Controlled particle coating from β-caryophyllene photo-oxidation: An aerosol dynamics modeling–assisted chamber method

The Texas A&M Environmental Chamber (TAMEC) was employed to generate secondary organic aerosols (SOA) by oxidizing (Formula presented.) -caryophyllene with hydroxyl radicals ((Formula presented.)) in the presence of ammonium bisulfate seed particles. The TAMEC consists of a 10-m³ fluorinated ethylene propylene (FEP) bag in a temperature-controlled insulated enclosure (between (Formula presented.) and (Formula presented.) °C) that is equipped with LED UV-C 273 nm lights. An aerosol dynamics model, namely TUTAMU Chamber Aerosol Model (TUTAMUChAM), was utilized in real-time during the experiments to assist in deriving precise organic coating thickness on the seed particles. By combining experimental and computational results, the threshold for (Formula presented.) -caryophyllene oxidation products to nucleate was determined. The results also demonstrate that the injected mass of H₂O₂, but not of (Formula presented.) -caryophyllene itself, controlled the concentration of the oxidation products in the environmental chamber. Thus, controlling the injection of H₂O₂ can effectively prevent nucleation in chamber experiments, achieving precise particle growth and SOA coating thickness onto the seed particles while not simultaneously introducing particles of a different type into the chamber, which are requisites for future multiphase chemistry studies with the chamber. The model was also used to construct a generic parameterization in estimating the maximum amount of H₂O₂ injection to prevent nucleation for any given initial particle concentration during the photo-oxidation of (Formula presented.) -caryophyllene by (Formula presented.)