AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Aging of Alpha-pinene First-Generation Ozonolysis Products Formed under High NO$_x Conditions by Reactions with OH
NINGXIN WANG, Neil Donahue, Spyros Pandis, Carnegie Mellon University
Abstract Number: 606 Working Group: Aerosol Chemistry
Abstract Secondary organic aerosol (SOA) formation from volatile organic compounds in the atmosphere can be thought of as a succession of oxidation steps. The production of later-generation SOA via continued oxidation of the first-generation products is defined as chemical aging. Our work investigates the hypothesis that while first-generation monoterpene SOA mass yields are generally lower at high-NO$_x (largely because formation of organonitrates terminates oxidation sequences), later-generation (aging) SOA formation could be enhanced. This could be due to three reasons: increased radical cycling, less fragmentation of later-generation SOA products, and reduced photolysis of SOA species.
A series of experiments was conducted in the environmental chamber at Carnegie Mellon University. SOA was first formed through reaction of alpha-pinene and ozone under high NO$_x conditions. During the second step, the first-generation products were allowed to react further with hydroxyl radicals (OH) generated via HNO$_2 photo-dissociation. The SOA was characterized by a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-AMS). Attenuated total reflectance (ATR-FTIR) was also employed to identify and quantify organonitrate functional groups. A second-generation aerosol mass yield was defined to quantify the aging effects. Potential hydrolysis effects of organonitrate compounds were also explored by performing experiments at low and high RH.