SootParticle-AMSor

LaserVaporizer-AMS

Aerodyne Research, Inc.

et al.

Outline

• SP-AMS technique and hardware• Reference material

• SP-AMS applications• Quick highlight a few applications

• SP-AMS quantification• Challenges and summary

SP-AMS hardwareSP Module

Second vaporizer in AMSDifferent ionization chamber configurationThree potential vaporizer configurations

ADQ, ePTOF, BWP (ebox) upgrades

Laser Vaporizer Module

Onasch et al. (AS&T 2012)

Ionizer Configurations

HR-AMS (Tungsten vaporizer)

• Filaments on sides of ion chamber

• Filament position is mechanically set

• Filament wire is typically well positioned with respect to well formed slits in ion chamber walls

• Narrow or Wide chamber widths

SP-AMS (Laser Vaporizer)

• Filament is on bottom of ion chamber

• Filament position is moveable (vert& horz)

• Filament slit width and breadth may vary due to custom procedure

• Large holes in sides to accommodate laser beam

• Narrow or Wide chamber widths

Need to optimize vertical position

Vaporizer Configurations

1. Tungsten Vaporizer (HR-AMS)2. Laser Vaporizer 3. Laser + Tungsten Vaporizers

SP-AMS Orthogonal Detection Axes

Sampled Particles

Ion Extraction and MS detection

• Characterization of particle-laser interaction region:• Vertical Particle Beam Walk• Horizontal/Vertical Beam Width Probe• Laser Beam Walk

Laser Vaporizer Detection Scheme

The laser is not the vaporizer, the absorbing particles are the vaporizer!!

Ambient Mass Spectrum

Nomenclature

Corbin et al., 2014 - ETH

4000 oC

PM = Particulate MatterNR = Non-RefractoryR = RefractoryL = Light Absorbing (1064 nm)

LR-PM:1. Refractory Black Carbon (rBC)2. Metals

SP-AMS applicationsAmbient rBC measurements (Massoli et al., 2015)

Source characterization of laboratory metal nanoparticles (Nilsson et al., 2015)

Dual vaporizer measurements including single particle detection (Lee et al., 2015)

CalNex 2010 – Massoli et al., 2014 JGR

Separate instruments operated side-by-side:• SP-AMS laser vaporizer• HR-AMS tungsten vaporizer

rBC particle chemical composition and size

• Increasing Photochemical aging• Observations of secondary

condensation• Observations of compaction

and growth of rBC particles

Direct comparison between rBC subset of particles and total aerosol loading

Chemical information Mass information

Source characterization of metal nanoparticles –Nilsson et al., 2015 Nano Research

• Chemical information, including metal composition, oxide formation, and contaminants

Source characterization of metal nanoparticles –Nilsson et al., 2015 Nano Research

• Size and effective density information

Dual vaporizer measurements of ambient rBC particles – Lee et al., 2015 ACP

• Single particle detection allows for the measurement of rBC particles even with dual vaporizer configurations

Average MS comparisons

• Apparent increased sensitivity to NR-PM vaporized in laser vaporizer!

SP-AMS QuantificationSensitivities

Refractory black carbon (rBC) [Laser]

Non-Refractory PM [Laser and Tungsten]

Collection EfficienciesTungsten Vaporizer

Laser Vaporizer

mIE calibrations

300 nm AN

NR-PM using tungsten vaporizer rBC using laser vaporizer

• We need to include a third calibration: NR-PM for laser vaporizer!

mIE NR-PM calibrations using laser vaporizer

• Difficult, but not impossible

• Two approaches attempted to date:1. Coat Regal black with DOS (Willis et al., 2014 AMT)

2. Atomize ammonium nitrate with Regal black (Carbone et al., 2015 AMTD)

• Coated Regal black particles with DOS to make spherical

• With thicker coatings, RIE_rBCincreased as the particle beam narrowed down closer to laser beam width

• Dual laser/tungsten vaporizer setup• Both rBC and Org ion signals

increased• NR-PM mIE for DOS appears to be

~2x larger from laser vaporizer than from tungsten vaporizer!

