Multiphase processing of organic hydroxynitrates in secondary organic aerosol from the radical-initiated oxidation of multi-olefinic monoterpenes

Abstract:

One of the greatest challenges facing atmospheric and climate science is understanding the impacts human activities have on the natural environment and atmospheric chemistry. The production of condensable organic compounds due to interactions between atmospheric oxidants, nitrogenous pollutants, and biogenic volatile organic compounds (BVOCs) emitted from the terrestrial biosphere can contribute significantly to the formation and growth of secondary organic aerosol (SOA). Aerosol particles influence atmospheric radiative transfer, cloud formation, and thus atmospheric temperatures. Due to their solubility in water and adsorptive nature, hydroxylated organic nitrates (HORONO₂) may contribute significantly to the formation and chemical aging of SOA, and serve as an important sink for NO_x (NO+NO₂). We recently observed that a monoterpene β-hydroxy-organic nitrate (C₁₀H₁₇NO₄), produced from the OH oxidation of α-pinene in the presence of NO_x, undergoes rapid processing in the aerosol phase via an acid-catalyzed and pH-dependent hydrolysis mechanism, potentially impacting SOA growth and molecular composition. Further processing in the aerosol phase via polymerization and formation of organosulfates is expected, yet studies related to product identification and their formation mechanisms are limited. In this presentation, I will discuss recent laboratory-based reaction chamber studies of gas-phase organic nitrate production, SOA formation, and acidity-dependent aerosol-phase processing of organic nitrates produced from the NO₃ oxidation of γ-terpinene. This BVOC is a diolefin, which as modeling studies suggest, may be an important nighttime organic nitrate precursor. Gas-phase organic nitrate compounds resulting from NO₃ oxidation were qualitatively identified applying I^- chemical ionization mass spectrometry (CIMS) and quantified via calibration using synthetic standards generated in our laboratory. Aerosol-phase analysis was carried out employing Fourier transform infrared spectroscopy (FT-IR) and high performance liquid chromatography electrospray ionization time-of-flight mass spectrometry (HPLC-ESI-ToF-MS). The results highlight the importance of the organic nitrate-peroxy radical fate in dictating nighttime particle formation.