R E S I D E N T I A L A I R C L E A N E R S

Indoor Air Quality (IAQ)

R E S I D E N T I A L A I R C L E A N E R S

EPA 402-F-09-002 | Revised August 2009 | www.epa.gov/iaq

(Second Edition)

A SUMMARY OF 

AVAILABLE INFORMATION
U.S. Environmental Protection Agency

Office of Air and Radiation

Indoor Environments Division

1200 Pennsylvania Avenue, NW

Mail code: 6609J

Washington, DC 20460

www.epa.gov/iaq 

Disclaimer

This document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approved 

for publication. Mention of trade names, products, or services does not convey, and should not be interpreted as 

conveying official EPA approval, endorsement or recommendation.
TABLE OF CONTENTS

Summary .............................................................................................................................................................. 2

Introduction.......................................................................................................................................................... 4

Indoor Air Pollutants ............................................................................................................................................ 5

Three Strategies To Reduce Indoor Air Pollutants ............................................................................................... 6

Types of Air Cleaners ........................................................................................................................................... 7

Removal of Particles...................................................................................................................................... 8

 Types of Particle-Removal Air Filters...................................................................................................... 8

 Defining Efficiency and Effectiveness ..................................................................................................... 9

 Air Filters - Available Guidance for Their Comparison........................................................................ 10

 Air Filters - Available Evidence of Their Usefulness............................................................................. 12

 Portable Air Cleaners - Available Guidance for Their Comparison ..................................................... 13

 Portable Air Cleaners - Available Evidence of Their Usefulness.......................................................... 14

Removal of Gaseous Pollutants by Sorbents ............................................................................................... 15

 Types of Sorbents Used for Gaseous Pollutant Removal...................................................................... 16

 Applications of Sorbents for Gaseous Pollutant Removal..................................................................... 17

Removal of Radon and Its Progeny.............................................................................................................. 17

Deactivation or Destruction of Pollutants................................................................................................... 18

 Ultraviolet Germicidal Irradiation Cleaners......................................................................................... 18

 Photocatalytic Oxidation Cleaners....................................................................................................... 20

 Ozone Generators............................................................................................................................... 21

Will Air Cleaning Reduce Health Effects from Indoor Air Pollutants? ................................................................ 23

Additional Factors to Consider .......................................................................................................................... 25

Installation ................................................................................................................................................... 25

Operations and Maintenance ...................................................................................................................... 25

Cost............................................................................................................................................................. 25

Inability to Remove Some Odors................................................................................................................ 26

Possible Effects of Particle Charging............................................................................................................ 26

Soiling of Walls and Other Surfaces............................................................................................................. 26

Noise........................................................................................................................................................... 26

Conclusion.......................................................................................................................................................... 27

Glossary ............................................................................................................................................................. 28

References.......................................................................................................................................................... 30
R E S I D E N T I A L A I R C L E A N E R S

2 www.epa.gov/iaq

SUMMARY

Indoor air pollution is among the top five 

environmental health risks. Usually the best way 

to address this risk is to control or eliminate 

the sources of pollutants and ventilate a home 

with clean outdoor air. But opportunities for 

ventilation may be limited by weather conditions 

or by contaminants in the outdoor air. 

If the usual methods of addressing indoor air 

pollution are insufficient, air-cleaning devices may 

be useful. Air filters and other air-cleaning devices 

are designed to remove pollutants from indoor air. 

Some are installed in the ductwork of a home’s 

central heating, ventilating, and air-conditioning 

(HVAC) system to clean the air in the entire 

house. Portable room air cleaners can be used to 

clean the air in a single room or in specific areas, 

but they are not intended to filter the air in the 

whole house. Air-cleaning devices are categorized 

by the type of pollutants—particulate and 

gaseous—that the device is designed to remove 

or destroy. 

Two types of air-cleaning devices can remove 

particles from the air: mechanical air filters and 

electronic air cleaners. 

Mechanical air filters, such as high efficiency 

particulate air (HEPA) filters, remove particles 

by capturing them on filter materials. Most 

mechanical air filters are good at capturing larger 

airborne particles—such as dust, pollen, some 

mold spores, and animal dander—and particles 

that contain dust mite and cockroach allergens. 

But because these particles settle rather quickly, 

mechanical air filters are not very good at 

completely removing them from indoor areas.

Electronic air cleaners, such as electrostatic 

precipitators, use a process called electrostatic 

attraction to trap particles. Ion generators, or 

ionizers, disperse charged ions into the air. These 

ions attach to airborne particles, giving them a 

charge so they can attach to nearby surfaces such 

as walls or furniture, or to one another, and settle 

faster. However, some electronic air cleaners can 

produce ozone, a lung irritant. 

Another type of air-cleaning device is a gas-phase 

filter designed to remove gases and odors by either 

physical or chemical processes.

Gas-phase air filters remove gaseous pollutants 

by using a material called a sorbent, such as 

activated carbon, to adsorb pollutants. Because 

these filters are targeted at one or a limited 

number of gaseous pollutants, they will not 

reduce concentrations of pollutants for which they 

were not designed. None are expected to remove 

all of the gaseous pollutants in the air of a typical 

home. Gas-phase filters are much less common in 

homes than are particle air filters. One reason may 

be the filter can become overloaded quickly and 

may need to be replaced often.

Three types of air cleaners on the market are 

designed to deactivate or destroy indoor air 

pollutants: ultraviolet germicidal irradiation 

(UVGI) cleaners, photocatalytic oxidation (PCO) 

cleaners, and ozone generators sold as air cleaners. 

UVGI cleaners use ultraviolet radiation from UV 

lamps that may destroy biological pollutants such 

as viruses, bacteria, and molds that are airborne 

or growing on HVAC surfaces (e.g., cooling 

coils, drain pans, or ductwork). UVGI cleaners 

should be used with, but not as a replacement for, 

filtration systems. Typical UVGI cleaners used 

in homes have limited effectiveness in killing 

bacteria and molds. Effective destruction of some 

viruses and most mold and bacterial spores usually 

requires much higher UV exposures than a typical 

home unit provides.

PCO cleaners use UV lamps along with a 

substance, called a catalyst, that reacts with the 

light. These cleaners are designed to destroy 

gaseous pollutants by changing them into 

harmless products, but they are not designed 

to remove particulates. The usefulness of PCO 

cleaners in homes is limited because currently 

available catalysts are ineffective in destroying 

gaseous pollutants in indoor air.
A Summar y of Available Information

www.epa.gov/iaq 3

Ozone generators use UV lamps or electrical 

discharges to produce ozone that reacts with 

chemical and biological pollutants and transforms 

them into harmless substances. Ozone is a potent 

lung irritant, which in concentrations that do not 

exceed public health standards, has little potential 

to remove indoor air contaminants. Thus ozone 

generators are not always safe and effective in 

controlling indoor air pollutants. 

Portable air cleaners generally contain a fan 

to circulate the air and use one or more of the 

air-cleaning technologies discussed above. They 

may be an option if a home is not equipped with 

a furnace or a central air-conditioning system. 

Many portable air cleaners have moderate to large 

air delivery rates for small particles. However, 

most of the portable air cleaners on the market do 

not have high enough air delivery rates to remove 

large particles such as pollen and particles that 

contain dust mite and cockroach allergens from 

typical-size rooms.

Several other factors should be considered when 

making decisions about using air-cleaning devices.

X Installation: In-duct air-cleaning devices have 

certain installation requirements that must be 

met, including sufficient access for inspection 

during use, repairs, and maintenance.

X Major costs: These costs include the initial 

purchase price and the cost of maintenance 

(such as cleaning or replacing filters and parts) 

and operation (electricity).

X Odors: Air-cleaning devices designed to 

remove particles cannot control gases and 

some odors. The odor and many of the 

carcinogenic gas-phase pollutants from 

tobacco smoke, for example, will remain.

X Soiling of walls and other surfaces: Typical 

ion generators are not designed to remove 

from the air the charged particles that they 

generate. These charged particles may settle 

on, and soil, walls and other room surfaces.

X Noise: Noise may be a problem with portable 

air cleaners that contain fans. Portable air 

cleaners that do not have fans tend to be 

much less effective than units that have them.

The ability to remove some airborne pollutants, 

including microorganisms, is not, in itself, an 

indication of an air-cleaning device’s ability 

to reduce adverse health effects from indoor 

pollutants. Although air-cleaning devices may 

help reduce levels of smaller airborne particles 

including those associated with allergens, they 

may not reduce adverse health effects, especially in 

sensitive populations such as children, people who 

have asthma and allergies, and the elderly. For 

example, the evidence is weak that air-cleaning 

devices are effective in reducing asthma symptoms 

associated with small airborne particles such as 

those that contain cat and dust mite allergens. 

There are no studies linking the use of gas-phase 

filtration, UVGI systems, or PCO systems in 

homes to reduced health symptoms in 

sensitive populations.
R E S I D E N T I A L A I R C L E A N E R S

4 www.epa.gov/iaq

The best way to address residential indoor air 

pollution usually is to control or eliminate the 

source of the pollutants and to ventilate the home 

with clean outdoor air. But ventilation may be 

limited by weather conditions or the levels of 

contaminants in the outdoor air.

If the usual methods of dealing with indoor air 

pollutants are insufficient, air-cleaning devices may 

be useful. Air filters and other air-cleaning devices 

are designed to remove pollutants from indoor 

air. They can be installed in the ductwork of most 

home heating, ventilating, and air-conditioning 

(HVAC) systems to clean the air in the entire 

house, or the same technology can be used in 

portable air cleaners that clean the air in single 

rooms or specific areas. Most air-cleaning devices 

are designed to remove particles or gases, but some 

destroy contaminants that pass through them. 

This publication focuses on air cleaners for 

residential use; it does not address air cleaners used 

in large or commercial structures such as office 

INTRODUCTION

buildings, schools, large apartment buildings, 

or public buildings. It should be particularly 

useful to residential housing design professionals, 

public health officials, and indoor air quality 

professionals. In addition to providing general 

information about the types of pollutants affected 

by air cleaners, this document discusses:

X The effectiveness of air cleaning compared to 

other strategies, such as source control and 

ventilation, for reducing indoor air pollutants.

X The types of air-cleaning devices available.

X Guidelines that can be used to compare aircleaning devices.

X The effectiveness of air-cleaning devices in 

removing indoor air pollutants.

X General information on the health effects of 

indoor air pollutants.

X Additional factors to consider when deciding 

whether to use an air-cleaning device.

Please Note: The U.S. Environmental Protection Agency (EPA) neither certifies nor recommends 

particular brands of home air-cleaning devices. While some home air-cleaning devices may be useful in 

some circumstances, EPA makes no broad endorsement of their use, nor specific endorsement of any 

brand or model. This document describes the performance characteristics of several types of air cleaners 

sold for in-home use.

Federal pesticide law requires manufacturers of ozone generators to list an EPA establishment number 

on the product’s packaging. This number merely identifies the facility that manufactured the product. 

Its presence does not imply that EPA endorses the product, nor does it imply that EPA has found the 

product to be safe or effective.

Some portable air cleaners sold in the consumer market are ENERGY STAR® qualified. Please note the 

following disclaimer on their packaging: “This product earned the ENERGY STAR by meeting strict 

energy efficiency guidelines set by EPA. EPA does not endorse any manufacturer claims of healthier 

indoor air from the use of this product.”
A Summar y of Available Information

www.epa.gov/iaq 5

INDOOR AIR POLLUTANTS 

There are two categories of indoor air pollutants 

that can affect the quality of air in a home: 

particulate matter and gaseous pollutants. 

Particulate matter (PM) is composed of 

microscopic solids, liquid droplets, or a mixture 

of solids and liquid droplets suspended in air. Also 

known as particle pollution, PM is made up of a 

number of components, including acids such as 

nitric and sulfuric acids, organic chemicals, metals, 

soil or dust particles, and biological contaminants. 

Among the particles that can be found in a 

home are:

X Dust as solid PM or fumes and smoke, which 

are mixtures of solid and liquid particles.

X Biological contaminants, including viruses, 

bacteria, pollen, molds, dust mite and 

cockroach body parts and droppings, and 

animal dander.

Particles come in a wide range of sizes. Small 

particles can be fine or coarse. Of primary concern 

from a health standpoint are fine particles that have 

a diameter of 2.5 micrometers (μm) or less. These 

particles (described as “respirable”) can be inhaled; 

they penetrate deep into the lungs where they 

may cause acute or chronic health effects. Coarse 

particles, between 2.5 and 10 μm in diameter, 

usually do not penetrate as far into the lungs; they 

tend to settle in the upper respiratory tract. Large 

particles are greater than 10 μm in diameter, or 

roughly one-sixth the width of a human hair. They 

can be trapped in the nose and throat and expelled 

by coughing, sneezing, or swallowing. 

Respirable particles are directly emitted into indoor 

air from a variety of sources including tobacco 

smoke, ozone reactions with emissions from indoor 

sources of organic compounds, chimneys and 

flues that are improperly installed or maintained, 

unvented combustion appliances such as gas stoves 

and kerosene or gas space heaters, woodstoves, and 

fireplaces. This category of particles also includes 

viruses and some bacteria.

Among the smaller biological particles found 

in a home are some bacteria, mold fragments 

and spores, a significant fraction of cat and dog 

dander, and a small portion of dust mite body 

parts and droppings. Larger particles include dust, 

pollen, some mold fragments and spores, a smaller 

fraction of cat and dog dander, a significant 

fraction of dust mite body parts and cockroach 

body parts and droppings, and skin flakes.

Gaseous pollutants include combustion gases 

and organic chemicals that are not attached to 

particles. Hundreds of gaseous pollutants have 

been detected in indoor air.

