Air cleaning — Luchtreiniging — Purificaton d’air — HEPA
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In this document you will find an overview of studies on the effectiveness of air cleaning to remove SARS-COV-2 from the air in different settings (schools, gym, hospitals, …) and thus greatly reduce the chance of infection.
A consumer model that purifies 600 m3/hour will cost approximately €500 to €600 at major brands. For a unit that cleans 300m3/hour you will pay approximately €300. These are recommended prices on which (quantity) discounts can certainly be obtained.
For instance delivering 40m3/h for every pupil in Flemish education (1.2 million pupils) would cost €80 million, or €15 per pupil per year amortised over 6 years, including 3 filters.
Cost Efficiency
“Exposure to airborne particles can have detrimental health impacts for human populations”. “The monetized health benefits of filter installations outweigh the operation costs by up to a factor of 10” https://www.sciencedirect.com/science/article/abs/pii/S0360132314003588?via%3Dihub
This is a very small investment relative to the costs of illness calculated by the Royal Academy of Engineering (UK): “We find that the annual expected costs of illness are equal to £15 billion for influenzatype pandemics and £8 billion for seasonal influenza, implying a total annual cost of £23 billion from influenza. This implies an annual cost of influenza of 1% of GDP in 2020”. “In 2020 we estimate that the total societal costs of influenza-type pandemics is about £1.3 trillion (or about 60% of GDP in 2020) and the impact is expected to grow over time”. “Most infection costs originate in local buildings such as schools, hospitals, and local community buildings (56%), with residential and commercial buildings accounting for a smaller share (20% and 17%, respectively)”. https://raeng.org.uk/media/fupdixju/nera-social-cost-benefit-analysis.pdf
A French study (2014) analysing the impact of only 6 pollutants (benzene, trichloroethylene, radon, carbon monoxide, fine particles and tobacco smoke) calculated that the yearly cost of those pollutants is already €19 billion, or 0.8% of the GDP of 2014. Taking into account viral and bacterial infections, and disease caused by mold, the cost would be substantially higher. https://www.oqai.fr/fr/campagnes/cout-socio-economique-de-la-pollution-de-l-air-interieur
Another study concluded that adding portable air cleaners to achieve equivalent of 12 ACH averted 54 infections & produced cost savings of more than $150,000 per year: “All 3 scenarios resulted in a net cost-savings and infections averted. For the base-case scenario, improving ventilation to 12 ACH was associated with 54 aerosol infections averted over 1 year, producing an estimated cost savings of $152,701 and 1.35 quality-adjusted life years (QALYs) gained.” https://link.springer.com/article/10.1186/s12962-022-00356-1
Practical considerations
Installation is no more difficult than installing a coffee machine. Maintenance costs are negligible. It is limited to cleaning the pre-filter approximately every month. This requires 2 minutes of work.
Depending on the model, the filters need to be replaced every 1 to 2 years and will cost between €50 and €100 for a consumer model.
The energy consumption is also negligible. For a model that cleans 600m3/h, you should count on 60Wh. Operating the same model at half speed (300m3/h) reduces the energy consumption to approximately 15Wh. Negligable compared to the heating costs caused by continuously having to fully open the windows.
One should also be attentive to the noise production, especially for consumer models. At the highest setting, most appliances produce too many decibels to operate at the most powerful setting all day. A lower setting is therefore recommended. And of course this has an impact on the number of devices needed. If, for example, you need a CADR of 800m3/h in a room, you will need 3 units with a CADR of 600m3/h working at e.g. half speed (3x300=900). Professional devices (with a cost of €3000-€5000) have a quieter operation.
The combination ventilation and air cleaning should change the air 6 times per hour (6 Air Changes per Hour, ACH) according to e.g. The Harvard T. Chan School of Public Health and the Deutsche Aerosolgesellschaft. Another approach is to change/clean at least 50 (preferably 80) m3/hour per person, see Supreme Health Council (HGR NR 9616, February 2021).
It is recommended to do both calculations and to apply the most stringent result. Consider oversizing the unit so that it does not have to operate at its highest setting to avoid noise pollution.
