EPA 600/R-00/096

October 2000

VOLATILIZATION RATES FROM WATER TO INDOOR AIR

PHASE II

National Center for Environmental Assessment–Washington Office

Office of Research and Development

U.S. Environmental Protection Agency

Washington, DC 20460
ii

DISCLAIMER

This document has been reviewed in accordance with U.S. Environmental Protection

Agency policy and approved for publication. Mention of trade names or commercial products

does not constitute endorsement or recommendation for use.
iii

EXECUTIVE SUMMARY

Contaminated water can lead to volatilization of chemicals to residential indoor air. 

Previous research has focused on only one source (shower stalls) and has been limited to

chemicals in which gas-phase resistance to mass transfer is of marginal significance. As a result,

attempts to extrapolate chemical emissions from high-volatility chemicals to lower volatility

chemicals, or to sources other than showers, have been difficult or impossible.

In this study two-phase dynamic mass balance models were developed for estimating

chemical emissions from washing machines, dishwashers, and bathtubs. An existing model was

adopted for showers only. The mass transfer theory and derivations of these models are further

described in chapter 2 of this report. Source- and chemical-specific mass transfer coefficients, as

well as air exchange (ventilation) rates were estimated based on a series of experiments. These

experiments were conducted using 5 tracer chemicals (acetone, ethyl acetate, toluene,

ethylbenzene, and cyclohexane) and 4 sources (showers, bathtubs, washing machines, and

dishwashers). Each set of experiments led to the determination of chemical stripping efficiencies

and mass transfer coefficients (overall, liquid-phase, gas-phase), and to an assessment of the

importance of gas-phase resistance to mass transfer. 

A set of protocols for estimating emission rates for chemicals other than those used in this

study was defined for each of the four sources. Example applications are provided and illustrate

the dynamic behavior of emissions and importance of chemical properties on such emissions. 

The experimental mass transfer coefficients, air exchange rates and protocols described in this

report can be used as direct input values or to estimate reasonable input values for the reported

emission models.

Stripping efficiencies ranged from 6.3% to 80% for showers, 2.6% to 69% for bathtubs,

18% to 100% for dishwashers, and 3.8% to 100% for washing machines. Acetone and

cyclohexane always defined the lower and upper bounds, respectively, of these ranges. 

The findings of this study lead to several conclusions. A detailed discussion of

conclusions is presented in chapter 9. Some of the most significant conclusions are summarized

below. 

• System operating conditions can have a significant effect on chemical emissions. In

particular, chemical stripping efficiencies for washing machines were observed to be

highly sensitive to system operating conditions.

• Water temperature was an important variable that affected stripping efficiencies and mass

transfer coefficients for all sources. 
iv

• Chemical stripping efficiencies increase as Henry’s law constant increases for lowervolatility chemicals. However, with the exception of the fill-cycle of bathtubs, chemical

stripping efficiencies are relatively insensitive to Henry’s law constant for chemicals with

constants greater than that of toluene. 

• Failure to account for gas-phase resistance to mass transfer can lead to significant

overestimates of chemical volatilization to indoor air. This is particularly true for lowervolatility chemicals or those sources with low values of gas- to liquid-phase mass transfer

coefficients (kg/kl

), e.g., washing machines.

• Results for shower experiments were reasonably consistent with those reported by other

researchers with stripping efficiencies ranging from 60% to 80% for chemicals with

Henry’s law constant equal or greater than that of toluene.

• Gas-phase concentrations were homogeneous throughout the shower stall demonstrating

that the frequent assumption of a well-mixed system is reasonably accurate.

• Dishwashers were determined to be very effective at removing chemicals from water to

air, with low but continuous emissions during operation and significant storage within the

dishwasher headspace. The most significant release of chemicals to indoor air would

occur if the dishwasher door is opened immediately after use.

• Washing machines during the rinse cycle with hot water and low clothes loading resulted

in stripping efficiencies that approached 100% for chemicals with Henry’s law constant

greater than toluene.

• Bathtubs may be more significant than showers with respect to human exposure to

chemicals dissolved in water because of longer exposure times.

