AAAR 32nd Annual Conference
September 30 - October 4, 2013
Oregon Convention Center
Portland, Oregon, USA
Abstract View
Alkane SOA Formation: Effect of Alkane Structure, NOx Conditions, Relative Humidity and Acidity
KATHERINE SCHILLING, Matthew Coggon, Jill Craven, Christine Loza, Tran Nguyen, Rebecca Schwantes, Lindsay Yee, Xuan Zhang, John Seinfeld, California Institute of Technology
Abstract Number: 147 Working Group: Aerosol Chemistry
Abstract Alkane SOA was generated in the Caltech Environmental Chamber from the photooxidation of structural isomers of dodecane to investigate the effects of structure, NOx conditions, relative humidity, and aerosol acidity on the formation of oligomeric species in the aerosol phase. Oligomer formation through acid-catalyzed condensation reactions has been predicted to be a significant contributor to SOA growth and mass in alkane photooxidation. n-Dodecane, 2-methylundecane, cyclododecane, hexylcyclohexane were subjected to photooxidation under moderate and high NOx conditions to probe the effect of structure and NOx on the gas-phase chemical mechanism and the chemical composition of the resultant SOA. To investigate the role of water on particle-phase chemistry, relative humidities (~5% and ~65% RH) were chosen to create seed particle surfaces mostly devoid of water and with multilayer coverage of water, respectively. Acidity was modified by varying seed particle composition; sodium chloride, ammonium sulfate, and ammonium sulfate with sulfuric acid were each used. The gas-phase precursors to oligomeric species in the aerosol were monitored by on-line chemical ionization mass spectrometry. SOA growth and chemical composition was monitored on-line by a time-of-flight aerosol mass spectrometer (Aerodyne, Inc.). Off-line analysis of alkane SOA collected by filters was done by solvent extraction and gas chromatography/mass spectrometry, and by direct analysis in real time (DART) – mass spectrometry. Together, these methods of analysis show the evolution of each parent compound’s resultant SOA population, and provide chemical insight into the products that partition into the particle phase and the oligomers that form in the aerosol phase.