The method problem
Most air-treatment studies measure how quickly a device reduces particle or viable bioaerosol concentrations in a chamber over time. This question remains useful for filtration devices, in-device UV systems, ducted treatment systems, and recirculating room purifiers because contaminated air generally must pass through the device or treatment zone.1,4,5
Active-in-air technologies can act elsewhere in the room. Rather than waiting for contaminated air to pass through a filter, fan, duct, lamp housing, or treatment cell, these technologies 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.1,2
This mechanism changes the test question. A standard multi-time-point decay method can measure longer-term reduction, but it may not isolate the earliest exposure window. For active-in-air devices, the first minute after emission can be especially important because it closely follows the point when newly airborne particles become available for inhalation.1
Room pretreatment design
ARE Labs designed the room-pretreatment method around a direct but technically difficult question: when an active-in-air product is operating before a bioaerosol event, can viable bioaerosol concentration be measured immediately afterward? The study did not replace standard long-duration chamber testing. It measured a different endpoint.1
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 operated 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 study held the bioaerosol generation process constant. ARE Labs used the same stock preparation, nebulization conditions, and physical generation setup so differences between the control and treatment trials could be associated with the pretreatment condition rather than a change in the challenge process.1
What the method measured
The room-pretreatment method measured viable bioaerosol concentration after a short, defined post-emission mixing period. Sampling occurred immediately after aerosolization and one minute of mixing, so this was not a CADR decay endpoint. Instead, the endpoint compared immediate viable concentrations under 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 varied by organism. MS2 bacteriophage showed a 90.66% reduction, Klebsiella aerogenes showed a 41.75% reduction, and Staphylococcus epidermidis showed a 30.80% reduction. This organism-dependent pattern keeps the interpretation grounded in the biological results rather than a single headline value.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 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 CADR from the difference between natural decay and device-assisted decay. The first-minute room-pretreatment endpoint measures something different.1,4,5
The room-pretreatment endpoint compares viable bioaerosol concentrations immediately after an event under untreated and pretreated room conditions. For active-in-air technologies, this comparison can capture an open-room-air interaction that a conventional decay curve may dilute or miss.1
Where standard methods still fit
Standard methods remain important because they provide structure and allow more consistent comparisons. ANSI/AHAM AC-1 establishes a uniform procedure for measuring 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. These standards help developers, building owners, regulators, and buyers compare technologies.3,4,5
Standard testing still has an important role. An additional method may be needed, however, when a product's mechanism falls outside the assumptions of the established test. A strong active-in-air data package may include both standard chamber reduction over time and a first-minute room-pretreatment study focused on early-event behavior.1,3
Regulatory and safety context
Air-treatment products with antimicrobial or pathogen-related claims may raise regulatory questions. EPA public device guidance identifies air purifiers, ozone generators, plasma generators, bipolar ionization generators, photocatalytic air-treatment devices, and certain UV lights or filters as products that may be regulated as pesticidal devices when pesticidal claims are made.7
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 defines both the product's effect on 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
This case showed why test timing must match the product mechanism. The first-minute room-pretreatment endpoint helped the client and ARE Labs examine 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 designed the endpoint around the mechanism, matched controls, viable sampling, and careful claim boundaries.1