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