By Peter Mostert, managing director at Filta-Matix

There have been significant recent advances in technology dealing with indoor air quality products – none more so than since the advent of the COVID-19 pandemic. Never before has there been such a global drive to develop technical solutions with almost no limits in funding to combat the Coronavirus disease.

Existing HVAC systems could not simply be upgraded to include HEPA filtration because the fans were not originally selected for the added resistance levels of high efficiency air filters. Engineers and scientists have worked tirelessly to develop technology which could be included into existing HVAC systems without having to make drastic changes in design.

Images by Filta-Matix

Images by Filta-Matix

It is fair to say that the global pandemic has evolved into a more managed state, but hospital associated infections and other airborne pathogens will continue to challenge society as a whole.

Exposure to airborne particulate matter on the other hand is associated with a range of adverse effects on human health, including effects on the respiratory and cardiovascular systems, leading to hospital admissions and mortality.

Statistical environmental contamination

  • Atmospheric air will contain contamination, including:
  • Particulate matter (PM)
  • Airborne pathogenic microorganisms
  • Pollutants in gas-phase

It is important to note that the testing methods for each of the above pollutants are entirely different and test results depicting efficacy will be limited to the test process in question.

Image by Filta-Matix

Image by Filta-Matix

Particulate matter test method (PM)

Test methods for ambient air quality relating to particulate matter (PM) are often misunderstood and in some instances incorrectly interpreted. There is also a clear and distinct difference in particle counting by size (micron) and particle counting by mass (µg/m³). The test methods and test results are completely different. ISO 16890 explains the international test standard for air filters and came into effect from 1 July 2018.

In a recent publication, a supplier of an electrostatic precipitator air purification device published the following test results: ‘PM2.5 Purification efficacy of 99%’; and then proceeded to compare the efficacy of the electrostatic precipitator to that of HEPA filters claiming 99.99% efficiency against particles of 0.3 micron in size during a single pass.

Imagine end users having to navigate and understand complex test methods in order to make informed decisions on products which have an impact on health and safety.

What does PM2.5 mean?

According to the ISO standard, filters are divided into four fine dust groups according to their filter efficiency:

Simply put, PM2.5 refers to particles of 0.3 – 2.5 µm in size and a claimed efficacy level of 99% naturally means that the device must remove the particles in accordance with the claim.

In addition to the above, the efficacy is referenced in µg/m³ which clearly refers to a mass measurement test and not a particle count test which would determine the efficacy for a given particle size. 1

Size estimation: This is a critical factor in determining mass. Since the volume of a sphere is the cube of its diameter it is imperative that we arrive at a reasonably accurate estimation of the actual size of all the particles we see. The table below shows an example of PM calculation by size for a 6-channel sensor. For the sample period this sensor saw nearly 13 000 particulates in the 0.3µm channel and only 79 particulates in the 2.5µm channel, yet, the estimated mass of the 2.5µm particulates in the 2.5µm channel is more than 5 times as large. It has a huge impact on the quality of this estimation and so the more accurately a sensor can estimate the size of particulates the more accurately that sensor can estimate particle mass for particulates in a channel (or multiple combined channels, as in PM2.5).


Channel Channel PM
(µm) (counts) (µg/m3)
0,3 12980 0,38
0,5 1413 0,28
1 181 0,45
2,5 79 1,93
5,0 12 2,34
10,0 9 14,04

 Claims of 99% efficacy by mass do not mean the device is effective in removing the finer particulate matter at the same efficiency levels. For example, a single 2.5 µm particle has the same mass as 600 0.3 µm or 2000 0.2 µm particles. An increased number of studies confirm that the fine particulates are not reported well using PM mass measurements. Efficacy by mass (µg/m³) should not be confused with efficacy by size (micron).

 Other factors

When estimating mass, a number of factors impact this estimation. The density, refractivity, and even the geometry of particles passing through the sensor can impact the mass estimation. As you might imagine a dark, and very dense particulate will have a much lower mass estimation than a less dense and paler particulate even if they are of identical size. High relative humidity can also have an effect on particulates. They can act like seeds and absorb moisture growing in apparent size within a sensor. This is more pronounced outdoors in high-humidity environments. In such environments, heaters can be installed on the inlet to attempt to remove the moisture from the incoming air stream in an attempt to improve sensor accuracy.

A PM (Particulate Matter) mass measuring particle counter is a device that is used to measure the mass concentration of airborne particulate matter in a given environment. Here’s a brief overview of how a PM mass measuring particle counter works:

  • Sampling: the particle counter draws in a sample of air from the environment being monitored. The air sample is usually passed through a filter to collect the particulate matter.
  • Weighing: once the air sample has been collected on the filter, it is weighed using a microbalance. The filter is typically made of a material with a known mass, such as a Teflon or quartz filter.
  • Data Analysis: the weight of the filter is measured before and after sampling, and the difference in weight is used to determine the mass concentration of the particulate matter in the air. The mass concentration is typically reported in units of micrograms per cubic metre.


