AAAR 33rd Annual Conference
October 20 - October 24, 2014
Rosen Shingle Creek
Orlando, Florida, USA
Abstract View
Aging of Alpha-pinene First-Generation Ozonolysis Products by Reactions with OH
NINGXIN WANG, Spyros Pandis, Neil Donahue, Carnegie Mellon University
Abstract Number: 134 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 aging of the SOA produced during alpha-pinene ozonolysis through smog chamber experiments. SOA is first formed through reaction of alpha-pinene and ozone. During the second step, the first-generation products are allowed to react further with hydroxyl radicals (OH) generated via H$_2O$_2 or HNO$_2 photo-dissociation.
All experiments were conducted in the environmental chamber at Carnegie Mellon University. The SOA was characterized by a High-Resolution Time-of-Flight Aerosol Mass Spectrometer. Vapor loss to the chamber walls represents an experimental challenge for these aging measurements. Introduction of OH at different times after the formation of the first-generation products is used to quantify this effect. The effects of NOx (high and low level) and relative humidity were also investigated. Exposures of the SOA to OH varying from approximately 10$^6 to 5x10$^7 hr molecules cm$^(-3) were used, covering a significant range of atmospherically relevant aging timescales. A second-generation aerosol mass yield is used to quantify the aging effects with different levels of exposure to OH. Changes in the aerosol chemical composition were also measured.