At the bottom of this blog, you will also find evidence for a substantial positive impact of the removal of air pollution on cognitive performance.
1. CDC
“The addition of two HEPA air cleaners that met the Environmental Protection Agency (EPA)–recommended clean air delivery rate (CADR) reduced overall exposure to simulated exhaled aerosol particles by up to 65% without universal masking. Without the HEPA air cleaners, universal masking reduced the combined mean aerosol concentration by 72%. The combination of the two HEPA air cleaners and universal masking reduced overall exposure by up to 90%”
https://www.cdc.gov/mmwr/volumes/70/wr/pdfs/mm7027e1-H.pdf
2. California Department of Public Health
3. Univ. Stuttgart
4. Testing mobile air purifiers in a school classroom: Reducing the airborne transmission risk for SARS-CoV-2
“the aerosol concentration was reduced by more than 90% within less than 30 min when running the purifiers (air exchange rate 5.5 h−1). The reduction was homogeneous throughout the room and for all particle sizes.”
https://www.tandfonline.com/doi/full/10.1080/02786826.2021.1877257
5. The removal of airborne SARS-CoV-2 and other microbial bioaerosols by air filtration on COVID-19 surge units
https://www.medrxiv.org/content/10.1101/2021.09.16.21263684v1.full.pdf
6. Real-world data show that filters clean COVID-causing virus from air
“Research at a hospital swamped by people with COVID-19 has confirmed that portable air filters effectively remove SARS-CoV-2 particles from the air — the first such evidence in a real-world setting1. The results suggest that air filters could be used to reduce the risk of patients and medical staff contracting SARS-CoV-2 in hospitals” https://www.nature.com/articles/d41586-021-02669-2
7. Use of portable air cleaners to reduce aerosol transmission on a hospital coronavirus disease 2019 (COVID-19) ward
“Aerosols rapidly travelled from the patient room into other parts of the ward. Air cleaners were effective in increasing the clearance of aerosols from the air in clinical spaces and reducing their spread to other areas. With 2 small domestic air cleaners in a single patient room of a hospital ward, 99% of aerosols could be cleared within 5.5 minutes.”
8. Ventilation and air cleaning to limit aerosol particle concentrations in a gym during the COVID-19 pandemic
“The gym test showed that ventilation with air-change rate ACH = 2.2 h−1, i.e. 4.5 times the minimum of the Dutch Building Code, was insufficient to stop the significant aerosol concentration rise over 30 min. Air cleaning alone with ACH = 1.39 h−1 had a similar effect as ventilation alone. Simplified mathematical models were engaged to provide further insight into ventilation, air cleaning and deposition. It was shown that combining the above-mentioned ventilation and air cleaning can reduce aerosol particle concentrations with 80 to 90% , depending on aerosol size. This combination of existing ventilation supplemented with air cleaning is energy efficient and can also be applied for other indoor environments.”
9. VITO (Vlaamse Instelling voor Technologisch Onderzoek) — Flemish Institute for Technological Research
10. Harvard T. Chan School of Public Health
11. THE LANCET COVID-19 COMMISSION
12. SARS-CoV-2 aerosol transmission in schools: the effectiveness of different interventions
“One HEPA filter was as effective as two windows partly open all day during the winter (2.5-fold decrease) while two filters were more effective (4-fold decrease). Combined interventions (i.e., natural ventilation, masks, and HEPA filtration) were the most effective (≥ 30-fold decrease). Combined interventions remained highly effective in the presence of a super-spreader. Natural ventilation, face masks, and HEPA filtration are effective interventions to reduce SARS-CoV-2 aerosol transmission. These measures should be combined and complemented by additional interventions (e.g., physical distancing, hygiene, testing, contact tracing, and vaccination) to maximize benefit.” SARS-CoV-2 aerosol transmission in schools: the effectiveness of different interventions (medrxiv.org)
13. Air filters on Addenbrooke’s wards removed nearly all traces of airborne Covid-19 virus, Cambridge University Hospitals study shows
