title: On-line characterization of organic aerosols formed from biogenic precursors using atmospheric pressure chemical ionization mass spectrometry.
abstract: A method to investigate the chemical composition of organic aerosols formed from biogenic hydrocarbon oxidation using atmospheric pressure chemical ionization mass spectrometry (APCI/MS) is described. The method involves the direct introduction of aerosol particles into the ion source of the mass spectrometer. Using this technique, reaction monitoring experiments of alpha-pinene ozonolysis show the formation of hetero- and homomolecular cluster anions (dimers) of the primary oxidation products (multifunctional carboxylic acids). Since the formation of dimers plays a profound role in new particle formation processes by homogeneous nucleation in the atmosphere and, at the same time, is an intrinsic feature of APCI, it is essential to differentiate between both processes when on-line APCI/MS is applied. In this paper, we compare the results from the investigations of organic aerosols and artificially generated dimer cluster ions of the same compounds using identical ionization conditions. The clusters and their formation processes are characterized by varying the analyte concentration, investigating the thermal stability of dimers, and studying collisional activation properties of both ion species. The investigations show a significant difference in ion stability: dimer anions measured on-line have an estimated stability that is 20 kJ mol(-1) higher than that of the corresponding artificially generated cluster ions. Hence, the technique provides the possibility to accurately characterize dimers as ionized reaction products from biogenic hydrocarbon oxidation and allows an insight into the process of new-particle formation by homogeneous nucleation.
authors.affiliation: ISAS, Institute of Spectrochemistry and Applied Spectroscopy, Dortmund, Germany.
authors.forename: U
authors.initials: U
authors.lastname: Kückelmann
authors.forename: B
authors.initials: B
authors.lastname: Warscheid
authors.forename: T
authors.initials: T
authors.lastname: Hoffmann
mesh_terms: D000336:Aerosols / Q000032:analysis*; D000399:Air Pressure; D006838:Hydrocarbons / Q000032:analysis; D013058:Mass Spectrometry; D009930:Organic Chemicals / Q000032:analysis*
chemical_list: D000336:Aerosols; D006838:Hydrocarbons; D009930:Organic Chemicals