Experiments were conducted in a dynamic chamber system to measure the formation of secondary organic aerosol (SOA) and particle-bound reactive oxygen species (ROS) produced from limonene ozonolysis in the presence of NO by varying the ratio of O3 to NO. A diffusion cell system was used to produce the constant input of limonene in to the chamber, and six sets of experiments were conducted. The concentration of SOA mass and ROS produced were measured at steady-state. ROS, including peroxides, peroxy radicals and ions, was determined using dichlorofluorescin (DCFH) and converted to equivalent H2O2 concentration. The particle mass was measured using a tapered element oscillating microbalance (TEOM) and a scanning mobility particle sizer (SMPS) was used to obtain particle volume distributions. The results showed that the SOA mass concentration ranged from 30.3 to 157.3 µg m–3, and the ROS concentration ranged from 6.1 to 29.4 nmol m–3 of H2O2. For the different combinations of NOx and O3, the concentration ratio of [O3]/[NO] around 1 was found to produce highest SOA mass and ROS, which is 157.3 µg m–3 and 29.4 nmol m–3. The SOA density was estimated by comparing the mass concentrations with the volume concentrations ranged from 1.21 to 1.48 g cm–3. The highest SOA density (1.48 g cm–3) occurred with the lowest concentration ratio of [O3]/[NO]. Compared with other monoterpene and linalool where each has one unsaturated carbon bond in other studies, limonene which has two unsaturated carbon bonds. Thus, it is the most efficient in generating the SOA and ROS concentrations in prior experiments without NO present.