Presentation on theme: "Surface-Atmosphere fluxes Surface-Atmosphere fluxes Alex Guenther Atmospheric Chemistry Division National Center for Atmospheric Research National Center."— Presentation transcript:
Surface-Atmosphere fluxes Surface-Atmosphere fluxes Alex Guenther Atmospheric Chemistry Division National Center for Atmospheric Research National Center for Atmospheric Research Boulder CO, USA Outline Introduction Introduction Major cycles Major cycles Recent scientific advances and challenges Recent scientific advances and challenges
1. Introduction What is in the atmosphere? How did it get there? How does it leave?
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 ( %), CFCs H2O, O3, CO, non-methane VOC, NOy, NH3, NO3, NH4, OH, HO2, H2O2, CH2O, SO2, CH3SCH3, CS2, OCS, H2S, SO4, HCN Well mixed Variable
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, N2O 1960s: 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.
Earth Cosmo s Where does the atmosphere come from? 1.Original atmosphere 2.Dead planet 3.Living planet 4.Anthropocene
Organic aerosol processes Photo- oxidant processes Cloud processes Global Biogeochemical Cycles Carbon Cycle Nitrogen Cycle Water & Energy Cycles Ozone and N deposition NO/NH3 emission CO 2 H2OH2O NO y NH 3 Precipitation and solar radiation Latent and sensible heat Biological particles and VOC emissions Air Quality: ozone and particles Weather/Climate: Temperature, sunshine, precipitation Ecosystem Health: Productivity, diversity, water availability Anthropogenic Natural
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.
Time (seconds) Eddy Covariance Flux Data Concentration and wind speed measurements above a forest canopy Sampling rate = 10 Hz The 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. Concentration Vertical wind speed Flux
Enclosure measurements 0 zizi MIXED LAYER Conc. Profile 0 HEIGHT Emission (deposition) rate is related to the increase (decrease) in mass Static: change with time Dynamic: difference between inflow and outflow Boundary Layer Budget Imaginary box May need to consider - chemical loss/production - horizontal advection - non-stationary Mass Balance Budgets
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).
Water Cycle: source of OH in the atmosphere Separating evapotranspiration into evaporation and transpiration components is an active area of research Atmospheric Chemistry and Global Change (1999). Brasseur et al. (editors).
THE NITROGEN CYCLE ATMOSPHERE N2N2 NO HNO 3 NH 3 /NH 4 + NO 3 - orgN BIOSPHERE LITHOSPHERE combustion lightning oxidation deposition assimilation decay nitrification denitri- fication biofixation burial weathering fixation SOIL/OCEAN Daniel Jacob 2008
Atmospheric ammonia sources and sinks (Tg per year) Sources Domestic animals: 21 Human excrement: 2.6 Industry: 0.2 Fertilizer losses: 9 Fossil fuel combustion: 0.1 Biomass Burning: 5.7 Soil: 6 Wild animals: 0.1 Ocean:8.2 Sinks Wet precipitation (land): 11 Wet precipitation (ocean): 10 Dry deposition (land): 11 Dry deposition (ocean): 5 Reaction with OH: 3 From Brasseur et al Does it add up? Sources: 52.9 Tg Sinks: 40 Tg This is good agreement considering the uncertainties of factors of 2 or more Anthropogenic Natural
Atmospheric NOx sources and sinks (Tg per year) Sources Aircraft: 0.5 Fossil fuel combustion: 20 Biomass Burning: 12 Soil: 20 Lightning: 8 NH3 oxidation: 3 Stratosphere: 0.1 Ocean:<1 Sinks Wet precipitation (land): 19 Wet precipitation (ocean): 8 Dry deposition: 11 From Brasseur et al Does it add up? Sources: 64 Tg Sinks: 43 Tg This is good agreement considering the uncertainties of factors of 2 or more
Vegetation and soils 0.4 to 1.2 Tg of H2S, DMS, OCS, CS2, DMDS The Sulfur Cycle Atmosphere Wet deposition Tg of SO2, SO4 SO2, SO4 Dry deposition Tg of SO2, SO4 H2S, DMS, OCS, CS2, DMDS Anthropogenic Tg of SO2, sulfates Volcanoes 7-10 Tg of H2S, SO2, OCS Ocean Tg of DMS, OCS, CS2, H2S Biomass burning 2-4 Tg of H2S, SO2, OCS