14. Are the Portable Air Cleaners (PAC) really effective to terminate airborne SARS-CoV-2?
“All the air samples collected before using PAC and 75% of swab samples were positive for SARS-CoV-2. After the PAC usage, all samples except one were negative, displaying a 80% device effectiveness. Portable HEPA cleaners usage allowed the removal of SARS CoV-2 and, therefore, they could be recommended for places with inadequate ventilation”
15. Aanbevelingen voor de praktische implementatie en bewaking van ventilatie en binnenluchtkwaliteit in het kader van COVID-19 Taskforce Ventilatie Version 2.O — 12 juli 2O21
“Het toepassen van luchtzuivering leidt tot een verlaging van de aerosol- of fijnstofconcentraties” https://werk.belgie.be/sites/default/files/content/documents/Coronavirus/Implementatieplan_ventilatie.pdf
16. Performance analysis of portable HEPA filters and temporary plastic anterooms on the spread of surrogate coronavirus
“Results suggested that the temporary anteroom alone could prevent the migration of nearly 98% of the surrogate aerosols into the adjacent corridor.”
“the best location of a single portable air purifier unit is inside the isolation room and near the patient’s bed”.
17. Hidden hazards of SARS-CoV-2 transmission in hospitals: A systematic review
“In addition, when HEPA filters were utilized, regardless of the type of ventilation, number of ACH or hospital area, minimal surface-borne & no airborne SARS-CoV-2 RNA was detected.”
“When HEPA filters were present, infrequent SARS-CoV-2 contamination was observed on surfaces (2/90 = 2.22%; p < 0.001; Appendix Table 1) and none found in the air (0/148=0.00%)”
“when HEPA filters were utilized, regardless off the type of ventilation, number of ACH or hospital area, minimal surface-borne and no airborne SARS-CoV-2 RNA was detected”
“Very low detection rates were observed in the presence of laminar flow ventilation in combination with and without negative pressure or HEPA filters. An alternative to such sophisticated ventilation systems with similar effects on airborne SARS-CoV-2 contamination proved to be mechanical ventilation with either HEPA filters, air purifiers, or strict fresh-air supply, which could be more readily utilized throughout the hospital. “ https://onlinelibrary.wiley.com/doi/10.1111/ina.12968
18. Efficacy of Ventilation, HEPA Air Cleaners, Universal Masking, and Physical Distancing for Reducing Exposure to Simulated Exhaled Aerosols in a Meeting Room
“The use of multiple HEPA air cleaners spread out around the room provides a faster and better mixing and cleaning of the room air, thereby reducing the overall concentrations for participants in the room and reducing the probability of SARS-CoV-2 transmission.” https://www.mdpi.com/1999-4915/13/12/2536/htm
19. Transmission and reduction of aerosols in classrooms using air purifier systems
“different scenarios with infected persons in the room have been analyzed, showing that the air purifier system leads to a significant reduction of airborne particles in the room dependent on the location of the infected person. The system can support additional ventilation strategies with fresh air, especially in cold seasons.” https://aip.scitation.org/doi/10.1063/5.0044046#_i33
20. Quebec: Number of cases in schools with air purifiers is three to four times lower.
This is not really a scientific research like the other ones in this document , but the following data are from a comparison of infections in schools with vs. schools without air purification. Unfortunately, as far as I know, there is no calculation of the number of cases per 100 pupils to be able to compare schools with air purification and schools without.
“In a sample of 677 schools with confirmed COVID-19 cases since the beginning of January, 4,223 cases found in total, an average of 6.8 cases per school. But in the 62 schools with purifiers, only 110 cases found or an average of 1.8 cases per school”
21. Effectiveness of In-Room Air Filtration and Dilution ventilation for Tuberculosis Infection control. (1996)
22. Air purifiers for schools: study results pave the way for long-term Corona strategy
“The use of the AiroDoctor with closed windows also reduced the risk by a good 50%. The device performed best when it was placed in the middle of the room. The use of the air purifier in combination with window ventilation was interesting: here the risk of infection dropped by a full 73%”
23. Quantifying environmental mitigation of aerosol viral load in a controlled chamber with participants diagnosed with COVID-19
“Ventilation, filtration, and humidification substantially reduce the environmental aerosol viral load, and therefore inhalation dose, and should be prioritized to improve building health and safety.” https://academic.oup.com/cid/advance-article/doi/10.1093/cid/ciac006/6498295?searchresult=1