Sources of indoor combustion gases such as 

carbon monoxide and nitrogen dioxide include 

combustion appliances, tobacco smoke, and 

vehicles whose exhaust infiltrates from attached 

garages or the outdoors.

Sources of airborne gaseous organic compounds 

include tobacco smoke, building materials 

and furnishings, and products such as paints, 

adhesives, dyes, solvents, caulks, cleaners, 

deodorizers, cleaning chemicals, waxes, hobby 

and craft materials, and pesticides. Organic 

compounds may also come from cooking food; 

from human, plant, and animal metabolic 

processes; and from outdoor sources. Some 

electronic air cleaners and laser printers may 

generate the lung irritant ozone by design or as a 

by-product.

Radon is a colorless, odorless, radioactive gas 

that can be found in indoor air. It comes from 

uranium in natural sources such as rock, soil, 

ground water, natural gas, and mineral building 

materials. As uranium breaks down, it releases 

radon, which in turn produces short-lived 

radioactive particles called “progeny,” some of 

which attach to dust particles. Radon progeny 

may deposit in the lungs and irradiate respiratory 

tissues. Radon typically moves through the 

ground and into a home through cracks and holes 

in the foundation. Radon may also be present 

in well water and can be released into the air 

when that water is used for showering and other 

household activities. In a small number of homes, 

building materials also can give off radon.1
R E S I D E N T I A L A I R C L E A N E R S

6 www.epa.gov/iaq

THREE STRATEGIES TO REDUCE INDOOR AIR POLLUTANTS

Three basic strategies to reduce pollutant 

concentrations in indoor air are source control, 

ventilation, and air cleaning. 

Source control eliminates individual sources of 

pollutants or reduces their emission. It is usually 

the most effective strategy for reducing pollutants. 

There are many sources of pollutants in the home 

that can be controlled or removed.2

 For example, 

solid wood or alternative materials can be used in 

place of pressed wood products that are likely to 

be significant sources of formaldehyde. Smokers 

can smoke outdoors. Combustion appliances can 

be adjusted to decrease their emissions.

Ventilation is also a strategy for decreasing indoor 

air pollutant concentrations. It exchanges air 

between the inside and outside of a building. The 

introduction of outdoor air is important for good 

air quality. In a process known as infiltration, 

outdoor air flows into the house through 

openings, joints, and cracks in walls, floors, and 

ceilings, and around windows and doors. Natural 

ventilation describes air movement through open 

windows and doors. Most residential forced airheating systems and air-conditioning systems do 

not bring outdoor air into the 

house mechanically. Two primary 

ventilation methods can be used 

in most homes: general ventilation 

and local ventilation.

	General ventilation of the 

living space, by way of 

infiltration, natural ventilation, 

or mechanical ventilation, 

brings outdoor air indoors, 

circulates air throughout the 

home, and exhausts polluted 

air outdoors. Although limited by weather 

conditions, this method removes or dilutes 

indoor airborne pollutants, thereby reducing 

the level of contaminants and improving indoor 

air quality (IAQ). Special consideration should 

be given to the outdoor air used for ventilation. 

It should be of acceptable quality and should 

not contain pollutants in quantities that would 

be considered objectionable or harmful if 

introduced indoors. The use of ventilation 

to reduce indoor air pollutants should be 

evaluated carefully where there may be outdoor 

sources of pollutants.

	Localized ventilation by means of exhaust fans 

in bathrooms and kitchens, and in some cases 

by open windows and doors, removes excess 

moisture and strong, local pollutants and keeps 

them from spreading to other areas. Using 

exhaust fans increases the amount of outdoor 

air that enters a house.

Advanced designs for new homes are starting to 

add a mechanical feature that brings outdoor 

air into the home through the HVAC system. 

Some of these designs include energy efficient 

heat recovery ventilators to mitigate the cost of 

cooling and heating this air during the summer 

and winter. 3, 4

Air cleaning may be useful when 

used along with source control 

and ventilation, but it is not a 

substitute for either method. The 

use of air cleaners alone cannot 

ensure adequate air quality, 

particularly where significant 

sources are present and ventilation 

is insufficient. While air cleaning 

may help control the levels of 

airborne particles including those 

associated with allergens and, 

in some cases, gaseous pollutants in a home, air 

cleaning may not decrease adverse health effects 

from indoor air pollutants.

 

The use of air 

cleaners alone 

cannot ensure 

adequate air 

quality.
A Summar y of Available Information

www.epa.gov/iaq 7

TYPES OF AIR CLEANERS

Various technologies can be used in air-cleaning 

devices. Filtration and electrostatic attraction 

are effective in removing airborne particles. 

Adsorption or chemisorption captures some 

gaseous and vaporous contaminants. Some air 

cleaners use ultraviolet light (UV) technology. 

Ultraviolet germicidal irradiation (UVGI) has 

been used to kill some microorganisms growing 

on surfaces. Photocatalytic oxidation (PCO), 

another UV light technology under development, 

has the potential to destroy gaseous contaminants. 

Ozone-generating devices sold as air cleaners use 

UV light or corona discharge and are meant to 

control indoor air pollutants.

Table 1 provides a brief summary of air-cleaning 

technologies and the pollutants they are designed 

to control. 

Some air-cleaning devices are designed to be 

installed in the ductwork of HVAC systems or to 

be used in portable, stand-alone units. 

In-duct or whole-house air-cleaning devices

typically are installed in the return ducts of HVAC 

systems, as shown in Figure 1. The typical furnace 

air filter is a simple air cleaner that captures 

particles in the airstream to protect fan motors, 

heat exchangers, and ducts from soiling. Such 

AIR-CLEANING 

TECHNOLOGIES

POLLUTANTS 

ADDRESSED LIMITATIONS

Filtration

Air filters Particles Ineffective in removing larger particles because most 

settle quickly from the air and never reach the filters.

Gas-phase 

filters Gases Used much less frequently in homes than particle air filters. The lifetime for removing pollutants may be short.

Other

Air Cleaners

UVGI Biologicals

Bacterial and mold spores tend to be resistant to UV 

radiation and require more light, longer exposures to UV 

light, or both to be killed.

PCO Gases

Application for homes is limited because currently 

available catalysts are ineffective in destroying gaseous 

pollutants in indoor air.

Ozone 

generators

Particles, gases, 

biologicals

Sold as air cleaners, they are not always safe and effective 

in removing pollutants. By design they produce ozone, a 

lung irritant.

TABLE 1: SUMMARY OF AIR-CLEANING TECHNOLOGIES

filters are not designed to improve indoor air 

quality, but the HVAC system can be upgraded by 

using more efficient air filters to trap additional 

particles. Other air-cleaning devices such as 

electrostatic precipitators, UV lamps, and gasphase filters use sorption and chemical reaction 

and are sometimes used in the ductwork of home 

HVAC systems. 

The fans in residential HVAC systems may 

operate intermittently or continuously. 

Continuous operation improves air circulation 

and air cleaning, but this operation mode also 

increases electrical energy consumption and costs.5

Portable air cleaners are available as small 

tabletop units and larger console units. They are 

used to clean the air in a single room, but not 

in an entire house. The units can be moved to 

wherever continuous and localized air cleaning 

is needed. Larger console units may be useful in 

houses that are not equipped with forced airheating systems and air-conditioning systems. 

Portable air cleaners generally have a fan to 

circulate the air and a cleaning device such as a 

mechanical air filter, electrostatic precipitator, ion 

generator, or UV lamp. Some units marketed as 

having the quietest operation may have no fan; 

however, units that do not have a fan typically are 
R E S I D E N T I A L A I R C L E A N E R S

8 www.epa.gov/iaq

much less effective than units that have one. Air 

cleaners may also have a panel filter with bonded 

fine particles of activated carbon, or an activated 

carbon filter encased in a frame, to remove gases 

and odors. Some portable air cleaners referred to 

as hybrid air cleaners use a combination of two or 

more of the devices discussed above.

In this publication, air cleaners are categorized by 

the types of pollutants, particulate and gaseous, 

that the devices are designed to remove or 

destroy.6, 7

Removal of Particles

Air filters are designed to remove particulate 

pollutants from indoor air. Their performance 

depends not only on the airflow rate through the 

filter media and the filter efficiency, but also on 

factors such as the:

 Particle size and mass.

	Amount of dust on the air filter.

	Airflow rate, velocity, path, and resistance 

through the filter media.

	Mixing of air leaving the filter with the air in 

the room.

	Leakage rate of air that bypasses the air filter.

Types of Particle-Removal Air Filters

Two general types of particle removal air-cleaning 

devices are available: mechanical air filters and 

electronic air cleaners. They are classified by the 

method employed to remove particles of various 

sizes from the air.

Mechanical air filters installed in a central 

HVAC system or in a portable air cleaner 

capture particles on filter media. Particles either 

become trapped in the fibers of the filter or stick 

to the filter because of an electrostatic charge. 

Mechanical air filters come in two major types: 

flat and pleated.

Flat or panel filters generally consist of coarse 

glass fibers, coated animal hair, vegetable fibers, 

synthetic fibers (such as polyester or nylon), 

synthetic foams, metallic wools, or expanded 

metals and foils. The filter media may be treated 

with a viscous substance, such as oil, that causes 

particles to stick to the fibers. Flat filters also 

may be made of three types of permanently 

electrostatically charged material: resin wool, 

a plastic film or fiber called “electret,” or an 

electrostatically sprayed polymer. Their static 

charge attracts and captures particles. The fibers 

of electret filters are somewhat larger than the 

fibers of other flat filters, resulting in relatively low 

pressure drop and greater efficiency in filtering 

smaller particles. The efficiency of electret filters 

decreases as the media become loaded with 

particles.

Pleated or extended surface filters are generally more 

efficient than flat filters in capturing respirable 

particles. Pleating the filter medium increases 

surface area, reduces air velocity, and allows the 

use of smaller fibers and increased packing density 

of the filter without a large drop in airflow rate. 

1 Return Air Duct

2 Air Filter Housing

3 Air Filter

3a Rigid Frame (such as a 

chipboard)

3b Filter Media Restrainer

3c Filter Media (installed inside 

the frame)

4 Air-Handling Unit that contains 

a recirculation fan, heating 

element, and cooling coil. (The 

unit may be in a basement, 

closet, or attic.)

5 Supply Air Duct

FIGURE 1: TYPICAL AIR FILTER INSTALLATION
A Summar y of Available Information

www.epa.gov/iaq 9

A wire frame in the form of a pocket or V-shaped 

cardboard separators may be used to maintain the 

pleat spacing. The media used in pleated filters are 

fiber mats, bonded glass fibers, synthetic fibers, 

cellulose fibers, wool felt, and other cottonpolyester material blends. 

High efficiency particulate air (HEPA) filters are 

a type of extended surface filter. HEPA filters 

usually are made of submicron glass fibers and 

have a texture similar to blotter paper. They also 

have a larger surface area and remove respirable 

particles more efficiently than pleated filters. 

Electronic air cleaners use a process called 

electrostatic attraction to trap charged particles. 

There are two types of electronic air cleaners: 

electrostatic precipitators and ion generators. 

Electrostatic precipitators have an ionization 

section and a collecting plate section, both of 

which use an external power source. The air 

cleaner draws air through the ionization section, 

where particles obtain an electrical charge. The 

charged particles accumulate on a series of flat 

plates called a collector that is oppositely charged. 

Cleaning the collector plates is essential to 

maintaining adequate performance.

Ion generators, or ionizers, disperse charged ions 

into the air, similar to an electrostatic precipitator, 

but ionizers do not have collecting plates. They 

produce ions by means of corona discharge or 

UV light. The ions attach to particles and give 

them a charge so they adhere to nearby surfaces 

such as walls, furniture, and draperies, or combine 

with other particles and settle on room surfaces. 

Ion generators are the simplest form of electronic 

air cleaner and come in tabletop, portable, and 

ceiling mounted units. 

Like mechanical filters, electronic air cleaners 

can be installed in HVAC systems or used in 

portable units. Although electronic air cleaners 

remove small particles, they do not remove gases 

or odors. And because electronic air cleaners 

use high voltage to generate ionized fields, they 

can produce ozone, either as a by-product or by 

design.8

 Residential indoor ozone concentrations 

may be affected by the amount of ozone emitted 

by electronic air cleaners, which varies among 

models. Even at concentrations below public 

health standards, ozone reacts with chemicals 

emitted by such common indoor sources as 

household cleaning products, air fresheners, 

deodorizers, certain paints, polishes, wood 

flooring, carpets, and linoleum. The chemical 

reactions produce harmful by-products that may 

be associated with adverse health effects in some 

sensitive populations. The ozone reaction byproducts that may result include ultrafine particles 

(smaller than 0.1 μm in diameter), formaldehyde, 

ketones, and organic acids.8, 9, 10 Concerns about 

ozone and ozone-generating devices are discussed 

in the EPA document Ozone Generators that are 

Sold as Air Cleaners, posted on the EPA Web site 

at www.epa.gov/iaq/pubs/ozonegen.html.

Defining Efficiency and Effectiveness 

To choose air-cleaning devices and use them 

properly, it is important to understand the 

difference between efficiency and effectiveness. 

The efficiency of an air-cleaning device, usually 

expressed as a percentage, is a measure of its 

ability to remove airborne particles or gaseous 

pollutants from the air that passes through it. The 

effectiveness of an air-cleaning device is a measure 

of its ability to reduce airborne particle or gaseous 

pollutant concentrations in an occupied space. 

The efficiency of air filters used in ducts of 

HVAC systems or in portable air cleaners varies 

based on the airflow rate and the particulate 

matter load. The effectiveness of an air-cleaning 

device in removing pollutants from an occupied 

space depends on three factors: its efficiency, 

the amount of air being filtered, and the path 

that the clean air follows after it leaves the filter. 

