Indoor air quality can be improved by essentially three methods:

1. Source Control of Pollutants
2. Air Cleaners / filteration
3. Ventilation Improvements to dilute the concentration of pollutants.

Source Control

Usually the most effective way to improve indoor air quality is to eliminate individual sources of pollution.

Cigarette smoking can be banned, asbestos containing substances like insulation can be sealed, formaldehyde from particle board, wooden ceilings, plywood can be eliminated by using varnish to reduce the release of irritating chemicals. Carpeting, when freshly installed should be aired before usage.

Restroom air freshners, paints and adhesives could be avoided.

HVAC ducts are a main source of contaminants and often act as breeding ground for mold, mildew and bacteria. As awareness of the importance of indoor air quality grows, more people are looking at duct cleaning as a way to solve indoor air quality problems. The duct cleaning industry is expanding fast to meet this demand, using extensive advertising to encourage people to use their services.

Does Duct Cleaning Really Help?

It should be first determined if contaminated ducts are the cause of the health problem. Even when contaminants are found in ducts, the source may be elsewhere. Moreover the dislodged pollutants and chemicals used during the cleaning process should be properly removed by either using. HEPA filteration on cleaning equipment and occupants vacating the premises during cleaning.

Air Cleaners

The second method of improving air quality is by removal of pollutants by using air cleaners. Air filters, ionizers and electrostatic precipitators can effectively rid indoor air of some microscopic particles such as dust and some combustion products but they do not totally'purify and revitalize the air.

There are many types and sizes of air cleaners on the market, ranging from relatively inexpensive tabletop models to sophisticated and expensive systems.

To understand how efficiently each one performs, the working principle, efficiencies and limitations need to be studied.

Air Purifiers - The oldest and most effective air purifiers are the ones using the HEPA cleaners. HEPA (high energy particulate accumulator) removes tiny particles like dust, molds, pollen and animal allergens from the space. HEPA filters have an efficiency of 99.7%, or simply put, when a blower, fan or other device is used to force air through a HEPA filter at least 99.97% of the particulate matter is removed from the air. However they are ineffective in trapping gaseous pollutants.

Morever these have been replaced by new and expensive electrostatic models.

Electrostatic Purifiers - These units utilize the electrostatic principle. The dust particles are fed through an electrostatic precipitator, where they are electrically charged and then trapped on a metal plate. Electrostatically charged surfaces have an increased tendency to collect dust. Even weak charges can increase particle deposition several times over. Large airborne particles are caught in a prefilter screen. Smaller particles continue past a series of high voltage ionizing wires and become electrically charged. They are attracted like magnets to oppositely charged collecting plates, which capture upto 95% of these pollutants.

Air lonizers - Ion generators act by charging the particles in a room so that they are attracted to walls, floors, tabletops, draperies occupants etc. Abrasion can result in these particles being resuspended into the air. In same cases these devices contain a collector to attract the charged particles back to the unit. While ion generators may remove small particles (e.g. those in tobbacco smoke) they do not remove gases or odours and may be relatively ineffective in removing large particles such as pollen and house
dust allergens.

Ozone, a lung irritant, is produced indirectly by ion generators and other electronic air cleaners and ozone generators. Sometimes the level of ozone generated can be significantly above levels which are harmful to human health. Although ozone can be useful in reducing odors and pollutants in unoccupied spaces, the levels needed to achieve this are above those generally thought to be safe for humans.

Are air cleaners effective in improving IAQ?

Ion generators and ozone generators and others like mechanical filter air cleaners, electronic precipitators and hybrid air cleaners utilizing two or more techniques are not appropriate single solutions to indoor air quality problems. However they can be useful as an adjunct to effective source control and adequate ventilation. Air cleaning alone cannot adequately remove all pollutants typically found in indoor air.

The value of any air cleaner depends upon a number of factors including it's basic efficiency, proper selection for the type of pollutant to be removed, proper installation in relation to the space and faithful maintenance. Drawback with various types may include inadequate pollutant removal, redispersernent of pollutants, deceptive masking rather than removal, generation of ozone and unacceptable noise levels.

Ventilation Improvement

The easiest way of increasing ventilation is by opening windows and doors. However in conditioned spaces, mechanical ventilation rate can be increased by installing a heat recovery ventilator (also known as air-to-air heat exchanger). These devices which can be installed in windows or as part of a central air system, increase ventilation by drawing outside air into the building and conserving energy by recovering the heat from air that is exhausted to the outdoors.

Heat Recovery Ventilator

The heat recovery ventilator draws stale, conditioned air from the space and transfers the energy in that air to the ambient fresh air being pulled into the house. This additional outdoor air can help dilute air pollutant concentrations indoors. If appropriately designed and installed these devices can reduce the energy costs associated with the increased ventilation.

The three methods of improving indoor air quality are source control, ventilation control and removal and though air cleaning is effective to some degree in particulate contaminants but gaseous contaminants will only be effectively removed by ventilation and dilution.