What is the best scientific evidence for the effectiveness of air filtration for filtering pathogens from the air?

We have put together our list of some of the top peer-reviewed scientific publications on air filtration. We have chosen these papers because we believe that they are some of the most rigorous and well-designed studies in the field.

 These are not our studies and we have no investment or interest in the studies, outside of looking for high-quality data on air filtration. All scientific research is a moving target and there may be things we haven’t noticed in these papers or subsequent research that changes the interpretation. With that in mind, here are some of our top papers as of January 2024.

Top 10 – air filtration’s effectiveness at filtering pathogens from the air

1. Efficacy of HEPA Air Cleaner on Improving Indoor Particulate Matter 2.5 Concentration

2. Effectiveness of HEPA Filters at Removing Infectious SARS-CoV-2 from the Air
   Conclusions: Our study shows that air filtration using HEPA filters can consistently remove infectious SARS-CoV-2 from the air. Under our experimental conditions, approximately 90% of the infectious SARS-CoV-2 still wafted in the air after the filtration of 1 chamber volume, and at least 7.1 chamber volumes were required to reduce the viral load to below the detection limit. This finding indicates that the air in the chamber does not pass through the air cleaner evenly and that there are areas where the aerosols tend to linger. Therefore, when using an air cleaner, in addition to using a HEPA filter, it would be desirable to filtrate the entire room, including areas where air tends to be congested. Alternatively, an air cleaner system in combination with air ventilation may achieve more efficient air cleaning in a short time.The capture ratios for SARS-CoV-2 in the air when the HEPA filter was coated with an antiviral agent were comparable to those with the conventional HEPA filter, and there was little effect on SARS-CoV-2 in the air that passed through the antiviral-reagent-coated HEPA filter. Although only one type of antimicrobial coating was tested in our study, and other, additional products should be evaluated, this finding suggests that once aerosols are captured on HEPA filters, they do not detach (15, 16); therefore, antiviral reagents on HEPA filters may have a slight effect on the removal of infectious SARS-CoV-2 from the air. Several methods of applying antiviral treatments to air filters have been attempted, and they appear to have inactivation effects on pathogens on the filter surface (17–19); therefore, applying antiviral reagents to HEPA filters may reduce the risk to personnel who change filters.Our data provide valuable information on the proper use and performance of HEPA-filtered air purifiers in hospitals and in daily life and will help in determining whether they need to be used in combination with other protective equipment (e.g., face masks or room ventilation) to prevent the spread of COVID-19.
3. Testing mobile air purifiers in a school classroom: Reducing the airborne transmission risk for SARS-CoV-2 Conclusions: Air purifiers can reduce the aerosol load in a classroom in a fast, efficient and homogeneous way. In situations when windows and doors are closed for a longer period of time a large reduction in the inhaled dose of particles containing virus RNA is achieved and therefore the risk of aerosol infection is likely to be lowered. Staying for 2 h in a closed room together with a highly infective person, we estimate that the inhaled dose via airborne transmission is reduced by a factor of six when using air purifiers with an air exchange rate of 5.7 h−1. The air purifiers should be equipped with HEPA filters (DOE STD 3020 2015, H13 or H14), and a high CADR of around 1000 m3/h or higher should be applied. In order to achieve high air exchange rates and homogeneous mixing in the entire room it can be of advantage to install several smaller purifier units. In addition to the HEPA filters, the purifiers need to be equipped with pre-filters to remove the coarse dust efficiently and the pre-filters need to be cleaned or exchanged regularly. If applied in school rooms, the noise levels from operating the air cleaners need to be considered. While large ventilation rates are desirable, the noise level needs to be sufficiently low in order to not disturb the ongoing classes.In summary, the operation of mobile air purifiers in classrooms seems feasible as a practical measure that can quickly be implemented during an epidemic. In order to reduce the risks of aerosol transmission for SARS-CoV-2 air purifiers can form an important additional measure of precaution, especially in cases where no fixed ventilation systems are installed and when windows cannot be opened properly. The implementation and maintenance costs need to be compared to the substantial advantages of reducing the amount of infections and Covid-19 cases, the reduced needs for contact tracing and the avoidance of major disruptions caused by school closures. Nevertheless, air purifiers do not replace other measures for the reduction of transmission such as wearing face masks, hygiene measures and social distancing. The purifiers should be considered as efficient additional measures. An important co-benefit of a standard operation of air purifiers is that average levels of particulate matter (PM) are considerably reduced leading also to a long-term health benefit.

   Rooms with a high density of people require frequent ventilation to reduce the CO2 mixing ratio. CO2 monitors should be used in order to ensure that CO2 limits are not exceeded and that ventilation measures are sufficient to reduce the CO2 levels in the room.

   While our study focuses on school classrooms, these results can in principle be transferred to similar situations in closed rooms that are occupied by more than a single person, such as meeting rooms, restaurants, bars, shared offices, waiting rooms and others.

4. Reducing transmission of SARS-CoV-2
   
   
5. Assessing Mitigation Strategies to Reduce Potential Exposures to Indoor Particle Release Events
   
   
6. SARS-CoV-2 indoor air transmission is a threat that can be addressed with science

7. Airborne transmission of respiratory viruses
   
   
8. Ten scientific reasons in support of airborne transmission of SARS-CoV-2
   
   
9. Can 10× cheaper, lower-efficiency particulate air filters and box fans complement High-Efficiency Particulate Air (HEPA) purifiers to help control the COVID-19 pandemic?

10. Efficacy of Do-It-Yourself air filtration units in reducing exposure to simulated respiratory aerosols