Air Pollution Final Study Guide - Air Pollution Final Study...

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Air Pollution Final Study Guide 18/03/2008 20:17:00 Los Angeles Urban Smog Photochemistry London smog o Discovered by Dr. Harold Des Voeux in 1905 o Comes from coal smoke + water vapor + liquid water in cool, humid, or foggy air o Conditions causing high concentration: Temperature inversions, humid, foggy air o Appearance of air: dirty, sooty, foggy LA Smog o Photochemical from automobile exhaust o 1943: Source: Factories? o Discovered by Arie Haagen-Smit in o Requires sunlight and ROG and NOx o Conditions causing high concentration: Temperature inversions, hot, sunny weather o Air appears hazy brownish color Hazy air can also come from ocean salt particles growing into small haze  droplets from relatively high levels of humidity found along coast Reactive Organic Gas (ROG): volatile organic compound (VOC) that in gaseous form tends  to promote certain oxidizing reactions in photochemical smog Primary pollutant: emitted directly from atmosphere o CO, NOx, ROG o In LA, mainly come from gasoline- or diesel- burning internal combustion engines
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Secondary pollutant: produced be chemical reactions in atmosphere o O2, NO2, PAN o Ozone: main secondary pollutant; classified as an oxidizer because it gives up third  atom to other compounds o Can come from a reaction between primary pollutants, between a primary and a  secondary, other secondary pollutants, or normal atmospheric constituents o Sources in LA: automobiles and stationary industrial sources Spontaneous Reactions: A   B + C + heat o Exothermic: gives off energy o Ex: radioactive decay o Not common in photochemical smog Collision Reactions: A + B + … (+ activation energy)   C + D + … (+ heat) o Two or more reactants collide o Either exothermic or endothermic (energy absorbed) o Some do not result in reactions because an activation energy barrier must be  crossed supplying energy to the reaction Photodissociation Reactions: A + light   B + C o Endothermic o Photon of light provides the energy to split molecule o Gives photochemical smog its name Null Cycle o Neither produces nor destroys anything overall o NO2 photodissociates, resulting in an oxygen atom which quickly combines with  molecule oxygen O2 to form Ozone O3 which does not last long and is then used to  oxidize nitric oxide NO back to NO2 starting cycle over o Relatively fast reactions producing short residence times for products and reactants
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o O3 is destroyed as fast as it is produced o Low concentrations of NO2 and ozone ROGs in Smog: contains reactive part R  plus H (RH) o Radicals: compounds with an open hydrogen bond; highly reactive o
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