24. Air Pollution Abstracts, Volume 4, Nrs 7–12. Environmental Protection Agency (US). Air Pollution Control Office.
25. Effectiveness of HEPA Filters at Removing Infectious SARS-CoV-2 from the Air
“The air cleaner with the HEPA filter continuously removed the infectious SARS-CoV-2 from the air in a running-time-dependent manner, and the virus capture ratios were 85.38%, 96.03%, and >99.97% at 1, 2, and 7.1 ventilation volumes, respectively.” https://journals.asm.org/doi/10.1128/msphere.00086-22#.Yvz7720nO
26. Portable HEPA Purifiers to Eliminate Airborne SARS-CoV-2: A Systematic Review
“Experimental studies provide evidence for portable HEPA purifiers’ potential to eliminate airborne SARS-CoV-2 and augment primary decontamination strategies such as ventilation”.
https://journals.sagepub.com/doi/epub/10.1177/01945998211022636
27. Characterizing the performance of a do-it-yourself (DIY) box fan air filter
“Overall, our results demonstrate that our Corsi-Rosenthal air cleaner efficiently reduces suspended particle concentrations in indoor environments.” https://www.tandfonline.com/doi/full/10.1080/02786826.2022.2054674?scroll=top&needAccess=true#
28. Effectiveness of portable air filtration on reducing indoor aerosol transmission: preclinical observational trials
“Portable air cleaning devices were very effective for removal of aerosols. The aerosols were cleared five times faster in a small control room with portable air cleaning devices than in the room with HVAC alone. The single-bed hospital room had an excellent ventilation rate (∼14 air changes per hour) and cleared the aerosols in 20 min. However, with the addition of two air cleaning devices, the clearance time was three times faster.”
29. Natural ventilation, low CO2 and air filtration are associated with reduced indoor air respiratory pathogens
“High CO2 and low natural ventilation were independent risk factors for detection. CO2 concentration and air filtration were independently associated with their concentration”
“Our results support the importance of ventilation and air filtration to reduce transmission”
“The odds of detecting a respiratory pathogen increased by 8.8% per 100 ppm increase in CO2 concentration. In contrast, odds decreased by 11% per stepwise increase in natural ventilation”
https://www.medrxiv.org/content/10.1101/2022.09.23.22280263v1.full.pdf
30. Bessere Luft für zu Hause (Stiftung wahrentest)
“We investigated the filter effect for aerosols in a test chamber with harmless paraffin oil droplets with a diameter of 0.12 millionths to 1 millionth of a meter. The Sars-CoV-2 virus measures about 0.12 millionths of a meter. With new filters, all air purifiers do their job well: We have converted the measurement results from the test chamber to an example room with 16 square meters, 2.50 meters in height and without people. In this room, the concentration of paraffin oil particles in the air drops by 90 to 96 percent after 20 minutes.”
31. The Usage of an Air Purifier Device with HEPA 14 Filter during Dental Procedures in COVID-19 Pandemic: A Randomized Clinical Trial
“The results showed the higher efficacy of the TEST Group on pollution abatement, 83% more than the Control fgroup. Additionally, the contamination was reduced by 69–80%.” https://www.mdpi.com/1660-4601/19/9/5139
32. Application of Portable Air Purifiers for Mitigating COVID-19 in Large Public Spaces
“The research results reveal that portable air purifiers with HEPA filtration provide an effective solution to help mitigate virus-carrying particles/droplets in large spaces where the central air conditioning system with HEPA filtration may not provide adequate dilution and/or effective ventilation. Deploying portable air purifier changes the local flow directions, and thus, reduces the cross-table airflows that may enhance the possibility of cross-infection.” https://www.mdpi.com/2075-5309/11/8/329/htm
33. Using an air purifier as a supplementary protective measure in dental clinics during the coronavirus disease 2019 (COVID-19) pandemic
“During dental treatments, saliva may become aerosolized, and microorganisms in such aerosols from the oral cavity contribute to the spread of infectious diseases.”
