Techniques for Determining Particle Size Distribution (PSD) of Particulate Matter
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How can we determine the size of particles suspended in the (particulate matter) and what are the challenges?
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Techniques for Determining Particle Size Distribution (PSD) of Particulate Matter
- 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 1 NCSU, 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 µ m large particle processor: AED 5 – 30 µ m • 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? http://www.particlecounters.org/optical/ •High level PM environment?
- 7. Optical Method for PSD Analysis: LS13 320 Multi-wave Length Laser Diffraction Particle Size Analyzer (0.04 – 2000 µ m) Polarization Intensity Differential Scattering (PIDS) Rayleigh Scattering Theory Mie Scattering theory (Source: Beckman Coulter, Miami, FL)
- 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) Source: Beckman Coulter, Miami, FL •Size calibrated with polystyrene spheres of known size • Current through the orifice • Counting rate – 3000 particles/s • 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 Condensation Nucleus Counter (CNC) • Exiting aerosol – slightly charged and nearly monodisperse –size controlled by the voltage on the central rod • 0.005 – 1.0 µ m 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 µ m • Testing aerosols with MMD ~ 10 µ m
- 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 (a) (b) (c) (d)
- 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 UIUC TAMU USDA LS13 320 LA-300 CCM3 CCM3 LS230 Winter PM samples Spring PM samples Winter PM samples Spring PM samples Testing aerosols 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 − Lognormal RD = × 100% Measured 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 (µ m) for Winter Samples: N=26 LS13 320 LA-300 CCM3 17.13±0.81 22.71±1.43 13.94±1.00
- 19. Results & Discussion Measured GSDs for Winter Samples: N=26 LS13 320 LA-300 CCM3 2.63±0.04 2.02±0.11 1.85±0.04
- 20. Results & Discussion Measured MMDs (µ m) for Spring Samples: N=26 LS13 320 LA-300 LS230 CCM3 18.44±1.44 22.62±2.68 18.47±1.38 13.99±0.74
- 21. Results & Discussion Measured GSDs for Spring Samples: N=26 LS13 320 LA-300 LS230 CCM3 2.67±0.11 1.99±0.15 2.65±0.22 1.84±0.04
- 22. Results & Discussion Measured PSDs of Testing Aerosols LS13 320 LA-300 LS230 CCM3 MMD MMD MMD MMD Testing aerosols (µm) GSD (µm) GSD (µm) GSD (µm) GSD Limestone 7.50 3.07 12.29 1.83 8.11 3.15 8.56 1.72 Starch 13.31 1.59 16.78 1.50 14.38 1.55 14.32 1.33 #3 Micro aluminum 5.28 1.98 7.62 1.56 5.37 1.93 5.03 1.42 #5 Micro aluminum 7.09 1.69 8.38 1.49 7.21 1.71 6.31 1.39
- 25. Results & Discussion PM10 and PM2.5 Mass Fraction Analyses (NCSU) LS13 320 Measured mass Lognormal mass Relative fraction (%) fraction (%) difference (%) PM10 36.16±2.73 34.92±2.71 3.44±0.85 PM2.5 8.40±0.61 3.56±0.66 57.9±5.37 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 PM10 and PM2.5 Mass Fraction Analyses (UIUC) LA-300 Measured mass Lognormal mass Relative fraction (%) fraction (%) difference (%) PM10 20.60±2.53 19.88±2.56 3.34±5.34 PM2.5 4.57±0.64 0.25±0.14 94.46±3.05 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 PM10 Mass Fraction Analyses (TAMU) CCM3 Measured mass Lognormal mass Relative fraction (%) fraction (%) difference (%) PM10 41.75±3.74 40.76±4.19 2.46±2.06 N= 26 for Winter
- 30. Results & Discussion TAMU-CCM3 (N=26)
- 31. Results & Discussion PM10 and PM2.5 Mass Fraction Analyses (USDA) Measured mass Lognormal mass Relative fraction (%) fraction (%) difference (%) PM10 33.71±3.29 33.39±2.99 0.79±4.45 LS230 PM2.5 8.18±0.96 3.28±1.06 60.44±11.53 PM10 41.11±3.68 40.93±3.50 0.39±0.80 CCM3 PM2.5 1.43±0.35 0.65±0.26 54.96±13.04 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
Hinweis der Redaktion
- Objective 2 is to investigate different techniques in PSD measurement. Three instruments were applied for this objective. First one is the laser diffraction particle size analyzer LS13 320 at NCSU, that we have introduced in the previous slides. The second one is laser scattering particle size analyzer LS-300 at UIUC. This is the analyzer.
- Three samplers were collocated on the first floor and the other three samplers were collocated on the second floor. This design provided three replicates in TSP samples on each floor. The placements of samplers were shown in the figure.
- Three replicate samples on each floor were distributed to three locations for analyses. Samples were analyzed under the same operation procedures. PSDs provided by these three analyzers are all in the form of particle size in equivalent spherical diameter (ESD), however, EPA regulated particle size in the form of AED. So, ESD needs to be converted to AED using this equation. In this equation, ρ p is particle density, it was measured as 1.4776 g/cm 3 . χ is shape factor of particles, it was assumed as 1.
- Here is the process chart of experimental design for the objectives. For the first objective, design was based on sampling, concentration calculation and PSD measurement. For the second objective, comparison of PSD measurements by three different analyzers was the key point. These three analyzers are laser diffraction particle size analyzer LS13 320 at NCSU, laser scattering particle size analyzer LA-300 at UIUC and Coulter Counter Multisizer 3 at TAMU or USDA.