For example, a filter may remove 99 percent of 

the particles from the air that passes through 

it (i.e., have 99 percent efficiency). However, 

if the airflow rate through the filter is only 10 

cubic feet per minute (cfm) in a typical room of 

approximately 1,000 cubic feet (e.g., 10’ x 12’ 

x 8’), the filter will be relatively ineffective at 

removing particles from the air (i.e., 10 times less 

effective than if the airflow rate were 100 cfm). 
R E S I D E N T I A L A I R C L E A N E R S

10 www.epa.gov/iaq

Higher efficiency filters remove larger and smaller 

airborne particles more efficiently. Homeowners 

should take care to properly install them in 

HVAC systems and make sure that leakage of air 

bypassing the filter is minimized. The higher a 

filter’s efficiency, the more attention must be paid 

to its sealed installation because increased airflow 

resistance is more likely to create leaks. Air filter 

effectiveness may be substantially reduced if air 

leaks through a poorly installed filter frame and 

its holding system.11, 12 Leakage of air bypassing a 

HEPA filter used in a portable, stand-alone unit 

may also reduce the filter’s expected efficiency. 

Effectiveness may be decreased if air exiting an 

exhaust grille of the HVAC system is not well 

mixed with room air before re-entering the 

system. This situation can occur if air return and 

intake vents are too close together. 

Air Filters - Available Guidance for Their 

Comparison

Several standardized methods have been 

developed to measure the efficiency of different 

types of air filters installed in the ductwork of 

HVAC systems. They can be used to compare 

the performance of air filters made by different 

companies. The American Society of Heating, 

Refrigerating and Air-Conditioning Engineers 

(ASHRAE) and the Institute of Environmental 

Sciences and Technology (IEST) have published 

voluntary standards for rating air filters. The 

IEST is now the recognized standard-setting 

organization for the former Military Standard 282 

developed by the U.S Department of Defense for 

rating HEPA filters. The standards do not rate the 

air filters’ effectiveness; rather, they compare the 

performance of various filters. 

Particle removal efficiency can be assessed by 

four standard methods: the weight arrestance 

test, atmospheric dust spot efficiency test, dioctyl 

phthalate (DOP) penetration test, and particle 

size removal efficiency (PSE) test.

The weight arrestance test,

13 defined in 

ASHRAE Standard 52.1-1992, * is generally 

used to evaluate low efficiency filters designed 

to remove the largest and heaviest particles. 

These filters are commonly used in residential 

furnaces and air-conditioning systems to protect 

system components, or as upstream filters to 

protect higher efficiency filters. In this test, a 

synthetic dust is fed into the air cleaner and the 

percentage by weight of the dust the filter traps, 

called “arrestance,” is determined. The weight 

arrestance test may be of limited value in assessing 

the removal of smaller, respirable particles because 

particles in the test dust are generally larger than 

those that can be inhaled deeply into the lungs.

The atmospheric dust spot efficiency test,

13

also defined in ASHRAE Standard 52.1-1992,* 

is generally used to rate medium-efficiency filters 

in removing fine airborne dust particles that can 

soil walls and other interior surfaces. A naturally 

occurring atmospheric dust is fed into the air 

cleaner to test its ability to reduce soiling of a 

clean paper target as an indication of the cleaner’s 

capability to remove fine particles from the air. 

The DOP penetration test,

14 described in the 

IEST-RP CC001.4 test method, is used to rate 

true HEPA filters. A DOP cloud of uniform 

0.3 μm particles is fed into the filter. The 

concentration of penetrating smoke measured 

upstream and downstream of the filter determines 

the filter efficiency, or the percentage of particles 

the filter removes. 

The PSE test,

15 described in ASHRAE Standard 

52.2-2007, provides a composite minimum 

efficiency for removing particles of specific size 

by filters incrementally loaded with synthetic 

dust. The PSE test method does not eliminate the 

need for DOP penetration and arrestance testing. 

Very low-efficiency air filters, such as furnace 

filters, must also be tested in accordance with 

the weight arrestance method. The composite 

minimum efficiency values are averaged and used 

to determine the air cleaner’s minimum efficiency 

reporting value (MERV). The MERV ranges 

from a low of 1 to a high of 20. The PSE test 

*ASHRAE Standard 52.1.1992, Gravimetric and Dust-Spot Procedures for Method of Testing Air-Cleaning Devices Used in General Ventilation for 

Removing Particulate Matter was withdrawn in spring 2009. Information previously found in this standard is now included via Addendum B to 

ANSI/ASHRAE Standard 52.2, Method of Testing General Ventilation Air-Cleaning Devices for Removal Efficiency by Particle Size. The addendum 

mandates calculation of weight arrestance for filters with Minimum Efficiency Reporting Values (MERVs) of 1 to 4 and atmospheric dust spot 

efficiency for filters with MERVs of 5 to 16. 
A Summar y of Available Information

www.epa.gov/iaq 11

ASHRAE Standard 52.2

ASHRAE 

Standard 

52.1

Application Guidelines

MERV

Particle Size Removal 

Efficiency, Percent in Particle 

Size Range, μm Dust-Spot 

Efficiency 

Percent

Particle Size and 

Typical Controlled 

Contaminant

Typical Applications Typical Air Filter/Cleaner 

Type

0.3 to 1 1 to 3 3 to 10

20

19

18

17

≥ 99.999 

≥ 99.999

≥ 99.99 

≥ 99.97

—

—

—

—

< 0.3 μm

Virus (unattached)

Carbon dust

Sea salt

All combustion smoke

Electronics manufacturing

Pharmaceutical 

manufacturing

Carcinogenic materials

HEPA/ULPA Filters*

16

15

14

13

> 95

85-95

75-85

< 75

> 95

> 90

> 90

> 90

> 95

> 90

> 90

> 90

—

> 95

90-95

80-90

0.3-1 μm 

All bacteria

Droplet nuclei (sneeze)

Cooking oil

Most smoke

Insecticide dust

Most face powder

Most paint pigments

Superior commercial 

buildings 

Hospital inpatient care

General surgery

Bag Filters – Nonsupported 

(flexible) microfine fiberglass or 

synthetic media, 12 to 36 inches 

deep. 

Box Filters – Rigid style 

cartridge, 

6 to 12 inches deep. 

12

11

10

9

—

—

—

—

> 80

65-80

50-65

< 50

> 90

> 85

> 85

> 85

70-75

60-65

50-55

40-45

1-3 μm

Legionella

Humidifier dust

Lead dust

Milled flour

Auto emission particles

Nebulizer drops

Superior residential

Better commercial 

buildings

Hospital laboratories

Pleated filters –Extended 

surface with cotton or polyester 

media or both, 1 to 6 inches 

thick. 

Box Filters – Rigid style 

cartridge, 

6 to 12 inches deep. 

8

7

6**

5

—

—

—

—

—

—

—

—

> 70

50-70

35-50

20-35

30-35

25-30

< 20

< 20

3-10 μm

Mold

Spores

Dust mite body parts and 

droppings

Cat and dog dander

Hair spray

Fabric protector

Dusting aids

Pudding mix

Powdered milk

Better residential

Commercial buildings

Industrial workplaces

Pleated filters –Extended 

surface with cotton or polyester 

media or both, 1 to 6 inches 

thick. 

Cartridge filters –Viscous cube 

or pocket filters

Throwaway –Synthetic media 

panel filters

4

3

2

1

—

—

—

—

—

—

—

—

< 20

< 20

< 20

< 20

< 20

< 20

< 20

< 20

> 10 μm

Pollen

Dust mites 

Cockroach body parts and 

droppings

Spanish moss

Sanding dust

Spray paint dust

Textile fibers

Carpet fibers

Minimum filtration

Residential window air 

conditioners

Throwaway – Fiberglass or 

synthetic media panel, 1 inch 

thick.

Washable – Aluminum mesh, 

foam rubber panel

Electrostatic – Self-charging 

(passive) woven polycarbonate 

panel

in 0.3 μm 

particle size

in 0.1 – 0.2 μm 

particle size

TABLE 2: MINIMUM EFFICIENCY REPORTING VALUE (MERV) PARAMETERS

This table is adapted from ANSI/ASHRAE Standard 52.2-2007. 15

*The last four MERV values of 17 to 20 are not part of the official standard test, but have been added by ASHRAE for comparison purposes. Ultra Low 

Penetration Air filters (ULPA) have a minimum efficiency of 99.999 percent in removing 0.3 μm particles, based on the IEST test method. MERVs between 17 

and 19 are rated for 0.3μm particles, whereas a MERV of 20 is rated for 0.1 to 0.2 μm particles.

** For residential applications, the ANSI/ASHRAE Standard 62.2-200716 requires a filter with a designated minimum efficiency of MERV 6 or better.
R E S I D E N T I A L A I R C L E A N E R S

12 www.epa.gov/iaq

may not be appropriate for evaluating electronic 

air cleaners because the dust used contains 

conductive carbon, which may cause electrical 

shorting and thus compromise the effectiveness of 

these devices and alter their MERV. The dustloading procedure may also affect the efficiency of 

electrostatically charged filters. 

A cross-reference of atmospheric dust spot 

efficiency tests to the MERV is shown in Table 2. 

This table shows the minimum PSE in three size 

ranges for each MERV. A consumer can use the 

table to identify the MERV required to control a 

specific pollutant. While these standards cannot 

by themselves predict the actual effectiveness of 

any filter over its lifetime, they can generally be 

used to compare the performance characteristics 

of one air filter with another. 

Air Filters - Available Evidence of Their 

Usefulness

Whether installed in the ducts of HVAC systems 

or used in portable air cleaners, 

most air filters have a good 

efficiency rating for removing 

larger particles when they remain 

airborne. These particles include 

dust, pollen, some molds, animal 

dander, and those that contain 

dust mite and cockroach body 

parts and droppings. But because 

these particles settle rather 

rapidly from the air, air filters are 

somewhat ineffective in removing 

them from indoor areas. And 

although human activities such 

as walking and vacuuming, or the high velocity 

air exiting supply vents, can re-suspend particles, 

most of the larger particles will resettle before they 

enter the HVAC system or portable air cleaner 

and are removed by a particle air filter. 

The appropriate type of particle removal air filter 

can be chosen by looking at its MERV rating in 

removing airborne particles from the airstream 

that passes through it. MERV ratings can also 

be used to compare air filters made by different 

manufacturers.

Flat or panel air filters with a MERV of 1 to 4 

have low efficiency on smaller airborne particles, 

but reasonable efficiency on large particles when 

they remain airborne. These filters have low 

airflow resistance and are relatively inexpensive. 

Typically 1⁄2 to 1 inch thick, they are commonly 

used in residential furnaces and air-conditioning 

systems, and they are often used as pre-filters for 

higher efficiency filters. For the most part, such 

filters are used to protect the HVAC equipment 

from the buildup of unwanted materials on fan 

motors, heat exchangers, and other surfaces.

Pleated or extended surface filters with a MERV 

of 5 to 13 have higher efficiency ratings than 

panel filters. These medium-efficiency filters are 

reasonably efficient at removing small-to-large 

airborne particles. The airflow resistance of these 

filters does not necessarily increase as the MERV 

increases. Higher efficiency filters with a MERV 

of 14 to 16 have a higher average resistance to 

airflow than medium-efficiency filters. Higher 

efficiency pleated filters, sometimes inaccurately 

called “high efficiency,” “HEPA,” 

or “HEPA-type” filters, are 

similar in appearance to true 

HEPA filters, which have MERV 

values of 17 to 20, but use less 

efficient filter media.

The depth of these pleated or 

extended surface filters may vary 

from approximately 1 to 6 inches 

for medium-efficiency models 

and 6 to 12 inches for higher 

efficiency filters. As the depth 

and pleating increases, so does the area of the 

filtration medium, helping to offset the increase 

in resistance to airflow across the filter. Because 

of their increased surface area, these filters often 

have an extended life. The operating resistance of 

a fully dust-loaded filter must be considered in 

the design, because it is the maximum resistance 

against which the fan operates. Generally, dust 

loading results in increased filtration efficiency 

along with an increase in pressure drop. Pressure 

drop in media-type filters is greater than that in 

electronic-type cleaners and slowly increases over 

the filters’ useful life.

Large particles 

settle from the air 

rapidly; therefore, air 

filters are somewhat 

ineffective in their 

removal.
A Summar y of Available Information

www.epa.gov/iaq 13

Some residential HVAC systems may not have 

enough fan or motor capacity to accommodate 

higher efficiency filters. Therefore, the HVAC 

manufacturer’s information should be checked 

prior to upgrading filters to determine whether it 

is feasible to use more efficient filters.

True HEPA filters with a MERV between 17 

and 19 are defined by the IEST test method as 

having a minimum efficiency between 99.97 

percent and 99.999 percent in removing 0.3 μm 

particles. A MERV of 20 is rated for 0.1 to 0.2 

μm particles. HEPA filters have higher efficiencies 

for removing both larger and smaller airborne 

particles. True HEPA filters normally are not 

installed in residential HVAC systems; installing 

a HEPA filter in an existing HVAC system would 

probably require professional modification of the 

system. A typical residential air-handling unit 

and the associated ductwork would not be able to 

accommodate such filters because of their size and 

increased airflow resistance. Specially built high 

performance homes may occasionally be equipped 

with true HEPA filters installed in a properly 

designed HVAC system.

