Residential Air Cleaners

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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


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U.S. Environmental Protection Agency

Ofce o Air and Radiation

Indoor Environments Division

1200 Pennsylvania Avenue, NWMail code: 6609J

Washington, DC 20460

www.epa.gov/iaq

DisclaimerThis document has been reviewed in accordance with U.S. Environmental Protection Agency policy and approvedor publication. Mention o trade names, products, or services does not convey, and should not be interpreted asconveying ocial EPA approval, endorsement or recommendation.


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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 ..................................................... 13Portable 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


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

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SUMMARY

Indoor air pollution is among the top veenvironmental health risks. Usually the best wayto address this risk is to control or eliminatethe sources o pollutants and ventilate a homewith clean outdoor air. But opportunities orventilation may be limited by weather conditionsor by contaminants in the outdoor air.

I the usual methods o addressing indoor airpollution are insucient, air-cleaning devices maybe useul. Air lters and other air-cleaning devicesare designed to remove pollutants rom indoor air.Some are installed in the ductwork o a homescentral heating, ventilating, and air-conditioning(HVAC) system to clean the air in the entire

house. Portable room air cleaners can be used toclean the air in a single room or in specic areas,but they are not intended to lter the air in thewhole house. Air-cleaning devices are categorizedby the type o pollutantsparticulate andgaseousthat the device is designed to removeor destroy.

Two types o air-cleaning devices can removeparticles rom the air: mechanical air lters andelectronic air cleaners.

Mechanical air lters, such as high eciencyparticulate air (HEPA) lters, remove particlesby capturing them on lter materials. Mostmechanical air lters are good at capturing largerairborne particlessuch as dust, pollen, somemold spores, and animal danderand particlesthat contain dust mite and cockroach allergens.But because these particles settle rather quickly,mechanical air lters are not very good atcompletely removing them rom indoor areas.

Electronic air cleaners, such as electrostaticprecipitators, use a process called electrostaticattraction to trap particles. Ion generators, orionizers, disperse charged ions into the air. Theseions attach to airborne particles, giving them acharge so they can attach to nearby suraces suchas walls or urniture, or to one another, and settleaster. However, some electronic air cleaners canproduce ozone, a lung irritant.

Another type o air-cleaning device is a gas-phaselter designed to remove gases and odors by eitherphysical or chemical processes.

Gas-phase air lters remove gaseous pollutantsby using a material called a sorbent, such asactivated carbon, to adsorb pollutants. Becausethese lters are targeted at one or a limitednumber o gaseous pollutants, they will notreduce concentrations o pollutants or which theywere not designed. None are expected to removeall o the gaseous pollutants in the air o a typicalhome. Gas-phase lters are much less common inhomes than are particle air lters. One reason maybe the lter can become overloaded quickly and

may need to be replaced oten.

Three types o air cleaners on the market aredesigned to deactivate or destroy indoor airpollutants: ultraviolet germicidal irradiation(UVGI) cleaners, photocatalytic oxidation (PCO)cleaners, and ozone generators sold as air cleaners.

UVGI cleaners use ultraviolet radiation rom UVlamps that may destroy biological pollutants suchas viruses, bacteria, and molds that are airborneor growing on HVAC suraces (e.g., cooling

coils, drain pans, or ductwork). UVGI cleanersshould be used with, but not as a replacement or,ltration systems. Typical UVGI cleaners usedin homes have limited eectiveness in killingbacteria and molds. Eective destruction o someviruses and most mold and bacterial spores usuallyrequires much higher UV exposures than a typicalhome unit provides.

PCO cleaners use UV lamps along with asubstance, called a catalyst, that reacts with the

light. These cleaners are designed to destroygaseous pollutants by changing them intoharmless products, but they are not designedto remove particulates. The useulness o PCOcleaners in homes is limited because currentlyavailable catalysts are ineective in destroyinggaseous pollutants in indoor air.


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A Summary of Available Informat

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Ozone generators use UV lamps or electricaldischarges to produce ozone that reacts withchemical and biological pollutants and transormsthem into harmless substances. Ozone is a potentlung irritant, which in concentrations that do notexceed public health standards, has little potential

to remove indoor air contaminants. Thus ozonegenerators are not always sae and eective incontrolling indoor air pollutants.

Portable air cleaners generally contain a anto circulate the air and use one or more o theair-cleaning technologies discussed above. Theymay be an option i a home is not equipped witha urnace or a central air-conditioning system.Many portable air cleaners have moderate to largeair delivery rates or small particles. However,

most o the portable air cleaners on the market donot have high enough air delivery rates to removelarge particles such as pollen and particles thatcontain dust mite and cockroach allergens romtypical-size rooms.

Several other actors should be considered whenmaking decisions about using air-cleaning devices.

X Installation: In-duct air-cleaning devices havecertain installation requirements that must bemet, including sucient access or inspectionduring use, repairs, and maintenance.

X Major costs: These costs include the initialpurchase price and the cost o maintenance(such as cleaning or replacing lters and parts)and operation (electricity).

X Odors: Air-cleaning devices designed toremove particles cannot control gases andsome odors. The odor and many o thecarcinogenic gas-phase pollutants romtobacco smoke, or example, will remain.

X Soiling o walls and other suraces: Typical

ion generators are not designed to removerom the air the charged particles that theygenerate. These charged particles may settleon, and soil, walls and other room suraces.

X Noise: Noise may be a problem with portableair cleaners that contain ans. Portable aircleaners that do not have ans tend to bemuch less eective than units that have them.

The ability to remove some airborne pollutants,

including microorganisms, is not, in itsel, anindication o an air-cleaning devices abilityto reduce adverse health eects rom indoorpollutants. Although air-cleaning devices mayhelp reduce levels o smaller airborne particlesincluding those associated with allergens, theymay not reduce adverse health eects, especially insensitive populations such as children, people whohave asthma and allergies, and the elderly. Forexample, the evidence is weak that air-cleaningdevices are eective in reducing asthma symptoms

associated with small airborne particles such asthose that contain cat and dust mite allergens.There are no studies linking the use o gas-phaseltration, UVGI systems, or PCO systems inhomes to reduced health symptoms insensitive populations.


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The best way to address residential indoor airpollution usually is to control or eliminate thesource o the pollutants and to ventilate the home

with clean outdoor air. But ventilation may belimited by weather conditions or the levels ocontaminants in the outdoor air.

I the usual methods o dealing with indoor airpollutants are insucient, air-cleaning devices maybe useul. Air lters and other air-cleaning devicesare designed to remove pollutants rom indoorair. They can be installed in the ductwork o mosthome heating, ventilating, and air-conditioning(HVAC) systems to clean the air in the entirehouse, or the same technology can be used inportable air cleaners that clean the air in singlerooms or specic areas. Most air-cleaning devicesare designed to remove particles or gases, but somedestroy contaminants that pass through them.

This publication ocuses on air cleaners orresidential use; it does not address air cleaners usedin large or commercial structures such as oce

INTRODUCTION

buildings, schools, large apartment buildings,or public buildings. It should be particularlyuseul to residential housing design proessionals,

public health ocials, and indoor air qualityproessionals. In addition to providing generalinormation about the types o pollutants aectedby air cleaners, this document discusses:

X The eectiveness o air cleaning compared toother strategies, such as source control andventilation, or reducing indoor air pollutants.

X The types o air-cleaning devices available.

X Guidelines that can be used to compare air-cleaning devices.

X The eectiveness o air-cleaning devices inremoving indoor air pollutants.

X General inormation on the health eects oindoor air pollutants.

X Additional actors to consider when decidingwhether to use an air-cleaning device.

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

particular brands o home air-cleaning devices. While some home air-cleaning devices may be useul insome circumstances, EPA makes no broad endorsement o their use, nor specic endorsement o anybrand or model. This document describes the perormance characteristics o several types o air cleanerssold or in-home use.

Federal pesticide law requires manuacturers o ozone generators to list an EPA establishment numberon the products packaging. This number merely identies the acility that manuactured the product.Its presence does not imply that EPA endorses the product, nor does it imply that EPA has ound theproduct to be sae or eective.

