Atmosphere

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- a protective covering of earths life against solar radiation and excessive heatingAtmosphere - a layer of gases (air) at the surface of the earth. Gas% by VolumeNitrogen, N278.03Oxygen, O220.99Argon, Ar0.94Carbon dioxide, CO20.033Neon, Ne0.0015Helium, He0.000542Krypton, Kr0.00014Xenon, Xe0.000006Source: Chang, R. Chemistry, 7th ed., McGraw-Hill, 2002Composition of Dry Air- nitrogen fixation can be natural or syntheticNitrogennitrogen is the most abundant element in the atmosphere but, its diatomic form, N2, is relatively inertit is not easily assimilated by living organisms and does not easily react with other chemicals to form new compoundsit has to be transformed into its reduced forms (such as ammonia, ammonium, nitrates, nitrites, and nitrogen oxides) the process of nitrogen fixation transforms this diatomic nitrogen to other compounds of nitrogen to be used in the formation of biological compounds (such as nucleic acids, amino acids, and proteins), industrial compounds (such as potassium nitrate for gun powder, nitroglycerin and nitro- toluene, and fertilizers), and many more.)

)Examples of Nitrogen Fixation1. Nitrogen fixation brought about by lightning Steps: N2(g) + O2(g) electrical energy 2NO(g 2NO(g) + O2(g) 2NO2(g)2NO2(g) + H2O(l) HNO2(aq) + HNO3(aq)2. Biological Fixation of Nitrogen, BFN- Organisms such as the Cyanobacter, Azotobacter, and Azospirillum can produce the enzyme nitrogenase which they use catalytically for the conversion of atmospheric N2 to NH3. Another group of organism, the Rhizobium works symbiotically with legumes and other plants to reduce N2.3. Synthetic Fixation by Haber-Bosch Industrial Process N2(g) + 3H2(g) 2NH3(g) Eventually the nitrogen from the plants and animals (together by industrial nitrogen) is converted to N2 by another group of microorganisms called the denitrifying bacteria. The Nitrogen Cycle Nitrogen in its consumable form is made possible by the process called the nitrogen cycle, in which nitrogen is taken from the atmosphere and converted to nitrates by nitrogen fixation. The nitrates are absorbed by plants converting them to proteins and nucleic acids which are further eaten by animals

The Nitrogen CycleThis continuous cycling of oxygen through these two processes for the stable concentration of oxygen in the atmosphere.The Atmospheric Oxygen - dry air contains approximately 20.99% O2 by volumea very reactive element, it easily reacts with other elements or substances and disappears from the atmosphereits concentration in the atmosphere is almost always constant Oxygen is removed mainly from the atmosphere by respiration The main route for the regeneration of the diatomic oxygen into the atmosphere is by the process of photosynthesisRespiration is the process by which energy is released from the cellular oxidation of glucose in a process called glycolysisEquation: C6H12O6 + 6O2 6CO2 + 6H2O + energyPhotosynthesis is the process by which plants convert light energy to chemical energy (stored in the chemical bonds of sugar) with the simultaneous release of oxygen gas.Equation: 6CO2 + 6H2O + energy C6H12O6 + 6O2 4. IonosphereLayers of the Atmosphere1. Troposhere2. Stratosphere3. Mesosphere

tropopose is the zone separating the troposphere from the next layer, the stratosphere.

Troposphere- thinnest layer, extends up to 10 - 11 km from the earths surfacemost dense, contains 80% of air mass- where all weather changes are observed, a region of rising and falling of packets of air- air pressure at the topmost part is 10% of that at sea level. The atmospheric pressure at sea level is 1 atm.- temperature is highest at the lowest portion and decreases with increasing altitude

The boundary between the stratosphere and the next layer is called the stratopauseStratosphere- situated between 10 50 miles from the earths surface- where the ozone layer is found-vertical stratified in temperature, with warmer layers higher up and cooler layers farther down. The topmost is about -30C - the formation of ozone from atomic oxygen and diatomic oxygen is exothermic. Ozone also absorbs ultraviolet rays turning them to heat energy. Thus, temperature increases towards the top of this layer where the ozone molecules concentrate. - The vertical stratification,reduces temperature convection. Thus no associated turbulence is observed, making this layer dynamically stable. For this reason, airplanes prefer to fly at the lower portion of the stratosphere. Balloons and other gliders can go as far as the lower portion of the stratosphere.

