1. Experimental Measurements for Heterogeneous ice nucleation of Mineral dust particles
By Gourihar Kulkarni
Steven Dobbie
Mike Smith
Jim McQuaid
(IUGG – July 2007)
Thanks. Good morning everybody. In this talk I will be speaking about the development of new instrument which has been used to investigate the nucleating ability of mineral dust particles.
which is capable of producing a range of SSi under different temperature gradients,

2. Research Aims
To build and operate a new ice thermal gradient diffusion chamber, and to
Investigate ice nucleating properties of mineral dust particles.

3. Motivated by … Atmospheric measurements Efficacy of some dust
(Cziczo et al., 2004; DeMott et al., 2003)
Efficacy of some dust
particles to serve as IN
(& at low SSi) (Kanji et al., 2006)
Increasing trend in dust
emissions (Prospero et al., 2003)
Quantification of nucleation
results (Kärcher & Lohmann 2003;
Fletcher 1958)
Ice Parameterizations
Laboratory data
Observational data
Mineral dust
/ Fly Ash
-ice crystal residue – possibly indirect effect
-increase trend in dust conc. correlates with rainfall deficits in North Africa.

4. Thermal Gradient Diffusion Chamber (TGDC)

5. Insulating box (Microscope housing)
Cold Room,
(2.5m x 3m x 2.2m,
-60 to +50 deg C)
TGDC

6. TGDC
Micrometer & sample holder

7. Experimental Procedure
(1)
- 20 oC
- 30 oC
(2)
SSi spectra

8. Results R.1 SEM analysis of dust samples from Sahara (AMMA) & Spain
R.2 Nucleation Onset determination
R.3 Active Fraction
R.4 Calculating number of ice particles from
heterogeneous nucleation rate.
-In the results section, firstly I will be showing the elemental composition of dust particles.

9. R.1 SEM –EDX Analysis –Single dust particle spectra
(Si, Al, Mg, K, Ca, S and Fe) Si
1) Dakar Airport O
2) Dakar O Si Al Al Ca Fe
S Cl Fe Ca
S Cl Si
3) Nigeria
4) Spain O Al Fe

10. R.2 Onset Nucleation Procedure
Ttop = deg C,
Tbot = deg C
SSi
108.2 %
108.3 %
108.0 %
107.2 %
105.5 %
103.2 %
100.0 %

11. Nucleation Onset Image – 1 SSi = 103.2 % , Time = 0 sec
125 micron

12. Nucleation Onset Image – 2
SSi = %, Time = 69 sec

13. Nucleation Onset Image – 3
SSi = %, Time = 78 sec

14. Nucleation Onset Image – 4
SSi = %, Time = 92 sec

15. Relationship of onset SSi with temperature
-here you are seeing the square points at which the onset nucleation was observed.
-The area of the square point implies the frequency of onset nucleation observations.
Dust Sample : Nigeria

16. Relationship of onset SSi with temperature
-Low SSi
-Trend of curves, after -38 you are in homogeneous regime.
-Spanish dust curve, surface chemical composition,
-At same temperature, there is a spread in the SSi for dust particles,
-Diehl 2006, latent heat release – increase in vertical updraft =>mixed phase cloud reach higher altitudes with further ice formation process.
-Onset of freezing depends upon the type of IN.

17. R.3 Active Fraction Determination
Active Fraction = Number of ice particles observed / Total number of dust particles
SSi = 116 %, Temp = -30 deg C
-Very interesting plot. One can understand several important properties of nucleation. The active fractions were determined at four different combinations of SSi and Temperature.
-after time lag time, the curve trends shows the random distribution of active IN (becz it has exponential shape)
-As we know in the nucleation there are two different points of views about how it takes place.
Time Lag
Importance of active sites over the dust particle.

18. Comparison of Active Fractions
-20 deg C
-20 deg C
-30 deg C
-30 deg C
-Variability in the dust particles
The active IN fraction of dust particles from two different locations, Dakar and Nigeria, as function of the SSi.

19. R.4 Calculation of maximum number of ice particles
Jhet = w / (t . As) [ Experimental ]
nice = ndust [1 - exp (-Jhet.Ap.T)] P&K 1997
nice = exp{a + b[ 100 (SSi – 1)]} Meyers 1992

20. Conclusions
Evidence of dust nucleating at low SSi and over wide temperature range.
ESEM-EDX analysis shows the dust particles have mixed mineralogical composition with varied percentages.
The nucleating properties of dust vary between source regions.
* Onset nucleation - Spain and Sahara,
* Active fraction and Time lag- Nigeria and Dakar
Active fraction at constant SSi increases with increase in
temperature, and also fraction increases with increase in SSi.
-Low SSi results are in agreement with other studies.
-Mineral dust particle concentration influences the active fraction (important in determining conditions for initiating the ice phase in the troposphere).
Nucleation ph
enomenon may be combination of the stochastic and singular mechanisms.

21. Thank You

22. Comparison of average heterogeneous rates at different temperatures and SSi from Dakar and Nigeria locations. In a nucleation rate experiment the average heterogeneous rates are determined at a time (t1) when first nucleation event on the dust particle is observed and at a time (t2) when after no further dust nucleation is observed.

23. Life history of water vapour
RAIN
SMALL
DROPS
COALESCENCE
EMBRYOS
LARGE
GRAUPEL
SNOW
Life history of water vapour
Turbulence
Coalescence
Condensation
Freezing
Riming
Continuous collection
Capture
Splintering
Vapour deposition
Aggregation
Fragmentation
Melting
Fallout
VAPOUR
SUPPLY
ICE
CRYSTALS
Ice
Nucleation
VAPOUR
SUPPLY
ICE
CRYSTALS
Ice
Nucleation
Small particles
Microphysical interaction between different categories of water substance
Conversions of water substance
These invididual processes may sometimes be isolated for study. However, in a natural cloud these processes occur simultaneously.
Large particles

24. Concept Development 1) 2) 3) 4)

25. SSi Validation Deliquescence of Ammonium Sulfate particles Esi T EsiB1 T1
DRH
Esi
Esi T
Deliquescence of Ammonium Sulfate particles

27. Ice Parameterizations
Laboratory data
Observational data