Environmental Health Perspectives • volume 119 | number 1 | January 2011 125

Research

Hazardous air pollutants (HAPs, or air 

toxics) are pollutants known to cause cancer or other serious health effects as well as 

environmental effects. The majority of air 

toxics originate from human-made sources, 

including mobile sources (e.g., automobiles) 

and stationary sources (e.g., factories). Under 

the Clean Air Act Amendments (CAAA) of 

1990, the U.S. Environmental Protection 

Agency (EPA) regulates 187 HAPs from both 

stationary and mobile sources. HAPs are 

distinct from the criteria pollutants, such as 

ozone, carbon monoxide, particulate matter, 

sulfur oxides, nitrogen dioxide, and lead, that 

generally have much more extensive information about health effects and are regulated 

under other CAAA authorities. For major 

stationary sources, the act requires the EPA to 

set maximum achievable control technology 

(MACT) standards to reduce HAP emissions 

(CAAA 1990). After setting these standards, 

the U.S. EPA evaluates the residual risks from 

exposure to HAPs to determine if further 

regulation is warranted. For smaller stationary 

sources of HAPs (e.g., gasoline distribution, 

auto body refinishing), the EPA is required 

to set technology standards, which are known 

as generally available control technology 

(GACT). To control mobile source air toxics, 

the EPA is required to set technology and fuel 

standards for motor vehicles. Since 1990, the 

EPA has made significant progress in issuing 

standards under the CAAA to reduce emissions of air toxics both from stationary and 

mobile sources. To determine the impact 

of these efforts, Section 812 of the CAAA 

requires the EPA to perform periodic, comprehensive analyses of the costs and total 

benefits of programs implemented pursuant to the Clean Air Act (CAA 1970). The 

EPA has completed two of these analyses: a 

retrospective analysis in 1997 of the original CAA covering the period from 1970 to

1990 (U.S. EPA 1997) and a prospective 

analysis in 1999 of the incremental costs and 

benefits of the CAAA from 1990 to 2010 

(U.S. EPA 1999). These and other studies 

have highlighted many of the challenges in 

estimating the benefits of reducing air toxics 

emissions.

Challenges for Air Toxics 

Benefits Assessment

Benefits analysis for any environmental 

regulation requires estimating how individuals 

and regulated entities respond to the regulation,

as well as estimating fate, transport, exposure,

and effects of environmental chemicals. Thus, 

this type of assessment is subject to significant 

limitations and uncertainties. The U.S. EPA 

estimates benefits in regulatory impact analyses 

(RIAs) for rules that have a significant impact 

on the economy, typically based on a sequential analysis of emissions estimation modeling, 

air quality and exposure modeling, health and 

environmental effects estimation, and economic 

valuation. For major air toxics rules, the EPA 

has estimated benefits based on reductions in 

fine particulate matter (referred to as PM2.5) 

or ozone rather than those based directly on 

reductions of air toxics [Fann et al. 2009; 

Krupnick 2006; National Research Council 

(NRC) 2002)]. To estimate the benefits of 

reducing air toxics directly, there is a need for 

both near-term and long-term benefits assessment specific to the issues of air toxics reduction. Challenges related specifically to benefits 

Address correspondence to M.R. Gwinn, EICG/

NCEA/ORD/USEPA, 1200 Pennsylvania Ave., 

NW, Mail Code 8623-P, Washington, DC 20460 

USA. Telephone: (703) 347-8565. Fax: (703) 347-

8692. E-mail: gwinn.maureen@epa.gov.

Special thanks for the contributions from presenters including H. Roman, T. Woodruff, V. Benignus, 

L. Zeise, R. Walsh, S. Banzhaf, J. Levy, K. Viscusi, 

A. Krupnick, M. Cropper, and D. Hattis.

This document summarizes the conclusions from 

the workshop—Estimating the Benefits of Reducing 

Hazardous Air Pollutants (HAPs), which was sponsored by the U.S. Environmental Protection Agency 

[EPA; Office of Air and Radiation (OAR), Office of 

Policy, Economics and Innovation (OPEI), and the 

Office of Research and Development (ORD)] with 

contract support from ICF International.

