Evaluating the Impact of Portable Air Purifiers on PM2.5 Reduction and Health Outcomes in Nurseries

Keywords: air purifiers, health, nursery, particle matters, PM2.5

Beyond their homes, children spend most of their time in schools, making it crucial to ensure good air quality in these environments. Compared to other educational settings, nurseries often report poorer indoor air quality (IAQ), which poses significant health risks to young children. Poor IAQ in nurseries can lead to respiratory issues, allergies, and developmental problems in children, thus necessitating a comprehensive understanding and improvement of IAQ in these settings. This study involved air quality monitoring in three London nurseries over 8-12 months. Indoor and outdoor pollutants were measured using both direct reading and passive monitoring methods. The mean reduction rate of PM2.5 with air purifiers was 63% with windows closed and 46% with windows open. The QALY gain was calculated at 292.8 per 10,000 children, with potential monetary benefits from air purifier use in all UK nurseries reaching £435.9 million annually. This article provides evidence for policymakers, strongly supporting the implementation and proper operation of HEPA filter air purifiers in schools to protect the health of vulnerable children.

Introduction

Children, especially those under six years old, are more vulnerable than adults to environmental pollutants because their immune and respiratory systems are not fully developed. Outside of the home, schools are where children spend most of their time (averaging 7-11 hours per weekday in classrooms) [1]. Poor indoor air quality has negative effects on human health and performance related to respiratory illnesses, allergies, and sick building syndrome symptoms (SBS). Exposure to air pollutants before the age of one year may contribute to the development of childhood asthma. It was estimated that the United Kingdom had a population of approximately 3.58 million children aged between 0 and 4 years. Additionally, around 1.2 million children aged 3 and 4 were registered for the 15-hour entitlement program (government-funded early years provision) in UK nurseries (national statistics, UK).

Studies about indoor air quality in nurseries are scarce, and poor indoor air quality is consistently reported in nursery settings. In nurseries, PM2.5 could be high and often exceeds the recommended level [2]. Previous studies reported mean indoor PM2.5 levels between 19.7 to 69.5 µg/m3 [3–6]. PM2.5 and smaller particles could easily penetrate the lungs and deposit in the respiratory bronchioles and the alveoli where gas exchange occurs. Particulate matter is one of the key risk factors for asthma. Asthma is a serious public health problem around the world. The global prevalence, morbidity and mortality related to childhood asthma among children has increased significantly over the last 40 years. The financial burden of asthma is relatively high with developed countries spending 1 to 2% of their healthcare budget on this condition [7]. In England, the national health service (NHS) notes that “the UK is one of the highest prevalence, emergency admission and death rates for childhood asthma in Europe, with around 1 in 11 children and young people living with asthma”.

Air cleaning technologies have been developed and studied to mitigate the indoor pollutant level, and HEPA filtration is recommended for its high efficiency at removing PMs without producing side products (e.g. O3, NOx). Previous studies have explored the health benefits of air purifiers in home environments for children, noting reduced asthma and nasal symptoms [8–10]. Yet, a recent review highlighted a lack of health research for younger children in schools and nurseries. More in-depth, context-specific studies are therefore essential to evaluate the effectiveness of interventions and to support policymakers in developing evidence-based guidelines for IAQ management in educational settings [11].

Methods

In May 2018, the Mayor’s Nurseries Air Quality Audits was launched to help improve the indoor air quality in nurseries in London. The work presented here was conducted as a part of the GLA’s nursery study. Based on the estimated ambient annual NO2, PM10 and PM2.5 concentrations reported by London Atmospheric Emissions Inventory, as well as other relevant datasets published by GLA, 15 nurseries in London with high exposure risks were contacted and 3 of them agreed to participant this study. Indoor and outdoor concentration data of PM2.5 was collected consistently for a 9 to 12 month period using direct reading instrument methods (Eltek TU1082-AQ110/112), data were collected at 5 min intervals and sent/stored to an online server.

Six air purifiers were installed in three nurseries, with three air purifiers in staffrooms and three air purifiers in classrooms. To check the purifier's operation, an optical pulse meter was positioned over the purifier's LED indicator, which flashes to signal that the equipment is turned on. Supplementary measurements of window status were also conducted.

