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Techniques for Determining PSD of PM: Laser Diffraction vs . Electrical Sensing Zone

Techniques for Determining PSD of PM: Laser Diffraction vs . Electrical Sensing Zone. A 242 nd ACS National Meeting Presentation: Paper ID18440. Z. Cao 1 , M. Buser 2 , D. Whitelock 3 , L. Wang-Li* 1 , Y. Zhang 4 , C.B. Parnell 5 1 NCSU, 2 OSU, 3 USDA-ARS, 4 UIUC, 5 TAMU. Introduction:.

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Techniques for Determining PSD of PM: Laser Diffraction vs . Electrical Sensing Zone

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  1. Techniques for Determining PSD of PM: Laser Diffraction vs. Electrical Sensing Zone A 242nd ACS National Meeting Presentation: Paper ID18440 Z. Cao1, M. Buser2, D. Whitelock3, L. Wang-Li*1, Y. Zhang4, C.B. Parnell5 1NCSU, 2OSU, 3USDA-ARS, 4UIUC, 5TAMU

  2. Introduction: • PM – NAAQS: PM10 & PM2.5 • Health effects, Source identification/estimation, Mitigation strategies – PM characteristics: • Physical properties • Mass, or number concentrations • Particle size distribution (PSD) • Morphology • Density, etc. • Chemical compositions • Biological properties

  3. Introduction: • Various techniques for PSD measurement (analysis) • Aerodynamic method (APS, Impactors, etc) • Optical method (optical counters, light scattering analyzers, etc) • Electrical sensing zone method (Coulter Counter) • Electrical mobility and condensation method (DMA+CNC) • Electron microscopy • No single agreed upon method – for different sources

  4. Aerodynamic Method for PSD Analysis: Aerodynamic Particle Sizer (APS) • Aerosol entering the tube is assumed to be uniform • Dilution system - reduce problems with particle coincidence in the sensor • Light scattered - changes rapidly with dp: • small particle processor : AED 0.5 – 15.9 mm • large particle processor: AED 5 – 30 mm • Monodisperse latex spheres are used for calibration of full size range of the APS • Not work for PSD on sampler filter • Field real-time measurement Ch5.8: pages 136-138 of Hinds

  5. Aerodynamic Method for PSD Analysis: Impactors • On-site measurements in mass concentration and PSD • Limited size ranges • Particle bounce • Particle losses

  6. Optical Method for PSD Analysis: Optical Particle Counters http://en.wikipedia.org/wiki/Particle_counter • Detect and counts one particle at a time • Calibration? • High level PM environment? http://www.particlecounters.org/optical/

  7. Optical Method for PSD Analysis: LS13 320 Multi-wave Length Laser Diffraction Particle Size Analyzer (0.04 – 2000 mm) Polarization Intensity Differential Scattering (PIDS) Rayleigh Scattering Theory (Source: Beckman Coulter, Miami, FL) Mie Scattering theory

  8. Optical Method for PSD Analysis: LA-300 Laser Scattering Particle Size Analyzer Fraunhofer Diffraction and LA-300 (Source: Horiba Instrument Inc, Irvine, CA)

  9. Electrical Sensing Zone Method for PSD Analysis: Coulter Counter Multisizer • Only suitable for insoluble particles • Not an onsite measurement • Ultrasonic bath – all particles are fully dispersed in the liquid solution (PM on filter) • Size calibrated with polystyrene spheres of known size • Counting rate – 3000 particles/s Source: Beckman Coulter, Miami, FL • Current through the orifice • Particle electrical resistance ~ dp • Change in current ~ dp

  10. Electrical Mobility Method for PSD Analysis: Differential Mobility Analyzer (DMA) • Used as a monodisper aerosol generator to produce sub-micrometer-sized aerosols for testing and calibration • Measure PSD in the sub-micrometer size range • Particles with greater mobility migrate to the center rod • Exiting aerosol – slightly charged and nearly monodisperse –size controlled by the voltage on the central rod • 0.005 – 1.0 mm Condensation Nucleus Counter (CNC) Ch15.9 of Hinds

