The current worldwide pandemic has changed the way we all live and will continue to do so for some time to come. More than ever we are now questioning the hygiene of different spaces we inhabit, our homes, our places of work and study, and even the businesses and Institutions we visit.
The places mentioned above often can be commended for their proactive responses, making decisions and applying procedures that mitigate the risks for all. What is difficult is navigating the various products on offer, from manufacturer to manufacturer and country to country, all have different standards they adhere to and some technologies are not as beneficial as they are promoted to be.
Filtercorp Health have taken the time digest some of the most common technologies in air purification and lay them out for you to make an informed decision, whether it's for your home, for your school or for your work place environment.
First we need to understand the two main groups of pollutants, PM's and gaseous pollutants.
PM can be composed of microscopic solids, liquid droplets, or a mixture of solids and liquid droplets suspended in air. Also known as particle pollution, PM can be made up of a number of components, including acids such as nitric and sulfuric acids, organic chemicals, metals, soil or dust particles, and biological contaminants.
Among the particles that can be found in a home are:
Dust, as solid PM
Fumes and smoke, which are mixtures of solid and liquid particles
Particles of outdoor origin, which are complex mixtures of solid and liquid particles
Biological contaminants, including viruses, bacteria, pollen, fungal spores and fragments, dust mite and cockroach body parts and droppings, and animal dander
These particles exist in a wide range of sizes but those of primary concern are those that are 2.5um or less. These particles have the ability to penetrate deep into lung tissue and even penetrate through the lung alveolar and translocate to the brain.
Gaseous pollutants include those related to heating combustion e.g., carbon monoxide and nitrogen dioxide as well as hundreds of other organic gases commonly referred to as Volatile organic compounds (VOC's) i.e., benzene, ethylene glycol, formaldehyde, xylene, toluene and methylene chloride. These are related to things like building materials, smoking, vehicle exhaust, paints, adhesives, pesticides, cleaning products and many others.
Control of Indoor Pollutants
There are three ways we can control indoor pollutants, Source Control, Ventilation and active air cleaning. Typically all three of these control measures should be employed where possible but for the purposes of evaluating cleaning technologies we will concentrate on the active air cleaning for this post.
Types of Air Cleaning Technologies
Within each category of air cleaner, one or more air-cleaning technologies may be used to accomplish its goals, and some air-cleaning technologies have clear advantages over others. The available technologies vary in the type of pollutant that they can remove or reduce (e.g., different PM sizes, different kinds of gases, airborne microbes), their mechanism of action (e.g., pollutant collection, conversion, inactivation, destruction), and the potential side effects of their use (e.g., primary energy use
requirements, secondary impacts on equipment performance, direct emissions of pollutants, secondary pollutant formation) (ASHRAE2008; NAFA 2007).
Some common Air Cleaning Technologies are:
Electrostatic precipitation (ESP)
Ionizers or Ion generators
Ultraviolet germicidal irradiation (UVGI)
Intentional ozone generation
Fibrous filter media
Electrostatic Precipitation (ESPs) and Ionizers
ESPs and Ionizers are portable air cleaners that use a powered electrostatic process to charge particles, which then become attracted to an oppositely charged plate or other indoor surfaces to remove airborne particles.
ESPs often have a pre filter (Fibrous filter media) that removes between 60 and 95% of the incoming particles depending on the air flow rate. ESPs then rely on the charged plates to capture the finest PM particles (2.5micron or less). The main disadvantage with this method is as the charged surface becomes covered with particles the efficiency drastically decreases. The second is that not all particles will act the same way and their properties will affect their ability to hold a charge.
Ionizers or ion generators use high voltage wire or carbon fibre brushes to electrically charge air molecules. This causes airborne particles to clump together and attach to nearby surfaces, furniture and walls etc. This removes the particles from the air and essentially deposits them on all surfaces in the room, soiling the environment. The possibility of re introducing these particles back into the air every time the surfaces of the room are disturbed by human activities is high.
Studies have also shown that charging particles has an effect on deposition in the respiratory tract so using ion generators may not reduce the dose of particles to the lungs, (Melandari et al. 1983; Offermannet al. 1985).
