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Title: Towards closing the gap between hygroscopic growth and CCN activation for secondary organic aerosols-Part 3: Influence of the chemical composition on the hygroscopic properties and volatile fractions of aerosols
Authors: Poulain, L.Wu, Z.Petters, M.D.Wex, H.Hallbauer, E.Wehner, B.Massling, A.Kreidenweis, S.M.Stratmann, F.
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Issue Date: 2010
Published in: Atmospheric Chemistry and Physics Vol. 10 (2010), No. 8
Publisher: Göttingen : Copernicus
Abstract: The influence of varying levels of water mixing ratio,r during the formation of secondary organic aerosol (SOA) from the ozonolysis of α-pinene on the SOA hygroscopicity and volatility was investigated. The reaction proceeded and aerosols were generated in a mixing chamber and the hygroscopic characteristics of the SOA were determined with the Leipzig Aerosol Cloud Interaction Simulator (LACIS) and a Cloud Condensation Nuclei counter (CCNc). In parallel, a High-Resolution Time-of-Flight Aerodyne Aerosol Mass Spectrometer (HR-ToF-AMS) located downstream of a thermodenuder (TD) sampling from the mixing chamber, to collect mass spectra of particles from the volatile and less-volatile fractions of the SOA. Results showed that both hygroscopic growth and the volatile fraction of the SOA increased with increases in r inside the mixing chamber during SOA generation. An effective density of 1.40 g cm-3 was observed for the generated SOA when the reaction proceeded with <1 g kg-1. Changes in the concentrations of the fragment CO2+ and the sum of CxH+y(short name CHO) and CxH+y (short name CH) fragments as measured by the HR-ToF-AMS were used to estimate changes in the oxidation level of the SOA with reaction conditions, using the ratios CO2 + to CH and CHO to CH. Under humid conditions, both ratios increased, corresponding to the presence of more oxygenated functional groups (i.e., multifunctional carboxylic acids). This result is consistent with the α-pinene ozonolysis mechanisms which suggest that water interacts with the stabilized Criegee intermediate. The volatility and the hygroscopicity results show that SOA generation via ozonolysis of &alpha;-pinene in the presence of water vapour (r <16.9 g kg-1) leads to the formation of more highly oxygenated compounds that are more hygroscopic and more volatile than compounds formed under dry conditions. © 2010 Author(s).
Keywords: aerosol; chemical composition; cloud condensation nucleus; hygroscopicity; mixing ratio; volatile element; water vapor
DDC: 540
License: CC BY 3.0 Unported
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