“On average, an air purifier with F6 class filter media removed 54% of aerosols that may carry airborne SARS-CoV-2, while the one with H12 class filter media removed 83% of such aerosols.”
34. Identifying behavior of long-distance virus transmission and mitigation performance from a COVID-19 outbreak of a daycare center
“In the experiment on air purifier fan modes, the concentration of virus-like particles decreased by about 27% and 86% in the weak (W) and strong (S) modes, respectively, compared to the condition with no air purifier”
https://www.sciencedirect.com/science/article/pii/S0013935122006454?via%3Dihub
35. Effects of purifiers on the airborne transmission of droplets inside a bus
“A purifier can effectively remove droplets from passengers’ coughs and reduce the infection risk of passengers.” https://aip.scitation.org/doi/10.1063/5.0081230
36. HEPA filters of portable air cleaners as a tool for the surveillance of SARS-CoV-2
“This study provides direct evidence of virus-containing aerosols trapped in HEPA filters and the possibility of using these PACs for environmental monitoring of SARS-CoV-2 while they remove airborne aerosols and trap the virus.” https://onlinelibrary.wiley.com/doi/10.1111/ina.13109
37. The Role of Portable Air Purifiers and Effective Ventilation in Improving Indoor Air Quality in University Classrooms
“In this study, we investigated the importance of improving indoor air quality in classrooms in light of the spread of SARS-CoV-2 variants.”
“The measurement campaign was carried out in three different phases: I) with no purifier in the classroom, II) with purifier at low flow rate of 267 m3/hr, and III) with purifier at high flow rate of 748 m3/hr.”
“The indoor CO2 levels in the analyzed classrooms (500–900 ppm) were below ASHRAE’s standard (700 ppm above outdoor level), indicating adequate ventilation and sufficient outdoor to indoor air circulation due to the high air exchange rates (2.63–8.63 hr-1). Moreover, operating the purifier at the maximum flow rate (748 m3 /hr) in classroom 3 resulted in increasing the particle decay rate from 3.9–4.8 hr-1 (without the purifier) to 6.5–6.7 hr-1, corresponding to a 50% reduction in indoor PM and PN after 10–15 minutes of switching off the aerosol source. The efficiency of HEPA air purifier exceeded 95% in capturing ultrafine and coarse particles; however, it was in the range of 82–88% in filtering particles in the accumulation range. This study highlighted the significance of mitigating indoor pollution in closed environments, especially in densely seated classrooms where the infection risk of viruses’ transmission is high. The findings of this study recommend the use of HEPA air purifiers in closed environments, especially when the ventilation system is not equipped with an efficient in-line filter.” https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4151658
38. Evaluation of a Commercial Air Filter for Removal of Viruses from the Air (1968)
39. Research by University Amsterdam on behalf of the Dutch Parliament — first results
“Het inzetten van professionele luchtreinigers kan leiden tot een 90% kleinere kans op indirecte Covid-19 besmetting. Dat is de uitkomst van een eerste proefopstelling, opgezet door de Nederlandse producent van luchtreinigers Euromate in samenwerking met de Universiteit van Amsterdam in opdracht van de Tweede Kamer. Het onderzoek toont tevens aan dat luchtreinigers ook het aanwezige fijnstof substantieel verlagen. Daarnaast zorgen de apparaten voor lagere energiekosten door een optimale verdeling van de gereinigde lucht.”
40. Efficacy of Do-It-Yourself air filtration units in reducing exposure to simulated respiratory aerosols
“The DIY air filtration units reduced aerosol exposure up to 73% depending on the design, filter thickness, and fan airflow.”