.
v

CONTENTS

List of Tables ............................................................... x

List of Figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xiii

Nomenclature and Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xv

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xviii

Authors, Contributors, and Reviewers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xix

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xx

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

1.2. Research Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1.3. Scope of Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

1.4. Organization of Research Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

2. Model Development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2.1. Mass Transfer Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2.1.1. Chemical Stripping Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

2.1.2. Mass Transfer Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

2.2. Ideal Reactor Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

2.2.1. Plug Flow Reactor Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-9

2.2.2. Continuous-Flow Stirred-Tank Reactor Model . . . . . . . . . . . . . . . . . . . . . 2-10

2.2.3. Batch Reactor Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

2.3. Source-Specific Mass Balance Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12

2.3.1. Dishwasher Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-12

2.3.2. Washing Machine Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-16

2.3.2.1. Washing Machine Fill Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-16

2.3.2.2. Washing Machine Wash/Rinse Cycles . . . . . . . . . . . . . . . . . . . . 2-18

2.3.3. Shower Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-18

2.3.4. Bathtub Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21

2.3.4.1. Bathtub Flow-Through Model . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21

2.3.4.2. Bathtub Fill Model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-21

2.3.4.3. Bathtub Surface Volatilization Model . . . . . . . . . . . . . . . . . . . . 2-21

2.4. Chemical Emission Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22
CONTENTS (continued)

vi

3. General Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.1. Source Chamber . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-1

3.2. Chemical Tracers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

3.2.1. Physicochemical Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-2

3.2.2. Chemical Tracer Addition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-3

3.3. Chemical Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

3.3.1. Liquid-Phase Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-4

3.3.2. Gas-Phase Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-5

3.4. Sample Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

3.4.1. Liquid Sample Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

3.4.2. Liquid Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7

3.4.3. Gas Sample Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9

3.4.4. Gas Standards . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-9

3.5. Quality Assurance Measures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11

3.5.1. Duplicate Samples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11

3.5.2. Replicate Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12

3.5.3. Experimental Blanks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13

3.5.4. Method Detection Limit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-13

3.6. Data Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-14

3.6.1. Chemical Stripping Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-15

3.6.2. Overall Mass Transfer Coefficients (KLA) . . . . . . . . . . . . . . . . . . . . . . . . 3-15

3.6.3. Ratio of Gas-to-Liquid Phase Mass Transfer Coefficients . . . . . . . . . . . . 3-17

3.6.4. Liquid- and Gas-Phase Mass Transfer Coefficients . . . . . . . . . . . . . . . . . . 3-18

3.7. Factorial Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

3.8. Mass Closure Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-18

4. Shower Stall Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.1. Experimental System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-1

4.2. Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-3

4.3. Source-Specific Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

4.3.1. Sample Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-4

4.3.2. Ventilation Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4.3.3. Parameter Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4.4 Shower Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5

4.4.1. Chemical Stripping Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-5
CONTENTS (continued)

vii

4.4.2. KLA Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-17

4.4.3. Liquid- and Gas-Phase Mass Transfer Coefficients . . . . . . . . . . . . . . . . . . 4-26

4.4.4. Mass Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-30

5. Dishwasher Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.1. Experimental System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-1

5.2. Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

5.3. Source-Specific Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

5.3.1. Sample Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4

5.3.2. Ventilation Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4

5.3.3. Parameter Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4

5.4. Dishwasher Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7

5.4.1. Ventilation Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7

5.4.2. Chemical Stripping Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8

5.4.3. KLA Values ................................................ 5-13

5.4.4. Liquid- and Gas-Phase Mass Transfer Coefficients .................. 5-20

5.4.5. Mass Closure ............................................... 5-21

6. Washing Machine Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.1. Fill Cycle Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.1.1. Experimental System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-1

