This then is the conundrum; we need air to circulate from outside to inside, but in areas with substantial external pollution that circulation continuously brings harmful outside pollution into our homes.
Outside vs Inside
Outside, Nature wages a powerful war of attrition against atmospheric pollution.
Wind disperses pollution, diluting its local effects. Natural chemical and photochemical interactions create an abundance of ‘hydroxyl radicals’ (called ‘Nature’s Detergent’ by scientists) which attack and neutralise a wide range of pollutants, and rain and snow wash pollution and its by-products out of the air.
Of course, in the urban environment, pollution can build up where it is created more quickly than nature can remove it.
Inside, the natural conditions which create hydroxyls are absent, and pollution, well, it hangs around for us to breathe it in!
What does the pollution consist of?
Before deciding on an effective strategy for reducing pollution leaking in from outside, it is necessary we understand the scope and nature of the pollution we are attempting to neutralise.
Historically, the main air pollution problem in both developed and rapidly industrialising countries has typically been high levels of smoke and sulphur dioxide emitted following the combustion of sulphur-containing fossil fuels such as coal, used for domestic and industrial purposes.
These days, the major threat to clean air is now posed by traffic emissions. Petrol and diesel powered vehicles emit a wide variety of harmful pollutants, principally carbon monoxide (CO), oxides of nitrogen (NOx), volatile organic compounds (VOCs) and particulate matter (PM2.5). Additionally, the photochemical reactions resulting from the action of sunlight on nitrogen dioxide (NO2) and VOCs create ozone.
Carbon Monoxide (CO)
CO (carbon monoxide) is a dangerous, colourless gas which reduces your blood’s ability to carry oxygen and can make you ill.
Oxides of Nitrogen (NOx)
The Committee on the Medical Effects of Air Pollution recently reviewed the evidence for the adverse health effects of NOx and concluded that:
Volatile Organic Compounds (VOCs)
VOCs include a variety of chemicals, some of which can have short- and long-term adverse health effects.
Ozone can trigger asthma attacks and cause shortness of breath, coughing, wheezing, headaches, nausea, and throat and lung irritation, even in healthy adults.
Particulate matter, also called PM or soot, consists of microscopically small solid particles or liquid droplets suspended in the air.
PM2.5 refers to what are termed “fine particles” of below 2.5 microns in diameter. The smaller the particles, the deeper they can penetrate the respiratory system and the more hazardous they are to breathe.
Ultrafine particles (UFPs) are particulate matter of nanoscale size (less than 0.1 microns in diameter). UFPs are the main constituent of airborne particulate matter. Owing to their numerous quantity and ability to penetrate deep within the lung, UFPs are a major concern for respiratory exposure and health
PM pollution can cause lung irritation, aggravates the severity of chronic lung diseases, causes inflammation of lung tissue, causes changes in blood chemistry and can increase susceptibility to viral and bacterial pathogens.
Step 1 - Reduce air leakage
Click here for a good basic guide on what can be done to both save energy (and money!) and reduce air leakage.
Simply reducing leakage won’t solve the pollution problem (reducing leakage by, say, 50%, won’t really help in pollution terms; the air inside will still be as polluted as the air outside), but the lower the leakage rate, the more effective the use of air cleaning technology will be.
Think about it this way: Sit an air cleaner, however effective, next to an open window, and it will be overwhelmed by new pollution to the point where it will have no effect. For an air cleaner to be effective, you have firstly to slow the flow of new air into a room to give it time to work.
So, reducing leakage is only the first step in mitigating the pollution problem. The second step is using an air cleaner that really works!
Step 2 – Remove or neutralise internal pollution
Having reduced air leakage, let’s look at our options for removing or neutralising polluting gasses and particulates before we breathe them in:
Can filters reliably remove or neutralise all of CO, NOx, VOCs and O3?
X No! CO, NOx, VOCs and O3 are gasses that cannot be filtered out by HEPA, Ionising (Ionic) or Electrostatic (Electronic) filters, which are all designed to filter out particulates, not gasses.
What about activated carbon filters?
These are sometimes suggested to remove these gasses from the air and can be implemented either as stand-alone filters or in combination with a HEPA filter to capture the larger particulates.
There are many problems with using this type of filter to address outside air pollution:
X So, all in all, activated carbon filters are not effective as a solution for removing gaseous pollutants.
OK, how about HEPA filters?
The ‘gold standard’ for particulate filters is the High Efficiency Particulate Air (HEPA) filter. Filters meeting the HEPA standard remove 99.97% of particles that have a size 0.3 microns or larger from the air passing through them.
However, 90% of particulates in the air, including the most harmful ones, are smaller than that, so most HEPA air purifiers only catch a fraction of all particulates, and none of the potentially most harmful ones.
X Hepa Filters will only remove 10% of the particulates.
So, filters simply aren't effective at removing industrial and traffic pollution?
Correct. And air filters don't work well in the real world anyway! Not only are there no suitable and affordable filters for the purposes we require, the unfortunate fact is that portable air filtration devices, of whatever type, are not very effective at treating any kind of pollution.
All portable air filters share the same fundamental shortcoming; even if they do filter the air passing through them effectively, they only clean that limited amount of air that passes directly through them, not all of the air in the room. You can find out more here.
