The method problem
Most air-treatment tests measure how quickly a device reduces particles or viable bioaerosols in a chamber over time. That remains a useful question for filtration devices, in-device UV systems, ducted treatment systems, and recirculating room purifiers because contaminated air generally must pass through the device or its treatment zone.2,3
Active-in-air technologies act at a different point in the room. Rather than waiting for contaminated air to pass through a filter, fan, duct, lamp housing, or treatment cell, these products place an active constituent into the room air before a bioaerosol event. The active may therefore already be present when a person breathes, coughs, sneezes, or talks.
That mechanism changes the test question. A standard multi-time-point decay method can measure longer-duration reduction, but it may not isolate the earliest exposure window. For active-in-air devices, the first minute after emission may matter because it is close to the point when newly airborne particles become available for inhalation.
Room pretreatment design
ARE Labs designed the room-pretreatment method around a simple but difficult measurement question: when an active-in-air product is already operating, what viable bioaerosol concentration can be measured immediately after a new challenge? The study was designed to answer a different question, not replace standard long-duration chamber testing.
The study compared two room conditions. In the control condition, the active product was not operating before the biological aerosol event. In the treatment condition, the product was operating before the bioaerosol was introduced. The objective was to measure viable bacterial and viral particles one minute after the simulated room event.
| 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 |
Holding bioaerosol generation constant was central to the design. ARE Labs used the same stock preparation, nebulization conditions, and physical generation setup in the control and treatment trials. This helped isolate the pretreatment condition as the basis for comparison rather than a change in the challenge process.
What the method measured
The room-pretreatment method measured viable bioaerosol concentration after a short, defined post-emission mixing period. Sampling followed aerosolization and the one-minute mixing period, so this was not a CADR decay endpoint. It was a direct comparison of viable concentrations between matched control and pretreated conditions.
View figure data as a table
| organism | One-minute net reduction |
|---|---|
| MS2 | 90.66% |
| K. aerogenes | 41.75% |
| S. epidermidis | 30.8% |
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 varied by organism. MS2 bacteriophage showed 90.66% reduction, Klebsiella aerogenes showed 41.75% reduction, and Staphylococcus epidermidis showed 30.80% reduction. These differences keep the interpretation tied to each organism's observed response rather than reducing the findings to a single headline number.
| 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 generally a time-based removal or reduction metric. It is useful for devices that remove particles from room air over time, and many chamber studies calculate it from the difference between natural decay and device-assisted decay. The first-minute room-pretreatment endpoint measures something different.2,3
The room-pretreatment endpoint compares viable concentrations immediately after a bioaerosol event in control and pretreated room conditions. For active-in-air technologies, this can capture a mechanism that a conventional decay curve may dilute or miss, particularly when the intended interaction occurs in open room air.
Where standard methods still fit
Standard methods remain important because they structure testing and make results easier to compare. 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 provides a building-level framework for infectious aerosol control. Together, they give developers, building owners, regulators, and buyers a more consistent basis for comparison.1,2,3
The goal is not to replace standard testing. When a product mechanism falls outside a familiar method's assumptions, an additional method may be warranted. An active-in-air data package may therefore pair standard chamber reduction over time with a first-minute room-pretreatment study of early-event behavior.1
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.5
For active-in-air technologies, efficacy testing often needs to be considered alongside safety-related work. This may include 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 describes both the product's effect on bioaerosols and what the product releases into the room.4,5
Testing framework
- Start with mechanism and use-case review so the method follows how the product is intended to work.
- Add physical aerosol characterization where particle size, active distribution, persistence, or room mixing matter.
- Use standard chamber reduction testing when long-duration control-corrected reduction or CADR-style performance is relevant.2,3
- Use a first-minute room-pretreatment endpoint when the claim depends on an active being present before the bioaerosol event.
- Map claims back to the exact method timing, organisms, controls, and safety evidence rather than treating all reductions as equivalent.5
Summary
This case showed why test timing must match the product mechanism. The first-minute room-pretreatment endpoint helped the client evaluate a question that standard decay testing does not isolate: what happens when a fresh bioaerosol enters air that has already been treated? ARE Labs designed the study around that mechanism, using matched controls, viable sampling, and explicit claim boundaries.