[SLS Pre-Defense] Lesly Franco

“Laboratory measurements of α-pinene oxidation products across a range of NOx levels”

Peroxy radical chemistry (e.g., RO2 + HO2, RO2 + NO, or RO2 isomerization) has a governing influence on the products formed from VOC oxidation reactions. In particular, RO2 fate controls the formation of oxygenated molecules that can partition into the particle phase to form secondary organic aerosol (SOA). However, most previous SOA chamber studies focused on only a limited range of RO2 regimes—primarily conditions in which RO2 + NO or RO2 + HO2 reactions dominate, and RO2 radicals have short bimolecular lifetimes. This stands in contrast to conditions representative of the global atmosphere, which is characterized by longer bimolecular lifetimes that allow for some RO2 isomerization reactions to dominate. In the present study, we measure gas-phase products from the OH-initiated photooxidation of a-pinene in a 7.5 m3 chamber spanning multiple RO2 conditions in the presence of NOx across a wide range of bimolecular lifetimes (~1s-1– 150 s-1). Gas-phase oxidation products are measured using a proton transfer reaction mass spectrometer (PTR-MS) and an iodide chemical ionization mass spectrometer (I-CIMS). Organonitrate formation is observed under all conditions, including when no NOx is added (reflecting NOx emissions from the chamber walls), though nitrate yields and carbon number distribution remain strongly NOx-dependent. Generalized Kendrick Analysis (GKA) enables the examination of the product distribution as a whole; applying these across all experimental conditions provides insights into the role of RO2 chemistry (and NOx levels in particular) on the composition and chemical properties of the α-pinene oxidation products.

Sack Lunch Seminar Series —
Informal seminar series within PAOC (Program in Atmospheres, Oceans, and Climate) that focuses on more specialized topics than the PAOC Colloquium. The presentations are either given by an invited speaker or by a member of PAOC and can focus on new research or discussion of a paper of particular interest.

Contact: sacklunch-committee@mit.edu