PM 2·5 : an important cause for chronic obstructive pulmonary disease?

With the advent of popular technology to measure particulate matter with an aerodynamic diameter of 2·5 μm or less (PM2·5) in the past few decades as a measure for air quality, a proliferation of publications linking ambient air pollution to various health outcomes has occurred. To demonstrate the acute effects of air pollution, such as London smog exacerbating existing asthma or chronic obstructive pulmonary disease (COPD), was quite simple, but to show an association with the development of these chronic conditions was more difficult.