6.1.2. Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

6.1.3. Source-Specific Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-3

6.1.3.1. Sample Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-4

6.1.3.2. Ventilation Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-5

6.1.3.3. Parameter Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-6

6.1.4. Fill Cycle Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-7

6.1.4.1. Ventilation Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8

6.1.4.2. Chemical Stripping Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9

6.1.4.3. KLA Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-11

6.1.4.4. Liquid- and Gas-Phase Mass Transfer Coefficients . . . . . . . . . . 6-12

6.1.4.5. Mass Closure ........................................ 6-14

6.2. Wash/Rinse Cycle Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14

6.2.1. Experimental System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-14

6.2.2. Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15
CONTENTS (continued)

viii

6.2.3. Source-Specific Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-15

6.2.3.1. Sample Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-16

6.2.3.2. Ventilation Rates ..................................... 6-17

6.2.3.3. Parameter Estimation ................................. 6-17

6.2.4. Wash/Rinse Cycle Results ..................................... 6-18

6.2.4.1. Ventilation Rates ..................................... 6-19

6.2.4.2. Chemical Stripping Efficiencies ......................... 6-23

6.2.4.3. KLA Values ......................................... 6-38

6.2.4.4. Liquid- and Gas-Phase Mass Transfer Coefficients .......... 6-51

6.2.4.5. Mass Closure ........................................ 6-54

7. Bathtub Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.1. Bathtub Flow-Through Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.1.1. Experimental System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.1.2. Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.1.3. Source-Specific Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.1.3.1. Sample Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-1

7.1.3.2. Ventilation Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

7.1.3.3. Parameter Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

7.1.4. Bathtub Flow-Through Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

7.1.4.1. Chemical Stripping Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

7.1.4.2. KLA Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5

7.1.4.3. Liquid- and Gas-Phase Mass Transfer Coefficients . . . . . . . . . . . 7-7

7.1.4.4. Mass Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-8

7.2. Bathtub Fill Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9

7.2.1. Experimental System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9

7.2.2. Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9

7.2.3. Source-Specific Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9

7.2.3.1. Sample Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-9

7.2.3.2. Ventilation Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11

7.2.3.3. Parameter Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11

7.2.4. Bathtub Fill Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-11

7.2.4.1. Chemical Stripping Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . 7-11

7.2.4.2. Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13

7.2.4.3. Liquid- and Gas-Phase Mass Transfer Coefficients . . . . . . . . . . 7-13
ix

7.2.4.4. Mass Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13

7.3. Surface Volatilization Experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14

7.3.1. Experimental System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-14

7.3.2. Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15

7.3.3. Source-Specific Methodology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15

7.3.3.1. Sample Schedule . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15

7.3.3.2. Ventilation Rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15

7.3.3.3. Parameter Estimation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-15

7.3.4. Bathtub Surface Volatilization Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-16

7.3.4.1. Chemical Stripping Efficiencies . . . . . . . . . . . . . . . . . . . . . . . . . 7-17

7.3.4.2. KLA Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-18

7.3.4.3. Liquid- and Gas-Phase Mass Transfer Coefficients . . . . . . . . . . 7-19

7.3.4.4. Mass Closure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-19

8. Model Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8.1. Shower Model Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-1

8.2. Dishwasher Model Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-7

8.3. Washing Machine Model Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-13

8.4. Bathtub Model Application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8-19

9. Summary and Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1

9.1. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-1

9.2. Conclusions: General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-3

9.3. Conclusions: Showers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-4

9.4. Conclusions: Dishwashers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9-5

9.5. Conclusions: Washing Machines ...................................... 9-6

9.6. Conclusions: Bathtubs .............................................. 9-7

9.7. Recommendations for Future Research .................................. 9-8

10. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10-1

Appendix: Chemical Volatilization Database . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A-1

LIST OF TABLES

3-1 Summary of physicochemical properties for selected chemical tracers . . . . . . . . . . . . . . 3-2

3-2 Duplicate sample results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-11
LIST OF TABLES (continued)

x

3-3 Replicate sample results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-12

3-4 Replicate sample results excluding replicate experiments associated with filling . . . . . 3-13

3-5 Method detection limits (MDLs) for liquid and gas samples . . . . . . . . . . . . . . . . . . . . . 3-14

4-1 Shower experiment operating conditions ..................................... 4-2

4-2 Acetone stripping efficiencies for experimental shower . . . . . . . . . . . . . . . . . . . . . . . . . . 4-7

4-3 Ethyl acetate stripping efficiencies for experimental shower . . . . . . . . . . . . . . . . . . . . . . 4-7

4-4 Toluene stripping efficiencies for experimental shower .......................... 4-9