Manufacturers market HEPA filters to allergy 

and asthma patients. Experimental data and 

theoretical predictions indicate that mediumefficiency air filters, MERV between 7 and 13, 

are likely to be almost as effective 

as true HEPA filters in reducing 

the concentrations of most 

indoor particles linked to health 

effects.17 Available data indicate 

that even for very small particles, 

HEPA filters are not necessarily 

the preferred option. For these 

small particles, relatively large 

decreases in indoor concentrations 

(around 80 percent) are 

attainable with medium filter 

efficiency (such as a MERV of 

13). Increasing filter efficiency 

above a MERV of 13 results in only modest 

predicted decreases in indoor concentrations of 

these particles.* Predicted reductions in indoor 

concentrations of cat and dust mite allergens 

carried on small particles vary from 20 percent 

with a MERV 7 filter to 60 percent using a 

HEPA filter. Increasing filter efficiency above 

a MERV of 11 does not significantly reduce 

predicted indoor concentrations of animal dander. 

Medium-efficiency air filters are generally less 

expensive than HEPA filters and allow quieter 

HVAC fan operation and higher airflow rates 

than HEPA filters because they have less airflow 

resistance. Pleated filters 1 to 2 inches thick 

that have a MERV of 12 are available for use 

in homes and may often be installed without 

modifying residential HVAC systems; however, 

manufacturer’s information should be checked 

prior to installation.

Electrostatic precipitators remove and collect 

small airborne particles and have an initial 

ASHRAE dust spot efficiency of up to 98 percent 

at low airflow velocity. This efficiency will be 

highest for clean electronic air cleaners. Electronic 

air cleaners exhibit high initial efficiencies in 

cleaning air, largely because of their ability to 

remove fine particles. Their efficiency decreases as 

the collecting plates become loaded with particles, 

or as airflow velocity increases or becomes less 

uniform.

Portable Air Cleaners - Available Guidance for 

Their Comparison

The effectiveness of a portable 

air cleaner depends on the aircleaning device’s efficiency in 

removing airborne pollutants, the 

quantity of air being filtered, the 

particle size, the size of the room 

the air cleaner serves, and its 

location in the space. A voluntary 

standard is available for measuring 

the effectiveness of portable air 

cleaners in reducing airborne 

pollutants in a room. It was 

developed by the Association of 

Home Appliance Manufacturers 

(AHAM), a private voluntary standard-setting 

trade association, and is recognized by the 

American National Standards Institute.18 The 

standard compares the effectiveness of portable 

*Some air filters may be effective at reducing tobacco smoke particles, but they will not remove gaseous pollutants from tobacco smoke. While some gasphase filters may remove specific gaseous pollutants from the complex mixture of chemical compounds in tobacco smoke, none is expected to remove all 

unwanted gaseous combustion products. Odorous and toxic organic gases may also evaporate from liquid tobacco smoke particles trapped by the air filter.12

Filters that have a 

MERV between 7 

and 13 are likely 

to be nearly as 

effective as true 

HEPA filters.
R E S I D E N T I A L A I R C L E A N E R S

14 www.epa.gov/iaq

air cleaners in a room size test chamber, measured 

by the clean air delivery rate (CADR) for each of 

three types of particles in indoor air: dust, tobacco 

smoke, and pollen. Although AHAM uses tobacco 

smoke particles to represent smaller airborne 

particles, air cleaning should not be construed as 

an effective way to address environmental tobacco 

smoke. There are thousands of particulate and 

gaseous chemical compounds, including many 

known carcinogens, in tobacco smoke that cannot 

be removed effectively by air cleaning.

Although AHAM uses the CADR concept to 

evaluate the performance of portable air cleaners 

in reducing particulate matter concentrations, the 

CADR can be applied equally to the removal of 

gaseous pollutants. The CADR does not apply 

to whole-house air-cleaning devices installed in 

HVAC ductwork.

The CADR is a measure of a portable air cleaner’s 

delivery of contaminant-free air, expressed 

in cubic feet per minute. For example, an 

air cleaner that has a CADR of 250 for dust 

particles can reduce dust particle levels to the 

same concentration as would be achieved by 

adding 250 cfm of clean air. 

The portable air cleaner’s 

removal rate competes with 

other removal processes 

occurring in the space, 

including deposition of 

particles on surfaces, sorption 

of gases, indoor air chemical 

reactions, and outdoor air 

exchange. While a portable 

air cleaner may not achieve 

its rated CADR under all 

circumstances, the CADR 

value does allow comparisons 

among portable air cleaners. 

AHAM has a portable aircleaner certification program 

and lists all certified cleaners 

and their CADRs on its Web site at 

www.cadr.org.

19 AHAM’s online directory of 

certified portable air cleaners allows searches by 

certified CADR ratings, suggested room size, 

manufacturer, or brand name. The CADR 

values reported for selected portable air cleaners 

are based on an 80-percent reduction in steady 

particle concentrations. AHAM’s recommended 

effectiveness of 80 percent produces meaningful 

reductions in contaminant concentrations 

indoors. This level of effectiveness corresponds to 

an air cleaner’s capability to provide an amount 

of clean air that is four to five times the volume of 

the specified size room.9

Indoor particle concentrations are not always 

constant over time. Some indoor pollutants might 

be produced periodically from sources such as 

hobby and craft materials or cooking food. These 

intermittent pollutant sources have only a modest 

effect on particle concentrations indoors compared 

to sources of steady pollutant concentrations.

Some portable air cleaners sold to consumers 

are ENERGY STAR® qualified. Earning the 

ENERGY STAR means a product meets strict 

energy efficiency guidelines set by EPA and the 

U.S. Department of Energy. The ENERGY STAR 

disclaimer label, which includes the following 

statement, is placed on the product packaging 

of ENERGY STAR qualified air cleaners: “This 

product earned the ENERGY STAR 

by meeting strict energy efficiency 

guidelines set by the US EPA. US EPA 

does not endorse any manufacturer 

claims of healthier indoor air from the 

use of this product.”

Portable Air Cleaners - Available 

Evidence of Their Usefulness

Many of the portable air cleaners 

AHAM tested have moderate-to-large 

CADR ratings for small particles 

when used in rooms of appropriate 

size.9 However, for typical room sizes, 

most portable air cleaners currently on 

the market do not have high enough 

CADR values to remove effectively 

large particles such as dust, pollen, 

some mold spores, animal dander, 

and particles containing dust mite and cockroach 

allergens. Some portable air cleaners that use 

electronic air cleaners may produce ozone, which 

is a lung irritant.

Most portable air 

cleaners don’t 

effectively remove 

large particles such 

as dust, pollen, 

some mold spores, 

and particles 

containing dust 

mite and cockroach 

allergens in rooms 

of typical size.
A Summar y of Available Information

www.epa.gov/iaq 15

Studies have assessed portable air cleaners’ 

performance in removing airborne particles 

as well as their limited clinical effects. Some 

tests addressed the removal of tobacco smoke 

particles.20, 21, 22 Limited testing on larger airborne 

particles including those that contain cat, dog, and 

dust mite allergens have also been performed.23, 24, 

25, 26, 27, 28 Many experimental studies used portable 

air cleaners equipped with HEPA filters, but the 

available sources indicate that HEPA filters may 

not be preferable to medium-efficiency filters 

because of HEPA filters’ lower air delivery due to 

air bypassing the filter and to higher resistance to 

airflow. In addition, portable air cleaners are not 

effective at removing large particles because large 

particles settle out of indoor air at a substantial 

rate. 

The effectiveness of portable air cleaners in 

removing particles from indoor air depends on 

the size of the particles. One paper9

 reported that 

air-cleaning effectiveness of at least 80 percent 

can be achieved by portable air cleaners that 

have moderate-to-high CADR ratings in homes 

where small particles are the main concern. On 

the other hand, for larger airborne particles, the 

combination of small room size and high CADR 

ratings may yield particle removal effectiveness of 

80 percent or more. However, for typical rooms 

larger than 200 square feet, most portable air 

cleaners on the market do not have high enough 

CADR values to remove large particles effectively. 

This fact may account for the finding that portable 

air cleaners are most likely to be effective in 

reducing indoor concentrations of smaller airborne 

particles such as those associated with cat or dust 

mite allergens.26 However, air cleaning was not 

found to be consistently and highly effective in 

reducing respiratory symptoms since much of the 

airborne allergens appear to be carried on 

larger particles.26

Some manufacturers consider their hybrid 

portable air cleaners, which use multiple aircleaning devices, to be more effective than 

portable air cleaners that use a single device. 

However, the effectiveness of these hybrid units 

may suffer because more air cleaners arranged in 

a series may mean increased air resistance, which 

could decrease air delivery or cause air to bypass 

the cleaner. Effectiveness may also be decreased 

if air exiting the portable air cleaner outlet is not 

adequately mixed with room air before re-entering 

the unit.

Useful information about portable air cleaners 

is available from Consumer Reports magazine. 

Published by Consumers Union, an independent, 

nonprofit organization, Consumer Reports provides 

an annual review of products, their updated 

reports, and ratings. The test method used by 

Consumers Union is not intended to be the basis 

for a standard for evaluating the performance 

of air-cleaning devices; rather, Consumers 

Union tests air cleaners using its own testing 

procedures, rates the cleaners based on a variety 

of criteria, and ranks them in charts that are easy 

to understand. According to Consumers Union, 

some portable air cleaners that use electrostatic 

precipitators may produce measurable amounts of 

ozone as a by-product.29 Electrostatic precipitators 

may also make a crackling sound as they 

accumulate dirt. 

The placement of any portable air cleaner may 

affect its performance. If there is a specific, 

identifiable source of pollutants, the unit should 

be placed so its intake is near that source. If there 

is no specific source, the air cleaner should be 

placed where it will force clean air into occupied 

areas. It should not be situated where walls, 

furniture, and other obstructions will block the 

intake and outlet. A portable air cleaner will 

be much more effective when all the doors and 

windows in a room are closed. If the door to a 

room where a portable air cleaner is located is 

open, or if the HVAC system is operating, the 

room air often will mix with air from throughout 

the house, and the air cleaner will not reduce the 

particle concentrations in the room as intended.

Removal of Gaseous Pollutants 

by Sorbents

Many different gas-phase air-filtration devices 

are available; however, comparing and rating 

the effectiveness of installed sorbent filters is 

difficult because there is no standard test method. 
R E S I D E N T I A L A I R C L E A N E R S

16 www.epa.gov/iaq

ASHRAE Standard Project Committee 145 is 

developing a standard method for evaluating 

the effectiveness of gas-phase filtration devices 

installed in the ductwork of residential HVAC 

systems, but not in portable air cleaners.30

Gas-phase air filters remove gases and odors 

by either physical or chemical processes. These 

filters typically are designed to remove one or 

more of the gaseous pollutants present at low 

concentrations in the airstream that passes 

through them. They are not, however, designed to 

eliminate all gaseous pollutants. Air cleaners that 

do not contain sorbent materials or photocatalytic 

oxidation technology, discussed on page 20, will 

not remove gaseous pollutants.

A sorbent filter’s behavior depends on many 

factors that can affect the removal of gaseous 

contaminants:

	Airflow rate and velocity through the sorbent.

	Concentration of contaminants.

	Presence of other gaseous contaminants.

	Total available surface area of the sorbent. 

(Some manufacturing techniques can 

significantly reduce a filter’s total surface area.)

	Physical and chemical characteristics of the 

pollutants and the sorbent (such as weight, 

polarity, pore size, shape, volume, and the type 

and amount of chemical impregnation).

	Pressure drop.

	Removal efficiency and 

removal capacity.

	Temperature and relative 

humidity of the gas stream.

Gas-phase filters are much 

less common than particle 

air-cleaning devices in homes 

because a properly designed 

and built gas-phase filtration 

system is too big for a typical residential HVAC 

system or portable air cleaner. Other factors 

that may contribute to the less frequent use of 

gas-phase filters in home HVAC systems are 

the filters’ limited useful life, the fact that the 

sorbent material must be targeted to specific 

contaminants, the purchase price of the filters, 

and the costs of adapting them to residential 

applications, when possible, and of operating 

them once they have been installed.

Types of Sorbents Used for Gaseous 

Pollutant Removal 

There are two main processes that remove 

gaseous contaminants: a physical process known 

as adsorption and a chemical reaction called 

chemisorption.

Adsorption results from the physical attraction of 

gas or vapor molecules to a surface. All adsorbents 

have limited capacities and thus require frequent 

maintenance. An adsorbent will generally adsorb 

molecules for which it has the greatest affinity 

and will allow other molecules to remain in the 

airstream. Adsorption occurs more readily at lower 

temperatures and humidity. Solid sorbents such 

as activated carbon, silica gel, activated alumina, 

zeolites, synthetic polymers, and porous clay 

minerals are useful because of their large internal 

surface area, stability, and low cost. 

Activated carbon is the most common adsorbent 

used in HVAC systems and portable air cleaners 

to remove gaseous contaminants. It has the 

potential to remove most hydrocarbons, many 

aldehydes, and organic acids. However, activated 

carbon is not especially effective against oxides of 

sulfur, hydrogen sulfide, low 

molecular weight aldehydes, 

ammonia, and nitrogen oxide.

Chemisorption occurs 

when gas or vapor molecules 

chemically react with sorbent 

material or with reactive agents 

impregnated into the sorbent. 

These impregnates react with 

gases and form stable chemical 

compounds that are bound 

to the media as organic or inorganic salts, or 

are broken down and released into the air as 

carbon dioxide, water vapor, or some material 

more readily adsorbed by other adsorbents. 

Many different chemicals may be impregnated 

on activated carbon; potassium permanganate 

The limited lifetime of 

gas-phase filters may 

contribute to their 

less frequent use in 

home HVAC systems.
A Summar y of Available Information

www.epa.gov/iaq 17

is a common chemisorbent impregnated into 

activated alumina. It reacts with many common 

air pollutants, including formaldehyde and sulfur 

and nitrogen oxides. Because a chemisorbent 

will react with only one or a limited number of 

reactive pollutants, it should not be expected to 

reduce others.

