HEPA空气净化器对学校室内颗粒物的净化效果研究

为了解HEPA（high efficiency particle air filter，高效空气过滤器）空气净化器在小学教室和寝室的净化效果，于2019年3—4月在北京市一所全寄宿小学开展了一项HEPA空气净化器的交叉干预研究.记录干预组、非干预组室内和室外PM_2.5、PM₁₀、PM₁的浓度，计算空气净化器的净化率；采用多元线性回归模型探索净化效果的影响因素.结果表明:①空气净化器对PM_2.5、PM₁₀、PM₁的净化率分别为41.3%〔Q_l~Q_u（下四分位数~上四分位数，下同）:0~53.1%〕、40.7%（10.5%~46.2%）和34.9%（9.6%~40.3%），其中对PM_2.5的净化率最高；寝室的净化率高于教室的净化率.②当室外PM_2.5浓度为115，150）μg/m3时对PM_2.5的净化率最高，为52.83%（50.26%~56.13%），PM₁₀和PM₁亦有类似结果.③多元线性回归分析表明，室外PM_2.5浓度 < 35 μg/m3时，开门通风和室内人员活动分别使室内PM_2.5浓度下降3.73 μg/m3〔95%置信区间（95% CI）:（0.60 μg/m3，6.86 μg/m3）〕和升高3.4 μg/m3（0.22 μg/m3，6.58 μg/m3）；室外PM_2.5浓度为35，150）μg/m3时，空气净化器使室内PM_2.5浓度下降33.36 μg/m3（16.47 μg/m3，50.25 μg/m3）；室外PM_2.5浓度≥150 μg/m3时，空气净化器和开门通风分别使室内PM_2.5浓度下降48.87 μg/m3（25.62 μg/m3，72.12 μg/m3）和升高37.65 μg/m3（5.60 μg/m3，69.69 μg/m3）.研究显示:空气净化器可同时降低室内PM_2.5、PM₁₀、PM₁的浓度；当室外PM_2.5浓度 < 35 μg/m3时，不需开启空气净化器；当室外PM_2.5浓度为35，150）μg/m3时，空气净化器有较好的净化效果，偶尔开窗通风不影响空气净化器的净化效果；当室外PM_2.5浓度≥150 μg/m3时，开启空气净化器时应关闭门窗，以免影响其净化效果. 

Purification Effect of HEPA Air Purifier on School Indoor Particulate Matter

In order to evaluate the actual purification effect of air purifiers in primary school classrooms and dormitories, a cross-intervention study was carried out in a boarding primary school in Beijing from March to April 2019. Classes for grades 4 to 5 were selected and divided into 2 groups. The air purifiers equipped with high efficiency particle air filter (HEPA) were placed in one group of classrooms and dormitories, while the air purifiers without HEPA were placed in the other group. After 4 days of intervention and a one-month washout period, the air purifiers were exchanged for the second intervention. The indoor and outdoor concentrations of PM_2.5, PM₁₀ and PM₁ were monitored in accordance with students' schedules, and the purification rates of the air purifiers were calculated based on the intervention group and non-intervention group. A multiple linear regression model was used to analyze the influence of outdoor PM_2.5 concentration, intervention, personnel activities, and ventilation on indoor PM_2.5, and to analyze the factors influencing the purification effect. The results showed that: (1) The purification rates of PM_2.5, PM₁₀ and PM₁ were 41.3% (lower quartile (Q_l)-upper quartile (Q_u): 0-53.1%), 40.7% (10.5%-46.2%), and 34.9% (9.6%-40.3%), respectively. PM_2.5 had the highest purification rate. The purification rates of PM_2.5 in dormitories were higher than that in classrooms, and similar findings were found for PM₁₀ and PM₁. (2) When the outdoor PM_2.5 concentrations was in the 115-150 μg/m3 group, the highest purification rate of the air purifier was 52.83% (50.26%-56.13%), and similar findings were found for PM₁₀ and PM₁. (3) Multiple linear regression analysis determined that when outdoor PM_2.5 concentration < 35 μg/m3, the indoor PM_2.5 concentration decreased by 3.73 μg/m3 (95% confidence interval (95%CI): (0.60 μg/m3, 6.86 μg/m3)) with open-door ventilation, and indoor PM_2.5 concentration increased by 3.4 μg/m3 (0.22 μg/m3, 6.58 μg/m3) in the case of indoor personnel activities. When the outdoor PM_2.5 concentration was between 35 μg/m3 and 150 μg/m3, the indoor PM_2.5 concentration was reduced by 33.36 μg/m3 (16.47 μg/m3, 50.25 μg/m3) with HEPA air purifier. When outdoor PM_2.5 concentration ≥150 μg/m3, the indoor PM_2.5 concentration was reduced by 48.87 μg/m3 (25.62 μg/m3, 72.12 μg/m3) with HEPA air purifier, while the indoor PM_2.5 concentration was increased by 37.65 μg/m3 (5.60 μg/m3, 69.69 μg/m3) with open-door ventilation. This study found that the use of air purifiers can not only reduce the concentration of indoor PM_2.5, but also reduce the concentration of PM₁₀ and PM₁ in the normal life and study of primary school students. When the outdoor PM_2.5 concentration is lower than 35 μg/m3, there is no need to turn on the air purifier. When the outdoor PM_2.5 concentration is in the range of 35 μg/m3 to 150 μg/m3, the air purifier has a good purification effect, and occasionally opening windows for ventilation does not affect the purification effect of the air purifier. In the case of a large number of students in the classroom, if the air purifier is turned on, proper ventilation can be used to maintain a better indoor air quality. When the outdoor PM_2.5 concentration is higher than 150 μg/m3, the doors and windows should be closed if the air purifier is turned on to avoid affecting the purification effect of the air purifier.