Mesopause is the layer that divides the mesosphere and the next atmosphere.Mesosphere- the mesosphere starts at 50 km above Earth's surface and goes up to 85 km high.- temperature decreases with altitude. The top of the mesosphere is the coldest part of Earth's atmosphere, around - 90 C.Most meteors from space burn up in this atmosphereNot so much is known about this layer because research instruments cannot easily be sent and maintained at this level. Thermosphere (ionosphere)- extends from 85 -90 km to 500 - 1,000 km above the earths surface.

- temperature increases with altitude with temperature (500C - 2,000C). - the air density is very thin. - temperatures can go very high but one would not feel warm in the thermosphere because there is so few contact with the atoms of the thin air. - sound transfer would also be very low because of very infrequent molecular collision

where the space shuttles orbit the earthThermosphere (ionosphere)- most of the ultraviolet rays and light photons from the sun are absorbed in this layer- the UV rays ionize the gases excited ions. and O2.The Ozone Layer- ozone is a triatomic molecule = O3- a blue colored gas with a very strong burnt odor- most ozone molecules are found in the stratosphere at 2-8 ppm concentration- the ozone layer absorbs much of the ultraviolet rays from the sun, preventing these rays from reaching the planets surface. - ultraviolet rays has been found to cause skin cancer, cataracts, and other genetic mutations both in animals and plant- Pale blue gas (O3) that is irritating, explosive, and toxic. It is formed by the photochemical action on the atmosphereit is used in water purification, deodorization, bleaching, and various chemical reactions that require a strong oxidizing agentOzone , O3O2 (in air) UVO + OO2 + O O3May also be manufactured on the spot by passing an electric discharge through oxygen or aircompared to chlorine, bacterial and viral disinfection with ozone is up to 5000 times more rapid.

Good Ozone or the ozone layer occurs in the stratosphere maximum ozone concentration is 5 1012 molecules/cm3 (more than 1000 times the the concentration of bad ozone at earth's surface)overexposure to UV is believed to be contributing to the increase in melanoma, the most fatal of all skin cancers. UV can also damage sensitive crops, such as soybeans, and reduce crop yieldozone-depleting substances (ODS), includes chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), halons, methyl bromide, carbon tetrachloride, and methyl chloroform. -This layer (atmospheric ozone) absorbs 9799% of the suns high frequency ultraviolet light (UV) which is damaging to life on Earth.[ Depletion of this ozone layer may increase the incidence of skin cancers.- Bad ozoneLocated at the troposphere layer at a usual concentration of 0.02 -0.03 ppm In polluted places such as cities where there are high densities of smog, O3 concentration could go higher than 0.1 ppmAt concentrations greater than 0.1 ppm, ozone is toxic and can be a potent bronchial irritant, making breathing difficult.it also damages crops, trees and other vegetation.Ground-level or "bad" ozone is the product of the chemical reactions between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight. Emissions from industrial facilities and electric utilities, motor vehicle exhaust, gasoline vapors, and chemical solvents are some of the major sources of NOx and VOCPhotochemical smog contains a high concentration of O3smog mixture of smoke and fogHow the ozone layer absorbs UV radiationsStep 2. An oxygen radical combines with another O2 to form an ozone, O3, molecule. O + O2 + M O3 + M Step 4. The cycle of steps 1 to and 3 is repeated all over or simultaneously occuring. This dynamic equilibrium process of generation and destruction of O3 by UV radiation accounts to the almost constant concentration of ozone molecules in the stratosphere. Depletion of the Ozone LayerODS- ozone depleting substances- group of chemicals containing chlorine (Cl) and bromine (Br)these are the chloroflourocarbons (CFC), hydrochloroflourocarbons (HCFC) carbon tetrachloride (CCl4) bromoflourocarbons, hydroflourocarbons, and oxides of nitrogen (NOX) - they are commonly used as coolants, refrigerants, aerosol propellants, foams, fire-fighting chemicals, soil fumigants, and solventsThe choroflourocarbons (CFC) - examples: CFCl3 (Freon 11) CF2Cl2 (Freon 12) C2F3Cl3 (Freon 113) and CF4Cl2 (Freon 114)- when these substances are discharged in the atmosphere, they remain stable for long periods of time. - when they reach the ozone layer, they react with the ozone molecules. Depletion of the ozone layer by CFCs2. The radical Cl reacts with O3: Cl + O3 ClO + O2 The radical ClO takes another O radical from the atmosphere: ClO + O Cl + O2 One Cl radical can destroy up to 100,000 ozone molecules before it is consumed by other reactions. The regenerated chlorine radical takes another O3 and the cycle is repeatedThe Cl radical catalyzes the decomposition of O3 much faster than the decomposition of O3 by UV. Depletion of the Ozone Layer by NOX - NOx, such as NO and NO2 are products of fuel gas combustion- Most of these NOx are released to the atmosphere by supersonic aircrafts- Reactions: Nitrogen dioxide (NO2) can reacts with the radical ClO forming chlorine nitrate, a very stable chlorine reservoir in the atmosphere. NO2 + ClO ClONO2Clorine nitrate(ClONO2) is a source of Cl in the formation of the ozone holes in the arctic and antarctic skiesThe Polar Ozone Holes- the repeated abnormal depletion of the ozone layer (to as much as 50%) over the arctic and antarctic regions during spring time

