Environmental Health Perspectives • VOLUME 109 | SUPPLEMENT 3 | June 2001 357

Observations of geographic differences in the

distribution of environmental pollution have

long been noted but received little governmental recognition until the 1970s, with

mention in the second annual report to the

President by the Council on Environmental

Quality in 1971 (1). During that decade the

environmental justice movement was seeded

by the joint concerns of civil rights activists

and environmentalists. The quality of the

environment in which minorities lived was

becoming a civil rights issue. In 1982 the

environmental justice movement took root

when the term “environmental racism” was

coined by Dr. Benjamin Chavis Jr., who was

then Executive Director of the United Church

of Christ Commission for Racial Justice (2)

and later became Executive Director and

CEO of the National Association for the

Advancement of Colored People. 

The catalyst for the environmental justice

movement was a plan by the State of North

Carolina to build a toxic waste landfill for

polychlorinated biphenyl–contaminated soil

in Warren County, a community almost

wholly comprising low-income and

racial/ethnic minority residents (1,2). Civil

rights activists and environmental advocates

joined forces to stage large demonstrations,

and Congress called for the U.S. General

Accounting Office to investigate siting practices in Southeastern States (3,4). A number

of other key studies and reports followed that

fueled the environmental justice movement

during the last two decades (2).

According to the U.S. Environmental

Protection Agency (U.S. EPA), environmental justice means, in part, that 

no group of people, including a racial, ethnic, or socioeconomic group, should bear a

disproportionate share of the negative environmental consequences resulting from

industrial, municipal, and commercial

operations or the execution of federal, state,

local and tribal programs and policies. (5) 

Although environmental justice activists have

brought inequities of urban air pollution to

the forefront of the federal government (6),

urban communities, where residents are

mainly minorities and have low income, continue to experience disproportionately higher

air pollution exposure levels and higher risks

for diseases than nonurban communities. A

recent report of the National Research

Council provides a perspective on environmental justice and the related needs for scientific research (7).

In response to the environmental and

health problems of racial/ethnic minority

groups and low-income communities, an

invited workshop on Urban Air Pollution and

Health Inequities was organized by the

American Lung Association to identify

disproportionate exposures to outdoor air

pollution in urban communities, develop a

set of priorities based on community health

needs, and recommend a coordinated

research agenda to address environmental

inequities. 

Participants were placed into working

groups charged with addressing key issues pertaining to urban air pollution and health

inequities. The first part of the workshop

focused on assessing the available scientific

information and identifying the knowledge

gaps in modeling and databases; personal

exposure assessment in urban environments;

health impacts of urban ambient air pollution;

and factors determining susceptibility in

urban populations. The agenda for the second

part of the workshop included setting priorities and recommendations for monitoring

ambient air pollution concentrations and

exposures; understanding health impacts and

susceptibility; and reducing inequities through

community-based intervention and public

policy. This article summarizes the background scientific information and presents the

recommendations of the working groups.

Background Scientific

Information

Health Effects of Ambient Air

Pollution

General overview of health effects research.

The evidence on the health effects of air pollution has been summarized in a state-of-theart review (8,9) and a recent monograph (10),

as well as in two recent U.S. EPA criteria

Over the past three decades, an array of legislation with attendant regulations has been

implemented to enhance the quality of the environment and thereby improve the public’s health.

Despite the many beneficial changes that have followed, there remains a disproportionately higher

prevalence of harmful environmental exposures, particularly air pollution, for certain populations.

These populations most often reside in urban settings, have low socioeconomic status, and include

a large proportion of ethnic minorities. The disparities between racial/ethnic minority and/or lowincome populations in cities and the general population in terms of environmental exposures and

related health risks have prompted the “environmental justice” or “environmental equity”

movement, which strives to create cleaner environments for the most polluted communities.

Achieving cleaner environments will require interventions based on scientific data specific to the

populations at risk; however, research in this area has been relatively limited. To assess the current

scientific information on urban air pollution and its health impacts and to help set the agenda for

immediate intervention and future research, the American Lung Association organized an invited

workshop on Urban Air Pollution and Health Inequities held 22–24 October 1999 in Washington,

DC. This report builds on literature reviews and summarizes the discussions of working groups

charged with addressing key areas relevant to air pollution and health effects in urban

environments. An overview was provided of the state of the science for health impacts of air

pollution and technologies available for air quality monitoring and exposure assessment. The

working groups then prioritized research needs to address the knowledge gaps and developed

recommendations for community interventions and public policy to begin to remedy the exposure

and health inequities. Key words: air pollution, community intervention, environmental justice,

environmental monitoring, genetic susceptibility, health status susceptibility, population surveillance,

public policy, urban health. — Environ Health Perspect 109(suppl 3):357–374 (2001).

http://ehpnet1.niehs.nih.gov/docs/2001/suppl-3/357-374samet/abstract.html

This article is based on the Urban Air Pollution and

Health Inequities Workshop held 22–24 October 1999

in Washington, DC. The views expressed in this report

are those of the workshop participants and do not necessarily represent the views of their organizational affiliations or the sponsoring organizations.

