10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Heterogeneous Reaction of Isoprene and Ozone on α-Al2O3 Particles Using Micro-FTIR Spectroscopy
Hongyang Lian, Pang Shufeng, YUNHONG ZHANG, Beijing Institute of Technology
Abstract Number: 58 Working Group: Aerosol Chemistry
Abstract Isoprene, a volatile organic compound (VOC), is mainly emitted from biogenic sources with global emissions of about 500 Tg yr-1. Though secondary organic aerosol (SOA) from isoprene ozonolysis through the gas-phase or aqueous reaction has been reported, the research on the heterogeneous reaction of isoprene is lack. As one of the typical oxide minerals, alumina contributes about 15% by mass to the total dust burden in the atmosphere, which has a defined chemical composition and is widely used as model minerals for studying heterogeneous reactions. In order to assess the impact of isoprene ozonolysis on the global SOA budget, it is important to understand heterogeneous reaction of isoprene ozonolysis on the mineral particles and SOA the formation.
The heterogeneous reactions of α-Al2O3 particles with the mixture of ozone (~60 ppm) and isoprene (~50 ppm) were studied as a function of relative humilities (RHs). The reactions were followed in real time using microscopic Fourier transform infrared (micro-FTIR) spectrometer to obtain kinetic data. The results show that ozone leads to rapid conversion from isoprene to carboxylate (COO-) on the surface of α-Al2O3 particles in initial stage. The amount of carboxylate ions on the sample was determined by the infrared absorption calibration curve in order to quantify the carboxylate ions formation rate d[COO-]/dt in terms of the reactive uptake coefficient. The reaction is sensitive to RHs and surrounding water significantly suppresses the formation of the carboxylate ions. For the isoprene ozonolysis reaction on the α-Al2O3 particles, the reactive uptake coefficient is strongly enhanced by over a factor of four as the RH decreases from 87% to 28%. The results imply that the Criegee intermediates generated from isoprene ozonolysis have low reactivity toward water resulting in the suppression of SOA formation.