The method problem
Most air-treatment tests ask how quickly a device reduces the concentration of particles or viable bioaerosols in a chamber over time. That question is still useful for filtration devices, in-device UV systems, ducted treatment systems, and recirculating room purifiers because those technologies generally need contaminated air to move through the device or treatment zone.1,4,5
Active-in-air technologies can work at a different point in the room. Instead of waiting for contaminated air to be pulled through a filter, fan, duct, lamp housing, or treatment cell, they place an active constituent into the room air before a bioaerosol event occurs. When a person breathes, coughs, sneezes, or talks, the active may already be present in the space.1,2
That changes the test question. A standard multi-time-point decay method can show long-duration reduction, but it may not isolate the earliest exposure window. For active-in-air devices, the first minute after emission can be one of the most important periods because it is close to the moment newly airborne particles become available for inhalation.1
Room pretreatment design
ARE Labs designed the room-pretreatment method around a simple but difficult measurement question: if an active-in-air product is already operating before a bioaerosol event, can the viable bioaerosol concentration be measured immediately after that event? The study did not replace standard long-duration chamber testing; it answered a different endpoint.1
The test scenario used two room conditions: a control condition without the active product operating before the biological aerosol event, and a treatment condition with the product operating before the bioaerosol was introduced. The objective was to measure viable bacterial and viral particles one minute after the simulated room event.1
| Parameter | Value or description |
|---|---|
| Test concept | Room pretreatment before bioaerosol introduction |
| Pretreatment period | 30 minutes |
| Bioaerosol generation | Collison 24-jet nebulizer |
| Post-aerosolization mixing before sampling | 1 minute |
| Chamber | Sealed 16 m3 stainless steel bioaerosol chamber |
| Sampling approach | AGI-30 impingers at opposite chamber locations |
| Enumeration | Serial dilution, plating, incubation, and viable count enumeration |
| Endpoint | Immediate viable bioaerosol concentration comparison against matched controls |
The core design choice was to hold the bioaerosol generation process constant. The same stock preparation, nebulization conditions, and physical generation setup were used so that the difference between control and treatment trials could be attributed to the pretreatment condition rather than to a changed challenge process.1
What the method measured
The room-pretreatment method measured viable bioaerosol concentration after a short, defined post-emission mixing period. Because the sample was taken immediately after aerosolization and one-minute mixing, the endpoint was not a CADR decay endpoint. It was an immediate viable concentration comparison between matched control and pretreated conditions.1
Source: approved ARE Labs room-pretreatment bioaerosol method summary.
- The endpoint is a one-minute viable concentration comparison, not a CADR decay result.
- Organism names are shortened in the chart labels for readability.
The reported one-minute net reductions were organism dependent. MS2 bacteriophage showed 90.66% reduction, Klebsiella aerogenes showed 41.75% reduction, and Staphylococcus epidermidis showed 30.80% reduction. That pattern is important because it keeps the interpretation grounded in biology instead of relying on one headline number.1
| Challenge organism | Organism type | One-minute net percent reduction |
|---|---|---|
| MS2 bacteriophage | Non-enveloped RNA virus surrogate | 90.66% |
| Klebsiella aerogenes | Gram-negative bacterium | 41.75% |
| Staphylococcus epidermidis | Gram-positive bacterium | 30.80% |
Values are net percent reductions from matched control and room-pretreatment trials in the approved source article.
Why this is different from CADR
CADR is typically a time-based removal or reduction metric. It is useful when a device removes particles from the room air over time, and many chamber studies calculate it from the difference between natural decay and device-assisted decay. That is not what the first-minute room-pretreatment endpoint is measuring.1,4,5
The room-pretreatment endpoint asks how different the viable concentration is immediately after the bioaerosol event when the room has already been pretreated. For active-in-air technologies, that endpoint can capture a mechanism that a conventional decay curve may dilute or miss, especially when the intended interaction occurs in open room air.1
Where standard methods still fit
Standard methods remain important because they provide comparability and structure. ANSI/AHAM AC-1 provides a uniform procedure for portable room air cleaner performance, AHAM AC-5 addresses bioaerosol reduction by portable air cleaners, and ASHRAE 241 adds a building-level infectious aerosol control framework. Those standards help developers, building owners, regulators, and buyers compare technologies more consistently.3,4,5
The point is not to abandon standard testing. The point is to add a method when the product mechanism falls outside the assumptions of the familiar method. A strong active-in-air data package may need both standard chamber reduction over time and a room-pretreatment first-minute study that measures early-event behavior.1,3
Regulatory and safety context
Air-treatment products that make antimicrobial or pathogen-related claims may raise regulatory questions. EPA public device guidance lists air purifiers, ozone generators, plasma generators, bipolar ionization generators, photocatalytic air-treatment devices, and certain UV lights or filters among air-treatment products that may be regulated as pesticidal devices when pesticidal claims are made.7
For active-in-air technologies, efficacy testing often belongs beside safety-related work such as device particle emissions testing, VOC or by-product emissions testing, ozone screening where relevant, active concentration assessment, surface-deposition review, and ventilation-sensitivity testing. A useful data package defines both what the product does to bioaerosols and what it releases into the room.1,6,7
Testing framework
- Start with mechanism and use-case review so the method follows how the product is intended to work.1
- Add physical aerosol characterization where particle size, active distribution, persistence, or room mixing matter.1
- Use standard chamber reduction testing when long-duration control-corrected reduction or CADR-style performance is relevant.1,4,5
- Use a first-minute room-pretreatment endpoint when the claim depends on an active being present before the bioaerosol event.1
- Map claims back to the exact method timing, organisms, controls, and safety evidence rather than treating all reductions as equivalent.1,7
Summary
In summary, the case showed that method timing has to match product mechanism. The first-minute room-pretreatment endpoint helped the client and ARE Labs evaluate a question that standard decay testing alone could not answer: what happens when a fresh bioaerosol enters air that has already been treated? ARE Labs supported the work by building the endpoint around the mechanism, controls, viable sampling, and careful claim boundaries.1