*See Appendix for list of participants.

Address correspondence to J.M. Samet,

Department of Epidemiology, Johns Hopkins School of

Public Health, 615 N. Wolfe St., Suite 6041, Baltimore,

MD 21205-2179 USA. Telephone: (410) 955-3286. Fax:

(410) 955-0863. E-mail: jsamet@jhsph.edu

This workshop was organized by the American

Lung Association with major support from the National

Institute for Environmental Health Sciences and additional support from the California Air Resources Board

and the U.S. Centers for Disease Control and

Prevention.

We thank K. Pruitt for workshop planning and logistics, R. Gray for her administrative support during the

workshop, and N. Lee for editing the workshop proceedings.

Received 9 November 2000; accepted 27 March

2001.

Urban Air Pollution and Health Inequities: A Workshop Report

The American Lung Association*
American Lung Association

358 VOLUME 109 | SUPPLEMENT 3 | June 2001 • Environmental Health Perspectives

documents (11,12). The identified adverse

health effects and biologic markers of

response, listed in Table 1 and taken from the

American Thoracic Society’s review (8), are

diverse in scope, severity, duration, and clinical significance. This diversity reflects the

multiple pathways of injury by air pollution

and the sweeping nature of the research evidence, which comes from epidemiologic

studies, human clinical exposures, animal toxicologic studies and in vitro experiments.

Moreover, clinical, biologic, and societal perspectives of what constitutes an adverse health

effect of air pollution have been evolving

(13–15). With biologic markers providing

early indications of injury, sensitive research

approaches offer evidence of subtle population effects, and quality-of-life has been

added as an outcome of interest. A growing

concern about a wider range of pulmonary

and extrapulmonary effects may expand this

list to include neoplasms, airway sensitization,

neurologic abnormalities, and developmental

toxicities, as well as other possible health

effects (15). The collective database still contains significant gaps, however, on the health

effects of single and multiple pollutant exposures (16), including exposures to diesel

exhaust and other complex mixtures. The

specific mechanisms responsible for the morbidity and mortality associated with increases

in levels of particulate matter [particulate

matter with an aerodynamic diameter less

than 10 μm (PM10)] are currently ill-defined

and poorly understood (17,18).

Research specific to urban populations.

The health effects experienced by urban populations exposed to air pollutants are expected

to be similar to those listed in Table 1. The

severity of the effects, however, may be

greater in urban and racial/ethnic minority

or special population groups in comparison

with the overall population or the white

majority. Although evidence is lacking, several factors point to this possibility (19,20).

Exposures to some outdoor pollutants may

be generally higher in the urban community

than in the general population. Routine

ambient monitoring may not accurately capture local or microenvironmental, high-level

exposures in urban settings (e.g., near diesel

bus depots). Such high-level exposures

would, of course, be expected to produce

proportionately larger risks to health.

Populations in urban locations may disproportionately include subpopulations more

susceptible to ambient exposures. Factors

contributing to the heightened susceptibility

may include preexisting disease, insufficient

access to optimal medical care, poor nutrition, socioeconomic stresses, and coexposure

to other pollutants such as bioaerosols.

Numerous epidemiologic studies have

addressed health effects across large-scale

urban areas and have provided a sizable baseline database of health status and health

effects. These studies have included both

open cohort (time–series) (21–26) and closed

cohort investigations (27–33) of the consequences of exposure to ambient PM10, ozone,

nitrogen dioxide, and other criteria pollutants, which must meet the National

Ambient Air Quality Standards (NAAQS) for

outdoor concentrations. Several studies have

shown that background levels of fine particulate matter [particulate matter with an aerodynamic diameter less than 2.5 μm (PM2.5)]

and ozone vary little across large U.S. urban

areas of 20–50 km in diameter (34,35).

Nevertheless, significant spatial and temporal

gradients in the sources, composition, and

concentrations of ambient gases and particles

may result in varying health effects of air pollution within the same city. Large-scale

studies, however, have not focused on intraurban or neighborhood differences in the distribution of health effects associated with

urban air pollutants.

Since 1993 epidemiologic studies have

reported health effects across small-scale,

intraurban areas, particularly in Europe and

Japan. Many of these studies have used traffic

congestion or density as a surrogate for exposure to mobile source pollutants, including

nitrogen dioxide, carbon monoxide, ultrafine

particles, and air toxics (36–45). By combining

comprehensive traffic flow information with

health data from ongoing geographic information systems, insights can be gained into the

effects of local traffic (exhaust) on respiratory

symptoms, lung function, and asthma. Many

studies have shown that heavy traffic flow (particularly truck traffic) is associated with

increased risks of childhood respiratory

symptoms, decreased lung function, and

increased doctor visits or hospital admissions

for asthmatic children, for example (36–45).

