While it has been known for over a century that outdoor air had germicidal effects, it wasn’t until the 1960s and 1970s that those effects were seriously researched, and then only in the context of the defence against biological weapons ^[1].

During the 1960s the UK’s bio-defence laboratory at Porton Down was charged with developing defences against potential biological weapons. An initial aspect of that research was to establish just how well, and how fast, any incident involving the release of a harmful biological weapon might spread.

The answer, to the surprise of the scientists, was that the spread of any such release was surprisingly small, far smaller than they expected. The question then became why? And how can we utilise that natural effect in our defence? This is where the Airora story really begins.

The scientists at Porton Down, realising that there was something natural in the air that limited the spread of biological weapons, set about characterising that effect. Firstly, they ascertained that the effect was prevalent outdoors but not indoors, which led them to name the unknown effect the ‘Open Air Factor’ (OAF).

From this they postulated that the active outdoor sanitising agent must be short lived, in that it somehow quickly ‘disappeared’ once outdoor air moved indoors, and so they carried out research to establish just how short lived.

By passing outdoor air through an indoor space at increasing rates until the indoor air was as effective at sanitising as outdoor air, they found that the answer was ‘very short lived indeed’. While the air inside a naturally ventilated building, such as a home, is typically replaced by outdoor air once or twice an hour, they found that the rate of replacement had to increase enormously, to more than 35 times an hour, for outdoor air’s natural germicidal action to equalise between indoors and outdoors.

Unfortunately for us, other than further postulating that the source of the OAF was potentially related to the toxicity of various ozonized olefins, this is about as far as this groundbreaking research went before the advent of the 1972 Biological Weapons Convention (BWC), which effectively prohibited the development, production, acquisition, transfer, stockpiling and use of biological and toxin weapons.

Once the BWC was established, the UK Government, unfortunately, but not unsurprisingly, decided that further research into the OAF was no longer a priority.

2. What Airora’s inventor discovered

While the OAF research at Porton Down was winding down, Alan Mole, then a young scientist, could see the transformative potential of OAF and he became determined to solve the question - what exactly is the very short lived ingredient of outdoor air that makes it such a powerful sanitising agent, and how could we replicate that in indoor air?

For over twenty years Alan continued that quest alongside his day job, focusing on the complex intersection of atmospheric chemistry, aerobiology and microbiology.

An early candidate for OAF was the very short lived hydroxyl radical (commonly hydroxyls, known as the ‘detergent of the atmosphere’) an abundant and powerful oxidant, but this was roundly dismissed on statistical grounds.

However, working independently, Alan discovered that a particular sub-set of hydroxyls, those from the natural condensing reaction of ozone with aromatic essential oils emitted from plants^[2], preferentially coated particles such as pathogens, and were indeed the powerful short lived sanitising agent.

The results of that discovery are both transformative and remarkable:

Inactivating high concentration benchmark MS-2 airborne virus in less than 5 minutes according to Public Health England (Porton Down no less!).

By testing against MS2, the US Centre for Disease Control (CDC) confirms that hydroxyls will inactivate pathogens in levels 1 – 4 of that Spaulding Classification, including all those in the coronavirus family, such as the SARS-CoV-2 coronavirus that causes COVID-19.

Level 5 of the Spaulding Classification, Mycobacteria, are basically no different in structure to other more susceptible bacteria and as Airora produces a never-ending supply of hydroxyls, even clumps of cells, thick layers and heavy cell walls can be expected to eventually succumb.

We at Airora are not aware of any pathogens which will not ultimately succumb to hydroxyl attack.

Inactivating high concentration surface MRSA on glass in 1 hour according to Public Health England.
Inactivating airborne, high concentration, multi drug resistant, Staphylococcus epidermidis bacteria in less than 2 minutes according to Public Health England.
A simulated sneeze test with high concentration of bacteria saw a greater than 99% reduction in transmitted live bacteria after only 600mm according to BRE & IOM Stafford – the hydroxyl cascade is so powerful it creates a real time person to person infection shield!