Some portable air cleaners that use ESPs and Ionizers produce ozone as a by-product and some makes and models increase indoor ozone concentrations that exceed public health standards (Morrison et al. 2014). Ozone production even at levels below public health standards are of concern as they can react with common household chemicals such as cleaning products air fresheners and deodorizers. The by-products of which can be associated with adverse health effects, especially those with sensitivity to chemicals like formaldehyde, ketones, peroxides and organic acids (Shaughnessy and Sextro 2006; U.S.EPA 2014; Wechsler 2006).
UVGI air cleaners primarily use UV-A or UV-C to kill or deactivate microorganisms. The types of UV lamps used in consumer air cleaners are typically low-pressure mercury vapor lamps that emit UV-C radiation at the wavelength of 254nm, this wavelength has been shown to have germicidal effects. The main condition that provides the ability to perform a germicidal function is exposure time, UV light can then have the time to penetrate the outer structure of the cell and alter the microorganisms DNA preventing replication and causing death.
However, some microorganisms are resistant to UV radiation and to make UV a reliable source of sterilization the lighting power must be high and exposure times must be long, in the orders of minutes or hours. Longer than air is inside typical UVGI air cleaners.
UVGI air cleaners also suffer from the same disadvantage as ESP and Ionizers in that ozone can be emitted by photolysis of oxygen in the air flow through the cleaner. To combat this some manufacturers apply special coatings to the UV generation lamps.
There is also no specific standard test method to evaluate the efficiency of UVGI air cleaners in HVAC and residential applications. Typical UVGI air cleaners designed for use in homes do not deliver sufficient UV doses to effectively kill or deactivate most airborne microorganisms because the exposure period is too short and/ or the intensity is too low. Thus, UVGI does not appear to be effective as a sole control device. When UVGI is used, it should be used in addition to—not as a replacement for—conventional particle filtration systems, because UVGI does not actually capture or remove particles (CDC
Sorbent Media and Chemisorbing media
Sorbent media air cleaners use materials that have a high surface are to volume ratio to capture gaseous pollutants and there are two main ways this is achieved. Absorption and Chemisorption.
Absorption medias like activated carbon, silica gels, activated alumina, zeolites, synthetic powders, and porous clay create a physical attraction for the gas or vapour. They all have limited capacities and require frequent replacement or replenishment. An absorbent will generally absorb the molecules it has the greatest affinity with and will allow other molecules to remain in the airstream. Activated carbon is the most common absorption media used however this is not effective with lower molecular weight aldehydes, ammonia and nitrogen oxide and hydrogen sulfide.
Chemisorption is a process whereby the target gas or vapor chemically reacts with other reagents impregnated into the media. These reagents from stable bonds with the target gas or vapor and are bound to the media and slowly broken down over time and released as carbon dioxide and water vapor or some other more readily absorbed compounds.
Sorbent and Chemisorbing medias are dependent on the following factors:
Airflow rate and velocity through the sorbent
Concentration of contaminants
Presence of other gaseous contaminants
Total available surface area of the sorbent (some manufacturing techniques can significantly reduce a filter’s total surface area)
Physical and chemical characteristics of the pollutants and the sorbent (such as weight, polarity, pore size, shape, volume, and the type and amount of chemical impregnation)
Pressure drop (how hard the air has to work to flow through the media)
Removal efficiency and removal capacity
Temperature and relative humidity of the gas stream
Photocatalytic Oxidation (PCO)
PCO uses high surface area plates coated in reactive catalysts that activate when irradiated with UV light. The photochemical reaction creates hydroxyl radicles that oxidise pollutants and converts organic pollutants to carbon dioxide and water.
Unfortunately PCO air cleaners are often ineffective at completely transforming pollutants and are also known to generate harmful by-products like formaldehyde, acetaldehyde, nitrogen dioxide and carbon monoxide. In addition to that the UV-C lamp could also produce Ozone if the lamp is not treated to inhibit this.
Because of the generation of harmful by-products PCO units often have absorbent medias downstream that can collect these.
