1. Formation of cirrus cloud by glassy aerosols
Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
Formation of cirrus cloud by glassy aerosols
Steven Dobbie
Benjamin Murray, Theodore Wilson, Zhiqiang Cui, Sardar Al-Jumur,
Ottmar Möhler, Martin Schnaiter, Robert Wagner, Stefan Benz, Monika Niemand, Harald Saathoff, Volker Ebert, Steven Wagner and Bernd Kärcher
University of Leeds
Karlsruhe Institute of Technology
University of Heidelberg
DLR

2. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
Ice supersaturations frequently exceed 100% RHi
Jensen, E. J. et al. Ice supersaturations exceeding 100% at the cold tropical tropopause: implications for cirrus formation and dehydration. Atm. Chem. Phys. 5, (2005).
Peter, T. et al. When dry air is too humid. Science 314, (2006).
Is something inhibiting the formation of cirrus?

3. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
Also in cloud:
Krämer, M. et al. Ice supersaturations and cirrus cloud crystal numbers. Atm. Chem. Phys. 9, 3505–3522 (2009).
Why aren’t supersaturations in cloud being quenched?

4. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
Cloud Processes Chamber, Leeds
- ICAS/Chem collab (Ben Murray)
share 3 PhD students
Studying ice nucleation of glassy aerosols relevant for TTL.
CP Chamber now cooled using liquid nitrogen
Kulkarni, G and S Dobbie, (2010) Ice nucleation properties of mineral dust particles: determination of onset RHi, IN active fraction, nucleation time-lag, and the effect of active sites on contact angles, Atmospheric Chemistry and Physics, 10, pp
Kulkarni, G; Dobbie, S; McQuaid, J B (2009) A new thermal gradient ice nucleation diffusion chamber instrument: design, development and first results using Saharan mineral dust, Atmospheric Measurement Technology, 2, pp

5. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
Glassy aerosols
”Temperature at which materials change from hard and brittle to soft and pliable”
“The temperature below which an amorphous material is a glassy solid and above which it is a viscous liquid“
“The glass transition temperature is a function of chain flexibility.  The glass transition occurs when there is enough vibrational (thermal) energy in the system to create sufficient free-volume to permit sequences of 6-10 main-chain carbons to move together as a unit.  At this point, the mechanical behavior of the polymer changes from rigid and brittle to tough and leathery”

6. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
Hypothesis:
Perhaps glassy particles in the TTL region are preventing ice formation leading to higher out of cloud supersaturations.

7. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
Peter 2009

8. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
AIDA Chamber, Karlsruhe
Aqueous citric acid was chosen as a model system because:
it has similar functionality to oxygenated organic compounds known to exist in atmospheric aerosols;
ii) its glass forming properties are similar to a range of other atmospherically relevant aqueous organic solutions and aqueous organic-sulphate mixtures; and
iii) its state diagram was recently mapped out

9. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
AIDA results:
Above 212K
(non-glassy regime)
Below 212K
(glassy regime)

10. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
AIDA results:
Above 212K
(non-glassy regime)
Below 212K
(glassy regime)

11. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
AIDA results:

12. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
APSC results:

13. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
APSC runs:

14. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
APSC results:

15. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
APSC results:

16. Conclusions: Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
Conclusions:
Lab studies:
Glassy aerosol particles nucleate ice heterogeneously below the glass temperature at about 122% RHi compared to about 160% for homogeneous
Modelling studies:
Including glassy aerosols:
Cloud number conc is order of magnitude lower
Mean size of ice is a factor of two higher
RHi less abrupt and asymptotes to about RHi (110%)

17. Conclusions: Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
Conclusions:
- New het pathway for nucleation at TTL region.
- Potential to explain observations of in-cloud super-saturations.

18. Future Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
Future
Experimental work:
- Return to AIDA this summer to investigate a range of glasses
Do other organics act in a similar way?
Are there organics with a higher glass transition temperature?
Can we observe glasses in the atmosphere?
Modelling work:
What is the impact of glassy aerosols on cirrus lifetime?
What is the impact on radiative properties?

19. Institute for Climate and Atmospheric Science (ICAS)
Cloud-Aerosol Meeting, Mar
Paper:
Glassy aerosols heterogeneously nucleate cirrus ice particles
Benjamin J. Murray, Theodore W. Wilson, Steven Dobbie, Zhiqiang Cui, Sardar M.R.K. Al-Jumur, Ottmar Möhler, Martin Schnaiter, Robert Wagner, Stefan Benz, Monika Niemand, Harald Saathoff, Volker Ebert, Steven Wagner and Bernd Kärcher. In press, Nature Geoscience, 2010