And the benefits go well beyond virus, bacteria and mould inactivation. Hydroxyls also remove all odours, break down all VOCs and most other polluting gasses and damage the protein and tertiary structure of allergens so that they are no longer recognised by the body's immune system^[3,4,5,6,7].

3. But are Hydroxyls safe for human beings?

While we then aimed to re-create the condensing hydroxyl cascade that occurs naturally outdoors, indoors, the obvious question was, are hydroxyls completely safe, and at what concentration?

As humans, animals, and non-pathogenic bacteria have evolved alongside outdoor levels of hydroxyls, it is reasonable to assume that they evolved mechanisms to protect themselves against the powerful oxidant that are hydroxyls^[6].

Indeed, research has shown that those mechanisms include:

The outer layer of our skin consists of a number of layers, of which the outer most, the Stratum Corneum is a layer of 20-30 cells thick that is made up of keratin and horny scales of dead keratinocytes. This layer is impenetrable to hydroxyls and provides protection against these molecules ^[8].
Hydroxyls play a role in the intercellular metabolism. As such, cells have a built-in protection against reactive oxygen species such as hydroxyls.

Inter- and extracellular protection of living cells against reactive oxygen species such as hydroxyl radicals occurs through antioxidants and enzymes such as superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase ^{[9; 10; 11; 12; 13]}.

As hydroxyls come into contact with soft tissue in the face such as eyes, nasal or oral cavity, they are rendered inactive by the action of these enzymes and naturally present vitamins such as vitamin C, E ^[13].

There was, and is, no doubt that hydroxyls are harmless to human beings, animals and plants. Indeed, hydroxyls employed as a sanitising agent, while people remain safely present, have been approved by regulators worldwide.

3.1 Measuring hydroxyl concentration indoors

Measuring indoor hydroxyl concentration is however not easy, and so the developers turned to both the UK’s National Health and Safety Laboratory (HSL) and Leeds University Atmospheric Chemistry Group to cross check measurements using different measurement techniques, and then calibrate the Hydroxyl Diffuser technology.

The HSL approach to measuring indoor hydroxyl concentration was to employ a trapping method based on that of Chen and Mopper^[14] and Leeds University used low pressure laser-induced fluorescence (LIF) spectroscopy, known in the atmospheric measurement community as the FAGE (Fluorescence Assay by Gas Expansion)^[15].

3.2 Matching Airora’s hydroxyl concentration to outdoors

The concentration of hydroxyls in the lower atmosphere has been determined to generally lie between 0.5x10⁶per cm³ and 5x10⁶ per cm^3[16] depending on many factors, including time of day, humidity, temperature, season etc.^[17]. In general, the concentration is lowest at the poles and highest at the equator.

By contrast, the continuous outdoor exposure in Northern America, India and Central Africa averages at about 20M hydroxyls per cm³. There is no record of any adverse effects of continuous exposure to OH in these high OH regions.

We at Airora decided to target hydroxyl creation well within the general range by targeting hydroxyl output from 1 to 3x10⁶per cm³ with a focus on 2x10⁶ per cm³. Performance within this range varies a little in terms of the time taken to inactivate pathogens, but the outcome over time is very similar.

For anyone who might have concerns as regards the level of hydroxyls created by Airora throughout an indoor space, this target level is only 10% of the maximum that occurs naturally outdoors.

Following further detailed experimentation, it was determined that the quantity of essential oil and ozone necessary to create the required hydroxyl concentration was fortunately very low, well below any cautionary, advisory or regulatory limits.

4. Technological development objectives

The objective was clear; to develop technology that safely reproduces that same reaction between trace levels of ozone and aromatic essential oils, indoors, as naturally occurs outdoors.

