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Single Aerosol Particle Analysis Using Aircraft Compatible Time-of-Flight Mass

Spectrometers in Real Time(A-ATOFMS & SPLAT II)

Suresh RegmiLiterature Seminar Presentation

CHEM 7800November 9, 2009

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Objective

To compare and contrast two TOF instruments ( A-ATOFMS & SPLAT II) developed for real time detection and analysis of single aerosol particles.

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Articles

Development and characterization of an aircraft aerosol time-of-flight mass spectrometerKerri A. Pratt, Joseph E. Mayer, John C. Holecek, Ryan C. Moffet, Rene O. Sanchez, Thomas P. Rebotier, Hiroshi Furutani, Marc Gonin, Katrin Fuhrer, Yongxuan Su, Sergio Guazzotti, and Kimberly A. Prather (University of California, San Diego, California).Anal. Chem. 2009, 81, 1792–1800

SPLAT II: an aircraft compatible, ultra-sensitive, high precision instrument for in-situ characterization of the size and composition of fine and ultrafine particlesAlla Zelenyuk ; Juan Yang ; Eric Choi ; Dan Imre (Pacific Northwest National Laboratory, Richland, Washington). Aerosol Sci. Technol. 2009, 43, 411–424,

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Why Study Aerosol?

Human health

air quality, airborne pathogen transport

Energy balance of earth

aerosol optical properties

direct/indirect effects

Cloud nucleation

Geochemical cycles

metals, nutrients, organics

Acidification (sulfur, nitrogen)

http://www.ucar.edu/learn/1_1_1.htm

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Why Single Aerosol Particles in Real Time?

Particle size is critical for health effects

Chemical composition of a particle and mixed composition particles

Individual particle size and composition represents its source. Prevents sampling artifacts / secondary pollutant formation during detection

Real picture of the air you breathe

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Research Challenges

Requires faster data acquisition speeds to provide high spatial resolution

No sample collection (advantages and disadvantages)

Difference in shape of the particles

Enormous variety, complexity, and fragility of particles

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Why Aircraft Based Study ? Direct and indirect radiative forcing depend on aerosol vertical and horizontal profiles.

Quantify the properties of particles as a function of altitude Horizontal distribution of particles, aircraft route selection Role of particles in cloud nucleation (Aerosol – cloud interaction)

http://earthobservatory.nasa.gov/Features/Aerosols/

Low aerosol concentration

High aerosol concentration

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Requirements for Aircraft Based Instrument

Size of the instrument

Weight of the instrument

Vibration shielding

Data acquisition

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Real Time -Single Aerosol Time of Flight Mass Spectrometer

particle collection/

focusing

Particle sizing

IonizationMass analysis

Detection

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Time of Flight Mass Spectrometer

ReflectronFlight tubeIonization chamber

Detector

Laser

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Aircraft-Aerosol Time of Flight Mass Spectrometer (A-ATOFMS)

Principal investigator: Dr. Kimberly Prather

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A-ATOFMS in Working Condition

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A-ATOFMS : On BoardPower consumption- 1.4 kW

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A-ATOFMS : Inside

7 × 10 -7 Torr

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Particle Sizing

Aerosol particle

Aerodynamic lens

SkimmersLaser

PMT

Po 210 neutralizer

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Ionization: Laser Desorption

266 nm Nd:YAG DI laser

+-

++

+

++

+

-

-

-

-

- ++

++-

Extractors

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A-ATOFMS : Separation and Detection

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A-ATOFMS

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Mass Spectra : Organic Carbon - Sulfate - Nitrate

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Mass Spectra : Dust - Sulfate - Nitrate

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Particle Concentration)

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Conclusions

Transportable and high data acquisition capability

Real time source apportionment software

Use of neutralizer Duel polarity mass analyzer

Field tested in ground and on board

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Single Particle Laser Ablation Time of Flight Mass Spectrometer II

(SPLAT II)Principal investigator

Dr. Alla Zelenyuk

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Real Time -Single Aerosol Time of Flight Mass Spectrometer

particle collection/

focusing

Particle sizing

Ionization

Mass analysis

Detection

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SPLAT II : Ready to Fly

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SPLAT II : Inside

Power consumption 3.5 kW Total wt – 400 kg

Dimension - 143 × 69.6 × 124.5 cm

2.25 × 10-6 Torr

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Particle Sizing

Zelenyuk et al. Aerosol Sci. Technol. 2009_2

532 nm, 300 mw

532 nm, 300 mw

Spot 330 µm

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Ionization: Evaporation + Laser Ablation

IR/UV ionization

Requires lower laser intensity Less fragmentation Flexibility for optimizationUV laser

IR laser

+ + ++ + +

10.6 µm CO2 laser, 50 ns pulse,110 mJ/pulse, spot -1 mm

193 nm UV excimer laser,8 ns pulse, 0.5-2 mJ/pulse,Focal spot- 550 × 750 µm

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Mass Spectrum : SPLAT II Vs. NIST

OC-Nitrate-Sulfate

Trans-sobrerol 170 Lab

Trans-sobrerol 170 70 ev EI ionization

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Mass Spectrum : IR/UV Vs. UV

OC-Nitrate-Sulfate

334 nmDOP- 390.56 Lab

DOP - 390.56

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Mass Spectra: Convair 580 Aircraft

Biomass burning particle

Dust particle

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Conclusion Transportable

Can size over 500 particles and record up to 100 individual particles mass spectra per second Real time source apportionment software

Can differentiate between spherical and aspherical particles

Two step ionization process

Field tested in ground and on board

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Summary/ Evaluation

Both papers summarize an important scientific investigation

Devoted in the development of instruments for real time detection and analysis of single aerosol particles

Improved version of their predecessor

Field as well as on board tested

Ionization - major difference

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A-ATOFMS Vs. SPLAT II

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Instrumentation

Components A-ATOFMS SPLAT II

Neutralizer Yes No

Particle sizing Light scattering Light scattering

Ionization Single laser ablation IR/UV laser ablation

Ion separation Dual polarity Single polarity

Dynamic range 70 nm - 1000 nm 125 nm - 600 nm

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UV Hard ionization

Irreproducible mass spectra

Easier optics alignment

Non-linear, multiphoton process

Matrix and charge transfer effects

IR/UV Soft /user controlled ionization

Reproducible mass spectra/ Independent of UV laser fluence

Difficult optics alignment

Linear relationships between the integrated mass spectral intensities and particle mass

Less influence by matrix and charge transfer

Ionization

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Dual Polarity Vs. Single Polarity TOF

?

http://www.internetvibes.net/gallery/disney-pixar-cars-images-from-the-cartoon/

Dual polaritySingle polarity

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Evaluation - Suggestion

Comparison with their own instrument

Competition to show the instrument portable

Stocked with TOF

Why not Ion trap?

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Alternative to Time of Flight MS: Ion Trap MS

Simpson et al. International Journal of Mass Spectrometry 281 (2009) 140–149

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Conclusions

Online analysis of single particle size, chemical composition, density, and optical properties

A-ATOFMS- more sensitive for detection limit and dynamic range

SPLAT II- Reproducible mass spectra, accurate chemical composition, differentiate spherical and aspherical particles

Ion trap instead of flight tube – smaller, and lighter instrument

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Acknowledgement

• Dr. Gilman• Dr. McCarley• Dr. Murray• Dr. Gilman’s research group• Audience