AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Evidence for Ambient Dark Aqueous SOA Formation in the Po Valley, Italy
AMY P. SULLIVAN, Natasha Hodas, Barbara Turpin, Kate Skog, Frank Keutsch, Stefania Gilardoni, Marco Paglione, Matteo Rinaldi, Stefano Decesari, M. Cristina Facchini, Laurent Poulain, Hartmut Herrmann, Alfred Wiedensohler, Eiko Nemitz, Marsailidh Twigg, Jeffrey Collett, Colorado State University
Abstract Number: 93 Working Group: The Role of Water in Aerosol Chemistry
Abstract Laboratory experiments suggest that water-soluble products from the gas-phase oxidation of volatile organic compounds can partition into fogs, clouds, and aerosol water where they are further oxidized forming low volatility products. These products can remain in the particle phase after water evaporation forming aqueous secondary organic aerosol (aqSOA). Prior evidence for ambient aqSOA includes (1) an apparent missing source of SOA based on the underestimation of model-predicted vs. measured OA and (2) smog chamber experiments form SOA via gas-phase chemistry that is less hygroscopic and oxygenated than atmospheric SOA. However, few studies have attempted to observe ambient aqSOA. Therefore, a suite of measurements, including near real-time measurements of PM2.5 WSOC (water-soluble organic carbon), inorganic anions/cations, and organic acids, and gas-phase glyoxal, was made during the PEGASOS (Pan-European Gas-AeroSols-climate interaction Study) 2012 campaign in the Po Valley, Italy to search for evidence of aqSOA. Our results suggest local aqSOA formation. When this was observed, a correlation of WSOC with organic aerosol, aerosol liquid water, relative humidity, and aerosol nitrate was found. Comparisons of WSOC with oxygenated organic aerosol (OOA) factors determined from application of positive matrix factorization analysis on aerosol mass spectrometer data suggested that the WSOC in the first and second parts of the study were different. When aqSOA formed locally, a high O/C (oxygen/carbon) ratio was observed. Key factors for local aqSOA production appear to include: air mass stagnation, the formation of substantial local nitrate during the overnight hours which promotes aerosol liquid water formation, and the presence of significant amounts of ammonia.