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Tropospheric Ozone: What are the links with climate and how well are we modeling them?

Tropospheric Ozone: What are the links with climate and how well are we modeling them?. Drew Shindell. Tropospheric ozone is:. a climate gas the only source of hydroxyl a governor of other reactive climate gases (e.g. methane, stratospheric ozone)

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Tropospheric Ozone: What are the links with climate and how well are we modeling them?

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  1. Tropospheric Ozone: What are the links with climate and how well are we modeling them? Drew Shindell

  2. Tropospheric ozone is: • a climate gas • the only source of hydroxyl • a governor of other reactive climate gases (e.g. methane, stratospheric ozone) • a factor in aerosol chemistry (e.g. in-cloud oxidation of sulfate) • a gas affecting local meteorology

  3. Atmospheric Evolution • Great Oxidation Event 2.1-2.4 Ga • Onset of oxidized iron in sediments • Disappearance of pyrite (reduced sulfur) • Sulfide inclusions in diamonds brought to surface by volcanism show mass-independent isotopic variations in sulfur prior to 2.4 Ga (Farquhar et al., Science, 2002). Only known process is UV photolysis (~190-220 nm) • Cyanobacteria • 2.7-2.8 Ga (Brocks et al., Science, 1999)

  4. Archean (3.8 - 2.5 Ga) • Reducing atmosphere • Plenty of carbonate rocks • Sulfate low (based on 34S depletion) • So sulfate-processing bacteria not processing organic carbon • Methanogenic bacteria? • Methane lifetime ~10,000 years (Kasting & Siefert, Science, 2002) • Methane greenhouse answer to ‘Faint sun paradox’? • Increased oxygen at G.O.E. -> less CH4 -> first known glaciation

  5. Paleocene/Eocene Thermal Maximum(~55.5 Ma) • High latitudes warmed 5-7 C • Tropics warmed 2-3 C • Methane from gas hydrates (~1500 GT C) • If oxidized to CO2, radiative forcing not large enough to give estimated warming • Methane lifetime increase by 50-100% • Combined radiative forcing gives reasonable warming • Historical doubled CO2 analog (Schmidt and Shindell, Paleoceanography, 2003)

  6. sun stratosphere Evaporation dry deposition HNO3 H2O2 surface emissions and lightning rainout surface emissions O3 +h, H2O +h, O2 OH + HC,CO NO2 NO + HO2

  7. Chemistry Temperature Water vapor Heterogeneous surfaces Radiation Photolysis rates Sources Stratospheric inflow Surface emissions In-situ (lightning) Sinks Wet deposition Dry deposition Links with Climate

  8. Chemistry • Temperature • reaction rates & O3 + h  O(1D) • Water vapor • O(1D) +H2O  2OH • Heterogeneous surfaces • Oxidation of sulfate • Photochemical formation from VOCs • Mineral dust : O3 chemistry budget -20 Tg/yr, burden -8 Tg (Martin et al., JGR, 2002) • Ice particles

  9. Water vapor Response to volcanism demonstrates water vapor sensitivity to surface temperature change (Soden et al., Science, 2002)

  10. Climate Sensitivity • 1.7 - 4.2 C for 2xCO2 (IPCC TAR) • ~0.5 - 1.0 C per W/m2 • Cloud feedbacks

  11. Radiation • Overhead ozone changes • +1% in 2040 global annual average column; positive in upper strat, negative in tropical and high latitude lower strat (Rosenfield et al., JGR, 2002) • -3% column from dT and dH2O in 2040; positive in upper strat, negative in lower (Shindell & Grewe, JGR, 2002) • Impacts on photolysis rates/OH formation • 1979-1992: +3.1% OH, -1.0% O3, -2.3% CO (De Winter-Sorkina, Atm. Env., 2001) • +2.8% OH 1979-1990 (~4% dO3 Strat) (Bekki et al., Nature, 1994) • +2% OH 1979-1992 (Krol et al., JGR, 1998) • Sensitivity of OH inversely proportional to NOx

  12. Sources • Stratospheric inflow (ozone and NOx) • Circulation increase or decrease? • Stratospheric abundance changes? • Surface emissions • Methane from wetlands • NMHCs from forests • NOx from soils • Biomass burning (CO, NOx, CH4, NMHCs) • In-situ (lightning NOx)

  13. Lightning & Ozone • Lightning sensitivity to warming • Ionospheric potential ~10%/K • Flash vs. cloud height ~10%/K • Schumann resonance ~250%/K • Seasonal variations ~50-800%/K • OTD data vs land temperatures ~40%/K • No correlation in tropics!

  14. Ozone response (Flash vs cloud height parameterization of Price and Rind) • +27 Tg = 8% for +3 TgN (GEOS-CHEM - Martin) • Chemistry budget +190 Tg/yr • +18 Tg = 6% for +2.2 TgN (GISS GCM - Shindell) • Chemistry budget +63 Tg/yr • 23% for ~0.5 TgN (1D/2D model - Toumi) • Radiative forcing • +0.1 W/m2 for +2.2 Tg, 0.03 W/m2 for 0.8 Tg (GISS) • +0.34 W/m2 (1D/2D)

