Experimental Measurements for Heterogeneous ice nucleation of Mineral dust particles

1. Experimental Measurements for Heterogeneous ice nucleation of Mineral dust particles By Gourihar Kulkarni Steven Dobbie Mike Smith Jim McQuaid (IUGG – July 2007)

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. Laboratory data Observational data Mineral dust / Fly Ash Ice Parameterizations Motivated by … Atmospheric measurements (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)

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. - 30 oC - 20 oC - 30 oC - 30 oC Experimental Procedure (1) (2) SSispectra

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.

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

10. R.2 Onset Nucleation Procedure Ttop = -26.0 deg C, Tbot = -34.0 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 = 105.5 %, Time = 69 sec

13. Nucleation Onset Image – 3 SSi = 105.5 %, Time = 78 sec

14. Nucleation Onset Image – 4 SSi = 105.5 %, Time = 92 sec

15. Relationship of onset SSi with temperature Dust Sample : Nigeria

16. Relationship of onset SSi with temperature

17. R.3 Active Fraction Determination Active Fraction = Number of ice particles observed / Total number of dust particles SSi = 116 %, Temp = -30 deg C 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 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.

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 VAPOUR SUPPLY VAPOUR SUPPLY Condensation Ice Nucleation Ice Nucleation SMALL DROPS Freezing ICE CRYSTALS ICE CRYSTALS Continuous collection Turbulence Continuous collection Vapour deposition COALESCENCE EMBRYOS Capture Splintering Fragmentation Aggregation Coalescence LARGE DROPS Freezing GRAUPEL Riming SNOW Fallout Melting Melting RAIN Small particles Large particles

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

25. Esi DRH T B1 T1 SSi Validation Esi T Deliquescence of Ammonium Sulfate particles

27. Laboratory data Observational data Ice Parameterizations