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Topic 8: Composition of Ice Nuclei

Topic 8: Composition of Ice Nuclei. Co- Leaders : Zamin Kanji & Heike Wex Contributors : Yvonne Boose , Paul DeMott Andrea Flossmann , and Martin Gallagher ICCP Workshop on Measurements of Ice in Clouds July 5-6, 2013, ETH - Zürich. Types Of Ice Clouds/Cirrus.

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Topic 8: Composition of Ice Nuclei

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  1. Topic 8: Composition of Ice Nuclei Co- Leaders: Zamin Kanji & Heike Wex Contributors: Yvonne Boose, Paul DeMott Andrea Flossmann, and Martin Gallagher ICCP Workshop on Measurements of Ice in Clouds July 5-6, 2013, ETH - Zürich

  2. Types Of Ice Clouds/Cirrus From Cziczo and Froyd (2013, in review)

  3. Techniques Used For Compositional Analysis of IRs/IN • IR flow directed into single particle instruments • In – situ: Single Particle Mass Spectrometry or Soot Photometry • Particle Analysis by Laser Mass Spectrometry (PALMS) • Aerosol Time of Flight Mass Spectrometry (ATOFMS) • Particle Soot Absorption Photometer (PSAP) • Offline: Electron Microscopy (EM) for imaging and morphology with Energy Dispersive X-ray (EDX) spectroscopy for compositional analysis

  4. Motivation for Studying IN Composition • Surface composition will influence functional group interaction with water/vapour (Pruppacher and Klett, 1997) • Clear-air particles subjected to known ice formation conditions show compositional bias toward freezing mechanisms (DeMott et al. 2003) Hom. reg. T < -38 °C, Het. reg. T > -38 °C. Storm Peak, PCVI to select IC and PALMS for composition

  5. Motivation for Studying IN Composition Pure organic IN contained evidence of oxidation Raman Spectroscopy, Coarse Mode >2µm, mode size 4 ±1.5µm AvgSice = 1.04 ± 0.05 and independent of T 210 - 230 K PALMS, Fine Mode <2µm, T = 230 ± 1 K Sice= 1.4 ± 0.05 Majority of particles in both modes are internally mixed with organics

  6. Summary of Key Outstanding Issues From July 2010 Workshop • Respective roles of homogeneous and heterogeneous ice formation in atmosphere • Aerosol composition can directly influence mode • Relationship between ice nuclei (IN) and ice crystal (IC) number • Any other types of IN that are not accounted for such as Bio-IN (Heike) • IN concentration << IC concentration • Secondary ice formation processes, how effective? • Freezing mechanisms below 205 K

  7. Measurement Sites for IN and Ice Residuals (IRs) • Mountain top sites - Jungfraujoch Station, Switzerland • High altitude stations - Storm Peak, Colorado, USA • In-flight sampling in-cloud and compared to clear air particles using CVI to sample IRs • Impaction to collect on filter or EM grids (offline) • Morphology and cold stage ice nucleation studies • CVI, Phase separator (on ground) – to sample IRs in mixed-phase clouds

  8. Ice Crystal Property Characterization From Cziczo and Froyd (2013, in review) Reduce shatter Re-design flow lines to reduce wake capture

  9. Counter Virtual Flow (CVI) Sampling From Cziczo and Froyd (2013, in review)

  10. Challenges With Current Techniques From Cziczo and Froyd (2013, in review) Ice crystal size limitation – missing larger diameter crystals due to CVI upper limit cut point

  11. Key Issues: Measurement of IN Composition • Multiplication and shattering on inlet (overcome?) • Small particles captured in wake of ice crystal • Inlet material contamination in IR composition (overcome?) • Sampling of residuals with CVI and re-activating as IN • Re-suspension of particles adhered to inlet when sampling ice crystals • Limited sampling of mixed-phase cloud IRs • Phase separator needed for aircraft studies • Lower size limit of EM/EDX (120 nm) and SPMS (100-200 nm)

  12. Summary of Studies Since 2010 Classes of IN detected (in-situ) in Atmosphere in Contrails or Cirrus

  13. Cziczo et al. (2004/2013), Cirrus Anvils, 12 Flights Taken from Cziczo et al. (2013) Composition aids in inference of dominant mechanism forming the cirrus cloud

  14. Cziczo et al. (2004), Cirrus Anvils, 12 Flights(CRYSTAL-FACE) • 2 flights encountered the Saharan Air Layer (SAL) • First study to use SPMS with CVI • CVI range 5 – 22 µm and IRs 0.2 – 2 µm with IR mode between 0.3 – 1 µm (larger particles corresponding to SAL) • Out-of-cloud (2126) and interstitial (299) observed to be >95% sulphate/organic/biomass • IRs (211) 9 of 12 flights were >60% mineral dust/fly ash and sea salt, 2 flights in SAL >60% mineral dust, 1 flight (127) with IRs mostly sulphate/organics/biomass was consistent with hom. freez.

