The article is about a time-series panel study of subjects with chronic …

• Abstract
• Introduction
• Methods
• Results
• Discussion
• Conclusion
• Abbreviations
• Competing interests
• Authors' Contributions
• Acknowledgements
• References
• Figures
• Tables

In conclusion our study, despite its limitations, suggests that the short-term negative impact of exposure to relatively low concentrations of air pollutants on lung function is limited to individuals with already impaired respiratory health. The fine fraction of ambient PM seems responsible for the observed effects among COPD cases, with zinc and iron having a potential role. These hints require confirmation from larger and more focused panel studies, using appropriate methods to overcome the problem of multiple comparisons [44].