Organic Aerosols (OA), which significantly affect the climate system and human health, often contain a substantial fraction of atmospherically processed species known as Oxygenated Organic Aerosol (OOA). However, the formation pathways and evolution of OOA remain poorly understood. To address this need, an experiment was conducted in a suburban forest in the Paris region to systematically study the evolution of OOA and their optical properties. Our results show that the photochemical processes drove significant increases in total submicron particle mass concentrations in the forest site, primarily via the production of OOA derived from both biogenic and anthropogenic emissions. Air mass origin critically influenced Particulate Matter (PM) pollution levels and photochemical activity: under elevated pollution and intense solar radiation during continental air mass-dominated periods, rapid formation of More-Oxidized OOA (MO-OOA) occurred. This MO-OOA dominated Brown Carbon (BrC) contributions, enhancing short-wavelength light absorption by 35 % on average after a relative ~24-hour photochemical aging process. Conversely, periods dominated by clean maritime air masses featured humid, low‑radiation conditions that yielded reduced pollution levels and an increased proportion of nitrogen‑enriched, Less‑Oxidized OOA (LO‑OOA). Suppressed photochemical activity during the clean maritime period limited MO-OOA production, resulting in a lower overall oxidation state of OA. These findings underscore the dual role of photochemistry in shaping aerosol optical properties and climate impacts, highlighting the necessity of accounting for air mass dynamics and oxidation pathways in suburban forest regions.