Investigation of APNs Chemistry from the Oxidation of Volatile Organic Compounds in the Atmospheric Simulation Chamber SAPHIR

Acyl peroxy nitrates (APNs) are important secondary pollutants in the troposphere, acting as reservoir for NOx (=NO₂+NO). The relatively long lifetime of APNs (around 40 min at 298K) allows them to be transported from highly polluted areas to remote areas, causing an increase in both NOx and ozone concentrations on site. Various techniques are used to measure APNs in both field and laboratory experiments. These include direct methods such as Gas Chromatography (GC), and Chemical Ionization Mass Spectrometry (CIMS), as well as indirect methods such as Thermal Decomposition (TD) where APNs are decomposed and NO₂ is detected.

In this contribution, the chemistry of APNs generated by the oxidation of different BVOCs (Biogenic Volatile Organic Compounds) is investigated at different levels of NOx. A series of experiments was conducted in the atmospheric simulation chamber SAPHIR, Forschungszentrum Jülich, Germany using a newly developed TD instrument which measures NO₂ by Iterative Cavity enhanced DOAS (ICAD). To investigate formation of APNs from species emitted by the chamber foil (e.g., acetaldehyde) experiments injecting only methane and/or CO were conducted to obtain a baseline value for the experiments with BVOCs. These were followed by experiments with isoprene, α-pinene, and β-pinene for NO ranging between 0.3 and 9 ppbv using hydroxyl (OH) and nitrate (NO₃) radicals as oxidants. Measured APNs as well as precursors and radicals were compared with results from zero-dimensional box model calculations using the Master Chemical Mechanism (MCM v 3.3.1).