Applications of Sorbents for Gaseous Pollutant 

Removal

Gas-phase filters that contain sorbents may be 

installed in HVAC systems or in portable air 

cleaners. They are usually located downstream 

of particle air filters. The air filter reduces the 

amount of particulate matter that reaches the 

sorbent, and the sorbent collects vapors that may 

be generated from liquid particles that collect on 

the particle filter. 

Some gas-phase filters may remove, at least 

temporarily, a portion of the gaseous pollutants in 

indoor air. Although some gas-phase air filters—if 

properly designed, used, and maintained—may 

effectively remove specific pollutants from indoor 

air, none is expected to remove adequately all 

of the gaseous pollutants in a typical home. For 

example, carbon monoxide is not readily captured 

by adsorption or chemisorption. In addition, 

gaseous-pollutant-removal systems usually have 

a limited lifetime before the sorbent must be 

replaced. There is also a concern 

that saturated sorbent filters may 

release trapped pollutants back 

into the airstream.31 

Tests of gaseous pollutant 

removal by activated carbon 

generally have been conducted 

using only high concentrations of 

pollutants, so little information is 

available on carbon’s effectiveness 

in removing chemicals present in 

the low concentrations (parts per 

billion [ppb]) normally found in 

indoor air. Tests performed at EPA measured the 

adsorption isotherms for three volatile organic 

compounds (VOCs) at concentrations of 100 

ppb to 200 ppb using three samples of activated 

carbon. The bed depth needed to remove the 

compounds was estimated assuming a 150 ppb 

concentration in the air, an exit concentration of 

50 ppb, and a flow rate of 100 cfm across a 

2’ x 2’ filter. The results of the study suggest that 

breakthrough of these chemicals would occur 

quickly in 6-inch deep carbon filters used for odor 

control.32

Because of their compact design, particle air 

filters that use impregnated media are available 

for residential HVAC systems and portable air 

cleaners. They use sorbent particles of carbon, 

permanganate alumina, or zeolite incorporated 

into fibrous filter media. Such filters generally 

range from 1/8 inch to 2 inches thick. They 

provide a combination of particulate and gasphase filtration with a minor increase in pressure 

drop across the filter. Their use in an existing 

HVAC system does not require extensive or 

expensive modifications to the system. However, 

their useful service life varies according to indoor 

pollution concentrations and exposure time. 

Breakthrough of the contaminants back into the 

room takes place very quickly in the thin layer 

impregnated with sorbents, resulting in a much 

shorter service life for the filter, which must be 

replaced frequently. Thus, these devices usually 

have limited effectiveness in removing odors.

Removal of Radon and Its Progeny

EPA does not recommend air 

cleaning to reduce the health 

risks associated with radon and 

the decay products of radon gas, 

which are called “radon progeny.” 

The Agency recommends the use 

of source control technologies 

to prevent radon from entering 

residential structures. The most 

effective radon control technique 

is active soil depressurization 

(ASD).1

 An ASD system uses 

an electric fan to minimize 

radon entry by drawing air 

from under the slab/floor and venting it to the 

outside above the building’s roofline. Another, less 

effective technique installed during construction 

is a passive radon reduction system, also known 

as radon-resistant new construction (RRNC). 

EPA does not 

recommend using 

air cleaners to 

reduce the health 

risks associated 

with radon.
R E S I D E N T I A L A I R C L E A N E R S

18 www.epa.gov/iaq

RRNC systems are “dual-purpose” systems. They 

typically do not have a fan, but if subsequent 

testing indicates an elevated radon level, a fan can 

be installed and the RRNC system will become, 

in effect, an ASD system.

A limited number of studies have investigated air 

cleaners’ effectiveness in removing radon and its 

progeny. They compared the removal efficiencies 

of various air cleaners, including mechanical air 

filters, electrostatic precipitators, and ionizers 

equipped with fans, and the risk reduction the 

air cleaners achieve. However, the degree of risk 

reduction found by these studies has 

been inconsistent.

Deactivation or Destruction of 

Pollutants

Three types of air cleaners on the market are 

designed to deactivate or destroy indoor air 

pollutants: ultraviolet germicidal irradiation 

(UVGI) cleaners, photocatalytic oxidation (PCO) 

cleaners, and ozone generators sold as air cleaners. 

Ultraviolet Germicidal Irradiation Cleaners

UVGI cleaners are intended to improve residential 

IAQ by deactivating indoor biological pollutants 

that are airborne or growing on the moist interiors 

of HVAC surfaces (e.g., cooling coils, drain pans, 

or ductwork). 

There is no standard test method to rate and 

compare the effectiveness of UVGI cleaners 

installed in either residential HVAC systems or 

portable air cleaners. Typical UVGI cleaners used 

in homes have limited effectiveness in killing 

bacteria and molds. The effective destruction of 

some viruses and most mold and bacteria spores 

usually requires much higher UV exposures 

than a typical home unit provides. Thus, UVGI 

does not appear to be effective as a sole control 

device. When UVGI is used, it should be used 

in addition to—not as a replacement for—

conventional particle filtration systems.33 Using 

UVGI in addition to HEPA filters in HVAC 

systems or in portable units offers only minimal 

infection control benefits over those provided by 

the HEPA filters alone.33, 34

Biological pollutants such as molds and 

bacteria enter a house by various routes, 

including open windows, joints and 

cracks in walls, and on clothing, food, 

or pets. Molds and some bacteria can 

be found in either the vegetative or the 

spore phase of their life cycle. Vegetative 

bacteria and molds are in the growth and 

reproductive phase; they are not spores. 

Some bacteria form spores, an inactive 

phase characterized by a thick protective 

coating, to survive harsh environmental 

conditions. Molds produce tiny spores 

in order to reproduce. Mold spores will 

germinate where moisture and nutrients 

are available, such as on basement walls, 

in refrigerators, on HVAC coils, on air 

filters, and in drip pans. 

Mechanical air filters will capture some 

biological pollutants, but some will bypass 

the filter along with the airstream, and 

many small microorganisms can pass 

through lower efficiency filter media. 

Microorganisms such as bacteria and 

molds also can enter the HVAC system by 

the following mechanisms.

	They may grow through the filter media 

when conditions are favorable, for 

example when moisture is present and 

temperatures are high.34, 35

	They can be introduced into the system 

during routine maintenance, for example 

a filter change.36

	Mold spores on the filters can be 

released back to the airstream when 

the air velocity suddenly increases, for 

example during HVAC system startup or 

off-and-on operation.37

Once bacteria and mold spores are 

downstream of the filter, they may grow in 

the presence of condensation on cooling 

coils, drain pans, and internal thermal 

insulation, or on the surfaces of the 

air-handling unit and ductwork.
A Summar y of Available Information

www.epa.gov/iaq 19

UVGI Technology

Most UV lamps used to kill germs in residential 

settings are low pressure mercury vapor lamps 

that emit UV radiation at a wavelength of 253.7 

nanometers, which has been shown to have 

germicidal effects.38 UV light can penetrate the 

outer structure of a microorganism’s cell and alter 

its DNA, permanently preventing replication and 

causing cell death. But some bacterial and mold 

spores are resistant to UV radiation.

Types of UVGI Cleaners and Their 

Effectiveness

There are two types of UVGI applications: 

cleaners designed for airstream disinfection, to 

reduce the viability of microorganisms as they 

flow through the HVAC system or portable 

air cleaner, and cleaners designed for surface 

disinfection, to prevent the reproduction of 

microorganisms on specific components of an 

HVAC system.38, 39

UVGI lamps for airstream or surface disinfection 

usually are located in the air duct of an HVAC 

system downstream of the filter and upstream 

of the cooling coil or in a portable air cleaner 

downstream of the filter.

If properly designed, the UVGI cleaner in a 

typical airstream disinfection application has 

the potential to reduce the viability of vegetative 

bacteria and molds and to provide low to moderate 

reductions in viruses but little, if any, reduction in 

bacterial and mold spores.33, 34, 40

Spores tend to be resistant to UV 

radiation, and killing them requires 

a very high dosage.38, 41, 42

When the fan in an airstream 

disinfection application is 

not operating, there is no air 

movement and no disinfection.

UVGI cleaners in a surface disinfection

application are installed in air-handling units to 

prevent or limit the growth of vegetative bacteria 

and molds on moist surfaces in the HVAC 

system.34, 39, 40, 43 One study reported a 99-percent 

reduction in microbial contaminants growing 

on exposed HVAC surfaces, but a reduction in 

airborne bacteria of only 25 to 30 percent.44 One 

reason that the surface disinfection application 

provides only a slightly noticeable reduction in 

airborne microbial concentrations may be that 

microorganisms in the airstream are exposed 

to the UV light for a shorter time. Conversely, 

microorganisms growing on exposed HVAC 

surfaces are given prolonged direct UVGI 

exposure. Another study found that UV lamps 

yielded somewhat lower levels of mold in the 

fiberglass insulation lining the air-handling unit.40 

Prolonged direct UVGI exposure can destroy 

vegetative microbial growth—but not most 

spores—on the surfaces of forced-ventilation 

units, filters, cooling coils, or drain pans. Killing 

molds and bacteria while they are still in the 

susceptible vegetative state reduces the formation 

of additional spores. UV radiation is ineffective in 

killing microorganisms if they proliferate inside 

the filter media, system crevices, porous thermal 

insulation, or sound-absorbing fibrous material 

liners.39

A review of scientific literature has shown that 

the effectiveness of UVGI cleaners in killing 

microorganisms may vary depending on UV 

irradiation dose, system design and application, 

system operation characteristics, and the 

microorganism targeted for deactivation. Further 

independent testing using a standardized test 

method is required before firmer conclusions can 

be made about the effectiveness of 

various UV cleaners in destroying 

microorganisms of concern.

Some manufacturers of UVGI 

cleaners used in HVAC systems 

or portable air cleaners claim their 

units reduce dust mite allergens, 

airborne microorganisms such as 

viruses, bacteria, molds, and their 

spores, and gaseous pollutants from indoor air. 

However, it is likely that the effective destruction 

of some viruses and most mold and bacterial 

spores requires much higher UV exposures than a 

typical residential UVGI unit provides.36, 38, 39 

UVGI cleaners might 

not reduce allergy or 

asthma symptoms.
R E S I D E N T I A L A I R C L E A N E R S

20 www.epa.gov/iaq

No research or studies were found that show UV 

disinfection is effective in reducing dust mite and 

mold allergenicity or that UV radiation has the 

potential to remove gaseous pollutants. Because 

mold is allergenic, whether dead or alive, it can 

cause allergic reactions in sensitive populations. 

Therefore, UVGI cleaners might not be effective in 

reducing allergy and asthma symptoms. If mold is 

growing indoors, it should be removed.45

Planning and Maintaining a UVGI System

A number of studies 34, 36, 38, 46, 47 report that the 

most important performance elements of a UVGI 

system are the type of UV lamp and ballast, the 

relative humidity, temperature, air velocity, and 

duct reflectivity.

High output UV lamps have been found to 

provide higher irradiance than low-output lamps. 

Lamps designated for low-temperature operation 

also appear to perform better. Increased relative 

humidity is commonly believed to decrease the 

irradiation of UVGI; however, the literature is 

contradictory and incomplete. Air temperature 

can affect the power output of UVGI lamps if it 

exceeds design temperatures. Operating a UVGI 

system at air velocity above 

design will degrade the system’s 

effectiveness. Reflectivity 

can be an economical way of 

intensifying the UVGI field 

in an enclosed duct. Polished 

aluminum is highly reflective 

of UV wavelengths, while 

typical duct liner material has 

little or no reflectance in the 

UV spectrum. 

Regular maintenance of 

UVGI systems is crucial and usually consists of 

cleaning the lamps of dust and replacing old lamps. 

Manufacturers’ recommendations regarding safety 

precautions, exposure criteria, maintenance, and 

monitoring associated with the use of UVGI 

systems should be followed. 

By-products Generated by UVGI Systems

According to two studies,38, 43 operating UV lamps 

installed in HVAC systems to irradiate the surfaces 

of air-handling units does not result in increased 

concentrations of ozone, VOCs, or other chemical 

by-products.

Photocatalytic Oxidation Cleaners

PCO cleaners are intended to destroy gaseous 

pollutants and their odors by converting them 

into harmless products, but they are not designed 

to remove particulate pollutants. PCO cleaners 

use a UV lamp and a photocatalyst, usually 

titanium dioxide, to create oxidants that destroy 

gaseous contaminants. When the photocatalyst 

is irradiated with UV light, a photochemical 

reaction takes place and hydroxyl radicals form. 

The hydroxyl radicals oxidize gaseous pollutants 

adsorbed on the catalyst surface. This reaction, 

called photocatalytic oxidation, converts organic 

pollutants into the carbon dioxide and water. 

To achieve effective conversion, the reaction 

rate of the PCO cleaner must match the rates 

of contaminant generation and infiltration rate 

minus the exfiltration rate (movement of the air 

from the space served to the outdoors).

There is no standard test method to compare and 

rate the effectiveness of PCO cleaners installed 

in residential HVAC systems or 

portable air cleaners. PCO is an 

emerging technology intended 

to improve residential IAQ by 

destroying gaseous contaminants. 

Although PCO is still under 

development, a few home air 

cleaners that use it are available in 

the United States. PCO cleaners are 

promoted for use in HVAC system 

ducts or in portable air cleaners. 

Some manufacturers claim PCO 

devices can remove tobacco smoke, 

microorganisms, and other indoor particulate 

pollutants even though the devices are not meant 

to remove particles. 

