FORMALDEHYDE FROM COMPOSITE WOOD PRODUCTS: 

EXPOSURE ASSESSMENT

Final Report

Exposure Assessment Branch

Economics, Exposure and Technology Division

Office of Pollution Prevention and Toxics

Office of Chemical Safety and Pollution Prevention

U.S. Environmental Protection Agency

1200 Pennsylvania Avenue, N. W. 

Washington, D.C. 20460

July 2012
i

ACKNOWLEDGMENT

EPA acknowledges the analytical and draft preparation support of Versar, Inc. of Springfield, 

Virginia in the preparation of this report, provided under Contract No. EP-W-10-005.

Notice

This is not an official guidance document and should not be relied upon to determine 

applicable regulatory requirements. This document was prepared to provide exposure

information for the rulemaking process, and to meet various administrative and legislative 

requirements. Due to the nature of the information available to EPA, the document 

contains various assumptions that may not reflect the regulatory determinations that an 

individual firm or organization would make were it to apply the rule's requirements to its 

specific circumstances. Persons seeking information on specific regulatory requirements 

should consult 40 CFR Part 770, and the preamble for the regulatory action.

Mention of the names of specific companies, organizations, or entities does not constitute 

an endorsement by EPA.
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TABLE OF CONTENTS

Section 1 EXECUTIVE SUMMARY......................................................................................... 1

1.1 BACKGROUND.............................................................................................................. 1

1.2 APPROACH .................................................................................................................... 2

1.3 RESULTS......................................................................................................................... 5

1.4 IMPLICATIONS.............................................................................................................. 8

Section 2 INTRODUCTION..................................................................................................... 10

2.1 BACKGROUND............................................................................................................ 10

2.1.1 Formaldehyde Uses and Emissions........................................................................ 10

2.1.2 Examples of Elevated Formaldehyde Levels in Residences.................................. 10

2.2 OBJECTIVES AND SCOPE ......................................................................................... 11

2.2.1 Rationale for the OPPT Exposure Assessment ...................................................... 11

2.2.2 Scope of the Assessment ........................................................................................ 13

2.3 THIS REPORT............................................................................................................... 14

Section 3 FORMALDEHYDE CONCENTRATIONS OUTDOORS AND INDOORS...... 15

3.1 FORMALDEHYDE IN OUTDOOR AIR..................................................................... 15

3.2 FORMALDEHYDE IN INDOOR AIR......................................................................... 16

3.2.1 Indoor Sources of Formaldehyde ........................................................................... 16

3.2.2 Recent Studies of Formaldehyde Concentrations Indoors..................................... 16

3.3 FORMALDEHYDE BACKGROUND CONCENTRATION ...................................... 18

Section 4 MODELING APPROACH....................................................................................... 19

4.1 MODEL USED FOR THE ASSESSMENT.................................................................. 20

4.2 FACTORS AFFECTING FORMALDEHYDE EXPOSURE INDOORS .................... 21

4.3 SENSITIVITY ANALYSIS........................................................................................... 22

4.4 MODEL INPUTS........................................................................................................... 25

4.4.1 Background Concentration..................................................................................... 25

4.4.2 Housing Types and House Volumes...................................................................... 25

4.4.3 Airflow Rates ......................................................................................................... 26

4.4.4 Emissions Half Life................................................................................................ 27

4.4.5 Indoor Temperature and Humidity......................................................................... 27

4.4.6 PWP Loadings – New-home Case ......................................................................... 31

4.4.7 PWP Loadings – Renovation Case......................................................................... 36

4.4.8 CWP Emission Rates.............................................................................................. 39

4.4.9 Exposure Groups and Activity Patterns ................................................................. 54

4.4.10 Concentrations at Locations Outside the Home ..................................................... 55

4.5 MODEL RUN MATRIX ............................................................................................... 57

Section 5 MODELING RESULTS ........................................................................................... 59

5.1 NEW-HOME CASE ...................................................................................................... 59

5.2 RENOVATION CASE .................................................................................................. 70

Section 6 DISCUSSION............................................................................................................. 81
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6.1 APPROACH AND RESULTS ...................................................................................... 81

6.1.1 Summary of Approach ........................................................................................... 81

6.1.2 Summary of Modeled Initial Formaldehyde Concentrations in Homes................. 81

6.1.3 Summary of Modeled ADCs for Exposure Groups ............................................... 84

6.2 DATA GAPS AND INFORMATION NEEDS............................................................. 87

6.2.1 Emissions Data ....................................................................................................... 87

6.2.2 Near-field Exposures.............................................................................................. 87

Section 7 REFERENCES .......................................................................................................... 88

Appendix A – Floor Plans by Structure Type

Appendix B – PWP Loading Spreadsheets

Appendix C – Section 3.2 of FIAM-pwp Model Documentation Report
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LIST OF TABLES

Table Page

1-1. Alternative Analytical Options Used for the Exposure Assessment ......................................4

3-1. Ambient Air Formaldehyde Levels (μg/m3) by Land Use Category ....................................14

3-2. Emission Rates of Selected Indoor Sources of Formaldehyde .............................................15

3-3. Summary of Recent Formaldehyde Field Monitoring Studies.............................................16

4-1. Input Values for Sensitivity Analysis – Base Condition for Conventional Home ...............23

4-2. Model Results for Base Condition for the Conventional Home...........................................23

4-3. Input Values for Sensitivity Analysis – Base Condition for Manufactured Home...............25

4-4. Model Results for Base Condition for the Manufactured Home ..........................................25

4-5. House Dimensions and Calculated Volume for Five Housing Types ..................................27

4-6. Summer and Winter Indoor Temperatures from RECS 2005, by Climate Zone..................30

4-7. Year-round Indoor Temperatures Derived from RECS 2005, by Climate Zone..................30

4-8. Modeled Year-round Indoor RH Level, by Climate Zone....................................................32

4-9. PWP Loading/Mix for SF Detached Homes (volume = 811 m3) – New Home...................33

4-10. PWP Loading/Mix for SF Attached Homes (volume = 523 m3

) – New Home ...................33

4-11. PWP Loading/Mix for Apartments (volume = 261 m3) – New Home.................................34

4-12. PWP Loading/Mix for Manufactured Homes (volume = 360 m3

) – New Home.................35

4-13. PWP Loading/Mix for Camper Trailers (volume = 61 m3

) – New Home ...........................36

4-14. PWP Loading/Mix for SF Detached Homes (volume = 811 m3) - Renovation ...................37

4-15. PWP Loading/Mix for SF Attached Homes (volume = 523 m3

) - Renovation....................37

4-16. PWP Loading/Mix for Apartments (volume = 261 m3) - Renovation .................................37

4-17. PWP Loading/Mix for Manufactured Homes (volume = 360 m3

) -- Renovation................38

4-18. PWP Loading/Mix for Camper Trailers (volume = 61 m3

) – Renovation ...........................38

4-19. Baseline Emission Levels (2013) For Domestically Produced CWPs, 

by Product Type and Emissions Certification Standard .......................................................39

4-20. Formaldehyde Emissions Standards in the CARB Air Toxic Control Measure for 

Formaldehyde Emissions from Compressed Wood Products (ppm)....................................40

4-21. Baseline Emission Levels for Non-Canadian Imported Composite Wood Products, 

by Product Type and Emissions Standard ............................................................................41

4-22. Baseline Emission Levels for Composite Wood Products by Product Type, Country of 

Origin, and Emissions Standard............................................................................................43

4-23. Alternative Analytical Options Evaluated in the Exposure Assessment..............................44

4-24. Emission Levels for CARB1 Regulatory Option by CWP Type, Origin, 

and Emissions Standard ........................................................................................................45

4-25. Emission Levels for CARB2 Analytical Option by CWP Type, Origin, and Emissions 

Standard ................................................................................................................................47

4-26. Emission Levels for NAF Scenario by CWP Type, Origin, and Emissions Standard .........48

4-27. Emission Levels for CARB2 Scenario with Laminates at NAF by CWP Type, 

Origin, and Emissions Standard............................................................................................49

4-28. Calculated Intercepts for Various Emission Levels for Each CWP Type............................51

4-29. Composite Intercepts by CWP Type – Baseline Scenario ...................................................52

4-30. Composite Intercepts by CWP Type and Emissions Scenario.............................................53
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4-31. Emission Rates for Underlayment and Coated CWPs – Baseline Scenario.........................53

4-32. Annual Hours at Home and Non-home Locations, by Exposure Group..............................56

4-33. Concentration Values for Non-home Locations – Baseline Scenario ..................................56

4-34. Derivation of Baseline Values for Daycare, School and Work Locations...........................57

4-35. Concentration Values for Selected Non-home Locations, by Emissions Scenario..............58

4-36. Model Run Matrix ................................................................................................................59

5-1. Modeled Initial Residential Concentrations for Eight Emissions Scenarios, 

ppb – New-home Case ..........................................................................................................61

5-2. Modeled Residential ADCs (House Age 0-1 Years) for Eight Emissions Scenarios, 

ppb – New-home Case ..........................................................................................................63

5-3. Modeled Residential ADCs by House Age for Manufactured Home in Climate Zone 3, 

by Emission Scenario, ppb – New-home Case .....................................................................64

5-4. Modeled ADCs (House Age 0-1 Years) for Infants for Eight Emissions Scenarios, 

ppb – New-home Case ..........................................................................................................65

5-5. Modeled ADCs (House Age 0-1 Years) for Preschool/School Children for Eight 

Emissions Scenarios, ppb – New-home Case .......................................................................66

5-6. Modeled ADCs (House Age 0-1 Years) for Non-industry Workers for Eight 

Emissions Scenarios, ppb – New-home Case .......................................................................67

5-7. Modeled ADCs (House Age 0-1 Years) for Fabrication-industry Workers for Eight 

Emissions Scenarios, ppb – New-home Case .......................................................................68

5-8. Modeled ADCs (House Age 0-1 Years) for Retirees for Eight Emissions Scenarios, 

ppb – New-home Case .......................................................................................................69

5-9. Modeled ADCs (House Age 0-1 Years) for Part-time Workers for Eight Emissions 

Scenarios, ppb – New-home Case ........................................................................................70

5-10. Modeled Initial Residential Concentrations for Eight Emissions Scenarios, 

ppb – Renovation Case .........................................................................................................72

5-11. Modeled Residential ADCs (House Age 0-1 Years) for Eight Emissions Scenarios, 

ppb – Renovation Case .........................................................................................................74

5-12. Modeled Residential ADCs by House Age for Manufactured Home in Climate Zone 3, 

by Emission Scenario, ppb – Renovation Case .....................................................................75

5-13. Modeled ADCs (House Age 0-1 Years) for Infants for Eight Emissions Scenarios, 

ppb – Renovation Case .........................................................................................................76

5-14. Modeled ADCs (House Age 0-1 Years) for Preschool/School Children for Eight 

Emissions Scenarios, ppb – Renovation Case ......................................................................77

5-15. Modeled ADCs (House Age 0-1 Years) for Non-industry Workers for Eight 

Emissions Scenarios, ppb – Renovation Case ......................................................................78

5-16. Modeled ADCs (House Age 0-1 Years) for Fabrication-industry Workers for Eight 

Emissions Scenarios, ppb – Renovation Case ......................................................................79

5-17. Modeled ADCs (House Age 0-1 Years) for Retirees for Eight Emissions Scenarios, 

ppb – Renovation Case .........................................................................................................80

5-18. Modeled ADCs (House Age 0-1 Years) for Part-time Workers for Eight Emissions 

Scenarios, ppb – Renovation Case........................................................................................81

6-1. Percent Reduction in Initial Formaldehyde Concentration, Relative to Baseline, by 

Alternate Emissions Scenario and Housing Type for New-home and Renovation Cases....85

6-2. Average Modeled ADC (House Age 0-1 Years) by Exposure Group and Emissions 

Scenario for New-home and Renovation Cases, ppb ...........................................................86
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LIST OF FIGURES

Figure Page

1-1. Modeled Initial Formaldehyde Concentrations by Housing Type – New-home Case ...........6

1-2. Modeled Initial Formaldehyde Concentrations by Housing Type – Renovation Case ..........6

1-3. Modeled ADCs (House Age 0-1 Years) for Exposure Groups – New-home Case ................7

1-4. Modeled ADCs (House Age 0-1 Years) for Exposure Groups – Renovation Case ...............8

1-5. Percent Reduction in Modeled Initial Formaldehyde Concentration by Alternate 

Emissions Scenario – New-home and Renovation Cases.......................................................9

1-6. Percent Reduction in Modeled ADCs for Exposure Groups by Alternate Emissions 

Scenario – New-home Case....................................................................................................9

4-1. Modeling Construct ..............................................................................................................18

4-2. Factors Affecting Indoor Formaldehyde Concentrations and Human Exposures................22

4-3. Relative Model Sensitivity for the Conventional Home.......................................................24

4-4. Relative Model Sensitivity for the Manufactured Home......................................................25

4-5. U.S. Climate Zones...............................................................................................................29

5-1. Modeled Initial Formaldehyde Concentrations by Emissions Scenario/Analytical Option 

and Housing Type – New-home Case ..................................................................................60

5-2. Modeled ADCs (House Age 0-1 Years) for Exposure Groups by Emissions 

Scenario/Analytical Option and Housing Type – New-home Case......................................62

5-3. Modeled Initial Formaldehyde Concentrations by Emissions Scenario/Analytical Option

and Housing Type – Renovation Case..................................................................................71

5-4. Modeled ADCs (House Age 0-1 Years) for Exposure Groups by Emissions 

Scenario/Analytical Option and Housing Type – Renovation Case.....................................73

6-1. Modeled Initial Formaldehyde Concentration by Emissions Scenario/Analytical Option 

for New-home and Renovation Cases...................................................................................83

6-2. Reduction in Modeled Initial Formaldehyde Concentration, Relative to Baseline, 

by Alternate Emissions Scenario for New-home and Renovation Cases.............................83

6-3. Percent Reduction in Modeled Initial Formaldehyde Concentration, Relative to Baseline, 

by Alternate Emissions Scenario for New-home and Renovation Cases.............................84

6-4. Percent Reduction in Modeled ADCs for Exposure Groups, Relative to Baseline, 

by Alternate Emissions Scenario for New-home Case .........................................................87

6-5. Percent Reduction in Modeled ADCs for Exposure Groups, Relative to Baseline, 

by Alternate Emissions Scenario for Renovation Case ........................................................87
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Section 1

EXECUTIVE SUMMARY

1.1 BACKGROUND

Formaldehyde is used widely by industry to manufacture certain types of building materials and 

household products. It also is a by-product of combustion and certain other natural processes. 

Indoor sources of formaldehyde include building materials such as composite wood products 

(CWPs1) and insulation, furnishings such as carpeting and furniture/flooring materials made with 

composite wood, tobacco smoke, household products such as cosmetics and paints, and unvented 

fuel-burning appliances such as gas stoves or kerosene heaters.

In residences, the most significant sources of formaldehyde are likely to be CWPs made with 

adhesives containing urea-formaldehyde (UF) resins (http://www.epa.gov/iaq/formalde.html). 

CWPs made for indoor use include: particleboard (PB, used as sub-flooring and shelving and in 

countertops, cabinetry and furniture); hardwood plywood (HWPW, used for decorative wall 

covering and in cabinets/furniture); and medium-density fiberboard (MDF, used for drawer 

fronts, cabinets, and furniture tops). MDF contains a higher resin-to-wood ratio than any other 

UF-based CWP and is generally recognized as being the highest formaldehyde emitter among 

CWPs.

Formaldehyde received national attention as recently as 2006, when the U.S. Federal Emergency 

Management Agency (FEMA) provided travel trailers and mobile homes for habitation by 

residents of the U.S. gulf coast who were displaced by Hurricane Katrina and Hurricane Rita. 

Some individuals who moved into these temporary homes complained of breathing difficulties, 

nosebleeds, and persistent headaches. In December 2007 and January 2008, the Centers for Disease 

Control and Prevention measured formaldehyde levels averaging 77 parts per billion (ppb; geometric 

mean) in a random sample of FEMA-supplied occupied travel trailers, park models, and mobile 

homes. In February 2008 U.S. health officials announced that potentially hazardous 

formaldehyde levels were found in both travel trailers and mobile homes provided by FEMA.

In April 2008 the California Air Resources Board (CARB) formally adopted an Airborne Toxic 

Control Measure (ATCM) to reduce formaldehyde emissions from CWPs sold, offered for sale, 

supplied, used, or manufactured for sale in California. The ATCM was intended to reduce the 

public’s exposure to formaldehyde by reducing emissions from HWPW, PB and MDF panels. At 

about the same time, the USEPA was petitioned under section 21 of TSCA by 25 organizations 

and approximately 5,000 individuals to adopt under TSCA Section 6(a) the CARB ATCM as a 

national standard. EPA found that the available information was not sufficient to support 

regulating formaldehyde emissions from composite wood products under TSCA Section 6(a). In 

response to the petition, EPA announced in the Federal Register on June 27, 2008 (73 FR 

36504)2 that EPA would initiate a proceeding to investigate whether and what type of regulatory 

or other action might be appropriate to protect against risks that may be posed by formaldehyde 

 1 In this report, the term “composite wood product” (CWP) refers only to hardwood plywood, medium density 

fiberboard or particleboard whereas “pressed wood product” (PWP) refers to a broader set of wood materials 

including, for example, softwood plywood and oriented strand board.

2 Available at http://www.gpo.gov/fdsys/pkg/FR-2008-06-27/pdf/E8-14618.pdf
2

emitted from composite wood products. In December 2008, EPA published an Advance Notice 

of Proposed Rulemaking (ANPR) to publicly initiate the investigation and obtain stakeholder 

input (73 FR 73620).3 On July 7, 2010, the Formaldehyde Standards for Composite Wood 

Products Act (FSCWPA) was signed into law. This statute, which adds a Title VI to TSCA, 

establishes formaldehyde emission standards for hardwood plywood, particleboard, and mediumdensity fiberboard that are identical to the CARB ATCM Phase II standards.4 TSCA Title VI

directs EPA to promulgate implementing regulations by January 1, 2013 that address: sellthrough dates for products; stockpiling; third-party testing and certification; auditing and 

reporting of third-party certifiers; recordkeeping; chain of custody; labeling; enforcement; 

products made with no-added formaldehyde (NAF) and ultra-low emitting formaldehyde (ULEF) 

resins; laminated products; finished goods; hardboard; and products containing de minimis

amounts of composite wood products. 

In support of the implementing regulations, as with other rulemakings that are determined to be 

“significant regulatory action[s]” under Executive Order 12866—Regulatory Planning and 

Review, EPA is required to conduct an economic analysis of the costs and benefits associated 

with the rulemaking. In support of this economic analysis, EPA assessed formaldehyde 

exposures indoors in recently constructed or renovated residential structures. That assessment is 

the subject of this report.

1.2 APPROACH

A modeling-based approach was chosen for the exposure assessment because of the number of 

situations of potential interest and the limited amount of current or recent monitoring data 

available. Both new-construction, or new-home, and renovation cases were examined. As a 

general rule, expected or average values were used for model inputs, as opposed to a range or 

distribution of values. Variability was introduced for certain input parameters expected to have a 

significant influence on the modeling results. Seven alternative emissions scenarios (analytical 

options) were modeled along with a baseline (year 2013) scenario. Model runs were made for 

five different housing types, in five different climates zones, for each emissions scenario. Six 

exposure groups were included in the assessment, which estimated not only at-home but also 

away-from-home formaldehyde exposure in the form of an average daily concentration (ADC) 

reflecting “around the clock” exposure.

The model used for the assessment – Formaldehyde Indoor Air Model - Pressed Wood Products, 

Version 2.0 (FIAM-pwp v2.0) – is an adaptation of one initially developed during the 1980s by 

Dr. Thomas Matthews and colleagues at the Oak Ridge National Laboratory. In brief, the 

“Matthews model” was designed to estimate the steady-state formaldehyde concentration indoors

due to emission sources such as PWPs. PWP emission rates are dependent on the formaldehyde

concentration in the vapor phase, in accordance with Fick’s Law describing the bulk-vapor 

interphase at the surface of a pressed wood emission source. The initial, “steady-state” indoor 

concentration estimated by the model is assumed to decrease over time as the reservoir of 

formaldehyde in various sources is gradually depleted; the gradual decrease is assumed to follow 

a first-order exponential process.

 3 Available at http://www.gpo.gov/fdsys/pkg/FR-2008-12-03/pdf/E8-28585.pdf 4 Available at http://www.arb.ca.gov/toxics/compwood/compwood.htm
3

Inputs to the FIAM-pwp model include the formaldehyde background concentration (intended to 

reflect the contribution of formaldehyde outdoors as well as indoor sources other than PWPs), 

the number of zones (1 or 2), zone volumes and airflows, indoor temperature and humidity, the 

types and amounts of PWPs installed in the structure and their emission rates, and exposure 

factors such as time spent in/out of the residence for exposure groups including children, workers 

and retirees. The results include modeled indoor formaldehyde concentrations, both initial 

steady-state values and those at later points in time, together with exposure estimates such as the 

daily average concentration (ADC) to which an individual is exposed.

Floor plans for representative structures were used as a guide in developing PWP loading rates 

for five housing types – single-family attached and detached homes, apartments, manufactured 

homes, and camper trailers. The loading rates differed for the new-home versus renovation cases.

For the renovation case, it was assumed that an entire kitchen was renovated, including cabinets, 

countertop and ancillary areas such as a pantry. It was further assumed that the vinyl covering 

the kitchen floor and adjacent hallway floor was replaced with engineered wood.

Because many CWP manufacturers are in the midst of modifying their production technology 

and raw materials to achieve compliance with Phase 2 of the CARB ATCM, using current 

emission levels to estimate emission levels in 2013 would not accurately reflect the 2013 

baseline. Instead, baseline emission levels were estimated using responses to a survey question 

about emission levels that mills planned to achieve within the next three years. These emission

levels were weighted by production levels that mills reported in the survey, in order to estimate 

average emission levels by certification standard. The survey data also were used to estimate the 

share of total production volume represented by products meeting each emissions standard. 

Among imported products, baseline emission levels were estimated separately for products from 

Canada versus those from the rest of the world. The known composite wood manufacturers in 

Canada were compared to the CARB list of certified mills, and most Canadian mills were found 

to be CARB-certified. As a result, Canadian mills were assumed to achieve the same baseline 

emissions as U.S. mills. The baseline emission levels for non-Canadian imported CWPs were 

estimated using data from a 2009 presentation by Professional Service Industries (PSI), a CARB 

Third Party Certifier (TPC). Although PSI is located in the U.S., the mills that it certifies are 

located in countries that are major sources of pressed wood products imported into the U.S. 

For the purposes of TSCA Title VI, laminated products are a subset of hardwood plywood. The 

statute defines a laminated product as one made by affixing a wood veneer to a particleboard, 

medium-density fiberboard, or veneer-core platform. The statutory definition goes on to state 

that laminated products are component parts used in the construction or assembly of a finished 

good, and that a laminated product is produced by the manufacturer or fabricator of the finished 

good in which the product is incorporated. EPA is given the authority to modify the statutory 

definition of laminated product through rulemaking, and also is directed to use all available and 

relevant information to determine whether the definition of HWPW should exempt engineered 

veneer or any laminated product. The Hardwood Plywood and Veneer Association has indicated

that laminated products represent about 30% of engineered wood flooring production. Therefore, 

this exposure analysis assumes that laminated products represent 30% of the volume of HWPW.

Seven alternative emissions scenarios or analytical options were used for the assessment, as 

listed and described briefly in Table 1-1. The first four scenarios – CARB1, CARB2/Statutory 
4

Option, CARB2/Statutory Option including laminated products at NAF, and NAF – assume that 

progressively higher percentages of CWPs meet stricter emission standards. The last three 

scenarios are similar to CARB1, CARB2/Statutory Option, and NAF, with the single exception 

that laminated products are not regulated as HWPW under TSCA. The methods and associated 

assumptions for estimating emission levels for the various scenarios are fairly involved and do 

not lend themselves to a convenient summary; instead, the reader is referred to the detailed 

descriptions that can be found in Section 4.4.8 of this report.

Table 1-1. Alternative Analytical Options Used for the Exposure Assessment

Analytical Option Description

CARB1, Including Laminated 

Products

All CWPs, including laminated productsa

, are at emission levels that 

meet CARB Phase 1 standards1. Products that meet CARB Phase 1 

standards at baseline are assumed to remain at that emission level.

CARB2/Statutory Option,

Including Laminated 

Productsb

All CWPs, including laminated products, are at emission levels that 

meet CARB Phase 2 standards. Products that meet CARB Phase 2 

standards at baseline are assumed to remain at that emission level.

CARB2/Statutory Option, 

with Laminated Products

Meeting NAF-based Resin 

Statutory Emission Standards

As above, except that laminated products are assumed to meet NAFc

statutory emission standards.

NAF, Including Laminated 

Products

All CWPs, including laminated products, are at emission levels that 

meet NAF standards. Products that meet NAF standards at baseline 

are assumed to remain at that emission level.

CARB1, Excluding 

Laminated Products

Like CARB1 above, except that laminated products are not regulated 

as HWPW and, thus, are assumed remain at baseline emission levels.

CARB2/Statutory Option,

Excluding Laminated 

Products

Like CARB2 above, except that laminated products are not regulated 

as HWPW and, thus, are assumed remain at baseline emission levels.

NAF, Excluding Laminated 

Products

Like NAF above, except that laminated products are not regulated 

and, thus, are assumed remain at baseline emission levels.

a 30% of all HWPW products are assumed to be laminated products. b The CARB emission standards for this scenario are equivalent to those specified in the FSCWPA. c NAF = no added formaldehyde.

This document discusses various options with respect to formaldehyde and composite wood 

products, including emissions standards that are different from those set in TSCA Title VI. This 

document discusses alternative emissions standards simply for informational purposes. The 

breadth of the discussion here should not necessarily imply that EPA has corresponding 

flexibility in implementing the statute.

The modeling also accounted for PWP types (e.g., structural plywood, structural composite 

lumber, oriented strand board, and glued laminated lumber) that would not be subject to emission 

standards because they are specifically exempt under TSCA Title VI. During the 1980s and up 

through the mid-1990s, emission rates for various types of PWPs were derived from sets of 

chamber emission tests that were conducted at multiple air exchange rates and/or product loading 

ratios. These multiple tests enabled estimation of model parameters – slope and intercept – that 
5

reflect the dependence of the emission rate on the indoor formaldehyde concentration. The slope 

is a mass transfer coefficient that reflects the “backpressure” effect of the indoor formaldehyde

concentration on the emission rate; the intercept reflects the hypothetical emission rate when the 

indoor formaldehyde concentration is zero.

Because multiple tests as described above are rarely conducted at present, it was not possible to 

directly estimate the slope and intercept for CWPs complying with various emission standards. 

American Society for Testing and Materials (ASTM, now known as ASTM International) 

Standard E1333-10, Standard Test Method for Determining Formaldehyde Concentrations in Air 

and Emission Rates from Wood Products Using a Large Chamber (ASTM 2010), is commonly 

used to demonstrate compliance with formaldehyde emission standards. The method prescribes 

both an air exchange rate and product loading ratios for the chamber tests. By using these rates 

together with an assumed slope (based on earlier testing) for each CWP type, it was possible to 

determine the corresponding intercept for a hypothetical source that meets a given emissions

standard. 