  15. Froyd et al. (2010), Subvisual Cirrus • Tropical Tropopause (over Costa Rica) • CVI with gold plating, IC range 5 – 25 µm diameter • IC# < 50/L, cloud probe designed for reduced shatter • 127 IRs compared to 873 Interstitial aerosol • Composition suggests hom. frez. but IC# not typical of hom. freez.

  16. Froyd et al. (2010), Subvisual Cirrus • Het. frez. of anhydrous salts and/or glassy organic aerosols maybe playing a role • Gold plated CVI was successfully used to show that ambient particles mixed with gold was produced as an artifact • Spectral feature attributed to inlet was minor Inlet plating modification successfully allows us to correct/report IRs chemical composition

  17. Cziczo et al. (2013) • BC not important for Het. cirrus cloud formation • Biological particles not implied in cirrus particles • 94% of cloud encounters inferred to form through het. ice nucleation

  18. Ice Forming Mechanism InferredNot Detected in-situ • The study of Ice Nuclei (IN) composition allows inference of ice forming mechanism • Soluble material vs insoluble species • Characterizing ice crystal (IC) properties such as size, and number densities within a cloud also suggests potential mechanism by which cloud is formed • Smaller crystals vs. larger crystals • Lower IN# vs. higher IN# • Homogeneous vs. Heterogeneous ice nucleation

  19. Classes of IN detected (offline) in Atmosphere in Cirrus/Contrails or Mixed-Phase Clouds

  20. Cziczo et al. (2013), MACPEX, Anvil and Synoptic Cirrus • Houston, Texas • Advanced CVI with Ne counter flow • Increased heat transfer and viscosity • Longer stopping distance • Inline laser to sublimate crystals • Composition and size/morphology with SEM/EDX • 433 IRs with size mode 0.3 – 0.5 µm • Supersaturationwrt ice near cirrus 120-140% • Cloud probe IC# < 200/L • Het. freezing inferred to be dominant

  21. Composition of IN detected (offline) • Only one case of a cloud formed from hom. freez. cloud observed during MACPEX Cziczo et al. (2013)

  22. Ebert et al. (2011), JFJ – MPCs, CLACE-5 • Ice – CVI used at -12 to -27 °C, presence of ice only clouds cannot be excluded • IC range 5 – 20 µm diameter, 3-cloud events, 3600 IRs and interstitial particle d > 0.7 µm • Except cloud event 1, d> 60 nm • Upper limit restricted to 20 µm – limit scavenging • Chemical composition, morphology, internal mixing state by ESEM – EDX • Mineralogical composition and Pb-containing particles by TEM – EDX and HR – TEM – EDX resp.

  23. Composition of IN detected (offline) Significantly enriched in IRs: Pb-containing, C,O,S and complex mixtures Anthropogenic components increase IN efficiency in mixed phase clouds at JFJ Ebert et al. (2011)

  24. PACDEX – Reconciliation of IN and IC#Stith et al. (2011) Warm Clouds • Sampling at – 24 to -29 °C, CVI for cloud residuals, CFDC at ambient conditions for IN, IC with 2DC • No shroud, reduced shattering • Mechanism inferred by comparing IN# to IC# • Simultaneous measurements • Biomass burning particles enhanced in ice phase via non-nucleation scavenging • Ice nucleating particles were slightly enhanced in calcium and less by sea-salt

  25. Questions Answered Since 2010 • Composition of IRs with signatures showing more than one class of compounds • internal mixing before ice nucleation, or • non-nucleation scavenging by ice crystal? • Influence on size distribution of IR • Ice formation mechanism inferred (hom. vs het.) • Composition information combined with ice crystal properties • IC size distributions and numbers by modifying inlet • Reduced shattering, increased sampling size range • Inlet contamination detectable in IR composition • Using known metal coating such as Au

  26. Open Questions Today • in-situ detection of ice crystals in MPCs • Particles remaining immersed vs those that freeze? • Current studies limited to ground sites • Large ICs not sampled – what is the composition of IR in these crystals – likely het. IN? • In-cloud sampling occurs well after ice nucleation? • Specific conditions for ice nucleation in aircraft studies? • In Cirrus are one or more of the het. mechanisms e.g. deposition vs. immersion distinguishable? • IR composition => hom. freez., IC# => het. freez. • Does indirect inference of mechanism always work? • Charecterization of shattering of crystals on inlet • Active area of research

  27. Anticipated Challenges for Future IN Composition Measurements • Develop phase-separator that can fly in mixed-phase clouds? • Measurements of near cloud RH/out-of-cloud RH are challenging but important to help decipher ice forming mechanism • Modification of CVI to include sampling of IR from large 2nd mode of anvil cirrus crystals? • Develop inlet with longer stopping distance to allow enough sublimation? Or different gas (neon), folding design? (used in MACPEX)

