Understanding the science behind indoor air purification helps facility managers choose systems that genuinely improve environmental health.
Indoor air quality has become a central issue across healthcare, education and commercial buildings. For cleaning and facility management professionals, the challenge lies in identifying which technologies deliver meaningful results beyond controlled laboratory testing.
Doug Hoffman, executive director of NORMI, argues that effective air purification begins with understanding the science behind the technologies involved.
Speaking during a recent industry roundtable, Hoffman highlighted a persistent gap between laboratory testing and real world performance.
“Clinical studies will tell you one thing about how something may work in a specific setting, like an air purifier in an eight by eight box,” Hoffman said. “But that doesn’t tell you anything about how it will work in the actual environment in somebody’s house.”
Laboratory trials often isolate a single contaminant, such as formaldehyde, in a sealed chamber and measure how efficiently a purifier removes it. While the results may appear impressive, Hoffman pointed out that real indoor environments contain a complex mix of pollutants.
“Who has ever been in a house that has just formaldehyde?” he asked. “Nobody.”
This difference between controlled testing and field performance has prompted growing interest in case studies and real world outcomes when evaluating air purification technologies.
Five core technologies
Despite the wide range of air purifiers available globally, Hoffman explained that nearly every system relies on some combination of five core technologies. These include filtration, ionisation, ozone generation, ultraviolet light and ultraviolet light paired with a target plate known as photocatalytic oxidation or PCO.
“If you know those five technologies it doesn’t matter what the air purifier is,” Hoffman said. “You know exactly what it does and what its strengths and limitations are.”
These technologies generally fall into two categories – passive and active approaches. Passive systems, such as filters, pull contaminated air toward the device. Active systems push treatment into the surrounding environment.
“If I’m bringing pollution to the solution I’m standing in the pollution,” Hoffman said. “If I’m taking the solution to the pollution I’m standing in the solution.”
In practice, he recommends combining both approaches to improve overall effectiveness.
Filters remain the most widely used method of air cleaning, particularly within HVAC systems. However, they present several practical limitations.
Research from ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) suggests only around 26 percent of air circulating within a building actually reaches the filter. The remainder moves through the space untreated.
Filters also capture particles only above certain sizes. High-efficiency particulate air filters, commonly known as HEPA filters, trap 99.9 percent of particles larger than 0.3 microns within the air that reaches them.
Smaller particles may pass through until dust accumulation narrows the filter openings. While this can increase efficiency, it can also restrict airflow and place stress on equipment, making regular replacement essential.
Layering technologies
Ionisation introduces a different strategy by electrically charging airborne particles so they cluster together. Once larger, these particles either settle out of the breathing zone or become easier for filters to capture.
“Instead of dealing with tiny particles around 0.3 microns or smaller, they begin to grow larger,” Hoffman said.
Combining ionisation with filtration improves the chances of capturing particles that would otherwise remain airborne.
Ozone adds another layer by chemically oxidising contaminants. Ozone molecules release oxygen atoms when they interact with other compounds, breaking down pollutants and disrupting the DNA or RNA (ribonucleic acid) structures of bacteria and mould.
Exposure levels remain important. The Environmental Protection Agency sets an ozone exposure limit of 0.05 parts per million, while the Occupational Safety and Health Administration workplace limit sits at 0.10 parts per million.
“It’s pretty amazing what ozone can do and how powerful it can be,” Hoffman said. “The challenge is making sure it’s controlled.”
Ultraviolet light provides another well-known method of microbial control. UV wavelengths between 184 and 256 nanometres damage bacteria, viruses and mould, although exposure time remains critical.
In high-airflow HVAC systems microorganisms may pass through the UV zone too quickly for full neutralisation, meaning the technology often performs best when installed near components such as cooling coils.
A more advanced approach combines UV light with a catalyst coated plate, typically using titanium dioxide. Known as PCO, this reaction generates oxidising compounds that travel through the air stream and break down contaminants.
These systems have evolved significantly in recent years, often incorporating honeycomb catalyst plates and longer-lasting LED light sources to improve performance.
Chemical free sanitisation
Hoffman also highlighted the growing use of chemical-free sanitisation methods that rely on ionisation and PCO technologies.
Instead of introducing disinfectant chemicals, these systems distribute oxidising compounds through the air to address both surfaces and airborne contaminants.
In remediation projects the technology can operate continuously within containment zones and then treat the entire building once the work concludes.
Hoffman argues this final step remains essential because containment areas often become cleaner than the surrounding building during restoration work. Once barriers come down, contaminants from the wider environment can spread back into the treated area.
“For remediation projects, the whole house should be sanitised once the work finishes,” he said.
The approach has proven particularly valuable for occupants with chemical sensitivities who cannot tolerate traditional disinfectants.
As more field data emerges from real world applications, Hoffman believes the industry is beginning to recognise the importance of evaluating air purification technologies based on practical outcomes as well as laboratory science.
A longer version of this article first appeared in Cleanfax.