Health impact assessments (HIA) were conducted focusing on the reduction of PM2.5 and its relation to childhood asthma, with calculations of QALY gains per child. The QALY is extensively employed in health economics as a comprehensive indicator of health outcomes, aiding in decisions about the allocation of healthcare resources. The calculation of QALYs involves multiplying the length of time in a specific health state by the utility weight assigned to that state. This measure has been frequently applied in some studies evaluating the health and economic impacts of asthma. The measured PM2.5 concentrations before and after the use of air purifiers were directly used in the HIA. In addition, the average indoor/outdoor (I/O) PM2.5 ratio derived from this study was applied to simulate indoor exposure scenarios, allowing the potential health benefits of air purifiers to be assessed at a broader scale (London and UK). Based on the population of nursery-aged children in the UK/London and the monetary value assigned to one QALY, along with the costs associated with air purifiers (both purchase and operational costs) for the assumed population, the monetary benefits could be evaluated.

Results

Indoor PM2.5 levels across different seasons

Figure 1 displays the recorded levels of PM2.5 both indoors and outdoors over two seasons. The median indoor PM2.5 levels in this study ranged between 0.3 and 6.1 µg/m3 during occupied hours (rooms with purifiers had median concentrations between 0.3 and 2.5 µg/m3, and rooms without air purifiers had median concentrations between 3.3 and 6.1 µg/m3). In most studied rooms, median concentrations were under the 5 µg/m3 (annual average exposure) recommended by WHO. However, in the seven classrooms without air purifier, only 54% of total occupied hours were below 5 µg/m3 across the study. For all rooms with air purifiers, the total occupied hours below 5 µg/m3 was as much as 88%.

Figure 1. Indoor and outdoor PM2.5 levels across different seasons (greyline indicates maximum indoor level recommended by WHO; *represents rooms with air purifiers).

Impact of air purifier on IAQ

Normal nursery settings

Figure 2 illustrates the differences of PM2.5 concentrations in studied rooms when air purifiers were either off or on (occupied hours and working days only). Even in staffrooms, which tended to have lower PM levels than classrooms, the reductions are clear. It is worth noting that when the air purifiers were turned off, the mean PM2.5 concentrations in two classrooms were 6.6 µg/m3 and 7.3 µg/m3, which were higher than the WHO guideline of 5 µg/m3 (annual mean). However, the air purifiers lowered the PM2.5 concentrations below the recommended level (3.4 µg/m3 and 2.3 µg/m3) in those classrooms (mean reduction in classrooms: 4.1 µg/m3).

Figure 2. PM2.5 concentrations in rooms with air purifiers; red boxes are when air purifiers were turned off; blues boxes are when air purifiers were turned on; the air flow rate of the air purifier selected is 820 m3/h, and the ideal ACH (air change per hour) for air purifier was kept around 3-4 in all studied rooms; N1_class5 represents N1_staff2 (it was used as classroom in heating season and staffroom in non-heating season).

Severe polluted settings

Figure 3 shows a special scenario when a nursery had been closed during summer vacation and some construction works were conducted in two classrooms which generated a lot of PMs (the work ended around 3 pm). The data were collected after the workers left, and rooms were unoccupied with all the windows and doors closed. The two rooms were next to each other, room 1 without an air purifier and room 2 with the air purifier on. Even with a high initial PM concentration, the PM2.5 level dropped close to 0 from the peak (165.2 µg/m3) within 45 minutes in room 2. However, in room 1without air purifier, the PM2.5 level dropped from 112.5 µg/m3 to 41.7 µg/m3, then dropped to 8 µg/m3 after 5 hours.

Figure 3. The decay curve of indoor PM2.5 with and without air purifier (a special scenario when nursery was unoccupied but with high PM levels). Room 1 without air purifier; room 2 with air purifier on for the whole period.

Impact of air purifier and window operation on IAQ

Figure 4 shows the indoor PM2.5 decay curves during the period of air purifier operation when opening and closing windows. Note, as purifiers typically started 1 hours before opening hours, peaks, likely associated with resuspension following the children’s arrival (around 9:00 a.m.), can often be seen around 60 mins after the purifier started operating. The plot aggregated the data during whole operation period of air purifier (around 200 working days), which includes different outdoor conditions and indoor activities.