To cover the various exposure situations that can depend on factors such as age and work status, 

the following exposure groups were defined:

• Infant (age 0 to <2)

• Pre-school/school-age children (age 2 to <16)

• Worker (age 16 to <64)

• Retiree (age 64 or greater)

The choice of age breaks to distinguish infants and pre-school/school children from adults was 

driven by the possible age dependency of cancer slope factors. The worker group was further 

divided among non-industry workers, fabrication-industry workers, and part-time workers. In 

terms of activity patterns, the retiree group also can be used to represent individuals of age 16 to 

<64 who are unemployed or working at home.

Locations outside the home where individuals spend time were considered in the assessment to 

provide a total or “around-the-clock” exposure perspective. Concentrations assigned to these 

locations for the baseline emissions scenario were derived from several sources. For example, 

both in-vehicle and outdoor concentrations were based on average values reported from EPA’s 

air monitoring network. Values assigned to workplaces were taken from a recent EPA report 

developed by OPPT’s Chemical Engineering Branch, wherein concentrations were estimated 

using a similar modeling approach to that described in this report. Values assigned to schools and 

daycare facilities were based largely on measurement results from field monitoring studies.

1.3 RESULTS

Figure 1-1 conveys the modeled initial steady-state concentrations for the new-home case. 

Results are shown for the baseline scenario and seven alternate analytical options, for each of the 

five housing types used in the assessment (results are averaged across climates zones for each 

type). The highest modeled concentrations are for camper trailers. The lowest concentrations 

occur for the case where CWPs are at emission levels that meet no-added-formaldehyde (NAF) 

standards, whether or not laminated products are assumed to be regulated. Figure 1-2 shows a 

very similar pattern for the renovation case, but with lower concentrations as compared to the 

new-home case.
6

Figure 1-1. Modeled Initial Formaldehyde Concentrations by Housing Type – New-home Case.

Figure 1-2. Modeled Initial Formaldehyde Concentrations by Housing Type – Renovation Case.

* Results shown are 

for Zone 1 of these 

two-zone structures

* Results shown are 

for Zone 1 of these 

two-zone structures
7

Figure 1-3 conveys the overall ADCs for the new-home case, reflecting combined in-home and 

away-from-home exposure, for each exposure group (results for each group are averaged across 

housing types and climate zones). The ADCs that are shown are for the first year following new 

construction (i.e., house age of 0-1 years). Differences across the exposure groups generally are 

no more than 20 percent, with the notable exception of workers in the fabrication industry who 

have a substantially higher overall exposure due to their elevated at-work exposure. Figure 1-4 

shows a similar pattern for the renovation case, but at lower exposure levels than for the case of 

new construction.

Figure 1-3. Modeled ADCs (House Age 0-1 Years) for Exposure Groups – New-home Case.
8

Figure 1-4. Modeled ADCs (House Age 0-1 Years) for Exposure Groups – Renovation Case.

1.4 IMPLICATIONS

Figure 1-5 indicates the percent concentration reduction for each alternate analytical option, 

relative to baseline, for both the new-home and the renovation cases (results are averaged across 

housing types and climate zones). In either case, the reduction clearly is the greatest for the NAF 

scenarios. Figure 1-6 indicates the percent ADC reduction per exposure group for the alternate 

emissions scenarios for the new-home case, again showing the greatest reductions for the NAF 

scenarios (the pattern is very similar for renovation).
9

Figure 1-5. Percent Reduction in Modeled Initial Formaldehyde Concentration by 

Emissions Scenario – New-home and Renovation Cases.

Figure 1-6. Percent Reduction in Modeled ADCs for Exposure Groups by Alternate 

Emissions Scenario – New-home Case.
10

Section 2

INTRODUCTION5

2.1 BACKGROUND

2.1.1 Formaldehyde Uses and Emissions

Formaldehyde is used widely by industry to manufacture certain types of building materials and 

household products. It also is a by-product of combustion and certain other natural processes. 

Thus, it may be present in substantial concentrations both indoors and outdoors. Indoor sources 

of formaldehyde include building materials such as composite wood products (CWPs6) and 

insulation, furnishings such as carpeting and furniture/flooring materials made with composite

wood, tobacco smoke, household products such as cosmetics, paints coatings and paper goods, 

and unvented fuel-burning appliances such as gas stoves or kerosene heaters. Formaldehyde, by 

itself or in combination with other chemicals, serves a number of purposes in manufactured 

products. For example, it is used to add permanent-press qualities to clothing and draperies, as a 

component of glues and adhesives, and as a preservative in some paints and coating products.

In residences, the most significant sources of formaldehyde are likely to be CWPs made with 

adhesives containing urea-formaldehyde (UF) resins (http://www.epa.gov/iaq/formalde.html). 

CWPs made for indoor use include: particleboard (PB, used as sub-flooring and shelving and in 

countertops, cabinetry and furniture); hardwood plywood (HWPW, used for decorative wall 

covering and in cabinets/furniture); and medium-density fiberboard (MDF, used for drawer 

fronts, cabinets, and furniture tops). MDF contains a higher resin-to-wood ratio than any other 

UF-based CWP and is generally recognized as being the highest formaldehyde emitter among 

CWPs (http://www.epa.gov/iaq/formalde.html). Products such as softwood plywood and oriented 

strand board (OSB) are produced primarily for exterior construction use and contain the dark or 

red/black-colored phenol-formaldehyde (PF) resin. Although formaldehyde is present in both 

types of resins, pressed woods that contain PF resin generally emit formaldehyde at considerably 

lower rates than those containing UF resin.

The rate at which products like pressed wood or textiles release formaldehyde can change over 

time. Formaldehyde emissions generally decrease as products age. High indoor temperature or 

humidity can cause increased formaldehyde release from these products, particularly when they 

are new.

2.1.2 Examples of Elevated Formaldehyde Levels in Residences

During the 1970s many homeowners had urea-formaldehyde foam insulation (UFFI) installed in 

the wall cavities of their homes as an energy conservation measure. Many of these homes were 

 5 Portions of this section were extracted or adapted from the following web sites or citations:

http://www.epa.gov/iaq/formalde.html

http://www.pbmdf.com

T. Salthammer, S. Mentese, and R. Marutzky. 2010 Formaldehyde in the Indoor Environment, Chem. Rev., 110: 

2536–2572; available at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2855181/

6 In this report, the term “composite wood product” (CWP) refers only to hardwood plywood, medium density 

fiberboard, or particleboard whereas “pressed wood product” (PWP) refers to a broader set of wood materials 

including, for example, softwood plywood and oriented strand board.
11

found to have relatively high indoor formaldehyde concentrations soon after UFFI installation. 

The use of UFFI insulation in residences has steadily declined to the point that recent 

installations, if any, are extremely rare. Because formaldehyde emissions from UFFI decline 

with time, homes in which UFFI was installed many years ago are unlikely to have high levels of 

formaldehyde now.

Elevated formaldehyde levels have been noted in prefabricated and mobile homes, largely 

because of the relatively high loading of higher-emitting CWPs used in their construction. Since 

1985, the Department of Housing and Urban Development (HUD) has permitted only the use of 

PB and HWPW products that conform to specified formaldehyde emission limits in the 

construction of manufactured homes. The Composite Panel Association (CPA) Formaldehyde 

Grademark Program7 has been developed to provide independent certification of formaldehyde 

emission levels from wood panel products. The Program includes requirements for initial 

qualification for product certification, plant quality control procedures, and periodic inspections 

to reasonably assure that certified unfinished composite panel products meet the emission limits 

specified in applicable standards. Although the Program originally was developed in response to 

HUD’s certification requirements, it can be used to certify conformance of different types of 

panel products to different governmental or voluntary industry standards.

In 2005 the U.S. Federal Emergency Management Agency (FEMA) provided travel trailers and 

mobile homes for habitation by residents of the U.S. gulf coast who were displaced by Hurricane 

Katrina and Hurricane Rita. Some individuals who moved into these temporary homes 

complained of breathing difficulties, nosebleeds, and persistent headaches. In December 2007 and 

January 2008, the Centers for Disease Control and Prevention (CDC) measured formaldehyde levels 

in a random sample of 519 FEMA-supplied occupied travel trailers, park models, and mobile homes 

(CDC 2008/2010; DHS 20009). In many of the homes tested, formaldehyde levels were higher than 

typical U.S. indoor levels. The geometric mean level of formaldehyde in the sampled structures was 

77 parts per billion (ppb), with a range from 3 to 590 ppb. Formaldehyde levels varied by trailer type, 

but all types tested had some levels at or above 100 ppb. In February 2008 U.S. health officials 

announced8 that potentially hazardous formaldehyde levels were found in both travel trailers and 

mobile homes provided by the agency.

2.2 OBJECTIVES AND SCOPE

2.2.1 Rationale for the OPPT Exposure Assessment

In April 2008 CARB formally adopted an Airborne Toxic Control Measure9 (ATCM) to reduce 

formaldehyde emissions from composite wood products sold, offered for sale, supplied, used, or 

manufactured for sale in California. The ATCM was intended to reduce the public’s exposure to 

formaldehyde by reducing emissions from HWPW, PB and MDF. 

On March 24, 2008, EPA was petitioned under section 21 of TSCA by 25 organizations and 

approximately 5,000 individuals to adopt under TSCA Section 6(a) the CARB ATCM as a 

national standard. EPA found that the available information was not sufficient to support 

regulating formaldehyde emissions from composite wood products under TSCA Section 6(a).

 7 See http://www.pbmdf.com/Certification---Formaldehyde-Grademark-Program 8 See http://www.msnbc.msn.com/id/23168160/ns/us_news-life/t/cdc-tests-confirm-fema-trailers-are-toxic/ 9 See http://www.arb.ca.gov/toxics/compwood/compwood.htm for recent activity related to this ATCM.
12

In response to the petition, EPA announced in the Federal Register on June 27, 2008 (73 FR 

36504)10 that EPA would initiate a proceeding to investigate whether and what type of regulatory 

or other action might be appropriate to protect against risks that may be posed by formaldehyde 

emitted from composite wood products. In December 2008, EPA published an Advance Notice 

of Proposed Rulemaking (ANPR) to publicly initiate the investigation and obtain stakeholder 

input (73 FR 73620).11 On July 7, 2010, the Formaldehyde Standards for Composite Wood 

Products Act (FSCWPA) was signed into law. This statute, which adds a Title VI to TSCA, 

establishes formaldehyde emission standards for hardwood plywood, particleboard, and mediumdensity fiberboard that are identical to the CARB ATCM Phase II standards.

12 TSCA Title VI

directs EPA to promulgate implementing regulations by January 1, 2013 that address: sellthrough dates for products; stockpiling; third-party testing and certification; auditing and 

reporting of third-party certifiers; recordkeeping; chain of custody; labeling; enforcement; 

products made with no-added formaldehyde (NAF) and ultra-low emitting formaldehyde (ULEF) 

resins; laminated products; finished goods; hardboard; and products containing de minimis

amounts of composite wood products. 

In support of the implementing regulations, as with other rulemakings that are determined to be 

“significant regulatory action[s]” under Executive Order 12866 – Regulatory Planning and 

Review, EPA is required to conduct an economic analysis of the costs and benefits associated 

with the rulemaking. In support of this economic analysis, EPA has assessed formaldehyde 

exposures indoors, due to CWPs, in recently constructed or renovated residential structures. In 

view of the considerable number of situations or structures of potential interest and the limited 

amount of current or recent monitoring data available, a modeling-based approach was chosen 

for the exposure assessment. The model that was used for the assessment – Formaldehyde 

Indoor Air Model - Pressed Wood Products (FIAM-pwp; USEPA 2012a) – is an adaptation of 

one that initially was developed during the 1980s by Dr. Thomas Matthews and colleagues at the 

Oak Ridge National Laboratory (Matthews et al. 1983; Matthews et al. 1987). 

In brief, the “Matthews model” was designed to estimate the steady-state formaldehyde

concentration due to emission sources such as PWPs in a single indoor compartment or zone.

Product emission rates in the model are dependent on the formaldehyde concentration in the 

vapor phase, in accordance with Fick’s Law describing the bulk-vapor interphase at the surface 

of a pressed wood emission source. The initial (steady-state) indoor concentration calculated by 

the model is assumed to decrease over time, in accordance with a first-order exponential process,

as the reservoir of formaldehyde in various sources (or sinks) is gradually depleted. A “backpressure” effect also was introduced by Matthews, which essentially is a dampening effect

produced by the amount of formaldehyde in the indoor air already. As noted earlier, there are 

many sources of formaldehyde including infiltration of outdoor air, gas-fired stoves and tobacco 

smoke. Fick’s law states that the migration of a substance is concentration dependent, with the 

chemical migrating from a higher-concentration medium to a lower-concentration one until 

equilibrium is established. The total amount of formaldehyde emitted from all sources could 

reduce the amount of formaldehyde emitted from individual PWPs because the concentration 

gradient is “pushing back” towards each PWP source. This effect will increase the amount of 

 10 Available at http://www.gpo.gov/fdsys/pkg/FR-2008-06-27/pdf/E8-14618.pdf 11 Available at http://www.gpo.gov/fdsys/pkg/FR-2008-12-03/pdf/E8-28585.pdf 12 Available at http://www.arb.ca.gov/toxics/compwood/compwood.htm
13

time over which emissions can occur from any specific PWP. In reality, this push and pull of 

formaldehyde from PWPs to indoor air may change many times during a day as the activity 

patterns of occupants change. For example, at night people who are sleeping would not be 

smoking, cooking, or bringing in dry cleaning, all potential sources of formaldehyde. The effects 

of activity patterns are explored in the sensitivity analysis later in this report.

In the mid-1990s an EPA-sponsored pilot study was undertaken (Koontz et al. 1996) to assess 

the contribution of UF-bonded wood products to formaldehyde levels in homes and to evaluate 

EPA exposure models. Shortly after this study was completed, Versar developed a modified 

version of the “Matthews model” for OPPT that included: (1) estimation of steady-state 

formaldehyde concentrations for the case of a two-zone indoor environment; and (2) 

incorporation of reversible (re-emitting) indoor sinks. The modified model also included the 

option to be run in a single-zone mode. The model was recently updated and has been subjected 

to peer review; the updated model has the capability to provide exposure estimates, primarily to 

support OPPT efforts such as the exposure assessment described in this document. 

2.2.2 Scope of the Assessment

As noted above, formaldehyde emissions tend to decrease as the formaldehyde-bearing materials 

age. This assessment focuses on formaldehyde concentrations and associated inhalation 

exposures in recently built or renovated residential structures. The FIAM-pwp model used to 

support the assessment provides estimates of indoor formaldehyde concentrations due to CWP 

emissions. As described in Section 3.2 of the model documentation (USEPA 2012a), the model 

calculates the initial indoor concentration(s) under an assumed steady-state condition. In real life, 

a true steady-state is never achieved, due to the dynamics of formaldehyde source emissions and 

indoor sinks. However, it has been observed in field studies that the combined actions of sources 

and sinks typically result in an initial rise in the indoor concentration, followed by a “levelingoff” period that may be fairly brief and then a longer period of gradual decline in concentration. 

The initial formaldehyde concentrations estimated by the model are intended to approximate 

indoor concentrations during the leveling-off period, which often occurs within 30 days or less 

following the installation of formaldehyde-bearing materials. 

Inputs to the FIAM-pwp model include the formaldehyde background concentration, the number 

of zones (1 or 2), zone volumes and airflows, indoor temperature and humidity, types and 

amounts of CWPs installed in the structure and their emission rates, and exposure factors such as 

time spent in/out of the residence for exposure groups including children, workers and retirees. 

The results include modeled indoor formaldehyde concentrations, both initial “steady-state” 

values and those at later points in time, together with exposure estimates such the daily average 

concentration (ADC) to which an individual is exposed. To support the exposure assessment, the 

model was run for a variety of scenarios by varying inputs such as the type of residence (e.g., 

single-family detached, apartment, mobile home), climate zone in which the structure is located,

amounts of CWPs, and exposure factors for exposed individuals. In addition, the impact on 

exposure of different analytical options (i.e., different emissions standards) was assessed.

This document discusses various options with respect to formaldehyde and composite wood 

products, including emissions standards that are different from those set in TSCA Title VI. This 

document discusses alternative emissions standards simply for informational purposes. The 
14

breadth of the discussion here should not necessarily imply that EPA has corresponding 

flexibility in implementing the statute.

2.3 THIS REPORT

Following a discussion of formaldehyde concentrations outdoors and indoors in Section 3 of this 

document, the modeling approach is described in Section 4. The description of approach 

includes: (1) the specific indoor environments (i.e., housing types) of interest; (2) factors 

affecting formaldehyde concentrations/exposures and their relative influence as inferred from 

sensitivity analysis; and (3) the sets of model inputs that were chosen to support the exposure 

assessment. Modeling results, both for indoor concentrations and for associated exposures, are 

provided in Section 5. The implications of these results, along with information gaps identified in 

the course of preparing for and conducting the assessment effort, are discussed in Section 6.

References cited throughout the document are listed in Section 7.
15

Section 3

FORMALDEHYDE CONCENTRATIONS OUTDOORS AND INDOORS 

3.1 FORMALDEHYDE IN OUTDOOR AIR

Formaldehyde is the most common aldehyde in the outdoor ambient environment and is usually 

present in the highest concentration of all the major aldehydes and ketones in ambient air 

(Finlayson-Pitts and Pitts, 2000). As summarized by ATSDR (1999), outdoor formaldehyde

levels are quite low (about 0.2 ppb) in unpopulated areas and range from 2 to 6 ppb in suburban 

areas and from 10 to 20 ppb in heavily populated or industrial areas. 

The most current ambient air monitoring data for formaldehyde come from the EPA’s air quality 

system database (EPA’s AirData website: http://www.epa.gov/air/data/index.html). These data 

have been collected from a wide variety of sources, including state and local environmental 

agencies, but have not been collected from a statistically based survey. The most recent data, for 

the year 2007, come from 188 monitors located in 33 states (USEPA 2012b). The annual means 

for these monitors range from 0.7 to 45.0 μg/m3 (0.56 - 36.3 ppb) and have an overall average of 

3.44 μg/m3 (2.77 ppb). Table 3-1 shows a breakout of the data by land use based on the 

combined data for 2005, 2006 and 2007. The mobile category (land near major highways or 

interstates such that it is primarily impacted by mobile sources) has the highest mean levels and 

agricultural lands have the lowest. The means in the table (in μg/m3) for agricultural, residential 

and commercial areas correspond to 1.7 ppb, 2.2 ppb and 2.65 ppb, respectively.

Most of the recent indoor-air formaldehyde monitoring studies described in Section 3.2 included 

outdoor formaldehyde measurements. The average outdoor formaldehyde concentration 

measured in these studies ranged from about 2 to 5 ppb.

Table 3-1. Ambient Air Formaldehyde Levels (μg/m3)by Land Use Category

Statistic Land Use Category

Agriculture Commercial Forest Industrial Mobilea Residential

No. of samples 17 166 19 61 16 282

Mean ± std. dev. 2.08 ± 0.98 3.26 ± 2.76 2.79 ± 2.17 6.28 ± 14.45 6.84 ± 7.28 2.75 ± 1.71

Minimum 0.34 0.20 0.40 0.14 2.02 0.17

Maximum 4.34 20.61 7.33 74.72 23.39 12.35 a “Mobile” is ambient air in locations primarily impacted by mobile sources.

Source: AirData for 2005, 2006, and 2007 (USEPA 2012b).
16

3.2 FORMALDEHYDE IN INDOOR AIR

3.2.1 Indoor Sources of Formaldehyde

As noted in Section 2.1, indoor sources of formaldehyde include building materials, tobacco 

smoke, household products, and unvented fuel-burning appliances. Household products include 

textile products, carpet, pads and tape, drapes, and a fairly wide array of consumer products 

(CARB 2005). The most comprehensive set of emission tests for formaldehyde-bearing products 

and materials was performed by Battelle for CARB (Kelly 1996; Kelly et al. 1999). 

Formaldehyde emissions were determined from bare UF and PF wood products, UF wood 

products with vinyl, paper and other coatings, and from decorative laminates, permanent-press 

fabrics, fiberglass insulation, paper goods, paints, cosmetics and acid-cured coatings.

Table 3-2 lists formaldehyde emission rates for selected indoor sources that were tested under 

this project. Although initial emission rates for wet products such as nail polish or floor finish 

generally are much higher than those for dry products such as CWPs, the dry-product emissions 

can persist for years whereas the emissions for wet products are relatively short-lived, often 

declining by orders of magnitude over a time period of 24 hours. The dry-product emissions also 

decrease in strength with the passage of time, but at a much slower rate of decline.

Table 3-2. Emission Rates of Selected Indoor Sources of Formaldehyde 

Source of Formaldehyde Emission Rate, 

μg/m2/hra

Bare Urea-Formaldehyde Wood Products 8.6 to 1,580

Coated Urea-Formaldehyde Products < 2.7 to 460

Permanent Press Fabrics 42 to 215

Decorative Laminates 4 to 51

Fiberglass Products 16 to 32

Bare Phenol-Formaldehyde Wood Products 4.1 to 9.2

Paper Grocery Bags and Towels < 0.6

Latex Paint 502

Fingernail Hardener 215,500

Nail Polish 20,700

Base Coat Floor Finish 1,050,000

Top Coat Floor Finish 421,000

a Values listed for wet products (e.g., latex paint, fingernail hardener) are average initial emissions.

3.2.2 Recent Studies of Formaldehyde Concentrations Indoors

One of the earlier major studies of formaldehyde indoors was conducted by Sexton and 

colleagues (1989) in the mid-1980s. Participants in this field monitoring study, involving 470 

mobiles homes in California, were volunteers solicited by mail. One-week formaldehyde

concentrations were measured in the kitchen and bedroom of each trailer in both winter and 
17

summer using passive monitors. The average measurement result was about 70 ppb during the 

summer and 80 ppb during the winter; 31 percent of the measurement results exceeded 100 ppb.

More recent formaldehyde field studies of note, mainly in residential structures, are summarized 

in Table 3-3. The first two studies – Offerman et al. (2008) and Hodgson et al. (2000) – both 

were conducted on new homes, with the Offerman study covering 100+ new single-family 

homes in California and the Hodgson study covering fewer structures in the eastern and 

southeastern regions of the U.S. but including both manufactured and site-built homes. The 

average (geometric mean) formaldehyde concentration indoors was between 30 and 35 ppb for 

both studies, with maximum values of 117 and 58 ppb reported by the two studies, respectively.

Studies of existing homes in urban U.S. areas by Liu et al. (2006) and Sax et al. (2006) measured 

lower average (median) formaldehyde concentrations, on the order of 10-15 ppb, and lower 

maximum values as well, with the highest reported maximum (45 ppb) in a Los Angeles home 

during the winter. Two Canadian studies (Gilbert et al 2006; Gilbert et al 2005) had nearly 

identical results; in each case the average (geometric mean) indoor formaldehyde concentration 

was around 25 ppb and the highest measured concentration was slightly above 70 ppb. 

Table 3-3. Summary of Recent Formaldehyde Field Monitoring Studies

Study/Reference Description (Location and 

Number/Types of Structures)

Formaldehyde Concentration, ppb

Central Value Range

Offerman et al. 

2008 108 new SF homes in CA 31.1 (median) 3.8 to 116.7

Hodgson et al. 

2000

New homes in eastern/SE U.S.:

4 new manufactured homes

7 new site-built homes

Geometric Means:

34

36

21 to 47

14 to 58

Liu et al. 2006 234 homes in Los Angeles County, CA; 

Elizabeth, NJ; and Houston, TX 16.3 (median) 10.2 to 26.4

(5th - 95th percentiles)

Sax et al. 2006

Inner-city homes:

NY City (46) – winter (W), summer (S)

Los Angeles (41) – Winter (W), fall (F)

Medians:

10 W, 15 S

15 W, 12 F

4-18 W, 5-41 S

6-45 W, 6-26 F

Gilbert et al. 2006 96 homes in Quebec City, Canada 24.0 (geo. mean) 7.8 to 73.2

Gilbert et al. 2005 59 homes in Prince Edward Island, 

Canada 27.0 (geo. mean) 4.5 to 71.1

Hodgson et al. 

2004 4 new relocatable classrooms 8 (average indooroutdoor level)

4 to 12

(indoor-outdoor)

CARB 2004 Portable and traditional classrooms in 

67 California schools (Phase II study)

Arithmetic Means:

15 (portable)

12 (traditional)

95th Percentiles:

26 (portable)

22 (traditional)

CDC 2008/2010;

DHS 2009

519 structures:

Travel trailers (360)

Park models (90)

Mobile homes (69)

77 (geo. mean)

---

---

---

3 to 590

3 to 590

3 to 160

11 to 320

Maddalena et al. 

2008 4 FEMA camper trailers 463 (average) 269 to 753

EPA BASE Studya 100 public/commercial buildings in 37 

cities 12 (median) 3.6 to 26.0

(5th - 95th percentiles)

a http://www.epa.gov/iaq/base/
18

Some other indoor environments of potential interest for this exposure assessment have been 

monitored on occasion. During December/January 2007-2008 the CDC measured formaldehyde 

levels in 500+ structures of the types (travel trailers, park models and mobile homes) used by 

FEMA for displaced Hurricane Katrina/Rita victims (CDC 2008/2010; DHS 2009). The average 

(geometric mean) formaldehyde concentration in these structures was 77 ppb and the maximum 

measured concentration was 590 ppb. Under an interagency agreement with the CDC, the 

Lawrence Berkeley National Laboratory (LBNL; Maddalena et al. 2008) studied four FEMA 

temporary housing units (camper trailers) to assess indoor emissions of aldehydes and other 

VOCs. Measured formaldehyde levels in these structures ranged from 269 to 753 ppb.

Formaldehyde measurements in buildings other than residential structures have been relatively 

rare. Probably the most comprehensive survey was the Building Assessment Survey and 

Evaluation (BASE) study conducted by EPA between 1994 and 1998 to characterize indoor air 

quality (IAQ) and occupant perceptions in representative public and commercial office buildings 

across the U.S. The BASE study used a standardized protocol to collect extensive IAQ data from 

100 randomly selected public and commercial office buildings in 37 cities. Formaldehyde was 

among the VOCs measured in this study. Measured formaldehyde levels averaged 13 ppb, with a 

median concentration of 12 ppb and a range (5th to 95th percentiles) from 3.6 to 26 ppb. CARB 

(2004) measured formaldehyde concentrations averaging 15 ppb in portable classrooms and 12 

ppb in traditional classrooms in California (Phase II study – measurements by field technicians), 

with 95th percentile values of 26/22 ppb for portable/traditional. Hodgson et al. (2004) measured 

formaldehyde concentrations ranging from 4 to 12 ppb in four new temporary classrooms.

3.3 FORMALDEHYDE BACKGROUND CONCENTRATION

As described in Section 3.2 of the model documentation (USEPA 2012a), the formaldehyde 

background concentration reflects the contribution to the indoor concentration of the outdoor 

formaldehyde concentration plus indoor sources other than CWPs (e.g., tobacco smoke, 

permanent press fabrics, paints, cosmetics). Although no studies have been conducted with the 

explicit purpose of characterizing the formaldehyde background concentration, such a value 

conceivably can be inferred from the formaldehyde concentration distribution characterized via 

field monitoring studies. For example, if the field survey focused on existing homes, then those 

toward the lower end of the concentration distribution presumably would be older homes with 

aged CWP sources and, thus, indicative of the background formaldehyde concentration.

Among the recent formaldehyde field studies summarized in the previous section, Liu et al. 

(2006) reported a 5th-percentile value of about 10 ppb. Minimum values from the Sax et al. 