Some portable air cleaners sold in the consumer market are ENERGY STAR qualied. Please note theollowing disclaimer on their packaging: This product earned the ENERGY STAR by meeting strict

energy eciency guidelines set by EPA. EPA does not endorse any manuacturer claims o healthierindoor air rom the use o this product.


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INDOOR AIR POLLUTANTS

There are two categories o indoor air pollutantsthat can aect the quality o air in a home:particulate matter and gaseous pollutants.

Particulate matter (PM) is composed omicroscopic solids, liquid droplets, or a mixtureo solids and liquid droplets suspended in air. Alsoknown as particle pollution, PM is made up o anumber o components, including acids such asnitric and suluric acids, organic chemicals, metals,soil or dust particles, and biological contaminants.Among the particles that can be ound in ahome are:

X Dust as solid PM or umes and smoke, which

are mixtures o solid and liquid particles.X Biological contaminants, including viruses,

bacteria, pollen, molds, dust mite andcockroach body parts and droppings, andanimal dander.

Particles come in a wide range o sizes. Smallparticles can be ne or coarse. O primary concernrom a health standpoint are ne particles that havea diameter o 2.5 micrometers (m) or less. Theseparticles (described as respirable) can be inhaled;

they penetrate deep into the lungs where theymay cause acute or chronic health eects. Coarseparticles, between 2.5 and 10 m in diameter,usually do not penetrate as ar into the lungs; theytend to settle in the upper respiratory tract. Largeparticles are greater than 10 m in diameter, orroughly one-sixth the width o a human hair. Theycan be trapped in the nose and throat and expelledby coughing, sneezing, or swallowing.

Respirable particles are directly emitted into indoorair rom a variety o sources including tobacco

smoke, ozone reactions with emissions rom indoorsources o organic compounds, chimneys andfues that are improperly installed or maintained,unvented combustion appliances such as gas stovesand kerosene or gas space heaters, woodstoves, andreplaces. This category o particles also includesviruses and some bacteria.

Among the smaller biological particles oundin a home are some bacteria, mold ragments

and spores, a signicant raction o cat and dogdander, and a small portion o dust mite bodyparts and droppings. Larger particles include dust,

pollen, some mold ragments and spores, a smallerraction o cat and dog dander, a signicantraction o dust mite body parts and cockroachbody parts and droppings, and skin fakes.

Gaseous pollutants include combustion gasesand organic chemicals that are not attached toparticles. Hundreds o gaseous pollutants havebeen detected in indoor air.

Sources o indoor combustion gases such ascarbon monoxide and nitrogen dioxide includecombustion appliances, tobacco smoke, andvehicles whose exhaust inltrates rom attachedgarages or the outdoors.

Sources o airborne gaseous organic compoundsinclude tobacco smoke, building materialsand urnishings, and products such as paints,adhesives, dyes, solvents, caulks, cleaners,deodorizers, cleaning chemicals, waxes, hobbyand crat materials, and pesticides. Organiccompounds may also come rom cooking ood;

rom human, plant, and animal metabolicprocesses; and rom outdoor sources. Someelectronic air cleaners and laser printers maygenerate the lung irritant ozone by design or as aby-product.

Radon is a colorless, odorless, radioactive gasthat can be ound in indoor air. It comes romuranium in natural sources such as rock, soil,ground water, natural gas, and mineral buildingmaterials. As uranium breaks down, it releasesradon, which in turn produces short-lived

radioactive particles called progeny, some owhich attach to dust particles. Radon progenymay deposit in the lungs and irradiate respiratorytissues. Radon typically moves through theground and into a home through cracks and holesin the oundation. Radon may also be presentin well water and can be released into the airwhen that water is used or showering and otherhousehold activities. In a small number o homes,building materials also can give o radon.1


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THREE STRATEGIES TO REDUCE INDOOR AIR POLLUTANTS

Three basic strategies to reduce pollutantconcentrations in indoor air are source control,ventilation, and air cleaning.

Source control eliminates individual sources opollutants or reduces their emission. It is usuallythe most eective strategy or reducing pollutants.There are many sources o pollutants in the homethat can be controlled or removed.2 For example,solid wood or alternative materials can be used inplace o pressed wood products that are likely tobe signicant sources o ormaldehyde. Smokerscan smoke outdoors. Combustion appliances canbe adjusted to decrease their emissions.

Ventilation isalso a strategy or decreasing indoorair pollutant concentrations. It exchanges airbetween the inside and outside o a building. Theintroduction o outdoor air is important or goodair quality. In a process known as inltration,outdoor air fows into the house throughopenings, joints, and cracks in walls, foors, andceilings, and around windows and doors. Naturalventilation describes air movement through openwindows and doors. Most residential orced air-heating systems and air-conditioning systems donot bring outdoor air into the

house mechanically. Two primaryventilation methods can be usedin most homes: general ventilationand local ventilation.

General ventilation o theliving space, by way oinltration, natural ventilation,or mechanical ventilation,brings outdoor air indoors,circulates air throughout thehome, and exhausts polluted

air outdoors. Although limited by weatherconditions, this method removes or dilutesindoor airborne pollutants, thereby reducing

the level o contaminants and improving indoorair quality (IAQ). Special consideration shouldbe given to the outdoor air used or ventilation.It should be o acceptable quality and shouldnot contain pollutants in quantities that wouldbe considered objectionable or harmul iintroduced indoors. The use o ventilationto reduce indoor air pollutants should beevaluated careully where there may be outdoorsources o pollutants.

Localized ventilation by means o exhaust ansin bathrooms and kitchens, and in some casesby open windows and doors, removes excessmoisture and strong, local pollutants and keepsthem rom spreading to other areas. Using

exhaust ans increases the amount o outdoorair that enters a house.

Advanced designs or new homes are starting toadd a mechanical eature that brings outdoorair into the home through the HVAC system.Some o these designs include energy ecientheat recovery ventilators to mitigate the cost ocooling and heating this air during the summerand winter. 3, 4

Air cleaningmay be useul whenused along with source controland ventilation, but it is not asubstitute or either method. Theuse o air cleaners alone cannotensure adequate air quality,particularly where signicantsources are present and ventilationis insucient. While air cleaningmay help control the levels oairborne particles including thoseassociated with allergens and,

in some cases, gaseous pollutants in a home, aircleaning may not decrease adverse health eectsrom indoor air pollutants.

The use o air

cleaners alone

cannot ensure

adequate air

quality.


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TYPES OF AIR CLEANERS

Various technologies can be used in air-cleaningdevices. Filtration and electrostatic attractionare eective in removing airborne particles.Adsorption or chemisorption captures somegaseous and vaporous contaminants. Some aircleaners use ultraviolet light (UV) technology.Ultraviolet germicidal irradiation (UVGI) hasbeen used to kill some microorganisms growingon suraces. Photocatalytic oxidation (PCO),another UV light technology under development,has the potential to destroy gaseous contaminants.Ozone-generating devices sold as air cleaners useUV light or corona discharge and are meant tocontrol indoor air pollutants.

Table 1 provides a brie summary o air-cleaningtechnologies and the pollutants they are designedto control.

Some air-cleaning devices are designed to beinstalled in the ductwork o HVAC systems or tobe used in portable, stand-alone units.

In-ductor whole-house air-cleaning devicestypically are installed in the return ducts o HVACsystems, as shown in Figure 1. The typical urnaceair lter is a simple air cleaner that captures

particles in the airstream to protect an motors,heat exchangers, and ducts rom soiling. Such

AIR-CLEANING

TECHNOLOGIES

POLLUTANTS

ADDRESSEDLIMITATIONS

Filtration

Air filters ParticlesIneffective in removing larger particles because most

settle quickly from the air and never reach the filters.

Gas-phase

filtersGases

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

lters are not designed to improve indoor airquality, but the HVAC system can be upgraded byusing more ecient air lters to trap additionalparticles. Other air-cleaning devices such aselectrostatic precipitators, UV lamps, and gas-phase lters use sorption and chemical reactionand are sometimes used in the ductwork o homeHVAC systems.

