Air purification — Luchtreiniging — Purificaton d’air — HEPA

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%”

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.”

5. The removal of airborne SARS-CoV-2 and other microbial bioaerosols by air filtration on COVID-19 surge units

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”

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

9. VITO (Vlaamse Instelling voor Technologisch Onderzoek) — Flemish Institute for Technological Research

10. Harvard T. Chan School of Public Health


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 (

13. Air filters on Addenbrooke’s wards removed nearly all traces of airborne Covid-19 virus, Cambridge University Hospitals study shows

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”

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.”

18. Efficacy of Ventilation, HEPA Air Cleaners, Universal Masking, and Physical Distancing for Reducing Exposure to Simulated Exhaled Aerosols in a Meeting Room

The coloration has been normalized to the concentration range observed among all trials, denoting purple as the lowest area sampler concentration and yellow as the highest. (A) HVAC system ventilation set at 2 ACH without HEPA augmentation; (B) one HEPA air cleaner placed in the back; © one HEPA air cleaner placed in the front; (D) two HEPA air cleaners placed in the front and back; (E) two HEPA air cleaners placed at the sides; (F) two HEPA air cleaners placed at the sides and raised upon 0.8 m tables; and (G) two HEPA air cleaners placed in the center of the room behind the aerosol source.

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.”

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.

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.”

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.”

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”.

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.”

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”

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.”

Warning concerning ionisation— plasma — UV

The Lancet COVID19 Commission

Impact on cognitive performance — learning outcomes

Air Filters, Pollution and Student Achievement

Air Quality and Error Quantity: Pollution and Performance in a High-Skilled, Quality-Focused Occupation

The Impact of Indoor Climate on Human Cognition: Evidence from Chess Tournaments




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