A new mechanism for aerosol particle formation and its potential role in the atmosphere

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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 ....)

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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

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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 ()
• .........
• .........
• .........

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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?

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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
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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)
• ........