Presentation on theme: "Surface-Atmosphere fluxes"— Presentation transcript:
1 Surface-Atmosphere fluxes Alex Guenther Atmospheric Chemistry DivisionNational Center for Atmospheric ResearchBoulder CO, USAOutlineIntroductionMajor cyclesRecent scientific advances and challenges
2 1. IntroductionWhat is in the atmosphere? How did it get there? How does it leave?
3 What is in the Atmosphere? N2 (78.084%), O2 (20.948%), Ar (0.934%), CO2 (0.039%), Ne (0.0018%), He ( %), CH4 ( %), H2 ( %), N2O ( %), Halogens ( %), CFCsH2O, O3, CO, non-methane VOC, NOy, NH3, NO3, NH4, OH, HO2, H2O2, CH2O, SO2, CH3SCH3, CS2, OCS, H2S, SO4, HCNWell mixedVariable
4 What is in the atmosphere? 1950s: Atmosphere is % composed of N2, O2, CO2, H2O, He, Ar, Ne. All are inert! (no chemistry). O3 in the stratosphere. Trace CH4, N2O1960s: Recognized that reactive compounds in the atmosphere were important even at extremely low levels.1970s: Regional air quality becomes a major research topic.1980s: Global atmospheric chemistry becomes a major research topic.
5 Where does the atmosphere come from? Original atmosphereDead planetLiving planetAnthropoceneCosmosAtmosphereEarth
6 Global Biogeochemical Cycles AtmosphereAir Quality:ozone and particlesWeather/Climate:Temperature, sunshine, precipitationEcosystem Health:Productivity, diversity, water availabilityCloud processesOrganic aerosol processesPhoto-oxidant processesBiological particles and VOC emissionsH2OCO2NOyNH3Latent and sensible heatNO/NH3 emissionWater & Energy CyclesCarbon CycleNitrogen CyclePrecipitation and solar radiationOzone and N depositionEarthAnthropogenicNaturalSurface
7 How do we measure surface exchange? Eddy covariance: The flux is related to the product of fluctuations in vertical wind and concentration. This is the only direct measurement.Gradient: The flux is related to vertical concentration gradient.Mass balance (Inverse Model): The flux is related to a concentration or concentration change.
8 Eddy Covariance Flux Data Concentration and wind speed measurements above a forest canopy Sampling rate = 10 HzThe flux of a trace gas is calculated as the covariance between the instantaneous deviation of the vertical wind velocity (w’) and the instantaneous deviation of the trace gas (c’) for time periods between 30 min and an hour.ConcentrationVertical wind speedFluxTime (seconds)
10 Enclosure measurements Mass Balance BudgetsEnclosure measurementsEmission (deposition) rate is related to the increase (decrease) in massStatic: change with timeDynamic: difference between inflow and outflowBoundary Layer BudgetziImaginary boxMay need to consider- chemical loss/production- horizontal advection- non-stationaryMIXED LAYERHEIGHTConc.Profile
11 2. The Cycles From the earth surface to the atmosphere and back again Chapter 5. Trace Gas Exchanges and Biogeochemical Cycles. In: Atmospheric Chemistry and Global Change (1999). Brasseur et al. (editors).
12 Water Cycle: source of OH in the atmosphere Separating evapotranspiration into evaporation and transpiration components is an active area of researchAtmospheric Chemistry and Global Change (1999). Brasseur et al. (editors).
13 THE NITROGEN CYCLE N2 NO HNO3 orgN NH3/NH4+ NO3- ATMOSPHERE fixation combustionlightningN2NOoxidationHNO3denitri-ficationbiofixationdepositionorgNdecayBIOSPHERENH3/NH4+NO3-assimilationnitrificationSOIL/OCEANburialweatheringLITHOSPHEREDaniel Jacob 2008
14 Atmospheric ammonia sources and sinks (Tg per year) AnthropogenicSourcesDomestic animals: 21Human excrement: 2.6Industry: 0.2Fertilizer losses: 9Fossil fuel combustion: 0.1Biomass Burning: 5.7Soil: 6Wild animals: 0.1Ocean: 8.2SinksWet precipitation (land): 11Wet precipitation (ocean): 10Dry deposition (land):Dry deposition (ocean):Reaction with OH:NaturalDoes it add up?Sources: 52.9 TgSinks: 40 TgThis is good agreement considering the uncertainties of factors of 2 or moreFrom Brasseur et al. 1999
15 Atmospheric NOx sources and sinks (Tg per year) Aircraft: 0.5Fossil fuel combustion: 20Biomass Burning: 12Soil: 20Lightning: 8NH3 oxidation: 3Stratosphere: 0.1Ocean: <1SinksWet precipitation (land): 19Wet precipitation (ocean): 8Dry deposition:Does it add up?Sources: 64 TgSinks: 43 TgThis is good agreement considering the uncertainties of factors of 2 or moreFrom Brasseur et al. 1999
16 The Sulfur Cycle Atmosphere SO2, SO4 H2S, DMS, OCS, CS2, DMDS Wet deposition Tg of SO2, SO4Dry deposition50-75 Tg of SO2, SO4Vegetation and soils 0.4 to 1.2 Tg of H2S, DMS, OCS, CS2, DMDSVolcanoes 7-10 Tg of H2S, SO2, OCSAnthropogenic Tg of SO2, sulfatesBiomass burning 2-4 Tg of H2S, SO2, OCSOcean Tg of DMS, OCS, CS2, H2S
