouds: 50% Ice: 35% Dark, wet soil: 5% Light, dry soil: 40% Asphalt: 5% Forest: 15% Grass: 20% Crops: 20% Water high incident angle 50% Water low incident angle 5% Average albedo of the earth s surface: 7%

21 Electromagnetic Radiation The atmosphere is generally transparent to shortwave radiation and opaque to longwave THE GREENHOUSE EFFECT

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23 Vertical Distribution of the Atmosphere

24 The Troposphere Layer of the atmosphere in contact with the surface Temperature decreases with height because the troposphere is heated from below (atmosphere is generally transparent to shortwave radiation) Layer that contains all weather and all clouds Extends to about 12 to 15 km; actual height varies with latitude and season (thicker as temperature increases) Much water vapor and dust from interactions with the surface Contains about 80% of the mass of the atmosphere

26 The Tropopause Small, isothermal layer above the troposphere Isothermal no temperature change with height About 12 to 15 km in height actual height varies with latitude and season

28 The Stratosphere Layer of the atmosphere above the troposphere Temperature increases with height because of absorption of ultraviolet light by ozone (O 3 ) Extends up to about 50 km in height Little exchange of air between troposphere and stratosphere little dust or water vapor Stable air layer little vertical motions because of the increasing temperature with height -- inversion

30 The Stratopause Small, isothermal layer above the stratosphere Isothermal no temperature change with height About 50 km in height

32 The Mesosphere Layer of the atmosphere above the stratosphere Temperature decreases with height because of a lack of contact with the ground and a lack of ozone Extends up to about 80 km in height

34 The Mesopause Small, isothermal layer above the mesosphere Isothermal no temperature change with height About 80 km in height

36 The Thermosphere Layer of the atmosphere above the mesosphere Temperature increases with height because of energy from gamma and x-ray absorption due to the earth s magnetic field (van Allen radiation belt) Density of air at this altitude is very thin and the thermosphere holds little heat Thermosphere essentially drifts off to nothingness above about 120 km

37 Lapse Rates: Temperature decreases with increasing altitude within the troposphere at an average rate of 6.4 C/km 6.4 C/km = Normal Lapse Rate The actual decrease in temp, or actual lapse rate may vary considerably from the normal lapse: environmental lapse rate

38 Pollution

39 The atmosphere is made up of two zones based in function: to remove harmful wavelengths of solar radiation and charged particles Ionosphere Ozonosphere Extends throughout the thermopause and into underlying mesosphere Absorbs cosmic rays, gamma rays, x-rays, and shorter wavelengths of UV rad Absorption changes atoms to +ve charged ions ~ ionosphere ozone layer that is within the stratosphere that contains O 3 Highly reactive to oxygen molecules Ozone is harmful to living creatures when present near the surface Is necessary as absorbs harmful wavelengths of UV rad and reradiates it as safer LW rad

40 Ozone Depletion CFC s- Chloroflurocarbons -became widely used in the 1920s for industry -valuable as propellants for aerosol sprays and as refrigerants -also used in industry as solvents and foaming agents Good for industry as were not flammable Cannot be broken down by atmospheric processes near the earth s surface Not water soluble and do not break down by biologic processes Can be broken down by UV radiation within the stratosphere Can be broken down by UV radiation within the stratosphere -CFC s migrate to the stratosphere over time

41 Breakdown of CFCs from UV radiation Separates single Cl atoms or chlorine monoxide (ClO) molecules from the CFC components Ozone is an unstable molecule (O 2 or O 3 ) Chlorine is a catalyst for the destruction of ozone One Cl atom can decompose 100,000 ozone molecules Cl atoms have a residence time within the ozone layer of yrs. Example of ozone breakdown

42 1970s noticed depletion in levels of ozone, studies into the effect of chemicals on ozone depletion 1978 US banned CFC s in aerosols but was still used in refrigerants and polyurethane foam 1981 banned CFC products still allowed to be exported 1985 British Ant Survey reported ozone hole over Antarctica 1987 peak in CFC sales since aerosol ban (1.32 million tons) 1990 (1992 & 1997) Montreal Protocol to reduce use of CFC s globally 1998 production of CFC s declined to 1/4 th that of the 1987 peak

43 Pollution Air Pollution an unwanted substance injected into the atmosphere from the earth s surface by either natural or human activities Come as aerosols, gases or particulates Aerosols small bits of matter in the air that move freely with normal air movements Gases molecular compounds mixed together to form air Particulates larger, heavier particles that sooner or later fall back to the surface (haze, smoke, dust)

44 Sources of Air Pollution Natural produce great quantities of pollutants than human sources Volcanoes, forest fires, plants, soil, and ocean Produce NOx, CO, HCx and CO2 Anthropogenic although less than natural sources, humans have yet to adapt to anthropogenic pollution as for natural Sources include every day activities by large numbers of people (cars!) Industrial burning of fossil fuels and ore smelting

45 Carbon Monoxide - consists of one carbon and one oxygen atom incomplete combustion of fossil fuels 90% produced by natural sources (decay of carbon sources wood) 10% anthropogenic, mainly cars Source of CO for individuals is first and second hand tobacco and smoke

46 Photochemical Smog interactions of sunlight and combustion products in automobile exhaust (NOx and VOC s) Result of increased automobile usage over the past century Smog combination of smoke and fog Aerosols and gas pollutants in urban areas Lets in light but can obscure objects in the sky Irritates eyes and throat difficult to breathe Corrodes structures over time

47 Acid Precipitation atmospheric acids brought to the surface by precipitation (rain, snow) or by dry dust Major source of SOx from industrial emissions Acid rain = rain/snow polluted with SO2 or NO2 Acid dust = sulfuric and nitric nuclei cling to dust particles Fall to earth and coat surface Increase the acidity of soil with wet Accumulate with snow and melt in spring as surge of acid water

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

49 Natural Factors Affecting Pollution Wind move pollutants from one area to another Pollution Dome dome of pollution over an urban area under calm, stable atmospheric conditions Pollution Plume plume of pollution originating over an urban area that is transported downwind from its urban source

50 But it s not all bad! Clean Air Act (1970) lead to decrease in pollutants and increase in human health Decrease in cancer rates Less acid rain 206,000 fewer deaths from air pollution in 1990