Ice Nuclei in MidLatitude Cirrus Results from a

Ice Nuclei in Mid-Latitude Cirrus: Results from a New Counterflow Virtual Impactor (CVI) Inlet Karl Froyd NOAA Earth Systems Research Lab CIRES, University of Colorado Dan Cziczo Massachusetts Institute of Technology MACPEX Science Team Meeting Jan, 2012

PALMS Instrument Single particle size and composition (0. 2 – 3 mm) detect a particle focus particles vaporize & ionize + +– + – – + Time-of-flight MS 193 nm analyze ions Mineral Dust particle Sulfate-Organic particle

PALMS Science Goals In Cloud: Sample cirrus particles with CVI inlet Composition of Ice Nuclei (IN) from cirrus residuals Ice-active aerosol types, nucleation mechanisms, **Improve IN sampling from aircraft** In Clear Air: Analyze composition for background conditions, cloud outflow, events Provide aerosol tracer data

PALMS Data Products Particle Type Number Fractions Chemical Info Sulfate-Organic Mixture Sulfate Mass Fraction Biomass Burning Organic Mass Fraction Mineral Dust Sulfate acidity (NH 4+: SO 42 -) Industrial/Metallic Methane Sulfonic Acid (marine) Sea Salt Oxidized Organics Elemental Carbon Aging, Cloud Processing Oil Combustion Lead All size-resolved Most useful chemical tracers for MACPEX Potential Ice Nuclei (IN)

Clear Air Aerosol

Clear Air Aerosol Summary North (>30˚) • Heavy regional Biomass Burning influence Tropopause Cirrus encounters • Sulfate-Organic mixtures dominate in UTLS • Mineral Dust: 10 -30% • Little Sea Salt in UT • Meteoric particles in stratosphere • Acidic sulfate only in stratosphere

Clear Air Aerosol Summary South (<29˚) • Biomass Burning only in troposphere • Sulfate-Organic mixtures dominate in UTLS • Mineral Dust: <10% UTLS • Acidic sulfate throughout

Cloud Outflow PALMS oxalate PALMS hydroxy-MSA PALMS large particles Cloudy fraction clear air RHi

Cloud Residuals

Ice Initiation in the UT • Homogeneous Freezing - supercooled liquid particles freeze – – – high fraction of aerosol particles freeze, once a threshold is reached high crystal concentrations (~1000 -10000 L-1) smaller crystals RHice >160% higher extinction crystal concentrations controlled by Cooling Rate • Heterogeneous Nucleation – solid particle acts as a seed for ice – – – special subset of aerosol forms ice – Ice Nuclei (IN) low crystal concentrations (~10 -100 L-1) RHice >120% larger crystals lower extinction crystal concentrations controlled by Aerosol Composition

Sampling Cirrus Residuals Typical CVI Inlet 5. online PALMS analysis of ‘residue’ Aerosols and Cirrus Crystals CVI inlet counterflow gas ~1 m/s exhaust 200 m/s 1. counterflow 2. sample only 3. equilibrate 4. heat to remove rejects aerosol cirrus crystals with flow water particles Crystals must stop! evaporate!

CVI - Fundamental challenges ‘Ice Bullets’ ‘Icebergs’ hard to stop – need >1 m inlet ! hard to evaporate – need >1 m inlet ! typical crystal sizes Sample • Most crystals too large to sample • Large crystals impact and generate artifacts 200 m/s Inlet material CVI inlet exhaust

New ‘Folded’ CVI Design Stop crystals Evaporate Counterflow rejects aerosol Counterflow enters here Cloud residuals extracted Reverse direction Exhaust flow exits at rear gas flow Aerosol Inlet New Design Elements Folded design – effectively doubles length Inlet Switching – CVI ↔ Aerosol inlets Neon carrier gas – higher viscosity & thermal conductivity than air. Inert, dry. Throttle sampling duct – reduce incoming crystal velocity Gold-plated interior – reduces ablation, unique tracer Vortex flow – increases time for evaporation IR laser – evaporates ice crystals prior to sampling

Crystal Sampling Improvement previous sampling range 5 -25 mm new sampling range 10 -60 mm Factor of 10 in mass

South: Subtropical Jet Cirrus 25 L-1 Apr 16 Cirrus alt 10 -11 km Nearby Aerosol Unclassified Cirrus Residuals Sulfate. Organic Oil Combustion Meteoric Mineral Dust & Metallic Sea Salt EC Biomass Burning • Aerosol and residuals have very similar composition • Minimal enhancement of Dust or Biomass Burning • Little Heterogeneous Nucl… Homogeneous Freezing?

North: Continental Cirrus 200 -2000 L-1 Apr 7, 13, 18, 25 Cirrus alt 9 -12 km Nearby Aerosol Unclassified Cirrus Residuals Sulfate. Organic Mineral Dust & Metallic Sea Salt EC Biomass Burning • Mineral Dust & Metallic strongly enhanced in residuals • No enhancement of other surface-emitted particles • Contribution from Heterogeneous Nucleation

Chemical Properties and Aging Fraction of UT particles… Clear air Cirrus residuals Dust with Pb inclusions: 10% 20% Dust with thick Org coating 22% 9% Oxalic acid 9% 11% Pyridine-like ? ? 2% 16% ‘Unclassified’

MACPEX Results - Context Broadly consistent with previous PALMS IN studies from aircraft (CRYSTAL-FACE, TC 4, CR-AVE) and also from high altitude ground sites with CFDC (INSPEC I & II)… Heterogeneous Nucleation for most UT cirrus cases, Homogeneous Freezing sometimes Lab studies predict effective IN Aircraft studies confirm effective IN in UT cirrus Mineral Dust Metallic Particles EC Biological Particles Meteoric Particles

PALMS Summary Science: Aerosol & IN • • North vs. South – different aerosol available Continental cirrus vs. STJ cirrus Historical consistency New type of IN – Pyridine salts? Engineering: CVI inlet • • Inlet design improves crystal sampling range Online cirrus residual sampling - Best effort to date Inconsistent performance – need controlled testing Fundamental limitations of CVI for cirrus residuals Thanks to Eric & Jay Karen & Lenny Hal & Ken NASA & NOAA funding Gourihar Kulkarni (PNNL) Rich Mc. Laughlin (NOAA) Dan Murphy (NOAA) SPEC, Inc.

Questions?

Dp(mm) TE 0. 2 71% 0. 5 73% 1 71% 2 65% 3 65% 4 27% 5 10%