Organic Carbon in the Troposphere: How much is there and can we predict the future? NCAR Seminar May 19, 2008 Colette L. Heald* *With acknowledgements to many people at the end!
TOPICS FOR TODAY I.Total Observed Organic Carbon: Concept and Field Observations II.Isoprene Emissions: Global Budgets and Predictions I.Total Observed Organic Carbon: Concept and Field Observations
CARBON IN THE ATMOSPHERE CO 2 (820 PgC) CH 4 (4 PgC) Organic Carbon (~10s TgC) + Short-lived (reactive) BUT important climate role : direct aerosol radiative forcing indirect via CCN oxidant chemistry (O 3, CH 4, …) CO (150 TgC)
RECONCILING THE ORGANIC AEROSOL BUDGET SOA measured/modeled = 4-100! [Volkamer et al., 2006] Global measurements (surface μgm -3 ) [Zhang et al., 2007] Good agreement between global model and IMPROVE observations for OC aerosol concentrations in the US [Park et al., 2003] OBS MODEL
GAS-PHASE CARBON MASS CLOSURE? 2847 organic compounds identified in the atmosphere [Graedel et al., 1986] ~10 4 compounds estimated to be present [Goldstein and Galbally, 2006] compounds quantified in typical measurement campaigns [Roberts et al., 1998] Chebogue Pt, 1993 (NARE) ΣC 2 -C 7 agree with total measured within measurement uncertainty T/S ~ 1+ UCLA, WINTER SUMMER T/S ~ 1+ T/S = Suggest that 20-45% NMOC unmeasured in photochemically aged airmasses [Chung et al., 2003]
PHASES OF ORGANIC CARBON GENERALLY CONSIDERED SEPARATELY OR ‘ONE-WAY’ Oxidation & Condensation POA SOA Deposition Oxidation to CO/CO 2
CONSIDER TOTAL ORGANIC CARBON (TOC) Oxidation & Condensation Deposition Oxidation to CO/CO 2 Oxidation & Re-volatization TOC Note: Similar to defining nitrogen family (NO y ) SEMI-VOLATILES CH 4 Oxidation
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 STP]
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.
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”.
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)
WHAT CONTROLS THE VARIABILITY OF TOOC? 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 (see next slide) Sulfate / Aerosol OC relationship driven by: sources, oxidants, loss?
BIOGENIC CONTROL ON TOOC? (SOA?) Isoprene HCHO 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 Anthro sources Conundrum: No strong indication of biogenic source of OC aerosol from observations, but 14 C indicates most OC aerosol is modern (=SOA?). Biogenic tracers too short- lived? Need an anthropogenic “trigger” for aerosol formation?
QUESTIONS RAISED? 1.More routine total NMVOC measurements alongside speciated measurements, and semi-volatiles 2.More ambient sampling in diverse environments (tropics, Asia, polar) 3.Time-resolved 14 C observations (with aerosol and gas-phase measurements) 1.How much of TOC is accounted for in TOOC? (key missing compounds?) 2.How representative are these observations of the atmosphere? WHAT DO WE NEED? [Heald et al., ACP, 2008]
TOPICS FOR TODAY I.Total Observed Organic Carbon: Concept and Field Observations II.Isoprene Emissions: Global Budgets and Predictions
ISOPRENE: CONTROLLING AIR QUALITY AND CLIMATE C 5 H 8 : Reactive hydrocarbon emitted from plants (primarily broadleaf trees) Annual global emissions ~ equivalent to methane emissions + OH O3O3 Depletes OH = ↑ CH 4 lifetime IPCC, 2007 Beijing CLIMATE AIR QUALITY
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 PAR LL TT [Guenther et al., 2006] SOIL MOISTURE suppressed under drought AMOUNT OF VEGETATION Leaf area index (LAI) Month LAI SUMMER LEAF AGE Max emission = mature Zero emission = new
ISOPRENE IN THE FUTURE Isoprene emissions projected to increase substantially due to warmer climate and increasing vegetation density. LARGE impact on oxidant chemistry and climate NPP ↑ Temperature↑ Surface O 3 ↑ ppb [Sanderson et al., 2003] Methane lifetime increases [Shindell et al., 2007] SOA burden ↑ > 20% [Heald et al., 2008]
A MISSING FACTOR: ISOPRENE EMISSION INHIBITION BY CO 2 Long-Term growth environment: gene adaptation Dependent on ambient CO 2 Short-term exposure: changes in metabolite pools and enzyme activity Dependent on intercellular CO 2 (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 CO 2 inhibition counteract predicted increases in isoprene (due to T and NPP)?
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 Community Atmospheric Model (CAM3) Chemistry Transport Radiation BVOC Emissions Vegetation Meteorology Radiation Precipitation Anthropogenic Emissions, GHG concentrations, SST
2100 (A1B): CO 2 INHIBITION COMPENSATES FOR TEMPERATURE INCREASE Future projected emissions drop from 696 TgC/yr to 479TgC/yr See that ↑in T activity factor ~ compensated by ↓ in CO 2 activity factor Dotted=2000 Solid=2100
CONCLUSION: ISOPRENE EMISSIONS PREDICTED TO REMAIN ~CONSTANT Important implications for oxidative environment of the troposphere… * With fixed vegetation
UNLESS…CO 2 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]
IMPLICATIONS FOR THE PAST? VOSTOK ICE CORE RECORD While the balance between T and CO 2 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. Vostok data source: Petit et al. [1999]
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 CO 2 – Isoprene work: Mick Wilkinson, Russ Monson, Clement Alo, Guiling Wang, Alex Guenther