Air Purifier

Source: Pierre Lajoie, Centre for Public Health of Quebec City

Air purifiers

The problem

The frequency of allergic and respiratory problems is high in the population. The prevalence of allergies is about 17% and that of asthma is approximately 7%. For children, the influence of environmental factors, including the quality of the air in homes is well known regarding the origin of these problems. It is not surprising to observe a trend of the public providing air purifiers for their home, whether it is installed on the central heating or portable devices. The health professionals, especially doctors, are often asked about the usefulness of these devices to prevent health problems.

Operation purifiers

The general principle of operation for domestic air purifiers is relatively simple. It is portable or stationary devices equipped with an air intake and filter system to capture contaminants, mainly particles, during the passage of air into the device. The filters can be installed individually or in sequence. Handheld devices can be on the table or floor while fixtures are installed on the ventilation system of central heating.

There are three types of air purifiers: mechanical, electronic and ionization. The operation of mechanical purifiers is based on the impaction of particles on many fibers constituting the filters, and some substances are also retained by the filters. The purifier HEPA (High Efficiency Particulates Air Filter) is a mechanical device with a typical example high density filter. This type of filter, integrated into a portable device was developed for military purposes during World War II by the Atomic Energy Commission of the United States to retain the radioactive dust.

In terms of electronic devices, their operation is based on the use of an electric field. In the case of the electrostatic precipitator, the particles contained in the air is positively ionized as they pass in the purifier. They subsequently bind to the filter, which is negatively charged by the passage of an electric current. There are also charged filter purifiers, which are composed of negatively charged plate, to capture particles in the air.

As the ionization devices, they do not contain a loaded filter plate. These devices negatively ionized particles from the air, which will bind to the surfaces of the house that are positively charged walls, furniture, fabrics. It is important to note that many modern devices are hybrids. These devices have, in fact, several types of mechanical or electrical equipment in sequence in order to increase their effectiveness. In many cases, even the devices also include activated carbon filters or other substances that capture the gas.

Efficiency of appliances

Indoor air can be contaminated by particles, gases or vapors. From the point of view of health, it is important that the purifier reduces concentrations of respirable particles and also non-respirable. Respirable particles have a diameter less than 10 microns (or thousandths of a millimeter). Combustion particles, tobacco smoke, for example, are of very small diameter, often less than 1 micron. The non-respirable particles of allergens such as pollen are formed, their diameter can be 50 or 100 microns. Mite feces (dust mites), as well as animal allergens, have a diameter greater than 10 microns. Note that the large particles do not stay long in the air. They tend to settle quickly on the ground and on surfaces.

There are few studies that have been done to evaluate the effectiveness of air purifiers from an air quality point of view. In the United States, a working group of experts in allergy and respiratory disease focused on the subject in the late 80s. They discussed the main devices used and the concentrations of the contaminants found in the air of homes. Following their analysis, the working group came to the following conclusions:

• Air purifiers, whether mechanical or electronic, can not capture the gases and vapors present in the air within that integrates with an activated carbon filter or a similar substance;
• The simplest mechanical purifiers have an efficiency of about 75% to remove large particles, such as pollen, they are very effective for small particles. However, the HEPA filter has a very high 99.97% to remove very small particles of 0.3 microns efficiency;
• Electronic cleaners, such as electrostatic precipitators, seem a little less effective than HEPA. However, an efficiency of nearly 100% for pollen and 80% for particles of tobacco has been reported.

Note that the ESPs require a much more common appliances HEPA filter maintenance. Poor maintenance is accompanied, in fact, a rapid and very significant drop in efficiency to remove house dust and particles from tobacco smoke.

A study on the evaluation of the effectiveness of air purifiers was recently conducted in Quebec. In general, the results of the evaluation of the performance of these devices confirm the results of the U.S. group. Appliances HEPA filters and electrostatic precipitators are roughly comparable in a timely evaluation.

Effective health

The intention of consumers in the purchase of an air purifier is oftenly the prevention or reduction of certain health problems for themselves or their families. The problems most frequently encountered are allergy and asthma. Problems rhinitis are often associated with these two conditions. Note that there are few recent studies where we assessed the effectiveness of the use of air purifiers to reduce allergies and asthma. Regarding allergy problems, the U.S. Task Force mentioned earlier separated the various studies into two main categories: seasonal allergies related to pollen and outdoor seasonal allergies not related to allergens house (dust, animals, etc. .).

The working group highlighted the following points:

• With regard to allergies due to pollen, an air purifier addition to a central air conditioning system produces a significant improvement, albeit small, symptoms;
• In terms of most handheld devices, studies have shown no significant improvement in symptoms due to pollen or house dust. Some reduction in symptoms and medication was observed when using a HEPA laminar flow in children allergic to house dust.

More recent studies have yielded conflicting results regarding the reduction in respiratory symptoms.

Some types of air purifiers such as electrostatic precipitators can produce ozone during operation. The ozone production tends to increase when the filters are poorly maintained. The concentrations found in the house would be low and well below the current standards. The standard for one hour currently in place in Canada for ambient air is 82 parts per billion (ppb). The odor threshold varies from 5 to 15 ppb. There is currently no independent study on ozone emissions from air cleaners in a domestic environment.

Solutions and advice

Before buying an air purifier, it is important for the consumer to follow these recommendations:

• Reduce the possible sources of dust, gas or vapor at home: tobacco smoke, carpet, excessive moisture. Indeed, domestic air purifiers are not a panacea. These are additional supportive measures that can help to improve the air quality after correcting the possible pollution at the source;
• Make a wise choice when buying an appliance. Learn about the type and characteristics of the device, as well as its effectiveness in removing particles and gases;
• Perform a rigorous maintenance of air purifiers following the manufacturer's instructions. Indeed, poor maintenance of these devices, such as electrostatic precipitators, is accompanied by a large and rapid drop in efficiency;
• Check with the retailer about the possibility of issuing ozone and consult the manufacturer about it. Declare the retailer anyway abnormal odor emitted by a device already installed.

For more information,

Do, S. From Cotret and PR (1991), "The air purifiers," Protect yourself, p. 6-17.

Nelson H.S., S.R. Hirsch J.L. Orman, T. Platts-Mills, CE and WR Reed Solomon (1988), "Recommendations For the Use of Residential Air Cleaning Devices in the Treatment of Allergic Respiratory Diseases," J. Allergy Clin. Immunol, 82. 661-9.

U.S. EPA (1990), Residential Air-Cleaning Devices. A Summary of Available Information, EPA 400/1 - 90-002, 22 pages, Washington.

The effectiveness of some types of equipment is likely to fall rapidly and dramatically if the filters are not maintained properly.