(2006) in two cities, during two seasons, were on the order of 5 ppb. The Offerman et al. (2008) 

study, albeit for new homes, had a minimum measured concentration of about 4 ppb. The EPA 

BASE study, for commercial buildings, had a 5th percentile value that also was close to 4 ppb. 

These results collectively suggest that an appropriate value for the formaldehyde background 

concentration would lie between 5 and 10 ppb.
19

Section 4

MODELING APPROACH

The primary objective of the modeling effort described in this section is to characterize 

residential formaldehyde exposures for different segments of the population, under different sets 

of assumptions and analytical options (e.g., baseline scenario, reduced emissions) regarding the 

strength of emissions from composite wood products (CWPs13). Under the specific emission 

scenarios examined, the average daily concentration (ADC) of formaldehyde can be used to 

examine cancer as well as non-cancer health endpoints such as sensory irritation and asthma. 

Although the focus is on residential exposure, formaldehyde exposures in other environments 

where individuals spend time also are considered to provide a total or “around-the-clock” 

exposure perspective.

The above construct is presented schematically in Figure 4-1. The schematic applies to a specific 

exposure group or population segment, of which there are several (exposure groups are described 

later in this section). For each group, baseline and alternative analytical options are contrasted in 

terms of residential exposure and the associated total exposure. The difference in exposure, as 

measured by the differential ADC (baseline vs. alternative), can be translated into a differential 

likelihood of an adverse health effect.

Figure 4-1. Modeling Construct.

Section 4.1 describes the model that was used for the assessment. As a general rule, expected or 

average values were used for model inputs, as opposed to a range or distribution of values. 

Variability was introduced for certain input parameters expected to have a significant influence 

on the modeling results (e.g., temperature). Factors affecting formaldehyde exposure indoors are 

described in Section 4.2 and an analysis to assess the model’s relative sensitivity to the values 

used for various inputs is provided in Section 4.3. Section 4.4 describes the values chosen for 

model input parameters and Section 4.5 summarizes the matrix of model runs that were made.

 13 In this report, the term “composite wood product” (CWP) refers only to hardwood plywood, medium density 

fiberboard, or particleboard whereas “pressed wood product” (PWP) refers to a broader set of wood materials 

including, for example, softwood plywood and oriented strand board.

Baseline Emissions Scenario

Residential Formaldehyde

Exposure

Residential Formaldehyde 

Exposure

Total Formaldehyde Exposure Total Formaldehyde Exposure

Differential 

Formaldehyde 

Exposure

Alternative Analytical Option
20

4.1 MODEL USED FOR THE ASSESSMENT

As noted in Section 2.2.2, the FIAM-pwp v2.0 model is being used to support the exposure 

assessment. Model inputs include formaldehyde background concentration, number of zones14

(one or two), zone volumes and airflows, indoor temperature and humidity, types and amounts of 

pressed wood products (PWPs) in the home and their emissions, and exposure factors such as 

amount of time spent in and out of the home. The results include modeled indoor formaldehyde 

concentrations, both initial steady-state values and those at later points in time, together with 

exposure estimates such as average daily concentration (ADC). As indicated in Section 2.2.1, the 

initial (steady-state) indoor concentration predicted by the model is assumed to decrease over 

time as the reservoir of formaldehyde in various sources (or sinks) is gradually depleted. The 

gradual decrease over time is assumed to follow a first-order exponential process.

The model, described more fully in a separate document (USEPA 2012a), provides contextsensitive help as well as an overview on each input/output screen. The user interface consists of 

three input screens – House Screen, Source Screen and Exposure Screen – together with a Run 

FIAM Model button that provides access to a Result Screen. The House Screen collects 

information on house volumes and air flows and provides certain options pertaining to model 

calculations. The Sources Screen allows the user to specify the types and amounts of PWPs

installed in the house and the zone in which each product is located. The Exposures Screen 

contains location/activity patterns (time spent in each zone of the house and environments away 

from home) for exposure groups such as infants, children, adults and retirees. The Results Screen

shows modeled indoor formaldehyde concentrations, both initial steady-state values and those at 

later points in time, together with exposure estimates such as average daily concentration and 

percent of time at or above a formaldehyde level of interest. The exposure estimates are shown 

on an annual basis, starting with year 1 (house age 0-1 years) and continuing through year 11 

(house age 10-11 years).

Implementation of the model for this exposure assessment required the ability to run the model 

efficiently, by reducing the number of model runs and the subsequent computations needed to 

estimate total (24-hour) exposures for a broad number of exposure groups. An equivalent Excel 

version, fully checked for identical results given identical sets of inputs, was developed for this 

purpose. When running FIAM-pwp v 2.0 and selecting the default values for each of the structure 

types (e.g., single-family home, camper trailer), the user will obtain results identical to those 

provided in this exposure assessment report. 

For this assessment, it was assumed in the modeling that formaldehyde emissions from PWPs 

installed during construction of a new residential structure would decay to a near-zero value 

within 10 years. Several exposure groups were modeled and the results were compiled within the 

spreadsheet – residential- and total-ADC estimates for each exposure group, for one-year time 

segments representing new homes and those aged one year, two years, ..., up to and including 10 

years. Beyond 10 years, the emissions from PWPs associated with new construction were

 14 In the context of indoor-air modeling, the term “zone” refers to a compartment or section of a structure, within 

which the concentration in air of a pollutant such as formaldehyde is assumed to be well mixed or relatively uniform. 

A two-zone structure has two such compartments, each with its own well-mixed concentration but with the average 

concentration differing between the two zones.
21

assumed to be zero or nearly so, such that the indoor formaldehyde concentration reverts to the 

assumed background level. These one-year time segments will be used in the benefits assessment.

4.2 FACTORS AFFECTING FORMALDEHYDE EXPOSURE INDOORS

Each factor shown in Figure 4-2 ultimately affects inhalation exposure to formaldehyde indoors, 

either through its effect on the initial concentration (e.g., emission rate), through its effect on the 

concentration at later points in time (emissions half life), or through human interaction (e.g., 

activity patterns) with the time-varying indoor concentration. All factors shown in the figure are 

available as input parameters in the FIAM-pwp version 2.0 of the model.

Figure 4-2. Factors Affecting Indoor Formaldehyde Concentrations and Human Exposures.

Background Concentration

Structure Volume & Airflows 

CWP Loadings & Emission Rates

Indoor Sinks

Temperature & Humidity

Initial Indoor Formaldehyde 

Concentration (steady-state)

Emissions Half Life

Indoor Concentrations 

at Later Points in Time

Activity Patterns (time spent in 

different locations/environments) 

Exposure Estimates:

ADCs for Exposure Groups
22

4.3 SENSITIVITY ANALYSIS

A preliminary sensitivity analysis was conducted to guide the choice of factors to be varied and 

the relative number of variations for each factor. The analysis was conducted for two cases 

available in the FIAM-pwp model – a conventional home (i.e., the single-family detached home

used in the EPA formaldehyde pilot study; see Section 2.2.1) and a manufactured home. The 

conventional home, with a volume of 471 cubic meters, is conceptualized as having two zones 

whereas the manufactured home is a single-zone structure with a volume of 222 cubic meters. 

As summarized in Table 4-1 for the conventional home, ten factors (input parameters) were 

systematically varied for the sensitivity analysis. The background concentration and average 

concentration encountered when an individual is away from home both were set to zero for this 

analysis, so that modeled concentrations and exposures would reflect only the impact of PWPs in 

the house. The source and sink loading areas in the table represent one of the actual loading 

conditions that were used in the pilot study. 

Sensitivity was examined by varying each input parameter – one at a time – by 20 percent in 

each direction (i.e., 20 % lower and 20 % higher) from the base condition shown in Table 4-1. 

Five model outputs were examined for sensitivity to the ten factors: (1) initial concentration in 

zone 1 (upstairs); (2) concentration 24 months later in zone 1; (3) average daily concentration 

(ADC); (4) average daily dose (ADD); and (5) % of time the concentration is ≥ 0.01 ppm (10 

ppb). Values of these outputs for the base condition are listed in Table 4-2.

Table 4-1. Input Values for Sensitivity Analysis – Base Condition for Conventional Home

Input Parameter(s) Base Value(s)

Air Exchange Rate (ACH) 0.59

Emissions Half Life (years) 2.92

Temperature (°C) 23

Relative Humidity (%) 50

Source Loading Areas

a (m2

) 46, 59, 35, 4

Sink Loading Areas

a (m2

) 94, 420

House Age at Move-in (years) 5

Years Lived in House 5

Hours in House on Weekday, Weekend Day 15, 18

Inhalation Rate (m3/day) 13.3 a Sources are underlayment, cabinets, interior doors, and countertop;

sinks are carpet/padding and painted wallboard.

Table 4-2. Model Results for Base Condition for the Conventional Home

Initial Conc in 

Zone 1, 

mg/m3

Conc 24 Months 

Later in Zone 1, 

mg/m3

Average Daily 

Concentration, 

mg/m3

Average Daily 

Dose, 

mg/kg-day

% of Time 

Concentration 

≥ 0.01 ppm

0.0514 0.0320 0.0061 0.0011 13.7
23

Changes in each model output associated with the change in each input, in each direction, were 

averaged and then expressed as a percent change from the result for the base condition. The 

sensitivity results are summarized in Figure 4-3 as the percent change for each model output 

associated with a 20 % change in each input. Certain inputs, by definition, do not affect certain

model outputs. For example, the emissions half life has no effect on the initial concentration and 

the inhalation rate affects only the average daily dose. Based on this analysis, the most sensitive 

input parameters, in order of relative sensitivity (most sensitive first), are indoor temperature, 

emissions half life, house age, and indoor humidity.

Figure 4-3. Relative Model Sensitivity for the Conventional Home.

For the manufactured home (Table 4-3), the same ten factors were systematically varied for the 

sensitivity analysis. As with the conventional home, the background concentration and average 

concentration encountered when an individual is away from home both were set to zero for the 

analysis. A broader set of PWPs, with generally higher loading rates, was used for this case. As a 

result, the modeled initial concentration was about three times as high as the conventional home

case (Table 4-4). Due to the higher concentration, a higher threshold (0.02 ppm) was used to 

examine the relative frequency of higher concentrations. As with the conventional home, the 

most sensitive input parameters for this case are indoor temperature, emissions half life, house 

age, and indoor humidity (Figure 4-4).
24

Table 4-3. Input Values for Sensitivity Analysis – Base Condition for Manufactured Home

Input Parameter(s) Base Value(s)

Air Exchange Rate (ACH) 0.50

Emissions Half Life (years) 2.92

Temperature (°C) 23

Relative Humidity (%) 50

Source Loading Areas

a (m2

) 95, 53, 26, 3, 43, 36

Sink Loading Areas

a (m2

) 72, 158

House Age at Move-in (years) 5

Years Lived in House 5

Hours in House on Weekday, Weekend Day 15, 18

Inhalation Rate (m3/day) 13.3 a Sources are PB underlayment, paneling, interior doors, countertop (particleboard), 

cabinets, and closet shelving (PB/MDF); sinks are carpet/padding and wallboard.

.

Table 4-4. Model Results for Base Condition for the Manufactured Home

Initial Conc in 

Zone 1, 

mg/m3

Conc 24 Months 

Later in Zone 1, 

mg/m3

Average Daily 

Concentration, 

mg/m3

Average Daily 

Dose, 

mg/kg-day

% of Time 

Concentration 

≥ 0.02 ppm

0.1507 0.0937 0.0178 0.0033 35.0

Figure 4-4. Relative Model Sensitivity for the Manufactured Home.

0.00%

10.00%

20.00%

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

90.00%

100.00%

Percent Change in Model Output Due to 20 % Change in Input Value

Initial Concentration

Conc @ 24 months

ADC

ADD

% Time ≥ 0.02 ppm
25

4.4 MODEL INPUTS

4.4.1 Background Concentration

As described in Section 3.3 of this document, the background concentration reflects the 

contribution to the indoor concentration of the outdoor formaldehyde concentration plus indoor 

sources other than pressed wood products (e.g., tobacco smoke, permanent press fabrics, paints, 

cosmetics). As noted in Section 3.3, results of field studies indicate that an appropriate value for 

the residential background concentration would lie between 5 and 10 ppb. The midpoint of this 

range – 7.5 ppb – was chosen as the background concentration for all modeling runs.

4.4.2 Housing Types and House Volumes

To limit the number of model runs, it is desirable to minimize the number of structure categories 

yet retain sufficient diversity to make appropriate or necessary distinctions. The first distinction 

is between a “one-zone” and a “two-zone” structure. One-zone means one floor or story, and 

pertains to structures such as manufactured homes, apartments, and camper trailers. Two-zone

pertains to structures that can have multiple stories, including single-family attached and 

detached homes.

Structure categories were established to sufficiently cover major housing types used in the 

American Housing Survey (AHS) (http://www.census.gov/hhes/www/housing/ahs/ahs.html) and in 

the Residential Energy Consumption Survey (RECS) (http://www.eia.doe.gov/emeu/recs/): singlefamily (SF) detached homes; SF attached homes; multi-unit structures (apartments); and 

manufactured/mobile homes or trailers. For the purpose of estimating structure volume, a further 

distinction was made for manufactured homes due to distinct size differences – single-wide (SW) 

versus double-wide (DW). Camper trailers and park models also are of interest because, like

manufactured homes, these housing types have been used for some residents displaced by natural 

disasters such as Hurricane Katrina. Camper trailers were chosen to represent the small-volume

temporary housing for displaced residents, as this type of housing accounted for 80 percent of the 

smaller-volume housing types that were tested as part of FEMA’s formaldehyde monitoring in 

such temporary housing (CDC 2008/2010; DHS 2009).

An apartment could be a challenging case for modeling because it interacts not only with the 

outdoors but also with adjacent apartments. However, an apartment unit that is adjacent to a new 

apartment can be assumed to be new as well, such that the adjoining apartments would have 

similar formaldehyde concentrations and, thus, could be safely ignored. With this assumption or 

caveat, apartments were modeled in the same manner as other one-zone residential structures. 

For SF detached/attached homes, apartments, and manufactured homes, the structure volume was 

inferred from statistics provided by the U.S. Department of Energy’s 2005 RECS15, using the 

average floor area for the most recently built category (years 2000-2005) and assuming a ceiling 

height of 8.5 feet. For camper trailers, a typical size assigned to displaced hurricane victims was

used, with an assumed ceiling height of 7 feet. 

 15 See, for example, http://www.eia.doe.gov/emeu/recs/contents.html
26

The following floor areas and associated dimensions were assumed for the five structure types:

1. SF detached home – 3456 sq ft (36 ft x 48 ft, 2 stories)

2. SF attached home – 2240 sq ft (28 x 40 ft, 2 stories)

3. Apartment – 1120 sq ft (28 ft x 40 ft)

4. Manufactured home – 1216 sq ft (16 ft x 76 ft) for SW; 1680 sq ft (28 ft x 60 ft) for DW

5. Camper trailer – 328 sq ft (8 ft x 35 ft with 4 ft x 12 ft “slide-out”)

The dimensions chosen for SF homes and apartments were consistent with their respective 

average floor areas as reported in the RECS 2005 survey results.

The dimensions listed above are exterior dimensions; for interior volume calculations, 0.5 ft was 

subtracted from both the length and width to account for the area occupied by exterior cladding, 

sheathing, studs and wallboard. For SF homes a simplifying assumption was made that the upper 

and lower floors are of identical dimensions. For manufactured homes, a weighted average of 

SW and DW volumes was used; based on statistics from the U.S. Census Bureau’s Manufactured 

Home Survey (MHS) for years 2000-2009 (http://www.census.gov/const/www/mhsindex.html), 

70 percent of the manufactured homes were assumed to be the double-wide type. The resultant 

house volumes are listed, along with the house dimensions, in Table 4-5.

Table 4-5. House Dimensions and Calculated Volume for Five Housing Types

Housing Type Number of 

Stories

Length, 

ft

Width, 

ft

Ceiling 

Height, ft

Volume, 

ft3 (m3)

SF Detached 2 48 36 8.5 28,666 (811)

SF Attached 2 40 28 8.5 18,466 (523)

Apartment 1 40 28 8.5 9,233 (261)

Manufactured

 Single-wide

 Double-wide

 Averagea

1

1

1

16

28

--

76

60

--

8.5

8.5

8.5

 9,947 (282)

13,908 (394)

12,720 (360)

Camper Trailer

 Main body

 Slide-out

1

1

35

12

8

4

7

7 2,147 (61)

a Weighted average of single-wide (30 %) and double-wide (70 %); see text.

4.4.3 Airflow Rates

A single air exchange rate, in air changes per hour (ACH), was assumed for each structure type. 

Because the modeling focus is on new housing, the chosen value was toward the lower end of the 

distribution, as newer structures tend to be better sealed and have lower air exchange rates. For 

residences, the Exposure Factors Handbook (EFH) suggests 0.45 ACH as a central value and 

0.18 as a lower-end value, based on statistics developed by Koontz and Rector (1995) from a 

database of perfluorocarbon tracer (PFT) measurement results. The EFH also cites a study by 

Murray and Burmaster (1995) using the same database; these authors summarized distributions 

for subsets of the data defined by climate region and season. The 10th percentile value ranged 

from 0.1 to 0.3 ACH across climates and seasons, averaging about 0.20 ACH. 
27

In a 2008 study by Offerman et al. on ventilation and formaldehyde in new California homes, the 

25th percentile value for air exchange rate was 0.2 ACH for the two larger subsets of homes that 

were studied. In a study by Maddalena (2008) concerning chemical emissions in four FEMA 

temporary housing units (camper trailers), the measured air exchange rate varied from 0.15 to 

0.39 ACH across the trailers, averaging 0.25 ACH. Persily et al. (2010) modeled air infiltration 

rate distributions for the U.S. housing stock; for single-family homes built in 1990 or later, the 

25th percentile value was 0.15 ACH and the 50th percentile value was 0.26 ACH. Given the 

above statistics, 0.2 ACH was chosen as the value to represent new homes, including 

detached/attached homes, apartments, manufactured homes, and camper trailers. For the 

renovation case a central value such as 0.45 ACH, as suggested in the EFH, may be more 

appropriate. However, the data on which that suggested value is based are somewhat dated and 

there has been a general tendency toward increasing airtightness of U.S. homes over time; for 

example, the median value reported for the Offerman et al. (2008) study is 0.33 ACH. Thus, a 

value of 0.40 ACH – double that used for new homes – was chosen for the renovation case.

The indoor-outdoor airflow rates that were used for modeling can be determined from the house 

volume and air exchange rate. For example, for an apartment with a volume of 261 m3 and an air 

exchange rate of 0.2 ACH or 0.2 air changes per hour, the indoor-outdoor airflow rate would be 

(261 m3x 0.2/h), or 52.2 m3/h. A balanced flow was assumed – that is, the airflow rate from 

outdoors to indoors was assumed to equal the rate from indoors to outdoors. For two-zone 

structures – SF detached or attached homes – the house volume was equally apportioned between 

the upper and lower stories/floors and identical indoor-outdoor airflow rates were assumed for 

each story. Further, as an expedience, it was assumed that the airflow rate between the two 

indoor zones was balanced and equal to the indoor-outdoor airflow rate. Thus, for example, for a 

SF detached home with a volume of 811 m3 or 405.5 m3 per story, both the airflow rate per story 

and the interzonal airflow rate were set to (405.5 m3 x 0.2/h), or 81.1 m3/h. 

4.4.4 Emissions Half Life

As described in Section 3.6 of the FIAM-pwp model documentation, suggested values for the 

formaldehyde emissions half life, reflecting its decay over time, range from 1.5 to 3 years. An 

estimate of 2.92 years was based on a cross-sectional analysis of homes of varying ages, as a 

proxy for time-series data from one or a few homes. If none of the materials or furnishings in 

such homes were changed by the occupants, then this approach might provide an unbiased 

estimate of the half life. However, as a house ages the occupants will tend to add or replace 

materials and furnishings, some of which may emit formaldehyde. Such changes introduce new 

sources, thereby raising the formaldehyde concentration and artificially inflating the half-life 

estimate; thus, the estimate is best viewed as an upper bound. A more likely value, based on 

chamber studies of collections of pressed wood products as they aged, is within the range of 1.5 

to 2 years. An emissions half-life of 1.5 years was chosen for this analysis; with this half life, the 

emission rate 10 years after new construction would be about 1 % of the initial value.

4.4.5 Indoor Temperature and Humidity

The FIAM-pwp model is more sensitive to indoor temperature than to any other single factor and 

also is relatively sensitive to indoor humidity (see Section 4.3). No nationally representative 

study was identified in which indoor temperature and humidity have been measured. The RECS, 

which is nationally representative, does ask survey respondents about usual temperatures 
28

maintained in the residence. One of the questions – “At what temperature does your household 

usually keep your home in the winter?” – is asked under three conditions: (1) during the day 

when someone is home; (2) during the day when no one is home; and (3) during sleeping hours. 

The same set of questions also is posed with reference to the summer season.

Temperature. The RECS database was analyzed for these questions to estimate the year-round 

average temperature in each of five different climate zones that have been defined by the U.S. 

Energy Information Administration (EIA). The five climate zones are delineated in Figure 4-5. 

Formaldehyde modeling was performed separately for each housing type in each climate zone.

Figure 4-5. U.S. Climate Zones.

Source: U.S. Energy Information Administration (http://www.eia.doe.gov/emeu/cbecs/climzonenew.gif)

Table 4-6 summarizes responses to the RECS questions on daytime temperature when someone 

is home and nighttime (sleeping hours) temperature by climate zone. The columns labeled 

“Overall” are weighted averages of the daytime and nighttime average temperatures for summer 

and winter, with weights of 2/3 for daytime and 1/3 for nighttime. The overall summer and 

winter temperatures, in turn, were averaged to derive a year-round average temperature, by 
29

weighting the season-specific averages by the number of months associated with each. The 

resultant year-round temperature estimates are listed in Table 4-7.

Table 4-6. Summer and Winter Indoor Temperatures from RECS 2005, by Climate Zone

Climate

Zone

Average Summer Temperature Average Winter Temperature

Day Night Overall Day Night Overall

1 (coldest) 73.4 73.3 73.4 69.1 65.8 68.0

2 73.0 73.0 73.0 69.6 67.6 68.9

3 73.2 73.2 73.2 69.8 68.1 69.3

4 73.9 73.2 73.7 70.9 68.6 70.1

5 (warmest) 75.1 74.8 75.0 72.4 70.6 71.8

Table 4-7. Year-round Indoor Temperatures Derived from RECS 2005, by Climate Zone

Climate

Zone

Summer Temperature Winter Temperature

Year-Round

Temperature Average 

Temperature

Number of 

Months

Average 

Temperature

Number of 

Months

1 (coldest) 73.4 3 68.0 9 69.4

2 73.0 4 68.9 8 70.3

3 73.2 4 69.3 8 70.6

4 73.7 5 70.1 7 71.6

5 (warmest) 75.0 7 71.8 5 73.6

Humidity. The RECS does not ask about humidity levels maintained in the residence. 

Consequently, a mass-balance modeling approach was applied to estimate the year-round 

average indoor relative humidity (RH) level for each climate zone. A representative city was 

chosen for each zone:

• Climate Zone 1 – Milwaukee, WI

• Climate Zone 2 – Chicago, IL

• Climate Zone 3 – New York, NY

• Climate Zone 4 – Charlotte, NC

• Climate Zone 5 – Houston, TX

Hourly outdoor temperatures for a typical meteorological year16 (TMY) were obtained for each 

city as inputs to the mass-balance model that was developed. The mass-balance approach, which 

is consistent with methods described in American Society for Heating, Refrigerating and Air-

 16 Available at http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/.
30

Conditioning Engineers (ASHRAE) Standard 160P (Criteria for Moisture-Control Design 

Analysis in Buildings), expresses moisture in the indoor air as a function of moisture in the 

outdoor air, indoor moisture generation by the occupants, and moisture removal by a central airconditioning (AC) system. More specifically, a steady-state mass-balance equation for the water 

concentration in indoor air can be expressed as follows: 

Where:

Cwi = Average hourly water concentration in the indoor air (g/m3)

Qinf = Hourly airflow rate due to natural ventilation (m3/s)

Cwo = Average hourly water concentration in the outdoor air (g/m3

)

QAH = Average hourly airflow rate through the air handler, factoring in run-time (m3/s)

CwAH = Water concentration in the air leaving the air conditioner coils, assumed to be at 

the dewpoint of the coil temperature (g/m3)

Si = Moisture generation rate due to occupant presence/activities (g/s)

An average floor area of 2,000 sq ft was assumed, together with an average of 2.5 occupants and 

an average of 1.8 bathrooms, based on statistics from the RECS and AHS surveys. An air 

exchange rate of 0.2 ACH was assumed, consistent with the value selected for formaldehyde

modeling (see Section 4.4.3). The calculations for moisture removal via air conditioning, which 

are not included in ASHRAE 160P, involved an AC sizing algorithm based on house size, design 

outdoor temperature, cooling thermostat setting equal to the overall summer temperature per 

Table 4-6, and an assumed coil temperature of 55 °F. 

The steady-state approach is an oversimplification, in that the hourly run time for the air handler 

actually is determined by dynamic processes affecting the indoor air temperature at any point in 

time. For example, during a period of rising outdoor temperature the air conditioner will not 

come on as soon as the outdoor temperature meets or exceeds the setpoint, due to the thermal lag 

in the indoor environment. Similarly, later in the day, when the outdoor temperature falls below 

the setpoint, the air conditioner will continue to run due to the thermal lag indoors. 

As an expedience, the run time for the air handler during the cooling season was determined 

based on the outdoor temperature relative to the thermostat setpoint (the overall RECS summer 

temperature in the above table was used as the setpoint for each per climate zone). This 

expedience is practical because we are interested in estimating an annual average RH value and 

the two types of biases noted above tend to cancel out. That is, the overestimation of run time 

when the outdoor temperature is rising early in the day generally is compensated by the 

underestimation later in the day. 

To account for the thermal lag, a running average of multiple hours (i.e., average of the current 

hour and some number of previous hours) was used for the outdoor temperature, with the number 

of hours to be used in the running average set as a user input. It was found, through 

experimentation with different values for the number of hours used to average the outdoor 

temperature, that the bottom-line model output – average indoor RH level over the entire year – 

AH

wo AH wAH i

wi Q Q

Q C Q C S C

+

+ + =

inf

inf
31

was not very sensitive to the length of time used in the running average, due largely to the selfcompensating effects of the thermal lag. 

A phenomenon similar to the temperature lag indoors also occurs with the RH level. When the 

outdoor temperature dictates that the AC will operate after a period of no operation, the model 

predicts the RH to immediately achieve the steady-state value whereas it actually would take 

several hours to dehumidify the air to that value. This bias is offset by periods, usually in the 

evening or night, when the AC is no longer needed after operating during previous hours. At 

such a time, the indoor RH will rise gradually over several hours because the AC is no longer 

removing moisture, whereas the model instantaneously predicts the relatively high RH value due 

to the AC not operating.

Modeling results are listed for each climate zone in Table 4-8 for two cases – with and without 

an AC unit – based on a 6-hour running average for outdoor temperature. The effect of the AC 

unit is most pronounced in Houston, due primarily to the higher outdoor temperature and, hence, 

the greater AC run time leading to greater moisture removal from the house. Because the vast 

majority of the U.S. housing stock has air conditioning17, the estimated RH values with AC were 

used in the formaldehyde modeling.

