Reactions of ozone with α‐pinene and β‐pinene in air: Yields of gaseous and particulate products

Abstract

Reactions of ozone with α‐pinene and β‐pinene were studied for the purpose of obtaining the quantitative yields of gaseous and particulate products. Major gaseous products from α‐pinene were CO, CO 2 , HCHO, and aldehydes mainly composed of pinonaldehyde and nor‐pinonaldehyde, while those from β‐pinene were CO 2 , HCHO, and 6,6‐dimethylbicyclo[3.1.1]heptan‐2‐one. Average molar yields from α‐pinene were CO; 9±1%, CO 2 ; 30±2%, HCHO; 22±1%, and aldehydes; 51±6%. Average molar yields from β‐pinene were CO 2 ; 27±2%, HCHO; 76±2%, and 6,6‐dimethylbicyclo[3.1.1]heptan‐2‐one; 40±2%. Particulate products were found to include pinonaldehyde, nor‐pinonaldehyde, pinonic acid, and nor‐pinonic acid from α‐pinene. The yields of the particulate aldehydes decreased with the reaction time, whereas the yields of the acids increased. This observation suggests the sequential oxidation of aldehydes to carboxylic acids. From β‐pinene, only 6,6‐dimethylbicyclo[3.1.1]heptan‐2‐one was identified as a particulate product. For α‐pinene, most of the products are explainable in terms of the reaction mechanism similar to that for the cyclohexene/ozone reaction, whereas for β‐pinene the principal reaction path is that of the doubly substituted Criegee intermediate. The total yields of organic aerosols from both α‐ and β‐pinene were measured with their concentrations at a lower ppb level. The yields were found almost constant in a pinene concentration range from 10 up to 100 ppb, being 18.3±1.1 and 13.8±0.8% for α‐ and β‐pinene, respectively, which are much lower than the previously reported values.