Industrial sources may release volatile

organic compounds (VOCs) and other toxic

chemicals into urban areas. The health effects

of exposure to VOCs or hazardous air pollutants have been evaluated in a few studies

(46–49). In the Kanawha County Health

Study (47), concentrations of petroleumrelated VOCs measured at local elementary

schools in West Virginia were associated with

the prevalence of persistent lower respiratory

symptoms, including asthma. In Taiwan, residents in a petrochemical-polluted area complained about more acute irritative symptoms

(i.e., eye irritation, nausea, throat irritation,

chemical odors) than residents in a lesspolluted comparison area (49).

Research on subpopulations. A few

studies have explicitly targeted children and

urban racial/ethnic minority populations or

focused on interracial differences in susceptibility to air pollution. Recent work suggests

that photochemical pollution and other

forms of air pollution have long-term effects

on children’s respiratory health (50,51).

Lung function is lower in children who

breathe more polluted air. These effects may

leave children more vulnerable to respiratory

disease and may result in a lower level of

lung function as they enter adulthood.

Moreover, higher air pollution levels have

also been directly linked with increased

prevalence of asthma in children (52). 

In the United States most morbidity and

most deaths from asthma occur in urban

areas. For example, when compared to

national asthma mortality rates in the 1990s,

Chicago, Illinois, had higher rates for all age

groups (53). The greatest disparity, however,

was among non-Hispanic blacks. In the

United States the asthma mortality rate

among blacks was 2.5 times higher than for

whites; in Chicago it was 4.7 times higher. In

1992 the rate of asthma hospitalizations in

Boston, Massachusetts, was twice as high as

the Massachusetts rate after adjusting for age

and gender (54). Further small-area ecologic

analysis showed positive correlations between

asthma hospitalizations and higher poverty

rate and proportion of nonwhite residents.

Small-area analysis of California by ZIP code

resulted in similar findings on asthma hospitalizations (55). In New York City the highest asthma mortality rate was in the

neighborhood of East Harlem and was four

times the citywide rate in the 1980s (56).

African Americans and Hispanics in

Philadelphia, Pennsylvania, have higher rates

of death from asthma, but only in areas with

higher poverty rates (57). Another small-area

study in Chicago also points to poverty rather

Table 1. Health effects and biologic markers of

response associated with air pollution.a,b

Excess cardiorespiratory mortality

Deaths from heart or lung disease in excess of number

expected

Increased healthcare utilization

Increased hospitalizations, physician visits, emergency

department visits

Asthma exacerbations

Increased physician visits, medication use

Decreased peak flow measurements

Increased respiratory illness

Increased respiratory infections, physician visits,

episodic symptoms

Increased respiratory symptoms

Decreased lung function

Spirometry, peak flow rates, airways resistance

Increased airways reactivity

Altered response to challenge with methacholine,

carbachol, histamine, cold air

Lung inflammation

Influx of inflammatory cells, mediators, proteins

Altered host defense

Altered mucociliary clearance, macrophage function,

immune response

aClinical or public health significance of some effects are

unknown. bData from the American Thoracic Society (8).
Urban air pollution and health inequities

than race as being a much stronger risk factor

for asthma mortality (58). When data for

blacks and whites were analyzed together,

asthma mortality was significantly associated

with lower socioeconomic status; this association was not significant when blacks were

analyzed separately.

Clinical studies (i.e., experimental

exposures of volunteers to air pollution) do

not show differential responses to air pollution by race. Seal and colleagues (59)

exposed healthy African–American and

Caucasian adults to different ozone exposure

concentrations and found no significant

racial group differences in respiratory symptoms and pulmonary function, although

there was a trend toward greater effects on

lung function among African–American

males. Similarly, a small clinical study (60)

found no significant group differences in

lung function or nasal lavage cells between

African–American and Caucasian males with

asthma after exposure to sulfur dioxide. 

Findings of observational studies are

similar. In a time–series substudy of the

National Cooperative Inner-City Asthma

Study (NCICAS), Mortimer et al. (61) found

that ambient ozone concentrations were associated with similar lung function decrements

in children with asthma who were African

American and Puerto Rican living in New

York City. Greater responses to ozone, however, were seen in Chicago in Mexican children with asthma compared to African

Americans. In a panel study of African–

American children with asthma in Los

Angeles, California, Ostro et al. (62) reported

that both ozone and PM10 were associated

with respiratory symptoms. On the basis of

emergency clinic visit data, White et al. (21)

found that inner-city African–American children with asthma may have their disease exacerbated by high ambient ozone pollution. 

Individuals with atopy constitute another

subpopulation that may be highly susceptible

to the effects of air pollutants (63–69).