The views expressed in this document are those 

of the authors and do not necessarily represent the 

views and policies of the U.S. EPA.

The authors declare they have no actual or potential 

competing financial interests.

Received 20 May 2010; accepted 4 October 2010.

Meeting Report: Estimating the Benefits of Reducing Hazardous Air 

Pollutants—Summary of 2009 Workshop and Future Considerations

Maureen R. Gwinn,1 Jeneva Craig,2 Daniel A. Axelrad,3 Rich Cook,4 Chris Dockins,3 Neal Fann,5 Robert Fegley,6

David E. Guinnup,5 Gloria Helfand,4 Bryan Hubbell,5 Sarah L. Mazur,6 Ted Palma,5 Roy L. Smith,5

John Vandenberg,7 and Babasaheb Sonawane1

1National Center of Environmental Assessment, Office of Research and Development, 2Office of Policy Analysis and Review, Office of 

Air and Radiation, and 3National Center for Environmental Economics, Office of Policy, Economics and Innovation, U.S. Environmental 

Protection Agency, Washington, DC, USA; 4Office of Transportation and Air Quality, Office of Air and Radiation, U.S. Environmental 

Protection Agency, Ann Arbor, Michigan, USA; 5Office of Air Quality Planning and Standards, Office of Air and Radiation, U.S. 

Environmental Protection Agency, Research Triangle Park, North Carolina, USA; 6Office of Science Policy, Office of Research and 

Development, U.S. Environmental Protection Agency, Washington, DC, USA; 7National Center of Environmental Assessment, Office of 

Research and Development, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA

Background: Quantifying the benefits of reducing hazardous air pollutants (HAPs, or air toxics) 

has been limited by gaps in toxicological data, uncertainties in extrapolating results from high-dose 

animal experiments to estimate human effects at lower doses, limited ambient and personal exposure monitoring data, and insufficient economic research to support valuation of the health impacts 

often associated with exposure to individual air toxics.

Objectives: To address some of these issues, the U.S. Environmental Protection Agency held 

the Workshop on Estimating the Benefits of Reducing Hazardous Air Pollutants (HAPs) in 

Washington, DC, from 30 April to 1 May 2009.

Discussion: Experts from multiple disciplines discussed how best to move forward on air toxics 

benefits assessment, with a focus on developing near-term capability to conduct quantitative benefits assessment. Proposed methodologies involved analysis of data-rich pollutants and application 

of this analysis to other pollutants, using dose–response modeling of animal data for estimating 

benefits to humans, determining dose-equivalence relationships for different chemicals with similar 

health effects, and analysis similar to that used for criteria pollutants. Limitations and uncertainties 

in economic valuation of benefits assessment for HAPS were discussed as well.

Conclusions: These discussions highlighted the complexities in estimating the benefits of reducing air toxics, and participants agreed that alternative methods for benefits assessment of HAPs 

are needed. Recommendations included clearly defining the key priorities of the Clean Air Act air 

toxics program to identify the most effective approaches for HAPs benefits analysis, focusing on 

susceptible and vulnerable populations, and improving dose–response estimation for quantification 

of benefits.

Key words: air toxics, benefit analysis, economic valuation, exposure modeling, hazardous air 

pollutants. Environ Health Perspect 119:125–130 (2011). doi:10.1289/ehp.1002468 [Online 

4 October 2010]
Gwinn et al.

126 volume 119 | number 1 | January 2011 • Environmental Health Perspectives

analysis for air toxics include uncertainties in 

emissions information, air quality and exposure 

modeling, effects estimation, and economic 

valuation, as well as distribution considerations. 

These challenges are described below.

Emissions. The U.S. EPA maintains an 

inventory of emissions for most of the 187 

air toxics, although the data are less reliable than the inventory for the six criteria 

pollutants. The National Emissions Inventory 

is updated every 3 years and provides information from major stationary sources, smaller 

area stationary sources, on-road and nonroad mobile sources, and other sources (e.g., 

wildfires). Unlike criteria pollutants, reporting air toxics is not mandatory and varies by 

state. Therefore, some of these area sources 

have limited emissions information and 

are estimated through modeling. The U.S. 

