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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

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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

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Motivation for Studying IN Composition

Raman Spectroscopy, Coarse Mode >2µm, mode size 4 ±1.5µmAvg Sice = 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

Pure organic IN contained evidence of oxidation

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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

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Ice Crystal Property Characterization

From Cziczo and Froyd (2013, in review)

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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

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Counter Virtual Flow (CVI) SamplingFrom Cziczo and Froyd (2013, in review)

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Types Of Ice Clouds/Cirrus

From Cziczo and Froyd (2013, in review)

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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

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

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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

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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?)

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Composition of IN detected (offline)

Twohy and Gandrud (1998)

Minerals mostly and metals partly intern. mixed with sulfur Unid. non-vol: could be silicates (not identified, EM grids) 757 contrail was cirrus free, DC-8 probably contained

natural cirrus

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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%)

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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.?

Do we need to combine, radar data and/or detailed modelling with in-situ studies to determine formation mechanism?

Twohy and Poellot (2005)

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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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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 Supersaturation wrt ice near cirrus 120-140% Cloud probe IC# < 200/L

Het. freezing inferred to be dominant

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Composition of IN detected (offline)

Cziczo et al. (2013)

Only one case of a cloud formed from hom. freez. cloud observed during MACPEX

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

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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?

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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.

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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

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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

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Composition of IN detected (in-situ)

a) Biological b) Mineral Dust

Pratt et al. (2009)

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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.

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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

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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

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Classes of IN detected In Mixed-Phase Clouds

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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

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Challenges With Current Techniques

Ice crystal size limitation – missing larger diameter crystals due to CVI upper limit cut point

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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)

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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?

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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)

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Classes of IN Studies in Laboratory

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Atmospheric Relevance of Lab – IN

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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?