AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Oxidation Chemistry and Secondary Organic Aerosol Yields from Isoprene when Alkylperoxyl Radical (RO2) Lifetimes Approach Ambient Values
TRAN NGUYEN, Rebecca Schwantes, Kelvin Bates, Xuan Zhang, Yuanlong Huang, Richard Flagan, Paul Wennberg, John Seinfeld, California Institute of Technology
Abstract Number: 274 Working Group: Aerosol Chemistry
Abstract The fate of the alkylperoxyl radicals (RO2) produced by the photooxidation of hydrocarbons is of fundamental importance to atmospheric chemistry. RO2 radicals in the atmosphere react with NO or HO2 on a timescale exceeding 10 seconds in biogenic regions. Yet, most chamber studies of hydrocarbon oxidation are investigated with radical levels that limit the RO2 lifetime to less than 0.1 second. A number of recent works have demonstrated the large impact of RO2 lifetime to gas-phase product distribution and, possibly, secondary organic aerosol (SOA) yields. For example, when RO2 lifetimes reach the ambient limit, the thermodynamic isomer distribution of first-generation products is favored over the kinetic distribution. Furthermore, isomerization of the RO2 radical followed by reaction with O2 (i.e., autoxidation), becomes a significant fate under this chemical regime. The isomerization mechanism rapidly incorporates oxygen into the hydrocarbon structure and is thought to be responsible for the prompt generation of “extremely low-volatility” SOA components in the monoterpene oxidation systems. These findings would suggest that longer RO2 lifetimes increase SOA yields, but the effect has not yet been investigated for isoprene. In this work, we explore the oxidation product distribution and SOA yields from isoprene when RO2 lifetimes are on the order of 50 seconds. We examine a variety of atmospheric conditions (T = 25 – 40 °C, RH = 4 – 85%, low – high seed particle area, a range of seed particle composition, etc.) and discuss the consistency of SOA yield data derived from isoprene when comparing the chamber to the atmosphere.