EPA also publishes an annual Toxics Release 

Inventory (TRI) that requires facilities to 

report releases of 666 chemicals and chemical 

categories (including most of the air toxics) to 

air, land, and water (U.S. EPA 2010).

Air quality and exposure modeling. The 

relationship between air emissions of toxics 

and human exposure is complex and often 

difficult to estimate. Air toxics vary widely 

in their sources, photochemical reactivity, and scale of spatial variability. In addition, exposure assumptions may differ 

significantly from actual individual exposures. 

For example, the typical assumption that 

people are exposed to the air outside their 

residences for 24 hr a day for a lifetime is 

used to simplify population analysis but introduces error in the exposure estimates, particularly when considered at the individual 

level (Isakov et al. 2009). Indoor sources may 

also be important components of individual 

exposure to air toxics and may be affected 

by emissions regulations (e.g., lawn and garden equipment in attached garages) (U.S. 

EPA 2007a; Weisel et al. 2002). Exposure 

assessment of average or cumulative exposures may miss significant acute exposures. 

The EPA National Air Toxics Assessment 

(NATA; U.S. EPA 2009b), which is currently available to the public with 2002 

data, estimates ambient concentrations at 

the census-tract level (large scale) for mobile 

and area source emissions and at the censusblock level (small scale) for major stationary 

source emissions]. The NATA then estimates 

inhalation exposure at the census-block level, 

which takes into account ambient exposures 

in various microenvironments, and calculates 

lifetime inhalation risks of cancer and noncancer health effects. The assessment does not 

provide estimates of ingestion risks that are 

important for certain air toxics such as mercury and lead (U.S. EPA 2001, 2009b).

Health and environmental effects estimation. The list of HAPs to be regulated by

the EPA is enumerated in the CAAA. For 

many chemicals on the list, the information 

on potential health effects is so limited that 

quantitative benefits analysis is not feasible 

(Goldstein and Carruth, 2003). This lack of 

information is in contrast to the criteria air 

pollutants for which there is extensive human 

exposure or epidemiological data on the health 

effects at ambient-exposure levels. For most of 

the air toxics, the available health information 

is based on animal studies. Therefore, reasoned 

assumptions about how these data relate to 

potential human health hazards are needed. 

The relatively smaller epidemiological data 

set for air toxics is based mostly on relatively 

high occupational exposures (e.g., for benzene) and has several limitations. These limitations include lack of information on multiple 

health end points across the life stages, susceptible populations, and differentially exposed 

groups. The potential for noncancer effects 

from exposure to air toxics is evaluated by 

comparing HAP concentrations with the reference concentration (RfC), which is a point 

estimate of the level expected to be without 

appreciable effects from chronic exposure 

in the population. The RfC definition does 

not incorporate any quantitative expression 

of risk. Furthermore, uncertainties related to 

quantitative values of risk for both cancer and 

noncancer health effects are rarely explored, 

understood, and characterized. For these and 

other reasons, characterizing the health effects 

of air toxics at ambient levels can be subject to a very high level of uncertainty; thus, 

using these health effects in economic benefits assessment is difficult. The recent NRC 

report, Science and Decisions: Advancing Risk 

Assessment, has provided recommendations 

applicable to issues related to benefits assessment of air toxics, including dose–response 

assessment, analysis of uncertainty and variability, default selection and use, and cumulative risk assessment (NRC 2009).

Economic valuation. Standard economic 

analysis for pollution reduction starts with 

estimates of reduced mortality and morbidity 

effects (and other nonhealth effects as appropriate) (U.S. EPA 2000). Currently, benefits 

are estimated by aggregating reduced mortality risks to an expected number of deaths 

avoided, which are then multiplied by an 

aggregate willingness-to-pay (WTP) figure 

called the value of a statistical life (VSL). 

Reduced morbidity benefits are estimated 

similarly, when dose–response information 

is available to estimate the expected cases 

avoided, which are then multiplied by either 

an estimate of WTP to avoid the illness or an 

estimate of the cost associated with the treatment of that illness. Applying these methods 

to air toxics requires estimates of the mortality 

and morbidity effects. In the absence of these 

estimates, the benefits of toxics reduction 

may not be included in the analysis, resulting in a default assumption of zero benefits. 

