AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Multi-generation Chemical Aging of Secondary Organic Aerosol Components
NINGXIN WANG, Neil Donahue, Spyros Pandis, Carnegie Mellon University
Abstract Number: 774 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. The first part of this study investigated aging in a well-constrained system through smog chamber experiments. The first-generation α-pinene ozonolysis products were allowed to react further with hydroxyl radicals (OH) formed via HONO photo-dissociation under either low-NOx or high-NOx initial conditions. The SOA was characterized by a High-Resolution Time-of-Flight Aerosol Mass Spectrometer (HR-ToF-AMS). Attenuated total reflectance (ATR-FTIR) was also employed to identify and quantify organonitrate functional groups for experiments with high-NOx initial conditions. A kinetics box model was deployed to monitor gas-phase species and shed light on the reaction mechanisms under high-NOx conditions. A 20-40 % increase in OA mass and a more oxygenated product distribution were observed after aging with an equivalent of 2-4 days of typical atmospheric oxidation conditions. Relative humidity did not have a significant effect on the additional SOA production. The high-NOx experiments suggested that the second-generation SOA formation was similar in magnitude or higher to that of the low-NOx case. Organonitrates accounted for about 20-40 % of the SOA formed.
The second part of this work investigated aging of ambient air through field perturbation experiments conducted in a portable dual-chamber facility. First experiments performed at a remote sampling site in Crete, Greece suggested significant SOA formation after exposing ambient air to additional OH.