The Filtration Working Group of the GO AQS convened to discuss recommendations for filtration given the multitude of existing options.

Filtration Technologies and Their Effectiveness

A poll on trusted filtration technologies revealed a broad consensus on mechanical filtration (HEPA and MERV filters) due to their proven performance according to their specifications. Similarly, absorbent filtration using activated carbon was generally trusted for gas removal. However, concerns were raised about activated carbon’s potential to release captured gases with temperature changes and its tendency to saturate quickly.

Electronic filtration, including ionizers and electrostatic filters, elicited more varied opinions. While some participants noted the emergence of products claiming high capture rates through electrical charges, skepticism remained regarding their overall effectiveness and potential for generating byproducts like ozone and other oxygen radicals. One participant’s testing indicated that electrostatic filters could capture particles but required frequent cleaning to prevent re-release. The crucial point was raised that some electronic filters employing high potential differences may be ionizing air, thus producing biocides, which might not be permissible in breathable areas. The importance of third-party lab certifications to verify the absence of harmful byproducts was underscored.

UV filtration, which deactivates pathogens without capturing particles, garnered moderate-low trust. Photocatalytic oxidation received the least trust among the discussed technologies. It was clarified that the effectiveness of technologies varies depending on the specific pollutants and application, with some being more suitable for biocidal action or particle precipitation in specific locations within ventilation systems.

Concerns Regarding Byproducts and the Need for Rigorous Testing

A significant part of the discussion focused on the potential byproducts generated by certain filtration technologies, particularly electronic ones. The difficulty in establishing comprehensive testing methods for all potential byproducts beyond ozone was highlighted due to the dependency on the composition of indoor and outdoor air. Belgium’s regulatory approach was presented, where certain technologies like room ionization, photogalic oxidation, cold plasma, and direct ozone/hydrogen peroxide distribution are prohibited due to potential risks. However, they approve mechanical inert filtration (HEPA 13/14, EPA 12), electrostatic precipitation, and UV within specific wavelength and air change rate limits. The necessity of proving safety and efficiency for any derogations from these regulations was stressed. The importance of third-party lab certifications was repeatedly emphasized to ensure that filtration systems do not produce harmful substances.

Balancing Energy Efficiency with Effective Filtration

The working group agreed that energy efficiency in filtration systems is very important. The discussion touched upon how different filtration methods and system designs impact energy consumption. It was suggested that optimized maintenance and housekeeping are crucial for energy efficiency in HVAC systems. The potential of filtration to reduce the need for extensive ventilation, thereby saving energy, was also mentioned, although the relationship between filtration and the overall carbon footprint of a building’s HVAC system sparked some debate. The efficiency of portable air purifiers in certain scenarios, potentially offering a lower carbon footprint compared to upgrading central HVAC systems for increased air changes, was noted.

Addressing Pollution Sources and Specific Pollutants

The importance of removing pollutants at their source was a recurring theme, especially for indoor sources. When addressing gaseous pollutants, activated carbon and other absorbents were mentioned. Less conventional methods like using water to absorb certain gases and specialized paints or plasterboards with absorbent properties were also discussed, with varying levels of evidence and practical considerations. The potential of electrostatic technology in reducing volatile organic compounds (VOCs) by affecting their weaker carbon bonds was presented, with claims of significant reduction rates certified by a European lab. The need to measure pollutant levels after implementing any mitigation technology to ensure compliance with exposure limits was stressed.

Towards Standardizing Measurement and Addressing Extreme Events

The working group discussed the need for more refined metrics for assessing filter effectiveness, considering particle count numbers for sub-micron particles (0.3 and 0.5 micron) in comparison to PM2.5 measurements. While recognizing the importance of this, the group acknowledged the current lack of substantial data to support specific limits and decided to propose these metrics in a future version of the GO AQS, inviting industry and researchers to contribute relevant data.

The significance of considering extreme outdoor air pollution events like wildfires and dust storms in the design and standards of filtration systems was raised. The challenge lies in determining how to adapt standards designed for typical conditions to these increasingly frequent and intense episodes.

Conclusion and Future Directions

The Filtration Working Group engaged in a comprehensive discussion covering various filtration technologies, their effectiveness, potential byproducts, energy implications, and the importance of source control and robust testing. The discussion highlighted the complexities and importance in selecting and implementing appropriate filtration strategies for diverse indoor environments and pollution challenges. The group recognized the need for clear and robust scientific evidence to support any recommendations, particularly given the potential for harmful byproducts from some technologies. Future efforts will focus on gathering more data on sub-micron particle filtration and considering the impact of extreme air pollution events on filtration standards. The ongoing work of the Filtration Working Group aims to provide well-founded recommendations to enhance indoor air quality through effective and safe filtration and ventilation practices.

• Recording: Filtration WG – 2025 April 04