Allergen sensitization is highly specific and

reflects prior allergen exposure. Subsequent

short exposures to allergens may cause prolonged increases in airway hyperresponsiveness, which indirectly affects susceptibility to

other airborne pollutants such as nitrogen

oxides and ozone. For example, allergen and

air pollutant exposures are both independently associated with exacerbation of

asthma, but they can also interact to intensify

the severity of response (70). Rates of sensitization to allergens have been studied in both

urban African–American and Hispanic populations and do not differ from rates seen in

other population groups. In the NCICAS,

Kattan et al. (71) found sensitization rates

around 78% among urban, school-aged asthmatic populations without differences among

African Americans, Hispanics, and other

ethnic groups. Overall, this rate did not differ

from the 88% rate of sensitization in the

more broadly based asthmatic population in

the Childhood Asthma Management

Program (72). At the same time, specific sensitization patterns may vary considerably

among different populations. For example,

urban populations may be less frequently sensitized to pollens but more frequently sensitized to cockroach and other indoor allergens. 

Factors Determining Susceptibility 

in Urban Populations

In a broad sense the term “susceptibility”

refers to a greater likelihood of an adverse

outcome given a specific exposure, in comparison with the population generally. For

example, when a given population is exposed

to air pollution at a given concentration and

for a given period of time, some proportion

of the population may experience adverse

health outcomes, whereas the rest of the population does not. Identification of the determinants and contribution of susceptibility to

the health effects of air pollution in urban

communities is a key element of the environmental justice agenda. 

Susceptibility is the result of both host

and environmental factors. Genetic susceptibility may be the most commonly studied

host factor, but other host factors to be considered include diet, physiologic state, and

psychologic status. Some determinants of susceptibility (e.g., age) represent normal developmental phases for all human beings, or

they may represent normal biologic attributes

(e.g., gender) whose meaning is shaped, to a

large degree, by the social context. Although

consideration of individual and group differences in genetic susceptibility to the effects of

air pollutants is relevant, the nonrandom distribution of population-level determinants of

susceptibility appears to play a dominant role

in influencing the observed pattern of health

outcomes. For example, poverty areas

(defined by social, economic, and geographic

attributes) manifest excess rates of morbidity

and mortality due to certain chronic conditions, including asthma, diabetes, and hypertension. We need to better understand these

population-level factors, including the loss of

social networks (73), as determinants of

susceptibility in affected communities.

Population data are thus important for

identifying specific subpopulations that may

exhibit factors associated with increased susceptibility, and for defining the geographic or

personal characteristics that determine risk for

disease outcomes in exposed populations.

Such information may be useful in contributing to rational planning of public health policies and specific intervention programs to

prevent diseases attributable to urban air

pollution. Before deciding if a particular

subpopulation (e.g., the very young) shows

increased susceptibility to the health effects of

an environmental exposure when compared

to the general population (as assessed by a

specific indicator of outcome), researchers

need to consider the following questions:

• Has the indicator been causally linked to

the exposure of interest?

• Is the risk for the health indicator associated with the exposure different between

the subpopulation and a comparison

population?

For example, children with asthma are

considered as likely to be at greater risk for

respiratory morbidity (e.g., respiratory symptoms) than children not having asthma. To

characterize children with asthma as susceptible to air pollution, researchers should show

that the risk in this group is greater than in

nonasthmatic children. The needed evidence

might compare the exposure–response relationships for the two groups with the anticipation that susceptibility would be manifest

as a steeper curve or perhaps a different form

than found for nonasthmatic children.

Age-related windows of vulnerability. For

many disease conditions the occurrence of disease is a reflection of the interaction between

host and environmental factors, with both sets

of factors possibly varying over the life span.

Fetuses and infants are considered to be more

susceptible to a variety of environmental toxicants than adults because of exposure patterns,

physiologic immaturity, and the longer life

span over which disease initiated in early life

can develop (74). For example, children have

higher breathing rates and therefore higher

intake of air pollutants per unit of body

weight (75). Developing organs may be more

susceptible to toxicants due to higher rates of

cell proliferation or changing metabolic capabilities (76). The first symptoms of asthma are

generally manifest before 6 years of age in

most individuals developing the disease, leading to the hypothesis that much of asthma

originates in childhood or infancy and may

even reflect in utero exposures. Studies of

maternal exposure to PM during pregnancy

have shown a negative impact on fetal development (74,77), but it is unclear whether prenatal exposures may translate into risk for the

development of diseases such as asthma.

Observational and biomarker studies in children and models of infant airway injury and

repair would be helpful for testing hypotheses

on the inception, pathogenesis, and outcomes

of lung diseases occurring in early life, including asthma and bronchopulmonary dysplasia.

Low birth weight is a risk factor for asthma

(78). Low birth weight, particularly common

among mothers in poor urban neighborhoods

(79), is strongly associated with the mother’s

psychosocial status (80).

