Michael Gradmann

Supervisor: Maria Berghof, Staffan Sjörgenand Göran Frank

Examiner: Carl Erik Magnusson

Lund UniversityDepartment of Physics

Characterisation of Differential Mobility Analysers for the Droplet

Aerosol Analyser instrument

Understand mechanisms of climate and weather

Provide a reliable weather forecast Understand how and how much weather is

affected by humans

The DAA instrument

Measures size of cloud droplets Dries the droplets Measures number and size of the particles

(CCN)

→ unique data set

The DAA instrument

Sketch by Maria Berghof

Differential Mobility Analyser

Cylindrical capacitor Radial electrical field

Sheath air flow Uncurled, smooth

→ precise manufacturing required

Picture courtesy of [3]

Differential Mobility Analyser

Radial electrical field

Radial velocity

Differential notation

E= U

r∗ln r ar i er

vr r =U∗Z

r∗lnrar i

dt=

r∗lnrar i U∗Z

dr

Differential Mobility Analyser

Different differential notation

Integration, transposition

Electrical mobility

dz=

r∗lnr ar i U∗Z

v z dr

Z=

Q∗lnrar i 2∗U∗l

Z=neCC

3 d p

DMA preparation

Cleaning Check for scratches or

damages Mesh size checked

Mesh replaced Leak test

Picture courtesy of [3]

Set-up

Transfer function

Ideal triangular function

Losses and broadening because of imperfections inside the DMA

Picture courtesy of [2]

Transfer function

f , , Z 0 , Z =∗1Q s

Qa ZZ 0

−1;1− QaQs

≤ ZZ 0

≤1

f , , Z 0 , Z =∗1Q s

Qa −ZZ 0

1;1≤ ZZ 0

≤1QaQ s

f , , Z 0 , Z =0 ;ZZ 0

1−Qa

Qs

∨ ZZ 0

1Qa

Qs

Experimental method

Experimental method

Experimental method

Theoretical data can be calculated by

compared with measurement

λ, μ changed (iteration), until X² has its smallest value

X 2=∑i

exi−thi 2

n2 Z iN 1

=∫ f 1 1,1,Z ' 0 , Z ∗ f 2 2, 2,Z i , Z dZ

∫ f 1 1,1,Z ' 0 , Z dZ

Results

DMA name λa

μa

λb

μb

DMA1a 0.599 0.903 0.660 1.022

DMA2a 0.917 NA 0.811 1.056

DMA2b 0.934 0.942 0.980 0.756

DMA2c 0.838 0.783 0.904 0.885

DMA1b 0.953 0.910 0.969 0.832

DMA2d 0.686 0.710 0.786 0.714

DMA2e 0.821 0.942 0.842 0.881

DMA2f 0.858 NA 0.958 0.921

UDMA 0.896 0.781 0.962 0.873

Discussion

Too clean DMAs Turbulances caused by changed flow ratio Modifications added to DMAs (plastic

mount/mesh) Unstable particle number concentration

Discussion

Discussion

DMA name λa

μa

λb

μb

DMA2b 0.980 0.756

DMA1b 0.953 0.910 0.969 0.832

DMA2e 0.821 0.942

DMA2f 0.858 NA

Reliable results

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

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

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

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