But many questions initially remained unanswered:

In terms of delivery technology, which aromatic essential oil would be most effective, would it be freely available, safe and affordable, how best to produce and diffuse the missing ingredients and how to ensure that they are distributed evenly throughout the space and reach every corner, would the distribution be disrupted by forced ventilation? and so on and so on …

And in terms of safety; will the natural ingredients Airora adds to indoor air nevertheless be at safe levels while creating sufficient hydroxyls? And, as indoor air is more polluted than outdoor air, when Airora delivers the missing ingredients to indoor air, will the reactions both between the added ingredients themselves, and with existing indoor pollutants, create any harmful by-products?

5. Independent scientific oversight and testing

Airora’s technology is both novel and pushes scientific boundaries. Consequently, Airora needed an independent scientific team, drawn from the best in the world, both to provide the necessary testing and research capability, and to ensure that any results obtained are, and are seen to be, independently derived.

Those independent bodies included:

	The UK Building Research Establishment’s Internal Air Quality Team and Laboratories		The University of Ottawa
	The UK Government’s Health and Safety Laboratory		The University of Leeds
	FDA Accredited Laboratory, Rochester, New York State		Cardiff Metropolitan University
	The UK’s Health Security Agency		Campden BRI Laboratories
	The Institute of Occupational Medicine \| IOM Stafford		The University of York

6. Regulatory compliance

Before embarking on technological development, it was imperative that we at Airora understood the requirements of regulatory safety and other approvals. By carefully preparing to meet those requirements in advance, Airora has been formally approved for use in the UK, USA, EU and Australia and in the large number of other countries that either accept or recognise those approvals.

UK regulators have approved Airora’s technology and products.
EU regulators have approved Airora’s technology and products under both CE Marking and the Biocidal Products Regulation.
Au regulators have approved Airora’s technology and products.
In the US, for regulatory purposes, Airora’s products are Type II medical devices, regulated by the FDA. Such devices can also be used outside of medical settings.

7. Safety first – Indoor Air Quality

To establish the safety of Airora’s technology, which both emits and eliminates trace levels of ozone, and linalool, a natural aromatic plant extract, Airora turned to one of the world’s pre-eminent Indoor Air Quality research and testing organisations, the UK’s Building Research Establishment’s (BRE) Indoor Air Quality group. Our brief to BRE was clear and straightforward:

“Review all worldwide Indoor Air Quality (IAQ) regulatory and advisory limits, to establish a framework within which our technology must perform to allow it to be safely used in each and every regulatory jurisdiction”.

“Devise a testing regime in accordance with the above and independently test our technology to establish our compliance”.

Airora then went further, much further. Having established the IAQ regulatory and advisory boundary, Airora aspired to not just fall within that boundary, but to do so by a wide margin in each and every case. Subsequent testing led to a series of technological changes with the result that, on almost all measures, Airora falls more than 75% below any IAQ regulatory or advisory limits, and it never exceeds 50% of any regulatory or advisory limit, however strict.

“Independently identify all by-products of Airora’s technology, including by-products from its interaction with common VOCs found in the indoor environment, and identify if any, other than Formaldehyde, are known to be harmful at the resulting mass density”.

7.1 VOC reaction by-products

Volatile Organic Compounds (VOCs) are common indoor air pollutants arising from various sources such as aerosol sprays, cleansers, disinfectants and air fresheners. Hydroxyls are known to break down VOCs and so BRE were asked to identify all by products of VOC breakdown for their safety.

The BRE consequently selected a representative group of those VOCs at the levels concomitant with domestic usage, to test against and establish if the consequent reactions caused by Airora created any hazardous by-products.

Together, BRE and Leeds and York Universities (York using a quite different prototype to see if it produced any different by-products, which it did not) initially employed Gas Chromatography and Mass Spectrometry (GC-MS) to identify all of Airora’s gaseous by products^[18,19].

The University of York also investigated the presence of potential other by products that might not be identified by GC-MS, such as organic acids as postulated by the ‘reactive chemistry’ hypothesis. By additionally using Proton Transfer Reaction Mass Spectrometry (PT-MS) York were able to establish that no such other by products existed.