  11. Electron Microscopy Method for PSD Analysis: Electron Scanning Microscopy (ESM) Fly-ash Corn Starch

  12. Objectives: • Differences in PSD measurements for PM with MMDs in micrometers (agricultural sources) • Light scattering method • Electrical sensing zone method • PM sample types • Filter-based PM samples with MMD>>10 mm • Testing aerosols with MMD ~ 10 mm

  13. Materials & Methods • PSD Analyzers • LS13 320 multi-wave length laser diffraction particle size analyzer - NCSU • LA-300 laser scattering particle size analyzer – UIUC • Coulter Counter Multisizer3 – TAMU • Coulter Counter Multisizer3 – USDA • LS230 laser diffraction particle size analyzer – USDA

  14. Materials & Methods PM Field Sampling – Low-volume TSP Samplers High-rise Layer House

  15. Materials & Methods • Field PM samples: filter-based • 26 samples/season for two seasons: distributed to the three locations • Analyzed under the same operation procedure • Testing materials: not filter-based aerosols • Limestone • Starch • No.3 Micro Aluminum • No.5 Micro Aluminum

  16. Materials & Methods PM Sample Assignment/Distribution PM Samples NCSU LS13 320 UIUC LA-300 TAMU CCM3 USDA CCM3 LS230 Winter PM samples Spring PM samples Testing aerosols Winter PM samples Spring PM samples Testing aerosols

  17. Materials & Methods • PM10 and PM2.5 mass fraction analyses • Measured by the analyzer • Calculated using the lognormal distribution equation • Checked for agreements (Relative Difference, %) Measured = PM10 or PM2.5 measured by the analyzer Lognormal = PM10 or PM2.5 calculated using the lognormal distribution equation

  18. Results & Discussion Measured MMDs (mm) for Winter Samples: N=26

  19. Results & Discussion Measured GSDs for Winter Samples: N=26

  20. Results & Discussion Measured MMDs (mm) for Spring Samples: N=26

  21. Results & Discussion Measured GSDs for Spring Samples: N=26

  22. Results & Discussion Measured PSDs of Testing Aerosols

  23. Results & Discussion

  24. Results & Discussion

  25. Results & Discussion PM10 and PM2.5 Mass Fraction Analyses (NCSU) LS13 320 N=52 (26 for Winter, 26 for Spring)

  26. Results & Discussion LS13 320 PM10 PM2.5 N=52 26 for Winter 26 for Spring)

  27. Results & Discussion LA-300 PM10 and PM2.5 Mass Fraction Analyses (UIUC) N=52 (26 for Winter, 26 for Spring)

  28. Results & Discussion LA-300 PM10 PM2.5 N=52 26 for Winter 26 for Spring

  29. Results & Discussion CCM3 PM10 Mass Fraction Analyses (TAMU) N= 26 for Winter

  30. Results & Discussion TAMU-CCM3 (N=26)

  31. Results & Discussion PM10 and PM2.5 Mass Fraction Analyses (USDA) LS230 CCM3 N= 26 for Spring

  32. Results & Discussion LS230 PM10 PM2.5 N=26 for Spring

  33. Results & Discussion CCM3 PM10 PM2.5 N=26 for Spring

  34. Conclusions • Different analyzers: significant differences in MMDs and GSDs for filter-based samples • LA-300: the largest MMDs; CCM3: the smallest MMD • LS13 320: the largest GSDs; CCM3: the smallest • The PSD results of testing aerosols - consistent with that of filter-based samples • LA-300: large MMDs • LS13 320 & LS230: large GSD • PSDs measured by LS13 320 & LS230 agreed well

  35. Conclusions • All RDs in PM10 mass fractions of the measured and the fitting values < 5%, which is acceptable • All RDs in PM2.5 mass fractions of the measured and the fitting values >> 5%, which is not acceptable.

  36. Acknowledgement • The USDA NRI Grant No. 2008-35112-18757 • Help from Qianfeng Li & Zifei Liu for field sampling • Support from the egg production farm

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