summary-information on air cleaners

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Information on the Capabilities of Air Cleaners

to Reduce Indoor Air Pollution

caused by Haze from Forest Fires*

by Angelika Heil

Version #1 dated 4/9/98


Air cleaning may achieve an additional reduction in the levels of certain pollutants when source control and ventilation do not result in acceptable indoor pollutant concentrations , as in case of high particle concentration in the ambient air during haze episodes or in urban areas. However, air cleaning alone cannot be expected to adequately remove all of the pollutants present in the typical indoor air environment. In particular, the effective removal capabilities for gaseous compounds has not yet been scientifically proven.

Air cleaners are usually classified by the method employed for removing particles of various sizes from the air. There are three general types of air cleaners on the market: mechanical filters, electronic air cleaners, and ion generators. Common mechanical filters on the market represent High Efficiency Particle Air Filter (HEPA). Hybrid units, using two or more of these removal methods, are also available. Air cleaners may be in-duct units (installed in the central heating and/or air-conditioning system) or stand-alone portable units. Additionally, single air-conditioner can be upgraded with special filters.

The effectiveness of air cleaners in removing pollutants from the air is a function of both the efficiency of the device itself (e.g., the percentage of the pollutant removed as it goes through the device) and the amount of air handled by the device. A product of these two factors (for a given pollutant) is expressed as the unit’s clean air delivery rate (CADR).

Portable air cleaners vary in size and effectiveness in pollutant reduction capabilities. They range from relatively ineffective table-top units to larger, more powerful console units. In general, units containing either electrostatic precipitators, negative ion generators, or pleated filters, and hybrid units containing combinations of these mechanisms, are more effective than flat filter units in removing tobacco smoke particles. Effectiveness within these classes varies widely, however. For removal of larger dust particles, negative ion generators, without additional particle capture mechanisms (e.g., filters), may perform poorly.

Some air cleaners, under the right conditions, can effectively remove small particles which are suspended in air. However, controversy exists as to the efficacy of air cleaners in removing larger particles such as pollen and house dust allergens, which rapidly settle from indoor air. In assessing the potential efficacy of an air cleaner in removing allergens, one should consider the relative contribution of airborne to surface concentrations of the allergens, particularly in the case of pollen and house dust allergens where natural settling may be so rapid that air cleaners contribute little additional effect. Animal dander may settle more slowly although, again, the surface reservoir far exceeds the amount in the air. Furthermore, control of the sources of allergens and, where allergens do not originate outdoors, ventilation should be stressed as the primary means of reducing allergic reactions.

Some of the air cleaners containing sorbents may also remove some of the gaseous pollutants in indoor air. However, no air-cleaning systems are expected to totally eliminate all hazards from gaseous pollutants and these systems may have a limited lifetime before replacement is necessary. In addition, air cleaning may not be effective in reducing the risks of lung cancer due to radon.

In choosing an air cleaner, several factors should be considered. These include:

  • The potential effectiveness of the device under the conditions it will be used.
  • The need for routine maintenance, including cleaning and replacement of filters.
  • The estimated capital and maintenance cost.
  • The installation requirements (e.g., power, access).
  • The manufacturer’s recommended operating procedures.
  • The possible production or redispersal of pollutants, such as ozone, particles, formaldehyde, and trapped gaseous pollutants.
  • The inability of air cleaners designed for particle removal to control gases and some odors, such as those from tobacco smoke.
  • Possible health effects from charged particles produced by ion generators.
  • Possible soiling of surfaces by charged particles produced by ion generators.
  • The noise level at the air flow rates that will be used.

Finally, the DOP method in Military Standard 282 which addresses only high efficiency air filters and two standards provided by independent standard-setting trade organizations, the ANSI/AHAM AC-1-1988 approved Clean Air Delivery Rate (CADR) and the atmospheric dust spot test of ASHRAE Standard 52-76, may be useful as guidelines in choosing an air cleaner for reduction of particles in indoor air. The CADR is simultaneously useful in estimating the effectiveness of the units in relation of the room size the device is applied. Similar standards are not currently available to compare the performance of air cleaners in removing gaseous pollutants or radon and its progeny.


Concluding from the literature studied for this paper, High Efficient Particulate Air (HEPA)-Filter air cleaning devices scientifically proven the highest efficiency in removing particles. Ion generators seen and the based ASHREA testing method of -HEPA-devices will significantly reduce indoor air pollution and the ensuing haze risk if operated properly. However, those devices are cost-intensive not only in purchase but also in maintenance (power, filter change).

As haze from forest fires represents only a temporary phenomenon with occurrence cycles of 2-4 years, and duration of less than 3 month, the expenses might exceed the benefits. For a temporary reduction of indoor haze pollution as an emergency response, upgrading your air-conditioner with special filters, however, represent the most simple and cost effective alternative.

It should be noted that air cleaning devices (portable air cleaners or upgrading air-conditioning ) are only effective if applied in sound relation of the device’ removal rate and the room used. Reducing indoor haze pollution in all rooms of your house/apartment will need high investments. The most practicable will be to reduce indoor pollution in one or two rooms only, most suitable parents and children’s sleeping rooms and two spend also most of the daytime in this rooms during high outdoor pollution levels.

If you are living in an area with high background particle concentrations, as present in most metropolitan areas of Indonesia, the purchase of portable air cleaners is recommended to permanently improved indoor quality and will simultaneously get protection of temporary haze.

For families with children or members with respiratory or cardio-vascular diseases – thus more susceptible persons to suffer haze related health impacts and particle exposure – the benefit of should considered with higher priority.

When purchasing an air cleaner, please be aware of the fact that there exists no international standard for testing their efficiency. Efficiency given should refer to the scientifically based and approved the DOP method in Military Standard 282, the ANSI/AHAM Standard AC-1-1988 based Clean Air Delivery Rate (CADR) or the atmospheric dust spot test ASHREA Standard 52-7.

References and more detailed information,

  1. as 1/9/98
  2. EPA document Residential Air-Cleaning Devices: A Summary of Available Information.

  3. as 1/9/98
  4. Homepage” Helping users to find the appropriate air cleaner”, “CADR-fact sheet” ,etc.

  5. as 1/9/98
  6. EPA Fact Sheet on Residential Air Cleaner

  7. as 4/4/98
  8. Environmental Ministry Singapore : Smoke Haze – Air Cleaning Devices for Home&Offices

  9. The Straits Times, 4th March 1998

  11. Allergy Management Systems: The MAReport , Volume 5/4, February 1990


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