In addition, people may be willing to pay for 

reducing toxics, even when the data on their 

effects are limited, to avoid perceived risks. 

The standard approach does not incorporate 

this willingness to pay.

Efficiency versus distributional considerations. Regulations focused on air toxics 

seek not only to improve overall public health 

but also to address disproportionate risk in 

a segment of the population. The U.S. EPA 

must issue additional standards for sources 

after MACT if necessary to protect public 

health with an adequate margin of safety 

(CAAA 1990). In these cases, protecting the 

most exposed individuals rather than maximizing risk reduction over the entire exposed 

population may be the guiding objective. In 

fact, the CAAA specifically refer to reducing 

lifetime excess cancer risks to individuals most 

exposed to emissions from a source. Existing 

cost–benefit techniques are not intended to 

address tradeoffs between net benefits and 

distributional and equity considerations (Levy 

et al. 2009).

Focus of 2009 Workshop

Discussions regarding best practices for 

estimating human health benefits from 

reductions in exposure to air toxics have 

been ongoing for years, but no consensus 

has been reached on methods that could be 

implemented for a broad selection of these toxics. Specifically, benefits analyses are inhibited 

by the lack of data relating exposures to health 

effects, uncertainties in extrapolating results 

from high-dose animal experiments to estimate 

human effects at lower doses, limited monitoring of ambient and personal exposure data, 

and insufficient economic research to support 

valuation of the health impacts often associated 

with exposure to individual air toxics.

Recognizing the uncertainties and research 

needs for many aspects of benefits assessment of reductions in air toxics, the U.S. EPA 

sponsored a workshop to explore the key issues 

related to health and environmental effects, 

economic valuation, and equity considerations 

(U.S. EPA 2009c). Highlights from these presentations are summarized below.

Lessons learned from recent research. Risk 

assessors have been working on alternative 

ways to assess the benefits related to reducing 

air toxics. Workshop participants explored four 

case studies that used alternative approaches. 

These case studies focused on approaches that 

could be implemented with existing information, could potentially be conducted at a reasonable cost, were the least likely to introduce 

bias, and were the most scientifically defensible. They included developing methodologies for data-rich HAPs (e.g., benzene) with 

a broader application to other HAPs, using 
Benefit analysis of HAPS reduction

Environmental Health Perspectives • volume 119 | number 1 | January 2011 127

animal data to estimate a dose–response curve 

for adverse health effects in humans (e.g., 

acrolein), using dose-equivalent relationships 

between chemicals with similar adverse health 

effects (e.g., toluene), and analyzing HAPs 

similar to that performed for criteria pollutants 

(e.g., lead) (Table 1). In addition to these four 

case studies, the workshop participants considered environmental quality in relation to 

changing community composition and equity 

tradeoffs. These alternative methodologies and 

key issues suggest potential options for analyzing benefits from air toxics reductions and 

highlight continued challenges in the field. 

The case studies are described in more detail 

below and summarized in Table 1.

Benefits of benzene reductions in 

Houston, Texas. In a case study designed to 

estimate the benefits of reducing benzene for 

a three-county area around Houston, Texas, 

scientists quantified changes in individual 

risk using air quality and exposure models 

and translated these changes into monetized 

benefits [Industrial Economics, Inc. (IEc) 

2009]. Benzene was used as an example of 

a data-rich air toxic pollutant to develop a 

methodology that could then be applied more 

widely. The case study modeled benzene exposures and health impacts using two scenarios: 

One assumed that all regulatory programs 

affecting benzene emissions were enacted in 

response to CAAA, and one assumed that 

no additional controls were implemented 

beyond the requirements existing in 1990. 

The difference in emissions between these two 

scenarios provided the basis for estimating 

the health benefits related to the reduction of 

benzene concentrations in Houston, Texas, 

because of the CAAA. As part of the Houston 

study, scientists examined the incidence of 

leukemias to estimate the health benefits from 

reductions in benzene exposure. The results 

demonstrated a decrease in fatal and nonfatal 

leukemias between 1990 and 2020. To measure the health outcomes, researchers used the 

VSL to monetize the avoided fatal leukemias 

and the WTP to monitize the nonfatal leukemias. This case study represents the uncommon situation where relatively complete 

information is available (e.g., human health 

evidence, air quality monitoring data) to estimate the health effects of air toxics and the 

benefits of reducing them. However, uncertainties and limitations of the approach used 

in this case study include large variations in the 

results because of the sensitivity of the model 

to unputs; for example, varying dose–response 

estimates or alternative cessation lags; the possibility that other health end points related 

to benzene exposure were not examined; and 

the limited age groups studied in the cohort. 

