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QUESTIONS

QUESTIONS. 1. How does the thinning of the stratospheric ozone layer affect the source of OH in the troposphere? 2. Chemical production of ozone in the troposphere is much faster in summer than winter. Explain.

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QUESTIONS

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  1. QUESTIONS 1. How does the thinning of the stratospheric ozone layer affect the source of OH in the troposphere? 2. Chemical production of ozone in the troposphere is much faster in summer than winter. Explain. 3. Why don’t reactions of hydrocarbons deplete (or titrate!) all the OH in the troposphere?

  2. CHAIN MECHANISM FOR O3 PRODUCTION: CH4 OXIDATION • Initiation: source of HOx (OH production) • Propogation: • CH4 + OH CH3 + H2O • CH3 + O2 + M  CH3O2 + M • CH3O2 + HO2  CH3OOH + O2 • CH3O2+ NO  CH3O + NO2 • CH3OOH + OH  CH2O + OH + H2O • CH3OOH + OH  CH3O2 + H2O • CH3OOH + hv  CH3O + OH • CH3O + O2  CH2O + HO2 • CH2O + OH  CHO + H2O • CH2O + hv + O2  CHO + HO2 • CH2O + hv  CO + H2 • CHO + O2  CO + HO2 • (…then CO oxidation…) * * • Oxidation from C(-IV) in CH4 through to C(+IV) in CO2 * * * O2 hn O3 hn NO2 NO O3 hn, H2O OH HO2 H2O2 Deposition CO, CH4

  3. METHANE OXIDATION SCHEME CH3O NO O2 hv, O2 OH O2 OH O2, M CH4 CH3 CH3O2 CO CH2O CHO hv HO2 OH hv CH3OOH OH NO2 HO2 HO2 HO2 In clean troposphere, ~70% of OH reacts with CO, 30% with CH4

  4. NOx EMISSIONS (Tg N yr-1) TO TROPOSPHERE • Zeldovich Mechanism: combustion and lightning • At high T (~2000K) oxygen thermolyzes: • O2 O + O • O + N2  NO + N • N + O2  NO + O STRATOSPHERE 0.2 LIGHTNING 5.8 SOILS 5.1 FOSSIL FUEL 23.1 BIOMASS BURNING 5.2 BIOFUEL 2.2 AIRCRAFT 0.5

  5. LIGHTNING FLASHES SEEN FROM SPACE (2000) DJF JJA

  6. USING SATELLITE OBSERVATIONS OF NO2 TO MONITOR NOx EMISSIONS SCIAMACHY data. May-Oct 2004 (R.V. Martin, Dalhousie U.) detection limit

  7. NOX CYCLING Example of PAN formation from acetaldehyde: CH3CHO + OH  CH3CO + H2O CH3CO + O2 + M  CH3C(O)OO + M CH3C(O)OO+NO2 + M  CH3C(O)OONO2 + M PAN carbonyl oxidation T NO3 O3 O3 M O2 hn N2O5 NO2 NO Combustion lightning H2O OH, M HO2 HNO3 O3 ~ 1 day

  8. PEROXYACETYLNITRATE (PAN) AS RESERVOIR FOR LONG-RANGE TRANSPORT OF NOx

  9. H DECOMPOSITION OF PAN LEADING TO OZONE PRODUCTION Chemistry: Changing NOy speciation Origin: Warm Conveyor Belt over Asia ECMWF Evolution: Split by blocking high pressure O3 CO [Heald et al., 2004]

  10. GLOBAL BUDGET OF TROPOSPHERIC OZONE Present-day Preindustrial O2 hn O3 STRATOSPHERE 8-18 km TROPOSPHERE hn NO2 NO O3 hn, H2O OH HO2 H2O2 Deposition CO, VOC NO+peroxy radicals is rate-limiting, so:

  11. Climatology of observed ozone at 400 hPa in July from ozonesondes and MOZAIC aircraft (circles) and corresponding GEOS-Chem model results for 1997 (contours). GLOBAL DISTRIBUTION OF TROPOSPHERIC OZONE GEOS-Chem tropospheric ozone columns for July 1997. [Li et al., 2001]

  12. 1996-2005 NOx EMISSION TREND SEEN FROM SPACE [Van der A et al., 2008]

  13. POWER PLANT EMISSION REDUCTIONS IN THE EASTERN US • Effects of NOx controls on large point sources in the Eastern US beginning in the late 1990s • Acid Rain Program, NOx SIP Call, NOx Budget Trading Program • Focus on coal-burning power plants • Improved burner technology, post-burner ammonia scrubbers Northeast Urban Corridor E(NOx) < 20% power plant Ohio River Valley 1997 E(NOx) ~ 50% power plant Ohio River Valley 2005 E(NOx) ~ 20% power plant Courtesy: Greg Frost (NOAA) [Kim et al., 2006]

  14. Colstrip North Valmy Dave Johnston/ Laramie River Intermountain Jim Bridger/ Naughton Hunter / Huntington Reid Gardener Craig/Hayden Bonanza Mohave Four Corners/ San Juan Navajo Cholla/Coronado/ Springerville POWER PLANT POINT SOURCES IN WESTERN US SEEN FROM SPACE Courtesy: Greg Frost (NOAA) [Kim et al., 2009]

  15. Tropospheric ozone Is the third anthropogenic greenhouse gas IPCC [2007]

  16. IPCC RADIATIVE FORCING ESTIMATE FOR TROPOSPHERIC OZONE (0.35 W m-2) RELIES ON GLOBAL MODELS …but these underestimate the observed rise in ozone over the 20th century Fitting to observations would imply a radiative forcing of 0.8 W m-2 Preindustrial ozone models } Observations at mountain sites in Europe [Marenco et al., 1994]

  17. RECENT TRENDS IN TROPOSPHERIC OHinferred from methylchloroform observations

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