Images by Filta-Matix

Images by Filta-Matix

Some PM mass measuring particle counters also use a laser-based method to estimate the particle size distribution in the sampled air, in addition to measuring the mass concentration. These instruments use a laser beam to illuminate the particles in the sample and measure the amount of light scattered at different angles to estimate the particle size distribution.

Images by Filta-Matix

Images by Filta-Matix

The mass of the particles is estimated and based on general mass data because one cannot assume that all particles of an identical size will weigh the same.

Overall, PM mass measuring particle counters are used to test general environmental conditions and atmospheric air filters but are not suitable for testing air in cleanrooms nor for testing HEPA filters.


So, how did we get here?

Well, as we know from professional air quality testing, air quality measurement arose out of a need to control manufacturing environments in the cleanroom space. The companies that serve this market created sophisticated particle counters to measure relatively small quantities of tiny particulates as one would expect to find in cleanrooms and hospital operating theatres. Over time these grew to be rather complex and expensive instruments.

The commercial and residential air quality space by contrast needed products that were much lower in cost and much simpler for the average user (not an air quality expert) to use. So, sensors were selected together that gave some measure of air quality, however crude, since something was better than nothing. I’ve heard that phrase repeated many times to explain the current state of sensors in this space. The reality is that it is true in cases where you understand the accuracy of the data and make allowances for the uncertainties when making decisions based on that data.  However, when sensors are inaccurate and estimating what the air quality might be based on data from external sources then, at best, inferring anything from that data puts you at great risk of making the wrong decision.

The purpose of this article is not to criticise particular companies or products. Discussions with most of the companies offering products in this space globally suggest that they are well-intentioned and trying to do the best they can for their clients, and most are eager to learn and evaluate new technology with an eye to improving products for their clients.

We are at an exciting time in this industry and have seen huge growth as an industry and air quality is increasingly on everyone’s mind and being considered more carefully than ever before. The readers of this publication are largely the stewards and experts in this space and as such it is our responsibility to help shape and guide progress in measurement so that we improve the quality of testing and make them as accurate and reliable as we can. In doing so we can safeguard the health and well-being of those who rely on us and the technology we use and provide.

Finally, it is clear from multiple papers that PM measurements only tell a small part of the story and that size distribution, particularly for ultra-fine particles, is increasingly critical in safe-guarding health and well-being. 2

Particle counting test method

Particle counts by number and size (micron) are determined and conducted to demonstrate compliance in cleanrooms to ISO standards 14644-1:2015. Table 1 below depicts the maximum allowable concentrations (particles /m³) for particles equal to and greater than the considered sizes:

Images by Filta-Matix

Images by Filta-Matix

A Particle Counter is a device that is used to measure the concentration and size distribution of airborne particles in a cleanroom or other controlled environment. Here’s a brief overview of how a Particle Counter works:

  1. Sampling: the Particle Counter draws in a sample of air from the environment being monitored, typically at a constant flow rate of 1 cubic foot per minute (CFM).
  2. Particle Detection: as the air sample passes through the instrument, it enters a measurement chamber where it encounters a laser beam. The laser illuminates the particles in the sample, causing them to scatter light in different directions.
  3. Light Detection: the scattered light is detected by a set of photodiodes positioned at different angles around the measurement chamber. Each photodiode detects light scattered at a different angle, allowing the instrument to determine the size and concentration of the particles in the sample.
  4. Data Collection: the instrument collects data on the number of particles detected at each size range and calculates the concentration of particles in the air, typically reported as particles per cubic meter or particles per cubic foot.
  5. Data Analysis: the data collected by the Particle Counter can be analysed to assess the cleanliness of the environment being monitored and to identify potential sources of contamination.
Images by Filta-Matix

Images by Filta-Matix

Overall, the Particle Counter uses laser light scattering technology to detect and measure airborne particles in real-time, providing accurate and reliable data on the cleanliness of controlled environments.

Images by Filta-Matix

Images by Filta-Matix

Test method for airborne pathogen neutralisation

There are very few laboratories around the world who have the infrastructure and ability to test air cleaning devices for efficacy against airborne pathogens.

The latest and most technically advanced laboratory has been designed and built by the EPA (Homeland Security Research Division) in the USA to develop and research methods for standardising airborne pathogen efficacy testing. The suggestion has been made that millions of dollars have been spent and largely funded by the United States government, to design a facility to test air cleaning devices for efficacy against SARS-CoV-2 and other airborne pathogens.

The testing which has been conducted will assist the EPA in researching standardised test processes and to better assess the efficacy of aerosol treatment technologies in reducing the transmission of airborne viruses and other diseases in enclosed spaces.



The purpose of the testing was to develop and research potential methods for standardising airborne pathogen efficacy testing for duct-mounted and in-room air purification devices, in addition to creating a rigorous test environment to evaluate air purification devices and their respective in-room efficacy against airborne pathogens. Results of the study were intended to evidence the potential added benefit that aerosol treatment technologies may have in reducing airborne disease transmission and inform the development of standardised methods for testing.