Environmental Health Perspectives • VOLUME 109 | SUPPLEMENT 3 | June 2001 359
American Lung Association

360 VOLUME 109 | SUPPLEMENT 3 | June 2001 • Environmental Health Perspectives

Health status as a determinant of

susceptibility. Epidemiologic studies suggest

that individuals with chronic cardiopulmonary conditions, including asthma, chronic

obstructive pulmonary disease (COPD), and

cardiovascular diseases, are at increased risk for

developing adverse health outcomes from

exposure to urban air pollution. 

Asthma. Even when mild in severity,

asthma is associated with increased airways

responsiveness and a tendency for increased

ventilation and more central deposition of

inhaled pollutants. Although it is known that

air pollutants can cause asthma exacerbations,

much remains to be learned about how environmental factors have contributed to the rise

of asthma-related morbidity. Of particular

interest is the interaction between exposure

patterns over time and increased asthma

prevalence (i.e., susceptibility) in some urban

populations of color. Little is known about

the relative contribution of local sources of air

toxics to asthma morbidity or how such local

sources interact with regional air pollution as

determinants of asthma morbidity. Research

on affected persons during the asthma epidemics in Barcelona, Spain, suggests that certain subgroups, namely atopic individuals, are

at increased risk for manifesting the asthmatic

syndrome following exposure to soybean dust

(81). Such susceptible subgroups need to be

characterized further in relation to specific

exposures to inform preventive strategies.

Chronic obstructive pulmonary disease.

The health status of persons with COPD is

affected by ambient air pollutants, including

ozone and PM10. Effects range from unscheduled hospital visits to mortality, but little is

known about the mechanisms by which these

ambient air pollutants increase morbidity and

mortality in people with COPD (10).

Cardiovascular diseases. Exposure to sufficiently high levels of carbon monoxide

causes asphyxia and may increase cardiovascular morbidity. Recent epidemiologic studies

indicate increased cardiovascular morbidity

and mortality in association with ambient

PM. Mechanisms that may increase cardiovascular mortality with exposure to particulate air pollution, particularly PM10 and

PM2.5, remain uncertain. Moreover, individuals with a variety of conditions, including

central abdominal obesity, smoking, hypercholesterolemia, and hypertension, are at

increased risk for adverse cardiovascular

events (9). Potential mechanisms underlying

interactions between exposure to air pollutants and these risk factors, as determinants

for cardiovascular morbidity and mortality,

have not yet been elucidated.

The role of genetic factors. Genetic factors

are likely important in the development, persistence, and exacerbation of chronic respiratory diseases, although research in this area is

only beginning (82,83). For example, the risk

for developing asthma increases with having a

first-degree relative with asthma, indicating a

role for heritability, but the etiology is

undoubtedly complex and the mode of transmission remains undefined. Specific genes for

asthma have yet to be identified definitively.

The sharp rise in asthma prevalence in just

the past two decades implies an environmental cause, as its time course is not that of a

genetic change in the population. Polymorphic genes for a vast array of physiologic

functions are suspect as determinants of susceptibility to COPD and asthma (84–88). In

addition, some hazardous air pollutants

(HAPs) are allergenic and have caused airway

hyperreactivity and asthma in occupational

settings (89–91). It is unclear, however,

whether the low-level exposures to environmental (ambient) air pollution can effect similar responses (16). Additional clinical and

epidemiologic studies and informative animal

models for studying the interactions of genes

and ambient air pollution are needed.

Gender-related differential. Statistics on

healthcare utilization suggest that women

may be more vulnerable to the chronic effects

of air pollutants. Scant comparative data are

available, however, on women’s time activity

patterns, smoking habits, behavioral attributes, occupational exposures, or hormonal

levels that may contribute to gender-related

differential susceptibility. 

Socioeconomic factors. There is ample evidence that socioeconomic status (SES) is a

strong determinant of susceptibility to the

adverse effects of air pollution. Not only are

conditions such as asthma more prevalent in

low-income communities, but there is evidence that increased prevalence of asthma is

quantifiably related to the extent of social

deprivation in low-income communities (92)

and the experience of stress (93). Thus, an

important direction of public health research

is to identify factors common in the context

of poverty that may increase exposure to environmental toxicants, increase susceptibility to

their health effects, or both.

Social exposures. The morbidity and

mortality experience of a population is more

likely to be adverse in the context of lower

SES and an unfavorable political climate

(73,94). The community history provides an

approach to characterizing existing resources

within a community. Facets of such community history include information flow, existing networks, strengths of networks, extent of

resource sharing, and the degree of the community’s political empowerment or lack

thereof, as well as cultural factors. Little data

are available, however, on the mechanisms by

which the social experience of a community

may contribute to increased susceptibility to

ambient air pollutants. 

Stress. Strong evidence that psychosocial

stress increases susceptibility to adverse effects

of air pollution comes from the NCICAS.

