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Explore various methods for analyzing Particle Size Distribution (PSD) of PM, including Aerodynamic, Optical, Electrical Sensing Zone, and Electron Microscopy techniques with emphasis on Laser Diffraction and Coulter Counter. Comparison of methodologies is presented along with real-time measurements and calibration practices.
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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
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
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
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
Aerodynamic Method for PSD Analysis: Impactors • On-site measurements in mass concentration and PSD • Limited size ranges • Particle bounce • Particle losses
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/
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
Optical Method for PSD Analysis: LA-300 Laser Scattering Particle Size Analyzer Fraunhofer Diffraction and LA-300 (Source: Horiba Instrument Inc, Irvine, CA)
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
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
Electron Microscopy Method for PSD Analysis: Electron Scanning Microscopy (ESM) Fly-ash Corn Starch
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
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
Materials & Methods PM Field Sampling – Low-volume TSP Samplers High-rise Layer House
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
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
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
Results & Discussion Measured MMDs (mm) for Winter Samples: N=26
Results & Discussion Measured GSDs for Winter Samples: N=26
Results & Discussion Measured MMDs (mm) for Spring Samples: N=26
Results & Discussion Measured GSDs for Spring Samples: N=26
Results & Discussion Measured PSDs of Testing Aerosols
Results & Discussion PM10 and PM2.5 Mass Fraction Analyses (NCSU) LS13 320 N=52 (26 for Winter, 26 for Spring)
Results & Discussion LS13 320 PM10 PM2.5 N=52 26 for Winter 26 for Spring)
Results & Discussion LA-300 PM10 and PM2.5 Mass Fraction Analyses (UIUC) N=52 (26 for Winter, 26 for Spring)
Results & Discussion LA-300 PM10 PM2.5 N=52 26 for Winter 26 for Spring
Results & Discussion CCM3 PM10 Mass Fraction Analyses (TAMU) N= 26 for Winter
Results & Discussion TAMU-CCM3 (N=26)
Results & Discussion PM10 and PM2.5 Mass Fraction Analyses (USDA) LS230 CCM3 N= 26 for Spring
Results & Discussion LS230 PM10 PM2.5 N=26 for Spring
Results & Discussion CCM3 PM10 PM2.5 N=26 for Spring
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
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.
Acknowledgement • The USDA NRI Grant No. 2008-35112-18757 • Help from Qianfeng Li & Zifei Liu for field sampling • Support from the egg production farm