One DU is 2.691016 ozone molecules per cm2

The Antarctic ozone hole is an area of the Antarctic stratosphere in which the recent ozone levels have dropped to as low as 50% of their pre-1975 values. During winter, polar stratospheric cloudContaining HCl and chlorine nitrate (ClONO2) is a Good source of Cl radical which reactswith ozone

As the UV and VIS rays strike the surface of the earth, earth molecules start to vibrate. This process produces another form of energy (heat energy). The earth surface releases this heat energy above the surface of the earth.Types of energy manifested by atoms and molecules: electronic energy absorbed at UV and VIS wavelength (ex: light radiation) vibration energy absorbed at IR or far IR wavelength (ex: heat radiation) rotational energy absorbed at the longer wavelengths like micro, radio, etc.) How heat is generated

Greenhouse gases are largely transparent to shortwavelengths like the ultraviolet rays (UV) and the visible rays VIS) (ex: light energy).Greenhouse gases absorb and reflect heat energy "greenhouse effect"- is the heating of the Earth due to the presence of greenhouse gases is the process by which absorption and emission of radiation by gases (called greehouse gases) in the atmosphere warm a planets lower atmosphere and surface.

Short wavelength (UV and VIS) solar radiation from the sun passes through earth's atmospherethen is absorbed by the surface of the Earth, causing it to warm. Heat energy involves longer wavelength IR

Part of the absorbed energy is then reradiated back to the atmosphere as long wave infrared radiation (heat).The greenhouse gases absorb these waves and reemits the waves in all directions including downward, causing the lower atmosphere to warm.Greenhouse effect: Is it good or bad?Good effect It controls the temperature of the atmosphere. Without it, the world with not be livable- It protects the earth from sub zero environmentBad effect-The overproduction of the so called greenhouse gases has made the geenhouseshield too thick, thus increasing the temperature of the earth to almost undesirableTemperature causing global warming and extreme weathersMost common greenhouse gases 1. Carbon dioxide (CO2) and carbon monoxide (CO)2. Methane (CH4)3. Chloroflourocarbons (CFCs)4. Nitrous oxide (NO2) over the past century, greenhouse gases and other air pollutants released into the atmosphere have been causing big changes like global warming, ozone holes, and acid rains naturally occurring greenhouse gases have a mean warming effect of about 33C Major Greenhouse GasFormulasLifetime (years)Carbon dioxideCO2MethaneCH412OzoneO3Other Gases of Anthropogenic OriginsDinitrogen oxideN2O114chloroflourocarbons CFC-12CCl2F2100 HCFC-22CHClF212 tetraflouromethaneCF450,000 hexaflouroethaneC2H610,000 Sulphur hexaflourideSF63,200Nitrogen triflourideNF3740Ex: GasPreindustrial levelCurrent levelIncrease since 1750Carbon dioxide280 ppm388 ppm108 ppmMethane700 ppb1745 ppb1045 ppbNitrous oxide270 ppb314 ppb44 ppbCFC-120533 ppt533 ppt

Carbon dioxide, CO2- a colorless, odorless non-flammable gas carbon Dioxide is emitted into the air as humans exhale, burn fossil fuels for energy, and deforest the planet.Cellular respiration: C6H12O6 + 6O2 6CO2 + 6H20Carbohydrate + O2 CO2 + H2OBurning: Methane, CH4

- a colorless, odorless, flammable gas. It stays in the atmosphere for only 10 years, but traps 20 times more heat than carbon dioxide. - it is formed when plants decay and where there is very little air (swamp gas) production is hastened by the presence of methanogens - are bacteria that are commonly found in deteriorating plants in the absence of oxygen and in the gut of animals- Burning of methane produces CO2 and H2O which are also greenhouse gases CH4 + 2O2 CO2 + 2H2OHalocarbons- hydrocarbons with halogen substituents, CFCs and the HFC Ex: dichlorodiflouromethane, CCl2F2Chlorodiflouromethane, CHClF2Tetraflouromethane, CF4- they also destroy the ozone layer- uses of CFCs are now being controlled under the terms of the Montreal Protocol they have no natural sources but are entirely synthesized as refrigerants, aerosol propellants for fire retardants, and cleaning solvents their production started in 1928 and since then there was an observed rise of CFCs in the atmosphere- they have long atmospheric lifetimes in the atmosphere.Ex: CCl2F2 ~ 100 years in the atmosphere CHClF2 ~ 12 years CF4 ~ 50,000 yearsNitrous oxide (N2O)- colorless greenhouse gas, however, it has a sweet odor - used as anaesthetic- (laughing gas)- released naturally from oceans and by bacteria in soils.- a by product of nitrogen based fertilizers- by product of gasoline decomposition by automobiles

