The COVID-19 pandemic has shed light on the importance of indoor air quality. While there are many strategies and technologies that are marketed to improve indoor air quality in buildings, which ones are right for your facility? Which technologies are most likely to reduce the risk associated with pathogens (like COVID-19), as well as other indoor air pollutants?

The answers depend on your goals, budget, and building characteristics. Each type of air cleaning technology has strengths and weaknesses, summarized in the table and explained in more detail below.

* Dry Hydrogen Peroxide is not a common technology, and is rarely used in buildings.

Impact categories

• Airborne Pathogens: Pathogens are bacteria, viruses, or other microorganisms that can cause disease. They vary in size and ability to be removed, diluted, and inactivated. COVID-19 is an airborne pathogen. The table shows whether the technology has shown an ability to inactivate, remove, or dilute pathogens, as documented in in 3^rd party studies or scientific research. The ability of a technology to dilute, inactivate or remove airborne pathogens will depend on dose, size, and application time.  Note that dilution reduces transmission risk, but does not inactivate microbes.
• PM2.5: Fine particulate matter, specifically particles smaller than 2.5 microns, can travel deeply into the respiratory tract, reaching the lungs. Exposure can cause short-term health effects and worsen medical conditions such as asthma and heart disease. These particles can come from indoors (tobacco smoke, cooking) as well as outdoors (vehicle exhaust, power plants). The table shows which technologies have the ability to remove or dilute particles 2.5 microns or smaller, as documented through 3^rd party studies or research.
• VOCs: Volatile organic compounds (VOCs) are emitted as gases from certain building materials and human activities. They include a variety of chemicals which may have short or long-term adverse health effects. The table shows whether the technology has documented ability to remove VOCs from the air in 3^rd party studies or scientific research.
• Free of Byproducts: The table indicates whether the technology has been noted in 3^rd party studies or scientific research to produce ozone, new VOCs, and/or ultrafine particles that are a product of the device itself, or partial reactions of the device with airborne pollutants as part of the purification process.
• Added Energy: This category denotes how much the  technology impacts future energy costs for a facility. Energy impact could be related to the technology causing the HVAC system to use more energy, or from the technology directly using energy in the purification process.
• Install Cost: The table presents a relative initial installation cost for the air cleaning technology based on the most current information.

Indoor Air Quality Technologies

Click on the links below for more detailed tech notes of each technology

• Natural Ventilation: Relies on building openings and wind- and pressure-driven airflow to bring in fresh air and flush out dirty air and is thus highly variable. Outdoor air can dilute interior air pollutants but can also introduce outdoor air pollution to the inside. Outdoor air must be conditioned to maintain comfort in the buildings, and ventilation from open windows/doors can overwhelm existing mechanical systems and increase energy costs significantly.
• Increased Ventilation: Increases outdoor air percentage settings and removes demand control ventilation from central air handler systems to increase the amount of outdoor air drawn in by the system. Outdoor air is filtered and conditioned, so this is a better option than straight outdoor air from windows but has a similar impact on energy consumption for buildings in that energy costs will be significantly higher to condition the added outdoor airflow.
• Improved Filtration: Increased filtration removes a greater portion of particulates from the air, usually at the expense of greater pressure drop across the filter unit. This increases fan power consumption to move airflow, or, if fan power cannot increase, reduces airflow and system capacity. Filters can be specified and selected to minimize pressure drop increases, but as more particles are being trapped, filter pressure drop increases faster as well, and may require more frequent filter changes.
• Chemical Filters: These include carbon filtration and photocatalytic oxidation (PCO). While carbon filtration adds energy due to increased pressure drop, it filters out some VOCs and pathogens through a process called adsorption, chemical bonding of substances to the filter. Carbon filters need to be pre-filtered to prevent clogging with dust to maintain a longer life-span, and thus the pressure drop and additional energy resulting from adding carbon filtration can be high. PCO devices use a catalyzing metal bonded to filter material and a UV lamp to generate reactive oxygen species on the catalyst metal. This material traps pathogens, VOCs, and fine particulates and breaks them down through oxidation into CO2 and water vapor.
• UVGI: UVGI is a method of air cleaning that kills microbes and spores in the airstream and/or on the cooling coil, improving overall air cleanliness when paired with a good air filter. Depending on the type of UVGI added to an air handler, the added energy cost can be slight or significant. UVGI applied to upper room air cleaning will have a high energy consumption. UVGI only controls pathogens in the air, and properly designed units produce no hazardous byproducts.
• Ionization: Ionization technologies include multiple types: bipolar ionizers, needlepoint bipolar ionizers, and plasma ion generators. These all follow a similar process: Oxidizing ions such as hydroxyl groups, hydrogen peroxide, and ozone created from water vapor and gases in the air attach to particles to make them either clump together and settle faster, more filterable, or stick to oppositely charged surfaces in the space. The ions can also inactivate pathogens by attaching to them and disrupting the ability to infect cells or reproduce, though tests so far show mixed results. These devices do not have standardized testing protocols, and many produce ozone or VOCs as hazardous byproducts of partial chemical reactions. Extreme caution is recommended in selecting products to ensure they are not going to create an unsafe indoor air condition.
• Dry Hydrogen Peroxide (DHP): This technology has been employed in hospitals, hotels, and restaurants since 2014 as a way to supplement manual cleaning for surface decontamination and noted airborne inactivation of drug-resistant bacteria as well. The studies we reviewed did not address whether DHP can remove viruses and other pollutants. When looking at hydrogen peroxide devices for application in buildings, be sure to carefully check whether the technology is dry hydrogen peroxide that can be used in occupied spaces, or a liquid hydrogen peroxide vaporizer that can only be used in unoccupied spaces. As with ionizer technologies, interaction of hydrogen peroxide with VOCs can produce hazardous byproducts.

Have a question about indoor air quality?

Reach out to SEDAC for technical assistance at sedac-info@illinois.edu.