Children’s mental health status was significantly associated with asthma morbidity,

specifically wheezing and functional status

(95). Several mechanisms have been proposed

to explain the physiologic response to chronic

stressors. Such mechanisms include cytokine

immunomodulation and disruption of the

hypothalamus–pituitary axis (96). Immunomodulation has been implicated in the mechanisms for several conditions associated with

exposure to chronic stressors, including low

macrophage concentrations (97–99).

Similarly, immunomodulatory effects of

chronic stressors are implicated in the

propensity to asthma exacerbations. Although

the mechanisms for such effects of stress

remain to be elucidated, the new body of

work on leptin and the adrenal hormones

may prove valuable in showing mechanisms

via stress (100,101). There are no data on

potential interactions between exposure to

ambient air pollution and the response to

stressors in individuals with chronic respiratory diseases. Coping behaviors and locus of

control may modify the impact of stressors in

the chronically exposed individual. We do

not understand how these behavioral characteristics may modify the consequences of

exposure to stressors and how mechanisms

underlying such effect modification.

Quantifying Urban Air Quality:

Available Technologies

Monitoring and air quality modeling are critical tools for characterizing population exposure variables and tracking the consequences

of air quality management programs.

Monitoring is routinely carried out in urban

areas, but geographic detail may be insufficient to establish differential exposures across

communities. Air quality models that incorporate emissions and meteorologic data may

be useful for this purpose.

Air quality monitoring and data collection. Data applicable to tracking air quality

are collected routinely and fall into three

classes: emissions inventories, ambient air

quality monitoring, and meteorologic data.

Each of these three types of databases provides information on a different dimension of

pollutant dynamics that directly affects quantitative air quality assessments. Accuracy of

the data depends on the methods of collection and the number of samples or frequency

of measurements.

Emissions inventories. Following the

approach of the U.S. EPA, emissions inventory databases can be divided into two pollutant categories: criteria pollutants and HAPs.

Within each of these categories, the emissions

are further subdivided as coming from point
Urban air pollution and health inequities

sources and area sources. Point sources are

those large single facilities that are required to

report emissions. In contrast, area sources are

the myriad smaller sources such as motor

vehicle emissions, and these inventories are

generally estimated using emissions models.

Similarly, emissions models have been used

substantially for criteria pollutants, while

emissions models are rapidly being developed

and modified for HAPs. 

Ambient air quality monitoring. As with

the emissions inventory databases, ambient

air quality databases can be divided into those

for criteria pollutants and HAPs. The ambient criteria pollutant databases are generally

more robust than the HAPs databases because

of the larger number of monitoring stations

and greater frequency of sampling. For example, in California alone there are over 250

ambient air–monitoring stations for criteria

pollutants. The ambient HAPs monitoring

network, on the other hand, consists of 22

ambient air–monitoring stations located

statewide that monitor 58 substances with a

sampling frequency of 1 day in 12. Excluding

diesel exhaust, the more commonly monitored substances are benzene, 1,3-butadiene,

hexavalent chromium, carbon tetrachloride,

and formaldehyde. 

Meteorologic data. Meteorologic data are

among the simplest to obtain, as the instrumentation needed to collect the data is readily

available with established protocols. The simplicity of data collection, however, is offset by

the fact that complex physical terrain limits

the representativeness of meteorologic data to

localized regions. In addition, studies that

require long-term estimates need at least 5

years of consecutive data; studies involving

short-term, episodic events require more

intensive data-gathering efforts. 

Using air quality information in modeling. Air quality models can be used to estimate atmospheric concentrations of air

pollution by simulating the physical atmospheric relationship between emission sources

and receptors, the points for which pollutant

concentrations are to be estimated. The construction of air quality models ranges from

representing simple atmospheric processes to

more complex situations. 

Models can estimate downwind concentrations as a function of source and environmental parameters, as well as evaluate the

effects of control measures. Modeling over a

large geographic scale, such as nationally, may

also provide information on a local scale,

which can be used for prioritizing and targeting important pollutants and areas that are in

need of further research. Models are also useful for estimating concentrations in circumstances where monitoring data are

unavailable, such as when there is insufficient

spatial or temporal ambient coverage. For a

proposed new source, air quality models are

useful in estimating expected concentrations. 

There are four primary data inputs to an

air quality model, as depicted in Figure 1.

These inputs are source parameters, meteorologic conditions, physical terrain data, and

ambient measurements. 

Source parameters. Emissions are the primary data for the source parameters, and they

should be characterized according to their

spatial and temporal distribution. Physical

variables constitute the secondary data for the

source parameters. The physical variables

include stack conditions (e.g., stack gas temperature, exit velocity, stack height, diameter)

and building dimensions, which should be

incorporated in a downwash analysis. Other

types of source information that can be input

for an air quality model are decay rates,

chemical reaction rates, and deposition rates

of various compounds.

Meteorologic conditions. Meteorologic

data are needed for the models to simulate

atmospheric transport, dispersion, and chemical transformations. Typical meteorologic

data from aloft measurements include wind

speed and direction and temperature at various heights above ground level. Additional

surface data may include horizontal wind

direction fluctuations, temperature lapse rate,

and incoming solar radiation.

