Wk 4a trop chem Ch1_part2 2008

Wk 4a trop chem Ch1_part2 2008 - Tropospheric Chemistry...

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Tropospheric Chemistry Chemistry of Remote Regions & Chemistry of Polluted Regions
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The Clean Atmosphere
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Chemistry of remote regions • remote regions have lower NO x emissions = lower [NO x ] as compared to polluted regions but all regions of the globe have been impacted by anthropogenic emissions how do we differentiate between natural and anthropogenic emissions? http://www.bbc.co.uk/paintingtheweather/csv/painting/springtime.shtml Peter West, National Science Foundation Peter West, National Science Foundation http://www.usatoday.com/weather/wcloud0.htm http://www.usatoday.com/weather/wcloud0.htm
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Natural vs Anthropogenic One method to follow anthropogenic emissions is to use the correlation between CO and O 3 CO is released during combustion processes in vehicles & industrial processes (with NO x CO is slow to react with OH τ ~ 90 days for [OH ] = 5 x 10 5 cm -3 photochemical reactions with VOC and NO x form O 3 Products will be present in the air mass also http://nature.org/aboutus/
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Emissions of Biogenic Organics There are substantial biogenic VOC emissions globally, the total may exceed anthropogenic emissions by 10x! Biogenic emissions are less important in urban regions bio HC’s in the South Coast Air Basin = 10% of total VOC emissions/typical day http://www.fs.fed.us/r1/gallatin/album/slide.shtml?11 http://www.fs.fed.us/r1/gallatin/album/slide.shtml?11
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There are 1000’s of biogenic VOCs best known: ethene, isoprene, and monoterpenes emitted by terrestrial plants Isoprene: major single non-methane VOC emitted by plants Ethene: plant hormone Some plant emissions increase (10-100x) when the plant is stressed (T change or a lack of H 2 O) some biogenically emitted hydrocarbons
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Estimated Global Annual Biogenic VOC Emissions (Tg yr - 1 ) Source Isoprene Monoterpenes Other VOCs Canopy foliage 460 115 500 Terrestrial ground cover and soils 40 13 50 Flowers 0 2 2 Ocean and freshwater 1 <0.001 10 Animals, humans, and insects 0.003 <0.001 0.003 Anthropogenic (including biomass burning) 0.01 1 93 Total ~500 ~130 ~650
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Mechanisms of production of biogenically emitted VOCs
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Larger VOCs Conifers tend be a source of larger terpenoids (molecules derived from isoprene) – a major component of these are C 10 monoterpenes the mechanisms of formation of terpenoids are closely linked, so emissions of more than one monoterpene often occur together ie. geranyl diphosphate is a precursor for α, β-pinene, limonene, and myrcene (all emitted) whereas ispoprene has no reservoir in leaves (emission can be controlled) monoterpenes are stored in the plant so there is less short-term control (light, T or H 2 O changes) α -pinene α -pinene limonene limonene myrcene myrcene g d g d
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An aside: Isoprene may be generated in small amounts by marine phytoplankton A variety of small HCs have been identified in seawater and the air
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This note was uploaded on 07/17/2008 for the course CHEM 641 taught by Professor Allen during the Winter '08 term at Ohio State.

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Wk 4a trop chem Ch1_part2 2008 - Tropospheric Chemistry...

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