Heterogeneous Reactions of α-Pinene on Mineral Surfaces: Formation of Organonitrates and α-Pinene Oxidation Products

J Phys Chem A. 2022 Jun 30;126(25):4068-4079. doi: 10.1021/acs.jpca.2c02663. Epub 2022 Jun 16.

Abstract

Organonitrates (ON) are important components of secondary organic aerosols (SOAs). α-Pinene (C10H16), the most abundant monoterpene in the troposphere, is a precursor for the formation of several of these compounds. ON from α-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 α-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 α-pinene with nitrogen oxides on hematite (α-Fe2O3) and kaolinite (SiO2Al2O3(OH)4) surfaces, common components of mineral dust, have been investigated. α-Pinene oxidizes upon adsorption on kaolinite, forming pinonaldehyde, which then dimerizes on the surface. Furthermore, α-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 α-pinene on mineral surfaces are shown to more strongly adsorb on the surface compared to α-pinene. Overall, this study reveals the complexity of reactions of prevalent organic compounds such as α-pinene with adsorbed nitrate and nitrogen dioxide, revealing new heterogeneous reaction pathways for SOA formation that is mineralogy specific.

MeSH terms

  • Aerosols / chemistry
  • Air Pollutants* / chemistry
  • Bicyclic Monoterpenes
  • Kaolin
  • Minerals
  • Monoterpenes / chemistry
  • Nitrates* / chemistry

Substances

  • Aerosols
  • Air Pollutants
  • Bicyclic Monoterpenes
  • Minerals
  • Monoterpenes
  • Nitrates
  • Kaolin
  • alpha-pinene