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Organic Carbon in the Troposphere

Organic Carbon in the Troposphere

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Organic Carbon in the Troposphere

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  1. Organic Carbon in the Troposphere Colette L. Heald* ( *With acknowledgements to many people at the end! NOAA Seminar June 11, 2008

  2. CARBON IN THE ATMOSPHERE CO2 (820 PgC) Organic Carbon (~10s TgC) + CO (150 TgC) CH4 (4 PgC) • Short-lived (reactive) • BUT important climate role : • direct aerosol radiative forcing • indirect via CCN • oxidant chemistry (O3, CH4, …)

  3. MODEL OBS RECONCILING THE ORGANIC AEROSOL BUDGET SOA measured/modeled = 4-100! [Volkamer et al., 2006] Good agreement between global model and IMPROVE observations for OC aerosol concentrations in the US [Park et al., 2003] Global measurements (surface 0.5-32 μgm-3) [Zhang et al., 2007]

  4. GAS-PHASE CARBON MASS CLOSURE? 2847 organic compounds identified in the atmosphere [Graedel et al., 1986] ~104 compounds estimated to be present [Goldstein and Galbally, 2006] 30-100 compounds quantified in typical measurement campaigns Chebogue Pt, 1993 (NARE) UCLA, 1999-2000 [Chung et al., 2003] [Roberts et al., 1998] WINTER T/S ~ 1+ T/S ~ 1+ SUMMER T/S =1.4-2.2 ΣC2-C7 agree with total measured within measurement uncertainty Suggest that 20-45% NMOC unmeasured in photochemically aged airmasses

  5. TOPICS FOR TODAY • Total Observed Organic Carbon: Concept and Field Observations • Isoprene Emissions: Global Budgets and Predictions • Primary Biological Aerosol Particles and AMAZE-08 • Total Observed Organic Carbon: Concept and Field Observations

  6. PHASES OF ORGANIC CARBON GENERALLY CONSIDERED SEPARATELY OR ‘ONE-WAY’ Oxidation to CO/CO2 Oxidation & Condensation SOA POA Deposition Deposition

  7. CONSIDER TOTAL ORGANIC CARBON (TOC) Oxidation to CO/CO2 TOC Oxidation & Condensation SEMI-VOLATILES Oxidation & Re-volatization CH4 Oxidation Deposition Note: Similar to defining nitrogen family (NOy)

  8. FIELD SITES AND CAMPAIGNS Eleven datasets upwind/over/downwind of North America with simultaneous observations of gas phase and particle phase OC. (Over 130 organic compounds measured) TOC = Σgas-phase OC + aerosol-phase OC TOOC = Total Observed Organic Carbon [μgCm-3 @ STP]

  9. MEAN DAYTIME TOOC OVER NORTH AMERICA Increasing “age” Mean TOOC ranges from 4.0 μgCm-3 (Trinidad Head, cleanest) to 456 μgCm-3 (Mexico City, polluted) and generally decreases with age. Aerosol makes up 3-17% of TOOC.

  10. ORGANIC AEROSOL VS SULFATE OVER NORTH AMERICA Mean POM ranges from < 1 to 24 μgm-3 OC aerosol equal/dominates sulfate at all sites, consistent with NH picture of Zhang et al. [2007]. No discernable trend with “age”.

  11. VARIABILITY OF TOOC OVER NORTH AMERICA Organic carbon concentrations span 2 orders of magnitude. Minimum of 2 μgCm-3 observed at any site. OC aerosol never makes up more than 50% of TOOC. Clean marine sites similar (IPX, BAE) Similar variability for platforms in the NE (RHB, TF, WP3)

  12. WHAT CONTROLS THE VARIABILITY OF TOOC AND ORGANIC AEROSOL? Gas-phase > particle-phase in ALL air masses, highest in NE US CO is a good predictor for TOOC (46-86% of variability), but could be of biogenic or anthropogenic origin in US Sulfate / Aerosol OC relationship driven by: sources, oxidants, loss?

