Indoor particulate matter (air pollution) is associated with worse COPD outcomes. In a research study, former smokers with moderate to severe COPD received either active or sham (pretend) high-efficiency particulate air cleaners for 6 months. Those who had an air filter experienced a greater reduction in respiratory symptoms, lower albuterol rescue use, and a lower rate of moderate but not severe flare-ups (exacerbations) compared with the sham group. Possible concerns of using an air cleaner include a higher electricity cost and possible noise when used in the bedroom if you are a "light" sleeper.