There are limited field investigations to validate the performance of PCO air cleaners and laboratory studies demonstrate high variability and often relatively low removal efficiency for many common indoor gases (Chen et al. 2005). The usefulness of PCO air cleaners depends on the amount of catalyst, the amount of contact time between gaseous pollutants and the catalyst, and the amount of UV light that is delivered to the catalyst surface. If any one of these factors is not addressed in the design of the device, a PCO air cleaner may fail to destroy pollutants completely and instead produce new indoor pollutants including irritants.
Plasma air cleaners apply a high-voltage discharge to ionize incoming gases, breaking their chemical bonds and chemically altering them (Bahri and Haghighat 2014). Thermal plasma air cleaners generate a high-temperature plasma flame using high voltage and high current. Non-thermal plasma air cleaners accelerate electrons to generate reactive ions and radicals, which convert compounds by oxidation reactions.
According primarily to controlled laboratory tests, plasma air cleaners can have high removal efficiency for some gases as well as particles, and they can also kill or deactivate airborne microorganisms. However, a number of harmful byproducts are known to form, including particles, ozone, carbon monoxide, and formaldehyde (Chen et al. 2009;
Van Durme et al. 2009).
Plasma emitted directly to indoor air contains ozone and other reactive oxygen species such as hydroxyl radicals, superoxide's, and hydrogen peroxide. Plasma air cleaners are sometimes combined with other air-cleaning technologies, such as PCO or adsorbent media, but very little information exists on the performance of these systems in real indoor settings.
Intentional Ozone Generators
Ozone generators as their name implies purposely create ozone to react with airborne particles. Ozone reacts with chemical pollutants breaking them down into other compounds at high concentrations and killing or deactivating biological pollutants.
However, ozone is classed as a lung irritant and as such units that produce ozone are banned or severely restricted in their use in most countries.
Fibrous Filter Media
Fibrous filter media remove particles from the air stream by physically capturing them, this could be because the pore size precludes the particle from passing by, the particle could impact the surface of the fibre, or the fibres charge can attract the particle to it. Fibrous media filters vary widely in their ability to remove particles and particle removal depends on a number of parameters including particle size, face velocity, filter thickness, filter porosity, filter fibre dimensions and dust loading.
Manufacturers of fibrous filters use a number of test standards to evaluate the particle removal efficiency of the fibrous media. The most common standards are EN779:2012, ISO16890 and Ashrae 52.2. Generally the higher the number assigned to a filter the more efficient it is, except for the ISO standard which specifically measures particle removal for the different categories of particles, PM10, PM2.5 and PM1. If the filter is not tested to one of these standards it cannot carry the filter classification associated with it.
HEPA filters which are common in air purifiers are tested and classified under specific standards and are unable to be sold as HEPAs unless they pass stringent testing regimes.
The performance of fibrous media air filters in residences depends not only on the removal efficiency of the media, but also on factors such as the:
Indoor particle size and size-specific mass concentrations
Amount of dust loaded on the air filter
Airflow rate, velocity, and resistance to airflow through the filter media
Bypass airflow that flows around the air filter because of poor installation
System or device runtime, which governs how much air passes through the filter
IQAir HealthPro units rely on tried-and-true filtration technology, the fibrous filters contained in the units are certified to worldwide filtration standards and have the longest lifespan of any air purifier in the market today.
Filter bypass is highlighted as one of the biggest impacts on efficiency when using fibrous filters and IQAir have gone to great lengths to solve this issue. IQair have independently tested their units to ensure that Total System Efficiency (TSE), that is the IQAir HealthPro unit including its filters, has a TSE of ≥99.97% for particles ≥0.3µm! There is no other air purifier on the market that can make this claim and support it with independent testing to the best of our knowledge in this filtration category.
Fibrous filters are used today in many areas society deems important enough to ensure the air is clean; Hospital isolation wards, Hospital operating theatres, hazardous chemical and substance laboratories and nuclear power plants to name a few. The research that exists for the efficacy of these types of filters is vast and well tested.
If you have areas in your home, business or educational institution that will benefit from the trusted and proven air purification offered by IQAir products. Please get in touch with us today and one of our filtration experts can suggest the IQAir model that enables a cleaner tomorrow for you, your family, your students and your colleagues.
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