Together, BRE and York were able to confirm that none of the VOC by-products was known to be hazardous, doubly so given their extremely low mass density.

7.2 Formaldehyde

In the context of common indoor pollutants, Formaldehyde is often considered separately from other VOCs, firstly because it is commonly emitted by building and decorating materials and consumer products and secondly because the very high levels found alongside some industrial processes has made it a subject of workplace concern.

Consequently, it is cautionary that any device to be used indoors does not significantly add to the indoor level of formaldehyde.

High levels of formaldehyde can cause sensory irritation

The threshold for formaldehyde objective sensory irritation is circa 1.0 mg/m³.

At that level some people might experience watery eyes, runny nose, burning sensations of the eyes, nose, and throat and coughing and wheezing

However, it is recognised that some highly sensitive people may experience sensory effects at even lower levels, and for this reason, the international WHO guideline is that indoor formaldehyde concentration should not exceed 0.1 mg/m³.

While very high persistent levels of formaldehyde have been linked to some types of cancer, the risk threshold has been established as being far higher than the WHO advisory limit.

Consumer cleaning products, air fresheners and even cooking can increase background formaldehyde levels by up to 40% of the WHO advisory limit.

What about Airora?

Airora’s technology involves, just as nature does outdoors, the breakdown of aromatic plant oils, which in turn has a small, temporary, impact on formaldehyde levels. However, Airora also creates hydroxyls which simultaneously break down formaldehyde.

To ensure its safety, Airora’s technology has been subject to extensive independent testing by BRE which has demonstrated that Airora’s impact on formaldehyde levels is marginal, does not accumulate, and reduces existing background levels of formaldehyde over time.

7.3 Volatile Organic Compounds (VOCs)

VOCs are common indoor air pollutants arising from various sources such as aerosol sprays, cleansers, disinfectants and air fresheners. VOCs are of concern as very high levels can potentially affect your health.

BRE have extensively tested Airora’s technology for its impact on VOC levels and found that any such impact is insignificant in terms of all existing advisory or regulatory limits.

Hydroxyls are however known to break down and remove VOCs and so we asked BRE to establish if Airora’s technology, which creates abundant hydroxyls, leads to the accelerated breakdown of common indoor polluting VOCs^[21].

In this experiment BRE introduced a representative mix of VOCs into the atmosphere and measured their rate of decay both with and without an Airora device being active.

That mix included VOCs commonly introduced into the indoor atmosphere by perfumes, sanitising gel, cleaning agents, paints, glues, air fresheners, scents, personal care products, air fresheners, cosmetics, dry cleaners and more.

BRE found that where an Airora device was active the totality of VOCs reduced slightly more quickly than where the Airora device was inactive.

7.4 Ozone

Why the concern regarding Ozone?

The gradual increase in ambient urban outdoor ozone concentrations has been matched by increased concern as regards its effects on health and outdoor ozone levels are now regularly monitored along with the rise in other urban pollutants.

As a result, interest has also grown in the impact of indoor ozone levels, which while they are typically (but not always) only 25 - 50% of the outdoor level, they can potentially be increased by a range of common consumer products.

Current advice and regulation

In the past, limits have commonly been set for industrial environments where ozone is produced, and this has recently been reflected in increased activity in attempting to passively control indoor ozone levels more generally.

There is no material evidence that typical indoor levels, of up to 50ppb (rated as Low / Good by the International Air Quality Index) are of concern, even for Asthmatics^[22,23].

However, the precautionary principle has led to some regulators requiring, and others advising, that the ozone output of various indoor devices should not exceed 50ppb^[24].

At the extreme, so as to be seen as not adding at all to background levels, some agents offer to certify that a device adds ‘zero ozone’ (typically defined as < 6ppb).

Solutions

Clearly, by passively restricting device ozone outputs to zero, you can stop indoor ozone levels increasing artificially, but equally they may already be too high, and such a restriction doesn’t reduce that background level.

