COPD is a disease characterized by increasing airflow obstruction caused by chronic inflammation in the lung. Although smoking remains an important risk factor for COPD, accumulating evidence has identified nonsmoking risk factors that also contribute to COPD development and progression. Therefore, the rationale of this study is to further investigate the proposal that a component of ambient air pollution such as Diesel Exhaust (DE), is one such risk factor for COPD. The acute effects of DE will be examined in a cohort of patients that currently have or are at risk of developing COPD, as well as in healthy controls. The purpose of the COPA study is to provide biological plausibility and deepen mechanistic understanding of the emerging epidemiology suggesting a strong role for air pollution in COPD. The novelty of COPA is that those with COPD have never before been a specific focus of a controlled human exposure to particulate air pollution and COPA also enjoys the advantage of including healthy and at risk subjects so that we may understand the very early stages of COPD development, oriented toward a framework of protection and prevention.