Objective To measure the concentrations of residential indoor and outdoor particulate matters (PM) during winter heating period in Beijing, and evaluate the effectiveness of household air purifiers on reducing indoor PM.
Methods From November 2015 to January 2016, fifteen residential houses were recruited from a district in Beijing and monitored for indoor and outdoor concentrations of PM2.5 and PM10 for 24 h before and after operating selected purifiers using highefficiency particulate air (HEPA) technique. Multi-channel particle monitor was used to monitor indoor PM2.5, PM10, and other smaller size-fractionated PM levels. Indoor/outdoor (I/O) PM ratios were used to indicate relative levels of indoor PM compared with outdoor PM levels, and Wilcoxon signed rank test for paired samples was applied to compare the I/O ratios with and without air purifiers operating. Purification rates of different PM fractions were used to evaluate the short-term effectiveness of air purifiers, and Friedman M test and Wilcoxon rank test were used to compare their difference.
Results The median and interquartile range of I/O ratios of PM2.5 daily averages without and with air purifiers operating were 1.79 (2.63) and 0.46 (0.49), respectively, and those of PM10 without and with air purifiers operating were 1.44 (1.65) and 0.40 (0.46), respectively. The differences between I/O ratios without and with air purifiers operating were significant for both PM2.5 and PM10 (P < 0.05). It took 3 h for air purifiers to reduce indoor PM to a stable level, and the average purification rates of PM with aerodynamic equivalent diameter (AED) ≤ 0.3 μm, > 0.3-0.5 μm, > 0.5-1 μm, ≤ 2.5 μm, and ≤ 10 μm were 59.03%, 63.08%, 67.00%, 63.60%, and 71.91%, respectively. The purification rates for PM with different AED were significantly different (P < 0.05).
Conclusion Household HEPA purifiers can reduce the concentrations of PM2.5, PM10, or other smaller size-fractionated PM, with 60% or higher reduction rate in 3 h. In addition, the purification effects for different fractions of PM are different.
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