4-5 Ethylbenzene stripping efficiencies for experimental shower ..................... 4-9

4-6 Cyclohexane stripping efficiencies for experimental shower ...................... 4-11

4-7 Acetone KLA values for experimental shower ................................ 4-20

4-8 Ethyl acetate KLA values for experimental shower ............................. 4-20

4-9 Toluene KLA values for experimental shower ................................ 4-21

4-10 Ethylbenzene KLA values for experimental shower ............................ 4-21

4-11 Cyclohexane KLA values for experimental shower ............................ 4-22

4-12 Liquid- and gas-phase mass transfer coefficients for shower experiments ........... 4-30

5-1 Dishwasher experimental operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7

5-2 Dishwasher ventilation rate experimental results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

5-3 Chemical stripping efficiencies (0) for experimental dishwasher . . . . . . . . . . . . . . . . . 5-10

5-4 Acetone KLA values for dishwasher experiments .............................. 5-14

5-5 Toluene KLA values for dishwasher experiments .............................. 5-14

5-6 Ethylbenzene KLA values for dishwasher experiments ......................... 5-15

5-7 Cyclohexane KLA values for dishwasher experiments .......................... 5-15

6-1 Washing machine fill cycle experimental conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-8

6-2 Washing machine fill cycle ventilation rates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9

6-3 Chemical stripping efficiencies (0) for washing machine fill cycles . . . . . . . . . . . . . . . 6-10

6-4 Values of KLA for washing machine fill cycles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-12

6-5 Liquid- and gas-phase mass transfer coefficients for washing machine fill cycle

experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-13

6-6 Washing machine wash/rinse cycle experimental operating conditions ............. 6-19

6-7 Ventilation rate experimental results ....................................... 6-21

6-8 Acetone stripping efficiencies for washing machine wash/rinse cycle—Factorial #1 . . 6-23

6-9 Acetone stripping efficiencies for washing machine wash/rinse cycle—Factorial #2 . . 6-25

6-10 Ethyl acetate stripping efficiencies for washing machine wash/rinse cycle—

Factorial #2. .......................................................... 6-25

6-11 Toluene stripping efficiencies for washing machine wash/rinse cycle—Factorial #1 . . 6-27
LIST OF TABLES (continued)

xi

6-12 Toluene stripping efficiencies for washing machine wash/rinse cycle—Factorial #2 . . 6-27

6-13 Ethylbenzene stripping efficiencies for washing machine wash/rinse cycle—

Factorial #1 ........................................................... 6-29

6-14 Ethylbenzene stripping efficiencies for washing machine wash/rinse cycle—

Factorial #2 ........................................................... 6-29

6-15 Cyclohexane stripping efficiencies for washing machine wash/rinse cycle—

Factorial #1 ........................................................... 6-31

6-16 Cyclohexane stripping efficiencies for washing machine wash/rinse cycle—

Factorial #2 ........................................................... 6-31

6-17 Acetone KLA values for washing machine wash/rinse cycle—Factorial #1 .......... 6-40

6-18 Acetone KLA values for washing machine wash/rinse cycle—Factorial #2 ......... 6-40

6-19 Ethyl acetate KLA values for washing machine wash/rinse cycle—Factorial #2 ...... 6-41

6-20 Toluene KLA values for washing machine wash/rinse cycle—Factorial #1 .......... 6-41

6-21 Toluene KLA values for washing machine wash/rinse cycle—Factorial #2 .......... 6-42

6-22 Ethylbenzene KLA values for washing machine wash/rinse cycle—Factorial #1 ...... 6-42

6-23 Ethylbenzene KLA values for washing machine wash/rinse cycle—Factorial #2 ...... 6-43

6-24 Cyclohexane KLA values for washing machine wash/rinse cycle—Factorial #1 ...... 6-43

6-25 Cyclohexane KLA values for washing machine wash/rinse cycle—Factorial #2 ...... 6-45

6-26 Liquid- and gas-phase mass transfer coefficients for washing machine 

wash/rinse cycle experiments—Factorial #1 ................................. 6-55

6-27 Liquid- and gas-phase mass transfer coefficients for washing machine 

wash/rinse cycle experiments—Factorial #2 ................................. 6-56

7-1 Bathtub flow-through operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-3