  15. Radiative Forcing dTs/dO3 Lightning Change 200 500 750 +0.8 TgN/yr+36% 1000

  16. Lightning NOx travels via stratosphere(Grewe et al., Chemosphere, 2002)

  17. VOC emissions • Biosphere model: T, precipitation, CO2, vegetation redistribution (no atmospheric chemistry) (Constable et al, Global Change Biology 1999) • ~+80% US isoprene emissions with 2xCO2 • vegetation redistribution alone causes decrease • CTM linked to a vegetation model (Sanderson et al, IGAC Symposium, 2002). • Global annual average isoprene from 549 to 697 Tg/yr • Without redistribution, from 549 to 736 Tg/yr (+34%) • Tropical forest dieoff • GCM with isoprene parameterization (Bell et al, GISS) • Without redistribution from 350 to 473 Tg/yr (+35%)

  18. Isoprene & climate • Red oak doubled isoprene emissions with elevated CO2 (Sharkey et al., Plant Cell Env., 1991) • Aspen showed 40% decrease (Sharkey et al., Plant Cell Env., 1991) • Cottonwood showed 21% decrease for 800 ppm CO2 (Rosenstiel et al., Nature, 2003) • Including 2xNPP, all increases (20%-400%) • Effect on ozone dependent upon NOx background

  19. Wetland Emissions Range ~100-260 Tg/yr Function of temperature, soil moisture, area

  20. Wetlands and climate • Sensitivity gauged by interannual variation during past ~15 years (e.g. Walter et al., JGR, 2001; Dentener et al., ACP, 2003) • Especially negative methane growth rate anomaly following Pinatubo • GCM simulation with parameterization of emissions: +103 Tg/yr for 2xCO2

  21. Other emissions • Bromine from sea ice (Roscoe et al., GRL, 2001) • Leads to tropospheric ozone loss • Small positive feedback from warming

  22. Sinks • Wet deposition • Hydrological cycle changes • Changes in pH of droplets • Dry deposition • Surface wind velocities (turbulent processes) • Surface temperature and pressure (boundary layer height) • Surface radiation (includes cloud changes) • Surface type (snow, ice, etc.)

  23. Models show…

  24. Budgets of TAR CTMs • Chemistry: -855 to +507 • Dry deposition: -533 to -1178 • Stratospheric influx: +391 to +1440 • All give ozone fields in ‘agreement’ with sonde observations

  25. Ozone budgets (Tg/yr) & 2xCO2

  26. Annual average dO3 (%)2xCO2 vs control 200 500 750 1000 -10 -8 -6 -4 -1 1 4 6 8 10

  27. Annual avg O3 chemistry change2xCO2 vs control (kg/s) 100 200 500 750 1000 -18 -10 -7 -4 -1 1 4 7 10 18

  28. Spatial pattern of surface chemistry changes (1E-16 kg/s/m2) -2 -1.4 -.9 -.6 -.3 -.1 .1 .3 .6 .9 1.4 2

  29. Dry deposition Total change = +101 Tg O3/yr, Snow/ice cover contributes +17

  30. Annual avg O3 chemistry change2xCO2 vs control (kg/s) 100 200 500 750 1000 -18 -10 -7 -4 -1 1 4 7 10 18

  31. dNOx (%) dHNO3 wet (kg/s)2xCO2 vs control 200 500 750 1000 -16 -13 -9 -6 -2 2 6 9 13 16 -8 -6 -5 -3 -1 1 3 5 6 8

  32. Change in PANs Increased temperatures lead to more thermal dissociation Global reduction 23% ~31% Met Office (Johnson et al., JGR, 1999)

  33. Annual average dOH (%)2xCO2 vs control 200 500 750 1000 -25 -19 -14 -8 -3 3 8 14 19 25

  34. Ozone budgets (Tg/yr) Dry deposition is sped up at high latitudes Increased stratospheric ozone with 2xCO2 (and no other change!) +40 Tg/yr from convective transport

  35. % O3 change including stratosphere 50 100 200 500 750 1000 -11 -8 -6 -4 -1 1 4 6 8 11 -11 -8 -6 -4 -1 1 4 6 8 11

  36. Stratosphere-Troposphere exchange dependence upon surface warming (dO3 %) 100 1000 -90 0 90 -90 0 90 -50 -20 -15 -10 -5 0 5 10 15 20 36 12 12 8 8 4 4 0 0 Rind et al., JGR, 2002

  37. 100 5 -5 -5 -10 1000

  38. 100 19 25 14 8 -8 1000

  39. Radiative forcing = 0.03 W/m22xCO2 vs control -.24 -.2 -.15 -.11 -.07 -.02 .02 .07 .11 .15 .20 .24

  40. +0.08 W/m2 -.24 -.2 -.15 -.11 -.07 -.02 .02 .07 .11 .15 .20 .24

  41. Meteorology changes Preindustrial vs present, Mickley et al., 2003 PI vs present, +10% radiative forcing and -1% OH due to O3/met

  42. 2xCO2 climate +7% 2100 NOx +34% 2100 CH4 -22% 2100 CO -6% 2100 NMHCs -5% All +17% +2% +25% +21% +2% +2% +60% Changes in context… dOH dO3

  43. Conclusions • Chemistry: Relatively good (global) • Climate sensitivity likely larger source of uncertainty than chemical response • However, still missing chemistry (chemistry-aerosols, NOx/HNO3 ratios, etc.) • Radiation: Relatively good • Future stratospheric ozone uncertain • Response relatively well-known • Overall effect likely small

  44. Conclusions: Sources

  45. Conclusions: Sinks • Wet deposition: Relatively poor • Cloud/hydrology response to climate change • Aerosol changes (e.g. CCN) • Dry deposition: Relatively poor • Vegetation changes • Snow & ice changes (Arctic, AO/NAO) • Turbulence sub-grid scale

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