Heterogeneous Reactions of alpha-Pinene on Mineral Surfaces: Formation of Organonitrates and alpha-Pinene Oxidation Products Published as part of The Journal of Physical Chemistry virtual special issue "Advances in Atmospheric Chemical and Physical Processes"

Organonitrates (ON) are important components of secondary organic aerosols (SOAs). alpha-Pinene (C10H16), the most abundant monoterpene in the troposphere, is a precursor for the formation of several of these compounds. ON from alpha-pinene can be produced in the gas phase via photochemical processes and/or following reactions with oxidizers including hydroxyl radical and ozone. Gas-phase nitrogen oxides (NO2, NO3) are N sources for ON formation. Although gas-phase reactions of alpha-pinene that yield ON are fairly well understood, little is known about their formation through heterogeneous and multiphase pathways. In the current study, surface reactions of alpha-pinene with nitrogen oxides on hematite (alpha-Fe2O3) and kaolinite (SiO2Al2O3(OH)(4)) surfaces, common components of mineral dust, have been investigated. alpha-Pinene oxidizes upon adsorption on kaolinite, forming pinonaldehyde, which then dimerizes on the surface. Furthermore, alpha-pinene is shown to react with adsorbed nitrate species on these mineral surfaces producing multiple ON and other oxidation products. Additionally, gas-phase oxidation products of alpha-pinene on mineral surfaces are shown to more strongly adsorb on the surface compared to alpha-pinene. Overall, this study reveals the complexity of reactions of prevalent organic compounds such as alpha-pinene with adsorbed nitrate and nitrogen dioxide, revealing new heterogeneous reaction pathways for SOA formation that is mineralogy specific.