The approach used in the Texas case study was 

data- and resource-intensive and may be difficult to expand to other air toxics.

Estimating risk from acrolein. The 

analysis of acrolein risks for respiratory 

effects examined the applicability of using 

dose–response modeling of animal data to 

estimate the benefits to humans. Using data 

from a study in rats exposed to acrolein (Costa 

et al. 1986), Woodruff et al. (2007) evaluated 

two end points that are indicators of reducded 

lung function. These end points were selected 

based on the presence of a significant doserelated trend, on data that was amenable to 

modeling, and on the relevance to changes in 

lung function in humans. Acrolein concentrations from the rat study were converted into 

human equivalent concentrations using U.S. 

EPA standard methods (U.S. EPA 2003), and 

the data for each end point were modeled 

using EPA Benchmark Dose Software (U.S.

EPA 2009a). Increased risk was then estimated as the proportion of the population 

that would experience a change in adverse 

lung function, considering ambient concentrations in the United States estimated in 

NATA. This case study represents the more 

typical situation where relatively little information is available (e.g., animal toxicology 

data) to estimate air toxics health effects and 

the benefits of reducing them.

Cost of neurobehavioral effects of toluene 

exposure. Benignus et al. (2005) estimated 

the economic benefits of reducing exposure to toluene by comparing these neurobehavioral effects with those of well-studied 

ethanol ingestion. The investigators used 

dose-equivalent relationships to estimate the 

costs of intoxication. Because many air toxics have effects on the nervous system that 

are very similar to those of ethanol, Benignus 

et al. (2005) quantified behavioral effects 

of toluene and ethanol in human subjects 

using a meta-analysis of studies from the 

peer-reviewed literature that measured the 

effects of the chemicals on choice reaction 

time (CRT). CRT is a two-choice reaction 

Table 1. Overview of case studies that explored various methodologies for benefits analysis of regulating air toxics.

Chemical name

Dose–response 

data

Health end point(s) 

analyzed

Methods for risk 

evaluation

Methods for 

valuation

Size of benefit/

potential utility Uncertainties Reference

Benzene Human 

epidemiological 

studies 

(occupational 

cohort)

Leukemias (fatal 

and nonfatal)

Life table approach VSL for fatal 

leukemias; 

approximation 

of willingness to 

pay for nonfatal 

leukemias

Model demonstrated 

percent reduction in 

risk by 2020 from 72 

to 98% depending on 

county

Model sensitive to 

inputs; only quantified 

leukemias and not 

other health effects; 

low-dose extrapolation 

issues

IEc 2009

Acrolein Analysis of 

existing animal 

studies with 

dose conversion 

to human 

equivalents

Respiratory effects 

(noncancer)

Dose–response 

functions combined 

with modeled ambient 

acrolein concentrations 

to estimate risks of 

adverse effects

Not carried out in 

this study; further 

analysis needed to 

relate respiratory 

outcomes 

observed in 

animals to likely 

human effects

Method used animal 

data to inform 

benefits of reduction 

in exposure in human 

populations

Assumptions based on 

low-dose extrapolation 

and human 

interpretation of end 

point (adverse effects 

as general indicators 

of potential human 

lung function changes)

Woodruff 

et al. 2007

Toluene Meta-analysis 

of human 

epidemiology 

studies on 

toluene and 

ethanol effects

Neurobehavioral 

effects

Dose-scaling comparison 

for acute effects of 

toluene exposure with 

those of ethanol intake

Effect of toluene 

scaled to that 

of ethanol; used 

costs of ethanol 

intoxication 

(e.g., automobile 

crashes)

