Mixing and sink effects of air purifiers on indoor PM2.5 concentrations: A pilot study of eight residential homes in Fresno, California

摘要

We measured real-time and integrated PM2.5 inside eight occupied single-family homes in Fresno, California to evaluate how turbulent air mixing and pollutant removal caused by a filter-based air purifier influences the levels of fine particles in everyday indoor environments. In each home, we used a real-time monitor to log PM2.5 levels every 5 min over 12 weeks during which air purifiers were operating, except for a designed 3-day shutdown period for baseline measurements. We assessed how the operation of air purifiers changed the patterns of the frequency distributions for short-term (5 min) concentrations, which included spikes produced by sporadic indoor activities or emissions. This allowed us to examine the reduction effectiveness of air purifiers on concentrations of both recently emitted and well-mixed background aerosols. We observed a systematic change in the 5-min PM2.5 distributions in different homes-while air purifiers reduced 96 of the 5-min concentrations, they increased the magnitudes of the top 4, representing transient concentration peaks. This phenomenon is consistent with what would be theoretically expected based on passive scalar turbulence in fluid physics. We also collected gravimetric filter samples for PM2.5 composition, finding mean reductions of the long-term (2-5 days) concentrations of 29-37 for indoor PM2.5 and endotoxin. A less significant reduction (19-26) was seen for Pb (Lead).