7-2 Chemical stripping efficiencies (0) for experimental bathtub flow-through 

experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-4

7-3 Values of KLA for bathtub flow-through experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-5

7-4 Liquid- and gas-phase mass transfer coefficients for bathtub flow-through 

experiments. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-7

7-5 Bathtub (fill) operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-12

7-6 Chemical stripping efficiencies (0) for bathtub (fill) experiments . . . . . . . . . . . . . . . . . 7-12

7-7 Values of KLA for bathtub (fill) experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-13

7-8 Liquid- and gas-phase mass transfer coefficients for bathtub (fill) experiments . . . . . . 7-14

7-9 Bathtub surface volatilization operating conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-17

7-10 Chemical stripping efficiencies for bathtub surface volatilization experiments . . . . . . . 7-18

7-11 Values of KLA for bathtub surface volatilization experiments . . . . . . . . . . . . . . . . . . . . 7-18
LIST OF TABLES (continued)

xii

7-12 Liquid- and gas-phase mass transfer coefficients for bathtub surface volatilization

experiments ........................................................... 7-21

8-1 Comparison of the three chemicals used in model applications . . . . . . . . . . . . . . . . . . . . 8-2

9-1 Summary of experimental stripping efficiencies and kg/kl . . . . . . . . . . . . . . . . . . . . . . . . 9-2
LIST OF FIGURES (continued)

xiii

LIST OF FIGURES

2-1 Plug flow reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-10

2-2 Continuous-flow stirred-tank reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

2-3 Batch reactor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-11

2-4 Dishwasher model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-13

2-5 Washing machine fill cycle model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-17

2-6 Washing machine wash/rinse cycle model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-18

2-7 Shower model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-19

2-8 Bathtub flow-through model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22

2-9 Bathtub fill model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-22

2-10 Bathtub surface volatilization model . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-23

3-1 Gas sampling experimental set up . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-6

3-2 Liquid-phase sample chromatogram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-7

3-3 Liquid-phase calibration curve for ethylbenzene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-8

3-4 Gas sample chromatogram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10

3-5 Gas-phase calibration curve for acetone . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-10

3-6 Matrix format used to determine kg/kl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3-19

4-1 Shower experimental system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4-2

4-2 Shower factorial experimental design ........................................ 4-3

4-3 Relationship between Henry’s law constant and average stripping efficiency ........ 4-18

4-4 Acetone experimental data for Experiment 7 ................................. 4-23

4-5 Ethyl acetate experimental data for Experiment 7 ............................. 4-25

4-6 Toluene experimental data for Experiment 7 ................................. 4-26

4-7 Ethylbenzene experimental data for Experiment 7 ............................. 4-27

4-8 Cyclohexane experimental data for Experiment 7 ............................. 4-28

4-9 Resistances to mass transfer for each chemical in Experiment 7 .................. 4-32

5-1 Dishwasher experimental system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

5-2 Factorial experimental design for dishwasher experiments . . . . . . . . . . . . . . . . . . . . . . . 5-3

5-3 Isobutylene decay due to ventilation for Experiment 18 . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

5-4 Comparison of measured Cg/Cl predicted Henry’s law constant for acetone ......... 5-17

5-5 Toluene concentrations for Experiment 8 .................................... 5-18

5-6 Amplification of Figure 30 to illustrate approach to equilibrium 

conditions for toluene ................................................... 5-19
LIST OF FIGURES (continued)

xiv

5-7 Ethylbenzene concentrations for Experiment 8 ............................... 5-20

5-8 Cyclohexane concentrations for Experiment 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-20

6-1 Washing machine fill cycle experimental system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6-2

6-2 Isobutylene decay due to ventilation for Experiment 13 . . . . . . . . . . . . . . . . . . . . . . . . . . 6-9

6-3 Wash/rinse cycle experimental system ...................................... 6-15

6-4 Wash/rinse cycle factorial experimental design ............................... 6-16