“Increasing the MERV 13 filter thickness, which is directly related to the surface area of the filters, resulted in significantly lower aerosol exposures for both types of DIY air filtration units.“
“In addition to increasing the filtration rate of the room air, using two DIY units instead of one also increased air mixing and produced a more uniform reduction in aerosol concentration. When a single DIY air filtration cube was placed at the front or back of the room, the cube substantially changed the airflow pattern in the room, causing some recipients to have a higher relative exposure. When a second unit was added to the room, exposure for all recipients was lower and the observed aerosol distribution was more consistent throughout the room.”
https://www.sciencedirect.com/science/article/pii/S0360132322011507
41. Indoor air surveillance and factors associated with respiratory pathogen detection in community settings in Belgium
“In conclusion, these results provide strong empirical support for the use of ventilation and air filtration to reduce transmission risk, consistent with previous studies.” https://www.nature.com/articles/s41467-023-36986-z
42. Can mobile indoor air cleaners effectively reduce an indirect risk of SARS-CoV-2 infection by aerosols?
“The results show that the aerosol concentration in a room with a size of 80 m2 can be reduced to a low level everywhere within a short time. In our opinion, indoor air cleaners with a large volume flow and high-quality filters of class H14 represent a very suitable technical solution to reduce the indirect risk of infection by aerosols in schools, offices, shops, waiting rooms, community and club houses, lounges and dining rooms, etc.”
43. Effectiveness of a portable personal air cleaner in reducing the airborne transmission of respiratory pathogens
2 scenarios were tested: proximity exposure scenario and shared indoor scenario. https://www.sciencedirect.com/science/article/abs/pii/S0360132323002494
Proximity exposure
shared indoor environment scenario
44. Establishment and application of test methodology demonstrating the functionality of air purification systems in reducing virus-loaded aerosol in indoor air
“The air purification systems realized a 97-99% reduction in viral load in air in 1 h. Captured infectious FCoV was reduced by 99.9%-99.99% by use of an ESP technology. Conclusions: The air purification systems, using ESP technology or HEPA filter, reduce the viral load in air. The ESP purifiers inactivate captured FCoV viruses. Therefore, air purification systems can be used as an adjunctive infection control measure.”
https://www.journalofhospitalinfection.com/article/S0195-6701(23)00078-6/pdf
45. Fit-Tested N95 Masks Combined With Portable High-Efficiency Particulate Air Filtration Can Protect Against High Aerosolized Viral Loads Over Prolonged Periods at Close Range
“Significant virus counts were detected on the face while the participants were wearing either surgical or N95 masks. Only the fit-testPASSED N95 resulted in lower virus counts compared to control (P = .007). Nasal swabs demonstrated high virus exposure, which was not mitigated by the surgical/fit-testFAILED N95 masks, although there was a trend for the fit-testPASSED N95 mask to reduce virus counts (P = .058). HEPA filtration reduced virus to near-zero levels when combined with fit-testPASSED N95 mask, gloves, gown, and face shield.” https://pubmed.ncbi.nlm.nih.gov/35535021/
46. Practical Mitigation Strategies for Countering the Spread of Aerosolized COVID-19 Virus (SARS-CoV-2) Using Ventilation and HEPA Air Purifiers: A Literature Review
“To develop an effective mitigation strategy, we reviewed the relevant literature assessing the use of ventilation and HEPA air purifiers for mitigating the spread of the aerosolized COVID-19 virus. Scientific evidence shows that air purifiers equipped with HEPA filters, combined with other types of ventilation, effectively reduced aerosolized spread of the COVID-19 virus.”
“For maximum protection indoors, all windows should be kept open at all times. If, for any reason, window ventilation must remain intermittent in nature, a hybrid approach with the use of HEPA air purifiers is strongly recommended.”
47. Effect of portable HEPA filters on COVID-19 period prevalence: an observational quasi-interventional study in German kindergartens
Opposed to all the other studies, this one doesn’t find a benefit of air cleaning: “While HEPA filters can significantly reduce the viral load in room air, this does not lead to reduced COVID-19 prevalence in the selected kindergartens in Germany”.
But this research is flawed. The following quotes from the study will make crystal clear why that’s the case:
“Ventilation forms a key preventive measure against contagion”.
“The Χ2 test indicates a significant difference in the pattern of ventilation between the intervention and control groups with more frequent ventilation in the control group”
“On average, the surface decontamination frequency is higher among the control group”
There is simply no valid comparison basis (c.q. no equal amount of ventilation in the control group and intervention group), which implies that it is impossible to draw the conclusion that air cleaning is ineffective.
https://bmjopen.bmj.com/content/13/7/e072284?s=09
48. Air purifiers brought to daycare centers reduced children’s illnesses by almost a third (first results of a Finnish study)
“In those daycare centers where air purification had been added, the children were clearly less sick, and the reduction was about 30 percent.”