  13. BIOGENIC CONTROL ON TOOC? (SOA?) Anthro sources HCHO Isoprene MVK/MACR Isoprene + oxidation products predict some of TOOC variability (but not OC aerosol) Methanol is best correlated tracer, with longest lifetime (~7days), but not solely biogenic Conundrum: No strong indication of biogenic source of OC aerosol from observations, but 14C indicates most OC aerosol is modern (=SOA?). Biogenic tracers too short-lived? Need an anthropogenic “trigger” for aerosol formation?

  14. QUESTIONS RAISED? • How much of TOC is accounted for in TOOC? (key missing compounds?) • How representative are these observations of the atmosphere? WHAT DO WE NEED? • More routine total NMVOC measurements alongside speciated measurements, and semi-volatiles • More ambient sampling in diverse environments (tropics, Asia, polar) • Time-resolved 14C observations (with aerosol and gas-phase measurements) [Heald et al., ACP, 2008]

  15. TOPICS FOR TODAY • Total Observed Organic Carbon: Concept and Field Observations • Isoprene Emissions: Global Budgets and Predictions • Primary Biological Aerosol Particles and AMAZE-08

  16. ISOPRENE: CONTROLLING AIR QUALITY AND CLIMATE C5 H8: Reactive hydrocarbon emitted from plants (primarily broadleaf trees) Annual global emissions ~ equivalent to methane emissions CLIMATE Depletes OH = ↑ CH4 lifetime + OH O3 AIR QUALITY Beijing IPCC, 2007

  17. METEOROLOGICAL AND PHENOLOGICAL VARIABLES CONTROLLING ISOPRENE EMISSION • LIGHT • Diffuse and direct radiation • Instantaneous and accumulated (24 hrs and 10 days) • TEMPERATURE (Leaf-level) • instantaneous and accumulated (24 hrs, 10 days) T L T PAR AMOUNT OF VEGETATION  Leaf area index (LAI) • LEAF AGE • Max emission = mature • Zero emission = new LAI SUMMER Month SOIL MOISTURE  suppressed under drought [Guenther et al., 2006]

  18. ISOPRENE IN THE FUTURE NPP ↑ Temperature↑ 2000 2100 Methane lifetime increases [Shindell et al., 2007] SOA burden ↑ > 20% [Heald et al., 2008] Surface O3 ↑ 10-30 ppb [Sanderson et al., 2003] Isoprene emissions projected to increase substantially due to warmer climate and increasing vegetation density.  LARGE impact on oxidant chemistry and climate 

  19. A MISSING FACTOR: ISOPRENE EMISSION INHIBITION BY CO2 Long-Term growth environment: gene adaptation Dependent on ambient CO2 Short-term exposure: changes in metabolite pools and enzyme activity Dependent on intercellular CO2(varies with photosynthesis and stomatal resistance) Mick Wilkinson and Russ Monson (UC Boulder) investigated these separately for 4 plant species and developed an empirical parameterization [Wilkinson et al., submitted] To what degree does this CO2 inhibition counteract predicted increases in isoprene (due to T and NPP)?

  20. MODELING FRAMEWORK Community Land Model (CLM3) Datasets: Lawrence and Chase [2007] LAI (MODIS) Plant Functional Types Soil moisture Vegetation Temperature BVOC Algorithms [Guenther et al., 1995; 2006] Monterpenes: GEIA Isoprene: MEGAN Vegetation Meteorology BVOC Emissions Radiation Precipitation Community Atmospheric Model (CAM3) Chemistry Transport Radiation Anthropogenic Emissions, GHG concentrations, SST

  21. 2100 (A1B): CO2 INHIBITION COMPENSATES FOR TEMPERATURE INCREASE Future projected emissions drop from 696 TgC/yr to 479TgC/yr Dotted=2000 Solid=2100 See that ↑in T activity factor ~ compensated by ↓ in CO2 activity factor

