Atmospheric Chemistry of Isoprene Hydroxyhydroperoxides

Abstract

Atmospheric oxidation of volatile organic compounds (VOCs) leads to the formation of ozone (O3) and secondary organic aerosol (SOA), known atmospheric pollutants. These compounds have been shown to have negative health effects and in the case of SOA, have significant impacts on radiative forcing. Understanding the mechanisms of the atmospheric oxidation of VOCs helps improve models and allows us to predict their effects on air quality. VOCs are emitted by both anthropogenic and biogenic sources. Isoprene dominates biogenic emissions on a global scale making isoprene oxidation a significant topic in atmospheric chemistry. Despite considerable research efforts, the oxidation of isoprene in remote locations, which represents a large fraction of emitted isoprene, is not well understood. Oxidation of isoprene in remote environments leads to the formation of organic hydroperoxides known as isoprene hydroxyhydroperoxides (ISOPOOH). Due to a lack of synthetic standards, the atmospheric oxidation of organic hydroperoxides in general has only been studied indirectly, e.g., during oxidation experiments starting with isoprene. In this work, we synthetize standards of the most important ISOPOOH isomers and study their fate in the atmosphere. Our work covers three topics: 1) Characterization of instrumentation commonly used for ambient VOC measurements. We find that ISOPOOH can interfere with measurements of methyl vinyl ketone and methacrolein, products of isoprene oxidation in anthropogenically influenced environments. 2) We study the role of ISOPOOH during in-cloud oxidation and show that ISOPOOH oxidation in clouds leads to SOA formation with distinct characteristics. 3) We investigate the gas-phase isoprene oxidation mechanism and its products using a combination of chamber experiments and modeling using the Master Chemical Mechanism. We suggest changes that improve the representation of isoprene oxidation under a variety of atmospheric conditions.