6-5 Isobutylene decay due to ventilation for Experiment 8 .......................... 6-23

6-6 Acetone concentrations for Experiment 6 .................................... 6-46

6-7 Amplification of Figure 6-6 for acetone gas-phase data ......................... 6-48

6-8 Toluene concentrations for Experiment 6 .................................... 6-49

6-9 Magnification of Figure 6-8 to illustrate toluene’s gas-phase 

concentration over time .................................................. 6-49

6-10 Ethylbenzene concentrations for Experiment 6 ............................... 6-51

6-11 Cyclohexane concentrations for Experiment 6 ................................ 6-51

6-12 Liquid- and gas-phase resistances to mass transfer for Experiment 6 . . . . . . . . . . . . . . 6-44

7-1 Bathtub flow-through experimental system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-2

7-2 Toluene experimental data for Experiment 4 replicate . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-6

7-3 Resistances to mass transfer for each chemical in Experiment 2 . . . . . . . . . . . . . . . . . . . 7-8

7-4 Bathtub fill experimental system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7-10

7-5 Toluene experimental data for Experiment 4 replicate . . . . . . . . . . . . . . . . . . . . . . . . . . 7-19

8-1 Mass emission rates for three chemicals for example shower event . . . . . . . . . . . . . . . . 8-2

8-2 Mass emission rates for three chemicals for example dishwasher event . . . . . . . . . . . . 8-11

8-3 Amplification of Figure 52 to show methyl ethyl ketone mass emission rate . . . . . . . . 8-12

8-4 Mass emission rates for three chemicals for example washing machine event . . . . . . . 8-18

8-5 Mass emission rates for three chemicals for example bathtub event . . . . . . . . . . . . . . . 8-20
1

 Note: Terms in parentheses denote units; M corresponds to mass; L corresponds to

length; T corresponds to time; (°) corresponds to temperature; dimensionless values are denoted

as (-).

xv

NOMENCLATURE AND ABBREVIATIONS1

A interfacial surface area between water and adjacent air (L2)

ACH air changes per hour

∆A differential 1area (L2)

C chemical concentration (M/L3)

Cexpt experimentally measured liquid- and gas-phase concentrations (M/L3)

Cg chemical concentration in air adjacent to water (M/L3)

Cg,in inlet concentration of contaminant in air (M/L3

)

Cg,0 initial chemical concentration in gas volume (M/L3)

Cg,t chemical concentration in air at any time t (M/L3)

Cin inlet chemical concentration (M/L3)

Cl chemical concentration in water (M/L3

)

Cl,end final chemical concentration in water (M/L3

)

Cl,in inlet chemical concentration in water (M/L3

)

Cl,out outlet concentration of contaminant in water (M/L3

)

Cl,0 initial chemical concentration in water (M/L3

)

Cm mathematically predicted liquid- and gas-phase concentrations (M/L3)

CFSTR continuous flow stirred tank reactor

cosh hyperbolic cosine

coth hyperbolic cotangent

Dg molecular diffusion coefficient for a chemical in air (L2/T)

Dgi molecular diffusion coefficient for chemical i in air (L2/T)

Dgj molecular diffusion coefficient for chemical j in air (L2/T)

Dl molecular diffusion coefficient for a contaminant in water (L2

/T)

Dli molecular diffusion coefficient for chemical i in water (L2/T) 

Dlj molecular diffusion coefficient for chemical j in water (L2

/T)

DBCM dibromochloromethane

DBCP 1,2-dibromo-3-chloropropane

Echem chemical mass emission rate (M/T)

FID flame ionization detector

GC gas chromatography
NOMENCLATURE AND ABBREVIATIONS (continued)

xvi

Hc Henry’s law constant (L3

gas/L3liq)

Hc,i Henry’s law constant for chemical i (L3

gas/L3liq)

Hc,j Henry’s law constant for chemical j (L3

gas/L3liq)

Hc,T Henry’s law constant at experimental temperature (L3

gas/L3liq)

ID inside diameter (L)

kg gas-phase mass transfer coefficient (L/T)

kgi gas-phase mass transfer coefficient for chemical i (L/T)

kgj gas-phase mass transfer coefficient for chemical j (L/T)