Table 4-8. Modeled Year-round Indoor RH Level, by Climate Zone

Climate Zone RH Level with AC RH Level without AC

1 (coldest) 59.1% 63.8%

2 58.1% 64.7%

3 56.3% 66.4%

4 59.8% 72.6%

5 (warmest) 61.4% 85.3%

4.4.6 PWP Loadings – New-home Case

The types and loading rates of PWPs, and the subset of CWPs, can vary both across structure 

types and over time within the same structure. Modeling results are not as sensitive to the 

loading rate (because of the “concentration feedback” effect) as to some other parameters, most 

notably temperature and humidity. On the other hand, CWPs are the focus of this assessment. To 

develop a representative loading rate, two loading rates (higher and lower) were defined for each 

housing type and then averaged.

The following philosophy was adopted in determining appropriate loading rates for different 

types of PWPs in the various structures. Technically, the specific source (cabinets, countertop, 

paneling, etc.) of each PWP type does not matter, as the model treats all sources in the same way. 

Thus, for each loading scenario it is sufficient to determine and then sum all exposed surface 

areas per PWP type. Floor plans were used as a basis for developing the loadings (see Appendix 

 17 According to the Residential Energy Consumption Survey, 84 percent of U.S. housing units had air-conditioning 

equipment as of 2005 (http://205.254.135.24/emeu/recs/recs2005/hc2005_tables/detailed_tables2005.html).

. 
32

A for examples). Spreadsheets were developed to document the specific PWP components (and 

associated loadings) comprising each general type or class listed in the tables in this section. 

Examples of these spreadsheets are provided in Appendix B.

The loading rates differed for the new-home versus renovation cases. The loadings are described 

for the new-home case below and for the renovation case in the next section (4.4.7).

Single-family Homes. Table 4-9 lists the loading and mix of PWPs, including the loading ratio –

the ratio of exposed surface area (m

2

) to volume (m3) – for single-family detached homes. Table 

4-10 provides the same information for single-family attached homes. For each of these twostory housing types, loading information is provided for each story, with the upstairs (sleeping 

area) labeled as Zone 1 and the downstairs (living area) labeled as Zone 2. The PWP types or 

classes in the tables generally refer to exposed PWP surfaces. Underlayment was assumed to be 

OSB and doors were assumed to have an MDF or largely hollow interior and an exterior covered 

with primer. Countertops were assumed to have bare PB on the underside and cabinet drawers 

were assumed to have bare MDF on the underside. Cabinet sides and backs, floor/ceiling trim, 

and the interiors of cabinet doors were assumed to be coated with a vinyl/plastic film. Shelves in 

the kitchen pantry and master bedroom closet, along with the top, sides and shelves of an 

entertainment center and the exteriors of cabinet doors, were assumed to be made of HWPW.

Table 4-9. PWP Loading/Mix for SF Detached Homes (volume = 811 m3) – New Home

PWP 

Type/Class

Higher 

Loading, m2

(Zone1, Zone 2)

Lower 

Loading, m2

(Zone1, Zone 2)

Average 

Loading, m2

(Zone1, Zone 2)

Loading 

Ratio, m2/m3

Underlayment 117.49, 117.49 104.44, 104.44 110.97, 110.97 0.274, 0.274

Doors 39.80, 19.90 39.80, 19.90 39.80, 19.90 0.098, 0.049

Countertopa 1.20, 3.44 0.96, 2.75 1.08, 3.10 0.003, 0.008

Cabinet drawers

a 2.79, 4.65 2.44, 4.06 2.62, 4.36 0.006, 0.011

Cabinet Sides/Backs, 

Floor/Ceiling Trim, 

Cabinet Doors Interior

26.48, 47.84 24.91, 43.60 25.70, 45.72 0.063, 0.113

Cabinet Doors Exterior, 

Shelves, ET Center 8.04, 24.17 7.60, 22.87 7.82, 23.52 0.019, 0.058

a Exposed underside

Table 4-10. PWP Loading/Mix for SF Attached Homes (volume = 523 m3) – New Home

PWP 

Type/Class

Higher 

Loading, m2

(Zone1, Zone 2)

Lower 

Loading, m2

(Zone1, Zone 2)

Average 

Loading, m2

(Zone1, Zone 2)

Loading 

Ratio, m2/m3

Underlayment 75.68, 75.68 67.61,67.61 71.65, 71.65 0.274, 0.274

Doors 34.64, 17.32 34.64, 17.32 34.64, 17.32 0.132, 0.066

Countertopa 1.49, 5.57 1.29, 4.84 1.39, 5.21 0.005, 0.020

Cabinet drawers

a 2.32, 5.11 2.03, 4.47 2.18, 4.79 0.008, 0.018

Cabinet Sides/Backs, 

Floor/Ceiling Trim, 

Cabinet Doors Interior

18.96, 41.90 17.58, 37.48 18.27, 39.69 0.070, 0.152
33

Cabinet Doors Exterior, 

Shelves, ET Center 9.17, 22.48 8.74, 21.17 8.96, 21.83 0.034, 0.083

a Exposed underside
34

Apartments. Table 4-11 lists the loading/mix of PWPs, together with the loading ratio, for 

apartments. Unlike single-family homes, apartments are assumed to be one-story and are 

conceptualized as consisting of a single zone. The types of PWPs assumed for apartments are the 

same as for single-family homes, but with different loading ratios in most cases.

Table 4-11. PWP Loading/Mix for Apartments (volume = 261 m3

) – New Home

PWP 

Type/Class

Higher 

Loading, m2

(Zone1, Zone 2)

Lower 

Loading, m2

(Zone1, Zone 2)

Average 

Loading, m2

(Zone1, Zone 2)

Loading 

Ratio, m2/m3

Underlayment 75.68 67.28 71.48 0.274

Doors 30.09 30.09 30.09 0.115

Countertopa 3.72 2.79 3.26 0.013

Cabinet drawers

a 5.11 4.18 4.65 0.018

Cabinet Sides/Backs, 

Floor/Ceiling Trim, 

Cabinet Doors Interior

49.18 46.97 48.08 0.184

Cabinet Doors Exterior, 

Shelves, ET Center 27.07 24.75 25.91 0.099

a Exposed underside
35

Manufactured Homes. Table 4-12 lists the loading/mix of PWPs, together with the loading ratio, 

for manufactured homes. The composite case in the lower third of the table, representing a 

weighted average of the single-wide (30%) and double-wide (70%) cases that also are shown in 

the table, was used for modeling. The composition of each PWP type/class was assumed to be 

the same as for single-family homes and apartments, except that cabinet sides and backs were 

assumed to be vinyl/plastic covered for the higher loading and HWPW for the lower loading18.

Table 4-12. PWP Loading/Mix for Manufactured Homes (volume = 360 m3) – New Home

PWP 

Type/Class

Higher 

Loading, m2

Lower 

Loading, m2

Average

Loading, m2

Loading 

Ratio, m2/m3

Single-wide (SW) (volume = 281 m3)

Underlayment 81.54 72.48 77.01 0.274

Doors 23.09 23.09 23.09 0.082

Countertopa 3.72 2.79 3.26 0.012

Cabinet drawers

a 4.18 3.25 3.72 0.013

Floor/Ceiling Trim, 

Cabinet Doors Interior 21.43 17.48 19.46 0.069

Cabinet Sides/Backsb 29.31 17.88 N/A 0.104, 0.064

Cabinet Doors Exterior, 

Shelves, ET Center 26.60 22.65 24.63 0.088

Double-wide (DW) (volume = 393 m3)

Underlayment 114.01 101.34 107.68 0.274

Doors 28.87 28.87 28.87 0.073

Countertopa 4.65 3.72 4.19 0.011

Cabinet drawers

a 5.11 4.18 4.65 0.012

Floor/Ceiling Trim, 

Cabinet Doors Interior 25.36 21.41 23.39 0.060

Cabinet Sides/Backs

b 34.42 22.99 N/A 0.088, 0.058

Cabinet Doors Exterior, 

Shelves, ET Center 30.40 26.45 28.43 0.072

Composite (30% SW; 70% DW) (volume = 360 m3)

Underlayment --- --- 98.48 0.274

Doors --- --- 27.14 0.075

Countertopa --- --- 3.91 0.011

Cabinet drawers

a --- --- 4.37 0.012

Floor/Ceiling Trim, 

Cabinet Doors Interior --- --- 22.21 0.062

Cabinet Sides/Backs

b 32.89 21.46 N/A 0.091, 0.060

Cabinet Doors Exterior, 

Shelves, ET Center --- --- 27.29 0.076

a Exposed underside

b Assumed to be vinyl/plastic-covered for higher loading and HWPW for lower loading

 18 Observations of new manufactured homes on dealers’ lots indicated that higher-priced models tend to have more 

cabinets, covered with vinyl/plastic, whereas lower-priced models tend to have fewer cabinets, made of HWPW.
36

Camper Trailers. Table 4-13 lists the loading and mix of PWPs, together with the loading ratio, 

for camper trailers. For this housing type, several additional pressed-wood furnishings were 

included, such as a wardrobe, a composite wood unit surrounding the refrigerator, and composite 

wood fronts for the lower portions of a bed, dinette and sofa, that are not included for any of the 

other housing types. The exterior portions of all cabinets, wardrobe, pantry, and bed/dinette/sofa 

fronts were assumed to be made of HWPW.

Table 4-13. PWP Loading/Mix for Camper Trailers (volume = 61 m3

) – New Home

PWP 

Type/Class

Higher 

Loading, m2

Lower 

Loading, m2

Average

Loading, m2

Loading 

Ratio, m2/m3

Underlayment 17.10 14.25 15.68 0.258

Doors 5.16 5.16

Countertopa 1.11 0.93 1.02 0.017

Cabinet drawers

a 2.32 1.86 2.09 0.034

Cabinet/Wardrobe/Pantry 

Doors/Fronts Interior + Trim 8.45 7.24 7.85 0.129

Cabinet/Wardrobe/Pantry 

Doors/Fronts Exterior, 

ET Center, Fridge Unit, 

Bed/dinette/sofa fronts

21.15 19.94 20.55 0.338

Cabinet/Wardrobe/Pantry 

Sides/Backs 24.13 19.28 24.23 0.399

a Exposed underside

4.4.7 PWP Loadings – Renovation Case

For this case, it was assumed that an entire kitchen was renovated, including cabinets, countertop 

and ancillary areas such as a pantry. It was further assumed that the vinyl covering the kitchen 

floor and adjacent hallway floor was replaced with engineered wood. Bathroom vanities also 

were assumed to be replaced. The interior doors, underlayment and trim throughout the house 

were assumed to remain as before the renovation, as were PWPs in any areas beyond the kitchen 

other than the hallway floor. Thus, for example, unlike the new-home case, it was assumed that a 

new entertainment center was not installed.

Single-family Homes. The PWP loading/mix for the renovation case is shown for single-family 

detached homes in Table 4-14 and for single-family attached homes in Table 4-15. As in the 

previous tables for the new-home case, loading information is provided for each zone of these 

two-story homes (Zone 1 is the upstairs/sleeping area and Zone 2 is the downstairs/living area).

The loadings for countertop and cabinet drawers are the same as the new-home case. The 

loadings for cabinet sides, cabinet backs and interior doors of the cabinets, all assumed to be 

vinyl/plastic covered, are somewhat lower than for the new-home case because certain areas of 

the house are unaffected by the renovation. The HWPW components are higher in the renovation 

case, however, because the addition of an engineered wood floor more than compensates for the 

HWPW that are unaffected by the renovation, such as the entertainment center and shelves in the 

master bedroom closet.
37

Table 4-14. PWP Loading/Mix for SF Detached Homes (volume = 811 m3

) - Renovation

PWP 

Type/Class

Higher 

Loading, m2

(Zone1, Zone 2)

Lower 

Loading, m2

(Zone1, Zone 2)

Average 

Loading, m2

(Zone1, Zone 2)

Loading 

Ratio, m2/m3

Countertopa 1.20, 3.44 0.96, 2.75 1.08, 3.10 0.003, 0.008

Cabinet drawers

a 2.79, 4.65 2.44, 4.06 2.62, 4.36 0.006, 0.011

Cabinet Sides/Backs, 

Cabinet Doors Interior 12.54, 33.91 10.97, 29.67 11.76, 31.79 0.029, 0.078

Cabinet Doors Exterior, 

Shelves, Engineered 

Wood Floor 

3.48, 39.71 3.05, 38.41 3.27, 39.06 0.008, 0.096

a Exposed underside

Table 4-15. PWP Loading/Mix for SF Attached Homes (volume = 523 m3) - Renovation

PWP 

Type/Class

Higher 

Loading, m2

(Zone1, Zone 2)

Lower 

Loading, m2

(Zone1, Zone 2)

Average 

Loading, m2

(Zone1, Zone 2)

Loading 

Ratio, m2/m3

Countertopa 1.49, 5.57 1.29, 4.84 1.39, 5.21 0.005, 0.020

Cabinet drawers

a 2.32, 5.11 2.03, 4.47 2.18, 4.79 0.008, 0.018

Cabinet Sides/Backs, 

Cabinet Doors Interior 11.03, 35.42 9.65, 30.99 10.34, 33.21 0.040, 0.127

Cabinet Doors Exterior, 

Shelves, Engineered 

Wood Floor

3.48, 27.34 3.05, 26.03 3.27, 26.69 0.012, 0.102

a Exposed underside

Apartments, Manufactured Homes and Camper Trailers. The PWP loading/mix for renovation 

is shown for apartments in Table 4-16, for manufactured homes in Table 4-17, and for camper 

trailers in Table 4-18. As noted previously, these homes all are one-story, single-zone structures. 

Differences as well as similarities between the renovation and new-home cases for these homes 

are along the same lines as described above for single-family detached and attached homes.

Table 4-16. PWP Loading/Mix for Apartments (volume = 261 m3

) - Renovation

PWP 

Type/Class

Higher 

Loading, m2

(Zone1, Zone 2)

Lower 

Loading, m2

(Zone1, Zone 2)

Average 

Loading, m2

(Zone1, Zone 2)

Loading 

Ratio, m2/m3

Countertopa 3.72 2.79 3.26 0.013

Cabinet drawers

a 5.11 4.18 4.65 0.018

Cabinet Sides/Backs, 

Cabinet Doors Interior 40.88 38.67 39.78 0.152

Cabinet Doors Exterior, 

Shelves, Engineered 

Wood Floor

23.11 20.79 21.95 0.084

a Exposed underside
38

Table 4-17. PWP Loading/Mix for Manufactured Homes (volume = 360 m3

) -- Renovation

PWP 

Type/Class

Higher 

Loading, m2

Lower 

Loading, m2

Average

Loading, m2

Loading 

Ratio, m2/m3

Single-wide (SW) (volume = 281 m3)

Countertopa 3.72 2.79 3.26 0.012

Cabinet drawers

a 4.18 3.25 3.72 0.013

Cabinet Doors Interior 9.29 8.13 8.71 0.031

Cabinet Sides/Backsb 22.06 17.88 N/A 0.079, 0.064

Cabinet Doors Exterior, 

Shelves, Engineered 

Wood Floor

23.90 25.80 24.85 0.088

Double-wide (DW) (volume = 393 m3)

Countertopa 4.65 3.72 4.19 0.011

Cabinet drawers

a 5.11 4.18 4.65 0.012

Cabinet Doors Interior 11.61 10.45 11.03 0.028

Cabinet Sides/Backsb 27.17 22.99 N/A 0.069, 0.058

Cabinet Doors Exterior,

Shelves, Engineered 

Wood Floor

30.10 30.10 30.10 0.077

Composite (30% SW; 70% DW) (volume = 360 m3)

Countertopa --- --- 3.91 0.011

Cabinet drawers

a --- --- 4.37 0.012

Cabinet Doors Interior --- --- 10.33 0.062

Cabinet Sides/Backsb 25.64 21.46 N/A 0.071, 0.060

Cabinet Doors Exterior, 

Shelves, Engineered 

Wood Floor

--- --- 28.53 0.076

a Exposed underside

b Assumed to be vinyl/plastic-covered for higher loading and HWPW for lower loading

Table 4-18. PWP Loading/Mix for Camper Trailers (volume = 61 m3) – Renovation

PWP 

Type/Class

Higher 

Loading, m2

Lower 

Loading, m2

Average

Loading, m2

Loading 

Ratio, m2/m3

Countertopa 1.11 0.93 1.02 0.017

Cabinet drawers

a 2.32 1.86 2.09 0.034

Cabinet/Wardrobe/Pantry 

Doors/Fronts Interior 4.76 4.18 4.47 0.074

Cabinet/Wardrobe/Pantry 

Doors/Fronts Exterior, 

Fridge Unit, Bed/dinette/sofa 

fronts, Engineered Wd Floor

11.06 11.06 11.06 0.182

Cabinet/Wardrobe/Pantry 

Sides/Backs 14.47 12.03 13.25 0.218

a Exposed underside
39

4.4.8 CWP Emission Rates

Baseline Emissions Scenario. Between June and October 2010, EPA administered a survey to 

domestic manufacturers of composite wood panels; the survey asked about both current and 

planned emission levels. Because many CWP manufacturers are in the midst of modifying their 

production technology and raw materials to achieve compliance with Phase 2 of the CARB 

ATCM, using current emission levels to estimate emission levels in 2013 would not accurately 

reflect the 2013 baseline. Instead, baseline emission levels were estimated using responses to a 

survey question about emission levels that mills planned to achieve within the next three years. 

These emission levels were weighted by production levels that mills reported in the survey, in 

order to estimate average emission levels by certification standard. The survey data also were 

used to estimate the share of total production volume represented by products meeting each of 

the emission standards. The survey results are reported in Table 4-19. For comparison purposes, 

the CARB emission limits (which are identical to the FSCWPA limits) are shown in Table 4-20. 

Table 4-19. Baseline Emission Levels (2013) For Domestically Produced CWPs, 

by Product Type and Emissions Certification Standard

Emissions Standard

Product Type

HWPW MDF PB

Weighted Average Emissions (ppm)

None 0.058 --- 0.058

CARB 1 a --- --- 0.090

CARB 2 0.032 0.082 0.057

CARB ULEF b 0.024 0.042

CARB NAF c 0.013 0.035 0.013

Share of Production

None 0.4% --- 0.2%

CARB 1 --- --- 1.8%

CARB 2 60.2% 86.1% 88.5%

CARB ULEF 4.6% 2.8%

CARB NAF 39.4% 9.3% 6.7%

a Some mills producing products currently certified under CARB Phase 1 (CARB 1) reported that they would 

continue this product line after the CARB Phase 2 (CARB 2) effective date.

b Hardwood plywood mills meeting CARB 2 and CARB Ultra Low Emission Formaldehyde (ULEF) were 

grouped together in the CARB 2 category. Several HWPW mills appeared to be meeting CARB ULEF 

standards but did not report this in their response. For example, they listed the certification standard as “CARB 

2” but the resin type as “ULEF” and/or reported maximum emissions that satisfy ULEF requirements. Due to 

difficulties in distinguishing between CARB 2 and CARB ULEF product lines and the fact that emission levels 

appeared similar among mills reporting either CARB 2 or CARB ULEF certification standards, these mills 

were grouped together.

c

NAF = No Added Formaldehyde.
40

Table 4-20. Formaldehyde Emissions Standards in the CARB Air Toxic Control Measure 

for Formaldehyde Emissions from Compressed Wood Productsa (ppm)

Emissions Standard HWPW MDF Particleboard

CARB 1 0.08 0.21 0.18

CARB 2 0.05 0.11b 0.09

CARB ULEF – 

less frequent testing 0.05 90% of samples < 0.06

All samples < 0.09c

90% of samples < 0.05

All samples < 0.08

CARB ULEF –

exemption from third 

party certification

90% of samples < 0.04

All samples < 0.05

90% of samples < 0.04

All samples < 0.06

90% of samples < 0.04

All samples < 0.06

CARB NAF 90% of samples < 0.04

All samples < 0.05

90% of samples < 0.04

All samples < 0.06

90% of samples < 0.04

All samples < 0.06 a The FSCWPA emission limits are the same as the CARB ATCM limits. b The CARB 2 emission limit for thin MDF is 0.13 ppm.

c The CARB ULEF limits for thin MDF are 90% of samples < 0.08 ppm and all samples < 0.11 ppm.

Among imported products, baseline emission levels were estimated separately for products from 

Canada versus those from the rest of the world. The known composite wood manufacturers in 

Canada were compared to the CARB list of certified mills, and most Canadian mills were found 

to be CARB-certified. As a result, Canadian mills were assumed to achieve the same baseline 

emissions as U.S. mills (whose emissions are shown above in Table 4-19).

The baseline emission levels for non-Canadian imported CWPs were estimated using data from a 

2009 presentation by Professional Service Industries (PSI 2009), a CARB Third Party Certifier 

(TPC). Although PSI is located in the U.S., the mills that it certifies are located mainly in Asia.19

The mills certified by PSI are located in countries that are major sources of pressed wood 

products imported into the United States; thus, the data from the PSI presentation were assumed 

to represent emission levels from all non-Canadian CWPs imported into the U.S. 

The PSI presentation included histograms of observed formaldehyde emission levels for 

hardwood plywood, MDF, and particleboard. The data included emission levels for 387, 198, 

and 193 samples of hardwood plywood, MDF, and particleboard, respectively, and for all three 

product types combined. After imputing the data underlying these graphs, the average emission

values reported in the presentation were successfully replicated.20 This information was used to 

estimate the number of samples at different emission levels.

 19 According to CARB’s list of certified mills, as of November 12, 2010, PSI was the TPC for 95 mills in 9 

countries. The countries, and the number of mills certified by PSI in each, are as follows: Argentina (1); Chile (1);

China (55); Ecuador (2); Indonesia (2); Malaysia (26); the Philippines (1); Taiwan (1); and Thailand (6). 20 The emission levels in the graphs seemed to be labeled according to the interval midpoints (e.g., a reported value 

of 0.05 ppm represented an interval of 0.0375 to 0.075 ppm). The maximum values reported in the presentation for 

MDF and particleboard were used for the maximum intervals. The median value was used for the median interval 

for MDF. The data in the hardwood plywood graphic were consistent with an average value of 0.07 ppm rather than 

the 0.05 ppm value that could be calculated from the summary statistics shown in the presentation for all three 

product types combined. For hardwood plywood, the three highest emission levels (all of which exceeded 1.0 ppm) 

seemed to be driving this discrepancy; thus, they were dropped from the analysis. After dropping these outliers the 

imputed average emissions matched the 0.05 ppm value that could be calculated from the other summary statistics 

shown in the presentation.
41

The emission levels reported in the PSI presentation ranged from near zero to levels exceeding

the CARB 2 emission standards by a substantial margin. The emission levels observed in these 

data were from a period after CARB 1 took effect but before CARB 2 did. Because many of the 

mills that met the CARB 1 standards at the time when samples were taken may subsequently 

achieve CARB 2 levels, baseline emissions were predicted by assuming that products with 

emission levels between the CARB 1 and CARB 2 levels in the PSI data would achieve CARB 2 

levels by 2013. Emission levels of 0.06 and 0.05 ppm were used for CARB 2 baseline emissions 

for MDF and particleboard, respectively, because these levels represent the midpoints of the 

highest emission intervals in the PSI data that meet the CARB 2 limits. None of the intervals in 

the PSI data for HWPW reflected the CARB 1 emission limits (the CARB 1 limit of 0.08 ppm is 

spanned by the interval of 0.075 to 0.125 ppm in the PSI data and the CARB 2 limit of 0.05 ppm 

is spanned by the interval of 0.0375 to 0.075 ppm). Therefore, no adjustments were made to 

hardwood plywood for the shift from CARB 1 to CARB 2. After making the MDF and PB 

adjustments, the average emissions by product type were calculated (see Table 4-21).

Although a number of samples in the PSI data had emission levels close to zero, it was not 

possible to determine whether the products qualify for certification as ultra low-emitting 

formaldehyde (ULEF) or no added formaldehyde (NAF)

21; the PSI presentation did not identify 

the resin type used for each sample. Also, as indicated in a footnote to Table 4-20 above, NAF 

and ULEF have emissions requirements that must be met by 90% of the samples from a mill as 

well a ceiling value that must be met by all samples. This distribution of emissions could not be 

determined from the PSI presentation; thus, baseline emission levels were not estimated 

separately for non-Canadian imports of ULEF and NAF products. Such products are included in 

the baseline emission estimates for the CARB-2 category.

Table 4-21 also includes the share of imports for each product type and emissions standard. This 

share was estimated by assuming that the fraction of samples for each category in the PSI 

presentation is equivalent to the share of imports for that category across all non-Canadian 

composite wood products imported into the U.S.

Table 4-21. Baseline Emission Levels for Non-Canadian Imported Composite Wood 

Products, by Product Type and Emissions Standard

Emissions Standard Hardwood Plywood MDF Particleboard

Average Emissions (ppm)

None 0.163 0.502 0.384

CARB 2 0.015 0.047 0.036

Share of Imports

None 26% 11% 38%

CARB 2 74% 89% 62%

 21 Resin formulations that meet the NAF definition are those that do not contain any added formaldehyde in their 

formulation.
42

The estimates presented above in Table 4-21 rely on several critical assumptions that are a 

source of uncertainty in this analysis, the most important being as follows:

• The sample is representative of imported non-Canadian composite wood products.

− It is not known whether the sample is representative of products destined for the 

United States. The destination of these products could be other countries or their 

country of origin. On the one hand, U.S. end users may be more likely to insist on 

lower-emitting products. On the other hand, U.S. end users not shipping to California 

face less stringent formaldehyde emissions standards than many other potential 

destinations. (Although many end users prefer to handle a single type of product, 

rather than one product that meets the California requirements and another type for the 

other 49 states). The fact that the samples were being tested for formaldehyde

emissions by a CARB TPC suggests that many of them were produced by mills whose 

products ultimately end up in the U.S. 

• The distribution of emission levels will not change for mills that were producing products 

with emission levels that currently exceed the CARB 1 standards.

− If some of these mills decide to obtain CARB 2 certification, it is not known whether 

these will be the higher or lower emitting mills on average. Some additional mills 

(aside from those below the CARB 1 limits but above the CARB 2 limits) may 

subsequently decide to lower their emission levels. 

− Conversely, the PSI data may under-represent imported products with very high 

emission levels. Mills making products likely to exceed the CARB levels may not 

have had their products tested because they intended to sell them in the other 49 states.

• The percentage of samples with current emissions below CARB 1 levels is a reasonable 

estimate of the percentage of mills that will be achieving CARB 2 levels in the baseline 

scenario.

− The PSI presentation was given after CARB 1 was in effect but before CARB 2 was. It 

is not known whether more overseas producers ultimately will meet the Phase 2 

emission limits than initially met the Phase 1 limits. 

For the purposes of TSCA Title VI, laminated products are a subset of hardwood plywood. The 

statute defines a laminated product as one made by affixing a wood veneer to a particleboard, 

medium-density fiberboard, or veneer-core platform. The statutory definition goes on to state 

that laminated products are component parts used in the construction or assembly of a finished 

good, and that a laminated product is produced by the manufacturer or fabricator of the finished 

good in which the product is incorporated. EPA is given the authority to modify the statutory 

definition of laminated product through rulemaking. EPA also is directed to use all available and 

relevant information to determine whether the definition of hardwood plywood should exempt 

engineered veneer or any laminated product. 