~2x CE

~2x mIE

rBC CE determination

NR-PM mIE determination

Willis et al., 2014 AMT

DOS coated BC with vaporizer and laser

AN coated BC with vaporizer and laser

Carbone et al., 2015 AMTD; Fortner lab experiments

• Dual vaporizers• Atomize solution of Regal

black and ammonium nitrate• Large [AN] likely produce

significant number of particles without Regal black

• Small [AN] likely produce Regal black particles with thin coatings of AN

• Apparent mIE for AN on laser vaporizer is ~2.3x tungsten vaporizer (laser OFF)

mIE NR-PM calibrations using laser vaporizer

• Need to further refine mIE calibrations for NR-PM on rBC particles

• Need to assess the differences between mIE for laser and tungsten vaporizer PM

• Need to verify whether the standard suite of RIE’s, determined using tungsten vaporizer only, hold for the laser vaporizer

Tungsten Vaporizer Collection Efficiency

EL = Aerodynamic Lens transmission EB = Incomplete vaporization due to particle BounceES = Particle beam divergence due to particle Shape (and size)

EL ~ 1 for dva = 70-700 nmEB ~ 0.5 due to solid/refractory particle bounceES = 1 as particle beam width < tungsten vaporizer width

Mass concentration of species “s”

EB governs the overall CE for Tungsten Vaporizer

CE = EL · EB · ES

Laser Vaporizer Collection Efficiency

Mass concentration of species “s”

ES governs the overall CE for rBC and NR-PM (laser only) Beam width probe measurement

EB complicates rBC (RBC) measurements

CELaser = EL · EB · ES

EL = Aerodynamic Lens transmission

EB = Incomplete vaporization **

ES = Particle beam divergence due to particle Shape (and size)

EL ~ 1 for dva = 70-700 nm

EB ≤ 1 due inefficient energy absorption/transfer issues **

ES < 1 as particle beam width < laser vaporizer width

Beam Width Probe (Huffmann et al./Salcedo et al.)

laser

wire

wire motion

Particle beam

BWP Results

• Two independent measures of narrowing of particle beam with coating• Decreasing particle beam width increases particle-laser beam overlap

Incomplete vaporization and laser power

• Laser Power Drop experiments show a stronger particle-laser beam overlap dependence for rBCthan NR-PM

SP-AMS CE’sVaporizer-dependent

Vaporizer Measured Species

Tungsten NR-PM * E B

Laser (rBC + R-PMǂ + NR-PM

ǂ) * E S

Laser and Tungsten (rBC + R-PMǂ + NR-PM

ǂ) * E S + (NR-PM - NR-PM

ǂ * E S ) * E B

NR-PM = Nonrefractory Particulate Material measured by a standard AMS [Jimenez et al., 2003 ]

R-PM = Refractory Particulate Material measured by the SP-AMS (see text for details)

rBC = Refractory black carbon measured by the SP-AMS (and SP2) [Schwarz et al., 2006 ]ǂ = Particulate Material on rBC particles as mesaured by the SP-AMS (see text for details)

E B = Particle bounce related Collection Efficiency of the AMS

E S = Size and shape related Collection Efficiency of the SP-AMS

Laser vaporizer only

Flame 3

Fortner et al., 2015

Regal black

Resistively heated tungsten vaporizer only

Refractory black carbon (rBC)

Tungsten vaporizer only

Dual vaporizers

Laser vaporizer only

PMF deconvolution

Laser ON vs OFF

Government Flats fire (8/21/2013). SP-AMS plume transect with dual vaporizers (left) and tungsten only (right)

Summary of quantification issues:

# Issue Importance Comments

1Differences between vaporizer

sensitivitiesmajor

mIE sensitivity issue likely due to vaporization temperatures of molecules and

subsent velocities in ion formation chamber. Difficult mIE measurements for NR-

PM from laser vaporizer. Laser vaporizer RIE's need verification (or

determination). Not well characterized to date.

2 Incomplete vaporization majorCollection efficiency (CE) issue that has not been characterized very well to date

and causes over-estimates of [NR-PM]/[rBC] ratios.

3 Particle beam - laser beam overlap major

Collection efficiency (CE) issue strongly depenent upon alignment and particle

morphologies. BWP will help with quantification, though difficult (and slow)

measurements.

4 Laser misalignment minorIncludes laser beam hitting tungsten vaporizer or ion formation chamber. Can be

mitigated through careful alignment procedures.

5 Cn+ ion interference from Org minor Problem for dual vaporizer measurements with significant NR-PM Organics. PMF

of rBC ion signals appears to effectively distinguish Cn+ ion sources.

6Large (mid and fullerene) Cn+ ion

formationminor

Apparent laser power issue that has yet to be resolved.

Summary

• SP-AMS hardware = laser vaporizer inside HR-AMS• Provides refractory PM detection (chemical, mass, and size information)

• Three vaporizer configurations (laser only, tungsten vaporizer only, dual vaporizers)

• Single particle detection

• SP-AMS technique finding applications in ambient measurements, source (combustion) characterization, laboratory measurements, metal nanoparticles, and single particle detection

• SP-AMS quantification is challenging, but we are making progress