The ans in residential HVAC systems mayoperate intermittently or continuously.Continuous operation improves air circulationand air cleaning, but this operation mode alsoincreases electrical energy consumption and costs.5

Portable air cleaners are available as smalltabletop units and larger console units. They areused to clean the air in a single room, but notin an entire house. The units can be moved towherever continuous and localized air cleaningis needed. Larger console units may be useul inhouses that are not equipped with orced air-heating systems and air-conditioning systems.Portable air cleaners generally have a an tocirculate the air and a cleaning device such as amechanical air lter, electrostatic precipitator, iongenerator, or UV lamp. Some units marketed as

having the quietest operation may have no an;however, units that do not have a an typically are


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much less eective than units that have one. Aircleaners may also have a panel lter with bondedne particles o activated carbon, or an activatedcarbon lter encased in a rame, to remove gasesand odors. Some portable air cleaners reerred toas hybrid air cleaners use a combination o two ormore o the devices discussed above.

In this publication, air cleaners are categorized bythe types o pollutants, particulate and gaseous,that the devices are designed to remove ordestroy.6, 7

Removal of ParticlesAir lters are designed to remove particulatepollutants rom indoor air. Their perormancedepends not only on the airfow rate through the

lter media and the lter eciency, but also onactors such as the:Particle size and mass.

Amount o dust on the air lter.

Airfow rate, velocity, path, and resistance

through the lter media.Mixing o air leaving the lter with the air in

the room.

Leakage rate o air that bypasses the air lter.

Types of Particle-Removal Air FiltersTwo general types o particle removal air-cleaningdevices are available: mechanical air lters andelectronic air cleaners. They are classied by themethod employed to remove particles o varioussizes rom the air.

Mechanical air lters installed in a centralHVAC system or in a portable air cleanercapture particles on lter media. Particles eitherbecome trapped in the bers o the lter or stickto the lter because o an electrostatic charge.Mechanical air lters come in two major types:fat and pleated.

Flator panel fltersgenerally consist o coarseglass bers, coated animal hair, vegetable bers,synthetic bers (such as polyester or nylon),

synthetic oams, metallic wools, or expandedmetals and oils. The lter media may be treatedwith a viscous substance, such as oil, that causesparticles to stick to the bers. Flat lters alsomay be made o three types o permanentlyelectrostatically charged material: resin wool,a plastic lm or ber called electret, or anelectrostatically sprayed polymer. Their staticcharge attracts and captures particles. The berso electret lters are somewhat larger than thebers o other fat lters, resulting in relatively low

pressure drop and greater eciency in lteringsmaller particles. The eciency o electret ltersdecreases as the media become loaded withparticles.

Pleatedor extended surace fltersare generally moreecient than fat lters in capturing respirableparticles. Pleating the lter medium increasessurace area, reduces air velocity, and allows theuse o smaller bers and increased packing densityo the lter without a large drop in airfow 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


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A wire rame in the orm o a pocket or V-shapedcardboard separators may be used to maintain thepleat spacing. The media used in pleated lters areber mats, bonded glass bers, synthetic bers,cellulose bers, wool elt, and other cotton-polyester material blends.

High eciency particulate air (HEPA) lters area type o extended surace lter. HEPA ltersusually are made o submicron glass bers andhave a texture similar to blotter paper. They alsohave a larger surace area and remove respirableparticles more eciently than pleated lters.

Electronic air cleaners use a process calledelectrostatic attraction to trap charged particles.There are two types o electronic air cleaners:

electrostatic precipitators and ion generators.

Electrostatic precipitators have an ionizationsection and a collecting plate section, both owhich use an external power source. The aircleaner draws air through the ionization section,where particles obtain an electrical charge. Thecharged particles accumulate on a series o fatplates called a collector that is oppositely charged.Cleaning the collector plates is essential tomaintaining adequate perormance.

Ion generators, or ionizers, disperse charged ionsinto the air, similar to an electrostatic precipitator,but ionizers do not have collecting plates. Theyproduce ions by means o corona discharge orUV light. The ions attach to particles and givethem a charge so they adhere to nearby suracessuch as walls, urniture, and draperies, or combinewith other particles and settle on room suraces.Ion generators are the simplest orm o electronicair cleaner and come in tabletop, portable, andceiling mounted units.

Like mechanical lters, electronic air cleanerscan be installed in HVAC systems or used inportable units. Although electronic air cleanersremove small particles, they do not remove gasesor odors. And because electronic air cleanersuse high voltage to generate ionized elds, theycan produce ozone, either as a by-product or bydesign.8 Residential indoor ozone concentrationsmay be aected by the amount o ozone emitted

by electronic air cleaners, which varies amongmodels. Even at concentrations below publichealth standards, ozone reacts with chemicalsemitted by such common indoor sources ashousehold cleaning products, air resheners,deodorizers, certain paints, polishes, wood

fooring, carpets, and linoleum. The chemicalreactions produce harmul by-products that maybe associated with adverse health eects in somesensitive populations. The ozone reaction by-products that may result include ultrane particles(smaller than 0.1 m in diameter), ormaldehyde,ketones, and organic acids.8, 9, 10 Concerns aboutozone and ozone-generating devices are discussedin the EPA document Ozone Generators that areSold as Air Cleaners, posted on the EPA Web siteat www.epa.gov/iaq/pubs/ozonegen.html.

Defining Efficiency and EffectivenessTo choose air-cleaning devices and use themproperly, it is important to understand thedierence between eciency and eectiveness.The eciency o an air-cleaning device, usuallyexpressed as a percentage, is a measure o itsability to remove airborne particles or gaseouspollutants rom the air that passes through it. Theeectiveness o an air-cleaning device is a measureo its ability to reduce airborne particle or gaseouspollutant concentrations in an occupied space.

The eciency o air lters used in ducts oHVAC systems or in portable air cleaners variesbased on the airfow rate and the particulatematter load. The eectiveness o an air-cleaningdevice in removing pollutants rom an occupiedspace depends on three actors: its eciency,the amount o air being ltered, and the paththat the clean air ollows ater it leaves the lter.For example, a lter may remove 99 percent othe particles rom the air that passes through

it (i.e., have 99 percent eciency). However,i the airfow rate through the lter is only 10cubic eet per minute (cm) in a typical room oapproximately 1,000 cubic eet (e.g., 10 x 12x 8), the lter will be relatively ineective atremoving particles rom the air (i.e., 10 times lesseective than i the airfow rate were 100 cm).


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Higher eciency lters remove larger and smallerairborne particles more eciently. Homeownersshould take care to properly install them inHVAC systems and make sure that leakage o airbypassing the lter is minimized. The higher alters eciency, the more attention must be paid

to its sealed installation because increased airfowresistance is more likely to create leaks. Air ltereectiveness may be substantially reduced i airleaks through a poorly installed lter rame andits holding system.11, 12 Leakage o air bypassing aHEPA lter used in a portable, stand-alone unitmay also reduce the lters expected eciency.Eectiveness may be decreased i air exiting anexhaust grille o the HVAC system is not wellmixed with room air beore re-entering thesystem. This situation can occur i air return and

intake vents are too close together.

Air Filters - Available Guidance for Their

ComparisonSeveral standardized methods have beendeveloped to measure the eciency o dierenttypes o air lters installed in the ductwork oHVAC systems. They can be used to comparethe perormance o air lters made by dierentcompanies. The American Society o Heating,Rerigerating and Air-Conditioning Engineers(ASHRAE) and the Institute o Environmental

Sciences and Technology (IEST) have publishedvoluntary standards or rating air lters. TheIEST is now the recognized standard-settingorganization or the ormer Military Standard 282developed by the U.S Department o Deense orrating HEPA lters. The standards do not rate theair lters eectiveness; rather, they compare theperormance o various lters.

Particle removal eciency can be assessed byour standard methods: the weight arrestance

test, atmospheric dust spot eciency test, dioctylphthalate (DOP) penetration test, and particlesize removal eciency (PSE) test.

The weight arrestance test,13 dened inASHRAE Standard 52.1-1992, * is generally

used to evaluate low eciency lters designedto remove the largest and heaviest particles.These lters are commonly used in residentialurnaces and air-conditioning systems to protectsystem components, or as upstream lters toprotect higher eciency lters. In this test, a

synthetic dust is ed into the air cleaner and thepercentage by weight o the dust the lter traps,called arrestance, is determined. The weightarrestance test may be o limited value in assessingthe removal o smaller, respirable particles becauseparticles in the test dust are generally larger thanthose that can be inhaled deeply into the lungs.