17 The Carbon Cycle Atmosphere CO2 VOC, CH4, CO Dry deposition and photosynthesisWet precipitationVegetation and soils VOC, CH4, CO2, COAnthropogenic VOC, CH4, CO2, COBiomass burning VOC, CH4, CO2, COOcean VOC, CH4, CO2, CO
19 There are hundreds of BVOCs emitted from Vegetation flowers~100’s of VOCscell wallsMeOH, HCHOphytohormonese.g. ethylene, DMNTcell membranesfatty acid peroxidationwound-induced OVOCsresin ducts / glandsterpenoid VOCscytoplasm/chloroplastC1-C3 metaboliteschloroplast19
20 Dry deposition and soil microbe uptake HalogensAtmosphereBr-, I-, Cl-CH3Cl, CH3Br, CH3IDry deposition and soil microbe uptakeVegetation and soilsAnthropogenicBiomass burningOcean
21 3. Surface-atmosphere exchange: Recent scientific advances and challenges
22 How will biogenic VOC emissions respond to future changes in landcover, temperature and CO2? Landcover, temperature and CO2 are changingBiogenic VOC (BVOC) emissions are very sensitive to these changesBut it is difficult to even predict the sign of future changes in BVOC emissions
23 NCAR CCSM Future Landcover Change Predictions CurrentFuture (2100)One unique aspect in this study is the consideration LULC changes in the future. Under the A2 scenario we estimated climate and human influence have large impacts on future LULC in the US.Percent land cover changesSnow or Ice-100%Mixed TundraWooden TundraWooded WetlandEvergrn. Broadlf.Mix Shrub/Grass1461%Bare Sparse Veg.1317%Dryland Crop.267%Urban205%
24 USDA predictions of tree species composition changes in the eastern U USDA predictions of tree species composition changes in the eastern U.S.Large increase in oak trees which have very high isoprene emissionsUSDA climate change tree atlasCurrent estimates are based on observations (FIA dist. Data). Future is based on 2x CO2 equil. climate vars from 3 GCMs (PCM, GFDL, HAD)Provides future state level estimates of 135 tree species for eastern U.S.
25 (Future Isoprene – Current Isoprene Emission factors mg m-2 h-1) Landcover change could result in a large regional increases and decreases in U.S. isoprene emissionsHigh = 5600Low = -5900(Future Isoprene – Current Isoprene Emission factors mg m-2 h-1)This is mostly due to a predicted decrease in broadleaf tree coverageHigh = 0%Low = 30%Broadleaf tree changeThe overall impact is a large decrease in U.S. average isoprene emission factor (~800 mg m-2 h-1)
26 BVOC emissions will increase with increasing temperatures 3but we don’t know if the response will be similar to what is observed for short-term variations or if there will be an additional long-term componentShort-term and Long-term response2.52Isoprene emission activity1.5Short-term response30354045Guenther et al. 2006Temperature (oC)
27 Decreasing emissions are expected for increasing CO2 but the magnitude is uncertain and there may be indirect CO2 effects (increasing LAI, changing species composition)Heald et al. 2008
28 of future changes in biogenic VOC emissions As a result of these uncertainties: Different models have substantially different predictionsof future changes in biogenic VOC emissionsYear 2050 BVOC – Year 2000 BVOC (g/m2/day)These differences have a large impact on predicted future ozone and particlesWeaver et al. 2009
29 Why do recent “state-of-the-art” estimates of secondary organic aerosol (SOA) production differ by a factor of 5?Goldstein and Galbally, ES&T, 2007Hallquist et al., ACP, 2009SOA: 134 TgC/yrlarge uncertainty in estimates of Volatile Organic Carbon (VOC) deposition
31 We evaluated model performance for oxyVOC with measurements at a wide range of field sites
32 Why are we underestimating VOC deposition? Our field flux measurements indicated that model Rc for oxygenated VOC is too high.Why are we underestimating VOC deposition?traditional modelmodified model
33 The models assume that oVOC deposition is just a physical process FL0 growth chamber experiments with Populus trichocarpa x deltoides
34 FL0 growth chamber experiments with Populus trichocarpa x deltoides Stomata ~20-30 μmWe suspected that the high deposition rates were due to a biological process.FL0 growth chamber experiments with Populus trichocarpa x deltoides
36 qPCR (quantitative polymerase chain reaction) biotic and a-biotic stress markersThis tells us that the plants turned on these genes to actively take up oVOCconversion of carbonyls (AAO2, ALDH2)and oxidative stress repair (MsrA)a-carbonic acid synthase (ACS)carboxylic acid oxidase (ACO1)ROS
37 Change in oVOC dry deposition when we put the new model in NCAR/MOZART model This has a significant impact on regional atmospheric chemistryGlobal increase in dry deposition: ~36%Global decrease in wet deposition: ~7%