AAAR 34th Annual Conference
October 12 - October 16, 2015
Hyatt Regency
Minneapolis, Minnesota, USA
Abstract View
Formation of Highly Oxidized Multifunctional Organic Compounds in the OH-Initiated Heterogeneous Oxidation of Squalene under Environmental Conditions
NADJA HEINE, Kevin Wilson, Lawrence Berkeley National Laboratory
Abstract Number: 646 Working Group: Aerosol Chemistry
Abstract As an abundant compound on human skin squalene plays an important role for indoor air quality, but it also serves as a proxy for unsaturated hydrocarbons relevant in combustion and atmospheric chemistry. Once released into the air, photochemical transformation can occur, e.g. via reaction with O3 or OH, leading to fragmentation, isomerization and/or functionalization. Recent studies have shown that in particular the formation of highly oxidized multifunctional molecules (HOM) contribute to extremely low-volatile organic compounds which may ultimately account for new particle formation and the promotion of nanodroplets to cloud condensation nuclei.
Continuous Flow Stirred Tank Reactor (CFSTR) experiments in combination with vacuum ultraviolet (VUV) photoionization aerosol mass spectrometry is used to monitor the kinetics of an OH-initiated reaction and to determine the chemical composition of an aerosol in the course of the reaction. The influence of varying OH concentration [OH] (10^5 – 10^7 molec./cm3) on the effective uptake coefficient is investigated, as well as the effect of trace gases on the reaction rate and product formation.
The present study shows that the effective uptake coefficient increases as a function of decreasing [OH]. While at high [OH] (2x10^8 molec./cm3) chain termination reactions involving OH radicals result in an effective uptake coefficient of 1.9, particle-phase secondary chain chemistry prevails at environmental [OH] (~10^6 molec./cm3) thus increasing the effective uptake to over 100. The reaction appear to form highly oxidized multifunctional reaction products with O/C ratios greater than 0.6. Preliminary analysis suggest that these products are multifunctional hydroperoxides.
In contrast to a previous study with saturated hydrocarbons, the uptake coefficient shows little influence upon the addition of trace gases. However, the formation of HOM is increased by a factor of two.