Reactions of ozone with α-prinene 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, CO2, HCHO, and aldehydes mainly composed of pinonaldehyde and nor-pinonaldehyde, while those from β-pinene were CO2, HCHO, and 6,6-dimethylbicyclo<3.1.1>heptan-2-one. Average molar yields from α-pinene were CO; 9¿1%, CO2; 30¿2%, HCHO; 22¿1%, and aldehydes; 51¿6%. Average molar yields from β-pinene were CO2; 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. ¿ American Geophysical Union 1989