This is the second piece in my two-part series on air quality, and follows on from the first article on why indoor air quality is so important. In a nutshell, indoor air quality (IAQ) has the potential to be far more polluted than outdoor air (for a number of reasons) and when you consider that we spend up to 90% of our lives indoors, it makes sense that if indoor air quality is poor, there will be associated poor health consequences.
Asthmatic and allergic reactions are just some of these, and can be caused by exposure to the gases, pollen, particulate matter, and micro-organisms found indoors. Because of this, IAQ has become a globally recognised concern, and the trapping and removal of allergens, viruses and bacteria that cause sickness, discomfort, and absenteeism is increasingly becoming a business priority.
How can we improve IAQ?
According to the EPA, “The most effective ways to improve your indoor air are to reduce or remove the sources of pollutants and to ventilate with clean outdoor air. In addition, research shows that filtration can be an effective supplement to source control and ventilation.”
We know that in a commercial or office environment it may not always be possible to remove the pollutants, nor practical to “ventilate with clean indoor air” - especially in winter. I can just imagine everyone sitting at their desks, shivering, as blasts of rainy, wintery air come in the window…
So what air filtration technology is available to us to improve indoor air quality?
Air filtration is the removal of particles from the air - also called air purifying. A good air purifier should filter out harmful airborne particles such as malodours, allergens, bacteria, viruses, spores, mildew, yeast, moulds and VOC’s and thus reduce the level of contamination in the air.
How does an air purifier do that?
The answer to that question is dependent on what sort of air purifier you have or are considering getting. At present, HEPA filters and activated carbon filtration systems make up 63% of the market’s offering to remedy poor indoor air quality and are replacing the use of ozone and electrostatic precipitators. Many modern air purification systems use HEPA filters and carbon filtration in conjunction, to ensure optimal filtration.
HEPA Filters and Carbon Filtration:
HEPA filters clean the air by removing 99.97% of harmful particles such as dust, dust mites, allergens, pet dander, bacteria, pollen and mould safely and easily. HEPA stands for High Efficiency Particulate Air, and is a designation specifically used to describe filters that are able to trap 99.97% of particles that are 0.3 microns (one micron is 1/1000 mm). 0.3 is referred to by scientists as the most penetrating particle size (MPPS) because that size of particle has been found to evade air filters more than other sizes.
Most modern HEPA filters consist of interlaced glass fibers that are twisted to create a fibrous maze. As particles move through this web, they’re taken out of circulation by either colliding with the fibres, or becoming ensnared.
Carbon filtration, on the other hand, absorbs odours and VOC’s. Carbon filters use small pores to capture chemicals, odors, and smoke that a HEPA filter might not catch.
An electrostatic precipitator uses electrostatic force to grab and hold dust and other particles. These air purifiers typically first pull air over an initial air filter, then pass the air over an electro-charging process. While they often don’t produce as much ozone as an ozone generator, ozone is a by-product of the air-charging process.
As air passes through the air purifier, it goes through a small internal chamber that exposes the particles to UV light. The light is not emitted into the room, nor can you see it. A UV light purifier works by disrupting the core DNA of these pathogens. This prevents them from multiplying, effectively killing all unwanted bacteria, germs and viruses.
It cannot trap or remove particles and the EPA advises that for actual destruction of mould and bacteria spores, you would need high levels of UV light and much longer exposure times. It also advises that mould particles can still cause allergies even when deactivated, and so UV air purifiers may not be effective for allergies and asthma.
Air purifiers that contain an ionizer create a high electric field of ions. The positive and negative ions attract other charged particles in the polluted air and release fresh air into the environment. Ionizers charge particles, however, they do not collect anything, so the particles simply stick to surfaces. The particles may not be in the air, but they still reside in the living space.
Something else to note when investigating air filtration is that many air purifiers declare a clean air delivery rate (CADR). CADR is a function of airflow and filtration efficiency, stating the volume of cleaned air delivered in a specific time, expressed as cubic meters per hour (m3/hr). As air purifiers use different filtration methods for particulates and volatile molecules, they may have different CADR values for different contaminants.
A few other questions to ask when choosing an air purifier:
Because an air purifying system can be a big investment, here are a few other questions to consider asking before you decide on which system is best for your home or business.
- Room size: what sized space (m squared) can the air purifier handle? You need to ensure the purifier you choose is big enough for the space.
- Filter reminders: does the unit remind you when the filters are due to be changed?
- Real-time indicator: does your device provide real-time information measuring temperature, humidity, VOC, airborne dust particles?
- Dynamic operating modes: does your device offer an intelligent response to respond to varying air quality levels?
- Tested and verified: has the unit passed any independent tests to verify the manufacturer’s claims?
Because air purifiers help to clean the air by trapping and removing airborne particles that may include harmful pathogens, a rigorous approach to health and safety is essential. Air purifiers must be serviced and inspected regularly, and the filters changed at regular intervals.