Unfortunately, such passive restrictions also don’t reflect any of the positive results from ozone levels typical of those we as a species evolved alongside outdoors.

Outdoors, in healthy fresh rural air, natural levels of ozone (up to 50ppb, Rated as Good by the International Air Quality Index) both accelerate the reduction in potentially harmful VOCs, and through their reaction with airborne terpenes, both destroy those terpenes and create germicidal hydroxyls, which keep us safe from infections and allergens.

Airora’s technology actively optimises indoor ozone concentration

By employing the latest developments in ozone sensor technology, Airora goes well beyond the previous passive standards.

Continuously measuring ambient levels, Airora actively reduces high indoor ozone levels to well below the 50ppb^[25] level.

Similarly, where ambient ozone levels are unnaturally low, Airora ensures that sufficient ozone is available to help break down potentially harmful VOCs and produce hydroxyls which provide infection protection, allergen neutralisation and the breakdown of indoor pollution and irritants.

7.5 Particulates

As the natural breakdown of aromatic plant oils such as linalool, in outdoor air, creates some particulates, Airora commissioned BRE to establish the levels created indoors by Airora’s technology so as to establish its safety.

Particulates come in many sizes and are typically grouped as PM10 (< 10µm) a principal visible component of ‘smoke’ at very high concentrations, PM2.5. (< 2.5µm) categorised as ‘fine’ particulate matter and PM1 (<1 µm) categorised as ‘ultra fine’.

All can be inhaled; indeed, we are inhaling them all of the time, both indoors and outdoors, but at very high concentrations they can potentially impact on health.

BRE have extensively tested Airora’s technology for its impact on PM10, PM2.5 and PM1 levels^[26] and found that any such impact is insignificant in terms of all existing advisory or regulatory limits.

7.6 Other common pollutants

In addition to the above BRE have routinely tested for Airora’s impact on other common indoor pollutants such as Carbon Monoxide, Nitrogen Oxide and Nitrogen Dioxide and found that while some reduced and some increased, any increases were insignificant in the context of any advisory guidelines or regulatory requirements.

8. Developing Airora’s product technology

Any entirely new technology poses problems that require solution, but in addition to solving those problems, we at Airora set ourselves clear additional product development objectives that went beyond affordability and reliability.

Knowing the technology would be overwhelmingly more effective, we also seized the opportunity to set ourselves apart with product utility objectives that went well beyond the existing generation of air filters.

While traditional air filters are heavy, we wanted our technology to weigh far less.
While traditional air filters are noisy, we wanted our technology to be whisper quiet.
While traditional air filters use significant amounts of energy, we wanted our technology to use far less energy.
While traditional air filter consumables (replacement filters) were expensive, we wanted our consumable (small bottles of linalool, a natural aromatic plant extract) to be far more affordable.

The results are clear, Airora is not just many times more effective than existing air filters, it is far lighter, quieter and more cost efficient, has lower environmental impacts and is more sustainable.

Today, you can be amongst the first to benefit from our successful technological journey.

9. From technology to product

Once Airora’s underlying technology had been shown to be both highly effective and safe, Airora commissioned PDR, a design and innovation research institution founded by Cardiff Metropolitan University, to design our first product, the iconic Airora Tabletop Pyramid which incorporates Airora’s revolutionary molecular air and surface cleaning technology.

PDR has developed a world-wide design and development reputation and is now ranked as the leading design centre in the UK, having been awarded over 50 major international design awards for its work.

Only Airora destroys or neutralises all types of germs, moulds, allergens and odours and most other irritants and harmful pollutants throughout entire indoor spaces.