  22. CONCLUSION: ISOPRENE EMISSIONS PREDICTED TO REMAIN ~CONSTANT * With fixed vegetation Important implications for oxidative environment of the troposphere…

  23. UNLESS…CO2 FERTILIZATION IS STRONG • CLM DGVM projects a 3x increase in LAI associated with NPP and a northward expansion of vegetation. • [Alo and Wang, 2008] • Isoprene emissions more than double! (1242 TgCyr-1) • BUT, recent work suggests that NPP increases may be overestimated by 74% when neglecting the role of nutrient limitation • [Thornton et al., 2007]

  24. IMPLICATIONS FOR THE PAST? VOSTOK ICE CORE RECORD Vostok data source: Petit et al. [1999] While the balance between T and CO2 is critical to future predictions of isoprene, the large T fluctuations over the last 400 thousand year remain the primary control on isoprene emission in the recent geological past.

  25. TOPICS FOR TODAY • Total Observed Organic Carbon: Concept and Field Observations • Isoprene Emissions: Global Budgets and Predictions • Primary Biological Aerosol Particles and AMAZE-08

  26. PRIMARY BIOLOGICAL AEROSOL PARTICLES (PBAP) ALGAE VIRUSES BACTERIA POLLEN FUNGUS From Andi Andreae (unpublished data) LARGE particles (> 10 µm) PLANT DEBRIS Jaenicke [2005] suggests may be as large a source as dust/sea salt (1000s Tg/yr) Elbert et al. [2007] suggest emission of fungal spores ~ 50 Tg/yr How much does this source contribute to sub-micron OC?

  27. ANY INDICATION OF PBAP IN AMAZE-08? Field site: close to Manaus, Brazil (in Amazonia), Feb-Mar SIMULATED OC Observations = 1-4 µg/m3 Early Feb: observe significantly more organic aerosol than simulated (rain ends this period). PBAP? ***PRELIMINARY AMS obs: Scot Martin, Qi Chen (Harvard). Jose Jimenez, Delphine Farmer (CU Boulder)

  28. OR A ANOTHER EXPLANATION…? Consistent air flow throughout campaign: Feb 1-9 Feb 21-29 MODIS fire counts: Fires in the region during early Feb. These are not reflected in model emission inventories. Acetonitrile concentrations are also elevated early in the campaign … but so is isoprene… No obvious indication of an important sub-micron PBAP in the “pristine” Amazon at this early stage…

  29. ACKNOWLEDGEMENTS Measurement Teams for ICARTT, PAQS, MILAGRO, IMPEX, ITCT-2K2: James D. Allan, Allison C. Aiken, Eric Apel, Elliot L. Atlas, Angela K. Baker, Timothy S. Bates, Andreas J. Beyersdorf, Donald R. Blake, Teresa Campos, Hugh Coe, John D. Crounse, Peter F. DeCarlo, Joost A. de Gouw, Edward J. Dunlea, Frank M. Flocke, Alan Fried, Paul Goldan, Robert J. Griffin, Scott C. Herndon, John S. Holloway, Rupert Holzinger, Jose L. Jimenez, Wolfgang Junkermann, William C. Kuster, Alastair C. Lewis, Simone Meinardi, Dylan B. Millet, Timothy Onasch, Andrea Polidori, Patricia K. Quinn, Daniel D. Riemer James M. Roberts, Dara Salcedo, Barkley Sive, Aaron L. Swanson, Robert Talbot, Carsten Warneke, Rodney J. Weber, Petter Weibring, Paul O. Wennberg, Douglas R. Worsnop, Ann E. Wittig, Renyi Zhang, Jun Zheng, Wengang Zheng NSF, NOAA, NASA Funding for TOOC Measurements NOAA Climate and Global Change Postdoctoral Fellowship CO2 – Isoprene work: Mick Wilkinson, Russ Monson, Clement Alo, Guiling Wang, Alex Guenther AMAZE-08 work: Qi Chen, Scot Martin, Delphine Farmer, Jose Jimenez, Andi Andreae