  28. Role of Lab Studies for IN Composition • Identifying size dependency • Larger particles – better IN • Accounting for size greatly reduced uncertainty in observed vs. predicted IN (DeMott et al. 2010) • Relative role of composition vs. size is still unclear • But how important in term of closure studies • Composition specific parameterizations

  29. Role of Lab Studies for IN Composition • Identifying types of het. IN in controlled T - RH conditions • Bio > MD > crystalline salts/organics/glassy > BC • Developing parameterisations based on nucleation rate or surface area • Type of param. depends on IN composition (Heike) • Relative role of composition vs. size is still unclear • Relative role of surface composition vs. morphology is also unclear • Maybe important for only some het. modes

  30. Hand over to Heike

  31. Back Up Slides

  32. Older Studies Classes of IN detected (in-situ) in Atmosphere in Contrails or Cirrus

  33. Ström and Ohlsson (1998), Contrails • Southern Germany, 5 flights • CVI –and diameter up to 60 µm • Absorbing aerosol detected using particle soot absorption photometer • Higher ice crystal densities in areas with increased mass of absorbing particles • Enhanced ratio of IC# to particle number ranged between 1.6 – 2.8 • Does this mean BC causes enhanced ice nucleation, or scavenging processes played a role?

  34. Pratt et al. (2009), 1 Orographic Cloud • Wyoming, altitude ~ 8km, temp of -31 to -34 °C • CVI lower cut point 7 µm diameter • Composition obtained by A-ATOFMS • 46 IRs sampled between 0.14 – 0.7 µm diameter • Biological material, inferred from the presence of organic carbon, nitrogen and phosphate • Biological and mineral dust IRs enhanced by a factor of 3 compared to particle composition in clear air • Het. ice formation or preferential scavenging suggested

  35. Composition of IN detected (in-situ) • a) Biological b) Mineral Dust Pratt et al. (2009)

  36. Older Studies Classes of IN detected (offline) in Atmosphere in Contrails or Cirrus

  37. Heitzenberg et al. (1996): First composition measurements of Cirrus IRs • Southern Germany and Austrian Alps • CVI – EM/EDX (morphology and composition) • CVI: IC# < 3000/L and diameter up to 25 µm • Cloud Probe IC#: 1- 10/L, IC size: 20 – 600 µm • 84 IRs , Dmed = 1 µm, only IRs>0.12 µm analysed • Sampling leg - IC# 90/L • Composition similar to mineral, but Fe enriched compared to interstitial or out-of-cloud mineral particles • Pitting of inlet by ice crystals – not considered

  38. Twohy and Gandrud (1998): Two contrails • South and north-western USA • CVI lower cutpoint 5-14 µm • IRs collected on 2-stage impactor (AEM) • 0.1-0.42 and >0.42 µm (Da, d = 1.8g/cm-3) • Total IR 12000/L • Non-Volatile (heated to 250 °C) 9000/L • Part of CVI flow on EM grids for X-ray spectr. • 76 particles from Boeing 757 and 36 from NASA DC-8 • SS and Ti particles (from inlet pitting?)

  39. Composition of IN detected (offline) • Twohy and Gandrud (1998) • Minerals mostly and metals partly intern. mixed withsulfur • Unid. non-vol: could be silicates (not identified, EM grids) • 757 contrail was cirrus free, DC-8 probably contained natural cirrus

  40. Twohy and Poellot (2005): Anvil Cirrus CloudsCRYSTAL-FACE • Southern USA (Florida) • CVI cut points not reported • IRs collected on 2-stage impactor (SEM) • 0.07-0.38 and >0.38 µm (Da, d = 1.7g/cm-3) • IR 30 - 300/L • 1115 IRs and 400 ambient particles analysed • Composition with EDX • Cloud probe data over counted ice crystals by an order of magnitude due to shattering • Compositional artifacts due to SS pitting (<2%)

  41. Composition of IN detected (offline) • Presence of salts in IRs-hom. frez. • Int. mixing of salts with carbon, likely biomass burning • Not clear if soot IRs due due to scavenging or ice formation • Is IN comp. And sampling T data enough to elucidate freezing mech.? Twohy and Poellot (2005) • Do we need to combine, radar data and/or detailed modelling with in-situ studies to determine formation mechanism?

  42. Taragino et al. (2006): 6 Flights, Cold Orographic Cirrus • North Atlantic, UK, North America, Western Russia • Cloud temperature > - 35 °C, Alt. 5 – 8 km • CVI cut points 4 – 55 µm (Noone, et al. 1992) • 609 IRs and classified into sub- and super-micron groups • Composition and size/morphology with SEM/EDX • 19.5% Al-Si rich and 24.1% Fe rich MD • 23.3% presumed organic and 6.7% sea salt • 7% with SS signatures considered IRs and 3% SS contamination

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