Comparison with 

another toxicant with 

the same mechanism 

of action that has 

been monetized can 

yield a quantitative 

benefits estimate

Assumptions needed for 

mechanisms of both 

toxicants and dose–

response comparisons

Benignus 

et al. 2005

Lead Human 

epidemiology 

studies

IQ Model changes in lead 

air quality for the 

exposed population and 

translated these into 

changes in blood lead

Present value of 

lifetime loss in 

earnings per IQ 

point lost

Provide a credible 

estimate of the 

human health benefits 

of attaining alternate 

lead NAAQS

Uncertainties in 

air-lead to bloodlead relationship; 

valuation method had 

substantial limitations

U.S. EPA 

2008

Abbreviations: IQ, intelligence quotient; NAAQS, National Ambient Air Quality Standards.
Gwinn et al.

128 volume 119 | number 1 | January 2011 • Environmental Health Perspectives

time test that is useful for assessing general 

alertness and motor speed. Models were used 

to estimate internal doses of ethanol and toluene associated with effects on CRT from 

exposure parameters provided in the published literature. This case study represents the 

scenario where relatively complete information is available for one chemical (ethanol) 

to estimate air toxics health effects and assess 

the benefits of reducing the effects for other 

chemicals with less information, such as toluene. The uncertainties of this method include 

the quality of the exposure data and the extent 

of the mechanistic similarity between the 

observed effects of the two compounds.

Human health benefits assessment for 

lead standards. The final case study was an 

analysis of the human health and welfare 

benefits associated with attaining alternative levels for the lead National Ambient 

Air Quality Standards (NAAQS). This case 

study was part of the RIA to estimate the 

expected benefits and costs of attaining a new 

NAAQS (U.S. EPA 2008). This was an example of methodologies that can be applied for 

environmental chemicals with extensive epidemiological data and highlighted the complications introduced by some key data gaps 

that may exist even for data-rich chemicals. 

The U.S. EPA quantified the monetary value 

of lead-associated changes in intelligence 

quotient (IQ). This analysis followed four 

basic steps. First, the U.S. EPA estimated the 

change in ambient lead resulting from attainment of alternate NAAQS levels, relative to 

baseline ambient lead levels in 2016. Then the 

EPA applied air-to-blood ratios to quantify the 

change in blood lead as a function of exposure 

to ambient lead. The third step was to apply 

relevant epidemiological studies to quantify 

the population-level change in IQ points. 

Finally, the EPA monetized the change in IQ 

points by using economic valuation functions 

to measure the foregone lifetime earnings per 

lost IQ point. As part of a sensitivity analysis 

to test the importance of key model inputs, 

the analysis concluded that total benefits 

were highly sensitive to the air quality estimates, the discount rate, and the air-to-blood 

ratio. The U.S. EPA approach to estimating 

ambient lead-related benefits may serve as a 

useful model for future analyses of air toxics 

with noninhalation exposure pathways.

Additional presentations related to air 

toxics benefits analysis. Two additional 

presentations addressed distributional considerations for benefits analysis. The first, an 

analysis of changing environmental quality on 

community composition, provided a simple 

model analysis of the relationship between 

TRI emissions and low-income communities and showed that reducing exposure in 

these communities would not necessarily 

have favorable distributional effects (Walsh 

and Banzhaf 2009). Using the example of 

the impact of TRI emissions reductions in 

California, it was concluded that estimating 

the true effects of reductions of air toxics on 

local communities requires a more thorough 

understanding of the relationships among 

environmental improvements, real estate 

markets, and demographics. This study underscored the role of sociological factors in air 

toxics benefits analyses. In the second study, 

Levy et al. (2007) highlighted recent research

that evaluated the efficiency–equality tradeoffs 

in health benefits analysis; they used a modeling framework that may have potential implications for air toxics emissions reduction. 

These tradeoffs are between the magnitude of 

(efficiency) and the distribution of the health 

benefits (equality). The challenge in their analysis was to find a simple, meaningful indicator 

that could capture the distribution of the benefits of pollution control from a source or set 

of sources. This analytical framework could 

be applied to capture the distribution of baseline risk from air toxics and the distribution 

of risk postcontrol. For this framework to 

be useful, multiple well-defined and realistic 

control scenarios would have to be developed. 

This study demonstrated that approaches for 

incorporating equity considerations may have 

applications for air toxics benefits assessment.