KL overall mass transfer coefficient for contaminant of interest (L/T)

kl liquid-phase mass transfer coefficient (L/T)

KLi overall mass transfer coefficient for chemical i (L/T)

kli liquid-phase mass transfer coefficient for chemical i (L/T)

KLj overall mass transfer coefficient for chemical j (L/T)

klj liquid-phase mass transfer coefficient for chemical j (L/T)

mc degree of mass closure (-)

MDL method detection limit

MEK methyl ethyl ketone

n1 power constant for ratio of liquid-phase diffusion coefficients (-)

n2 power constant for ratio of gas-phase diffusion coefficients (-)

OD outside diameter (L)

P perimeter (L)

pFR plug flow reactor

Pv vapor pressure (L Hg)

Q volumetric flowrate (L3/T)

Qg gas flowrate (L3/T)

Qin inlet volumetric flowrate (L3

/T)

Ql liquid flowrate (L3/T)

Qout outlet volumetric flowrate (L3/T)

rA area reaction rate (M/L2•T)

rg rate of surface renewal for the gas side of the interface (1/T)

rl rate of surface renewal for the liquid side of the interface (1/T)

rV volume reaction rate (M/L3•T)

sinh hyperbolic sine

sr standard deviation of replicate analyses
NOMENCLATURE AND ABBREVIATIONS (continued)

xvii

t time (T)

T temperature (°C)

Tb boiling point (°C)

TCE trichloroethene

TKE total kinetic energy

V volume (L3

)

∆V differential volume (L3)

Vg local volume of air (L3

)

Vl local volume of water (L3

)

z direction of flow

δg thickness of a hypothetical gas film adjacent to the interface and 

through which contaminant transport is solely by molecular diffusion (L)

δl thickness of a hypothetical liquid film adjacent to the interface and through

which contaminant transport is solely by molecular 

diffusion (L)

η chemical stripping efficiency (-)

ρ density (M/L3)

Ψg gas-phase mass transfer relational coefficient (-)

Ψl liquid-phase mass transfer relational coefficient (-)

Ψm overall mass transfer relational coefficient (-)
xviii

PREFACE

This report was prepared under the direction of the National Center for Environmental

Assessment (NCEA) of EPA’s Office of Research and Development (ORD). The purpose of this

report is to provide a methodology for estimating chemical emissions from washing machines,

dishwashers, showers, and bathtubs. The methodology presented in this report was derived from

volatilization experiments conducted by The University of Texas at Austin under a Cooperative

Agreement with NCEA. Results of these experiments are included in the report.
xix

AUTHORS, CONTRIBUTORS, AND REVIEWERS

This report was prepared under Cooperative Agreement #CR 824228-01 between The

University of Texas at Austin and the National Center for Environmental Assessment (NCEA),

Office of Research and Development. It covers a period from June 1, 1995 to August 31, 1997,

and work was completed as of August 31, 1997. Jackie Moya was responsible for the overall

coordination, direction, and technical assistance.

AUTHORS

Cynthia Howard-Reed

formerly Graduate Research Assistant with The University of Texas at Austin

presently with the Indoor Air Quality Group at the National Institute of Standards and

Technology (NIST)

Richard L. Corsi

Principal Investigator

Environmental and Water Resources Engineering Program

The University of Texas at Austin

REVIEWERS

The following individuals have reviewed this report and provided valuable comments:

Environmental Protection Agency Reviewers

Jacqueline Moya 

Nancy Chiu

Lance Wallace

External Reviewers

John Little

Associate Professor

Civil and Environmental Engineering 

Virginia Tech

Blacksburg, VA

Nicholas J. Giardino

Toxicologist

Brooks AFB, Texas
xx

ACKNOWLEDGMENTS

The authors wish to thank EPA Project Officer Jacqueline Moya for her general guidance and

enthusiasm regarding this project. The authors also wish to acknowledge Albert Chung, Jennifer

Pettibon, Javier Ramirez, Tony Smith, and Ross Strader, undergraduate students at The

University of Texas at Austin, for their assistance during experiments.