Background

More than 90% of the world's population lives in areas where outdoor air pollution levels exceed health-based limits. In these areas, individuals may use indoor air filtration, often on a sporadic basis, in their residences to reduce exposure to respirable particles (PM_2.5 ). Whether this intervention can lead to improvements in health outcomes has not been evaluated.

Methods

Seventy non-smoking healthy adults, aged 19 to 26 years, received both true and sham indoor air filtration in a double-blinded randomized crossover study. Each filtration session was approximately 13 h long. True and sham filtration sessions were separated by a two-week washout interval. The study was carried out in a suburb of Shanghai.

Results

During the study period, outdoor PM_2.5 concentrations ranged from 18.6 to 106.9 μg/m³ , which overlapped with levels measured in Western Europe and North America. Compared to sham filtration, true filtration on average decreased indoor PM_2.5 concentration by 72.4% to 10.0 μg/m³ and particle number concentration by 59.2% to 2316/cm³ . For lung function measured immediately after the end of filtration, true filtration significantly lowered airway impedance at 5 Hz (Z₅ ) by 7.1% [95% CI: 2.4%, 11.9%], airway resistance at 5 Hz (R₅ ) by 7.4% [95% CI: 2.4%, 12.5%], and small airway resistance (R₅ -R₂₀ ) by 20.3% [95% CI: 0.1%, 40.5%], reflecting improved airway mechanics especially for the small airways. However, no significant improvements for spirometry indicators (FEV₁ , FVC) were observed. True filtration also significantly lowered von Willebrand factor (VWF) by 26.9% [95% CI: 7.3%, 46.4%] 24 h after the end of filtration, indicating reduced risk for thrombosis. Stratified analysis in male and female participants showed that true filtration significantly decreased pulse pressure by 3.3% [95% CI: 0.8%, 7.4%] in females, and significantly reduced VWF by 42.4% [95% CI: 17.4%, 67.4%] and interleukin-6 by 22.6% [95% CI: 0.4%, 44.9%] in males. Effect modification analyses indicated that filtration effects in male and female participants were not significantly different.

Conclusion

A single overnight residential air filtration, capable of reducing indoor particle concentrations substantially, can lead to improved airway mechanics and reduced thrombosis risk.