The atmospheric dust spot eciency test,13also dened in ASHRAE Standard 52.1-1992,*is generally used to rate medium-eciency lters

in removing ne airborne dust particles that cansoil walls and other interior suraces. A naturallyoccurring atmospheric dust is ed into the aircleaner to test its ability to reduce soiling o aclean paper target as an indication o the cleanerscapability to remove ne particles rom the air.

The DOP penetration test,14 described in theIEST-RP CC001.4 test method, is used to ratetrue HEPA lters. A DOP cloud o uniorm0.3 m particles is ed into the lter. Theconcentration o penetrating smoke measured

upstream and downstream o the lter determinesthe lter eciency, or the percentage o particlesthe lter removes.

The PSE test,15 described in ASHRAE Standard52.2-2007, provides a composite minimumeciency or removing particles o specic sizeby lters incrementally loaded with syntheticdust. The PSE test method does not eliminate theneed or DOP penetration and arrestance testing.Very low-eciency air lters, such as urnacelters, must also be tested in accordance withthe weight arrestance method. The compositeminimum eciency values are averaged and usedto determine the air cleaners minimum eciencyreporting value (MERV). The MERV rangesrom a low o 1 to a high o 20. The PSE test

*ASHRAE Standard 52.1.1992, Gravimetric and Dust-Spot Procedures or Method o Testing Air-Cleaning Devices Used in General Ventilation orRemoving Particulate Matterwas withdrawn in spring 2009. Inormation previously ound in this standard is now included via Addendum B to

ANSI/ASHRAE Standard 52.2,Method o Testing General Ventilation Air-Cleaning Devices or Removal Efciency by Particle Size. The addendummandates calculation o weight arrestance or lters with Minimum Eciency Reporting Values (MERVs) o 1 to 4 and atmospheric dust spoteciency or lters with MERVs o 5 to 16.


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ASHRAE Standard 52.2

ASHRAE

Standard

52.1

Application Guidelines

MERV

Particle Size Removal

Efficiency, Percent in Particle

Size Range, mDust-Spot

Efficiency

Percent

Particle Size and

Typical Controlled

Contaminant

Typical Applications Typical Air Filter/CleanerType

0.3 to 1 1 to 3 3 to 10

20

19

18

17

99.999

99.999

99.99

99.97

< 0.3 m

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 m

All bacteria

Droplet nuclei (sneeze)Cooking oil

Most smoke

Insecticide dust

Most face powder

Most paint pigments

Superior commercialbuildings

Hospital inpatient care

General surgery

Bag Filters Nonsupported

(flexible) microfine fiberglass orsynthetic 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 m

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 m

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 Extendedsurface with cotton or polyester

media or both, 1 to 6 inches

thick.

Cartridge filters Viscous cube

or pocket filters

ThrowawaySynthetic media

panel filters

4

3

2

1

< 20

< 20

< 20

< 20

< 20

< 20

< 20

< 20

> 10 m

Pollen

Dust mites

Cockroach body parts and

droppings

Spanish moss

Sanding dustSpray 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 m

particle size

in 0.1 0.2 m

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 m particles, based on the IEST test method. MERVs between 17

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

** For residential applications, the ANSI/ASHRAE Standard 62.2-200716 requires a filter with a designated minimum efficiency of MERV 6 or better.


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may not be appropriate or evaluating electronicair cleaners because the dust used containsconductive carbon, which may cause electricalshorting and thus compromise the eectiveness othese devices and alter their MERV. The dust-loading procedure may also aect the eciency o

electrostatically charged lters.

A cross-reerence o atmospheric dust spoteciency tests to the MERV is shown in Table 2.This table shows the minimum PSE in three sizeranges or each MERV. A consumer can use thetable to identiy the MERV required to control aspecic pollutant. While these standards cannotby themselves predict the actual eectiveness oany lter over its lietime, they can generally beused to compare the perormance characteristics

o one air lter with another.

Air Filters - Available Evidence of Their

UsefulnessWhether installed in the ducts o HVAC systemsor used in portable air cleaners,most air lters have a goodeciency rating or removinglarger particles when they remainairborne. These particles includedust, pollen, some molds, animaldander, and those that contain

dust mite and cockroach bodyparts and droppings. But becausethese particles settle ratherrapidly rom the air, air lters aresomewhat ineective in removingthem rom indoor areas. Andalthough human activities suchas walking and vacuuming, or the high velocityair exiting supply vents, can re-suspend particles,most o the larger particles will resettle beore theyenter the HVAC system or portable air cleaner

and are removed by a particle air lter.

The appropriate type o particle removal air ltercan be chosen by looking at its MERV rating inremoving airborne particles rom the airstreamthat passes through it. MERV ratings can alsobe used to compare air lters made by dierentmanuacturers.

Flator panel air lters with a MERV o 1 to 4have low eciency on smaller airborne particles,but reasonable eciency on large particles whenthey remain airborne. These lters have lowairfow resistance and are relatively inexpensive.Typically to 1 inch thick, they are commonly

used in residential urnaces and air-conditioningsystems, and they are oten used as pre-lters orhigher eciency lters. For the most part, suchlters are used to protect the HVAC equipmentrom the buildup o unwanted materials on anmotors, heat exchangers, and other suraces.

Pleatedor extended surace lters with a MERVo 5 to 13 have higher eciency ratings thanpanel lters. These medium-eciency lters arereasonably ecient at removing small-to-large

airborne particles. The airfow resistance o theselters does not necessarily increase as the MERVincreases. Higher eciency lters with a MERVo 14 to 16 have a higher average resistance toairfow than medium-eciency lters. Highereciency pleated lters, sometimes inaccurately

called high eciency, HEPA,or HEPA-type lters, aresimilar in appearance to trueHEPA lters, which have MERVvalues o 17 to 20, but use lessecient lter media.

The depth o these pleated orextended surace lters may varyrom approximately 1 to 6 inchesor medium-eciency modelsand 6 to 12 inches or highereciency lters. As the depth

and pleating increases, so does the area o theltration medium, helping to oset the increasein resistance to airfow across the lter. Becauseo their increased surace area, these lters otenhave an extended lie. The operating resistance oa ully dust-loaded lter must be considered inthe design, because it is the maximum resistanceagainst which the an operates. Generally, dustloading results in increased ltration eciencyalong with an increase in pressure drop. Pressuredrop in media-type lters is greater than that inelectronic-type cleaners and slowly increases overthe lters useul lie.

Large particles

settle rom the air

rapidly; thereore, air

flters are somewhat

ineective in their

removal.


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13www.epa.gov/iaq

Some residential HVAC systems may not haveenough an or motor capacity to accommodatehigher eciency lters. Thereore, the HVACmanuacturers inormation should be checkedprior to upgrading lters to determine whether itis easible to use more ecient lters.

True HEPA lters with a MERV between 17and 19 are dened by the IEST test method ashaving a minimum eciency between 99.97percent and 99.999 percent in removing 0.3 mparticles. A MERV o 20 is rated or 0.1 to 0.2m particles. HEPA lters have higher ecienciesor removing both larger and smaller airborneparticles. True HEPA lters normally are notinstalled in residential HVAC systems; installinga HEPA lter in an existing HVAC system would

probably require proessional modication o thesystem. A typical residential air-handling unitand the associated ductwork would not be able toaccommodate such lters because o their size andincreased airfow resistance. Specially built highperormance homes may occasionally be equippedwith true HEPA lters installed in a properlydesigned HVAC system.

