Background <p>South Korea has one of the highest levels of fine particulate matter (PM_2.5) exposure among Organization for Economic Co-operation and Development (OECD) member countries, while also experiencing a combination of external and domestic sources. Therefore, PM_2.5 collected from South Korean air with these characteristics is an optimal sample for animal studies focused on analyzing the potential effects of PM_2.5 on human health. Evidence from numerous human cohort studies and animal experiments suggests that chronic exposure to PM_2.5 significantly increases the risk of lung cancer. However, most of these studies relied on commercially available PM_2.5 rather than samples collected directly from ambient air.</p> Objectives <p>This study aimed to investigate the pathology of how PM_2.5 collected directly from the ambient air affects the development of neoplasms, fibrosis, and inflammation in the lung tissue of animal models. Tumors were categorized according to pathological classification as hyperplasia, adenoma, or carcinoma.</p> Results <p>The mean number of adenomas was significantly higher in the urethane + PM group than in the saline group. The mean maximum adenoma diameters in the urethane + PM and PM groups were significantly greater than in the saline group. In addition, the mean maximum adenoma diameter in the urethane + PM group was significantly greater than in the urethane group.</p> Conclusion <p>Our data show that exposure to PM influences the formation and growth of lung adenomas. Further studies are needed to elucidate the long-term effects of PM exposure and its underlying mechanisms, which could aid in developing preventive strategies.</p>