India homes 13 of 25 most polluted cities in the world. This speaks volume about the appalling condition of air in the sprawling Indian cities. Delhi was making headlines all over the world past winter because of smog and dangerous levels of pollutants. According to one of the studies, 4.4 million school children in India have developed irreversible lung damage from the poisonous air. That’s for India but talking about global air conditions, World Health Organization (WHO) have estimated that 4.3 million premature deaths so far are a result of household air pollution from multiple sources and poor ventilation.
Shockingly, air pollution levels in the home can be up to 10 times more than the outdoor pollution. Primary causes of such high level of indoor pollution in the usage of incense stick, mosquito coil alongside emission from cooking and pet dander. Though the situation might appear dismaying, there are ways we can mitigate the ill-impact of rising indoor air pollution using filters and purifiers. Air conditioners (ACs) usually come with different types/layers of filters. On the other hand, air purifiers come as a dedicated option to combat rising indoor air pollution. In this article, we will cover different types of air filters fitted inside the AC and air purifiers. We will also understand the technologies they come with and finally conclude which one is better—an AC or a air purifier.
Different Types of Filters
Prefilter is usually the first layer of filter fitted ahead of the main filter specially to remove large particles of dust from the air. These are general filters that do the basic job of getting rid of pet hair, dust, and larger microbes. They are generally made of nylon or foam and are usually washable. They are found in most of the air purifiers and few AC brands like Blue Star and Daikin. Prefilters when used in isolation aren’t considered effective for people suffering from severe respiratory disorder like asthma or allergies
You would have probably heard this term (HEPA) if you happen to surf air purifier specifications/details. HEPA filters are the most important type of filters used to filter out microscopic particles; even of the tiniest size. Formally speaking, HEPA filters are expected to remove at least 99.97% of airborne particles sizing 0.3 µm or more. Microns are one-millionth of a meter. To give you a better idea, the diameter of human hair is 50-100 µm. In fact, humans cannot see anything less than 10 microns. The typical size of various airborne impurities are as follows:
- Bacteria: 0.3–60 microns
- Car emissions: 1–150 microns
- Spores: 3–40 microns
- Mold: 3–12 microns
HEPA filters tend to use two quite different mechanisms to clean the airstream. First, there are one or more outer filters that work like sieves to prevent the larger particles of dirt, dust, and hair to pass through. Inside those filters, there is a concertina of that appears like a folded paper. The paper is actually a mat of very thick glass fibers. It simply doesn’t filter out minute dust particle but instead used three different mechanisms to grab the dust particle in the air. At high airspeeds, some particles are easily trapped as they smash directly into the fibers, while others snag on the fibers as they try to brush by. At lower airspeeds, dust particles tend to flow more randomly through the filter (a phenomenon called Brownian motion) and may stick to its fibers in the process of random flow. This mechanism allows the HEPA filters to catch particles that are both larger and smaller than a certain target size (0.3 µm).
Beware of the products that claim to be HEPA-type/HEPA-like/HEPA-style as they do not satisfy stringent standardization and may not have been tested in independent laboratories. Real HEPA filters are classified using the five letters A through E, based on how well they capture particles and resist the airflow. Type A is the least effective but still meet the fundamental criteria for HEPA, while type E (at the opposite end of the grading) are military grade filters capable of dealing with even radiological, chemical or biological particles. Based on the combustion characteristics they are also classified as fire resistant (type 1) or semi-combustible (type 2).
Interestingly HEPA filter was originally developed by the nuclear industry to clean up dangerous radioactive particles but was subsequently patented to be used in the air purifier by Swedish company IQAir. Besides the air purifiers, HEPA filters are also used in hospitals, aircrafts and new models of Tesla cars.
PM 2.5 Filter
This is arguably most important filter to reduce indoor air pollution when it comes to air conditioners. According to World Health Organization (WHO) levels of air pollution have tremendously increased in the developing economies with low and middle income including India. Lately, air pollution has been linked to an increased in respiratory diseases including lung cancer. The risk due to particulate type pollution is said to be like what is seen with second-hand smoke exposure. That is the reason why is imperative to have PM 2.5 filter in order to filter out the microscopic impurities.
Particulate matter, PM 2.5 consist of very fine particles present in the air which are of the size two and a half microns in width (or even less). As we mentioned earlier, a micron is unit of measurement at a microscopic scale with one-inch equating to 25,000 microns. Emission from vehicles alongside the burning of wood and oil are the primary sources of PM 2.5 particulates.
So, you might wonder what are the sources of PM 2.5?
- Fine particles emitted from:
- Other off-road vehicles
- Minute material expelled from the exhausts of:
- Construction equipment
- Burning of:
- Grass fire
PM 2.5 can cause major health impairment as they can travel through the respiratory tract reaching the lungs. PM 2.5 can result in the following health impairments:
- Eye and nose irritation
- Throat and lung irritation
- Coughing and sneezing
- Increased rates of chronic bronchitis
- Reduction in smooth lung functioning
Reputed brands like Whirlpool, LG, Carrier etc comes with AC models that are equipped with PM 2.5 filters. In fact, premium LG ACs come with a specialized sensor which comes with PM 1 sensor which senses, monitors and apprises the user of the PM 1 levels through the dedicated app.