Then along came Airora…
Let us return to where we started, outdoors.
Outside, Nature wages a powerful and successful war of attrition against atmospheric pollution by employing natural chemical and photochemical interactions to create an abundance of ‘hydroxyl radicals’ (known as ‘Nature’s Detergent’ by scientists) which attack and neutralise a wide range of pollutants.
Find out more about how Airora breaks down harmful gasses and vaporises key ultra-fine particulates that are too small to be trapped by HEPA filters here.
Noise pollution adversely affects the lives of millions of people. Multiple studies have shown the direct links between noise and health.
According to one study, around 50,000 people in just the European Union die prematurely each year from heart attacks caused by traffic noise. Another study showed that people living in streets with average noise levels above 65-70dB, the average risk of heart disease is 20% higher than for people living in quieter streets.
Other problems that have been proven to be related to noise include stress related illnesses, high blood pressure, speech interference, hearing loss, sleep disruption, and lost productivity.
Traditional filter-based air purifiers
Most air purifiers on the market use HEPA or Electrostatic filters, and these air purifiers typically create a noise of over 70dB at their most effective (highest) fan speed. Indeed, manufacturers tacitly recognise that this noise level is unbearably high in the home, so most have a ‘sleep’ / ‘quiet’ mode which makes them a little quieter but effectively cripples their effectiveness!
In other words, to use a traditional air purifier at its most effective fan speed, exposes people to a noise level similar to street traffic inside their home.
In fact, according to the World Health Organisation’s Night Noise Guidelines, above 40db (rainfall, a refrigerator or an air conditioner at 100 feet, a quiet suburb) of noise can have adverse health effects and noise at this level may well affect most people’s sleep.
So-called ‘silent’ air purifiers
You may have come across ‘silent’ air purifiers, these are air purifiers without a fan.
There are basically two types of ‘silent’ air purifier:
And then there is Airora …
This means that hydroxyls can reach every nook and cranny of a room within seconds, acting on all of the air and all exposed surfaces.
Why all the focus on air filter efficiency?
Designers of traditional air purifiers have a tough job. There are lots of different air purifiers, so how to stand out from the crowd? Well, a little like high end music systems, ‘measures of performance’ are created which appear important to potential buyers but which are pretty meaningless in practice, and then competing products can be compared, and superiority claimed, based on that same measure.
One such misleading measure is ‘filter efficiency’ where you often see a focus on the percentage of particulates (pollens, mould spores, pet dander and house dust mite excretions) captured by the filter in the air purifier. For example “my filter captures 99.7% of all particles and yours only captures 99.2%”, or “my filter captures smaller particles than yours does” and so on.
And it isn't just the %, some manufacturers stoop to terms such as 'True HEPA' to muddy the waters, when in fact there is no such thing, a filter either meets the standard for HEPA filters or it doesn't!
Sadly, the fact is that such measures are pretty much meaningless in the real world. But, you say, surely it matters how much of the particulates in the air, which may well be allergens, irritants and other pollution, the device filters out?
My reply is that there are at least two major problems with using this measure of air purifier effectiveness, both of which make the number, be it 90%, 95% or 99.97% ( or even in fact 100%! ), pretty much meaningless!
The filter % measures the wrong thing
Measuring the percentage of particulates that are captured from the air passing through the filter measures only that, the percentage of particulates captured from the air passing through the filter. It doesn’t measure the percentage reduction of particulates in the air in the room, and the relationship between the two is tenuous at best!
The unfortunate truth is that the air in the room is constantly changing (typically it is replaced hourly with contaminated air from outside and elsewhere in the home), the air passing through the device is immediately remixed with unclean air in the room and some of the air in the room never goes through the device at all. Some air never goes through the device because of insufficient air flow, temperature stratification and the formation of eddies (where the air in parts of the room rotates in a circular motion without ever moving through the air purifier).
Furthermore, as pointed out by the US Environmental Protection Agency;
"for typical room sizes, most portable air cleaners currently on the market do not have high enough air flows to effectively remove large particles such as pollen, dust mite and cockroach allergens"
The reason being that the larger (and heavier) particles, such as pollen, simply sink to the floor or onto other surfaces, ready to be re-distributed into the air when they are next disturbed!
If you model how air cleaners work and include the constant infiltration of polluted air from elsewhere, they can take hours to reach a stable minimum of pollution and that minimum is related to many factors, but only marginally to the efficiency of the filter itself.
Think of it this way, imagine that an air filter, which captures 99.7% of particulates, effectively reduces the amount of particulates in the air of a room, after several hours, by say 50%. Changing the filter to one which captures only 90% will only have a marginal effect, perhaps limiting the reduction to, say, only 46%.
Be it either 50% or 46%, it doesn’t matter – neither are nearly enough!
What about gasses?
Well, a HEPA filter only ‘traps’ particles down to a particular size, below that size they are not captured at all. And all of the basic technologies, HEPA, electrostatic and ionic completely fail to capture or neutralise polluting gasses which can themselves be breathing irritants and cause asthma attacks.
Then along came Airora ...
The problems outlined above have earned traditional air purifiers a poor reputation, to the point where physicians will generally only say “well try one, it might help”.
Dr Wyatt blogs on his lifetime's experience of Indoor Air Quality Issues.