Multi-Center Clean Air Randomized Controlled Trial in COPD

The intervention is two active air cleaners with high efficiency particulate air (HEPA) filters which remove PM, as well as activated carbon filters to remove NO2 (and other trace gases). These will be run for a year in a participant's house.

The sham intervention is two sham air cleaners that have the internal HEPA and carbon filters removed, but which will run normally, including similar noise, airflow, and overall appearance compared to active air cleaners, thus blinding participants to filter status. These will be run for a year in a participant's house.