Investigation of organic nitrate product formation during hydroxyl radical initiated photo-oxidation of β-pinene

A series of experiments have been carried out in the York University smog chamber designed to study the products and pathways of the HO radical oxidation of β-pinene. Experiments on the oxidation of β-pinene and its most prominent oxidation product, pinaketone, by HO radicals with initial NO ranging from 0 to 2.5 ppm have been undertaken. An atmospheric pressure chemical ionization (API) mass spectrometer was operated for online, real-time identification and time profiling of the gas phase oxidation products. The formation of six organic nitrate products has been distinguished of which two have been assigned identifications, C10 dihydroxy nitrate (C10H17NO5) and nitrooxy-pinaketone (C9H13NO4). The real-time profiling and sensitivity to initial NO mixing ratio of each product has provided new insight into the β-pinene + HO radical oxidation mechanism. The distinguished products exhibited either no sensitivity or enhanced formations upon increasing the initial NO mixing ratio. The results also provide evidence supporting the formation of higher order organic nitrate products with formation pathways independent of pinaketone oxidation.