Project Summary The goal of this proposal is to characterize the transitions into chronic obstructive pulmonary disease (COPD) among former workers and volunteers at the WTC disaster site. The investigators will apply diagnostic criteria for COPD, classify its severity, investigate the diagnostic stability, progression, and transitions, characterize structural abnormalities as assessed by chest CT imaging, and examine the interaction of WTC-related exposure levels with tobacco smoking on increasing the risk of chronic obstructive pulmonary disease. This project will be conductted in the occupational cohort followed at Mount Sinai, and in a parallel study at the occupational cohort followed by the New York City Department of Health WTC Health Registry. To that end, we will utilize the WTC Pulmonary Evaluation Unit Chest CT Imaging Archive, a large repository with more than 3000 chest CT images on 1700 WTC workers, as well as linked datasets with disease symptoms, both pre-WTC and WTC-related occupational exposures, detailed pulmonary function and longitudinal spirometry measurements and weight trends, visual imaging classification and grading, and quantitative computer assisted method (QCAM) measurements of airway, and pulmonary parenchymal abnormalities.