Manuacturers market HEPA lters to allergyand asthma patients. Experimental data andtheoretical predictions indicate that medium-

eciency air lters, MERV between 7 and 13,are likely to be almost as eectiveas true HEPA lters in reducingthe concentrations o mostindoor particles linked to healtheects.17 Available data indicatethat even or very small particles,HEPA lters are not necessarilythe preerred option. For thesesmall particles, relatively largedecreases in indoor concentrations(around 80 percent) areattainable with medium ltereciency (such as a MERV o13). Increasing lter eciencyabove a MERV o 13 results in only modestpredicted decreases in indoor concentrations othese particles.* Predicted reductions in indoorconcentrations o cat and dust mite allergens

carried on small particles vary rom 20 percentwith a MERV 7 lter to 60 percent using aHEPA lter. Increasing lter eciency abovea MERV o 11 does not signicantly reducepredicted indoor concentrations o animal dander.Medium-eciency air lters are generally less

expensive than HEPA lters and allow quieterHVAC an operation and higher airfow ratesthan HEPA lters because they have less airfowresistance. Pleated lters 1 to 2 inches thickthat have a MERV o 12 are available or usein homes and may oten be installed withoutmodiying residential HVAC systems; however,manuacturers inormation should be checkedprior to installation.

Electrostatic precipitators remove and collect

small airborne particles and have an initialASHRAE dust spot eciency o up to 98 percentat low airfow velocity. This eciency will behighest or clean electronic air cleaners. Electronicair cleaners exhibit high initial eciencies incleaning air, largely because o their ability toremove ne particles. Their eciency decreases asthe collecting plates become loaded with particles,or as airfow velocity increases or becomes lessuniorm.

Portable Air Cleaners - Available Guidance for

Their ComparisonThe eectiveness o a portableair cleaner depends on the air-cleaning devices eciency inremoving airborne pollutants, thequantity o air being ltered, theparticle size, the size o the roomthe air cleaner serves, and itslocation in the space. A voluntarystandard is available or measuringthe eectiveness o portable air

cleaners in reducing airbornepollutants in a room. It wasdeveloped by the Association oHome Appliance Manuacturers

(AHAM), a private voluntary standard-settingtrade association, and is recognized by theAmerican National Standards Institute.18 Thestandard compares the eectiveness o portable

*Some air lters may be eective at reducing tobacco smoke particles, but they will not remove gaseous pollutants rom tobacco smoke. While some gas-phase lters may remove specic gaseous pollutants rom the complex mixture o chemical compounds in tobacco smoke, none is expected to remove allunwanted gaseous combustion products. Odorous and toxic organic gases may also evaporate rom liquid tobacco smoke particles trapped by the air lter. 12

Filters that have a

MERV between 7

and 13 are likely

to be nearly as

eective as true

HEPA flters.


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14 www.epa.gov/iaq

air cleaners in a room size test chamber, measuredby the clean air delivery rate (CADR) or each othree types o particles in indoor air: dust, tobaccosmoke, and pollen. Although AHAM uses tobaccosmoke particles to represent smaller airborneparticles, air cleaning should not be construed as

an eective way to address environmental tobaccosmoke. There are thousands o particulate andgaseous chemical compounds, including manyknown carcinogens, in tobacco smoke that cannotbe removed eectively by air cleaning.

Although AHAM uses the CADR concept toevaluate the perormance o portable air cleanersin reducing particulate matter concentrations, theCADR can be applied equally to the removal ogaseous pollutants. The CADR does not apply

to whole-house air-cleaning devices installed inHVAC ductwork.

The CADR is a measure o a portable air cleanersdelivery o contaminant-ree air, expressedin cubic eet per minute. For example, anair cleaner that has a CADR o 250 or dustparticles can reduce dust particle levels to thesame concentration as would be achieved byadding 250 cm o clean air.The portable air cleanersremoval rate competes with

other removal processesoccurring in the space,including deposition oparticles on suraces, sorptiono gases, indoor air chemicalreactions, and outdoor airexchange. While a portableair cleaner may not achieveits rated CADR under allcircumstances, the CADRvalue does allow comparisonsamong portable air cleaners.

AHAM has a portable air-cleaner certication programand lists all certied cleanersand their CADRs on its Web site atwww.cadr.org.19 AHAMs online directory ocertied portable air cleaners allows searches bycertied CADR ratings, suggested room size,manuacturer, or brand name. The CADR

values reported or selected portable air cleanersare based on an 80-percent reduction in steadyparticle concentrations. AHAMs recommendedeectiveness o 80 percent produces meaningulreductions in contaminant concentrationsindoors. This level o eectiveness corresponds to

an air cleaners capability to provide an amounto clean air that is our to ve times the volume othe specied size room.9

Indoor particle concentrations are not alwaysconstant over time. Some indoor pollutants mightbe produced periodically rom sources such ashobby and crat materials or cooking ood. Theseintermittent pollutant sources have only a modesteect on particle concentrations indoors comparedto sources o steady pollutant concentrations.

Some portable air cleaners sold to consumersare ENERGY STAR qualied. Earning theENERGY STAR means a product meets strictenergy eciency guidelines set by EPA and theU.S. Department o Energy. The ENERGY STARdisclaimer label, which includes the ollowingstatement, is placed on the product packagingo ENERGY STAR qualied air cleaners: This

product earned the ENERGY STARby meeting strict energy eciencyguidelines set by the US EPA. US EPA

does not endorse any manuacturerclaims o healthier indoor air rom theuse o this product.

Portable Air Cleaners - Available

Evidence of Their UsefulnessMany o the portable air cleanersAHAM tested have moderate-to-largeCADR ratings or small particleswhen used in rooms o appropriatesize.9 However, or typical room sizes,

most portable air cleaners currently onthe market do not have high enoughCADR values to remove eectivelylarge particles such as dust, pollen,some mold spores, animal dander,

and particles containing dust mite and cockroachallergens. Some portable air cleaners that useelectronic air cleaners may produce ozone, whichis a lung irritant.

Most portable air

cleaners donteectively remove

large particles such

as dust, pollen,

some mold spores,

and particles

containing dust

mite and cockroach

allergens in rooms

o typical size.


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15www.epa.gov/iaq

Studies have assessed portable air cleanersperormance in removing airborne particlesas well as their limited clinical eects. Sometests addressed the removal o tobacco smokeparticles.20, 21, 22 Limited testing on larger airborne

particles including those that contain cat, dog, anddust mite allergens have also been perormed.23, 24,25, 26, 27, 28 Many experimental studies used portableair cleaners equipped with HEPA lters, but theavailable sources indicate that HEPA lters maynot be preerable to medium-eciency ltersbecause o HEPA lters lower air delivery due toair bypassing the lter and to higher resistance toairfow. In addition, portable air cleaners are noteective at removing large particles because largeparticles settle out o indoor air at a substantial

rate.

The eectiveness o portable air cleaners inremoving particles rom indoor air depends onthe size o the particles. One paper9 reported thatair-cleaning eectiveness o at least 80 percentcan be achieved by portable air cleaners thathave moderate-to-high CADR ratings in homeswhere small particles are the main concern. Onthe other hand, or larger airborne particles, thecombination o small room size and high CADRratings may yield particle removal eectiveness o

80 percent or more. However, or typical roomslarger than 200 square eet, most portable aircleaners on the market do not have high enoughCADR values to remove large particles eectively.This act may account or the nding that portableair cleaners are most likely to be eective inreducing indoor concentrations o smaller airborneparticles such as those associated with cat or dustmite allergens.26 However, air cleaning was notound to be consistently and highly eective inreducing respiratory symptoms since much o theairborne allergens appear to be carried onlarger particles.26

Some manuacturers consider their hybridportable air cleaners, which use multiple air-cleaning devices, to be more eective thanportable air cleaners that use a single device.However, the eectiveness o these hybrid unitsmay suer because more air cleaners arranged in

a series may mean increased air resistance, whichcould decrease air delivery or cause air to bypassthe cleaner. Eectiveness may also be decreasedi air exiting the portable air cleaner outlet is notadequately mixed with room air beore re-enteringthe unit.

Useul inormation about portable air cleanersis available rom Consumer Reportsmagazine.Published by Consumers Union, an independent,nonprot organization, Consumer Reportsprovidesan annual review o products, their updatedreports, and ratings. The test method used byConsumers Union is not intended to be the basisor a standard or evaluating the perormanceo air-cleaning devices; rather, ConsumersUnion tests air cleaners using its own testing

procedures, rates the cleaners based on a varietyo criteria, and ranks them in charts that are easyto understand. According to Consumers Union,some portable air cleaners that use electrostaticprecipitators may produce measurable amounts oozone as a by-product.29 Electrostatic precipitatorsmay also make a crackling sound as theyaccumulate dirt.