Note that baseline emissions data are not available for hardwood plywood defined as laminated 

products. The CARB 1 standard for hardwood plywood is used to represent the average baseline 

emission level for laminated products made in the U.S. and Canada. The CARB 1 level 

represents the average emission level that CARB found prior to promulgating the ATCM. It 

reflects a mix of products using different resin types, including both UF and NAF resins. This 
43

level is considered to be a reasonable proxy for domestically produced laminated products. These 

products are thought to generally be made with UF or PVA resin, so their emissions may be 

similar to those from stock hardwood panel products before the ATCM went into effect. 

For laminated products made outside the U.S. and Canada, average baseline emissions were 

assumed to be the same as the levels for imported hardwood plywood that does not meet an 

emission standard (estimated from the PSI presentation). Emissions data prior to the CARB 

ATCM are not available for non-Canadian imported hardwood plywood. Because the PSI 

presentation was given after CARB 1 was in effect, it presumably reflects a reduction in 

emissions compared to pre-ATCM levels. Therefore, if baseline laminated product emissions are 

similar to pre-ATCM emissions, using the average of all non-Canadian imported hardwood 

plywood would underestimate emission levels for laminated products. Using the estimated 

average emissions from hardwood plywood that does not meet an emissions standard reflects the 

possibility that many of these imported laminated products are made with UF resins.

Table 4-22 lists the emission levels used for the baseline 2013 scenario for CWPs, including 

laminated products; the values listed reflect the assumptions and choices described above. The 

estimated share of U.S. consumption also is listed in the table for each product type and 

associated country of origin.

Table 4-22. Baseline Emission Levels for Composite Wood Products by Product Type, 

Country of Origin, and Emission Standard

Emissions 

Standard

Hardwood Plywood MDF Particleboard Laminated Products

U.S./Can. NonU.S./Can. U.S./Can. NonU.S./Can. U.S./Can. NonU.S./Can. U.S./Can. NonU.S./Can.

Average Emissions (ppm)

None 0.058 0.163 --- 0.502 0.058 0.384 0.058 0.163

CARB 1 --- --- --- --- 0.090 --- --- ---

CARB 2 0.032 0.015 0.082 0.047 0.057 0.036 --- ---

CARB ULEF 0.024 0.042

CARB NAF 0.013 0.035 0.013

Share of U.S. Consumption

None 0.1% 16.6% --- 0.8% 0.2% 1.1% 36.0% 64.0%

CARB 1 --- --- --- --- 1.7% --- --- ---

CARB 2 19.7% 47.4% 79.2% 7.2% 85.0% 1.9% --- ---

CARB ULEF 4.2% 3.0%

CARB NAF 16.2% 8.6% 7.1%
44

Analytical Option Scenarios. Seven analytical options were evaluated in the assessment, as 

listed and described briefly in Table 4-23. The first four options – CARB1, CARB2/Statutory 

Option, CARB2/Statutory Option including laminated products at NAF, and NAF – assume that 

progressively higher percentages of CWPs meet stricter emission standards. The last three 

scenarios are similar to CARB1, CARB2/Statutory Option, and NAF, with the single exception 

that laminated products are not regulated as HWPW under TSCA. 

Table 4-23. Alternative Analytical Options Evaluated in the Exposure Assessment

Analytical Option Description

CARB1, Including 

Laminated Products

All CWPs, including laminated productsa

, are at emission levels that meet 

CARB Phase 1 standards1. Products that meet CARB Phase 1 standards at 

baseline are assumed to remain at that emission level.

CARB2/Statutory Option,

Including Laminated 

Productsb

All CWPs, including laminated products, are at emission levels that meet 

CARB Phase 2 standards. Products that meet CARB Phase 2 standards at 

baseline are assumed to remain at that emission level.

CARB2/Statutory Option, 

with Laminated Products

at NAF

As above, except that laminated products are assumed to meet NAFc

standards.

NAF, Including 

Laminated Products

All CWPs, including laminated products, are at emission levels that meet 

NAF standards. Products that meet NAF standards at baseline are assumed 

to remain at that emission level.

CARB1, Excluding 

Laminated Products

Like CARB1 above, except that laminated products are not regulated as 

HWPW and, thus, are assumed remain at baseline emission levels.

CARB2/Statutory Option,

Excluding Laminated 

Products

Like CARB2 above, except that laminated products are not regulated as 

HWPW and, thus, are assumed remain at baseline emission levels.

NAF, Excluding 

Laminated Products

Like NAF above, except that laminated products are not regulated and, 

thus, are assumed remain at baseline emission levels.

a 30% of all HWPW products are assumed to be laminated products. b The CARB emission standards for this scenario are equivalent to those specified in the FSCWPA. c NAF = no added formaldehyde.

In the economic analysis presented to the Small Business Advocacy Review (SBAR) Panel for 

the formaldehyde rule, EPA estimated that HWPW production (excluding engineered wood 

flooring) was 1,749 thousand square feet (on a 3/8-inch basis) in 2006, and that laminated 

product production (excluding engineered wood flooring) was about 408 million square feet on a 

5/8-inch basis, equivalent to about 680 million square feet on a 3/8-inch basis. Thus, based on 

these estimates, laminated products account for about 28% of combined HWPW production. The 

Hardwood Plywood and Veneer Association has indicated that laminated products represent 

about 30% of engineered wood flooring production (HPVA 2010). Therefore, this exposure 

analysis assumes that laminated products represent 30% of the volume of HWPW.
45

Table 4-24 lists emission levels and market shares for the same set of CWPs under the 

assumption that CARB1 emission limits are in effect for all CWPs, including laminated 

products. In compiling this table, it was first assumed that emission levels of all products 

meeting CARB1 or stricter (CARB2/ULEF/NAF) standards at baseline would not change. Next, 

it was assumed that any products listed as not meeting any emission standard at baseline, but 

whose emission levels would comply with CARB1, also would remain at their baseline emission 

levels. For example, some U.S.-produced HWPW and PB products are not certified as meeting 

an emission standard at baseline but nonetheless have emission levels that comply with CARB 

Phase 1 emission limits; thus, their emission levels are assumed to remain at the baseline level 

under this scenario/analytical option. As noted in a table footnote, for the CARB1 analytical

option laminated products were assumed to be at the same emission levels as HWPW if 

regulated and at baseline emission levels (see Table 4-22) if not regulated.

Table 4-24. Emission Levels for CARB1 Analytical Option by CWP Type, Origin, and Emissions Standard

Emissions 

Standard

Hardwood Plywooda MDF Particleboard

U.S. Non-U.S. U.S. Non-U.S. U.S. Non-U.S.

Average “Emissions” (ppm)

None --- --- --- --- --- ---

CARB1 

(previously NOT

CARB1)

0.058b 0.058 --- 0.14c 0.058b 0.090

Already at

CARB1 --- --- --- --- 0.090 ---

CARB2 0.032 0.015 0.082 0.047 0.057 0.036

ULEF --- --- 0.024 --- 0.042 ---

NAF 0.013 --- 0.035 - 0.013 -

Share of U.S. Consumption

None --- --- --- --- --- ---

CARB1 

(previously NOT

CARB1)

0.1% 16.6% --- 0.8% 0.2% 1.1%

Already at

CARB1 --- --- --- --- 1.7% ---

CARB2 19.7% 47.4% 79.2% 7.2% 85.0% 1.9%

ULEF --- --- 4.2% --- 3.0% ---

NAF 16.2% --- 8.6% --- 7.1% ---

a For the CARB1 scenario that includes laminated products, those products are assumed to have the same emission

levels as hardwood plywood; for the CARB1 scenario that excludes laminated products, those products are assumed 

to have baseline emission levels as listed in Table 4-22. b Products in these cells have baseline emission levels that comply with CARB1, even though producers reported 

that they were not intentionally meeting any particular standard. Because the baseline levels comply with CARB1, 

the emission levels for these products are assumed not to change and, thus, are the same as listed in Table 4-14. c Products in this cell are not CARB1-compliant at baseline; thus, their emission levels are assumed to change for 

the CARB1 scenario. The assumed emission level is 67 % of the level that would exactly comply with CARB1; as 

noted in the text, industry generally sets target emission levels below the standard to ensure that it is being met, 

given variability across/within production lots as well as measurement uncertainty.
46

For the CARB1 scenario it was further assumed that products listed as not meeting any emission 

standard at baseline, and whose emission levels exceed the CARB Phase 1 limit, would attain 

emission levels equal to those of corresponding U.S. products listed as not meeting any emission 

standard but nonetheless complying with CARB1 at baseline. For example, non-U.S. HWPW not 

complying with CARB1 at baseline, with an average emission level of 0.163 ppm, was assumed 

to match the level (0.058 ppm) of U.S.-produced HWPW complying with CARB1 at baseline, 

and its market share (16.6%) was shifted from “None” to “CARB1” in the table. 

Lastly, it was assumed that products not meeting any emission standard at baseline, and for 

which there are no comparable products complying with CARB1 at baseline, would obtain an 

emission level equal to 67% of the CARB1 limit – the CWP industry generally sets targets for 

emission levels below the standard to ensure that it is being met, considering the variability 

across/within production lots as well as measurement uncertainty. For example, non-U.S. MDF, 

with an emission level at baseline (0.502 ppm) that is not CARB1-compliant, was assumed to 

change to a level equal to 67 percent of the CARB1 standard (0.67 x 0.21 ppm = 0.14 ppm).

Table 4-25 lists emission levels and market shares for the analytical option where CARB2/TSCA 

Title VI statutory emission limits are in effect. As with the CARB1 scenario, it was assumed that 

emission levels of all products already meeting CARB2 or stricter standards (ULEF/NAF) would 

not change. Next, it was assumed that products not meeting CARB2 at baseline (including those 

meeting the less strict CARB1 standard) would obtain emission levels equal to U.S. products22 of 

the same CWP type that comply with CARB2 at baseline. For example, both U.S.-produced 

HWPW (baseline level of 0.058 ppm) and non-U.S. HWPW (baseline level of 0.163 ppm) were 

assumed to shift to a CARB2-compliant emission level of 0.032 ppm. For this analytical option, 

laminated products were assumed to be at the same emission levels as HWPW if regulated and at 

baseline emission levels (see Table 4-22) if not regulated.

 22 Emission levels for U.S. CARB2-compliant products (as opposed to non-U.S. products) were chosen because 

the data set from which average emission levels were determined was larger and, thus, considered more reliable.
47

Table 4-25. Emission Levels for CARB2 Analytical Option by CWP Type, Origin, and Emissions Standard

Emissions 

Standard

Hardwood Plywooda MDF Particleboard

U.S. Non-U.S. U.S. Non-U.S. U.S. Non-U.S.

Average “Emissions” (ppm)

None --- --- --- --- --- ---

CARB1 --- --- --- --- --- ---

CARB2 

(previously NOT

CARB2)

0.032 0.032 - 0.082 0.057 0.057

Already at

CARB2 0.032 0.015 0.082 0.047 0.057 0.036

CARB2 --- --- 0.024 --- 0.042 ---

ULEF 0.013 --- 0.035 --- 0.013 ---

NAF --- --- --- --- --- ---

Share of U.S. Consumption

None --- --- --- --- --- ---

CARB1 --- --- --- --- --- ---

CARB2 

(previously NOT

CARB2)

0.1% 16.6% --- 0.8% 1.9% 1.1%

Already at

CARB2 19.7% 47.4% 79.2% 7.2% 85.0% 1.9%

CARB2 --- --- 4.2% --- 3.0% ---

ULEF 16.2% --- 8.6% --- 7.1% ---

NAF --- --- --- --- --- ---

a For the CARB2 scenario that includes laminated products, those products are assumed to have the same emission

levels as hardwood plywood; for the CARB2 scenario that excludes laminated products, those products are assumed 

to have baseline emission levels as listed in Table 4-22.

Table 4-26 lists emission levels and estimated percentages under the analytical option whereby

NAF emission limits are in effect. First, it was assumed that emission levels of all products 

meeting the NAF standard at baseline would not change. Next, it was assumed that products not 

meeting NAF at baseline (including those meeting less strict standards) would attain the 

emission levels for U.S. products of the same CWP type that are NAF-certified at baseline. For 

example, U.S.-produced HWPW accounts for 36 percent of all HWPW production. A subset of 

the U.S. HWPW production, accounting for 19.8 percent, does not comply with NAF at baseline 

but attains a NAF-compliant emission level of 0.013 ppm under the NAF analytical option; the 

remaining 16.2 percent, already NAF-compliant, likewise has an emission level of 0.013 ppm. 

Lastly, it was assumed that MDF products meeting ULEF at baseline, but with average emission 

levels lower than those for NAF-compliant MDF products at baseline, would not change. As 

with the analytical options described above (CARB1 and CARB2), for the NAF analytical option

laminated products were assumed to be at the same emission levels as HWPW meeting the NAF 

standard if regulated and at baseline emission levels (see Table 4-22) if not regulated.
48

Table 4-26. Emission Levels for NAF Scenario by CWP Type, Origin, and Emissions Standard

Emissions 

Standard

Hardwood Plywooda MDF Particleboard

U.S. Non-U.S. U.S. Non-U.S. U.S. Non-U.S.

Average “Emissions” (ppm)

None --- --- --- --- --- ---

CARB P1 --- --- --- --- --- ---

CARB P2 --- --- --- --- --- -

NAF (previously 

not NAF with 

non-NAF 

emissions)

0.013 0.013 0.035 0.035 0.013 0.013

NAF (previously 

not NAF with 

NAF emissions)

--- --- 0.024 --- --- ---

Already at NAF 0.013 --- 0.035 --- 0.013 ---

Share of U.S. Consumption

None --- --- --- --- --- ---

CARB P1 --- --- --- --- --- ---

CARB P2 --- --- --- --- --- ---

NAF (previously 

not NAF with 

non-NAF 

emissions)

19.8% 64.0% 79.2% 8.0% 89.9% 3%

NAF (previously 

not NAF with 

NAF emissions)

--- --- 4.2% --- --- ---

Already at NAF 16.2% --- 8.6% --- 7.1% ---

a For the NAF scenario that includes laminated products, those products are assumed to have the same emission

levels as hardwood plywood; for the NAF scenario that excludes laminated products, those products are assumed to 

have baseline emission levels as listed in Table 4-22.

Table 4-27 lists emission levels and market shares under the analytical option whereby CARB2

emission limits are in effect, but with the added assumption that all laminated products (assumed 

to account for 30 percent of all HWPW production) are NAF-compliant (e.g., using NAF cores 

laminated with NAF resins) at an emission level of 0.013 ppm. Note that the estimated 

percentages for the U.S. and non-U.S. HWPW columns have been adjusted in the table such that 

all HWPW production, including laminates, sums to 100 percent.
49

Table 4-27. Emission Levels for CARB2 Scenario with Laminates at NAF by CWP Type, Origin, 

and Emissions Standard

Emissions 

Standard

Hardwood Plywood MDF Particleboard Laminated 

Productsa

U.S. Non-U.S. U.S. Non-U.S. U.S. Non-U.S. U.S. Non-U.S.

Average “Emissions” (ppm)

None --- --- --- --- --- --- --- ---

CARB1 --- --- --- --- --- --- --- ---

CARB2 

(previously 

NOT CARB2)

0.032 0.032 --- 0.082 0.057 0.057 --- ---

Already at

CARB2 0.032 0.015 0.082 0.047 0.057 0.036 --- ---

CARB2 --- --- 0.024 --- 0.042 --- --- ---

ULEF 0.013 --- 0.035 --- 0.013 --- --- ---

NAF --- --- --- --- --- --- 0.013 0.013

Share of U.S. Consumption

None --- --- --- --- --- --- --- ---

CARB1 --- --- --- --- --- --- --- ---

CARB2 

(previously 

NOT CARB2)

0.1% 11.6% --- 0.8% 1.9% 1.1% --- ---

Already at

CARB2 13.8% 33.2% 79.2% 7.2% 85.0% 1.9% --- ---

CARB2 --- --- 4.2% --- 3.0% --- --- ---

ULEF 11.3% --- 8.6% --- 7.1% --- --- ---

NAF --- --- --- --- --- --- 10.8% 19.2%

a Assumed to account for 30% of all HWPW production.
50

Slopes and Intercepts for Emission Rates. Section 2.3 of the FIAM-pwp model documentation 

report lists emission rates for various types of PWPs that were derived from sets of chamber 

emission tests conducted during the 1980s and up through the mid-1990s. A distinguishing 

feature of these chamber tests is that they were conducted at multiple air exchange rates and/or 

product loading ratios, enabling estimation of model parameters – slope and intercept – that 

reflect the dependence of the emission rate on the indoor formaldehyde concentration. The slope 

is a mass transfer coefficient that reflects the “backpressure” effect of the indoor formaldehyde 

concentration on the emission rate, whereas the intercept reflects the hypothetical emission rate 

when the indoor formaldehyde concentration is zero.

The following equation was used as a basis for determining the intercept (b) associated with 

products meeting certain emission standards:

[ ] [ ]

D

CH O

PEX VOL

b Area

CH O out

SS

2

2

*

*

+

= (Eqn. 4-1)

where:

[CH2O]SS = steady-state formaldehyde concentration inside the 

compartment (mg/m3)

[CH2O]out = steady-state formaldehyde concentration outside the 

compartment (mg/m3)

b = the emission rate at zero CH2O concentration in the air 

(mg/m2-hr)

Area = Exposed surface area of the source (m2)

PEX = the compartment’s air exchange rate with outdoors (hr-1

), 

assuming a mixing factor equal to unity

VOL = the volume of the compartment (m3)

D = 

PEX VOL

m Area

*

*

1+

m = the mass transfer coefficient (m/hr).

Assuming that [CH2O]out is zero, substituting for D in Eqn. 4-1, and denoting PEX * VOL as Q 

(i.e., the airflow rate in/out of the chamber, in m3/hr), we can solve for b as follows:

b = [CH2O]SS * (1 + m * Area / Q) * (Q / Area) (Eqn. 4-2)

ASTM E1333-10, Standard Test Method for Determining Formaldehyde Concentrations in Air 

and Emission Rates from Wood Products Using a Large Chamber (ASTM 2010), is a commonly 

used method for demonstrating compliance with formaldehyde emission standards. The method 

prescribes an air exchange rate for testing of 0.5 hr-1 (i.e., 0.5 ACH) and product loading ratios of 

0.43 m2/m3for PB, 0.95 m2/m3for HWPW, and 0.26 m2/m3for MDF. Using these rates along with 

an assumed slope (m) for a given PWP type, the corresponding intercept can be determined for a 

hypothetical source that just meets a given emissions standard. 
51

For example, the CARB2 emission standard for MDF is 0.11 ppm or 0.135 mg/m3

. An arbitrary 

chamber volume of 100 m3, which together with a PEX of 0.5 hr-1 yields a value of 50 m3/hr for 

Q, was used in the calculation. The volume assumed does not matter, as the exposed surface area 

scales to the volume via the loading ratio – with a volume of 100 m3 the corresponding surface 

area is 26 m2. A slope of 1.06 m/hr was assumed; this value is the average slope from about 30 

tests of different MDF specimens, as listed in the FIAM-pwp model documentation report. 

Substituting the assumed values given above in Eqn. 4-2, the intercept (b) that corresponds to the 

CARB2 emission standard for MDF is calculated as follows:

b = 0.135 mg/m3 * (1 + 1.06 m/hr * 26m2 / 50 m3) * (50 m3 / 26 m2)

= 0.40 mg/m2-hr

Table 4-28 lists the calculated intercepts associated with various emission levels for HWPW, 

MDF and PB, as listed previously in Tables 4-15 through 4-19, using the calculation method 

described above and an assumed slope for each CWP type as indicated in the table.

Table 4-28. Calculated Intercepts for Various Emission Levels for Each CWP Type

Emission Standard – Origin

Emission Levela Assumed 

Slope

Calculated 

Intercept

ppm mg/m3 m/hr mg/m2/hr

Hardwood Plywood

None – U.S. 0.058 0.072 0.27 0.057

None – non-U.S. 0.163 0.201 0.27 0.160

CARB1 – U.S. & non-U.S. 0.058 0.072 0.27 0.057

CARB2 – U.S. 0.032 0.040 0.27 0.031

CARB2 – non-U.S. 0.015 0.019 0.27 0.019

NAF – U.S. 0.013 0.016 0.27 0.013

Medium Density Fiberboard

None – U.S. --- --- 1.06 ---

None – non-U.S. 0.502 0.620 1.06 1.849

CARB1 – U.S. 0.140 0.173 1.06 0.516

CARB2 – U.S. 0.082 0.101 1.06 0.302

CARB2 – non-U.S. 0.047 0.058 1.06 0.173

ULEF – U.S. 0.024 0.030 1.06 0.088

NAF – U.S. 0.035 0.043 1.06 0.129

Particleboard

None – U.S. 0.058 0.072 0.7 0.133

None – non-U.S. 0.384 0.474 0.7 0.883

CARB1 – U.S. 0.058 0.072 0.7 0.133

CARB1 – non-U.S. 0.090 0.111 0.7 0.207

CARB2 – U.S. 0.057 0.070 0.7 0.131

CARB2 – non-U.S. 0.036 0.044 0.7 0.083

NAF – U.S. & non-U.S. 0.013 0.016 0.7 0.030 a mg/m3 formaldehyde = ppm formaldehyde * 1.23
52

Providing standard-specific slopes and intercepts for each CWP type would prove cumbersome, 

exceeding the number of input rows available for sources in the FIAM-pwp model. It was 

determined experimentally that using a composite intercept together with the corresponding total 

exposed surface area for a given CWP type yielded identical modeling results to that from the 

more tedious approach of using values for the individual components meeting different emission 

standards. The composite intercept was calculated as a weighted average of the individual 

intercepts, using the market share as the weight; the resultant composite intercepts are shown for 

the baseline scenario in Table 4-29 for each CWP type, along with standard-specific intercepts. 

Table 4-29. Composite Intercepts by CWP Type – Baseline Scenario

Emission Standard – Origin Slope Intercept Market 

Share

Hardwood Plywood

None – U.S. 0.27 0.057 0.1%

None – non-U.S. 0.27 0.160 16.6%

CARB2 – U.S. 0.27 0.031 19.7%

CARB2 – non-U.S. 0.27 0.015 47.4%

NAF – U.S. 0.27 0.013 16.2%

Composite 0.27 0.042 100 %

Medium Density Fiberboard

None – non-U.S. 1.06 1.849 0.8%

CARB2 – U.S. 1.06 0.302 79.2%

CARB2 non-US 1.06 0.173 7.2%

ULEF – U.S. 1.06 0.088 4.2%

NAF – U.S. 1.06 0.129 8.6%

Composite 1.06 0.281 100 %

Particleboard

None – U.S. 0.70 0.133 0.2%

None – non-U.S. 0.70 0.883 1.1%

CARB1 – U.S. 0.70 0.207 1.7%

CARB2 – U.S. 0.70 0.131 85.0%

CARB2 – non-U.S. 0.70 0.083 1.9%

ULEF – U.S. 0.70 0.097 3.0%

NAF – U.S. 0.70 0.030 7.1%

Composite 0.70 0.131 100 %

Composite intercepts for baseline and other emission scenarios – CARB1, CARB2 and NAF –

are shown by CWP type in Table 4-30, without the underlying details. The most notable 

difference across scenarios is that the NAF intercepts are substantially lower than for the other 

three scenarios, for each CWP type.
53

Table 4-30. Composite Intercepts by CWP Type and Emissions Scenario

CWP Type Composite Intercept

Baseline CARB1 CARB2 NAF

Hardwood Plywood 0.042 0.025 0.021 0.013

Medium Density Fiberboard 0.281 0.271 0.269 0.127

Particleboard 0.131 0.124 0.122 0.030

The modeling also accounted for some PWP types that would not be subject to emission 

standards because they are specifically exempt from TSCA Title VI. Underlayment in homes 

typically is either tongue-and-groove softwood plywood (SWPW) or oriented strand board 

(OSB). The emission rates from earlier chamber tests on SWPW are thought to be applicable to 

either type; for example, a study by Hodgson et al. (2000) reported virtually the same intercept 

(0.029) for OSB as did the earlier tests for SWPW (0.030). 

Interior doors were represented using estimated emission rates from chamber testing of 6-panel 

white doors that were used in the EPA pilot study; this is the only known study in which such 

doors have been tested at multiple air exchange/loading rates, enabling calculation of both a 

slope and an intercept. The emission rates for these doors also were used to represent those for 

coated (but not laminated) CWP materials, assuming a similar barrier effect.

Because the interiors of such coated materials presumably would be in compliance with any rules 

governing CWP emissions, the intercept for interior doors and coated CWPs was varied across 

emission scenarios. It was observed that, at baseline, the intercept for these products was close to 

halfway between the intercepts for HWPW and PB. Thus, the average of those two intercepts for 

other emission scenarios – CARB1, CARB2 and NAF – was used for doors and coated CWPs;

the average intercepts were 0.074 for CARB1, 0.071 for CARB2, and 0.0215 for NAF.

Emission factors for underlayment, interior doors, and coated CWPs are listed in Table 4-31.

Table 4-31. Emission Rates for Underlayment and Coated CWPs – Baseline Scenario

PWP Type/Class Proxy Used for Emission Rate Slope Intercept

Underlayment (OSB) Softwood Plywood

(PF Resin) 0.61 0.030

Interior Doors & Coated CWPsa 6-panel Doors Used

in EPA Pilot Study 0.52 0.082

a CWPs could be coated, for example, with primer/paint, vinyl film, or thermally fused paper.
54

4.4.9 Exposure Groups and Activity Patterns

To cover the various exposure situations that can depend on factors such as age and work status, 

the following exposure groups were defined:

• Infant (age 0 to <2)

• Pre-school/school (age 2 to <16)

• Worker (age 16 to <64)

• Retiree (age 64 or greater)

The choice of age breaks to distinguish infants and pre-school/school children from adults was 

driven by the possible age dependency of cancer slope factors. The USEPA has developed agedependent adjustment factors (ADAFs)23 to address the potential for differential potency 

associated with exposure during early life (below 16 years of age). There sometimes is a 10-fold 

adjustment for ages 0 to <2 years and a 3-fold adjustment for ages 2 to <16 years; there is no 

adjustment for ages 16 years and older. Workers were split into full-time and part-time 

subgroups; full-time workers were further divided to distinguish non-industry workers from 

wood-industry segments where higher occupational formaldehyde exposures can occur. As 

described in a separate EPA report (ERG 2011), three such industry segments were examined –

manufacturing, fabrication and wholesale. However, sufficient data to support the current 

exposure assessment were available only for the fabrication segment. In terms of activity 

patterns, the retiree group also can be used to represent individuals of age 16 to <64 who are 

unemployed or working at home.

The 2009 Exposure Factors Handbook (EFH) update24 (draft) was the primary source of 

information on activity patterns, that is, how an individual’s time is allocated among residential 

and non-residential locations. Estimates of annual hours at selected home and non-home location 

groupings are provided for each exposure group in Table 4-32. The total time spent at home was 

determined from EFH tables that indicate the time spent at home in all rooms combined; the time 

at home in Zone 1 was defined as the sum of time spent in the bedroom or bathroom. EFH

statistics indicate that infants spend, on the average across the population, one hour per day at 

daycare facilities. Children of school age were assumed to spend 6.5 hours per day at school, for 

180 days per year. Full-time workers were assumed to spend 8 hours per day at work, for 250 

days per year. The hours at work or school for part-time workers and retirees were based on EFH

statistics, as were the hours in a vehicle for each exposure group. The time spent in “all other”

environments was determined by subtraction from the total time budget of 8760 hours per year.

 23 See, for example, http://www.epa.gov/oswer/riskassessment/sghandbook/chemicals.htm. 24 http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=209866
55

Table 4-32. Annual Hours at Home and Non-home Locations, by Exposure Group.