Three particular issues relating specifically to the estimation of air toxics benefits 

reduction were also explored in more depth: 

valuing reductions in individual risks, WTP 

for reducing air toxics, and alternatives to 

pollutant-by-pollutant dose–response estimation. Valuing large reductions in individual 

mortality risks focused on evaluating whether 

the magnitude of estimated risks being 

reduced requires new valuation methods or 

adjustments in current values to reflect the 

extent of risk changes. Labor market estimates 

of VSL provide the wage–risk tradeoffs for 

small risks. The degree to which these values 

are applicable to a particular benefits analysis 

depends, in part, on the magnitude of the risk 

reduction (Viscusi 2009).

WTP analysis for the large number of 

air toxics creates a challenge when using a 

damage-function approach to assess benefits, 

as it requires a dose–response relationship for 

each HAP. Key issues for valuation of reduced 

air toxics risks include what benefits to value, 

whether altruistic values should be included, 

whether to value subjective or objective risks, 

and whether valuation results could be applied 

to different policies (Cropper and Krupnick 

2009). Ideally, a WTP approach would separate risk assessment from valuation.

A major issue for assessing HAPs is that 

the measures for estimating noncancer health 

risks (e.g., RfC) do not lend themselves to 

quantification of risk reductions for benefit analysis (Hattis et al. 2002). Methods to 

overcome the barriers to the quantification of 

noncancer health risks were discussed. More 

specifically, research that focuses on estimating risks without extensive chemical-specific 

toxicity information, creating a framework for 

understanding and quantifying the uncertainties created by missing data that can be the 

basis for value-of-information analysis, and 

facilitating comparisons and priority setting 

for controlling exposure to different air toxics 

is needed (Hattis and Lynch 2009).

Road map on benefits assessment for 

air toxics. Air toxics benefits assessment has 

focused on a limited number of pollutants 

based on available dose–response and exposure 

information, generally on a worst-first basis. 

One main purpose of the workshop was to 

discuss other near-term benefits assessment 

options as laid out in the draft roadmap (U.S.

EPA 2009c). Although the roadmap also listed 

many areas for long-term research, the workshop participants focused more on the five 

near-term options in the roadmap:

•Qualitatively assess air toxics reduction benefits

with no attempt at quantification. This 

approach gives risk assessors the flexibility to make a qualitative case for air toxics 

control, while not exposing the analysis (or 

the regulation it supports) to the drawbacks 

and uncertainties associated with estimating 

benefits in quantitative terms from air toxics 

reductions based on the current state of the 

science. A concern with this approach is that 

some will assume that benefits are negligible 

rather than unquantifiable, and therefore 

the value of the air toxics program and its 

regulations may be underestimated.

• Use the existing frameworks to sketch out minimum benefits from a national perspective.

This approach would build on work that is 

ongoing regarding benefits analysis looking 

pollutant by pollutant. For example, risk 

assessors could use the benzene methodology

to estimate benefits of reducing benzene 

exposure on a wider geographic scale and 

to estimate benefits of reducing other 

carcinogens with human data on inhalation 

exposures (e.g., 1,3-butadiene); to adapt the 

acrolein methodology to estimate effects 

of other priority inhalation noncancer 

pollutants (e.g., manganese); and to use the 

lead methodology to estimate benefits from 

other noninhalation risks (e.g., mercury). 

This approach would build on peer-reviewed 

work and provide an assessment of fatal and 

nonfatal cancer effects for certain pollutants, using standard benefits methods. It 

could also focus on the pollutants that risk 

assessors believe are driving the majority 

of the risks from a national perspective. 

However, this approach would not address 

some of the challenges laid out earlier, such 

as possible underestimation of health effects 

from hot spots or short-term exposures and 
Benefit analysis of HAPS reduction

Environmental Health Perspectives • volume 119 | number 1 | January 2011 129

effects of interactions among pollutants on 

adverse health outcomes in a population 

across life stages and/or in disproportionately exposed populations.