Evaluation of indoor PM2.5 exposure in London/UK Settings

The monitored mean indoor PM2.5 level in three nurseries was 8.3 µg/m3 in 2021. Without air purifiers in operation, the mean level was 7.0 µg/m3; and with air purifiers in operation, the mean level was 2.9 µg/m3 in the studied rooms. For subsequent indoor exposure simulations, two different ambient outdoor levels were employed for UK and London. The annual mean concentration of PM2.5 in the UK was 8.3 µg/m3 in 2022 (data from LAEI). In addition, as calculated from the pollutant map of LAEI, the mean outdoor PM2.5 level of London nurseries was 9.8 µg/m3. Thus, simulated indoor PM2.5 levels were calculated based on the predicted mean outdoor level and are listed in Table 1.

Table 1. Annual mean I/O ratios under different scenarios it’s indoor PM2.5 exposure.

1. Evaluated indoor levels in 2022; unit: µg/m3.

2. Evaluated indoor levels in 2025; unit: µg/m3.

Quantification of health impact

QALY gains based on monitored and simulated data

As shown in Table 2, using appropriately sized and well-functioning air purifiers in the nursery was estimated to save 200.7 QALYs per 10,000 children per year from childhood asthma in 2021.

Table 2. Health impact calculations by harm class and air purifier use.

1. Nursery opened to children 7 hours a day and 38 weeks a year in the UK.

Different QALY gains u in London/UK nursery settings were calculated and shown in Table 3. For nurseries in London, the QALY gain was 360.7 per 10,000 children. For the UK national nursery children population, the QALY gain was 292.8 per 10,000 children.

Table 3. QALY gains in London/UK nursery settings.

Monetary benefit of QALY gains

Total monetary benefit of reducing PM2.5 concentrations in UK nurseries is listed in Table 4. The QALY loss equivalent for health care cost (cost of using air purifier) was 2280.4 QALYs and 15.2 QALYs for UK and London (local authority nurseries), respectively. In England, the net QALY gain was 33,791 QALYs for nursery children using air purifiers, with monetary benefits of £435.9 million. For nurseries in London, the net QALY gain was 7,740 QALYs, with monetary benefits of £99.8 million. This amount could be higher if children spend more time in nursery or assuming a higher cost-per-QALY.

Table 4. Total monetary benefit of reducing PM2.5 concentrations in UK nurseries.

1. Equivalent population of registered nursery children in 2021

2. £12,900/QALY was applied based on NHS cost

3. The health care cost was mainly about air purifier related costs (the initial investment in the unit, utility and filter cost)

4. Local authority nurseries in London (77 in total)

Discussion

The impact of air purifiers on IAQ

Although the median PM2.5 levels in most studied classrooms were lower than the guideline of 5 µg/m3 (the annual average exposure) suggested by WHO, in the classrooms without air purifier, only 54% of total occupied hours fulfilled the WHO guideline (in rooms with air purifier, the percentage could reach 89%). In this study, the deployment of air purifiers in classrooms led to a mean PM2.5 reduction of 4.1 µg/m3. The performance of the air purifier might be affected by the operation of windows and the level of outdoor air pollution. When evaluating the performance of the air purifier, season and region factors should be considered, as there may be variations in window operation and outdoor pollution levels.

Health and monetary benefits of using air purifiers

Air purifier could be used indoors for children with asthma. The asthma costs per patient per year (including all asthmatics: intermittent, mild, moderate, and severe asthma) in Europe was $1,900 (approximate £1,532) [12], and around 160,000 patients (reported by British Lung Foundation) received an asthma diagnosis each year. Thus, the financial burden would be around £245 million a year related to asthma in the UK. In this study, the costs of air purifier were £29.4 million per year, and it could potentially bring £435.9 million monetary benefits. Although £29.4 million per year is not a small budget, compared with financial burden and monetary benefit, it seems like reasonable to use air purifier indoor, especially for vulnerable group. For stakeholder and government, promoting the use of air purifiers in schools or homes is highly recommended. In most cases, the health benefits and savings outweigh the initial investment required for using air purifiers.