Physical terrain data. Elevation and type

of land use constitute physical terrain data.

The land use is important for placing receptors as well as estimating dispersion due to

surface roughness and heat island effects. The

more sophisticated models can use elevation

to better describe the transport and dispersion

of pollutants at the surface.

Ambient measurements. Ambient data

are necessary for evaluating model performance. Although model performance is not

part of every analysis, evaluation is necessary

for establishing the credibility of the models.

Once an air quality model has performed successfully under controlled conditions, it can

then be used to evaluate emissions for different uncontrolled conditions. Photochemical

grid-based models, which are generally used to

evaluate widespread control strategies, almost

always require performance evaluations using

ambient data. On the other hand, a Gaussianbased model can be used for a single source

under certain environmental conditions without a performance evaluation, such as when

the emissions are from a proposed facility.

Types of air quality models. There are several types of air quality models available; the

optimal model provides the most accurate

representation of atmospheric transport, dispersion, and chemical transformations in the

area of interest. The most commonly used

models can be grouped into three categories,

which are complementary: receptor-based

models, regional/urban scale models, and

microscale models.

Receptor-based models. Receptor-based

models provide a predicted estimate of air pollutant concentrations at different geographic

points, or receptors. They are observation

based and dependent on measurements of specific ambient pollutants and detailed emissions inventories. In other words, they require

profiles of the emission sources that are timeand pollutant-specific in order to describe

concentrations at particular locations. Because

the results of receptor-based models are

dependent on ambient measurements, they

are generally considered to be a good foundation for risk assessments. Limitations to receptor-based models are that a) concentrations

can only be estimated at receptor locations,

and b) locations of higher concentrations may

be unobserved. The chemical mass balance

model is a typical receptor-based model.

Regional/urban scale models. Regional or

urban scale models provide projections of

concentrations across geographic domains on

the scale of large urban areas or regions. They

typically use a gridded approach to simulate

the three-dimensional transport, chemistry

and dispersion of emissions. These grid-based

models generally are used to evaluate control

measures, and they require a gridded hourly

emission inventory and meteorologic data as

inputs, as well as ambient data to evaluate

their performance. Grid-based models have a

high computational demand; a 1-day simulation could use 1 day of computation time.

Typical models in this category are the Urban

Airshed Model, Models-3, and CALPUFF.

Microscale models. Microscale models

generally are best suited for hot spot (i.e.,

near major stationary sources) analyses to estimate concentrations for receptors on a finescale resolution at distances from 50 m to a

few kilometers from the source. These models

are routinely used beyond these limits, however, at distances as close as 20 m and as far as

50 km. Microscale models are commonly

used to evaluate the emissions of current or

proposed facilities. Routine meteorologic data

are input to establish the transport and diffusion of the emissions, but chemistry is usually

not considered. Models in this category are

the Industrial Source Complex 3 models, the

American Meteorological Society/U.S. EPA

Environmental Health Perspectives • VOLUME 109 | SUPPLEMENT 3 | June 2001 361

Figure 1. Data inputs to air quality model.

Estimated

concentration Air quality

model

Meteorologic

parameters

Terrain

 conditions

Source

parameters

Ambient

data
American Lung Association

362 VOLUME 109 | SUPPLEMENT 3 | June 2001 • Environmental Health Perspectives

Regulatory Model (AERMOD) and

CALPUFF. CALPUFF transcends both

microscale and urban scale types of models.

Cumulative exposure modeling of

hazardous air pollutants. Currently there are

two models for cumulative exposure from

multiple HAP emission sources: the

Assessment System for Population Exposure

Nationwide (ASPEN) model and the

Multiple Air Toxics Exposure Study II

(MATES II) model. Development of the

ASPEN model was sponsored by the U.S.

EPA as part of the Cumulative Exposure

Project (CEP), which estimates long-term

outdoor concentrations of 148 of the 188

HAPs listed in the Clean Air Act of 1970

(102) for every census tract in the contiguous

United States in 1990 (totaling 60,803 census tracts) (103,104). The CEP uses ASPEN,

a Gaussian dispersion model (103), to estimate outdoor concentrations of HAPs on the

basis of emission rates of the HAPs, frequencies of various meteorologic conditions, and

effects of atmospheric processes such as decay,

secondary formation and deposition.

Formulated around the Industrial Source

Complex Long Term air dispersion model,

ASPEN includes relatively simplified treatment of atmospheric chemistry, transport,

and diffusion. Advantages of using these

approaches include the ability to perform

multiple runs of the model to evaluate sensitivity parameters with relatively short computing times, and analysis of a large

domain—up to the entire nation. 

