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SMPS

SMPS. Inhalt. Atmosphärisches Aerosol Messgeräte : SMPS, DMA & CPC, DMPS, PM10 oh je oh je Datenauswertung Ausblick : FOX. Atmosphärisches Aerosol. Atmosphärisches Aerosol. Aerosole. Wie gross sind Aerosole ?. Typical Aerosol Particle Size Ranges.

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SMPS

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  1. SMPS

  2. Inhalt • Atmosphärisches Aerosol • Messgeräte: SMPS, DMA & CPC, DMPS, PM10 oh je oh je • Datenauswertung • Ausblick: FOX

  3. AtmosphärischesAerosol

  4. AtmosphärischesAerosol

  5. Aerosole

  6. WiegrosssindAerosole?

  7. Typical Aerosol Particle Size Ranges Cloud droplets: ~ 4 - 100µm Fog droplets: ~ 5 - 20µm From Friedlander: Smoke, Dust and Haze

  8. Grössenverteilung

  9. Geographische Variation

  10. MessinstrumenteSMPS, DMA & CPC, DMPS, PM10 oh je oh je

  11. In-situ Grössen & Anzahlmessung How do we measure particle number and particle size ? • Following techniques have been used to count particles in the past: • microscope (particles collected on a plate) • picture (cloud chamber) • single particle in a continuous flow (most popular in situ aerosol instrument ) In-situ: man misstwo die Partikelsind Ex-situ: man misst von ausserhalb (z.B. Radar)

  12. 1. Anzahl: Condensation Particle Counter Important instruments in aerosol technology are Condensation Particle Counters (CPC). They are used to measure the particle number concentration down to the nanometer size range. The particles are enlarged due to supersaturation and a subsequent condensation of a condensable gas (normally Butanol, now also water!). The particles reach a size at which they can be optically detected. The number concentration is measured for all particle larger than the lower detection diameter.

  13. 1. Anzahl: Condensation Particle Counter • CPCs are used to measure the number concentration in the submicrometer size range. • The lower detection diameter is determined by: • the Kelvin diameter (supersaturation) • diffusion coefficient of the condensable gas • the particle material • The upper and lower detection limits are specific for each CPC type.

  14. 1.Continuous Flow CPC Modern CPCs operate with continuous aerosol flows and are able to count each single particle. Model TSI 3010, 3760, 3762,…: Principal: continuous flow, single particle counting Lower detection Buthanol: 10 nm (Model 3025: 3 nm,) diameter: Water CPC: 5nm Upper detection diameter: ca. 3000nm Concentration range: 0-10,000 cm-3 (Model 3025: 0-105 cm-3) Accuracy: 10% compared to a reference instrument Aerosol flow: 1.0 l/min

  15. 1. Schematic sketch of the CPC models TSI 3010 (also 3760, 3762)

  16. 1. Functioning The aerosol flow is saturated with butanol in a slightly heated saturator. The the temperature of the butanol-aerosol mixture is decreased by 17-27°C in the condenser of the CPC. Here, the butanol become supersaturated and condenses onto the particles. The particles grow to droplets of several µm in diameter. The droplet flow is focused in a nozzle and introduced into a counting optic. The droplets pass a laser beam, and each single particle creates a light pulse. Pulses with an amplitude above a certain threshold are counted. The particle number concentration can be calculated by knowing the aerosol flow rate (critical orifice).

  17. 1. CPC Data Teamviewer: 153 161 526 8814

  18. Wiemisst man die GrösseeinesAerosols? Unser Massband: Differential Mobility Analyser

  19. Wasist die GrösseeinesAerosols? Apfel: Durchmesser Soot: ???

  20. Wasist die GrösseeinesAerosols? Partikel mit gleicher electricalmobility

  21. Wasist die GrösseeinesAerosols? APS SMPS Partikel mit gleicher electricalmobility

  22. 2. Particle Size - Differential Mobility Analyzer

  23. 2.1 Electric Mobility Electrically charged particles move in an electric field according to their electrical mobility. The electrical mobility ZP of a particle with a certain electric charge is defined to (given in [cm2/Vs]): With ve derived analog to the sedimentation velocity The electrical mobility depends mainly on the particle size and electricalcharge. The smaller the particle the higher is the electrical mobility. The higher the electrical charge the higher is the electrical mobility. n = number of charges e = elementary charge B = particle mobility (“velocity per unit force”)

  24. 2. 2 Funktionsweise Assumption: All particles carry only one electrical charge. The electrical mobility is than only a function of the particle size in case of constant temperature and pressure. Example: An electrically charged polydisperse aerosol is led through a plate capacitor. Electrically charged particles are separated and deposited according their size.