The placement o any portable air cleaner mayaect its perormance. I there is a specic,identiable source o pollutants, the unit should

be placed so its intake is near that source. I thereis no specic source, the air cleaner should beplaced where it will orce clean air into occupiedareas. It should not be situated where walls,urniture, and other obstructions will block theintake and outlet. A portable air cleaner willbe much more eective when all the doors andwindows in a room are closed. I the door to aroom where a portable air cleaner is located isopen, or i the HVAC system is operating, theroom air oten will mix with air rom throughoutthe house, and the air cleaner will not reduce theparticle concentrations in the room as intended.

Removal of Gaseous Pollutants

by SorbentsMany dierent gas-phase air-ltration devicesare available; however, comparing and ratingthe eectiveness o installed sorbent lters isdicult because there is no standard test method.


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16 www.epa.gov/iaq

ASHRAE Standard Project Committee 145 isdeveloping a standard method or evaluatingthe eectiveness o gas-phase ltration devicesinstalled in the ductwork o residential HVACsystems, but not in portable air cleaners.30

Gas-phase air lters remove gases and odorsby either physical or chemical processes. Theselters typically are designed to remove one ormore o the gaseous pollutants present at lowconcentrations in the airstream that passesthrough them. They are not, however, designed toeliminate all gaseous pollutants. Air cleaners thatdo not contain sorbent materials or photocatalyticoxidation technology, discussed on page 20, willnot remove gaseous pollutants.

A sorbent lters behavior depends on manyactors that can aect the removal o gaseouscontaminants:

Airfow rate and velocity through the sorbent.

Concentration o contaminants.

Presence o other gaseous contaminants.

Total available surace area o the sorbent.(Some manuacturing techniques cansignicantly reduce a lters total surace area.)

Physical and chemical characteristics o thepollutants and the sorbent (such as weight,polarity, pore size, shape, volume, and the typeand amount o chemical impregnation).

Pressure drop.

Removal eciency andremoval capacity.

Temperature and relativehumidity o the gas stream.

Gas-phase lters are muchless common than particle

air-cleaning devices in homesbecause a properly designedand built gas-phase ltrationsystem is too big or a typical residential HVACsystem or portable air cleaner. Other actorsthat may contribute to the less requent use ogas-phase lters in home HVAC systems arethe lters limited useul lie, the act that thesorbent material must be targeted to specic

contaminants, the purchase price o the lters,and the costs o adapting them to residentialapplications, when possible, and o operatingthem once they have been installed.

Types of Sorbents Used for Gaseous

Pollutant RemovalThere are two main processes that removegaseous contaminants: a physical process knownas adsorption and a chemical reaction calledchemisorption.

Adsorption results rom the physical attraction ogas or vapor molecules to a surace. All adsorbentshave limited capacities and thus require requentmaintenance. An adsorbent will generally adsorbmolecules or which it has the greatest anity

and will allow other molecules to remain in theairstream. Adsorption occurs more readily at lowertemperatures and humidity. Solid sorbents suchas activated carbon, silica gel, activated alumina,zeolites, synthetic polymers, and porous clayminerals are useul because o their large internalsurace area, stability, and low cost.

Activated carbon is the most common adsorbentused in HVAC systems and portable air cleanersto remove gaseous contaminants. It has thepotential to remove most hydrocarbons, many

aldehydes, and organic acids. However, activatedcarbon is not especially eective against oxides o

sulur, hydrogen sulde, lowmolecular weight aldehydes,ammonia, and nitrogen oxide.

Chemisorption occurswhen gas or vapor moleculeschemically react with sorbentmaterial or with reactive agentsimpregnated into the sorbent.

These impregnates react withgases and orm stable chemicalcompounds that are bound

to the media as organic or inorganic salts, orare broken down and released into the air ascarbon dioxide, water vapor, or some materialmore readily adsorbed by other adsorbents.Many dierent chemicals may be impregnatedon activated carbon; potassium permanganate

The limited lietime o

gas-phase flters may

contribute to their

less requent use in

home HVAC systems.


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17www.epa.gov/iaq

is a common chemisorbent impregnated intoactivated alumina. It reacts with many commonair pollutants, including ormaldehyde and sulurand nitrogen oxides. Because a chemisorbentwill react with only one or a limited number oreactive pollutants, it should not be expected to

reduce others.

Applications of Sorbents for Gaseous Pollutant

RemovalGas-phase lters that contain sorbents may beinstalled in HVAC systems or in portable aircleaners. They are usually located downstreamo particle air lters. The air lter reduces theamount o particulate matter that reaches thesorbent, and the sorbent collects vapors that maybe generated rom liquid particles that collect on

the particle lter.

Some gas-phase lters may remove, at leasttemporarily, a portion o the gaseous pollutants inindoor air. Although some gas-phase air ltersiproperly designed, used, and maintainedmayeectively remove specic pollutants rom indoorair, none is expected to remove adequately allo the gaseous pollutants in a typical home. Forexample, carbon monoxide is not readily capturedby adsorption or chemisorption. In addition,gaseous-pollutant-removal systems usually have

a limited lietime beore the sorbent must bereplaced. There is also a concernthat saturated sorbent lters mayrelease trapped pollutants backinto the airstream.31

Tests o gaseous pollutantremoval by activated carbongenerally have been conductedusing only high concentrations opollutants, so little inormation is

available on carbons eectivenessin removing chemicals present inthe low concentrations (parts perbillion [ppb]) normally ound inindoor air. Tests perormed at EPA measured theadsorption isotherms or three volatile organiccompounds (VOCs) at concentrations o 100ppb to 200 ppb using three samples o activatedcarbon. The bed depth needed to remove the

compounds was estimated assuming a 150 ppbconcentration in the air, an exit concentration o50 ppb, and a fow rate o 100 cm across a2 x 2 lter. The results o the study suggest thatbreakthrough o these chemicals would occurquickly in 6-inch deep carbon lters used or odor

control.32

Because o their compact design, particle airlters that use impregnated media are availableor residential HVAC systems and portable aircleaners. They use sorbent particles o carbon,permanganate alumina, or zeolite incorporatedinto brous lter media. Such lters generallyrange rom 1/8 inch to 2 inches thick. Theyprovide a combination o particulate and gas-phase ltration with a minor increase in pressure

drop across the lter. Their use in an existingHVAC system does not require extensive orexpensive modications to the system. However,their useul service lie varies according to indoorpollution concentrations and exposure time.Breakthrough o the contaminants back into theroom takes place very quickly in the thin layerimpregnated with sorbents, resulting in a muchshorter service lie or the lter, which must bereplaced requently. Thus, these devices usuallyhave limited eectiveness in removing odors.

Removal of Radon and Its ProgenyEPA does not recommend aircleaning to reduce the healthrisks associated with radon andthe decay products o radon gas,which are called radon progeny.The Agency recommends the useo source control technologiesto prevent radon rom enteringresidential structures. The mosteective radon control technique

is active soil depressurization(ASD).1 An ASD system usesan electric an to minimizeradon entry by drawing air

rom under the slab/foor and venting it to theoutside above the buildings roofine. Another, lesseective technique installed during constructionis a passive radon reduction system, also knownas radon-resistant new construction (RRNC).

EPA does not

recommend using

air cleaners to

reduce the health

risks associated

with radon.


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18 www.epa.gov/iaq

RRNC systems are dual-purpose systems. Theytypically do not have a an, but i subsequenttesting indicates an elevated radon level, a an canbe installed and the RRNC system will become,in eect, an ASD system.

A limited number o studies have investigated aircleaners eectiveness in removing radon and itsprogeny. They compared the removal eciencieso various air cleaners, including mechanical airlters, electrostatic precipitators, and ionizersequipped with ans, and the risk reduction theair cleaners achieve. However, the degree o riskreduction ound by these studies hasbeen inconsistent.

Deactivation or Destruction of

PollutantsThree types o air cleaners on the market aredesigned to deactivate or destroy indoor airpollutants: ultraviolet germicidal irradiation(UVGI) cleaners, photocatalytic oxidation (PCO)cleaners, and ozone generators sold as air cleaners.