• Use NATA or other existing modeling tools to 

pursue national or regional or local analysis 

focusing on reduction of individual risk levels. This approach has been used with the 

1999 NATA framework as part of the 2007 

Mobile Source Air Toxics Rule (U.S. EPA 

2007b). In that rule, air toxics modeling was 

done for 1999 and several future years, with 

and without controls. The 1999 NATA was 

modified to account for the pollutant gradients near roads, analyzing 19 mobile source 

air toxics. The analysis included estimates 

of monetized benefits from PM reductions 

that also occurred as a result of the rule but 

did not monetize reductions in toxics risk. 

This is primarily because the NATA framework is not adequate for extrapolation to 

incidence estimations or benefits assessment 

(U.S. EPA 2001, 2007b). The model has 

several limitations, including the inability 

to estimate specifics for different age groups 

and the lack of accounting for indoor 

sources and potentially important exposure 

scenarios. The strengths of this approach 

include the ability to examine multiple 

pollutants at the same time and look across 

various geographic areas to estimate impacts 

on individual risk levels.

• Estimate benefits of air toxics emissions reductions in conjunction with the criteria air 

pollution program. Many regulations and 

implementation actions to meet criteria air 

pollution goals affect the same sources that 

emit significant air toxics. In some cases, the 

emissions that contribute to ambient concentrations of ozone, PM, and other criteria 

air pollutants are also air toxics. To date, 

with the significant exception of mobile 

source regulations of volatile organic compound and PM precursor emissions, the U.S. 

EPA has not assessed the air toxics impacts 

of the criteria air pollutant programs. 

Because these criteria pollutant programs are 

often very broad in nature, covering many 

sources and geographic areas, the cumulative impact on air toxics may be large. At 

the very least, risk assessors could estimate 

changes in population-weighted concentrations of air toxics, even in the absence of 

appropriate concentration–response functions linking concentrations with health end

points. This approach would provide a consistent air-quality framework for integration 

with other benefits analyses. However, without concentration–response functions, this 

approach still does not provide quantified 

health impacts or economic benefits.

• Expand benefits assessment efforts to include 

equity considerations. As noted earlier, there is 

an emerging literature on addressing equity 

considerations in addition to traditional 

analyses of efficiency. These approaches use 

statistical measures of inequality to determine the change in the population distribution of air toxic risks. These changes in 

equity can then be compared with changes 

in total public health benefits to identify 

possible complementarities in health benefits and equity or the tradeoffs between 

health benefits and equity.

Conclusions

The workshop provided new perspectives 

on benefits assessment of air toxics from 

participants with a wide range of expertise. 

Some key recommendations that emerged 

on moving forward on benefits assessment 

include the following:

• A clear definition of the purpose(s) of 

HAPs benefits analysis to frame long-term 

research priorities is needed. The near-term

and long-term approaches would vary based 

on whether the focus should be on reducing air toxics for the general population, for 

hotspots and regions of interest, or for the 

most susceptible populations. A value-ofinformation approach was recommended 

to prioritize future research based on what 

would have the greatest impact on benefit 

assessment outputs and what would reduce 

uncertainties most effectively.

• Grouping by emissions sources would 

address more closely the issue of hotspots 

or highly exposed populations, whereas 

grouping by chemical class would allow the 

use of toxicology and health data for wellstudied chemicals to inform those with more 

limited information but of similar structure 

or mode of action.

• Different population groups may be of 

particular concern for air toxics exposures,

depending on the spatial and temporal distribution of exposures. Therefore, accounting for the heterogeneity in temporal and 

spatial distribution, specifically for emissions and receptors (e.g., children and other 

vulnerable populations) is critical for benefits analysis.

• The National Health and Nutrition 

Examination Survey work on exposure distributions could be used to inform both 

exposures and health end points (CDC 

2010).

• Analytical methods to define and measure equity considerations should be better 

supported.

• There is a critical need to improve dose–

response estimations, potentially through 

use of models for probabilistic estimation of 

noncancer health risks.

• More research on surveillance and biomonitoring is needed to understand more fully 

how reductions in air toxics related to 

specific health effects.

• More support for research on the use of predictive biomarkers of exposure and health 

effects would allow for an early measurement 

of the impact in reduction of air toxics.

The above key recommendations provide 

some specific steps forward in advancing analysis 

of the benefits from air toxics reductions and 

suggest some future studies to inform many of 

the challenges in this field.

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