  25. 2. Particle Size - Differential Mobility Analyzer Plate mobility analyzer: aerosol d sheath air

  26. 2.3 Theory of a plate mobility analyzer: The most simple mobility analyzer is a plate capacitor. A laminar particle-free sheath air flow Qsh is led through the capacitor (x-direction). An electric field is put between the plates (z-direction). The aerosol flow QA (x-direction) is fed into the capacitor close to one plate.   The total volume flow is  The particle velocity in x-direction is given to: The particle velocity in z-direction is defined to:

  27.   with w = width of the capacitor d = distance between plates The electrical mobility for a certain deposition place is given to: The voltage to select a certain mobility can be calculated by:

  28. 2.4 Theory of cylindrical mobility analyzer:  :

  29. Folie neu drucken 2.4 Theory of cylindrical mobility analyzer:  : The theory is analogous to the plate capacitor. The total flow is given to:  The particle velocity in x-direction is given to:  The radial velocity due to the electric field is described to:  with 

  30.  The electrical mobility for a certain deposition place is given to: The voltage to select a certain electrical mobility incl. the electrical mobility from Stokes‘ law can be calculated to:  The particle size for a certain deposition place and voltage cannot be analytically solved:

  31. 2. Differential Mobility Analyzer The voltage to select a certain electrical mobility incl. the electrical mobility from Stokes‘ law can be calculated to: e = elemental charge 1,602·10-19 As n = number of charges The particle size for a certain deposition place is: ∆DP= 1 nm or DP =10nm ± 0.5nm

  32. 2. Differential Mobility Analyzer Aerosol particles can be classified due to their electrical mobility in a DMA. A small volume flow Qs with particles of a defined mobility is taken out of the DMA through a slit at the end of the inner rod.   The mean mobility of these particles can be calculated to: The ideal width of the mobility bin is described to: for  QA=QS and QA =1/10 QSh

  33. 2. Differential Mobility Analyzer Example: DP= 10 nm with ZP = 2.078.10-2 cm/Vs and ∆ ZP = 4.156·10-3 cm/Vs ∆DP= 1 nm or DP =10nm ± 0.5nm the size resolution is excellent! The size resolution depends mainly on the ratio of the volume flow rates QA/QSh. The greater the ratio, the better becomes the size resolution.  

  34. 2. 5 Transfer function The transfer probability over the mobility bin is not unity. The DMA-transfer function depends on the particle size and sample flow ratio.   Example: QA= Qs The transfer function has the form of a symmetric triangle. The transfer probability of the mean electrical mobility is unity. The transfer probability of the upper and lower limit of the mobility bin is Zero. For QA>QS und QA<QS, the transfer function becomes asymmetric. This cases are not discussed, because they are not the standard applications.

  35. 2. 5 Transfer function Ideal transfer function:

  36. 2. 5 Transfer function • Real transfer function: • In reality, the DMA transfer function depends also on the DMA-design. • The transfer function becomes a function of the particle diameter. • The reasons are: • Diffusion broadening for ultrafine particles • Particle losses in the aerosol inlet and outlet of the DMA. • The transfer function becomes broader and the maximum transfer probability decreases. 

  37. 2.6 Generator for Monodisperse Particles • The DMA can select a quasi monodisperse aerosol from a polydisperse aerosol population. • A generator for monodisperse aerosol particles consists of: • a polydisperse aerosol generator (atomizer, tube furnace) • a bipolar diffusion charger • a DMA  • The monodisperse aerosol with the size DP1 can however contain larger particles with the same electrical mobility carrying more elementary charge units. • Example: • DP1 = 100 nm (singly charged) • DP2 = 152 nm (doubly charged) • DP3 = 196 nm (triply charged)

  38. 3. DMA + CPC How do we measure particle number and particle size ? Combination of DMA+CPC (most common application for atmospheric measurements)

  39. Electrical Mobility Spectrometer • The DMA can be used to measure the number size distribution of a polydisperse aerosol. • There exist two different principles: • 1. The voltage is increased stepwise (DMPS) • 2.The voltage is continuously increased (SMPS) • A electrical mobility spectrometer consists of: • a bipolar diffusion charger • a DMA • a CPC

  40. Electrical Mobility Spectrometer A electrical mobility spectrometer can measure a size distribution only for a certain size range. This size range depends on the DMA-geometry and the sheath air flow rate. Longer DMA  larger particle diameter Higher sheath air flow rate  smaller particle diameter

  41. Computer inversion routine: • The computer inversion routine calculates the number size distribution out of the mobility distribution. • For a complete inversion routine must be known: • The mobility distribution • The bipolar charge distribution • The size dependent DMA transfer function • The CPC detection efficiency curve

  42. Differential Mobility Particle Sizer (DMPS) A pre-impactor removes all particles larger than the upper diameter of the size range to be measured The particles are brought in the bipolar charge equilibrium in the bipolar diffusion charger. A computer program sets stepwise the voltage for each selected mobility bin. After a certain waiting time, the CPC measures the number concentration for each mobility bin. The result is a mobility distribution. The number size distribution must be calculated from the mobility distribution by a computer inversion routine.

  43. Scanning Mobility Particle Sizer (SMPS) The design of the system is identical to the DMPS. The difference lies in the measurement principle. The voltage is continuously increased. There is no waiting time any longer. The particle concentration is measured as function of time. The relationship between electrical mobility and time (time between DMA entrance and CPC detection) must be determined for each SMPS system. The results is again a mobility distribution. The number size distribution must be calculated from the mobility distribution by a computer inversion routine.

  44. Scanning Mobility Particle Sizer (SMPS) Teamviewer 498 662 983 2272

  45. MessinstrumenteSMPS, CPC & DMA, DMPS & PM10 istjetztklar?

  46. Datenauswertung

  47. Scanning Mobility Particle Sizer (SMPS) • Output: • APS • Average • config • Contour • diagnostics • integral • Inverted • Raw • raw long

  48. Particle Size Distributions

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