Exposure Group

Location

Home

Zone 1a

Home

Zone 2

Work or 

School or

Daycare

In

Vehicle

All

Other

Total, all 

Locations

Infants 4958 1652 365 252 1533 8760

Pre-school/School 4253 1292 1170 356 1689 8760

Full-time Workers 3327 2032 2000 590 811 8760

Part-Time Workers 3935 2038 1000 401 1386 8760

Retirees 3607 3538 107 372 1136 8760

a Zone 1 – upstairs (sleeping area); Zone 2 – downstairs (living area).

4.4.10 Concentrations at Locations Outside the Home

As noted in the beginning of Section 4, locations outside the home where individuals spend time 

were considered in the assessment to provide a total or “around-the-clock” exposure perspective. 

Concentrations assigned to these locations for the baseline emissions scenario (see Table 4-33) 

were derived from several sources. In-vehicle and outdoor/other concentrations were based on 

average values reported from EPA’s air monitoring network (see Section 3.1). The value 

assigned to vehicles (6 ppb) is the average reported for the “mobile” land use category; the value 

assigned to outdoors/other (3 ppb) is the average of values reported for “residential” and 

“commercial” land use categories, with consideration also given to outdoor formaldehyde levels 

measured in residential monitoring studies. The value assigned to the fabrication-industry 

workplace was taken from a recent EPA report (ERG 2011). The values assigned to daycares, 

schools and non-industry workplaces involved calculations that are described below.

Table 4-33. Concentration Values for Non-home Locations – Baseline Scenario

Location Formaldehyde Concentration

ppb μg/m3

Daycare 9.8 12.0

School 8.7 10.7

Work, Non-Industry 10.0 12.3

Work, Fabrication 199.5 244.9

Vehicle 6.0 7.4

Outdoors/Other 3.0 3.7
56

In developing the baseline concentrations for daycare, school and non-industry work locations, it 

was assumed that 10 percent25 of the buildings in each category were of recent construction or 

were recently renovated. As with the fabrication-industry workplace, the value for newer 

buildings associated with the non-industry workplace was taken from the recent EPA report 

referenced above. Newer schools were assigned the 95th percentile formaldehyde concentration, 

thought to represent newer or recently renovated buildings, from a relatively large monitoring 

study of portable and traditional classrooms in California schools (CARB 2004; see Section 3.2). 

The value assigned to newer daycare facilities is an average of the concentration for non-industry 

work and averages from field studies of newer homes (see Section 3.2) by Offerman et al. (2008) 

and Hodgson et al. (2000). For older daycare, school and non-industry buildings, the 25th

percentile for formaldehyde levels measured in the EPA BASE study was used. Table 4-34

shows the derivation of the age-weighted baseline concentration values for these building types. 

Table 4-34. Derivation of Baseline Values for Daycare, School and Work Locations

Location

Formaldehyde Concentration, ppb

Older 

Buildings

Newer 

Buildings

Compositea of

Older & Newer

Daycare 7.0 35.0 9.8

School 7.0 24.0 8.7

Work, Non-Industry 7.0 36.5 10.0

a Composite value = 90% x (value for older buildings) + 10% x (value for newer buildings).

The values for vehicle and outdoor/other concentrations were kept constant across analytical 

options whereas those for the other locations were varied (see Table 4-35), because the 

formaldehyde concentrations in the fabrication workplace as well as newer/renovated daycares, 

schools and non-industry workplaces could be affected by a new rule for formaldehyde. As with 

the baseline values, the concentrations assigned to the other analytical options for newer nonindustry workplaces were taken from the EPA report referenced above. For daycare facilities the 

percent reductions across analytical options that were used for fabrication and non-industry work 

were applied. A similar approach was used for schools, except that the percent reductions were 

lowered slightly (i.e., by 10 percent) to account for generally higher prevailing air exchange rates 

in schools, which would tend to temper the effect of formaldehyde emission reductions.

 25 The most recent DOE/EIA Commercial Building Energy Consumption Survey (CBECS) indicated that about 5 % 

of office buildings and 8 % of education buildings were of recent construction (i.e., 3 years old or less); see 

http://www.eia.gov/emeu/cbecs/cbecs2003/detailed_tables_2003/detailed_tables_2003.html, Table B-8.
57

Table 4-35. Concentration Values for Selected Non-home Locations, by Emissions Scenario

Location Formaldehyde Concentration, ppb

Baseline CARB1 CARB2 NAF

Daycarea 9.8 (35.0) 9.5 (30.7) 9.4 (29.7) 8.0 (16.0)

Schoola 8.7 (24.0) 8.1 (17.8) 8.0 (17.3) 7.3 (10.2)

Work, Non-Industrya 10.0 (36.5) 9.4 (32.0) 9.3 (31.0) 7.9 (16.7)

Work, Fabrication 199.5 192.0 190.8 93.0

a The values assigned to these locations are a weighted average of those for older buildings (see Table 4-31) and 

newer buildings (values in parentheses).

4.5 MODEL RUN MATRIX

The matrix of model runs (Table 4-36) to support the exposure assessment consists of 200 cells

that represent all possible combinations of values for the three factors that were varied across 

model runs – housing type (5 types), climate zone (5 zones), and analytical option (8 scenarios). 

The results are saved in a spreadsheet for each run, including ADCs for each environment where 

exposure groups spend time and a total ADC, for all environments combined, for each exposure 

group. These results are provided for cases representing new homes as well as those aged one 

year, two years, etc., up to and including 10 years. 

The matrix shown in Table 4-33 was used for two separate cases – new homes and recently 

renovated homes. The differences between the two cases were in the air exchange rates (see 

Section 4.4.3) and the PWP loadings (see Sections 4.4.6 and 4.4.7) that were used.
58

Table 4-36. Model Run Matrixa

Housing Type

Climate Zone

1 2 3 4 5

Baseline Emissions Scenario

SF Detached

SF Attached

Apartment

Manufactured

Camper Trailer

CARB1 Analytical Option, Including Laminated Products

SF Detached .

.

.

CARB2 Analytical Option, Including Laminated Products

SF Detached .

.

.

CARB2 Analytical Option, with Laminates at NAF

SF Detached .

.

.

NAF Analytical Option, Including Laminates

SF Detached .

.

.

CARB1 Analytical Option, Excluding Laminates

SF Detached

.

.

.

CARB2 Analytical Option, Excluding Laminates

SF Detached .

.

.

NAF Analytical Option, Excluding Laminates

SF Detached .

.

.

a Applied to both the new-home and the renovation cases; see text.
59

Section 5

MODELING RESULTS

5.1 NEW-HOME CASE

Table 5-1 lists one set of modeling results – initial modeled formaldehyde “steady-state” 

concentrations – for new residential construction. As described in Section 2 it has been observed 

that, for new construction, the combined actions of sources and sinks typically result in an initial 

rise in the indoor concentration followed by a “leveling-off” period that may be fairly brief and 

then a longer period of gradual decline. The initial formaldehyde concentrations estimated by the 

model are intended to approximate indoor concentrations during this leveling-off period, which 

often occurs within 30 days or less following the installation of formaldehyde-bearing materials.

The initial concentrations are listed for each of eight emissions scenarios (columns in the table), 

five housing types (sub-headings within the table), and five climate zones (table rows). Some 

general patterns apparent from inspection of the table are as follows:

• The highest modeled concentrations are for camper trailers

• Within each housing type, the highest concentrations are in the South (climate zone 5)

• Among the analytical options, the lowest concentrations occur for the case where CWPs 

are at emission levels that meet no-added-formaldehyde (NAF) standards (see Table 4-23 for

brief descriptions of each emissions scenario), whether laminates are regulated or not.

Figure 5-1, where initial modeled concentrations are averaged across climate zones, shows more 

clearly the patterns of results across emissions scenarios/analytical options and housing types.

Figure 5-1. Modeled Initial Formaldehyde Concentrations by Emissions 

Scenario/Analytical Option and Housing Type – New-home Case.

* Results shown are 

for Zone 1 of these 

two-zone structures
60

Table 5-1. Modeled Initial Formaldehyde Concentrations for Eight Emissions Scenarios, ppba – New-home Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 43.4, 45.4 40.5, 42.0 39.5, 40.8 39.4, 40.6 26.0, 26.6 40.8, 42.4 39.8, 41.3 24.6, 25.4

2 44.8, 46.9 41.8, 43.4 40.7, 42.1 40.6, 42.0 26.7, 27.2 42.1, 43.8 41.0, 42.6 25.3, 26.1

3 44.2, 46.3 41.3, 42.8 40.2, 41.5 40.1, 41.4 26.4, 26.9 41.5, 43.2 40.5, 42.0 25.0, 25.8

4 49.6, 52.0 46.2, 48.0 45.0, 46.6 44.9, 46.4 28.8, 29.4 46.5, 48.4 45.3, 47.1 27.6, 28.5

5 57.1, 59.9 53.2, 55.2 51.7, 53.6 51.6, 53.3 32.2, 32.9 53.5, 55.7 52.1, 54.2 31.2, 32.3

Single-family Attached Homes (Zone 1, Zone 2)

1 47.2, 46.8 43.7, 43.0 42.4, 41.7 42.3, 41.5 24.4, 23.6 44.0, 43.5 42.8, 42.3 24.9, 24.3

2 48.8, 48.4 45.1, 44.4 43.8, 43.1 43.7, 42.9 25.1, 24.2 45.4, 44.9 44.2, 43.7 25.6, 25.0

3 48.1, 47.7 44.5, 43.8 43.2, 42.5 43.1, 42.3 24.8, 23.9 44.8, 44.3 43.6, 43.0 25.3, 24.7

4 54.0, 53.6 49.9, 49.1 48.5, 47.6 48.3, 47.4 27.3, 26.3 50.3, 49.7 48.9, 48.3 28.0, 27.2

5 62.4, 61.9 57.5, 56.6 55.8, 54.8 55.6, 54.5 30.9, 29.7 58.0, 57.2 56.3, 55.6 31.6, 30.8

Apartments

1 58.9 53.5 51.6 51.3 26.9 54.1 54.1 29.6

2 61.0 55.3 53.3 53.0 27.6 56.0 55.8 30.4

3 60.0 54.5 52.6 52.3 27.3 55.1 55.0 30.0

4 67.8 61.4 59.2 58.9 30.2 62.2 61.6 33.4

5 78.6 71.1 68.5 68.1 34.3 72.0 70.7 38.0

Manufactured Homes

1 50.4 45.5 43.9 43.5 25.6 46.2 44.9 26.9

2 52.1 47.0 45.3 44.9 26.3 47.8 46.3 27.7

3 51.3 46.3 44.7 44.3 26.0 47.1 45.7 27.4

4 57.8 52.0 50.1 49.7 28.7 52.9 51.3 30.3

5 66.8 60.0 57.8 57.3 32.5 61.1 59.1 34.4

Camper Trailers

1 72.3 57.6 53.6 51.9 30.2 61.3 58.3 36.5

2 74.9 59.6 55.4 53.7 31.1 63.5 60.3 37.7

3 73.7 58.7 54.6 52.9 30.7 62.5 59.4 37.2

4 83.5 66.2 61.5 59.6 34.1 70.6 67.1 41.5

5 97.1 76.8 71.2 69.0 38.9 81.9 77.7 47.6 a Modeled residential concentrations, in μg/m3

, were converted to ppm using the relationship ppm = μg/m3 x CF, where CF is a temperature-dependent conversion 

factor; the CF varied with climate zone from 0.8032 (climate zone 1) to 0.8096 (climate zone 5), in accordance with the year-round temperatures given in Table 4-7.
61

Table 5-2, arranged in the same manner as Table 5-1, lists the average daily concentration 

(ADC) within each housing type during the first year (i.e., house age 0-1 years) following 

construction. The patterns of results for the two tables are very similar (e.g., highest levels in 

camper trailers and in the South).

Table 5-3 illustrates the decline in formaldehyde concentrations over the 10-year period that was 

modeled, using ADCs for manufactured homes in climate zone 3 (see Figure 4-9 for a depiction 

of U.S. climate zones). As noted in Section 4, an emissions half life of 1.5 years was assumed for 

the exponential decay of formaldehyde from initial modeled values; with this half life, the 

formaldehyde concentrations 10 years after construction due to CWP emissions are about one 

percent of their initial values. As evident in the bottom row of the table, the formaldehyde levels 

have nearly reached background (7.5 ppb) at this time. 

Tables 5-4 through 5-9 list overall ADCs reflecting combined in-home and away-from-home 

exposure (i.e., “around-the-clock” exposure) for infants, children, non-industry workers, 

fabrication-industry workers, retirees and part-time workers during the first year following house 

construction; the time allocations for these exposure groups were previously given in Section 

4.10. Differences across the exposure groups generally are no more than 20 percent, with the 

notable exception of fabrication-industry workers who have substantially higher overall exposure 

due to their elevated at-work exposure. Such differences can be seen more clearly in Figure 5-2, 

wherein the ADCs for each exposure group are averaged across housing types and climate zones.

Figure 5-2. Modeled ADCs (House Age 0-1 Years) for Exposure Groups by Emissions 

Scenario/Analytical Option and Housing Type – New-home Case.
62

Table 5-2. Modeled Residential ADCs (House Age 0-1 Years) for Eight Emissions Scenarios, ppb – New-home Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 36.2, 37.8 34.0, 35.1 33.1, 34.2 33.0, 34.1 20.9, 21.4 34.1, 35.4 33.3, 34.5 21.2, 21.8

2 37.3, 39.1 35.0, 36.2 34.1, 35.2 34.0, 35.1 21.5, 21.9 35.2, 36.5 34.4, 35.6 21.8, 22.4

3 36.9, 38.6 34.5, 35.7 33.6, 34.8 33.6, 34.6 21.3, 21.7 34.7, 36.1 33.9, 35.2 21.5, 22.1

4 41.2, 43.1 38.5, 39.9 37.5, 38.8 37.4, 38.6 23.2, 23.7 38.7, 40.2 37.8, 39.3 23.6, 24.4

5 47.2, 49.5 44.0, 45.7 42.9, 44.4 42.8, 44.2 26.1, 26.6 44.3, 46.1 43.2, 44.9 26.5, 27.4

Single-family Attached Homes (Zone 1, Zone 2)

1 39.3, 39.0 36.5, 36.0 35.5, 34.9 35.3, 34.8 21.0, 20.4 36.7, 36.3 35.8, 35.3 21.4, 21.0

2 40.5, 40.2 37.7, 37.1 36.6, 36.0 36.4, 35.8 21.6, 20.8 37.9, 37.4 36.9, 36.4 22.0, 21.5

3 40.0, 39.7 37.1, 36.5 36.1, 35.5 36.0, 35.3 21.3, 20.7 37.4, 36.9 36.4, 36.0 21.8, 21.3

4 44.8, 44.4 41.5, 40.8 40.3, 39.6 40.2, 39.4 23.4, 22.6 41.8, 41.3 40.6, 40.2 23.9, 23.3

5 51.4, 51.1 47.6, 46.8 46.1, 45.4 46.0, 45.2 26.2, 25.3 47.9, 47.4 46.6, 46.0 26.8, 26.1

Apartments

1 48.7 44.3 42.8 42.6 23.0 44.8 43.5 25.1

2 50.3 45.8 44.3 44.0 23.6 46.3 44.9 25.8

3 49.6 45.2 43.6 43.4 23.3 45.6 44.3 25.5

4 55.8 50.6 48.9 48.6 25.6 51.3 49.7 28.2

5 64.4 58.4 56.3 56.0 28.9 59.1 57.2 31.9

Manufactured Homes

1 41.8 37.9 36.6 36.4 22.0 38.6 37.4 23.1

2 43.2 39.1 37.8 37.5 22.6 39.7 38.6 23.7

3 42.6 38.6 37.3 36.9 22.3 39.2 38.1 23.4

4 47.7 43.1 41.6 41.3 24.5 43.9 42.6 25.7

5 55.0 49.5 47.8 47.4 27.5 50.4 48.8 29.1

Camper Trailers

1 59.4 47.6 44.4 43.1 25.7 50.6 48.2 30.8

2 61.5 49.2 45.9 44.5 26.4 52.3 49.8 31.7

3 60.5 48.5 45.2 43.9 26.1 51.6 49.1 31.2

4 68.3 54.5 50.8 49.2 28.8 58.1 55.2 34.8

5 79.3 63.0 58.5 56.8 32.6 67.1 63.7 39.7
63

Table 5-3. Modeled Residential ADCs by House Age for Manufactured Home in Climate Zone 3, by Emission Scenario, ppb –New-homeCase

House Age 

(years) at Start of 

Exposure Period

Baseline CARB1 Incl. 

Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

0 42.6 38.6 37.3 36.9 22.3 39.2 38.1 23.4

1 29.6 27.0 26.2 26.1 16.8 27.5 26.7 17.5

2 21.4 19.8 19.3 19.2 13.4 20.0 19.6 13.8

3 16.3 15.3 15.0 14.9 11.2 15.5 15.1 11.5

4 13.0 12.4 12.2 12.2 9.8 12.5 12.3 10.0

5 10.9 10.5 10.5 10.5 8.9 10.6 10.5 9.1

6 9.7 9.4 9.3 9.3 8.5 9.5 9.4 8.5

7 8.9 8.7 8.7 8.7 8.1 8.8 8.7 8.1

8 8.4 8.3 8.2 8.2 7.9 8.3 8.3 7.9

9 8.1 8.0 8.0 8.0 7.7 8.0 8.0 7.7

10 7.8 7.8 7.8 7.8 7.6 7.8 7.8 7.6
64

Table 5-4. Modeled ADCs (House Age 0-1 Years) for Infants for Eight Emissions Scenarios, ppba – New-home Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 29.2 27.3 26.6 26.6 17.1 27.5 26.8 17.4

2 30.0 28.0 27.4 27.3 17.5 28.3 27.6 17.8

3 29.6 27.7 27.0 27.0 17.3 27.9 27.2 17.6

4 32.8 30.7 29.9 29.8 18.8 30.9 30.1 19.1

5 37.4 34.9 34.0 33.8 20.9 35.1 34.2 21.3

Single-family Attached Homes (Zone 1, Zone 2)

1 31.1 28.9 28.1 28.0 17.0 29.1 28.4 17.4

2 32.0 29.7 28.9 28.8 17.4 30.0 29.2 17.8

3 31.6 29.3 28.5 28.4 17.2 29.6 28.8 17.6

4 35.2 32.6 31.7 31.5 18.7 32.8 32.0 19.1

5 40.1 37.1 36.0 35.8 20.8 37.4 36.3 21.3

Apartments

1 38.4 35.0 33.9 33.6 18.7 35.4 34.4 20.3

2 39.5 36.1 34.9 34.7 19.1 36.5 35.4 20.8

3 38.9 35.5 34.4 34.2 18.8 35.9 34.9 20.5

4 43.6 39.7 38.4 38.1 20.6 40.2 38.9 22.6

5 50.0 45.5 43.8 43.6 23.0 46.0 44.6 25.3

Manufactured Homes

1 33.2 30.1 29.1 28.9 17.8 30.6 29.7 18.7

2 34.1 31.0 30.0 29.7 18.2 31.4 30.6 19.1

3 33.6 30.6 29.6 29.3 18.1 31.0 30.1 18.9

4 37.5 34.0 32.8 32.6 19.7 34.5 33.6 20.7

5 42.9 38.7 37.4 37.1 21.9 39.4 38.2 23.1

Camper Trailers

1 46.6 37.6 35.1 34.1 20.7 39.8 38.0 24.5

2 48.1 38.7 36.2 35.1 21.2 41.1 39.1 25.3

3 47.3 38.1 35.6 34.6 20.9 40.5 38.5 24.9

4 53.2 42.7 39.8 38.6 23.0 45.4 43.2 27.5

5 61.3 48.9 45.5 44.2 25.8 52.1 49.5 31.1 a Modeled overall (24-hour) ADCs, in μg/m3

, were converted to ppm using the relationship ppm = μg/m3 x CF, where CF is a temperature-dependent conversion 

factor; the CF that was used – 0.8147 – corresponds to an assumed temperature of 25 °C (77 °F).
65

Table 5-5. Modeled ADCs (House Age 0-1 Years) for Preschool/School Children for Eight Emissions Scenarios, ppb – New-home Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 25.5 23.9 23.3 23.2 15.3 24.0 23.5 15.6

2 26.2 24.5 24.0 23.9 15.6 24.7 24.1 15.9

3 25.8 24.2 23.6 23.5 15.5 24.4 23.8 15.7

4 28.6 26.7 26.1 26.0 16.7 26.9 26.2 17.0

5 32.4 30.2 29.4 29.3 18.5 30.4 29.7 18.8

Single-family Attached Homes (Zone 1, Zone 2)

1 27.1 25.3 24.6 24.5 15.2 25.4 24.8 15.5

2 27.9 25.9 25.3 25.2 15.6 26.2 25.5 15.8

3 27.5 25.6 24.9 24.8 15.4 25.7 25.2 15.6

4 30.6 28.4 27.5 27.5 16.6 28.5 27.8 16.9

5 34.7 32.1 31.2 31.0 18.3 32.3 31.5 18.8

Apartments

1 33.2 30.4 29.4 29.2 16.5 30.7 29.8 17.9

2 34.2 31.2 30.2 30.1 16.9 31.6 30.6 18.4

3 33.7 30.8 29.8 29.7 16.8 31.1 30.2 18.2

4 37.6 34.3 33.2 33.0 18.2 34.7 33.6 19.8

5 43.0 39.1 37.8 37.6 20.2 39.6 38.4 22.2

Manufactured Homes

1 28.8 26.2 25.4 25.3 16.0 26.6 25.9 16.6

2 29.7 27.0 26.1 25.9 16.3 27.4 26.6 16.9

3 29.2 26.6 25.7 25.6 16.1 27.0 26.3 16.8

4 32.5 29.5 28.5 28.4 17.4 30.0 29.1 18.2

5 37.0 33.5 32.3 32.1 19.4 34.0 33.0 20.3

Camper Trailers

1 40.1 32.5 30.4 29.6 18.2 34.4 32.8 21.5

2 41.4 33.4 31.3 30.4 18.7 35.4 33.8 22.1

3 40.7 33.0 30.9 30.0 18.5 35.0 33.3 21.8

4 45.7 36.7 34.4 33.4 20.2 39.0 37.2 24.0

5 52.5 42.0 39.2 38.0 22.6 44.6 42.5 27.0
66

Table 5-6. Modeled ADCs (House Age 0-1 Years) for Non-industry Workers for Eight Emissions Scenarios, ppb – New-home Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 25.8 24.2 23.6 23.5 15.6 24.4 23.8 15.8

2 26.5 24.8 24.2 24.2 15.9 24.9 24.4 16.1

3 26.2 24.5 24.0 23.9 15.7 24.7 24.1 16.0

4 28.8 27.0 26.3 26.2 16.9 27.1 26.6 17.3

5 32.6 30.4 29.6 29.5 18.7 30.6 29.8 19.0

Single-family Attached Homes (Zone 1, Zone 2)

1 27.3 25.3 24.7 24.6 15.4 25.6 24.9 15.7

2 28.0 26.0 25.3 25.3 15.7 26.2 25.6 16.1

3 27.6 25.7 25.0 24.9 15.6 25.9 25.3 15.9

4 30.6 28.4 27.5 27.5 16.8 28.5 27.9 17.1

5 34.5 31.9 31.0 31.0 18.4 32.2 31.4 18.8

Apartments

1 33.2 30.4 29.4 29.2 16.8 30.7 29.8 18.1

2 34.1 31.2 30.2 30.1 17.1 31.5 30.6 18.5

3 33.6 30.8 29.8 29.7 16.9 31.1 30.2 18.3

4 37.4 34.1 33.1 32.9 18.4 34.5 33.6 20.0

5 42.6 38.8 37.5 37.3 20.3 39.3 38.0 22.2

Manufactured Homes

1 28.9 26.4 25.6 25.4 16.1 26.7 26.1 16.9

2 29.7 27.0 26.2 26.1 16.5 27.5 26.7 17.2

3 29.3 26.7 25.9 25.7 16.3 27.1 26.4 17.0

4 32.5 29.5 28.6 28.4 17.7 30.0 29.2 18.4

5 36.8 33.3 32.3 32.0 19.5 33.9 32.9 20.4

Camper Trailers

1 39.8 32.4 30.4 29.6 18.4 34.3 32.8 21.6

2 41.1 33.3 31.2 30.4 18.8 35.3 33.6 22.2

3 40.4 32.9 30.8 30.0 18.7 34.8 33.2 21.8

4 45.2 36.6 34.2 33.2 20.3 38.7 36.9 24.0

5 51.7 41.6 38.9 37.7 22.6 44.2 42.0 26.9
67

Table 5-7. Modeled ADCs (House Age 0-1 Years) for Fabrication-industry Workers for Eight Emissions Scenarios, ppb – New-home Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 69.1 65.8 65.0 65.0 35.0 66.0 65.3 35.2

2 69.7 66.5 65.7 65.6 35.3 66.6 65.8 35.5

3 69.4 66.2 65.3 65.3 35.1 66.3 65.5 35.4

4 72.1 68.7 67.7 67.6 36.4 68.8 67.9 36.7

5 75.9 72.0 71.0 70.9 38.0 72.3 71.3 38.5

Single-family Attached Homes (Zone 1, Zone 2)

1 70.6 67.1 66.2 66.1 34.8 67.2 66.3 35.1

2 71.3 67.7 66.7 66.6 35.1 67.9 67.0 35.4

3 70.9 67.4 66.5 66.4 35.0 67.5 66.6 35.3

4 73.8 70.0 69.0 68.9 36.2 70.2 69.3 36.5

5 77.8 73.7 72.5 72.3 37.8 73.9 72.8 38.3

Apartments

1 76.4 72.0 70.8 70.6 36.2 72.3 71.2 37.6

2 77.4 72.8 71.6 71.5 36.6 73.2 72.0 38.0

3 76.9 72.4 71.2 71.1 36.3 72.8 71.6 37.7

4 80.7 75.9 74.5 74.3 37.8 76.2 75.0 39.4

5 85.9 80.5 78.9 78.7 39.8 80.9 79.5 41.6

Manufactured Homes

1 72.2 68.0 67.0 66.8 35.6 68.4 67.5 36.3

2 73.0 68.8 67.6 67.5 35.9 69.2 68.2 36.6

3 72.6 68.4 67.3 67.1 35.8 68.8 67.8 36.4

4 75.8 71.2 70.0 69.8 37.1 71.6 70.6 37.8

5 80.1 75.0 73.7 73.4 38.9 75.5 74.3 39.8

Camper Trailers

1 83.1 74.1 71.8 71.0 37.8 75.9 74.1 41.0

2 84.3 75.0 72.7 71.8 38.3 76.9 75.1 41.6

3 83.7 74.5 72.3 71.4 38.0 76.4 74.6 41.3

4 88.5 78.2 75.6 74.6 39.7 80.4 78.4 43.4

5 95.0 83.3 80.3 79.2 42.0 85.9 83.5 46.4
68

Table 5-8. Modeled ADCs (House Age 0-1 Years) for Retirees for Eight Emissions Scenarios, ppb – New-home Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 31.4 29.3 28.6 28.5 18.2 29.6 28.8 18.6

2 32.3 30.1 29.4 29.3 18.7 30.4 29.7 19.0

3 31.9 29.7 29.0 28.9 18.4 30.0 29.2 18.7

4 35.5 33.1 32.2 32.1 20.0 33.3 32.5 20.4

5 40.5 37.6 36.6 36.4 22.3 37.9 36.9 22.8

Single-family Attached Homes (Zone 1, Zone 2)

