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Ultrafine Particles and Climate Change

Ultrafine Particles and Climate Change. Peter J. Adams. HDGC Seminar November 5, 2003. Overview. Introduction climate effects of aerosols aerosol size distribution, mass / number concentrations Ultrafine particles and clouds. Overview. Introduction climate effects of aerosols

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Ultrafine Particles and Climate Change

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  1. Ultrafine Particles and Climate Change Peter J. Adams HDGC Seminar November 5, 2003

  2. Overview • Introduction • climate effects of aerosols • aerosol size distribution, mass / number concentrations • Ultrafine particles and clouds

  3. Overview • Introduction • climate effects of aerosols • aerosol size distribution, mass / number concentrations • Ultrafine particles and clouds • Theme: • Aerosol (particulate matter) models developed for PM regulations / visibility are inadequate for newer issues

  4. Theme • Regulations based on mass concentrations (PM10 and PM2.5) • less attention to modeling number concentrations (i.e. ultrafines)

  5. Theme • Regulations based on mass concentrations (PM10 and PM2.5) • less attention to modeling number concentrations (i.e. ultrafines) • Ultrafines cause concern • health effects • climate change

  6. Theme • Regulations based on mass concentrations (PM10 and PM2.5) • less attention to modeling number concentrations (i.e. ultrafines) • Ultrafines cause concern • health effects • climate change • Sources of ultrafines poorly understood: • direct (primary) emission by combustion • atmospheric formation from supersaturated gases (nucleation)

  7. J.T. Houghton: “The science of climate change” Earth’s Energy Budget Anthropogenic GHGs 2.5 W m-2

  8. Aerosols and Climate: Direct Effect Direct Effect: Scattering and absorption by particles photo: SeaWifs website

  9. Aerosols and Climate: Direct Effect Direct Effect: Scattering and absorption by particles Roughly proportional to aerosol mass concentration photo: SeaWifs website

  10. Indirect Effect on Climate Aerosol Particles Cloud Droplets activation / nucleation

  11. Indirect Effect on Climate Aerosol Particles Cloud Droplets Clean Air Polluted Air

  12. Indirect Effect on Climate Aerosol Particles Cloud Droplets “First” indirect effect: albedo “Second” indirect effect: lifetime Clean Air Brighter, more persistent clouds Polluted Air

  13. Aerosols and Climate: Indirect Effect AVHRR observation of indirect effect Red: visible Green: 3.7 mm solar IR Blue: infrared

  14. Aerosols and Climate: Indirect Effect AVHRR observation of indirect effect Power plant Lead smelter Port Oil refineries Red: visible Green: 3.7 mm solar IR Blue: infrared

  15. Aerosol Activation Diameter • “Activation” = formation of cloud droplet • involves a competition between solute and surface tension effects Number

  16. Aerosol Activation Diameter • “Activation” = formation of cloud droplet • involves a competition between solute and surface tension effects Depends on number concentration above “critical diameter” Number

  17. Source: IPCC Third Assessment Report

  18. Typical Number Distribution

  19. Typical Mass Distribution

  20. Previous Work Mechanistic: number of cloud drops depends on number of particles large enough to activate Ultrafine CCN Cloud Droplets (cm-3) Boucher & Lohmann, 1995 Sulfate Mass (mg m-3) Empirical: number of cloud drops correlated with sulfate mass based on observations

  21. Previous Work I: Martin et al. [1994]: -0.68 W/m2 II: Martin et al. with background CCN: -0.40 W/m2 III: Jones et al. [1994]: -0.80 W/m2 IV: Boucher and Lohmann [1995]: -1.78 W/m2 Cloud Droplets (cm-3) Sulfate Mass (mg m-3) “It is argued that a less empirical and more physically based approach is required…” Kiehl et al. [2000]

  22. Aerosol Microphysics Diameter Nucleation Emissions Coagulation Condensation Deposition Number

  23. M1 N1 M2 N2 ... ... mo 2mo … Mass Two-Moment Sectional Algorithm • This work: two moments of the size distribution (mass and number) are tracked for each size bin. • Air quality “regulatory” model: tracks mass in each size bin Tzivion et al., JAS 44, 3139 – 3149, 1987 Adams et al., JGR 10.1029/2001JD001010, 2002

  24. M1 N1 M2 N2 ... ... mo 2mo … Mass Two-Moment Sectional Algorithm • This work: two moments of the size distribution (mass and number) are tracked for each size bin. • Air quality “regulatory” model: tracks mass in each size bin • Two-moment method conserves both mass and number precisely • Prevents numerical diffusion present in single-moment methods • Excellent size resolution: 30 sections from .01 mm to 10 mm Tzivion et al., JAS 44, 3139 – 3149, 1987 Adams et al., JGR 10.1029/2001JD001010, 2002

  25. Aerosol Microphysics Coagulation: • ~30,000 grid cells • 1 year • Adaptive time steps General Dynamic Equation Condensation:

  26. Model Structure • Aerosol composition • Current: Sulfate / Sea-salt • Development: Organic / Elemental carbon • Future: Mineral dust • Processes • Emissions • Chemistry • Microphysics • Cloud processing • Size-resolved dry / wet deposition

  27. Size Distributions

  28. Size Distributions

  29. Van Dingenen et al., 1995 JGOFS cruise Sep/Oct, 1992

  30. CCN (cm-3): 0.2% Supersaturation

  31. Uncertainties • Particulate Emissions • Most sulfate aerosol mass results from gas-phase SO2 emissions • Particulate sulfate: <5% of anthropogenic sulfur emissions • Nucleation of new aerosol particles • Important uncertainties in mechanism and rate • Both processes contribute significant numbers of small particles • insignificant contribution to sulfate mass • important contribution to aerosol number concentrations and size distributions

  32. Sensitivity Scenarios • Base Case • 1985 sulfur emissions • all emissions as gas-phase SO2 • nucleation based on critical concentration from binary (H2SO4-H2O) theory • Primary Emissions • 3% of sulfur emissions as sulfate • Enhanced Nucleation • critical H2SO4 concentration factor of 10 lower • Pre-industrial • no anthropogenic emissions

  33. Vertical Profiles

  34. CCN Vertical Profiles

  35. CCN Vertical Profiles

  36. Ultrafine Particles and CCN Diameter Number

  37. Ultrafine Particles and CCN Diameter Condensation to accumulation mode does not produce new CCN Condensation Number Growth

  38. Ultrafine Particles and CCN Diameter Additional ultrafine particles result in enhanced CCN formation Condensation to accumulation mode does not produce new CCN Condensation Number Growth

  39. Impact of Particulate Emissions SO2 emissions SO2/SO42- emissions

  40. Summary and Conclusions • A “regulatory” model (mass concentrations) omits important physics • Ultrafine particles have a significant impact on clouds via CCN number concentrations • Require better knowledge of sources of ultrafines • nucleation • “primary” emissions from combustion • Future changes in ultrafine emissions?

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