Sources:- SF6 (sulfurhexafluoride) and NF3 or N2F6 (nitrogen triflouride) Other greenhouse gases- They occur in very small amount but they are very potent greenhouse gasesThey are gases with high global warming potential (GWP) GPW a measure of how much heat is trapped by the gasNote: Major atmospheric constituents, N2, O2, and Ar are not greenhouses- They do not absorb energy at IR wavelengthNote: Carbon monoxide is not a greenhouse gas- can react with O2 to form CO22CO + O2 2CO2Water, H2O

water vapor is a potent greenhouse gas owing to the presence of the hydroxyl bond which strongly absorbs energy in the infrared region higher concentration of water vapor is then able to absorb more thermal IR energy, thus further warming the atmosphere. the latent heat of vaporization, which is released to the atmosphere whenever condensation occurs contributes to further environmental heating - positive feedback loopgreenhouse water vapor reflects heat to the earthEarth atmosphere becomes hotterHigher temperature allows higher water evaporation from seas/oceans/riversThe warmer atmosphere can then hold more water vapor and so on and so on. - a higher concentration of water vapor would be able to absorb more thermal IR energy radiated from the Earth, thus further warming the atmosphere. Causes of global warming or increase in greenhouse production 1. Increasing population growth- garbage to decompose: decomposition leads to more CO2 production3. Increase in the use of refrigerants using CFC gases. 2. Increase in energy consumption increase in the release of CO2 increase in the release of NO2- after use, these gases stay in the atmosphere for a long time4. Increase in methane gas production.- Farts from cattle contain high percentage of methane gas- Methane gases from marshes, swamps, and rice paddy fields- Methane resulting from termite bitesPredictable effects of global warming if the amount of CO2 now present is doubled1. Melting of the arctic and antarctic ice edges increasing the sea levels- Coastal areas or islands would be swamped and inundated- Areas already below sea levels would be flooded 2. Faster evaporation of water would lead to dry lands getting drier- Rainfall pattern would be disrupted- There would be drastic changes in the existing climate3. Change in life patterns- Some plants and animals may cease to exist- Food supply would drastically be lessened- Inevitable population migration (great migration)What can you do to arrest global warming?Acidic solution one which contains an excess of the hydrogen ion concentration pH- negative logarithm of the H+ concentration (-log H+)a measure of the hydrogen ion concentration of a solutionpH = 7, neutralpH < 7, acidicpH > 7, basicnormal rain slightly acidic - has a pH of below 7 but not lower than 5.7Distilled water pH = 7Acid Rain- any form of wet (rain, snow, sleet, fog, cloudwater, dew) and dry (other particulates and gases) deposition from the atmosphere containing higher than normal amounts of nitric and sulfuric acids.- high H+ - low pH, could go as low as 2.0 - the large emission of sulfur dioxide (SO2) and nitrogen oxides (NOx) to the atmosphere

Main Cause of Acid Rainaverage pH = 4.2l- product of phytoplankton metabolismEmission of SO2- from volcanoes - a by-product in power plant generation where coal is used- combustion of fuels for motor vehiclesindustries (like the pulp and paper industries) that produce as byproduct the volatile flammable liquid dimethyl sulfideEmission of NOX- by-product in power plant generation where coal is used- combustion of fuels for motor vehiclesEffects of Acid Rain, - acidification of lakes and bodies of waterpH of below 5 does not allow fish eggs to hatch- acceleration of corrosion of metals some fishes may not be able to tolerate low pHcorals which are mainly made up of limestone may be weakened - soil biology and chemistry is changed acids can make the metallic ions such as aluminum, calcium, and magnesium more soluble, removing them as food source of plants microbial organisms may not be able to tolerate the high acidity- forests and plants may be damageddry precipitation (SO2 and NOX gases) contribute to lung diseases asthmabronchitiscoronary obstructive diseaseskin allergies- erosion of stone statues made mainly of limestone and marble. CaCO3 (s) + H2SO4 (aq) CaSO4 (s) + CO2 (g) + H2O (l)