Ultraviolet Germicidal Irradiation CleanersUVGI cleaners are intended to improve residentialIAQ by deactivating indoor biological pollutantsthat are airborne or growing on the moist interiorso HVAC suraces (e.g., cooling coils, drain pans,

or ductwork).

There is no standard test method to rate andcompare the eectiveness o UVGI cleanersinstalled in either residential HVAC systems orportable air cleaners. Typical UVGI cleaners usedin homes have limited eectiveness in killingbacteria and molds. The eective destruction osome viruses and most mold and bacteria sporesusually requires much higher UV exposuresthan a typical home unit provides. Thus, UVGI

does not appear to be eective as a sole controldevice. When UVGI is used, it should be usedin addition tonot as a replacement orconventional particle ltration systems.33 UsingUVGI in addition to HEPA lters in HVACsystems or in portable units oers only minimalinection control benets over those provided bythe HEPA lters 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 thespore 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 airfilters, 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 oroff-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.


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19www.epa.gov/iaq

UVGI TechnologyMost UV lamps used to kill germs in residentialsettings are low pressure mercury vapor lampsthat emit UV radiation at a wavelength o 253.7nanometers, which has been shown to havegermicidal eects.38 UV light can penetrate the

outer structure o a microorganisms cell and alterits DNA, permanently preventing replication andcausing cell death. But some bacterial and moldspores are resistant to UV radiation.

Types o UVGI Cleaners and TheirEectivenessThere are two types o UVGI applications:cleaners designed or airstream disinection, toreduce the viability o microorganisms as theyfow through the HVAC system or portable

air cleaner, and cleaners designed or suracedisinection, to prevent the reproduction omicroorganisms on specic components o anHVAC system.38, 39

UVGI lamps or airstream or surace disinectionusually are located in the air duct o an HVACsystem downstream o the lter and upstreamo the cooling coil or in a portable air cleanerdownstream o the lter.

I properly designed, the UVGI cleaner in a

typical airstream disinection application hasthe potential to reduce the viability o vegetativebacteria and molds and to provide low to moderatereductions in viruses but little, i any, reduction inbacterial and mold spores.33, 34, 40Spores tend to be resistant to UVradiation, and killing them requiresa very high dosage.38, 41, 42

When the an in an airstreamdisinection application isnot operating, there is no airmovement and no disinection.

UVGI cleaners in a surace disinectionapplication are installed in air-handling units toprevent or limit the growth o vegetative bacteriaand molds on moist suraces in the HVACsystem.34, 39, 40, 43 One study reported a 99-percentreduction in microbial contaminants growing

on exposed HVAC suraces, but a reduction inairborne bacteria o only 25 to 30 percent.44 Onereason that the surace disinection applicationprovides only a slightly noticeable reduction inairborne microbial concentrations may be thatmicroorganisms in the airstream are exposed

to the UV light or a shorter time. Conversely,microorganisms growing on exposed HVACsuraces are given prolonged direct UVGIexposure. Another study ound that UV lampsyielded somewhat lower levels o mold in theberglass insulation lining the air-handling unit.40

Prolonged direct UVGI exposure can destroyvegetative microbial growthbut not mostsporeson the suraces o orced-ventilationunits, lters, cooling coils, or drain pans. Killing

molds and bacteria while they are still in thesusceptible vegetative state reduces the ormationo additional spores. UV radiation is ineective inkilling microorganisms i they prolierate insidethe lter media, system crevices, porous thermalinsulation, or sound-absorbing brous materialliners.39

A review o scientic literature has shown thatthe eectiveness o UVGI cleaners in killingmicroorganisms may vary depending on UVirradiation dose, system design and application,

system operation characteristics, and themicroorganism targeted or deactivation. Furtherindependent testing using a standardized testmethod is required beore rmer conclusions can

be made about the eectiveness ovarious UV cleaners in destroyingmicroorganisms o concern.Some manuacturers o UVGIcleaners used in HVAC systemsor portable air cleaners claim theirunits reduce dust mite allergens,airborne microorganisms such asviruses, bacteria, molds, and their

spores, and gaseous pollutants rom indoor air.However, it is likely that the eective destructiono some viruses and most mold and bacterialspores requires much higher UV exposures than atypical residential UVGI unit provides.36, 38, 39

UVGI cleaners might

not reduce allergy or

asthma symptoms.


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No research or studies were ound that show UVdisinection is eective in reducing dust mite andmold allergenicity or that UV radiation has thepotential to remove gaseous pollutants. Becausemold is allergenic, whether dead or alive, it cancause allergic reactions in sensitive populations.

Thereore, UVGI cleaners might not be eective inreducing allergy and asthma symptoms. I mold isgrowing indoors, it should be removed.45

Planning and Maintaining a UVGI SystemA number o studies 34, 36, 38, 46, 47 report that themost important perormance elements o a UVGIsystem are the type o UV lamp and ballast, therelative humidity, temperature, air velocity, andduct refectivity.

High output UV lamps have been ound toprovide higher irradiance than low-output lamps.Lamps designated or low-temperature operationalso appear to perorm better. Increased relativehumidity is commonly believed to decrease theirradiation o UVGI; however, the literature iscontradictory and incomplete. Air temperaturecan aect the power output o UVGI lamps i itexceeds design temperatures. Operating a UVGIsystem at air velocity abovedesign will degrade the systemseectiveness. Refectivity

can be an economical way ointensiying the UVGI eldin an enclosed duct. Polishedaluminum is highly refectiveo UV wavelengths, whiletypical duct liner material haslittle or no refectance in theUV spectrum.

Regular maintenance oUVGI systems is crucial and usually consists ocleaning the lamps o dust and replacing old lamps.Manuacturers recommendations regarding saetyprecautions, exposure criteria, maintenance, andmonitoring associated with the use o UVGIsystems should be ollowed.

By-products Generated by UVGI SystemsAccording to two studies,38, 43 operating UV lampsinstalled in HVAC systems to irradiate the suraces

o air-handling units does not result in increasedconcentrations o ozone, VOCs, or other chemicalby-products.

Photocatalytic Oxidation CleanersPCO cleaners are intended to destroy gaseous

pollutants and their odors by converting theminto harmless products, but they are not designedto remove particulate pollutants. PCO cleanersuse a UV lamp and a photocatalyst, usuallytitanium dioxide, to create oxidants that destroygaseous contaminants. When the photocatalystis irradiated with UV light, a photochemicalreaction takes place and hydroxyl radicals orm.The hydroxyl radicals oxidize gaseous pollutantsadsorbed on the catalyst surace. This reaction,called photocatalytic oxidation, converts organic

pollutants into the carbon dioxide and water.To achieve eective conversion, the reactionrate o the PCO cleaner must match the rateso contaminant generation and inltration rateminus the exltration rate (movement o the airrom the space served to the outdoors).

There is no standard test method to compare andrate the eectiveness o PCO cleaners installed

in residential HVAC systems orportable air cleaners. PCO is anemerging technology intended

to improve residential IAQ bydestroying gaseous contaminants.Although PCO is still underdevelopment, a ew home aircleaners that use it are available inthe United States. PCO cleaners arepromoted or use in HVAC systemducts or in portable air cleaners.Some manuacturers claim PCOdevices can remove tobacco smoke,

microorganisms, and other indoor particulate

pollutants even though the devices are not meantto remove particles.

The useulness o PCO cleaners in homes islimited because available photocatalysts (i.e.,substances that react with light) are ineectivein completely destroying gaseous pollutantsin indoor air.48, 49, 50 Other application andengineering issues are not ully resolved,

Application o

PCO cleaners or

homes is limited in

destroying gaseous

pollutants rom

indoor air.


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including the relatively large power consumptiono PCO units; the complexity o the PCOprocess, which combines the operation o a UVlight and a catalyst; and the need to removemultiple compounds rom the contaminatedairstream. Some PCO cleaners ail to destroy

pollutants completely and instead produce newindoor pollutants that may cause irritation o theeyes, throat, and nose. Until more data becomeavailable, inormation on the perormance o PCOcleaners will remain limited and inconclusive.