The usefulness of PCO cleaners in homes is 

limited because available photocatalysts (i.e., 

substances that react with light) are ineffective 

in completely destroying gaseous pollutants 

in indoor air.48, 49, 50 Other application and 

engineering issues are not fully resolved, 

Application of 

PCO cleaners for 

homes is limited in 

destroying gaseous 

pollutants from 

indoor air.
A Summar y of Available Information

www.epa.gov/iaq 21

including the relatively large power consumption 

of PCO units; the complexity of the PCO 

process, which combines the operation of a UV 

light and a catalyst; and the need to remove 

multiple compounds from the contaminated 

airstream. Some PCO cleaners fail to destroy 

pollutants completely and instead produce new 

indoor pollutants that may cause irritation of the 

eyes, throat, and nose. Until more data become 

available, information on the performance of PCO 

cleaners will remain limited and inconclusive.

Effectiveness of PCO Systems

One study 51 reported that PCO devices installed 

in portable air cleaners did not effectively 

remove any of the test VOCs present at the low 

concentrations normally found in indoor air. This 

study compared the VOC-removal efficiencies 

of 15 air cleaners that use 

different types of technology. 

A mixture of 16 VOCs 

commonly found indoors 

was used. The report 

indicated that the PCO 

devices studied might not 

work as advertised. The 

findings also showed that 

some devices appear not to 

have fully implemented PCO technology. 

A review of the literature suggests that more 

research is needed to further advance PCO as 

an effective technology in removing low levels 

of gaseous contaminants from the indoor air 

of residences.49, 50, 51 This additional research 

should include many important performance 

characteristics that influence the effectiveness of 

PCO cleaners, such as whether:

X A decrease in light irradiance with illumination 

time inhibits performance.49

X Photocatalyst deactivation in the presence of 

chemicals such as toluene, benzene, ethanol, or 

hexamethyldisilazane decreases performance.

49, 50, 52

X An increase in reaction temperature or water 

vapor content increases the PCO reaction 

rate.53

X Competitive adsorption between gaseous 

contaminants affects the PCO reaction 

mechanism.49, 54

Estimated costs of PCO technology are significantly 

higher than those of activated carbon technology. A 

major factor influencing PCO costs is the intensity 

of UV light required at the inlet to destroy a range 

of VOCs at the low concentrations that typify IAQ 

problems.48

PCO By-products

PCO of certain VOCs may create by-products 

that are indoor pollutants if the system’s design 

parameters and catalyst metal composition do not 

match the compound targeted for decomposition, 

particularly in the presence of multiple reactive 

compounds commonly found in residential settings. 

One study reported that no detectable 

by-products formed during the PCO of 

17 VOCs using titanium dioxide under 

the experimental conditions.55 However, 

two studies on the degradation of 4 

chlorinated VOCs found by-products 

including phosgene and chlorides.56, 57 In 

addition, the PCO of trichloroethylene 

in air using titanium dioxide as the 

catalyst yielded as by-products carbon 

monoxide, phosgene, carbon dioxide, hydrogen 

chloride, and chlorine. 

Ozone Generators

Ozone generators sold as air cleaners and marketed 

as in-duct or portable units use UV light or corona 

discharge to produce ozone, which is dispersed by a 

fan into occupied spaces.8

Some manufacturers and vendors of ozone 

generators suggest that ozone reacts with both 

chemical and biological pollutants and transforms 

them into harmless substances. They also often 

make statements and distribute materials that 

lead the public to believe that these devices are 

always safe and effective in controlling indoor air 

pollutants. However, ozone is an irritant gas that 

reacts with lung tissue and can cause asthma attacks; 

coughing; chest discomfort; irritation of the nose, 

throat, and trachea; and other adverse health effects. 

Ozone is a lung 

irritant that can 

cause adverse health 

effects.
R E S I D E N T I A L A I R C L E A N E R S

22 www.epa.gov/iaq

As ozone reacts with chemical pollutants, it can 

produce harmful by-products.8, 9, 10

Available scientific evidence shows that, at ozone 

concentrations below public health standards, 

ozone has little potential to remove indoor 

air contaminants such as many odor-causing 

chemicals, viruses, bacteria, molds, and tobacco 

smoke; thus, ozone is generally ineffective in 

controlling indoor air pollution. Some controlled 

studies show that the concentration of ozone 

produced by ozone generators can exceed 

standards even when consumers follow the 

manufacturer’s instructions. No federal agency 

has approved ozone generators for use in occupied 

spaces.

There is a large body of written material 

on ozone and the use of ozone indoors, but 

much of this material makes claims or draws 

conclusions without substantiation and a basis in 

sound science. In developing Ozone Generators 

that Are Sold as Air Cleaners, EPA reviewed a 

wide assortment of this literature, including 

information provided by a leading manufacturer 

of ozone-generating devices. In keeping with 

EPA’s policy of ensuring that the information 

it provides is based on sound science, only peer 

reviewed, scientifically supported findings and 

conclusions were relied on in developing this 

document. The document is posted on the EPA 

Web site at www.epa.gov/iaq/pubs/ozonegen.html.

The public is advised to use methods proven to 

be safe and effective in controlling indoor air 

pollution. These methods include eliminating 

or controlling pollutant sources and increasing 

outdoor air ventilation.

Federal pesticide law requires manufacturers of 

ozone generators to list an EPA establishment 

number on the product’s packaging. This number 

merely identifies the facility that manufactured 

the product. The presence of this number on a 

product’s packaging does not imply that EPA 

endorses the product, nor does it imply that EPA 

has found the product to be safe or effective. 
A Summar y of Available Information

www.epa.gov/iaq 23

WILL AIR CLEANING REDUCE HEALTH EFFECTS FROM INDOOR 

AIR POLLUTANTS?

Air-cleaning devices may help reduce levels of 

smaller airborne allergens, particles, or, in some 

cases, gaseous pollutants in a home. However, air 

cleaners may not decrease adverse health effects 

particularly in sensitive populations such as 

children, people with asthma and allergies, and 

the elderly.

Clinicians frequently recommend that patients 

who have asthma or allergies use HEPA air filters 

in HVAC systems or in portable air cleaners. 

Regardless of how efficient and effective aircleaning devices are in removing pollutants, a 

question still remains about their ability to reduce 

adverse health effects.

How effectively air-cleaning devices alleviate 

allergic and other health symptoms remains 

uncertain. Strong data linking air-cleaning 

devices to reduced health symptoms do not 

exist. Many studies have associated air-cleaning 

devices with reductions in airborne indoor 

pollutant concentrations, but more clinical studies 

are needed to determine whether air cleaners 

significantly affect health outcomes. A literature 

review documented only a limited number of 

studies that attempted to evaluate the clinical 

outcomes of air cleaner use. These studies focused 

on more sensitive groups, such as asthmatic and 

allergic individuals, children, and the elderly. A 

number of the studies had important limitations, 

such as small study size, short duration, and 

lack of blinding (i.e., subjects and scientists were 

aware of air cleaner operation), which may result 

in a placebo effect. The results were also more 

suggestive than conclusive. 

Many indoor pollutants related to asthma and 

allergies are either airborne particles or irritants, 

such as the gaseous components of secondhand 

smoke or nitrogen dioxide, chemicals linked 

with gas cooking appliances, fireplaces, wood 

stoves, and unvented kerosene and gas space 

heaters. Most studies involving subjects who 

have perennial and seasonal allergy or asthma 

symptoms tested portable air cleaners equipped 

with HEPA filters. 

Few studies tested gas-phase filtration and air 

cleaners using UV light technology, such as UVGI 

cleaners and PCO cleaners. The scarcity of data 

results in little scientific evidence that these devices 

are associated with a reduction in health symptoms.

The effects of particle air cleaners on allergy 

and asthma symptoms have been reviewed by 

the Institute of Medicine (IOM) Committee 

on the Assessment of Asthma and Indoor Air of 

the National Academy of Sciences.26 The IOM 

concluded that:

The results of existing experimental studies are 

inadequate to draw firm conclusions regarding 

the benefits of air cleaning for asthmatic 

and allergic individuals.... Air cleaners are 

helpful in some situations in reducing allergy 

or asthma symptoms, particularly seasonal 

symptoms, but it is clear that air cleaning, as 

applied in the studies, is not consistently and 

highly effective in reducing symptoms.

The use of air cleaners may help reduce levels of 

smaller airborne allergens or particles, but should 

not be expected to effectively reduce health 

symptoms.

Several factors should be considered in evaluating 

whether an air cleaner is beneficial in alleviating 

health effects.

X Many studies on the health benefits of air 

cleaning involve multiple interventions and 

thus are not useful in determining the effects of 

air cleaners alone.

The health benefits of air cleaners are often 

studied along with other interventions such as 

mattress and pillow covers, exclusion of pets 

from the bedroom, weekly baths for pets, or 

vacuum cleaning. Studies that consider air 

cleaning concurrently with other interventions 

have relatively little value in determining 

the clinical outcome resulting from the use 
R E S I D E N T I A L A I R C L E A N E R S

24 www.epa.gov/iaq

of air cleaners because it is not clear if any 

improvements demonstrated are due to 

the air-cleaning devices or to the other 

interventions.23, 24, 25, 27, 28, 58, 59

X An air cleaner’s ability to 

remove some airborne 

pollutants, including 

microorganisms, is not, 

in itself, an indication of 

the air cleaner’s ability to 

reduce health symptoms.

As discussed previously, 

pollen, dust mite and 

cockroach allergens, some mold spores, and 

animal dander carried on large particles 

settle rapidly before they can be removed 

by filtration. Because these particles do not 

remain airborne, air-cleaning devices are 

relatively ineffective in their removal.9, 26, 60

Therefore, effective allergen control requires 

routine cleaning and dust control including 

the weekly washing of bed sheets, frequent 

vacuuming of carpets and furniture, and 

regular dusting and cleaning of hard surfaces. 

(For more on allergen control, visit

www.epa.gov/asthma.)

A significant fraction of cat and dog allergens 

and a small portion of dust mite allergens 

associated with mite feces are carried on 

small particles. Consequently, they are more 

easily dispersed throughout a house, remain 

airborne longer, and are more likely to be 

removed by air cleaners.23, 61 Although there 

is evidence that some air cleaners can remove 

a portion of smaller particles from the air, 

there is little evidence that these reductions 

in particle levels alleviate 

health symptoms. This lack 

of improvement in symptoms 

may be due in part to the fact 

that, once sensitized, allergic 

and asthmatic individuals 

respond to much lower levels 

of pollutants. 

There is little clinically 

confirmed support for the 

effectiveness of UVGI cleaners in reducing 

health symptoms in either airstream or surface 

applications. Despite UVGI’s ability to 

deactivate some surface-grown microorganisms, 

data linking the effectiveness of UVGI 

systems to reduced health symptoms in 

sensitive populations such as children, 

asthmatic and allergic individuals, 

and the elderly are not available for 

residential settings. 

X Some air cleaners may produce 

new, potentially toxic pollutants or may 

re-disperse old ones.

A limited number of studies report that 

irradiation by UVGI lamps reduce vegetative 

bacteria and molds that are either airborne or 

growing on moist HVAC surfaces.34, 39, 40, 43, 44 

However, the dead mold spores may still cause 

allergic reactions in some people. 

High moisture and elevated temperatures 

can promote bacteria and mold growth in 

particulate filter media.35 Air filters may reemit bacteria and mold spores during HVAC 

startup and off-and-on operations when air 

velocity suddenly increases.37

Ozone generators sold as air cleaners for use in 

occupied indoor spaces produce ozone, a lung 

irritant.8 Electronic air cleaners, such as ion 

generators and electrostatic precipitators, have 

the potential to emit potentially dangerous 

levels of ozone.5, 22, 29 Contamination of 

electrode surfaces in electronic air cleaners 

may cause increased ozone levels.62 There also 

have been reports of electronic air cleaners 

producing fine particulate material from the 

reaction of ozone produced in 

the corona discharge with other 

chemicals indoors.9, 10, 63

Liquid tobacco smoke particles 

trapped by an air filter may give 

off odorous organic gases.12

Saturated sorbent filters may also 

release trapped gaseous pollutants 

back into the airstream.31 If a 

PCO system’s design parameters 

An air cleaner’s ability 

to remove some 

airborne pollutants is 

not an indication of 

its ability to reduce 

health symptoms.

Air cleaning may have 

a useful role when 

used in conjunction 

with source control 

and ventilation with 

clean outdoor air. 
A Summar y of Available Information

www.epa.gov/iaq 25

do not match the pollutant targeted for 

decomposition, the PCO cleaner may create, 

as a result of the oxidation process of certain 

VOCs in indoor air, by-products that are 

indoor air pollutants. 

Current evidence suggests that air cleaning 

may have a useful role when used in 

conjunction with source control and 

ventilation with clean outdoor air. 

ADDITIONAL FACTORS 

TO CONSIDER

Several factors other than the ability of aircleaning devices to reduce airborne pollutant 

concentrations should be considered when 

deciding whether to use air cleaners.

Installation 

In-duct air-cleaning devices require sufficient 

access for inspection during use, repair, and 

maintenance. Electronic air cleaners and UV 

lamps should have an accessible power supply 

and an indicator showing when electrical service 

is off. The installation of UV lamps requires 

the addition of access holes into the duct, and 

the holes must be properly sealed to maintain 

HVAC efficiency. Mechanical air filters should 

be installed so that the directional arrow printed 

on the side of the filter points in the direction of 

airflow within the system. Incorrectly designed 

or installed filter frames can cause air seepage, 

which significantly decreases filter effectiveness. 

High efficiency filters require well sealed frames 

to prevent leaks. Installing a higher efficiency 

and HEPA filter would probably require sheet 

metal modifications to the existing ductwork to 

permit the installation of the thicker air cleaner. 

In addition, a more powerful fan often must be 

installed to overcome the higher pressure drop. 