The EPA utilised one of the largest available test chambers, a specifically designed 3 000 cu.ft. biosafety room, to simulate a high turbulence indoor environment with a highly concentrated viral load. Purification devices were duct-mounted to a real-world HVAC fan system operating at 350 cubic feet per minute (CFM) to provide a nominal 8 ACH and to simulate real-world air exchange rates.

The EPA used a non-enveloped viral surrogate MS2, which is 4x-7x smaller that SARS-CoV2 and more resistant than coronaviruses.

Billions of nano-sized viral aerosols were nebulised in sterilised deionised water directly downstream of two floor-mounted mixing fans operating at 1 443 feet per minute (FPM). The count median diameter of the aerosolised particles was 46nm (0,046 µm) at the beginning of each test (time = 0 minutes) and increased over the duration of the test to 100nm (0.1 µm) at the end of 120 minutes.

Aerosol samples were collected at 5ft. high from each end of the room while operating at a humidity level of approximately 30% RH, the most challenging humidity condition for neutralising MS2⁴.


Introducing Purifi Labs

There are 15 patents filed, nine awarded and six pending

  • Exclusive: Wave pattern technology creates significantly more (-) ions
  • Exclusive: SMART monitor automatically reacts to particulate levels
  • Exclusive: Catalyst/Corona tube process converts harmful Ozone to Oxygen

Purifi’s Airborne Molecular Purification (AMP) technology naturally deactivates tested viruses and bacteria in the air and on surfaces. It effectively neutralises odours while driving aerosols and particulates out of the breathing zone.

The Purifi generator removes unwanted ozone by means of a proprietary Purifi O₂ Catalyst. The Catalyst captures ozone molecules whilst allowing the ions to pass through. This gives you powerful air purification without the negative effect of ozone. Independent tests have been conducted for ozone by the Underwriters Laboratory (UL) which verify that the device actually removes ozone from the environment.

Purifi Labs validates product efficacy by replicating real-world test environments under real-world HVAC mechanical conditions to ensure products are installed and tested the same way they will be used.

The airborne Molecular Purification Technology uses the HVAC system’s airflow to blanket every room with natural, high energy, molecular ions attacking the contaminants at the source.

The natural ionisation process enhances the performance of air filters due to the proprietary cold plasma energy core which divides and charges the molecules in the HVAC system airflow. The system generates a high-volume patented blend of natural positive and negative ions and removes impurities and pathogens from the breathing zone which would normally remain in suspension for hours, while simultaneously cleansing walls and surfaces of harmful impurities.

Images by Filta-Matix

Images by Filta-Matix

The high energy positive and negative ions attract particles creating a cluster effect of contaminants. The process will oxidise pollutants and agglomerate particles, removing them from the air space.

Sounds too good to be true?

The technology has been verified by the EPA (Homeland Security Research Division), under highly rigorous HVAC mechanical conditions. The tests are conducted in a large biosafety room to simulate a high turbulence indoor environment with a highly concentrated viral load.

Billions of nano-sizes viral aerosols were nebulised in sterile deionised water directly downstream of two floor mounted mixing fans to thoroughly mix and disperse the viral aerosol.

The count median diameter of the aerolised particles was 46nm (0.046 µm) at the beginning of each test (time = 0 minutes) and increased over the duration of the test to 100 nm (0.1 µm) at the end of 120 minutes.

The aerosol samples were collected at 1,5m height from each end of the room while operating at 30% RH, the most challenging humidity conditions for neutralising MS2⁴.


99% total neutralisation was achieved in 60 minutes with absolutely no ozone or other harmful particulate generation during the process.


SARS-CoV-2 B1.617.2 (DELTA) variant: In the case of Delta a 95% reduction was experienced in 29 minutes, with a progressive reduction of 99.999% in 59 minutes.
SARS-CoV-2 B.1.1.529 (OMICRON) variant: In the case of Omicron a 92% airborne reduction was experienced in 29 minutes with a progressive reduction of 99.998% in 59 minutes.


Images by Filta-Matix

Images by Filta-Matix

Ozone detection

The Underwriters Laboratory tested the air downstream of the Purifi Labs system using a Thermo Electron Corporation Ozone Analyser, transferred through non-reactive (Teflon) tubing.

The results from TEC 49i O₃ analyser revealed that the maximum measured Ozone emission concentration was 0.012 ppm during a 48-hour uninterrupted test.


There are some 14 independent test reports and papers which verify the efficacy levels of Purifi Labs (AMP) technology. This technology will most certainly challenge most other devices and technologies because of its efficacy without the potentially harmful effect of ozone and UVC radiation.


  1. Conclusion by David Pariseau, one of the world’s leading authorities on air quality analyses and the founder of Lighthouse and co-founder of Particle Plus – USA
  2. Particle Plus, 30 March 2019

Register for free to gain access the digital library for RACA Journal publications