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AMS Experiments at SUNY Albany

AMS Experiments at SUNY Albany. Frank Drewnick Atmospheric Sciences Research Center State University of New York at Albany AMS Users Meeting Fall 2001. The ASRC Aerosol Lab. Constant monodisperse/polydisperse aerosol at RH of 10-90%

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AMS Experiments at SUNY Albany

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  1. AMS Experiments at SUNY Albany Frank Drewnick Atmospheric Sciences Research Center State University of New York at Albany AMS Users Meeting Fall 2001

  2. The ASRC Aerosol Lab Constant monodisperse/polydisperse aerosol at RH of 10-90% Size: 0.01 - 0.5 mm with Atomizer/DMA; 0.5 – 20 mm with VOG

  3. Nitrate Experiments 250 nm Particles, Heater @ 1.7 V

  4. Nitrate Experiments (II) Changing NH4NO3 Solution Concentration in Atomizer: • m30 / m46 Signal Ratio decreases with increasing Solution/Particle Concentration

  5. Heater Experiments Size Distribution Width for 200 nm NH4NO3, NaNO3 and KNO3 Particles for different Heater Voltages : • Above Threshold Heater Temperature instantaneous Evaporation • Threshold Heater Temp. depends on Boiling Point

  6. Heater Experiments (II) Relative m30 and m46 Signal Intensity (m30 = 100 %) : • Signal Ratio dependent on Heater Voltage  Thermal Decomposition ?

  7. Heater Experiments (III) 200 nm NH4NO3 Particles at different Heater Voltages: Flight Time of Size Distribution Maximum: • Low Vapor Pressure Particles: Size Distribution shiftet to larger Particle Sizes !

  8. Heater Experiments (IV) Counting Efficiency for m30, 200 nm Particles, for NaNO3 and KNO3 :

  9. Heater Experiments (V) Size Distribution Width for 200 nm Sulfate Particles, for different Heater Voltages : • No change above Threshold Heater Temperature

  10. Heater Experiments (VI) Relative Intensity of m48, m64 and m80 Signal for different Heater Voltages : • Large Changes in relative Signal Intensities for (NH4)2SO4 • No significant Changes in Signal Intensities for CuSO4

  11. Heater Experiments (VII) Counting Efficiency Dependency on Particle Size and Heater Voltage : • Counting Efficiency increases with increasing Particle Size • No Counting Efficiency Increase above sufficient Heater Temperature • Count. Eff. Significantly larger for CuSO4 than for (NH4)2SO4

  12. Sulfate-Nitrate Mix Experiments Mixtures of Ammonium Sulfate and Ammonium Nitrate, 300 nm Particles, Sulfate/Nitrate Signal :

  13. Sulfate-Nitrate Mix Experiments (II) Mixtures of Ammonium Sulfate and Ammonium Nitrate, 300 nm Particles, relative Signal Intensities : • For Nitrates and for Sulfates the relative Signal Intensities change, when the Mix changes

  14. Sulfate-Nitrate Mix Experiments (III) Sulfate/Nitrate Mix Particles, 300 nm, Counting Efficiency: • Small Addition of Sulfate decreases Nitrate C.E. • Addition of Nitrate increases Sulfate C.E. • Different C.E. at Sulfate/ Nitrate Masses for same Mixture

  15. Conclusions • Broadening of Size Distributions of low-Vapor-Pressure Species disappears with sufficient Heater Temperature, almost instantaneous Evaporation observed for all investigated species • Fractionation Ratio (m30/m46 for Nitrate, m48/m64/m80 for Sulfate) depends on several Analysis Conditions as Heater Temperature, Sample Concentration, Matrix; Typically shift to smaller Fragments observed with increasing heater Temperature (thermal decomposition?) • Delayed Evaporation at low Heater Temperature causes Shift of Size Distribution to larger Sizes

  16. Conclusions (II) How to solve the ‘Sulfate Problem’ ??? Aren’t Sulfate Particles focused as good as Nitrate Particles due to their non-spherical shape, which causes the observed lower Counting Efficiency ? Imre: ‘Ammonium Nitrate particles are always droplets and therefore perfect spheres, Ammonium Sulfate particles aren’t.’ Mix Experiment: Addition of Sulfate decreases Counting Efficiency of Nitrate Particles; Addition of Nitrate increases Counting Efficiency of Sulfate Particles – due to a Change in Particle Shape ?

  17. Is there any other reason, why Sulfate has lower Recovery than Nitrate – like Evaporation or Ionization Issues ? Experiments: Counting Efficiency for ALL investigated Nitrates – even for the ones with low Vapor Pressure, that are non-spherical Crystals – is ca. 100 %; Counting Efficiency for BOTH investigated Sulfates are well below 100 % ( even for sufficient Heater Temperature for instantaneous evaporation). Flight-time Data indicate larger Variations of shape factor (and therefore ‘Deviation from Sphere’) within the Group of Nitrates than for Ammonium Nitrate/Sulfate.

  18. Solution: Further Experiments, that clearly distinguish between sampling on Heater and Detection by QMS. For example: Collection of Nitrates/Sulfates Spots on Filters at Heater Location and at Surrounding of Heater and weighing of collected mass. …

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