Operations and Maintenance

In some cases, consumers have been left with 

no useful manufacturer’s instructions that 

recommend replacement of various air-cleaning 

devices over their lifetime other than the general 

manufacturer’s operating and maintenance 

procedures to be followed to ensure adequate 

air cleaner performance. Air cleaners should be 

selected to match operating conditions, such as 

degree of air cleanliness needed, type of pollutant 

to be removed, and allowable pressure drop. A fan 

that has sufficient capacity (pressure and airflow 

ratings) to move air through the filter media must 

also be included.

Filters and sorbents must be replaced, and the 

plates or charged media of electronic air cleaners 

must be cleaned. Electronic air cleaner efficiency 

decreases as the collecting plates become loaded 

with particles, so the plates must be cleaned, 

sometimes frequently, as required by the 

manufacturer. The cleanings should be scheduled 

to keep the unit operating at peak efficiency. 

Special attention must be given to cleaning the 

ionizing wires of electronic air cleaners designed 

to target certain contaminants.

During cleaning or replacement of air cleaners, an 

effort should be made to ensure that pollutants are 

not re-emitted into the air. For example, excessive 

movement or air drafts should be avoided when 

filters are removed. Used filters should be placed 

in plastic bags or other containers for disposal.

To avoid electrical and mechanical hazards, 

consumers should make sure air-cleaning devices 

that require an electrical power supply are listed 

on the Underwriters Laboratories Web site 

at www.ul.com or with another recognized 

independent safety testing laboratory.

Cost

Cost may also be a consideration. Major costs 

include the initial purchase price, maintenance 

(such as cleaning or replacing filters and parts), 

and operation (such as electricity).

The most effective air cleaners—those with 

high airflow rates and efficient particle capture 

systems—generally are the most costly. 

Maintenance costs vary depending on the device, 

and these costs should be considered when 

choosing a particular unit. Operating cost is as 

important as purchase cost because air cleaning 
R E S I D E N T I A L A I R C L E A N E R S

26 www.epa.gov/iaq

is a continuing process. The cost of professional 

installation of an electronic air filter or a 

HEPA filter in the HVAC system must also be 

considered. Consumers should consider obtaining 

information on purchase and annual operating 

costs for various products from Consumer Reports 

magazine and other sources.

Inability to Remove Some Odors

Air-cleaning devices designed to remove particles 

are incapable of controlling gases and some 

odors. For example, the odor and many of the 

carcinogenic gas-phase pollutants from tobacco 

smoke will remain in filtered air. Particles of liquid 

tobacco smoke trapped by an air filter may give 

off odorous organic gases.12 

Possible Effects of Particle Charging

Another factor to consider related to ion 

generators is the effect of particle charging on 

deposition in the respiratory tract. Experiments 

have shown that particle deposition increases with 

charge, so using ion generators may not reduce 

the dose of particles to the lungs.63, 64 The effect of 

charge on very fine particles results in their higher 

deposition rate in the lungs compared to that of 

uncharged particles.

Soiling of Walls and Other Surfaces

Ion generators generally are not designed to 

remove from the air the charged particles that they 

generate. These charged particles deposit on and 

soil room surfaces such as walls and curtains.63, 64

Consequently, there is no true effective removal of 

the particles from the space. Deposited particles, 

especially those larger than approximately 2 μm, 

may be re-suspended from the surfaces when 

disturbed by human activities such as walking 

or vacuuming.

Noise

Noise may also be a consideration in selecting a 

portable air cleaner that contains a fan. Portable 

air cleaners that do not have fans typically are 

much less effective than units that have them. In 

tests by Consumers Union, the largest portable air 

cleaners were the noisiest on their most effective 

high speed settings.65 However, some performed 

more quietly at low speed than many smaller 

cleaners do on high. Some larger portable units 

operating at low speed were found to be quiet 

enough for most households.22
A Summar y of Available Information

www.epa.gov/iaq 27

CONCLUSION

Indoor air pollution is among the top five environmental risks to public health. The best way to address 

this risk is to control or eliminate the sources of pollutants and to ventilate a home with clean outdoor 

air. The ventilation method, however, may be limited by weather conditions or undesirable levels of 

contaminants in outdoor air. If these measures are insufficient, an air-cleaning device may be useful. 

While air-cleaning devices may help control the levels of airborne particles including those associated 

with allergens and, in some cases, gaseous pollutants in a home, air cleaning may not decrease adverse 

health effects from indoor air pollutants. 

This document was prepared to provide housing design professionals, public health officials, and indoor 

air quality professionals with useful information on the available types of air-cleaning devices and their 

overall effectiveness in reducing air pollutants and associated health impacts. It is important to remember 

that there is no scientific evidence that shows air-cleaning devices to be consistently and highly effective 

in reducing adverse health effects from indoor air pollutants.
R E S I D E N T I A L A I R C L E A N E R S

28 www.epa.gov/iaq

Acute Having a rapid onset and following a short but potentially severe course.

Adsorption The physical process that occurs when liquids, gases, or suspended matter adhere to 

the surfaces or in the pores of a material. 

Air cleaner A device used to remove particulate or gaseous impurities from the air; examples 

include electrostatic precipitator, ion generator, ultraviolet germicidal irradiation 

cleaner, photocatalytic oxidation cleaner, and gas-phase air filter.

Air filter A device that removes particulate material from an airstream, also called an “air 

cleaner.”

Airflow resistance See Pressure drop.

Allergen A chemical or biological substance (e.g., pollen, animal dander, or house dust mite 

proteins) that can cause an allergic reaction characterized by hypersensitivity (an 

exaggerated response).

Allergic respiratory disease Impairment of the normal state of the respiratory system resulting from exposure—

usually by inhalation—to an allergen.

Allergy An exaggerated or pathological reaction to breathing, eating, or touching substances 

that have no comparable effect on the average individual.

Asthma A usually chronic inflammatory disorder of the airways characterized by intermittent 

episodes of wheezing, coughing, and difficulty breathing, sometimes associated with 

an allergy to inhaled substances.

Bacterial spore Inactive phase of bacteria, with a thick protective coating that allows the bacteria to 

survive harsh environmental conditions.

CADR The Clean Air Delivery Rate (CADR) is the measure of portable room air cleaner 

performance. This is defined as the measure of the delivery of contaminant-free air by a 

portable household electric room air cleaner, expressed in cubic feet per minute (cfm). 

CADRs are always the measurement of a unit’s performance as a complete system.

Chemisorption A process whereby a chemical substance adheres to a surface through the formation 

of a chemical bond.

Chronic Marked by long duration, by frequent recurrence over a long time, and often by 

slowly progressing seriousness.

Corona discharge An electrical discharge brought on by the ionization of a fluid surrounding a 

conductor, which occurs when the potential gradient exceeds a certain value.

Dander Minute scales of skin. Dander also may contain hair or feathers.

Disinfection The process of any reduction or prevention of growth in a microbial population with 

no percentage efficiency specified.

Double-blind study A type of clinical trial study design in which the study participants and the 

investigators do not know the identity of the individuals in the intervention and 

control groups until data collection has been completed.

GLOSSARY
A Summar y of Available Information

www.epa.gov/iaq 29

HEPA filter High-efficiency particulate air filter. Extended surface mechanical air filter having 

a minimum particle removal efficiency of 99.97 percent for all particles of 0.3 μm 

diameter, with high efficiency for both larger and smaller particles.

HVAC Heating, ventilating, and air conditioning.

IAQ Indoor air quality.

MERV Minimum efficiency reporting value.

Mold spore Tiny reproductive structures produced by vegetative mold.

Ozone An unstable, poisonous allotrope of oxygen that is formed naturally in the ozone 

layer from atmospheric oxygen by electric discharge or exposure to ultraviolet 

radiation, also produced in the lower atmosphere by the photochemical reaction of 

certain pollutants.

Particulate A small discrete mass of solid or liquid matter that remains individually dispersed in 

gas or liquid emissions (usually considered to be an atmospheric pollutant).

PCO Photocatalytic oxidation.

Placebo effect A usually, but not necessarily, beneficial effect attributable to an expectation that a 

treatment will have an effect; an effect that is due to the power of suggestion; a sense 

of benefit felt by a patient that arises solely from the knowledge that treatment has 

been given.

Pressure drop The loss of force applied over a filtering media surface due to resistance to airflow.

Rhinitis Inflammation of the mucous membrane lining of the nose.

Sorption The common term used for adsorption.

ULPA Ultra low penetration air filter. Extended surface mechanical air filter having a 

minimum particle removal efficiency of 99.999 percent for all particles of 0.3 μm 

diameter, with high efficiency for both larger and smaller particles.

UV Ultraviolet.

UVGI Ultraviolet germicidal irradiation.

VOCs Volatile organic compounds; chemicals that contain carbon and are vaporous at room 

temperature and pressure.

Vegetative bacteria 

and molds

Microorganisms that are in the growth and reproductive phase, i.e., not spores.
R E S I D E N T I A L A I R C L E A N E R S

30 www.epa.gov/iaq

REFERENCES

1. Consumer’s Guide to Radon Reduction. 

U.S. Environmental Protection Agency. 

EPA 402-K-06-094. Revised December 

2006.

2. The Inside Story: A Guide to Indoor Air 

Quality. U.S. Environmental Protection 

Agency. EPA 402-K-93-007. April 

1995.

3. Chapter 25. Air-To-Air Energy Recovery. 

Heating, Ventilating, and AirConditioning: Systems and Equipment: 

2008 ASHRAE Handbook. American 

Society of Heating, Refrigerating and 

Air-Conditioning Engineers, Inc. 2008.

4. Chapter 36. Owning and Operating 

Costs. Heating, Ventilating, and AirConditioning: HVAC Applications: 

2007 ASHRAE Handbook. American 

Society of Heating, Refrigerating and 

Air-Conditioning Engineers, Inc. 2007. 

5. Evaluation of Residential Furnace Filters. 

Bowser Technical Inc. for Canada 

Mortgage and Housing Corporation. 

1999.

6. Chapter 28. Air Cleaners for Particulate 

Contaminants. Heating, Ventilating, 

and Air-Conditioning: Systems 

and Equipment: 2008 ASHRAE 

Handbook. American Society of 

Heating, Refrigerating and AirConditioning Engineers, Inc. 2008.

7. NAFA Guide to Air Filtration. National 

Air Filtration Association. 4th Edition. 

2007.

8. Ozone Generators that are sold as air 

cleaners: An assessment of effectiveness 

and health consequences. U.S. 

Environmental Protection Agency. 

http://www.epa.gov/iaq/pubs/

ozonegen.html 

9. Shaughnessy, R.J., and Sextro, R.G. 

2006. What Is an Effective Portable 

Air-Cleaning Device? A Review. Journal 

of Occupational and Environmental 

Hygiene. Vol. 3, pp. 169-181.

10. Weshler, C. J. 2006. Ozone’s Impact 

on Public Health: Contributions 

from Indoor Exposures to Ozone and 

Products of Ozone-Initiated Chemistry. 

Environmental Health Perspectives. Vol. 

114, No 10, pp. 1489-1496. 

11. Fugler, D., Browser, D., and Kwan, 

W. 2000. The effects of improved 

residential furnace filtration on 

airborne particles. ASHRAE 

Transactions 2000. pp. 317-326.

12. Offermann, F. J., Loisell, S.A., and 

Sextro, R.G. 1992. Performance of 

air cleaners in a residential forced air 

system. ASHRAE Journal. July 1992. 

Pp. 51-57.

13. Gravimetric and dust-spot procedures 

for method of testing air-cleaning devices 

used in general ventilation for removing 

particulate matter. ANSI/ASHRAE 

Standard 52.1-1992. American Society 

of Heating, Refrigerating and AirConditioning Engineers Inc. 1992.

14. HEPA and ULPA Filters. 

Recommended Practices and Standards 

IEST-RP CC001.4. Institute 

of Environmental Sciences and 

Technology. Mt. Prospect, Illinois. 

1993.

15. Method of testing general ventilation 

air-cleaning devices for removal efficiency 

by particle size. ANSI/ASHRAE 

Standard 52.2-2007. American Society 

of Heating, Refrigerating and AirConditioning Engineers, Inc. 2007.

16. Ventilation and acceptable indoor air 

quality in low-rise residential buildings. 

ANSI/ASHRAE Standard 62.2.-

2007. American Society of Heating, 

Refrigerating, and Air-Conditioning 

Engineers, Inc. 2007.

17. Fisk, W.J., Faulkner, D., Palonen, 

J., and Seppanen, O. Particle air 

filtration in HVAC supply air streams: 

performance and cost implications of 

various methods of reducing indoor 

concentrations of particles. HPAC 

Engineering, Heating/Piping/Air 

Conditioning. July 2003.

18. Method for Measuring Performance 

of Portable Household Electric Room 

Air Cleaners. Standard ANSI/AHAM 

AC-1-2006. Association of Home 

Appliance Manufacturers (AHAM). 

2006.

19. Directory of Certified Room Air 

Cleaners. Edition No.1 – January 

2008. Association of Home Appliance 

Manufacturers (AHAM). 

http://www.aham.org. On line 

searchable directory 

http://www.cadr.org/consumer/

certified.html. Toll-free phone number 

800-267-3138. 2004. 

20. Bascom, R., Fitzgerald, T. K., 

Kesavanathan, J., and Swift, D. L. 

1996. A portable air cleaner partially 

reduces the upper respiratory response 

to sidestream tobacco smoke. Appl. 

Occup. Environ. Hyg. Vol.11, No. 6, 

pp. 553-559. 

21. Battistoni, P., and Fava, G. 1993. 

Electrostatic air cleaner in the 

control of tobacco smoke. Intern. J. 

Environmental Studies Vol. 44 

pp. 299-305.

22. Air Cleaners: Behind the hype.

Consumer Reports. Vol. 68, No. 10, pp. 