1 33.2 30.7 29.9 29.7 17.8 31.0 30.2 18.3

2 34.1 31.6 30.7 30.6 18.2 31.9 31.0 18.7

3 33.6 31.2 30.3 30.2 18.1 31.4 30.6 18.5

4 37.5 34.7 33.7 33.6 19.7 35.0 34.1 20.2

5 42.9 39.5 38.4 38.2 21.9 39.8 38.8 22.5

Apartments

1 41.1 37.4 36.2 36.0 19.8 37.9 36.7 21.6

2 42.3 38.5 37.3 37.1 20.2 39.0 37.8 22.1

3 41.7 38.0 36.7 36.6 20.0 38.5 37.3 21.8

4 46.7 42.5 41.1 40.8 21.9 43.0 41.7 24.0

5 53.7 48.7 47.0 46.8 24.5 49.3 47.7 27.0

Manufactured Homes

1 35.4 32.1 31.0 30.8 19.0 32.7 31.7 19.8

2 36.4 33.1 31.9 31.7 19.4 33.6 32.7 20.3

3 35.9 32.6 31.5 31.3 19.1 33.2 32.2 20.0

4 40.1 36.3 35.0 34.8 20.9 36.9 35.8 22.0

5 45.9 41.4 40.0 39.7 23.4 42.1 40.9 24.6

Camper Trailers

1 49.9 40.2 37.5 36.4 22.0 42.6 40.7 26.2

2 51.5 41.4 38.6 37.5 22.6 44.0 41.9 26.9

3 50.8 40.8 38.0 37.0 22.2 43.3 41.2 26.6

4 57.1 45.7 42.6 41.3 24.4 48.6 46.2 29.4

5 65.8 52.5 48.8 47.3 27.5 55.8 53.0 33.3
69

Table 5-9. Modeled ADCs (House Age 0-1 Years) for Part-time Workers for Eight Emissions Scenarios, ppb – New-home Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 27.2 25.4 24.8 24.8 16.1 25.6 25.0 16.4

2 27.9 26.2 25.5 25.4 16.5 26.3 25.7 16.7

3 27.6 25.8 25.2 25.1 16.3 26.0 25.4 16.5

4 30.6 28.6 27.9 27.8 17.7 28.8 28.1 18.0

5 34.7 32.3 31.5 31.4 19.6 32.6 31.8 20.0

Single-family Attached Homes (Zone 1, Zone 2)

1 28.8 26.7 26.0 25.9 15.9 27.0 26.2 16.2

2 29.6 27.5 26.7 26.6 16.2 27.7 27.0 16.6

3 29.2 27.1 26.4 26.3 16.1 27.3 26.6 16.5

4 32.4 30.1 29.2 29.1 17.4 30.3 29.5 17.8

5 36.9 34.1 33.1 33.0 19.2 34.4 33.5 19.7

Apartments

1 35.4 32.3 31.3 31.1 17.4 32.7 31.7 18.9

2 36.4 33.2 32.2 32.0 17.8 33.6 32.7 19.4

3 35.9 32.8 31.7 31.5 17.6 33.2 32.2 19.1

4 40.1 36.6 35.4 35.1 19.2 37.0 35.8 20.9

5 45.9 41.7 40.3 40.1 21.3 42.2 40.9 23.5

Manufactured Homes

1 30.6 27.9 27.0 26.8 16.8 28.3 27.5 17.5

2 31.5 28.7 27.7 27.5 17.1 29.1 28.3 17.9

3 31.0 28.3 27.4 27.1 16.9 28.7 27.9 17.7

4 34.6 31.4 30.3 30.1 18.4 31.9 31.0 19.3

5 39.4 35.6 34.5 34.1 20.4 36.3 35.2 21.4

Camper Trailers

1 42.8 34.5 32.3 31.4 19.3 36.7 35.0 22.8

2 44.2 35.6 33.3 32.3 19.7 37.8 36.0 23.4

3 43.5 35.1 32.8 31.9 19.6 37.2 35.5 23.1

4 48.8 39.2 36.6 35.5 21.3 41.6 39.7 25.5

5 56.1 44.9 41.8 40.6 24.0 47.7 45.4 28.8
70

5.2 RENOVATION CASE

The same set of results as shown in the previous section for the new-home case is provided here 

for the renovation case. Table 5-10 lists initial modeled “steady-state” formaldehyde

concentrations for residential renovation. The initial concentrations are listed for each of eight 

emissions scenarios/analytical options (columns in the table), five housing types (sub-headings 

within the table), and five climate zones (table rows). Although the formaldehyde concentrations 

are lower in this case, the same general patterns as for the new-home case are apparent in the 

table:

• The highest modeled concentrations are for camper trailers

• Within each housing type, the highest concentrations are in the South (climate zone 5)

• Among the analytical options, the lowest concentrations occur for the case where CWPs 

are at emission levels that meet no-added-formaldehyde (NAF) standards, whether laminates 

are regulated or not.

Figure 5-3, wherein the initial modeled concentrations are averaged across climate zones, shows 

more clearly the patterns of results across emissions scenarios/analytical options and housing 

types. Although the concentrations are lower for renovation than for new residential 

construction, the scale in Figure 5-3 was kept the same as in Figure 5-1 to enable direct 

comparisons.

Figure 5-3. Modeled Initial Formaldehyde Concentrations by Emissions 

Scenario/Analytical Option and Housing Type – Renovation Case.

* Results shown are 

for Zone 1 of these 

two-zone structures
71

Table 5-10. Modeled Initial Residential Concentrations for Eight Emissions Scenarios, ppb – Renovation Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 20.0, 24.6 18.2, 21.8 17.7, 21.0 17.5, 20.7 11.0, 12.3 18.5, 22.4 18.0, 21.7 11.6, 13.2

2 20.4, 25.3 18.6, 22.4 18.1, 21.5 17.9, 21.3 11.2, 12.4 18.9, 23.0 18.5, 22.2 11.7, 13.4

3 20.2, 25.0 18.4, 22.1 17.9, 21.3 17.7, 21.0 11.1, 12.4 18.7, 22.7 18.3, 22.0 11.7, 13.3

4 22.1, 27.6 20.0, 24.3 19.4, 23.3 19.3, 23.0 11.7, 13.1 20.4, 24.9 19.9, 24.1 12.3, 14.2

5 24.7, 31.2 22.3, 27.3 21.5, 26.1 21.4, 25.8 12.4, 14.1 22.7, 28.1 22.1, 27.1 13.1, 15.4

Single-family Attached Homes (Zone 1, Zone 2)

1 25.0, 32.1 22.8, 28.7 22.1, 27.6 22.0, 27.4 12.4, 14.3 23.1, 29.2 22.5, 28.3 13.0, 15.2

2 25.7, 33.0 23.4, 29.5 22.7, 28.4 22.5, 28.2 12.6, 14.5 23.7, 30.1 23.1, 29.2 13.2, 15.5

3 25.4, 32.6 23.1, 29.1 22.4, 28.1 22.3, 27.8 12.5, 14.4 23.5, 29.7 22.8, 28.8 13.1, 15.4

4 28.0, 36.3 25.4, 32.3 24.6, 31.1 24.5, 30.8 13.3, 15.4 25.8, 33.0 25.1, 31.9 13.9, 16.5

5 31.7, 41.5 28.6, 36.8 27.7, 35.3 27.5, 35.0 14.3, 16.9 29.1, 37.6 28.3, 36.3 15.0, 18.2

Apartments

1 37.5 33.5 32.2 31.9 15.6 34.1 33.0 16.6

2 38.7 34.5 33.2 32.9 15.9 35.1 34.0 17.0

3 38.2 34.1 32.7 32.5 15.8 34.7 33.5 16.8

4 42.7 38.0 36.5 36.2 17.0 38.7 37.4 18.2

5 49.0 43.4 41.7 41.3 18.7 44.3 42.7 20.1

Manufactured Homes

1 30.2 25.6 24.3 23.8 13.8 26.7 25.6 15.6

2 31.1 26.3 25.0 24.5 14.1 27.4 26.4 16.0

3 30.7 26.0 24.7 24.2 14.0 27.1 26.0 15.8

4 34.1 28.7 27.2 26.7 14.9 30.0 28.8 17.0

5 38.9 32.5 30.7 30.1 16.3 34.0 32.6 18.7

Camper Trailers

1 48.5 38.6 36.1 34.9 19.8 41.2 39.3 24.1

2 50.1 39.9 37.2 36.0 20.3 42.5 40.5 24.8

3 49.4 39.3 36.7 35.5 20.1 41.9 40.0 24.5

4 55.5 44.0 41.0 39.7 21.9 47.0 44.8 27.0

5 64.1 50.6 47.0 45.4 24.5 54.1 51.4 30.5
72

Table 5-11, arranged in the same manner as Table 5-10, lists the average daily concentration 

(ADC) within each housing type during the first year (i.e., house age 0-1 years) following 

construction. The patterns in these two tables are very similar to one another; for example, in 

both tables the highest formaldehyde levels are in camper trailers and in the South.

Table 5-12 illustrates the decline in formaldehyde concentrations over the 10-year period that 

was modeled, using ADCs for manufactured homes in climate zone 3 (see Figure 4-9 for a 

depiction of U.S. climate zones). As with the new-home case, the concentrations 10 years after 

construction due to CWP emissions are about one percent of their initial values. As evident in the 

bottom row of the table, the formaldehyde levels have nearly reached background (7.5 ppb) at 

this time. 

Tables 5-13 through 5-18 list overall ADCs reflecting combined in-home and away-from-home 

exposure (i.e., “around-the-clock” exposure) during the first year following construction for 

infants, children, non-industry workers, fabrication-industry workers, retirees and part-time 

workers. Differences across the exposure groups for this case are similar in magnitude to those 

for the new-home case, and fabrication-industry workers again have the highest overall exposure 

due to their elevated at-work exposure. Such differences can be seen more clearly in Figure 5-4, 

wherein the ADCs for each exposure group are averaged across housing types and climate zones.

Figure 5-4. Modeled ADCs (House Age 0-1 Years) for Exposure Groups by Emissions 

Scenario/Analytical Option and Housing Type – Renovation Case.
73

Table 5-11. Modeled Residential ADCs (House Age 0-1 Years) for Eight Emissions Scenarios, ppb – Renovation Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 17.5, 21.2 16.1, 19.0 15.7, 18.3 15.5, 18.1 10.4, 11.3 16.3, 19.4 15.9, 18.9 10.8, 12.0

2 17.9, 21.8 16.4, 19.4 15.9, 18.7 15.8, 18.5 10.5, 11.4 16.7, 19.9 16.3, 19.3 10.9, 12.2

3 17.7, 21.5 16.3, 19.2 15.8, 18.5 15.7, 18.4 10.4, 11.4 16.5, 19.6 16.1, 19.1 10.8, 12.2

4 19.2, 23.6 17.5, 21.0 17.0, 20.2 16.9, 19.9 10.8, 11.9 17.8, 21.5 17.4, 20.8 11.3, 12.8

5 21.3, 26.5 19.3, 23.3 18.8, 22.4 18.6, 22.2 11.4, 12.8 19.7, 24.0 19.2, 23.2 12.0, 13.8

Single-family Attached Homes (Zone 1, Zone 2)

1 21.5, 27.1 19.8, 24.5 19.2, 23.6 19.1, 23.5 11.4, 12.9 20.0, 24.9 19.5, 24.2 11.9, 13.7

2 22.0, 27.9 20.2, 25.1 19.6, 24.3 19.6, 24.1 11.6, 13.1 20.5, 25.6 20.0, 24.9 12.1, 13.9

3 21.8, 27.6 20.0, 24.8 19.5, 24.0 19.3, 23.7 11.5, 13.0 20.3, 25.3 19.8, 24.6 12.0, 13.8

4 23.9, 30.6 21.9, 27.4 21.2, 26.4 21.1, 26.2 12.1, 13.9 22.2, 27.9 21.6, 27.1 12.7, 14.8

5 26.9, 34.6 24.4, 30.9 23.6, 29.8 23.5, 29.5 13.0, 15.0 24.8, 31.6 24.1, 30.6 13.5, 16.0

Apartments

1 31.5 28.3 27.3 27.1 14.0 28.8 27.9 14.8

2 32.5 29.1 28.1 27.8 14.2 29.6 28.7 15.1

3 32.0 28.7 27.7 27.5 14.2 29.2 28.3 15.0

4 35.6 31.9 30.7 30.5 15.1 32.5 31.4 16.0

5 40.7 36.3 34.9 34.6 16.5 36.9 35.7 17.6

Manufactured Homes

1 25.7 22.0 21.0 20.6 12.6 22.8 22.0 14.0

2 26.4 22.5 21.5 21.1 12.8 23.4 22.6 14.2

3 26.1 22.3 21.3 20.8 12.7 23.2 22.4 14.2

4 28.8 24.5 23.3 22.8 13.5 25.5 24.5 15.2

5 32.6 27.5 26.1 25.6 14.5 28.7 27.6 16.5

Camper Trailers

1 40.3 32.4 30.4 29.5 17.3 34.5 32.9 20.8

2 41.6 33.4 31.3 30.3 17.7 35.6 34.0 21.3

3 41.1 33.0 30.9 29.9 17.5 35.1 33.5 21.1

4 46.0 36.8 34.4 33.3 19.0 39.1 37.3 23.1

5 52.9 42.0 39.1 37.9 21.1 44.8 42.7 25.9
74

Table 5-12. Modeled Residential ADCs by House Age for Manufactured Home in Climate Zone 3, by Emission Scenario, ppb –RenovationCase

House Age 

(years) at Start of 

Exposure Period

Baseline CARB1 Incl. 

Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

0 26.1 22.3 21.3 20.8 12.7 23.2 22.4 14.2

1 19.2 16.8 16.2 15.9 10.8 17.4 16.8 11.7

2 14.9 13.4 13.0 12.8 9.6 13.7 13.4 10.1

3 12.2 11.2 10.9 10.9 8.8 11.4 11.2 9.2

4 10.4 9.8 9.7 9.6 8.3 10.0 9.8 8.5

5 9.3 8.9 8.9 8.9 8.1 9.0 8.9 8.1

6 8.7 8.5 8.4 8.4 7.8 8.5 8.5 7.9

7 8.2 8.1 8.1 8.1 7.7 8.1 8.1 7.7

8 8.0 7.9 7.8 7.8 7.6 7.9 7.9 7.6

9 7.8 7.7 7.7 7.7 7.6 7.7 7.7 7.6

10 7.6 7.6 7.6 7.6 7.6 7.6 7.6 7.6
75

Table 5-13. Modeled ADCs (House Age 0-1 Years) for Infants for Eight Emissions Scenarios, ppb – Renovation Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 15.2 13.9 13.5 13.4 9.1 14.2 13.9 9.5

2 15.5 14.2 13.8 13.7 9.2 14.4 14.1 9.6

3 15.3 14.1 13.7 13.6 9.1 14.3 13.9 9.5

4 16.5 15.1 14.7 14.6 9.5 15.4 15.0 9.9

5 18.2 16.5 16.1 15.9 9.9 16.9 16.4 10.5

Single-family Attached Homes (Zone 1, Zone 2)

1 18.7 17.1 16.6 16.5 10.0 17.4 16.9 10.4

2 19.1 17.5 17.0 16.9 10.2 17.8 17.3 10.6

3 18.8 17.3 16.8 16.7 10.1 17.5 17.1 10.5

4 20.6 18.8 18.2 18.1 10.6 19.1 18.6 11.1

5 23.0 20.9 20.2 20.1 11.2 21.2 20.6 11.8

Apartments

1 25.3 22.7 22.0 21.8 11.7 23.1 22.4 12.4

2 25.9 23.4 22.6 22.3 11.9 23.7 23.0 12.5

3 25.6 23.1 22.2 22.1 11.8 23.5 22.7 12.5

4 28.3 25.4 24.5 24.3 12.5 25.8 25.0 13.3

5 32.0 28.6 27.5 27.3 13.5 29.2 28.2 14.4

Manufactured Homes

1 20.8 17.9 17.1 16.9 10.7 18.6 17.9 11.7

2 21.3 18.3 17.5 17.2 10.8 19.0 18.3 11.9

3 21.0 18.1 17.4 17.0 10.7 18.8 18.2 11.8

4 23.1 19.7 18.8 18.5 11.2 20.5 19.8 12.5

5 25.9 22.0 20.9 20.5 12.1 22.9 22.0 13.5

Camper Trailers

1 31.9 25.9 24.4 23.6 14.3 27.5 26.3 16.9

2 32.9 26.6 25.0 24.3 14.6 28.3 27.0 17.4

3 32.4 26.3 24.7 24.0 14.4 27.9 26.6 17.1

4 36.2 29.1 27.2 26.5 15.6 31.0 29.6 18.7

5 41.2 33.0 30.8 29.8 17.0 35.1 33.5 20.7
76

Table 5-14. Modeled ADCs (House Age 0-1 Years) for Preschool/School Children for Eight Emissions Scenarios, ppb – Renovation Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 13.8 12.6 12.3 12.2 8.6 12.9 12.5 8.9

2 14.0 12.9 12.5 12.5 8.6 13.0 12.8 9.0

3 13.9 12.8 12.5 12.4 8.6 13.0 12.6 9.0

4 14.9 13.6 13.3 13.1 8.9 13.9 13.5 9.3

5 16.3 14.8 14.3 14.3 9.3 15.1 14.7 9.7

Single-family Attached Homes (Zone 1, Zone 2)

1 16.6 15.3 14.9 14.8 9.4 15.5 15.2 9.7

2 17.0 15.6 15.2 15.1 9.5 15.8 15.4 9.8

3 16.8 15.5 15.0 14.9 9.4 15.6 15.3 9.8

4 18.2 16.7 16.2 16.1 9.8 16.9 16.5 10.2

5 20.3 18.4 17.8 17.8 10.3 18.7 18.2 10.8

Apartments

1 22.2 20.0 19.4 19.3 10.8 20.4 19.8 11.3

2 22.8 20.6 19.9 19.7 10.9 20.9 20.3 11.5

3 22.5 20.4 19.6 19.5 10.8 20.6 20.0 11.4

4 24.8 22.3 21.5 21.3 11.5 22.6 22.0 12.1

5 27.9 25.0 24.1 23.9 12.3 25.4 24.6 13.0

Manufactured Homes

1 18.5 16.1 15.3 15.1 9.9 16.5 16.1 10.8

2 18.9 16.4 15.6 15.4 10.0 16.9 16.4 10.9

3 18.7 16.2 15.5 15.2 9.9 16.8 16.2 10.8

4 20.4 17.6 16.8 16.5 10.4 18.2 17.6 11.5

5 22.7 19.5 18.5 18.2 11.1 20.2 19.5 12.3

Camper Trailers

1 27.9 22.7 21.4 20.9 13.0 24.0 23.1 15.2

2 28.7 23.3 21.9 21.3 13.2 24.7 23.6 15.5

3 28.3 23.1 21.7 21.1 13.0 24.4 23.4 15.3

4 31.4 25.4 23.9 23.1 13.9 27.0 25.7 16.5

5 35.7 28.7 26.8 26.0 15.2 30.5 29.1 18.3
77

Table 5-15. Modeled ADCs (House Age 0-1 Years) for Non-industry Workers for Eight Emissions Scenarios, ppb – Renovation Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 14.7 13.5 13.1 13.0 9.1 13.7 13.4 9.5

2 15.0 13.7 13.4 13.3 9.2 13.9 13.6 9.5

3 14.8 13.6 13.3 13.2 9.2 13.9 13.5 9.5

4 15.9 14.5 14.1 14.0 9.5 14.7 14.3 9.9

5 17.3 15.7 15.2 15.1 9.9 16.0 15.6 10.3

Single-family Attached Homes (Zone 1, Zone 2)

1 17.6 16.2 15.8 15.7 9.9 16.4 16.1 10.3

2 18.0 16.5 16.1 16.0 10.0 16.8 16.4 10.4

3 17.8 16.4 16.0 15.8 10.0 16.6 16.2 10.3

4 19.3 17.7 17.2 17.0 10.4 17.9 17.4 10.8

5 21.3 19.4 18.8 18.7 10.9 19.7 19.1 11.4

Apartments

1 22.5 20.4 19.8 19.6 11.2 20.7 20.1 11.7

2 23.1 20.9 20.2 20.0 11.3 21.2 20.6 11.9

3 22.8 20.7 20.0 19.9 11.2 20.9 20.4 11.8

4 25.0 22.6 21.8 21.7 11.8 22.9 22.2 12.5

5 28.0 25.2 24.3 24.1 12.6 25.6 24.8 13.4

Manufactured Homes

1 18.9 16.5 15.8 15.6 10.3 17.0 16.5 11.2

2 19.3 16.8 16.1 15.9 10.4 17.4 16.9 11.3

3 19.1 16.6 16.0 15.7 10.3 17.2 16.7 11.2

4 20.8 18.0 17.2 16.9 10.8 18.6 18.0 11.9

5 23.1 19.8 18.9 18.6 11.4 20.5 19.8 12.7

Camper Trailers

1 27.9 23.0 21.7 21.1 13.3 24.3 23.3 15.4

2 28.8 23.5 22.2 21.6 13.5 24.8 23.9 15.7

3 28.4 23.3 21.9 21.3 13.4 24.6 23.5 15.6

4 31.4 25.6 24.0 23.4 14.3 27.0 25.9 16.8

5 35.5 28.7 26.9 26.2 15.5 30.5 29.1 18.4
78

Table 5-16. Modeled ADCs (House Age 0-1 Years) for Fabrication-industry Workers for Eight Emissions Scenarios, ppb – Renovation Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 57.9 55.2 54.6 54.5 28.6 55.4 54.8 28.9

2 58.3 55.4 54.7 54.7 28.6 55.6 55.1 29.0

3 58.1 55.2 54.7 54.6 28.6 55.5 54.9 28.9

4 59.1 56.1 55.5 55.4 28.8 56.4 55.8 29.2

5 60.5 57.4 56.6 56.5 29.2 57.6 56.9 29.7

Single-family Attached Homes (Zone 1, Zone 2)

1 60.9 57.8 57.2 57.1 29.3 58.1 57.4 29.7

2 61.3 58.2 57.5 57.4 29.5 58.4 57.8 29.8

3 61.1 58.0 57.4 57.3 29.4 58.3 57.6 29.7

4 62.6 59.3 58.6 58.5 29.8 59.6 58.9 30.2

5 64.6 61.1 60.3 60.1 30.4 61.3 60.6 30.8

Apartments

1 65.8 62.1 61.2 61.0 30.6 62.4 61.5 31.1

2 66.3 62.6 61.6 61.5 30.7 62.9 62.0 31.3

3 66.1 62.3 61.4 61.3 30.6 62.7 61.8 31.2

4 68.3 64.2 63.2 63.1 31.3 64.6 63.6 31.9

5 71.3 66.8 65.7 65.5 32.1 67.3 66.2 32.8

Manufactured Homes

1 62.2 58.2 57.3 57.0 29.7 58.7 57.9 30.6

2 62.6 58.5 57.5 57.3 29.8 59.1 58.3 30.8

3 62.4 58.3 57.4 57.2 29.7 58.9 58.1 30.7

4 64.0 59.6 58.7 58.3 30.2 60.3 59.4 31.3

5 66.3 61.4 60.3 60.0 30.9 62.2 61.2 32.1

Camper Trailers

1 71.2 64.7 63.1 62.6 32.7 65.9 64.7 34.8

2 72.0 65.3 63.6 63.1 32.9 66.6 65.3 35.1

3 71.6 64.9 63.4 62.8 32.8 66.2 65.0 35.0

4 74.6 67.2 65.4 64.8 33.6 68.7 67.3 36.2

5 78.8 70.4 68.4 67.5 34.9 72.1 70.6 37.9
79

Table 5-17. Modeled ADCs (House Age 0-1 Years) for Retirees for Eight Emissions Scenarios, ppb – Renovation Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 16.8 15.2 14.7 14.7 9.7 15.6 15.2 10.2

2 17.1 15.6 15.1 14.9 9.8 15.8 15.4 10.3

3 16.9 15.4 14.9 14.8 9.7 15.6 15.3 10.2

4 18.4 16.6 16.1 15.9 10.1 16.9 16.5 10.7

5 20.4 18.2 17.7 17.4 10.7 18.7 18.2 11.3

Single-family Attached Homes (Zone 1, Zone 2)

1 20.9 19.1 18.5 18.3 10.8 19.3 18.8 11.3

2 21.3 19.5 18.9 18.7 10.9 19.8 19.2 11.5

3 21.1 19.2 18.7 18.6 10.8 19.6 19.1 11.4

4 23.1 21.0 20.4 20.2 11.4 21.3 20.8 12.0

5 26.0 23.5 22.6 22.5 12.2 23.9 23.2 12.9

Apartments

1 26.9 24.2 23.3 23.1 12.3 24.6 23.9 13.0

2 27.6 24.8 24.0 23.8 12.5 25.3 24.4 13.2

3 27.2 24.5 23.6 23.5 12.4 24.9 24.1 13.1

4 30.1 27.0 26.1 25.8 13.2 27.5 26.6 14.0

5 34.2 30.6 29.3 29.2 14.3 31.0 30.1 15.2

Manufactured Homes

1 22.0 19.0 18.1 17.8 11.2 19.6 19.0 12.3

2 22.6 19.4 18.5 18.2 11.3 20.1 19.4 12.5

3 22.3 19.1 18.3 18.0 11.2 19.9 19.2 12.5

4 24.5 20.9 20.0 19.6 11.8 21.8 20.9 13.2

5 27.5 23.4 22.2 21.8 12.6 24.4 23.4 14.3

Camper Trailers

1 34.1 27.6 25.9 25.2 15.1 29.3 28.0 17.9

2 35.1 28.4 26.6 25.8 15.4 30.1 28.8 18.3

3 34.6 28.0 26.2 25.5 15.2 29.7 28.4 18.2

4 38.6 31.0 29.0 28.2 16.5 33.0 31.5 19.8

5 44.2 35.2 32.9 31.9 18.1 37.6 35.8 22.0
80

Table 5-18. Modeled ADCs (House Age 0-1 Years) for Part-time Workers for Eight Emissions Scenarios, ppb – Renovation Case

Climate 

Zone Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

Single-family Detached Homes (Zone 1, Zone 2)

1 14.8 13.5 13.2 13.1 9.0 13.8 13.4 9.3

2 15.1 13.8 13.4 13.3 9.0 14.0 13.7 9.5

3 15.0 13.7 13.3 13.2 9.0 13.9 13.6 9.4

4 16.1 14.7 14.3 14.1 9.3 14.9 14.6 9.8

5 17.8 16.1 15.5 15.4 9.7 16.3 15.9 10.3

Single-family Attached Homes (Zone 1, Zone 2)

1 18.1 16.6 16.1 16.1 9.9 16.9 16.5 10.3

2 18.6 16.9 16.5 16.4 9.9 17.2 16.8 10.3

3 18.3 16.8 16.3 16.2 9.9 17.0 16.6 10.3

4 20.0 18.2 17.7 17.6 10.3 18.5 18.0 10.8

5 22.2 20.2 19.6 19.5 11.0 20.5 20.0 11.5

Apartments

1 23.5 21.2 20.5 20.4 11.2 21.6 20.9 11.7

2 24.1 21.8 21.0 20.9 11.4 22.1 21.4 12.0

3 23.8 21.5 20.8 20.6 11.2 21.8 21.2 11.9

4 26.2 23.6 22.8 22.6 12.0 24.0 23.3 12.6

5 29.7 26.6 25.6 25.3 12.9 27.0 26.2 13.6

Manufactured Homes

1 19.5 16.9 16.1 15.9 10.2 17.4 16.9 11.2

2 19.9 17.2 16.5 16.2 10.3 17.8 17.3 11.4

3 19.6 17.0 16.3 16.1 10.3 17.6 17.0 11.3

4 21.5 18.5 17.7 17.4 10.8 19.2 18.5 12.0

5 24.0 20.5 19.6 19.2 11.5 21.3 20.5 12.9

Camper Trailers

1 34.1 24.1 22.6 22.0 13.5 25.5 24.4 15.9

2 35.1 24.7 23.2 22.6 13.8 26.2 25.1 16.3

3 34.6 24.4 23.0 22.3 13.6 25.8 24.8 16.1

4 38.6 27.0 25.3 24.5 14.7 28.6 27.4 17.4

5 44.2 30.5 28.5 27.6 16.0 32.4 31.0 19.3
81

Section 6

DISCUSSION

6.1 APPROACH AND RESULTS

6.1.1 Summary of Approach

A modeling-based approach was chosen for the exposure assessment to accommodate the 

number of situations of potential interest and the limited amount of current or recent monitoring 

data available. Both new-construction, or new-home, and renovation cases were examined. As a 

general rule, expected or average values were used for model inputs, as opposed to a range or 

distribution of values. Variability was introduced for certain input parameters expected to have a 

significant influence on the modeling results. Seven alternative emissions scenarios (analytical

options) were modeled along with a baseline (2013) scenario. Model runs were made for five 

different structure types, in five different climates zones, for each emissions scenario/analytical 

option. Six exposure groups – infants, children, non-industry workers, fabrication industry 

workers, retirees, and part-time workers – were included in the assessment, which estimated not 

only at-home but also away-from-home formaldehyde exposure in the form of an average daily 

concentration (ADC) reflecting “around the clock” exposure.