Because of increased pollution, the air we breathe consist of various hazardous gases/compounds and VOCs are one of them. Volatile Organic Compounds (VOCs) are organic compounds that easily become vapors or gases owing to their high vapor pressure at room temperature. Midea ACs come with an anti-VOC filter for removal of VOC. Typical sources of VOCs are burning of fuel like gasoline, wood, coal, natural gas, etc. The residues from paints, glues, and solvents also add to the concentration of VOC in the air. Many VOCs are hazardous because when combined with nitrogen oxides, they react with them forming ground-level ozone, or smog, which leads to climate change. Certain VOCs are infamous for impacting liver, kidney and nervous system. Anti-VOC filter used in Midea split ACs eliminates toxic VOCs like formaldehyde to ensure air is debarred of such impurities.
Activated Carbon Filter
Activated carbon filters are granular or powdered pieces of carbon that have been treated to be extremely porous. In fact, that just one gram of activated carbon can easily have a surface area of approximately 100 acres. So, now you can realize filtering capacity of a pinch size activated carbon. In carbon filtering a bed of activated carbon is used to remove contaminants and impurities, using chemical adsorption technique. Adsorption is a process wherein organic compounds present in the air react chemically with the activated carbon, which causes them to stick to the filter. Reacting with oxygen opens millions of its pores which traps a large amount of gas and odor. The more porous the activated carbon is, the more impurities it will capture. These filters are most notably used to remove the plethora of hazardous impurities like:
- Volatile organic compounds (VOCs)
Indian AC brands like Voltas and Blue Star come with an activated carbon filter in their ACs. Most of the new air purifiers now come with an activated carbon filter and it’s imperative to have an activated carbon filter given its natural ability to trap the impurity.
Mi air purifiers come with what is called activated coconut carbon filter which is a very useful offering. Activated carbon from coconut shell has pores predominantly in the micro pore range (around 85-90%). As opposed to macro and meso pore found in activated carbon from other sources like peat and wood, micro pores match with the size of contaminant molecules present in the air and traps them. Owing to its natural composition activated coconut carbon filters are tight in its structure and has a good mechanical strength and hardness which ensures good durability. Blueair air purifiers, on the other hand, come with carbon filters infused with other compounds like magnesium dioxide and copper oxide in their air purifiers to remove even more hazardous pollutants from the air, such as carbon monoxide, ethylene oxide, and ozone.
Electrostatic filters are washable air filters that usually do not need a replacement for a very long time. This filter is used in few Daikin AC models. The electrostatic filter has multiple layers of vented metal through which the air passes. As the air passes through the first layer of filtration, the air molecules get charged positively due to the friction between the air and the filter. These positively charged air molecules attach themselves to the next few layers as they pass through the rest of the filter. Though electrostatic filters have a lower replacement cycle, it takes a longer time to clean the electrostatic filter. Because these filters use static electricity, particles that make through this filter are like to stick inside the duct line. This accumulated dust is difficult to clean as it is ionically charged and have a tendency to remain glued to the surface. Also, electrostatic filter tends to block airflow more compare to other filters, which would mean ACs would need to toil hard to cool the room.
Many air purifiers and ACs come with Photocatalytic filter. The catalyst in the photocatalytic filter that cleans the air is typically titanium dioxide which is nothing but a semiconductor (like silicon). It is energized by ultraviolet (UV) light—a short-wavelength light of the electromagnetic spectrum that our eyes can’t see. Not much of a titanium dioxide is used in this filter; just a thin film covering the surface of a substrate. The substrate is usually made from a ceramic or a piece of metal (such as aluminum).
When a UV light shines on the titanium dioxide, electrons (negatively charged particles inside atoms) are released at its surface. It’s the electrons that do the useful work of filtering the air. The electrons react with water molecules (H2O) in the air, breaking down into hydroxyl radicals (OH·), which are super reactive, short-lived, uncharged forms of hydroxide ions (OH−). These small, agile hydroxyl radicals then attack bigger organic (carbon-based) pollutant molecules, breaking apart their chemical bonds. Post-reaction pollutant molecules are converted into relatively harmless chemicals like carbon dioxide and water. This is a classic example of oxidation and that’s why certain air purifiers that work this way market the filtration as PCO technology (photocatalytic oxidation).
The biggest drawback of the photocatalytic filter is that they also produce small amounts of ozone (O3)—a chemical variant of the oxygen that itself is a toxic air pollutant. So, it’s better to avoid purchasing technologies which use photocatalytic oxidation as it produces ozone into the home environment which is a paradox for air purification. Also, UV sterilization is also not recommended for indoors as it can cause sunburns and it’s only best suited for places with zilch human presence.
