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Organic aerosols

Organic aerosol particles, and specifically Secondary Organic Aerosol (SOA) is a major component of tropospheric aerosol and has multiple effects on the climate change and air quality perspectives. EUCAARI studied SOA formation and aging extensively by laboratory, field and modeling exercises.

The yields of SOA formation from Boreal and Mediterranean trees showed that in warming climate the monoterpene emissions will increase, possibly producing a cooling feedback on the climate system. However, isoprene emission increases can significantly dampen the effect, as presence of isoprene suppresses nucleation as well as SOA mass formation. There are indications that plant stress (e.g. droughts or hear-waves) induced emissions have the potentials to enhance SOA formation (sesquiterpenes) but also to suppress particle formation (leaf alcohols).

Ageing of the organic particles significantly affect their chemical composition and physical properties. Ageing became manifest in a distinctive increase of the O/C ratio in the particles and in the condensational growth of the particles, indicating the photo-chemical formation of condensable material. Depending on the substrate, the hydrophilicity of organic surfaces changes, which is important for CCN activation of organic particles and thus on the aerosol climate effects.

The model development resulted in a set of models and chemical mechanisms that enable consistent description of the chemical transformation and aging of organic aerosol components under a wide range of different conditions. Work within EUCAARI employed two newly developed techniques to provide vapour pressure measurements of atmospherically representative multifunctional organic compounds for model development, which enables future studies to use realistic vapour pressures in determining the gas-particle equilibrium.