ICCP Workshop on Measurements of Ice in Clouds

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

2. 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

3. 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

4. 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

5. Ice Crystal Property Characterization From Cziczo and Froyd (2013, in review)

6. 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 seperator (on ground) – to sample IRs in mixed-phase clouds

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

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

9. 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

10. Classes of IN detected (offline) in Atmosphere in Contrails or Cirrus

11. 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

12. 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?)

13. 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

14. 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%)

15. 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?

16. 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

17. 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

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

19. Classes of IN detected (in-situ) in Atmosphere in Contrails or Cirrus

20. 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?

21. 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.

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

23. 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

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

25. 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.

26. Froyd et al. (2010), Subvisual Cirrus • Het. frez. of anhydrous salts and/or glassy organic aerosols maybe playing a role • Gold plated CVI was succesfully 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

27. 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

28. Classes of IN detected In Mixed-Phase Clouds

29. Type of Information Collected/Inferred(answered (?) questions) • Basic composition classes • IRs with signatures showing more than one class of compounds • Internally mixed before ice nucleation • Scavenging after ice nucleation? • Ice formation mechanism inferred • Composition information combined with ice crystal properties • IR size distributions • Truly reflective of IN or biased due to scavenging • IC Size distributions

30. Challenges With Current Techniques Ice crystal size limitation – missing larger diameter crystals due to CVI upper limit cut point

31. Limitations of Current Methods • Hard to sample mixed-phase cloud IRs • Phase seperator needed for aircraft • Multiplication and shattering on inlet (overcome?) • Inlet material contamination in IR composition (overcome?) • Small particles captured in wake of ice crystal • Re-suspension of particles adhered to inlet when sampling ice crystals • Lower size limit of EM/EDX (120 nm) and SPMS (100-200 nm)

32. Type of Data Desired but not Collected(unanswered questions) • In-situ detection of ice crystals in mixed phase clouds, i.e. Which particles remain immersed vs those that induce freezing? • Current studies limited to ground sites that encounter mixed phase clouds • Large ice crystals 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 are not measured in aircraft studies • In Cirrus can we distinguish between one or more of the het. ice nucleation mechanism e.g. deposition vs. immersion?

33. 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), different folding design? (used in MACPEX)

34. Classes of IN Studies in Laboratory

35. Atmospheric Relevance of Lab – IN

36. Role of Laboratory Studies in Aiding Such Measurements • Understanding the roles of how the various classes of compounds detected in the field nucleate ice – i.e. Temp, RH, and Mode? • But run into other factors, size, morphology, instrument techniques detection method, make reporting of composition influence complicated • Compositions used in the lab, how realistic are they?