Eectiveness o PCO SystemsOne study51 reported that PCO devices installedin portable air cleaners did not eectivelyremove any o the test VOCs present at the lowconcentrations normally ound in indoor air. This

study compared the VOC-removal eciencieso 15 air cleaners that usedierent types o technology.A mixture o 16 VOCscommonly ound indoorswas used. The reportindicated that the PCOdevices studied might notwork as advertised. Thendings also showed thatsome devices appear not tohave ully implemented PCO technology.

A review o the literature suggests that moreresearch is needed to urther advance PCO asan eective technology in removing low levelso gaseous contaminants rom the indoor airo residences.49, 50, 51 This additional researchshould include many important perormancecharacteristics that infuence the eectiveness oPCO cleaners, such as whether:

X A decrease in light irradiance with illuminationtime inhibits perormance.49

X Photocatalyst deactivation in the presence ochemicals such as toluene, benzene, ethanol, orhexamethyldisilazane decreases perormance.49, 50, 52

X An increase in reaction temperature or watervapor content increases the PCO reactionrate.53

X Competitive adsorption between gaseouscontaminants aects the PCO reactionmechanism.49, 54

Estimated costs o PCO technology are signicantlyhigher than those o activated carbon technology. A

major actor infuencing PCO costs is the intensityo UV light required at the inlet to destroy a rangeo VOCs at the low concentrations that typiy IAQproblems.48

PCO By-productsPCO o certain VOCs may create by-productsthat are indoor pollutants i the systems designparameters and catalyst metal composition do notmatch the compound targeted or decomposition,particularly in the presence o multiple reactive

compounds commonly ound in residential settings.One study reported that no detectableby-products ormed during the PCO o17 VOCs using titanium dioxide underthe experimental conditions.55 However,two studies on the degradation o 4chlorinated VOCs ound by-productsincluding phosgene and chlorides.56, 57 Inaddition, the PCO o trichloroethylenein air using titanium dioxide as thecatalyst yielded as by-products carbon

monoxide, phosgene, carbon dioxide, hydrogen

chloride, and chlorine.

Ozone GeneratorsOzone generators sold as air cleaners and marketedas in-duct or portable units use UV light or coronadischarge to produce ozone, which is dispersed by aan into occupied spaces.8

Some manuacturers and vendors o ozonegenerators suggest that ozone reacts with bothchemical and biological pollutants and transorms

them into harmless substances. They also otenmake statements and distribute materials thatlead the public to believe that these devices arealways sae and eective in controlling indoor airpollutants. However, ozone is an irritant gas thatreacts with lung tissue and can cause asthma attacks;coughing; chest discomort; irritation o the nose,throat, and trachea; and other adverse health eects.

Ozone is a lung

irritant that can

cause adverse health

eects.


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As ozone reacts with chemical pollutants, it canproduce harmul by-products.8, 9, 10

Available scientic evidence shows that, at ozoneconcentrations below public health standards,ozone has little potential to remove indoor

air contaminants such as many odor-causingchemicals, viruses, bacteria, molds, and tobaccosmoke; thus, ozone is generally ineective incontrolling indoor air pollution. Some controlledstudies show that the concentration o ozoneproduced by ozone generators can exceedstandards even when consumers ollow themanuacturers instructions. No ederal agencyhas approved ozone generators or use in occupiedspaces.

There is a large body o written materialon ozone and the use o ozone indoors, butmuch o this material makes claims or drawsconclusions without substantiation and a basis insound science. In developing Ozone Generatorsthat Are Sold as Air Cleaners, EPA reviewed a

wide assortment o this literature, includinginormation provided by a leading manuacturero ozone-generating devices. In keeping withEPAs policy o ensuring that the inormationit provides is based on sound science, only peerreviewed, scientically supported ndings and

conclusions were relied on in developing thisdocument. The document is posted on the EPAWeb site at www.epa.gov/iaq/pubs/ozonegen.html.The public is advised to use methods proven tobe sae and eective in controlling indoor airpollution. These methods include eliminatingor controlling pollutant sources and increasingoutdoor air ventilation.

Federal pesticide law requires manuacturers oozone generators to list an EPA establishment

number on the products packaging. This numbermerely identies the acility that manuacturedthe product. The presence o this number on aproducts packaging does not imply that EPAendorses the product, nor does it imply that EPAhas ound the product to be sae or eective.


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WILL AIR CLEANING REDUCE HEALTH EFFECTS FROM INDOOR

AIR POLLUTANTS?

Air-cleaning devices may help reduce levels osmaller airborne allergens, particles, or, in some

cases, gaseous pollutants in a home. However, aircleaners may not decrease adverse health eectsparticularly in sensitive populations such aschildren, people with asthma and allergies, andthe elderly.

Clinicians requently recommend that patientswho have asthma or allergies use HEPA air ltersin HVAC systems or in portable air cleaners.Regardless o how ecient and eective air-cleaning devices are in removing pollutants, aquestion still remains about their ability to reduceadverse health eects.

How eectively air-cleaning devices alleviateallergic and other health symptoms remainsuncertain. Strong data linking air-cleaningdevices to reduced health symptoms do notexist. Many studies have associated air-cleaningdevices with reductions in airborne indoorpollutant concentrations, but more clinical studiesare needed to determine whether air cleanerssignicantly aect health outcomes. A literature

review documented only a limited number ostudies that attempted to evaluate the clinicaloutcomes o air cleaner use. These studies ocusedon more sensitive groups, such as asthmatic andallergic individuals, children, and the elderly. Anumber o the studies had important limitations,such as small study size, short duration, andlack o blinding (i.e., subjects and scientists wereaware o air cleaner operation), which may resultin a placebo eect. The results were also moresuggestive than conclusive.

Many indoor pollutants related to asthma andallergies are either airborne particles or irritants,such as the gaseous components o secondhandsmoke or nitrogen dioxide, chemicals linkedwith gas cooking appliances, replaces, woodstoves, and unvented kerosene and gas spaceheaters. Most studies involving subjects whohave perennial and seasonal allergy or asthmasymptoms tested portable air cleaners equippedwith HEPA lters.

Few studies tested gas-phase ltration and aircleaners using UV light technology, such as UVGI

cleaners and PCO cleaners. The scarcity o dataresults in little scientic evidence that these devicesare associated with a reduction in health symptoms.

The eects o particle air cleaners on allergyand asthma symptoms have been reviewed bythe Institute o Medicine (IOM) Committeeon the Assessment o Asthma and Indoor Air othe National Academy o Sciences.26 The IOMconcluded that:

The results o existing experimental studies areinadequate to draw rm conclusions regardingthe benets o air cleaning or asthmaticand allergic individuals. Air cleaners arehelpul in some situations in reducing allergyor asthma symptoms, particularly seasonalsymptoms, but it is clear that air cleaning, asapplied in the studies, is not consistently andhighly eective in reducing symptoms.

The use o air cleaners may help reduce levels osmaller airborne allergens or particles, but should

not be expected to eectively reduce healthsymptoms.

Several actors should be considered in evaluatingwhether an air cleaner is benecial in alleviatinghealth eects.

X Many studies on the health benets o aircleaning involve multiple interventions andthus are not useul in determining the eects oair cleaners alone.

The health benets o air cleaners are otenstudied along with other interventions such asmattress and pillow covers, exclusion o petsrom the bedroom, weekly baths or pets, orvacuum cleaning. Studies that consider aircleaning concurrently with other interventionshave relatively little value in determiningthe clinical outcome resulting rom the use


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o air cleaners because it is not clear i anyimprovements demonstrated are due tothe air-cleaning devices or to the otherinterventions.23, 24, 25, 27, 28, 58, 59

X An air cleaners ability to

remove some airbornepollutants, includingmicroorganisms, is not,in itsel, an indication othe air cleaners ability toreduce health symptoms.

As discussed previously,pollen, dust mite andcockroach allergens, some mold spores, andanimal dander carried on large particlessettle rapidly beore they can be removed

by ltration. Because these particles do notremain airborne, air-cleaning devices arerelatively ineective in their removal.9, 26, 60Thereore, eective allerg

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