1. A new mechanism for aerosol particle formation and its potential role in the atmosphere Birgitta Svenningsson Div. of Nuclear Physics (from February 1) (Geocentre II, room 466 until....)

2. AIM Explore a mechanism creating high supersaturation of vapours in the vicinity of evaporating droplets and thereby trigger particle formation. The physical basis is not new, but it has not been acknowledged in this context before. Characterize it under laboratory conditions, where it has been observed Explore its relevance for the atmospheric aerosol

3. Some bacckground High supersaturations are needed to trigger particle formation, due to particle surface curvature and surface tension! The Kelvin effect. Still! Particle formation is observed under many atmospheric conditions. In boreal forests (?) Over a sub-arctic mire (?).......... Outflow of clouds (+) Coastal areas (+) During dissipation of fog in Arctic (+).........

4. Characteristics ”Local” supersaturation in the vicinity of droplets: the whole air parcel does NOT have to be supersaturated! Relatively high concentration needed in individual pre- existing Aitken (accumulation?) mode particles For substances that are ”water mixable” but have a low solubility (deliquescence close to 100% RH). For substances that have both a particle and vapour phase. Examples: –dicarboxylic acids (adipic and succinic acid)! –cis-pinonic acid, a monoterpene oxidation product! –fatty acids ?

5. This mechanism suggests a new pathway in the well- known Whitby figure. Aitken (Accumulation?) mode particles acting as sources for condensable material. Now, they are only considered as sinks, competing for the vapour

6. In the project... Relevant atmospheric conditions will be identified Candidate substances will be identified Laboratory studies on these substances + biogenic secondary aerosol will be performed Modelling Technical applications? Support from FORMAS for 50% of my salary in 3 years + some expenses Cooperation with –Merete Bilde; CCAR, Copenhagen (reaction chamber studies) –Ilona Riipinen and Markku Kulmala, Univ. of Helsinki (modelling) –........