Abstract. The molecular composition of particle phase ozonolysis products of o•-pinene is investigated to comprehend the aerosol formation process following the VOC oxidation, focusing on an understanding of new particle formation. Two analytical approaches are applied to identify lowvolatile oxidation products in the particle phase; off-line investigations using preconcentration on Tenax TA © followed by solvent extraction and liquid chromatography/mass spectrometry as well as an on-line technique, in which the organic aerosols are introduced directly into the ion source of a mass spectrometer (atmospheric pressure chemical ionization / mass spectrometry (APCI/MS)). Both techniques showed the formation of difunctional carboxylic acids, compounds whose physico-chemical properties will govern most of their mass into the particle phase. Furthermore, stable binary diacid adducts could be identified by MSn-experiments. These observations might give insight into the process of new particle formation by heteromolecular homogeneous nucleation, indicating that the initial cluster formation cannot be described by macroscopic properties of single oxidation products. Instead, strong intermolecular forces between different diacids might play a key role in the formation of initial nuclei and their subsequent growth.

A method is presented for the determination of acidic products from terpene oxidation in filter samples of the atmospheric particle phase. Oxidation products of monoterpenes are believed to add a large fraction to the secondary organic aerosol (SOA) in the troposphere. Those products with structures containing one or more carboxylic acid groups have especially low vapour pressures and therefore they are believed to contribute substantially to the particle phase. Although many experiments were performed in simulation chambers to study the SOA generation by oxidation of terpenes, concentration measurements of products in the atmospheric particle phase are still rare. This is especially true for oxidation products of terpenes other than alpha- and beta-pinene. Therefore, we developed a method for the quantification of acidic products from terpene oxidation in atmospheric aerosol samples. After passing a PM 2.5 (PM = particulate matter) pre-separator to remove coarse particles, fine atmospheric particles were collected onto quartz fibre filters. A backup filter was placed behind the first filter to estimate possible sampling artifacts. The filters were extracted in an ultrasonic bath using methanol. After enrichment and re-dissolving in water the samples were analysed using a capillary-HPLC-ESI(-)-MS(n) set-up. The ion trap mass spectrometer could be used to gain structural information about the analytes and to enhance the selectivity of the measurements by using its MS/MS capability. A variety of products from different terpenes could be identified and quantified in samples of the ambient atmosphere using reference data from chamber experiments. Due to strong matrix effects quantification of samples from the real atmosphere had to be done by the standard addition method.

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In this contribution, iodine chemistry in the Marine Boundary Layer (MBL) is introduced. A series of methodologies for the measurements of iodine species in the gas and particle phases of the coastal atmosphere has been developed. Iodine species in the gas phase in real air samples has been determined in two field campaigns at the west coast of Ireland, indicating that gaseous iodo-hydrocarbons and elemental iodine are the precursors of new particle formation. Particulate iodine speciation from the same measurement campaigns show that the non-water-soluble iodine compounds are the main iodine species during the marine particle formation. A seaweed-chamber experiment was performed, indicating that gaseous I 2 is one of the important precursors that lead to new particle formation in the presence of solar light in the ambient air at the coastal tidal area.

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