A whiff of fresh air

Jagvir Goyal

With Diwali just around the corner, the concern over air pollution is once again in the forefront. Actually with the air pollution reaching alarming levels in several cities, this is no longer just a Diwali-related issue. While it is common in cities like Delhi to see people wearing masks to avoid breathing in the toxic air, within homes too, the popularity of air purifiers is growing steadily.  These contain a set of air filters that can extract pollutants from the air to make it breathable before recirculating it in a particular room. Pollutants can be particulate matter, volatile organic compounds, odours, gases, smoke, bacteria, mould, pollen, fungi and so on. Different types of filters are required for different types of pollutants. The fans provided in these purifiers draw air from the room and push it through the filters to extract the pollutants. Air purifiers are also known as air cleaners. There is no chemical treatment of air and only filtration process is used.  

Here are a few points about these “smart” gadgets that are going to become as essential as fans and ACs in homes soon: 

Effectiveness for dust & smoke

Most people buy air purifiers to draw Particulate Matter (PM) from the air. PM 10 and PM 2.5 are two popular terms related to Particulate Matter. PM 10 means particulate matter of size 10 micrometers or smaller and PM 2.5 means particulate matter of 2.5 micrometers or smaller in size. Particles in smoke, fungi, moulds, bacteria are finer in size and mostly come under PM 2.5 category. Particles in dust, pollen and some fungi fall under PM 10 category. All these particles are respirable and can harm lungs. Air Purifiers fitted with HEPA filters are the most effective to draw Particulate Matter from the air. HEPA filter means High Efficiency Particulate Air filter. These filters can draw more than 99 per cent of the particulates from the air. So while buying an air purifier to eliminate dust, smoke, pollen, fungi, bacteria from the air, one needs to look for a purifier fitted with HEPA filters.

Effectiveness for odour, gases and VOCs

In newly built houses, VOCs often trouble people, especially in the dress and walk-in-closet areas. Paints, polishes, varnishes, adhesives, glues used in houses often emit Volatile Organic Compounds (VOCs) that may make your eyes burn. Formaldehyde and other compounds used in ply boards also emit VOCs and sometimes, you find it difficult to stand for long in a dressing room when you open the wardrobe. Odours and gases may also occur due to smoking, cooking, use of pesticides etc. All these VOCs, odours and gases can be effectively removed by air purifiers fitted with Activated Carbon Filters. While the purifiers fitted with these filters can remove odours and gases, for removal of VOCs, the Activated Carbon Filter needs to have an extra chemical to trap and absorb the VOCs. Therefore, while buying an air purifier, it should be checked that it is fitted with an Activated Carbon filter suitable to remove VOCs also.

Effectiveness for germs and bacteria

Some purifiers are fitted with antibacterial and germicidal filters to remove bacteria and germs from the air. These filters sometimes use Ultra Violet (UV) rays to kill the bacteria and germs. Instead of buying purifiers fitted with such filters, it is better to look for those fitted with HEPA filters where HEPA filters are especially treated with special agents that kill germs and bacteria in the air. If you are keeping some pets, the germ quotient in the air may be higher. In such cases, air purifiers able to remove germs and bacteria should be preferred.

Final filter choice

Thus look for an Air Purifier fitted with both HEPA filters as well as Activated Carbon filters. Further see that HEPA filters are treated and enabled to kill germs and bacteria while Activated Carbon filters are enabled to absorb VOCs. If air has heavy particulate matter then a purifier fitted with pre-filter should be bought. Pre-filters remove heavy particles from the air before passing air to other filters. These are sometimes washable, too, while other filters are not. Say no to UV filtration and Ozone air purifiers. 

Avoid Ion generators and ESPs

Some purifiers are fitted with ion and ozone generators. These are strictly not filters but make impurities stick to them and produce ozone also. However, the verdict doesn’t go in favour of them as ozone is not considered good for lungs. Similarly Electrostatic Precipitators (ESPs) fitted in some air purifiers also filter out impurities from air but are known to produce ozone which again causes respiratory problems. Therefore, it is advisable to avoid purifiers fitted with Ozone generators and ESPs.

Area to be covered

Air purifiers can be provided for the whole of the house or for individual rooms. Whole-house filters, however, are not cost effective as these require ducting like central air conditioning and are not marketed by most companies due to their poor demand. These are not as effective in purifying air as the portable air purifiers provided in individual rooms. Portable air purifiers can be provided in one, two or many rooms. These prove performance effective and cost effective.  

Whether you need it or not

Sitting in your house, you may not feel the necessity of providing an air purifier in a room until and unless you have any breathing or suffocation problem. There are days when stubble burning is at its peak, when the vehicular emissions enter your house if you are located near the main road, when the smog makes you gasp for fresh air. In such times, air purifier, if  provided in a room, may prove highly useful. Technically, one may look for Indoor Air Quality Test. This test is now available in many cities like Delhi, NCR at a cost less than Rs 1000. Under this test, air quality meters are used by professionals to check air quality and determine the presence of Particulate Matter PM 2.5, harmful and toxic gases like Carbon Monoxide, Nitrogen Oxide and hydrogen sulphide in the air. Proper test report along with permissible range of each gas or item is given to you to decide whether to equip your house with an Air Purifier or not. 

Market availability

Air purifiers produced by many reputed brands are available in the market. These are available in different capacities. The cost varies from as low as Rs 5000 to as high as Rs 50000. One should check product reviews of different brands on review websites like mouthshut.com before finalising a particular brand under which further features can be checked.

Main features

Main features of an air purifier include the type of filters provided in it, its Clean Air Delivery Rate, Its Air Change per hour capacity, its energy efficiency and its size. 

• An air purifier should essentially have a High Efficiency Particulate Air filter (HEPA filter) and Activated Carbon filter. 
• Its clean air delivery rate (CADR) should be more than 300 cubic meter per hour, its air change per hour (ACH) should be more than four. By Air change per hour we mean that the Air purifier should be able to change room air with cleaned air at least 4 times in an hour. 
• The energy efficiency of the purifier should be high and it should consume small amount of electricity per hour, not more than 100 watts. 
• The size of Air Purifier should be chosen with respect to the size of the room to make real value addition to your house. Another important feature to be checked is the frequency of cleaning of air filters and replacement of air filters provided in the air purifier. The Air purifier shouldn't demand frequent replacement of air filters though frequent cleaning may be required depending upon the level of pollution in the air. 
• Smart Features: Look for Air Quality Monitor. It may show a red indicator if air needs purification and light may go green when the air is cleaned. Another feature is Filter Replacement indicator that tells you that it’s time to replace the filters. Child lock, timer and sleep mode are other features as an air purifier need not be run continuously. 
• One must ensure that the air purifier is the silent type and doesn’t produce more than 35 Db sound. Air purifiers running fans at high speed make more noise. It is better to look for a purifier that has bigger size and filter and cleans at low or medium fan speed. You may look for remote control operation.

— The writer is HOD and Engineer-in-Chief, Civil Engineering Department in a Punjab PSU