Air cleaners, yes … but ionizers and uv sources NO!

The COVID-19 pandemic has challenged the status quo in a number of ways. From helping the world realize that you can run scientific conferences that are accessible for people who cannot (or will not) travel, to rising the very thorny question of "should kids be learning in the classroom, even though their risk of infection will be higher?"

Particularly around the issue of indoor gatherings, the use of air cleaners has been getting more attention ... even some quite striking headlines from Australia!

As an air quality scientist, who have worked on atmospheric chemistry for more years that I care to count I have been asked my thoughts on air cleaners and to be honest my response is quite simple. FILTER ALL THE AIR!

Now, some might remember my position on outdoor air scrubbers and ask why I recommend air cleaners for indoor environments. Well, and this may come as a shock to some, indoor environments are smaller than the whole atmosphere :-) Put simply, portable air cleaners work really well for small enclosed environments like offices, classrooms or homes because the volume of air they need to process to make a difference in those environments is relatively small.

Take a "not too large" room of 60$m^2$ and ceilings at 3m ... that's 180$m^3$ of air and a mid-size air cleaner can deliver 400$m^3$ of clean air per hour.

High Efficiency Particulate Air (HEPA) filters are really good at removing particles from the air and therefore removing the pathogens that are attached to those particles. Apart from these filter-based solutions, there are other air purifiers that use ionization or uv-light to sanitize the air but there are quite significant issues with these technologies

The problem is relatively simple, we need to clean the air from airborne pathogens, and we can, in principle, use similar solutions than what’s used to sanitize surfaces, water or clothing. However, the use of certain chemicals is not suitable for air that is intended to be breathed in.

Ionization: Do you want some ozone with that?

A number of air purifiers use ionization techniques to help with the cleaning of the air. The basic idea of these devices is the use of ion generators (e.g. corona discharges) that charge the particles that pass through it, which then are attracted to the surfaces in the air cleaner, greatly increasing their filtering efficiency.

That sounds harmless enough, right? Well, the main problem with these devices is that the same process that generates ions, also generates ozone which is a pollutant that has harmful acute impacts on people’s health.

Indoor air chemistry is a largely under-researched topic but the information that does exist points to an unacceptable risk with the general use of ionizers in indoor environments. The US-EPA warns that only a very small number of devices, specifically designed to use ozone as a disinfectant agent, are approved by the US-FDA for use under certain conditions but in general, adding ozone to an occupied indoor environment is adding unnecessary risks. A study specifically looking at the benefits, or otherwise, of the use of ionizing air cleaners in school environments found that air ionizers in school classrooms reduced particulate matter concentrations which led to some improvements in respiratory health among 11-14 year old children, but that the ionizers had an adverse effect on heart rate variability (a measure of cardiovascular health), meaning that any benefit to the lungs came at a cost to the heart.

UV-C: Do you want a smog chamber? Because that’s how you get smog chambers

Ultraviolet light (uv) has long been used to disinfect water because the high energy uv light denaturalizes some proteins which render pathogens inert. The same principle has been used in hospital settings where quick sanitization is required, and the objects are not suitable to be put through a high-pressure steam treatment in an autoclave. This process has been identified as safe, as long as people are not directly exposed to this uv radiation (because if it’s denaturalizing proteins in a bacteria, it will do the same to the cells in our body … enter cancer). However, because of the general disconnect between health research and indoor air chemistry, the secondary issues of using high energy light sources like uv lamps have been largely ignored. It has been reported that uv-light can induce photolysis in certain types of volatile compounds (VOC) and can also help generate conditions for new particle formation. 

So ... what then?

There are many ways of framing this but in essence, the question we should always keep in mind is why add a risk to a situation if there are perfectly viable solutions that don’t add unknown risks?

In this case, the perfectly viable solutions are straight-up filters. There is no need to add ionization, or uv-light sources because the filters already do a hell of a goot job in removing particles (and the pathogens attached to them) from the air so instead of trying to over-complicate the question, just get a bunch of good quality HEPA filters for your indoor environments and leave the uv-treatments for the hospitals (where the risk calculation is different) and the ion generation processes for aerosol scientists.

How good is good enough? -- chasing the dream of accurate and reliable low cost sensors in air quality

a few years now, there are a number of projects around consumer level (as opposed to research grade) air quality sensors. (Air Quality Egg, Speck, Dustduino, Air Beam and my own PACMAN). The goal of most of these projects has been to empower the general public about air quality and bring the problem closer to home so that people don't see themselves as passive receptors in this but relevant actors who can have an impact through their individual actions.

The success of these initiatives has been varied with some developing a relatively large community (AQEgg), others with more institutional support (SPECK, Air Beam) and some with not so great results yet (TZOA). However, all of them eventually face the data quality monster and things can get very ugly very quickly if not taken seriously!

Good data ... but good for what?

Why is Particulate Matter so special?

Air pollution is one of those things, like weather and climate, that because it affects everyone we all have an opinion about it. This makes it an ideal area for "citizen" and "traditional" scientists to collaborate and work towards improving our lives. However, air pollution is not easy (I've been at it for 15 years and I still can't claim to get it) and clarity on the concepts used is key to maintain the communication and collaboration. 

One of those concepts that is very easy to get confused about is particulate matter (PM).

The case of the large scrubber farm

Every now and then people get "creative" with their solutions about air pollution. Back in Santiago (Chile) I saw a number of ideas being floated, with various levels of "seriousness" and I always thought that the responses from the authorities and the researchers were either dismissive or incomplete, keeping the door open for these ideas to come back and not clarifying what the good things were about those ideas and what the problems were so they were again received with the same responses.

One of those ideas was the use of what basically amounted to large outdoor air purifiers (scrubbers or filters). The first time I heard about that was back in the 1990's when the air pollution in Santiago started to be taken more seriously by the population (after other much more urgent issues were addressed as practical) and hence the elected were pushed to try and solve the problem.

Under the [global] Dome

It took me a few weeks to watch it completely (life affords little spare time nowadays) and I am very impressed by the clarity of the message and the thoroughness of the investigation. It does have some hints of "how great is China's response to air pollution" and it does focus more on the emitting activities rather than the drivers for those processes (economic growth measured as increased industrial output) but overall it is an excellent summary of the air pollution problem not only for China but other places as well (don't look away NZ!). In fact I think that many air quality management institutions should look at this piece and learn how to communicate some of the complexities of this issue.

Take this statement:

"Fine Particles impact the respiratory system, exacerbate inflammation of the respiratory tract and affect the entire cardiovascular system. Small particles correlate with a higher chance of heart failure due to reduced cardiac blood supply"

That's quite standard language for the so called "public messages" from air quality managers everywhere but as Chai Jing says "I don't understand any of that jargon" so she and some scientists made an animation to explain what's the current understanding of the effect of fine particles on people's health (see between 09:57 and 12:30 of the video).

That's just one example.

To me the most important message is that air pollution is not the goal of any human activity. Nobody does something with the explicit objective to degrade air quality ... it just happens. It's the unintended consequence of burning stuff to warm ourselves, to cook our food and to cause little explosions in our engines to make us go faster from here to there.

Air pollution is not an air pollution problem, it is an energy supply problem, a transport management problem, an urban design problem ... ultimately, it is a human problem that needs answers from all aspects of human activities.