Conclusion

Impact of air purifiers and window operations on IAQ

·         Air purifiers were effective at reducing mean PM2.5 levels by 46% (with at least one window open) and 63% (with windows closed), increasing the total occupied hours with PM2.5 below 5 µg/m3 to 88%. This level of IAQ improvement could substantially reduce exposure of PM2.5 to children in nursery care even with significant natural ventilation.

·         When assessing air purifier performance, it's crucial to consider several specific factors separately: the state of windows (as indicators of ventilation), the level of outdoor pollution, and the background of seasonal and regional variations. Each element could impact air quality: window states influence indoor pollutant levels, outdoor pollution sets the baseline air quality, and seasonal/regional factors affect window behaviours.

Health and monetary benefits of using air purifiers

·         The results suggested that by applying air purifiers in nurseries across the UK, a substantial QALY gain of 292.8 per 10,000 children in the UK (360.7 per 10,000 children in London) can be achieved.

·         With the cost of £29.4 million per year for installing and operating air purifiers in UK nurseries, the potential monetary benefits could range from of £435.9 million. These findings strongly advocate for the widespread adoption of air purifiers in schools, particularly for the well-being of vulnerable children.

References

[1]     Almeida SM, Canha N, Silva A, Do Carmo Freitas M, Pegas P, Alves C, et al. Children exposure to atmospheric particles in indoor of Lisbon primary schools. Atmos Environ 2011;45:7594–9. https://doi.org/10.1016/j.atmosenv.2010.11.052.

[2]     Zhang S, Mumovic D, Stamp S, Curran K, Cooper E. What do we know about indoor air quality of nurseries? A review of the literature. Building Services Engineering Research and Technology 2021:014362442110098. https://doi.org/10.1177/01436244211009829.

[3]     Zuraimi MS, Tham KW. Indoor air quality and its determinants in tropical child care centers. Atmos Environ 2008;42:2225–39. https://doi.org/10.1016/j.atmosenv.2007.11.041.

[4]     Nunes RAO, Branco PTBS, Alvim-Ferraz MCM, Martins FG, Sousa SIV. Particulate matter in rural and urban nursery schools in Portugal. Environmental Pollution 2015;202:7–16. https://doi.org/10.1016/j.envpol.2015.03.009.

[5]     Canha N, Mandin C, Ramalho O, Wyart G, Ribéron J, Dassonville C, et al. Assessment of ventilation and indoor air pollutants in nursery and elementary schools in France. Indoor Air 2016;26:350–65. https://doi.org/10.1111/ina.12222.

[6]     Rim D, Gall ET, Kim JB, Bae GN. Particulate matter in urban nursery schools: A case study of Seoul, Korea during winter months. Build Environ 2017;119:1–10. https://doi.org/10.1016/j.buildenv.2017.04.002.

[7]     Serebrisky D, Wiznia A. Pediatric asthma: A global epidemic. Ann Glob Health 2019;85. https://doi.org/10.5334/aogh.2416.

[8]     James C, Bernstein DI, Cox J, Ryan P, Wolfe C, Jandarov R, et al. HEPA filtration improves asthma control in children exposed to traffic-related airborne particles. Indoor Air 2020;30:235–43. https://doi.org/10.1111/ina.12625.

[9]     Park HK, Cheng KC, Tetteh AO, Hildemann LM, Nadeau KC. Effectiveness of air purifier on health outcomes and indoor particles in homes of children with allergic diseases in Fresno, California: A pilot study. Journal of Asthma 2017;54:341–6. https://doi.org/10.1080/02770903.2016.1218011.

[10]   Butz AM. A Randomized Trial of Air Cleaners and a Health Coach to Improve Indoor Air Quality for Inner-City Children With Asthma and Secondhand Smoke Exposure. Arch Pediatr Adolesc Med 2011;165:741. https://doi.org/10.1001/archpediatrics.2011.111.

[11]   Cheek E, Guercio V, Shrubsole C, Dimitroulopoulou S. Portable air purification: Review of impacts on indoor air quality and health. Science of the Total Environment 2021;766. https://doi.org/10.1016/j.scitotenv.2020.142585.

[12]   Nunes C, Pereira AM, Morais-Almeida M. Asthma costs and social impact. Asthma Res Pract 2017;3. https://doi.org/10.1186/s40733-016-0029-3.