Nano Silver Filter
Indian AC brand like Voltas and BlueStar comes with nano silver filter in their new ACs. The nano silver filter incessantly releases the silver ions to sterilize the bacteria. The silver ion filter not only kills bacteria in the air but also inhibits the growth of microbes like bacteria, virus, fungi, and spores. They destroy their inner configuration by absorbing the cells elements. If you own a pet or suffer from seasonal allergies, a nano silver filter can be extremely beneficial due to its effectiveness to remove pet dander, pollen, and dust. Manufacturers claim it removes 600+ types of bacteria, leading to 99.99% disinfection of the filtered air. But on the downside, Friends of Earth Germany, an environmental watchdog has reprimanded the usage of silver nano for its toxic effect it can cause on the different kinds of cell.
Most of the AC filters and air purifiers have some or the other form of anti-bacterial filters. Though their naming convention and construction may vary. Some call it anti-bacterial, some call it anti-microbial while some call it biofilter. Anti-bacterial filters are good for scrubbing the air from harmful microorganisms and inhibits their growth. These filters use a special microstructure charge that grabs pollen, dust, mildew, smoke and mold spores. The charge pulls in the additional microorganisms from the air while the system of fibers firmly traps and holds captured airborne particles.
Acaro Bacterium filter used in Voltas AC captures ticks, mites and other small organisms that are harmful to the human body. They also have antiseptic property in the filter which kills harmful bacteria, thereby maintaining a healthy environment inside the air-conditioned room. Anti-bacterial filter used in Blue Star ACs removes 95% Escherichis Coli and Staphylococcus Aureus bacteria which are infamous for causing boils, infections, and diarrheal diseases. Biofilter used in Carrier ACs traps airborne microscopic particles, bacteria, and fungi.
Anti-bacterial filters provide a constant flow of pure air throughout the room. Good thing is that these filters can be easily cleaned by a vacuum cleaner or even through a usual hand wash.
Japanese AC manufacturers like Toshiba, Panasonic, Mitsubishi are heavily using Catechin filter in their new ACs. Catechin filters are remarkably effective at freeing the indoor air of ugly odors. Catechin filters get their name from a naturally occurring antioxidant found in a green tea. They strip the passage of odor-causing pollutants such as tobacco smoke and pet smells owing to their anti-dust and anti-bacterial properties. An equally important utility is that they trap and exterminate microscopic bacteria and viruses which could otherwise lead to cold, cough and other respiratory disorders. Following the Japanese brands, even Indian AC brand like Voltas and Blue Star have started using Catechin filter in their ACs to filter household smoke and other pollutants
Vitamin C Filter
Interestingly few AC models from brands like Blue Star, Midea, Voltas come with Vitamin C filter. Sounds nutritious? Well, manufacturers claim that the Vitamin C filter fills the air with vitamin C, which softens the skin, reduces stress and provides therapeutic benefits.
Now, vitamin C is essential for the synthesis of molecules necessary for healthy skin. Mixing vitamin C into the air conditioner air flow is intended to bring a moisturizing effect to the skin. To mix vitamin C into the airflow, a ceramic additive in the filter releases vitamin C in the presence of moisture in the air. Zeolite, a moisture absorbent is also added to provide a steady release of vitamin C in dry conditions during winters when moisturization is direly needed. Also, manufacturers say that this filter last for a couple of years without needing a replacement.
Do You Really Need an Air Purifier or an AC is Enough?
Big question is do you really need an air purifier or is it wise to buy an AC with a good filtration system? Well, this is a tough question to give a generic answer. Because it depends on a number of parameters. If you live in a village or small town and assuming indoor air pollution is not alarmingly high like metros, you can surely go for an AC with a good filtration system. In that case, having PM 2.5 filter is a must and couple of big brands come with that. In fact, LG has launched new models which can also sense PM 1 levels in the room apart from offering filtration of PM 2.5 pollutants. But in case you live in a big city or doubt your indoor pollution is higher on account to the proximity of the construction site/industrial site then you should go for a dedicated air purifier. But make sure that the air purifier contains HEPA filter and not the HEPA-type/HEPA-like filters which are unregulated cheap replicates of HEPA filters. Now it’s important to note that ACs don’t come with HEPA filter and it’s almost impossible to modify the AC filtration system to imbibe HEPA filters. HEPA filters are used to filter out extremely minute impurities of the level 0.3 µm and if they are used in ACs they would lead to several complications like:
- Reduced airflow
- Higher maintenance cost
- Premature breakdown
So, it’s best to go with an air purifier with true HEPA filter than to expect the AC filter to clean the indoor air pollution if the air quality has reached alarmingly high levels. Also, make sure air purifiers have activated carbon filter which removes the smoke, fumes and other foul odors. It is best to avoid air purifiers with the electrostatic or photocatalytic filter because during the filtration stage because they produce ozone which damages the environment. Though AC filters and air purifiers can work on tiny particulates, dust, dander or even bacteria and allergens they do little to protect users from toxic chemical gases like carbon monoxide, carbon dioxide, nitrogen dioxide etc. So here you can use natural options like keeping plants such as areca palm or money plant which are known for their air purifying capabilities.
About the Author:
Hussain Kanchwala is an Electronics Engineer from University of Mumbai. As an Analyst at BijliBachao he keeps a tab on latest technologies in gadgets and appliances, tracks businesses of white goods companies and monitors the consumer behavior. With a background in engineering, penchant for detail, and flair for writing he regularly write reviews about brands and their products. More from this author.