26-29. October, 2003.

23. Custovic, A., Simpson, A., Pahdi, H., 

Green, R.M., Chapman, M.D., and 

Woodcock, A. 1998. Distribution, 

aerodynamic characteristics, and 

removal of the major cat allergen Fed 

d I in British homes. Thorax, British 

Medical Association, Vol. 53, pp. 33-38.

24. De Blay, F., Chapman, M.D., and 

Platts-Mills, A.E. 1991. Airborne Cat 

Allergen (Fel d I): Environmental 

control with the cat in situ. American 

Review of Respiratory Disease, Vol.143,

pp. 1334-1339.

25. Green, R., Simpson, A., Custovic, 

A., Faragher, B., Chapman, M., and 

Woodcock, A. 1999. The effect of air 

filtration on airborne dog allergen. 

Allergy. Vol. 54, pp. 484-488.

26. Clearing the Air: Asthma and Indoor 

Air Exposures. Committee on the 

Assessment of Asthma and Indoor 

Air, Division of Health Promotion 

and Disease Prevention, Institute of 

Medicine. 2000.
A Summar y of Available Information

www.epa.gov/iaq 31

27. Van der Heide, S., Aalderen, W. M.C., 

Kauffman, H.F., Dubois, A.E.J., and 

de Monchy, J.G.R. 1999. Clinical 

effects of air cleaners in homes of 

asthmatic children sensitized to pet 

allergens. Journal of Allergy and Clinical 

Immunology. Vol. 104, No. 2, pp. 

447-451.

28. Wood, R. A., Johnson, E.F., Van Natta, 

M.L., Chen, P.H., and Eggleston, P.A. 

1998. A placebo-controlled trial of 

a HEPA air cleaner in the treatment 

of cat allergy. American Journal of 

Respiratory and Critical Care Medicine 

Vol. 158, pp. 115-120.

29. New Concerns about Ionizing Air 

Cleaners. Consumer Reports. Pp. 22-25. 

2005.

30. Field test methods to measure 

contaminant removal effectiveness of 

gas-phase air filtration equipment – 

phase II, 791-RP (1098-TRP). SPC 

145. American Society of Heating, 

Refrigerating and Air-Conditioning 

Engineers, Inc. 2004.

31. Miller, J.F., Rodberg, J.A., and 

Keller, G.H. 1991. Benzene 

adsorption onto activated carbon and 

benzene destruction by potassium 

permanganate-loaded alumina.

Union Carbide Chemicals and Plastics 

Company. South Charleston, WV.

32. Ramanathan, K., Debler, V.L., 

Kosusko, M., Sparks, L.E. 1988.

Evaluation of control strategies for 

volatile organic compounds in indoor 

air. Environmental Progress. Vol. 7, No. 

4, pp. 230-235. 

33. Guidelines for environmental infection 

control in health care facilities. U.S. 

Department of Health and Human 

Services. Centers for Disease Control 

and Prevention. 2003.

34. Kowalski, W.J. and Bahnfleth, W. 

1998. Airborne respiratory diseases 

and mechanical systems for control 

of microbes. Heating/Piping/Air 

Conditioning. Vol. 70, No. 7, pp. 

34-48.

35. Kemp, S.J., Kuehn, T.H., 

and Pui, D.Y.H. 1995. Filter 

Collection efficiency and growth of 

microorganisms on filters loaded with 

outdoor air. ASHRAE Transaction 3853 

(RP-625). Pp. 228-237.

36. Scheir, R., and Fencl, F. 1996. Using 

UVC technology to enhance IAQ.

Heating/Piping/Air Conditioning. 

Vol, 68.

37. Jankowska, E., Reponen, T., Willeke, 

K., Grinshpun, S.A., and Choi, K. J. 

2000. Collection of fungal spores on 

air filters and spore reentrainment from 

filters into air. J. Aerosol. Sci. Vol. 31,

No.8, pp. 969-978.

38. VanOsdell, D., and Foarde, K. 2002. 

Defining the effectiveness of UV lamps 

installed in circulating air ductwork. 

Prepared for the Air-Conditioning 

and Refrigeration Technology 

Institute, RTI International. ARTI21CR/610-40030-01.

39. Kowalski, W.J. and Bahnfleth, W. 

2000. UVGI design basics for air and 

surface disinfection. Heating/Piping/

Air Conditioning. Vol. 72, No. 1, pp. 

100-110.

40. Levetin, E., Shaughenessy, R., Rogers, 

C., and Scheir, R. 2001. Effectiveness 

of germicidal UV radiation for 

reducing fungal contamination 

within air-handling units. Applied and 

Environmental Microbiology. Vol. 67, 

No. 8, pp. 3712-3715.

41. Cundith, C.J., Kerth, C.R., Jones, 

W.R., McCaskey, T.A., and Kuhlers, 

D.L. 2002. Microbial reduction 

efficiencies of filtration, electrostatic 

polarization, and UV components of a 

germicidal air-cleaning system. Journal 

of Food Science. Vol. 67, No.6, pp. 

2278-2281.

42. Xu, P., Peccia, J., Fabian, P., Martyny, 

J.W., Fennelly, K.P., Hernandez, M., 

and Miller, S.L. 2002. Efficacy of 

ultraviolet germicidal irradiation of 

upper room air in inactivating airborne 

bacterial spores and mycobacteria 

in full scale studies. Atmospheric 

Environment. Vol. 37, pp. 405-419.

43. Menzies, D., Pasztor, J., Rand, T., 

and Bourbeau, J. 1999. Germicidal 

ultraviolet irradiation in airconditioning systems: effect on office 

worker health and wellbeing: A pilot 

study. Occupational and Environmental 

Medicine. Vol. 56, pp. 397-402.

44. Menzies, D., Popa, J., Hanley, J.A., 

Rand, T., and Milton, D.K. 2003. 

Effect of ultraviolet germicidal lights 

installed in office ventilation systems 

on workers’ health and wellbeing: 

double-blind multiple crossover trial. 

The Lancet. Vol. 362, pp. 1785-1791.

45. Mold Remediation in Schools 

and Commercial Buildings. U.S. 

Environmental Protection Agency. EPA 

402-K-01-001. March 2001.

46. Germicidal lamps and applications. 

Phillips Lighting Division. 1985. 

47. Disinfection by UV – radiation. Phillips 

Lighting Division. 1992. 

48. Henschel, B. 1998. Cost analysis of 

activated carbon versus photocatalytic 

oxidation for removing organic 

compounds from indoor air. J. Air & 

Waste Management Association. Vol.48,

No. 10, pp. 985-994.

49. Tompkins, D.T., Lawnicki, B.J., 

Zeltner, W.A., and Anderson, M.A. 

2003. Evaluation of photocatalysis for 

gas-phase air cleaning - Part 1: Process, 

Technical and Sizing Considerations. 

ASHRAE Research Project 1134-

RP. Conducted: December 1999 

– November 2002, University of 

Wisconsin.

50. Tompkins, D.T., Lawnicki, B.J., 

Zeltner, W.A., and Anderson, M.A. 

2003. Evaluation of photocatalysis 

for gas-phase air cleaning - Part 2: 

Economics and Utilization. ASHRAE 

Research Project 1134-RP. Conducted: 

December 1999 – November 2002, 

University of Wisconsin.

51. Chen, W., Zhang, J., and Zhang, Z. 

2005. Performance of air cleaners for 

removing multiple volatile organic 

compounds in indoor air. ASHRAE 

Transactions 111 (2005), pp. 1101-

1114. 

52. Turchi, C.S., Rabago, R., Jassal, A. 

1995. Destruction of volatile organic 

compound (VOC) emissions by 

photocatalytic oxidation (PCO): Bench 

scale test results and cost analysis.

Sematech. Technology Transfer # 

95082935A-ENG.
R E S I D E N T I A L A I R C L E A N E R S

32 www.epa.gov/iaq

53. Zorn, M.E., Tompkins, D.T., Zeltner, 

W.A., and Anderson, M.A. 1999. 

Photocatalytic oxidation of acetone 

vapor on TiO2/ZrO2 thin films.

Applied Catalysis B: Environmental. Vol. 

23, pp. 1-8.

54. Zorn, M.E. 2003. Photocatalytic 

oxidation of gas-phase compounds 

in confined areas: investigation 

of multiple components systems. 

Proceedings of the 13th Annual 

Wisconsin Space Conference. August 

14-15, 2003. 

55. Jardim, W. F., and Alberci, R.M. 1997. 

Photocatalytic destruction of VOC in 

the gas-phase using titanium dioxide. 

Applied Catalysis B: Environmental. Vol. 

14. No 1, pp. 55-68.

56. Blake, D.M., Jacoby, W.A., and 

Nimlos, M. 1992. Identification of 

by-products and intermediates in the 

photocatalytic oxidation of gas-phase 

trichloroethylene. Proceedings. 6th 

International Symposium on Solar 

Thermal Concentrating Technologies, 

September 28 – October 2, 1992, Vol. 

2. 

57. Alberci, R.M., Mendes, M.A., Jardin, 

W.F., and Eberlin, M.N. 1998. Mass 

spectrometry on-line monitoring 

and MS2 product characterization of 

TiO2/UV photocatalytic degradation 

of chlorinated volatile organic 

compounds. Journal of the American 

Society for Mass Spectrometry. Vol. 9. No 

12, pp. 1321-1327.

58. Reisman, R.E., Mauriello, P.M., Davis, 

G.B., Georgitis, J.W., and DeMasi, 

J. 1990. A double-blind study of 

the effectiveness of a high-efficiency 

particulate air (HEPA) filter in the 

treatment of patients with perennial 

allergic rhinitis and asthma. J. Allergy 

Clin. Immunol. Vol. 85, No. 6, pp. 

1050-1057.

59. Morgan, W.J., Crain, E.F., Gruchalla, 

R.S., O’Connor, G.T., Kattan, 

M. 2004. Results of Home-Based 

Environmental Intervention among 

Urban Children with Asthma. The New 

England Journal of Medicine, 352, pp. 

1068-1080.

60. Wood, R. 2002. Air-filtration devices 

in the control of indoor allergens.

Current Allergy and Asthma Reports. 

Vol. 2, pp. 397-400.

61. Luczynska, C.M., Li, Y., Chapman, 

D., and Platts-Mills, T.A.E. 1988. 

Airborne concentrations and particle 

size distribution of allergen derived 

from domestic cats (Felis domesticus): 

Measurements using cascade impactor, 

liquid impinger and a two site 

monoclonal antibody assay for Fel d I. 

Presented to the American Academy of 

Allergy Meeting in Los Angeles. March 

4, 1988.

62. Dorsey, J. and Davidson, J.H. 1994. 

Ozone production in electrostatic air 

cleaners with contaminated electrodes. 

IEEE Transactions on Industry 

Applications, Vol. 30, No. 2, pp. 370-

376.

63. Offermann, F.J., Sextro, R.G., Fisk, 

W.J., Grimsrud, D.T., Nazaroff, W.W., 

Nero, A.V., Revzan K.L., and Yater J. 

1985. Control of respirable particles in 

indoor air with portable air cleaners. 

Atmospheric Environment. Vol. 19, No. 

11, pp. 1761-1771.

64. Melandari, C., Tarrani, G., Prodi, V., 

De Zaiacomo, T., Formignani, M., and 

Lombardi, C.C. 1983. Deposition of 

charged particles in the human airways. 

J. Aerosol Sci., Vol. 14, pp. 184-186.

65. Clearing the air: A guide to reducing 

indoor pollution. Consumer Reports. p. 

41-49. February, 2002.
A Summar y of Available Information

www.epa.gov/iaq 33

ADDITIONAL INFORMATION

Visit our Web site for any additional information about indoor air quality at http://www.epa.gov/iaq.

An electronic copy of this document Residential Air Cleaners (Second Edition) A Summary of Available Information, 

EPA 402-F-09-002, August 2009, is available at http://www.epa.gov/iaq/pubs/residair.html

An electronic copy of the EPA brochure Guide to Air Cleaners in the Home, EPA 402-F-08-004, May 2008, 

addressed to the general public is available at http://www.epa.gov/iaq/pdfs/aircleaners.pdf

For hard copies of Guide to Air Cleaners in the Home and other EPA indoor air publications, contact:

National Service Center for Environmental Publications (NSCEP) 

P.O. Box 42419

Cincinnati, OH 42419

phone: (800) 490-9198 

fax: (301) 604-3408 

Web site: http://www.epa.gov/nscep

ADDITIONAL RESOURCES

Residential Air-Cleaning Devices – Types, Effectiveness and Health Impact. American Lung Association. 

Web site: http://www.lungusa.org

Air-Cleaning Devices for the Home, Frequently Asked Questions. California Air Resources Board and the California 

Environmental Protection Agency. 

Web site: http://www.arb.ca.gov/research/indoor/acdsumm.pdf

Survey of the Use of Ozone-generating Air Cleaners by the California Public. California Air Resources Board and the 

California Environmental Protection Agency, January 2007. 

Web site: http://www.arb.ca.gov/research/apr/past/05-301.pdf

Hodgson, A.T., Hugo Destaillats, H., Hotchi, T., Fisk, W.J. 2007. Evaluation of a Combined Ultraviolet 

Photocatalytic Oxidation (UVPCO)/Chemisorbent Air Cleaner for Indoor Air Applications. Lawrence Berkeley 

National Laboratory. Paper LBNL-62202. 

Hodgson, A.T., Sullivan, D.P., Fisk, W.F. September 30, 2005. Evaluation of Ultra-Violet Photocatalytic Oxidation 

(UVPCO) for Indoor Air Applications: Conversion of Volatile Organic Compounds at Low Part-per-Billion 

Concentrations. Lawrence Berkeley National Laboratory. Paper LBNL-58936.