6.1.2 Summary of Modeled Initial Formaldehyde Concentrations in Homes

For the baseline 2013 scenario, modeled formaldehyde levels (initial values, representing the 

“steady state” condition shortly after installation of new PWPs) had the following ranges across 

climate zones for the five structure types that were included in the assessment:

• Single-family detached homes – 43 to 60 ppb (new house); 20 to 31 ppb (renovation)

• Single-family attached homes – 47 to 62 ppb (new house); 25 to 42 ppb (renovation)

• Apartments – 59 to 79 ppb (new house); 38 to 49 ppb (renovation)

• Manufactured homes – 50 to 67 ppb (new house); 30 to 39 ppb (renovation)

• Camper trailers – 72 to 97 ppb (new house); 49 to 64 ppb (renovation)

The modeled concentrations were higher, and the ranges somewhat broader, for the new-home 

case than for the renovation case. As noted in Section 4.4.8, using current emission levels to 

estimate emission levels in 2013 would not accurately reflect the 2013 baseline, because many 

CWP manufacturers are modifying their production technology and raw materials to achieve 

compliance with Phase 2 of the CARB ATCM. Instead, baseline emission levels were estimated 

on the basis of responses to a survey question about emission levels that mills planned to achieve 

within the next three years.

Figure 6-1 depicts the initial modeled indoor concentrations at baseline and under the seven 

analytical options for both the new-home and the renovation cases, with results averaged across 

housing types and climate zones. Figure 6-2 indicates the concentration reduction for each 

option, relative to baseline, for the same two cases. In either case, the reduction clearly is the 

greatest for the NAF option, whether laminates are regulated or not. 
82

Figure 6-1. Modeled Initial Formaldehyde Concentration by Emissions Scenario/Analytical 

Option for New-home and Renovation Cases.

Figure 6-2. Reduction in Modeled Initial Formaldehyde Concentration, Relative to 

Baseline, by Alternate Emissions Scenario for New-home and Renovation Cases.

0

10

20

30

40

50

60

70

80

Initital Formaldehyde Concentration, ppb

New-home Case

Renovation Case
83

Figure 6-3, with the concentration reductions expressed in percentage terms, again shows the 

substantially greater reduction for the NAF option. Table 6-1 lists some of the underlying details, 

with the percent differences shown separately by housing type. The percent reductions clearly 

are greatest for camper trailers, but the advantage of the NAF option relative to the other 

analytical options is not quite as great for this structure type. The percent reductions are 

somewhat greater for apartments and manufactured homes than for single-family attached and 

detached homes.

Figure 6-3. Percent Reduction in Modeled Initial Formaldehyde Concentration, Relative to 

Baseline, by Alternate Emissions Scenario for New-home and Renovation Cases.
84

Table 6-1. Percent Reduction in Initial Formaldehyde Concentration, Relative to Baseline, 

by Alternate Emissions Scenario and Housing Type for New-home and Renovation Cases

Housing 

Type

CARB1 

Incl. 

Laminates

CARB2 

Incl. 

Laminates

CARB2 

with Lam. 

@ NAF

CARB 

NAF Incl. 

Laminates

CARB1 

Excl. 

Laminates

CARB2 

Excl. 

Laminates

CARB 

NAF Excl. 

Laminates

New-home Case

SF Detached 

Homes 6.7% 9.2% 9.4% 44.9% 6.2% 8.5% 44.0%

SF Attached 

Homes 7.5% 10.2% 10.5% 49.0% 6.8% 9.4% 47.9%

Apartments 9.4% 12.6% 13.1% 55.1% 8.2% 11.2% 50.5%

Manufactured 

Homes 9.9% 13.1% 13.8% 49.9% 8.3% 11.1% 47.2%

Camper 

Trailers 20.6% 26.1% 28.4% 58.8% 15.3% 19.6% 50.0%

Renovation Case

SF Detached

Homes 9.2% 11.9% 12.7% 46.6% 7.6% 9.9% 43.8%

SF Attached 

Homes 9.2% 12.0% 12.5% 52.1% 7.8% 10.3% 49.8%

Apartments 11.0% 14.5% 15.2% 59.7% 9.3% 12.4% 57.0%

Manufactured 

Homes 15.7% 20.1% 21.6% 55.7% 12.0% 15.5% 49.6%

Camper 

Trailers 20.6% 26.0% 28.4% 60.2% 15.3% 19.3% 51.1%

6.1.3 Summary of Modeled ADCs for Exposure Groups

For the baseline 2013 scenario, modeled ADCs for the first year immediately following new 

construction or renovation had the following ranges across structure types for the six exposure 

groups that were included in the assessment:

• Infants – 32 to 51 ppb (new house); 16 to 35 ppb (renovation)

• Children – 28 to 44 ppb (new house); 15 to 30 ppb (renovation)

• Non-industry workers – 28 to 44 ppb (new house); 15 to 30 ppb (renovation)

• Fabrication industry workers – 72 to 87 ppb (new house); 59 to 73 ppb (renovation)

• Retirees – 34 to 55 ppb (new house); 18 to 37 ppb (renovation)

• Part-time workers – 29 to 47 ppb (new house); 15 to 33 ppb (renovation)

The ranges listed for each exposure group are across housing types, based on averages across 

climate zones within each type. As with the initial modeled formaldehyde concentrations, 

exposures are higher for new construction than for renovation. The range of exposures (ADCs) 

within each group is 15-25 ppb, for both the new-home and renovation cases. Individuals living 

in single-family detached homes have the lowest modeled exposures and those living in camper 

trailers have the highest. The much higher overall/total exposures for workers in the fabrication 

industry are due to their elevated at-work exposures.
85

Table 6-2 lists the ADCs for each exposure group at baseline and under the seven analytical options for both the new-home and the 

renovation cases, with results averaged across housing types and climate zones. The reduction in ADCs is the greatest for the NAF 

option, whether laminates are regulated or not. The higher reductions for the NAF option, on the order of 50 percent, can be seen more 

clearly in Figures 6-4 (new-home case) and 6-5 (renovation case), wherein percentage reductions relative to baseline are shown.

Table 6-2. Average Modeled ADC (House Age 0-1 Years) by Exposure Group and Emissions Scenario for New-home and 

Renovation Cases, ppb

Exposure 

Group Baseline CARB1 Incl. Laminates

CARB2 Incl. 

Laminates

CARB2 with 

Lam. @ NAF

CARB NAF 

Incl. Lam.

CARB1 Excl. 

Laminates

CARB2 Excl. 

Laminates

CARB NAF 

Excl. Lam.

New-home Case

Infants 39.1 34.7 33.4 33.0 19.6 35.5 34.4 21.2

Children 33.8 30.1 29.0 28.7 17.4 30.8 29.8 18.7

Non-industry 

Workers 33.8 30.1 29.0 28.8 17.6 30.8 29.8 18.8

Fabrication 

Workers 77.1 71.8 70.4 70.1 37.0 72.4 71.2 38.3

Retirees 41.9 37.2 35.7 35.3 20.9 38.0 36.7 22.6

Part-time 

Workers 36.0 32.1 30.8 30.6 18.3 32.8 31.8 19.7

Renovation Case

Infants 24.2 21.0 20.1 19.8 11.7 21.7 21.0 12.9

Children 21.3 18.6 17.8 17.6 10.8 19.1 18.6 11.7

Non-industry Workers 21.8 19.1 18.4 18.2 11.2 19.7 19.1 12.1

Fabrication 

Workers 65.1 60.8 59.8 59.6 30.6 61.3 60.5 31.5

Retirees 26.2 22.6 21.7 21.3 12.4 23.4 22.6 13.7

Part-time 

Workers 22.7 19.8 19.0 18.7 11.2 20.4 19.8 12.3
86

Figure 6-4. Percent Reduction in Modeled ADCs (House Age 0-1 Years) for Exposure 

Groups, Relative to Baseline, by Alternate Emissions Scenario for New-home Case.

Figure 6-5. Percent Reduction in Modeled ADCs (House Age 0-1 Years) for Exposure 

Groups, Relative to Baseline, by Alternate Emissions Scenario for Renovation Case.
87

6.2 DATA GAPS AND INFORMATION NEEDS

6.2.1 Emissions Data

Considering the factors that can influence formaldehyde concentrations indoors, particularly in 

the context of modeling the impact of PWPs on concentrations and associated exposures, one 

notable information gap is the lack of emissions data for recently manufactured PWPs. Most 

emission rates in the FIAM model are based on emission tests conducted around the mid-1990s 

or earlier. One feature of these tests is that they were conducted at multiple air exchange and/or 

product loading rates, to enable estimation of slope and intercept parameters that convey the 

dependence of the emission rate on the prevailing indoor formaldehyde concentration. 

In the absence of similar data for recent CARB-compliant PWPs, it was necessary to estimate 

these factors using some assumptions, as described in Section 4.4.8 of this report. Ideally, 

appropriate sets of emission tests to support the model’s input needs would be conducted for a 

variety of CARB-compliant products. Similar tests for products or ensembles such as 

entertainment centers, kitchen cabinets and interior doors also would be useful, as their emission

profiles have not been well characterized.

6.2.2 Near-field Exposures

One of the assumptions inherent in the FIAM model is complete mixing; that is, formaldehyde

concentrations are assumed to be uniform throughout each compartment that is modeled. 

Whereas this assumption may be reasonable for PWPs that are dispersed throughout the 

residence, a notable exception that has received some recent attention is infant cribs with pressed 

wood components. A potential concern here is the infant’s near-field exposure due to close 

proximity to the formaldehyde source when sleeping. 

Available data on this particular exposure situation are quite scarce. The Environment California 

Research & Policy Center (Madsen and Gibson 2008) purchased26 21 consumer products, mainly 

baby nursery furnishings such as cribs and changing tables, and arranged for chamber testing of 

these products. Emission rates determined from these tests covered a very broad range, from 1 to

3,580 μg/unit per hour. 

As implied above, such near-field exposures present a challenging case for indoor air modeling, 

possibly involving fairly complex analytical techniques such as computational fluid dynamics 

(CFD). A simpler alternative, compatible with the FIAM model, would involve a two-zone 

modeling approach with one of the zones representing the “virtual air space” surrounding the 

infant while sleeping in a crib. This two-zone approach has been described, for example, in

ASTM D6178-97, Standard Practice for Estimation of Short-term Inhalation Exposure to 

Volatile Organic Chemicals Emitted from Bedding Sets (ASTM 2008). The validity of this 

approach, as well as that of the more complex CFD technique, would require assessment through 

detailed spatial and temporal monitoring. 

 26 The cited report is dated May 2008 but does not indicate when the tested products were purchased. An appendix 

in the report lists the product name, product sample ID, and manufacturer ID for each product that was tested.
88

Section 7

REFERENCES

ASTM. 2010. Standard Test Method for Determining Formaldehyde Concentrations in Air and 

Emission Rates from Wood Products Using a Large Chamber. Designation E1333-10, American 

Society for Testing and Materials, Philadelphia, PA.

ASTM. 2008. Standard Practice for Estimation of Short-term Inhalation Exposure to Volatile 

Organic Chemicals Emitted from Bedding Sets. Designation D6178-97 (2008), American Society 

for Testing and Materials, Philadelphia, PA.

ATSDR. 1999. Toxicological Profile for Formaldehyde, U.S. Department of Health and Human 

Services, Public Health Service, Agency for Toxic Substances and Disease Registry, July 1999.

CARB. 2004. Environmental Health Conditions in California’s Portable Classrooms. Report to 

the California Legislature by the California Air Resources Board (CARB) and the California 

Department of Health Services, November 2004.

CARB. 2005. Indoor Air Pollution in California. Report to the Legislature, Pursuant to Health & 

Safety Code §39930. California Air Resources Board (CARB), Research Division, Sacramento, CA.

CDC. 2008/2010. Final Report on Formaldehyde Levels in FEMA-Supplied Travel Trailers, 

Park Models, and Mobile Homes. Centers for Disease Control and Prevention. Available at: 

http://www.cdc.gov/nceh/ehhe/trailerstudy/assessment.htm#final. July 2008 (amended December 

2010).

DHS. 2009. FEMA Response to Formaldehyde in Trailers. OIG-09-83. Department of Homeland 

Security, Office of Inspector General, Washington, DC. 

B. J. Finlayson-Pitts, and J. N Pitts. 2000. Upper and Lower Atmosphere. Academic Press, San

Diego, CA.

N.L. Gilbert, M. Guay, J.D. Miller, S. Judek, C.C. Chan, and R.E. Dales. 2005. Levels and 

Determinants of Formaldehyde, Acetaldehyde, and Acrolein in Residential Indoor Air in Prince 

Edward Island, Canada. Environmental Research 99(1): 11-17.

N.L. Gilbert, D. Gauvin, M. Guay, M.E. Héroux, G. Dupuis, M Legris, C.C. Chan, R.N. Dietz, 

and B. Lévesque. 2006. Housing Characteristics and Indoor Concentrations of Nitrogen Dioxide 

and Formaldehyde in Quebec City, Canada. Environmental Research 102(1): 1-8.

A.T Hodgson, A.F. Rudd, D. Beal, and S. Chandra. 2000. Volatile Organic Compound 

Concentrations and Emission Rates in New Manufactured and Site-Built Houses. Indoor Air 10: 

178-192.

A.T. Hodgson, D. G. Shendell, W.J. Fisk, and M.G. Apte. 2004. Comparison of Predicted and 

Derived Measures of Volatile Organic Compounds inside Four New Relocatable Classrooms. 

Indoor Air 14 (Supplement 8): 135-144.

HPVA. 2010. Personal communication with HPVA. Conversation between with Kip Howlett 

(Hardwood Plywood and Veneer Association) and Abt Associates Inc., November 2010.
89

T.J. Kelly. 1996. Determination of Formaldehyde and Toluene Diisocyanate Emissions from 

Indoor Residential Sources. Final Report prepared by Battelle for CARB Research Division 

under Contract No. 93-315, Sacramento, CA.

T.J. Kelly, D.L. Smith, and J. Satola. 1999. Emission Rates of Formaldehyde from Materials and 

Consumer Products Found in California Homes. Environmental Science & Technology 33(1): 

81–88.

M.D. Koontz and H.E. Rector. 1995. Estimation of Distributions for Residential Air Exchange 

Rates, Report prepared under EPA Contract No. 68-D9-0166, Work Assignment No. 3-19, U.S. 

Environmental Protection Agency, Office of Pollution Prevention and Toxics, Washington, DC. 

M. Koontz, H. Rector, D. Cade, C. Wilkes, and L. Niang. 1996. Residential Indoor Air 

Formaldehyde Testing Program: Pilot Study. Report No. IE-2814, prepared by GEOMET 

Technologies, Inc. for the USEPA Office of Pollution Prevention and Toxics under EPA 

Contract No. 68-D3-0013, Washington, DC.

W. Liu, J. Zhang, L. Zhang, B.J. Turpin, C.P. Weisel, M.T. Morandi, T.H. Stock, S. Colome, and 

L.R. Korn. 2006. Estimating Contributions of Indoor and Outdoor Sources to Indoor Carbonyl 

Concentrations in Three Urban Areas of the United States. Atmospheric Environment 40: 2202-

2214.

R. Maddalena, M. Russell, D.P. Sullivan, and M.G. Apte. 2008. Aldehyde and Other Volatile 

Organic Chemical Emissions in Four FEMA Temporary Housing Units – Final Report. LBNL254E, Ernest Orlando Lawrence Berkeley National Laboratory, Environmental Energy 

Technologies Division, Berkeley, CA.

T. Madsen and R. Gibson. 2008. Toxic Baby Furniture: The Latest Case for Making Products 

Safe from the Start. Environment California Research & Policy Center, Los Angeles, CA.

T. Matthews, T. Reed, B. Tromberg, C. Daffron, and A. Hawthorne. 1983. Formaldehyde 

Emissions from Combustion Sources and Solid Formaldehyde Resin Containing Products: 

Potential Impact on Indoor Formaldehyde Concentration and Possible Corrective Measures. 

Proceedings of ASHRAE Symposium Management of Atmospheres in Tightly Enclosed Spaces, 

Santa Barbara, CA. 

T. Matthews, A. Hawthorne, and C Thompson. 1987. Formaldehyde Sorption and Desorption 

Characteristics of Gypsum Wallboard. Environmental Science & Technology 21: 629-634.

D.M. Murray and D.E. Burmaster. 1995. Residential Air Exchange Rates in the United States: 

Empirical and Estimated Parametric Distribution by Season and Climatic Region. Risk Analysis

15: 459-465. 

F. J. Offermann, J. Robertson, D. Springer, S. Brennan, and T. Woo. 2008. Window Usage, 

Ventilation, and Formaldehyde Concentrations in New California Homes: Summer Field 

Sessions. ASHRAE IAQ 2007 Conference, Baltimore, MD.

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Housing. Indoor Air 20: 473-485.

A.K. Persily. 1989. Ventilation Rates in Office Buildings. IAQ 1989, American Society of 

Heating, Refrigerating and Air-Conditioning Engineers, Inc., Atlanta, GA, pp 128-136.
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PSI. 2009. Professional Services Industries, Inc. (PSI). “The TPC Perspective,” available at 

http://university.ahfa.us/documents/fmhyde309_schutfort.pdf.

S.N. Sax, D.H. Bennett, S.N. Chillrud, P.L. Kinney, and J.D. Spengler. 2004. Differences in 

Source Emission Rates of Volatile Organic Compounds in Inner-City Residences of New York 

City and Los Angeles. Journal of Exposure Analysis and Environmental Epidemiology 14 

(Supplement 1): S95-S109.

K. Sexton, M. Petreas, and K. Liu. 1989. Formaldehyde Exposures inside Mobile Homes.

Environmental Science & Technology 23(8): 985-988.

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Composite Wood Products. U.S. Environmental Protection Agency, Office of Pollution 

Prevention and Toxics, Chemical Engineering Branch, 1200 Pennsylvania Avenue NW, 

Washington, DC 20460. 6 October 2011.

USEPA. 2012a. Formaldehyde Indoor Air Model – Pressed Wood Products, Version 2.0 (FIAMpwp v2.0): Model User Manual and Documentation. U.S. Environmental Protection Agency, 

Office of Pollution Prevention and Toxics, Exposure Assessment Branch, 1200 Pennsylvania 

Avenue NW, Washington, DC 20460. July 2012.

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Data Mart, available at http://www.epa.gov/airdata/.
Appendix A

Floor Plans by Structure Type
A-1

SINGLE FAMILY DETACHED (2 Story)
A-2

SINGLE FAMILY ATTACHED (2 Story)
A-3

APARTMENT
A-4

SINGLE-WIDE MANUFACTURED HOME
A-5

DOUBLE-WIDE MANUFACTURED HOME
A-6

CAMPER TRAILER
Appendix B

PWP Loading Spreadsheets
B-1

SINGLE-FAMILY DETACHED HOME – HIGH LOADING, NEW-HOME CASE
B-2

SINGLE-FAMILY ATTACHED HOME – HIGH LOADING, NEW-HOME CASE
B-3

APARTMENT – HIGH LOADING, NEW-HOME CASE
B-4

SINGLE-WIDE MANUFACTURED HOME – HIGH LOADING, NEW-HOME CASE
B-5

DOUBLE-WIDE MANUFACTURED HOME – HIGH LOADING, NEW-HOME CASE
B-6

CAMPER TRAILER – HIGH LOADING, NEW-HOME CASE
B-7

SINGLE-FAMILY DETACHED HOME – HIGH LOADING, RENOVATION CASE
B-8

SINGLE-FAMILY ATTACHED HOME – HIGH LOADING, RENOVATION CASE
B-9

APARTMENT – HIGH LOADING, RENOVATION CASE
B-10

SINGLE-WIDE MANUFACTURED HOME – HIGH LOADING, RENOVATION CASE
B-11

DOUBLE-WIDE MANUFACTURED HOME – HIGH LOADING, RENOVATION CASE
B-12

CAMPER TRAILER – HIGH LOADING, RENOVATION CASE
Appendix C

SECTION 3.2 OF FIAM-pwp MODEL DOCUMENTATION REPORT
C-1

3.2 Steady-State Model for Initial Formaldehyde Concentration in One Zone

A model developed in the 1980s by Matthews and colleagues was designed to estimate the steadystate formaldehyde concentration resulting from emission sources in a single indoor zone or 

compartment. The following discussion is in large part excerpted from Matthews et al.1 The 

underlying model theory and its derivation are described in the same document and in another by 

Matthews and colleagues.2

At steady state, the formaldehyde (CH2O) concentration in a single compartment can be 

expressed as follows:

[CH2O]SS = [CH2O]out + CH2OER/(F * ACH * VOL) (Eqn. 3-2)

where:

[CH2O]SS = steady-state formaldehyde concentration inside the 

compartment (mg/m3)

[CH2O]out = steady-state formaldehyde concentration outside the 

compartment (mg/m3)

CH2OER = emission rate of a formaldehyde source inside the 

compartment (mg/h)

F = fraction of air coming into the compartment that mixes 

within the volume (i.e., the mixing factor)

ACH = air exchange rate with outdoors for the compartment (hr-1)

VOL = volume of the compartment (m3

).

Assuming that F is equal to unity and using Q (airflow rate into and out of the compartment, in 

m3/hr) to denote the product of ACH * VOL, Equation 3-2 becomes:

[CH2O]SS = [CH2O]out + CH2OER/Q (Eqn. 3-3)

Application of the model as expressed in Equation 3-3 is simplified by assuming that all 

parameters in the equation remain constant (at steady state) and that there are no permanent 

losses of formaldehyde due to irreversible sorption to sinks.

Emissions from pressed-wood sources are area-dependent in that the magnitude of the emission 

is a direct function of the surface area (Area) of the source in the compartment. The equivalent of 

Equation 3-3 for an area-dependent source is:

[CH2O]SS = [CH2O]out + (CH2OER′ * Area)/Q (Eqn. 3-4)

with CH2OER′ in units of mg/m

2

-hr and area in m2.

 1 T. Matthews, T. Reed, B. Tromberg, C. Daffron, and A. Hawthorne. 1983. Formaldehyde Emissions from 

Combustion Sources and Solid Formaldehyde Resin Containing Products: Potential Impact on Indoor 

Formaldehyde Concentration and Possible Corrective Measures. In Proceedings of ASHRAE Symposium 

“Management of Atmospheres in Tightly Enclosed Spaces,” Santa Barbara, CA. 2 T. Matthews, A. Hawthorne, C. Daffron, T. Reed, and M. Corey. 1983b. Formaldehyde Release from Wood 

Products. In Proceedings of the 17th International Particleboard Symposium, Washington State University, 

Pullman, WA.
C-2

The formaldehyde emission rate, CH2OER′, is formulated consistent with a one-dimensional 

representation of Fick’s Law3, describing the emission rate as the release rate when the 

formaldehyde air concentration is zero, reduced by the product of the mass transfer coefficient 

and the vapor-phase concentration. This formulation can be expressed as follows:

CH2OER′ = -m * [CH2O]V + b (Eqn. 3-5)

where:

m = the mass transfer coefficient (m/hr)

[CH2O]V = the CH2O concentration in the vapor phase (mg/m3)

b = a constant; the emission rate at zero CH2O concentration 

in the air (mg/m2-hr).

As noted by Matthews, Hawthorne and Thompson (see footnote on this page):

“Thus, the modeled CH2O emission rates maximize at zero CH2O concentration and decrease 

linearly to a net emission rate of zero at some equilibrium CH2O concentration. If the CH2O 

concentration is raised beyond the equilibrium level with the addition of new CH2O sources, 

extrapolation of the model to higher CH2O concentrations indicates that sorption of the CH2O by 

the original ‘emitter’ is expected to occur. Experimental results of individual and paired emitters 

in small-scale environmental chambers by Pickrel et al.4 and Godish et al.5 are consistent with this 

theory. Paired source contributions of pressed-wood products, insulation, carpeting and UFFI 

typically yielded CH2O concentrations less than the sum of the concentrations for the individual 

emitters. In addition, Godish found that the CH2O emission strength of many weaker emitters in 

paired source combinations was enhanced following brief exposure to a stronger emitter. This 

suggests a temporary sorptive mechanism for CH2O followed by reemission of CH2O at reduced 

CH2O concentrations.”

The vapor-phase concentration, [CH2O]V, by definition is equal to [CH2O]SS at steady state; 

therefore, substitution of [CH2O]SS and Equation 3-5 into Equation 3-4 results in the following 

expression:

[ ]

[ ]

Q

m Area

CH O

Q

b Area

CH O

out

SS *

1

*

2

2

+

+

= (Eqn. 3-6)

In the case of multiple pressed-wood sources, Equation 3-4 becomes:

[CH2O]SS = [CH2O]out + Σ(CH2OER′k* Areak) /Q (Eqn. 3-7)

where the subscript k refers to the k

th source. By extension, Equation 3-6 then becomes:

[ ]

( )

[ ]

( )

Q

m Area

CH O

Q

b Area

CH O

k

k k

out

k

k k

SS ∑

∑

+

+

= *

1

*

2

2 (Eqn. 3-8)

 3 T. Matthews, A. Hawthorne, and C. Thompson. 1987. Formaldehyde Sorption and Desorption Characteristics of 

Gypsum Wallboard. Environmental Science & Technology 21: 629-634. 4 J. Pickrel, L. Griffis, B. Mokier, G. Kanapilly, and C. Hobbs. 1984. Formaldehyde Release Rate Coefficients 

from Selected Consumer Products. Environmental Science & Technology 18: 682-686. 5 T. Godish and B. Kanyar. 1985. Formaldehyde Source Interaction Studies. Forest Products Journal 35: 13-17.