Vegetation and soils VOC, CH4, CO2, CO The Carbon Cycle Atmosphere Wet precipitation CO2 Dry deposition and photosynthesis VOC, CH4, CO Anthropogenic VOC, CH4, CO2, CO Ocean VOC, CH4, CO2, CO Biomass burning VOC, CH4, CO2, CO
Carbon Emissions: Methane
There are hundreds of BVOCs emitted from Vegetation flowers ~100’s of VOCs cell walls MeOH, HCHO phytohormones e.g. ethylene, DMNT cell membranes fatty acid peroxidation wound-induced OVOCs resin ducts / glands terpenoid VOCs cytoplasm/chloroplast C1-C3 metabolites chloroplast terpenoid VOCs
3. Surface- atmosphere exchange: Recent scientific advances and challenges
How will biogenic VOC emissions respond to future changes in landcover, temperature and CO2? Landcover, temperature and CO2 are changing Biogenic VOC (BVOC) emissions are very sensitive to these changes But it is difficult to even predict the sign of future changes in BVOC emissions
NCAR CCSM Future Landcover Change Predictions Mix Shrub/Grass1461% Bare Sparse Veg.1317% Dryland Crop.267% Urban205% Snow or Ice-100% Mixed Tundra-100% Wooden Tundra-100% Wooded Wetland-100% Evergrn. Broadlf.-100% Current Future (2100) Percent land cover changes
USDA predictions of tree species composition changes in the eastern U.S. USDA climate change tree atlas Current estimates are based on observations (FIA dist. Data). Future is based on 2x CO 2 equil. climate vars from 3 GCMs (PCM, GFDL, HAD) Provides future state level estimates of 135 tree species for eastern U.S. Large increase in oak trees which have very high isoprene emissions
Landcover change could result in a large regional increases and decreases in U.S. isoprene emissions High = 5600 Low = (Future Isoprene – Current Isoprene Emission factors g m -2 h -1 ) The overall impact is a large decrease in U.S. average isoprene emission factor (~800 g m -2 h -1 ) This is mostly due to a predicted decrease in broadleaf tree coverage High = 0% Low = 30% Broadleaf tree change
Temperature ( o C) Isoprene emission activity Short-term response Short-term and Long-term response BVOC emissions will increase with increasing temperatures but 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 component Guenther et al. 2006
Decreasing emissions are expected for increasing CO 2 but the magnitude is uncertain and there may be indirect CO 2 effects (increasing LAI, changing species composition) Heald et al. 2008
As a result of these uncertainties: Different models have substantially different predictions of future changes in biogenic VOC emissions Year 2050 BVOC – Year 2000 BVOC (g/m2/day) Weaver et al These differences have a large impact on predicted future ozone and particles
Hallquist et al., ACP, 2009 SOA: 134 TgC/yr 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, 2007 large uncertainty in estimates of Volatile Organic Carbon (VOC) deposition
Resistance Model CACA CUCCUC CSCS C LC CGCG RARA RBRB RSRS RMRM RLURLU R SL R ML R AG R GS : R C C for estimating dry deposition Aerodynamic resistance (turbulent diffusion) Boundary layer resistance (molecular diffusion) Canopy resistance
We evaluated model performance for oxyVOC with measurements at a wide range of field sites
Our field flux measurements indicated that model R c for oxygenated VOC is too high. traditional model modified model Why are we underestimating VOC deposition?
The models assume that oVOC deposition is just a physical process FL0 growth chamber experiments with Populus trichocarpa x deltoides
Stomata ~20-30 μm FL0 growth chamber experiments with Populus trichocarpa x deltoides We suspected that the high deposition rates were due to a biological process.
qPCR (quantitative polymerase chain reaction) ROS conversion of carbonyls (AAO2, ALDH2) and oxidative stress repair (MsrA) a-carbonic acid synthase (ACS) carboxylic acid oxidase (ACO1) biotic and a-biotic stress markers This tells us that the plants turned on these genes to actively take up oVOC
Global increase in dry deposition: ~36% Global decrease in wet deposition: ~7% Change in oVOC dry deposition when we put the new model in NCAR/MOZART model This has a significant impact on regional atmospheric chemistry