AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Transitions from Functionalization to Fragmentation Reactions of Laboratory Secondary Organic Aerosol (SOA) Generated from the OH Oxidation of Alkane Precursors
ANDREW LAMBE, Timothy Onasch, David Croasdale, Justin Wright, Alex Martin, Jonathan Franklin, Paola Massoli, Jesse Kroll, Manjula Canagaratna, William Brune, Douglas Worsnop, Paul Davidovits, Aerodyne Research, Inc.
Abstract Number: 212 Working Group: Aerosol Chemistry
Abstract Functionalization (addition of oxygen) and fragmentation (loss of carbon) reactions governing secondary organic aerosol (SOA) formation from the OH oxidation of alkane precursors were studied in a flow reactor in the absence of NOx. SOA precursors were n-decane (n-C$_(10)), n-pentadecane (n-C$_(15)), n-heptadecane (n-$_(C17)), tricyclo[5.2.1.0$^(2,6)]decane (JP-10), and vapors of diesel fuel and Southern Louisiana crude oil. Aerosol mass spectra were measured with an Aerodyne high-resolution time-of-flight aerosol mass spectrometer, from which normalized SOA yields, hydrogen-to-carbon (H/C) and oxygen-to-carbon (O/C) ratios, and C$_xH$_y$^+, C$_xH$_yO$^+, and C$_xH$_yO$_(>1)$^+ ion abundances were extracted as a function of OH exposure. Normalized SOA yield curves exhibited an increase followed by a decrease as a function of O/C (OH exposure), with maximum yields at O/C ratios ranging from 0.29 to 0.74. The decrease in SOA yield correlates with an increase in oxygen content and decrease in carbon content, consistent with transitions from functionalization to fragmentation. For a subset of alkane precursors (n-C$_(10), n-C$_(15), and JP-10), maximum SOA yields were estimated to be 0.39, 0.69, and 1.1. In addition, maximum SOA yields correspond with a maximum in the C$_xH$_yO$^+ relative abundance. Measured correlations between OH exposure, O/C ratio, and H/C ratio may enable identification of alkane precursor contributions to ambient SOA.