[Purpose] We examined factors affecting annual change in pulmonary function in residents previously exposed to air pollution in an area where pollution has been reduced and a long time period has elapsed. [Subjects and Methods] Data of 730 officially acknowledged victims of pollution-related illness from an annual survey during 2000 to 2009 were analyzed. The primary outcome was forced expiratory volume in 1 second (FEV1), along with factors such as age, body composition, smoking habits, respiratory symptoms, and classification of medical management (an index of the need for treatment). Multiple regression analyses were used to identify factors associated with the annual change in FEV1. [Results] Three significant factors were identified: smoking habit, classification of medical management, and gender. Smoking habits and classification of medical management had stronger effects on the annual change in FEV1 than gender. [Conclusion] With an improved environment, continuation of smoking accelerates the decline in FEV1.