“- The price of one day of sick leave for the employer is approximately 370 euros. If we could get rid of 30 percent of sick days caused by children, as well as diseases that go home to parents with children, it would be a big saving. This does not even include the costs of health care, costs related to drug courses or long-term harm, let alone the harm to the quality of life, how it affects the dynamics and well-being of the family, Sanmark reflects”
49. CDC advises to use air cleaning to prevent viral infections
https://www.cdc.gov/coronavirus/2019-ncov/prevent-getting-sick/Improving-Ventilation-Home.html
Warning concerning ionisation— plasma — UV
Safe+Work+TF+Desigining+infectious+disease+resilience+April+2021.pdf (squarespace.com)
As a consumer, the safest thing to do is to simply opt for appliances that are limited to the use of a HEPA filter (and possibly a carbon filter). Avoid appliances with ionisation, plasma, UV-C, unless you have reliable test reports from reputable institutes that show that the appliance in question is safe and does its job properly.
Impact on cognitive performance — learning outcomes
Air Filters, Pollution and Student Achievement
https://www.edworkingpapers.com/ai20-188
“Substantial improvements in student achievement: air filter exposure led to a 0.20 standard deviation increase in mathematics and English scores, with test score improvements persisting into the following year.”
“The results indicate that air filter installation is a highly cost-effective policy to raise student achievement and, given that underprivileged students attend schools in highly polluted areas, one that can reduce the pervasive test score gaps that plague public education.”
Air Quality and Error Quantity: Pollution and Performance in a High-Skilled, Quality-Focused Occupation
https://www.journals.uchicago.edu/doi/full/10.1086/698728
“We find that a 1 ppm increase in 3-hour CO causes an 11.5% increase in the propensity of umpires to make incorrect calls and a 10 μg/m3 increase in 12-hour PM2.5 causes a 2.6% increase (an extra 0.4 incorrect calls per 100 decisions)”.
“Chang et al. (2016b) find that higher outdoor PM2.5 levels lead to lower productivity for indoor workers at a pear-packing plant”.
“Lavy et al. (2014) separately examine the association between ambient concentrations of a number of local criteria pollutants on the performance of Israeli students taking the Bagrut, a high-stakes high school exit exam. They find that a one-unit increase in PM2.5 leads to a 0.046 standard deviation decrease in test scores”. To have a better idea of the impact of these data, let’s compare with a recent research studying the impact of teacher shortages and school closures: “one percentage point increase in unfilled vacancies is associated with a a decrease of -0.04 SD in the Dutch language, and -0.05 SD in math proficiency” https://feb.kuleuven.be/research/economics/ces/documents/DPS/DPS2023/dps%202301.pdf
The Impact of Indoor Climate on Human Cognition: Evidence from Chess Tournaments
https://conference.iza.org/conference_files/environ_2019/palacios_j24419.pdf
“The results indicate air pollution (PM2.5) is the deterring factor hindering cognitive performance. We find that an increase of 10 µg/m3 raises the probability of making an error by 1.5 percentage points, and increases the magnitude of the errors by 9.4%. The impact of pollution is exacerbated by time pressure. When players approach the time control of games, an increase of 10 µg/m3 , corresponding to about one standard deviation, increases the probability of making a meaningful error by 3.2 percentage points, and errors being 17.3% larger. Our results have important implications for high-skilled office workers, in particular, for those executing non-routine cognitive tasks whose share is steadily increasing in developed countries.”
PARTICULATE POLLUTION AND THE PRODUCTIVITY OF PEAR PACKERS
https://www.nber.org/system/files/working_papers/w19944/w19944.pdf
“We find that an increase in PM2.5 outdoors leads to a statistically and economically significant decrease in packing speeds inside the factory, with effects arising at levels well below current air quality standards.”
“We find that a 10-unit change in PM2.5 significantly decreases worker productivity by roughly 6 percent. Importantly, PM2.5 begins to affect productivity at levels well below current US air quality standards”
