Investigation of Gas-Phase Products from the NO₃ Radical Oxidation of Δ-3-Carene

Organic aerosol in the atmosphere has an impact on climate, visibility, and human health. Oxidation of biogenic volatile organic compounds forms secondary organic aerosols by lowering the volatility of the product molecules and thus enhancing partitioning to the particle phase. The NO3-initiated oxidation of Δ-3-carene was studied because it connects the interaction between biogenic and anthropogenic emissions to form aerosols. This work characterized the first-generation gas-phase products of the NO3-initiated oxidation of Δ-3-carene in a 7.4 m3 Teflon FEP chamber using a Vocus proton-transfer-reaction time-of-flight mass spectrometer (Vocus) and a high-resolution time-of-flight chemical-ionization mass spectrometer (CIMS) using iodide adducts. The mass spectra not only show the presence of most of the expected products, including dicarbonyl, hydroxy nitrate, carbonyl nitrate, hydroxy dicarbonyl, and dicarbonyl nitrate but also show significant fragmentation of the parent ions in the Vocus through the loss of water and/or nitric acid and other neutral fragments. Parent and fragment ions were grouped together, taking advantage of gas-wall interactions in Teflon tubing, which separate the molecules by their inlet delay time. After grouping product ions, the Vocus signals were used to determine the gas-phase product yields for the NO3 + Δ-3-carene reaction. A comparison between the Vocus and iodide CIMS data allowed the sensitivity of the iodide CIMS to be investigated. Understanding the mechanism of the oxidation of Δ-3-carene by NO3 radicals allows for a better understanding of the sources of organic nitrate in the atmosphere and can improve the interpretation of field data and the representation of this chemistry in models.