You can find out all about Airora at airora.com

And contact us at support@airora.com

References:

Hobday RA, (2019) The open-air factor and infection control, Journal of Hospital Infection, 2019
Geyer A, Bächmann K et al. (Jan 2003) “Nighttime formation of peroxy and hydroxyl radicals during the BERLIOZ campaign: Observations and modelling studies”. Journal of Geophysical Research: Atmospheres
Martínez VR, Arañó LM et al. (April 2020) “Evidence of OH· radicals disinfecting indoor air and surfaces in a harmless for humans method”. International Journal of Engineering Research & Science
Finlayson-Pitts BJ, Pitts, JN Jr. (1999) “The Chemistry of the Upper and Lower Atmosphere”. Academic Press, San Diego
Garrison, Warren M. (2020) “Reaction mechanisms in the radiolysis of peptides, polypeptides, and proteins Chemical Reviews” 87 (2): 381–398
Kawamoto S et al. (2006) “Decrease in the Allergenicity of Japanese Cedar Pollen Allergen by Treatment with Positive and Negative Cluster Ions”. International Archive of Allergy and Immunology Vol.141, No. 4
Kazuo Nishikawa et al. (2016) “Exposure to positively and negatively charged plasma cluster ions impairs IgE binding capacity of indoor cat and fungal allergens”. World Allergy Organization Journal 2016
Yousef, H., Alhajj, M. and Sharma, S., (2020). Anatomy, Skin (Integument), Epidermis. [online] Ncbi.nlm.nih.gov. Available at: <https://www.ncbi.nlm.nih.gov/books/NBK470464/> [Accessed 8 October 2020].
Lipinski, B., (2011). Hydroxyl Radical and Its Scavengers in Health and Disease. Oxidative Medicine and Cellular Longevity, 2011, pp.1-9.
Yim, M., Chock, P. and Stadtman, E., (1990). Copper, zinc superoxide dismutase catalyzes hydroxyl radical production from hydrogen peroxide. Proceedings of the National Academy of Sciences, 87(13), pp.5006-5010.
Willcox JK, Ash SL, Catignani GL. (2004) Antioxidants and prevention of chronic disease. Review. Crit. Rev. Food. Sci. Nutr. 2004;44:275–295.
Genestra M. (2007). Oxyl radicals, redox-sensitive signalling cascades and antioxidants. Review. Cell Signal. 2007;19:1807–1819.
Young, I., (2001). Antioxidants in health and disease. Journal of Clinical Pathology, 54(3), pp.176-186.
X. Chen and K. Mopper, 2000 Determination of tropospheric hydroxyl radical by liquid phase scrubbing and HPLC: preliminary results Journal of Atmospheric Chemistry, 36, p 81-105.
D. E. Heard, (2006). “Atmospheric field measurements of the hydroxyl radical using laser induced fluorescence spectroscopy”, invited review in Annual Review of Physical Chemistry, 57, 191-216 (2006).
NASA (December 2018) “Detergent-like Molecule Recycles Itself in Atmosphere” https://earthobservatory.nasa.gov/images/144358/detergent-like-molecule-recycles-itself-in-atmosphere 17/06/2023
ESPERE Climate Encyclopaedia – www.espere.net - Lower Atmosphere More - page 3
Rowley J, Dengle A, (2010) VOC by-products & baseline identifications, BRE & Leeds University School of Chemistry
Hamilton J, Lewis A (2012). Identification of X Compounds, University of York
See Airora White Paper “About Formaldehyde”
Dengle A, (2015). Assessment of the ability of a Tri-Air technology to remove VOCs, BRE Test Report W/15/02/02
Critical review of long-term ozone exposure and asthma development, Ke Zu, Liuhua Shi, Robyn L. Prueitt, Xiaobin Liu & Julie E. Goodman, Inhalation Toxicology, June 2018.
Ozone Exposure and Asthma Attack in Children, Wanting Huang, Jinzhun Wu and Xiaoliang Lin, Frontiers in Paediatrics, April 2022.
Air cleaners sold in California must be CARB certified for ozone emissions, which must be no higher than 50 parts per billion (ppb).
Dengle A (2022). Independent testing of an air purifying device in a 41m³chamber, BRE Test Report P123651-1000
Dengle A (2020) Independent testing of an Air Purifying Device, BRE Test Report P117978-1000

The Airora Technical Library