- PM 10 and PM 2.5 mass fraction can be measured by the analyzer, they can also be calculated using lognormal distribution equation. If results from these two methods agree with each other, it means PSD follows lognormal distribution. Relative difference between these two methods can be described by this equation.
- This is the comparison of MMDs measured by three instruments in winter. In this figure, x axis represents number of observations, y axis represents MMD. From this figure, significant but constant differences were observed among three analyzers. Red line, representing UIUC provided the largest MMD, green line, representing TAMU provided the smallest MMD. In general, MMD provided by NCSU was 17.13 plus or minus 0.81 micrometers, by UIUC was 22.71 plus or minus 1.43 micrometers, by TAMU was 13.94 plus or minus 1.00 micrometers.
- This is the comparison of MMDs measured by three instruments in winter. In this figure, x axis represents number of observations, y axis represents MMD. From this figure, significant but constant differences were observed among three analyzers. Red line, representing UIUC provided the largest MMD, green line, representing TAMU provided the smallest MMD. In general, MMD provided by NCSU was 17.13 plus or minus 0.81 micrometers, by UIUC was 22.71 plus or minus 1.43 micrometers, by TAMU was 13.94 plus or minus 1.00 micrometers.
- This is the comparison of MMDs measured by three instruments in winter. In this figure, x axis represents number of observations, y axis represents MMD. From this figure, significant but constant differences were observed among three analyzers. Red line, representing UIUC provided the largest MMD, green line, representing TAMU provided the smallest MMD. In general, MMD provided by NCSU was 17.13 plus or minus 0.81 micrometers, by UIUC was 22.71 plus or minus 1.43 micrometers, by TAMU was 13.94 plus or minus 1.00 micrometers.
- This is the comparison of MMDs measured by three instruments in winter. In this figure, x axis represents number of observations, y axis represents MMD. From this figure, significant but constant differences were observed among three analyzers. Red line, representing UIUC provided the largest MMD, green line, representing TAMU provided the smallest MMD. In general, MMD provided by NCSU was 17.13 plus or minus 0.81 micrometers, by UIUC was 22.71 plus or minus 1.43 micrometers, by TAMU was 13.94 plus or minus 1.00 micrometers.
- To reduce uncertainty produced by different samples in PSD measurement comparison, four types testing aerosols were analyzed by four analyzers at three locations. This summarized table shows the PSDs obtained from four analyzers. USDA have two analyzers, one is laser diffraction particle size analyzer LS230, which is similar with what we have in our lab, the other one is coulter counter multisizer, which is the same with what TAMU has.
- This figure shows comparison of MMDs measured by four analyzers. X axis represents type of testing aerosols, y axis represents MMD. From this figure, significant difference from UIUC and other three was observed. This is consistent with that from filter-based samples.
- This figure shows comparison of MMDs measured by four analyzers. X axis represents type of testing aerosols, y axis represents MMD. From this figure, significant difference from UIUC and other three was observed. This is consistent with that from filter-based samples.
- This table summarized PM 10 and PM 2.5 mass fraction obtained from two methods at NCSU, as well as the relative difference between these two methods. It was noticed that the RD for PM10 was 3.44 plus or minus 0.85 %, which is within 5%, it is reasonable. RD for PM2.5 was 57.9 plus or minus 5.37 %, which is not acceptable.
- This two figures shows differences in PM10 and PM2.5 mass fractions produced between two methods. X axis represents number of observations, y axis represents PM10 or PM2.5 mass fraction. From the left figure, PM10 mass fractions obtained from two methods agree with each other good. From the right figure, PM2.5 mass fractions obtained from two methods are quite different.
- This table summarized PM 10 and PM 2.5 mass fraction obtained from two methods at UIUC, as well as the relative difference between these two methods. It was noticed that the RD for PM10 was 3.34 plus or minus 5.34 %, which is reasonable. RD for PM2.5 was 94.46 plus or minus 3.05 %, which is not acceptable.
- This two figures shows differences in PM10 and PM2.5 mass fractions produced between two methods. From the left figure, PM10 mass fractions obtained from two methods agree with each other good. From the right figure, PM2.5 mass fractions obtained from two methods are quite different.
- This table only summarized PM 10 mass fraction obtained from two methods at TAMU, as well as the relative difference between these two methods. It was noticed that the RD for PM10 was 2.46 plus or minus 2.06 %, which is reasonable. PM2.5 mass fraction was not available by TAMU, because the diameter of the lowest channel is larger than 2.75 micrometer ,which is larger than 2.5 micrometers.
- From this figure, quite good fit can be observed.
- This table summarized PM 10 and PM 2.5 mass fraction obtained from two methods at UIUC, as well as the relative difference between these two methods. It was noticed that the RD for PM10 was 3.34 plus or minus 5.34 %, which is reasonable. RD for PM2.5 was 94.46 plus or minus 3.05 %, which is not acceptable.
- This two figures shows differences in PM10 and PM2.5 mass fractions produced between two methods. From the left figure, PM10 mass fractions obtained from two methods agree with each other good. From the right figure, PM2.5 mass fractions obtained from two methods are quite different.
- This two figures shows differences in PM10 and PM2.5 mass fractions produced between two methods. From the left figure, PM10 mass fractions obtained from two methods agree with each other good. From the right figure, PM2.5 mass fractions obtained from two methods are quite different.
- From this figure, quite good fit can be observed.
- From this figure, quite good fit can be observed.