The activation of aerosol particles into cloud droplets in the Earth's atmosphere is both a key process for the climate budget and a main source of uncertainties. Its investigation is facing major experimental challenges as no technique can measure directly the two physical chemical parameters that are controlling these processes, the Raoult's term and the surface tension, in sub-micron particles. Comparisons between theory and observations have thus been very indirect until now.1Here we present recent laboratory and field studies opening new perspectives on the role of surfactants in these processes.A first study focused on the dynamic behavior of surfactants extracted from atmospheric aerosols2 and evidenced adsorption barriers at the air-liquid interface making these compounds much more efficient in cloud activation than currently described in partitioning models. These barriers also correspond to equilibration times that are beyond the detection of most on-line instruments, suggesting strong limitations in their experimental investigation and understanding until now. A second study had for objective to bring direct atmospheric evidences for the role of surfactants in cloud activation during the third Pallas Cloud Experiment, at the Pallas GAW station, Finland.3The first results obtained from observing simultaneously cloud events and surface tension measurements in PM1 aerosols at this site will be presented.References 1McFiggans, G., et al. The Effect of Physical and Chemical Aerosol Properties on Warm Cloud Droplet Activation. Atmos. Chem. Phys. 6, 2593�2649 (2006).2Nozi�re, B., Baduel, C., Jaffrezo, J.-L., The dynamic surface tension of atmospheric aerosol surfactants reveals new aspects of cloud activation, Nat. Commun. 5:3335, doi: 10.1038/ncomms4335 (2014).3Anttila, T., Brus, D., Jaatinen, A., Hyv�rinen, A.-P., Kivek�s, N., Romakkaniemi, S., Komppula, M., Lihavainen, H., Relationships between particles, cloud condensation nuclei and cloud droplet activation during the third Pallas Cloud Experiment, Atmos. Chem. Phys. 12, 11435�11450 (2012).

Towards a better understanding of the physical chemistry of surfactants in cloud activation: Laboratory results and field observations at the Pallas GAW station, Finland

248th National Meeting (2014)

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