oh in the tropical upper troposphere and its relationships to solar radiation and reactive nitrogen...
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OH in the tropical upper troposphere and its relationships to solar radiation and reactive nitrogen
Ru-Shan Gao, Karen Rosenlof, David Fahey, Paul Wennberg, Eric Hintsa, and Tom Hanisco
and
the STRAT team
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OH in the tropical upper troposphere (TUT)
• Low concentration but important for pollutant degradation
• Direct source: O3 + hn ® O2 + O(1D) (R1)O(1D) + H2O ® 2OH (R2)
• Low O3, low H2O conditions in the TUT ® Low OH?- Kley et al., Science 1996
• Recent work by Markus Rex – Effect of low OH in TUT
• Tightly coupled to HO2
- Easier to model HO2/OH than OH
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Box model results, Jaeglé et al., AE 2000
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Box model results, Jaeglé et al., AE 2000
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5Hanisco et al., JPC, 2001
OH in the lower stratosphere correlates with SZA
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OH in the lower troposphere correlates with J(1D)
Rohrer and Berresheim, Nature, 2006
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Measurements in TUT during STRAT
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OH measurements in TUT
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O3 + hn ® O2 + O(1D), O(1D) + H2O ® 2OH
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[OH] vs. JO(1D) * [O3] * [H2O]
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Measurements in TUT during STRAT
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• The cycling time between OH and HO2 is much shorter than the lifetime of HOx
• OH <-> HO2:OH + CO (+ O2) ® HO2 + CO2 (R3)HO2 + NO ® OH + NO2
(R4)
• OH is controlled by R3, R4, and HOx sources and sinks
• O3+H2O is not the dominant HOx source
• Main HOx sink:NOy (high NOy) or HOx self reactions (low NOy)
• When NOy is low, NO determines [OH]
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Concluding remarks:
1) A simple functional description for [OH] in the tropical upper troposhpere (TUT) is accurate to ±50%
- It appears that the TUT OH has no dependence on O3 and H2O
- Spread in [OH] at a given SZA needs further examination
2) Low [OH] air parcels do exist in TUT- O3, NO, and NOy are very low in these air parcels- Low NO appears to be the main cause
3) Where to find low [OH] air parcels:• Source: aged marine boundary air (low O3, NO, and
NOy)• Strong convection without lightning – marine
convection• Most likely place – the west Pacific warm pool• Low O3 can be an indicator of low NO and low OH!
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Measurements in TUT during STRAT
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