1. Status and plans of the CLOUD experiment CLOUD’s contribution to understanding global aerosols and climate
Ken Carslaw
Jasper Kirkby, Hamish Gordon, Eimear Dunne, Kamalika Sengupta, Cat Scott
The CLOUD Consortium
CERN SPSC June 2017
CLOUD-ITN
CLOUD-TRAIN
BACCHUS
CRESCENDO

2. Aerosol particles and climate
Scattering and absorption of solar radiation
Intergovernmental Panel on Climate Change
Changes in the properties of clouds 2

3. Climate prediction needs mechanistic models
Ice cores record greenhouse gas concentrations
They also record sulphate (aerosol) mass concentration
No information on the number of aerosol particles
We need climate models that include the physical processes
CO2 concentration
Climate warming
Sulphate (aerosol)
concentration
Climate cooling

4. Aerosol particles in the atmosphere
About half of climate-relevant particles

5. The CLOUD experiment
A unique chamber simulating near-atmospheric conditions with ~40 instruments measuring gases, ions, molecular clusters, particles and cloud droplets

6. CLOUD breakthroughs

7. Understanding aerosol particle concentrations in the atmosphere
Prior to 2015
Nucleation schemes based on theory and crude ambient observations
Now (from CLOUD)
Mechanistic nucleation rates based on laboratory measurements
(This has been the case for gas phase chemistry for 30 years!)
H2SO4-H2O nucleation
Primary particles
Primaries
Other nucleation
Total particle concentration / cm-3

8. Towards a mechanistic understanding
Climate model simulations over many decades requires a mechanistic understanding of nucleation:
Which species other than H2SO4?
How important are ions?
What is the role of the biosphere?
What happens at low temperature?

9. Biogenic control of particle concentration seasonal cycle
Under-prediction of summertime particle concentrations is solved using CLOUD mechanism from Riccobono et al., Science, 2014
Pearson correlation coeff (R)
Observations
Old H2SO4-H2O “mechanism”
Riccobono et al., Oxidation Products of Biogenic Emissions Contribute to Nucleation of Atmospheric Particles, Science (2014)

10. Discovery of “pure biogenic” nucleation
A new nucleation mechanism involving ions and highly oxidised multi-functional organic molecules (HOMs)
Ion effect
Kirkby et al., Ion-induced nucleation of pure biogenic particles, Nature (2016)

11. Pure biogenic nucleation and climate
% change in particles caused by “pure biogenic nucleation”
Pre-industrial
Present day
Forcing reduced by 23%
Implies a reduction in climate sensitivity
Gordon et al. Reduced anthropogenic aerosol radiative forcing caused by biogenic new particle formation, Proc. Nat. Acad. (2016)

12. Importance of preindustrial aerosol
Carslaw et al. Large contribution of natural aerosols to uncertainty in indirect forcing, Nature (2013)

13. What about nucleation in the rest of the atmosphere?
Total particle concentration / cm-3

14. Global model based on experimental nucleation rates
The most extensive measurements of nucleation rates covering atmospheric conditions (T, ions, trace gases)
Ammonia
Ions
Dunne et al. Global atmospheric particle formation from CERN CLOUD measurements, Science (2016)

15. Global model based on experimental nucleation rates
350 nucleation rate measurements from CLOUD campaigns 3, 5 and 7 to build global model mechanisms
208 K
223 K
248 K
278 K
292 K
Dunne et al. Global atmospheric particle formation from CERN CLOUD measurements, Science (2016)

16. Global model based on experimental nucleation rates
Nucleation rates separated into different pathways for the first time
Dunne et al. Global atmospheric particle formation from CERN CLOUD measurements, Science (2016)

17. Global model based on experimental nucleation rates
“Nearly all nucleation throughout the present-day atmosphere involves ammonia or biogenic organic compounds, in addition to sulfuric acid”
Observations
New model
Neutral H2SO4 only
Dunne et al. Global atmospheric particle formation from CERN CLOUD measurements, Science (2016)

18. Global importance of nucleation
65% of climate-relevant aerosol particles in the preindustrial atmosphere come from nucleation, and 55% today
H2SO4/NH3 + H2SO4/Biogenic + Pure biogenic
Pre-industrial nucleation frac.
Present day nucleation frac.
Gordon et al. Causes and importance of new particle formation in the present-day and pre-industrial atmospheres, submitted to Journal of Geophysical Research

19. Importance of ions for nucleation
H2SO4/NH3 + H2SO4/Biogenic + Pure biogenic
Global mean
Note the very large contribution of ions
Gordon et al. Causes and importance of new particle formation in the present-day and pre-industrial atmospheres, submitted to JGR

20. Collaboration Issues CERN CLOUD team:
CLOUD thanks CERN EP for providing an Applied Fellow for CLOUD Run Coordinator (starting 1 Jan 2017)
CLOUD also joined by open-choice Research Fellow who is focussing her research on global modelling (1 Jan 2017)
CLOUD-MOTION:
CLOUD has been awarded an unprecedented third Marie Curie Innovative Training Grant (3.9M€) within EC Horizon framework
15 ESRs for 10 CLOUD partners (coordinator: Goethe University Frankfurt)
2 ESRs will join CERN team
Project expected to run from 1 Sep 2017 until 30 Aug 2021

21. CLOUD12 Beam Request 18 Sep - 27 Nov 217 (9 wk, inc. 1 wk GCR at end)
Aims:
Coastal/Arctic marine nucleation and growth involving iodine compounds (2 wk):
Growth rates of pure sulphuric acid particles at small sizes (3 d):
Multi-component aerosol particle nucleation and growth (4 wk):
Anthropogenic aerosol particle nucleation and growth (2 wk):

22. CLOUD requests Dedicated CLOUD meeting room/open office:
CLOUD has no offices for collaboration members
CLOUD has on average 30 researchers at CERN during experimental runs - and up to 50 at certain times
CLOUD needs CERN’s support to find a permanent solution for a 50 m2 meeting room near the T11 zone to use as a daily meeting/planning room and office working space for visiting experimenters
CLOUD operation during LS2 East Area Renovation, :
CLOUD requests to run with cosmics during the fall 2018 and fall periods when CERN accelerators are off:
Importance/urgency of CLOUD scientific results for climate assessments
CLOUD-MOTION ESRs (15 PhD students) will rely on CLOUD data in runs
In close discussions with East Area Renovation team (project leader Sebastian Evrard/EN-EA-AC) to explore how essential CLOUD services can be maintained to allow operation in fall 2019 and fall 2020, without impacting East Area Renovation schedule

23. Summary
CLOUD is the pre-eminent aerosol experiment in the world
CLOUD has transformed how aerosols are represented in global climate models
Gone from theoretical/empirical models to mechanistic models based on laboratory data
An ambitious research programme ahead: marine/Arctic environments, more complex multi-component systems, polluted urban environments