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Characterisation of Differential Mobility Analysers for the Droplet Aerosol Analyser instrument

Michael Gradmann Supervisor: Maria Berghof, Staffan Sjörgen and Göran Frank Examiner: Carl Erik Magnusson Lund University Department of Physics. Characterisation of Differential Mobility Analysers for the Droplet Aerosol Analyser instrument. Understand mechanisms of climate and weather

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Characterisation of Differential Mobility Analysers for the Droplet Aerosol Analyser instrument

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  1. Michael GradmannSupervisor: Maria Berghof, Staffan Sjörgenand Göran FrankExaminer: Carl Erik MagnussonLund University Department of Physics Characterisation of Differential Mobility Analysers for the Droplet Aerosol Analyser instrument

  2. Understand mechanisms of climate and weather • Provide a reliable weather forecast • Understand how and how much weather is affected by humans

  3. The DAA instrument • Measures size of cloud droplets • Dries the droplets • Measures number and size of the particles (CCN) • → unique data set

  4. The DAA instrument • Sketch by Maria Berghof

  5. Differential Mobility Analyser • Cylindrical capacitor • Radial electrical field • Sheath air flow • Uncurled, smooth • → precise manufacturing required • Picture courtesy of [3]

  6. Differential Mobility Analyser • Radial electrical field • Radial velocity • Differential notation

  7. Differential Mobility Analyser • Different differential notation • Integration, transposition • Electrical mobility

  8. DMA preparation • Cleaning • Check for scratches or damages • Mesh size checked • Mesh replaced • Leak test • Picture courtesy of [3]

  9. Set-up

  10. Transfer function • Ideal triangular function • Losses and broadening because of imperfections inside the DMA • Picture courtesy of [2]

  11. Transfer function

  12. Experimental method

  13. Experimental method

  14. Experimental method • Theoretical data can be calculated by • compared with measurement • λ, μ changed (iteration), until X² has its smallest value

  15. Results

  16. Discussion • Too clean DMAs • Turbulances caused by changed flow ratio • Modifications added to DMAs (plastic mount/mesh) • Unstable particle number concentration

  17. Discussion

  18. Discussion Reliable results

  19. Conclusion • Values for λ and μ depend on the stability of particle number concentration • Broad distribution of particle number has a larger effect than slow changes • The time a particle takes to reach a CPC is important

  20. Perspective • Check of well known flow ratio to reproduce results published in [1] and [2] • Small changes made on the set-up • Particle number concentration distribution could be reduced to less than 2% • Significantly better results

  21. References • [1] Martin N.A. Karlsson, Bengt G. Martinsson, Methods to measure and predict the transfer function size dependence of individual DMAs, J. Aerosol Sci., 34, 603-625, 2003 • [2] Bengt G. Martinsson, Martin N.A. Karlsson, and Göran Frank, Methodology to estimate the transfer function of individual Differential Mobility Analyzers, Aerosol Sci. Techn., 35, 815-823, 2001 • [3] Anna Persson, Design av mätmetodik för droppaerosolanalysatorn, Examensarbete för Kandidatsexamen, Lunds Universitet, 2008 • [4] William C. Hinds, Aerosol Technology, 2nd edition, Wiliey Interscience, 1999 • [5] Göran Frank and Bengt G. Martinsson, An instrument for studies of the relation between cloud droplet size and dry residual particle size - The Droplet Aerosol Analyser, Proceedings of the International Conference on Cloud and Precipitation (Abstract), 2008 • Thank you for your attention • You are welcome to ask questions

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