By contrast, the MATES II approach uses

a grid-based model with some limited chemistry and a microscale model for evaluation at

a finer resolution. Although conceptually this

is an ideal approach, the computational

requirements are high for large domains, and

this may limit sensitivity analysis on large

scales. Developed by the South Coast Air

Quality Management District in California as

part of their study to assess toxic exposures in

southern California, the MATES II approach

uses the Urban Airshed Model with the

Industrial Source Complex Short Term 3

(ISCST3) model for microscale analysis.

The California Air Resources Board is

currently developing an exposure assessment

model designed to evaluate health risk. This

model, the Hot Spots Analysis and Reporting

Program, comprises three modules: a) an

emissions module, the California Emission

Inventory Development and Reporting

System; b) an air dispersion module, including ISCST3 and AERMOD; and c) a risk

assessment module developed by the

California Office of Environmental Health

Hazard Assessment (Stochastic Approach). It

may be possible to use the Hot Spots Analysis

and Reporting Program to evaluate cumulative exposure on a neighborhood scale basis,

providing an informative tool for analyses

directed at environmental justice issues.

Although the models described can provide some information on relatively small

geographic scales (e.g., neighborhoods), they

are most appropriate for larger-scale areas.

There is a need for a modeling approach that

can couple the existing models to the neighborhood scale. There will, however, be substantial technical challenges to developing

such approaches.

Exposure Assessment in Urban

Communities

The environmental justice movement has

raised concerns about the potential for disproportionate exposures to air pollution

among disadvantaged or racial/ethnic minority populations in urban areas due to the

proximity of polluting sources such as bus

depots, trucking facilities, high-volume roadways, waste treatment and transfer stations,

and industrial point sources. Although some

data are available on personal air pollution

exposures of urban residents, little is known

about variations in personal exposures across

communities in relation to local sources.

Impacts of local air pollution sources.

Factors that can influence personal air pollution exposures of urban residents, as shown in

Figure 2, include regional-scale polluted air

masses, proximity to local ambient sources,

indoor penetration of outdoor pollution,

indoor pollution sources, time–activity patterns, and individual characteristics and

behavior. Sorting out the relative importance

of these diverse factors in driving differential

urban air pollution exposures is a complex

and daunting task, and one for which only

limited data are yet available. Answers will

likely differ for different urban air pollutants

and locations. 

Assessing exposure to outdoor sources of

air pollution requires information on concentrations to which people are exposed as well as

the frequency and duration of that exposure.

Factors such as local meteorology, pollutant

volatility, and the time residents spend proximate to sources (e.g., on the street) are significant determinants of personal exposures.

Furthermore, the degree of air exchange from

outdoors to indoors has a significant impact

on the contribution of outdoor sources to

exposures. For instance, residents who live in

dwellings without air conditioning may be

exposed to outdoor air most of the day during

the summer months because windows remain

open to increase ventilation or because more

time is spent outdoors. 

Local levels of air pollution are also influenced by the contribution of regional sources,

especially for fine particles and ozone.

For some people there are also significant

contributions to total air pollution exposure

from indoor sources such as kerosene heaters

and smoking. It should be noted that these

indoor pollution sources may contribute to

the total exposure and health burden experienced by urban residents. 

Given the model depicted in Figure 2,

systematic differences in exposures across population subgroups could arise from disparities

in either outdoor pollution concentrations or

from time–activity patterns. Thus, to measure

these systematic differences in exposure

between urban and nonurban communities,

information is needed both on where and how

people spend their time as well as the pollution concentrations in each location. 

Current knowledge of personal exposure

assessment in urban environments. Although

some data are available on personal exposures

of urban residents to air pollutants, little is

known about variations in personal exposures

between or within communities in relation to

local outdoor sources. The recently completed MATES I and II studies in Southern

California examined spatial variations in outdoor air toxic concentrations related to

sources and found local traffic to be an

important determinant of local concentrations (105). The U.S. EPA Total Exposure

Assessment Methodology studies of carbon

monoxide and traffic in Denver, Colorado,

and Washington, DC, addressed personal

exposures, time–activity patterns, and housing characteristics, though not in low SES

populations (106).

The Kanawha County Health Study

reported associations between concentrations

of VOCs and other pollutants and residential

proximity to industrial sources in a workingclass rural mining community in West

Virginia (47). Studies have been completed

and are in progress that address housing,

traffic, VOC concentrations, and other

factors in African–American neighborhoods

Figure 2. Factors influencing personal exposures to air

pollution in urban environments.

Housing

characteristics

• Ventilation

• Heating/cooling

• Indoor sources

• Other

Local air

pollution sources

• Proximity

• Traffic

• Industrial sites

• Dry cleaners

• Other

Time–activity patterns

• Indoor/outdoor time

• Transportation modes

• Other

Individual factors

• Smoking

• Hobbies

• Occupation

Chemical

transformation

Political, economic, and social context

Global, regional, and local

air pollution background

Local and neighborhood

meteorology
Urban air pollution and health inequities

of Baltimore, Maryland (14,107–109). The

ongoing TEACH study (Toxic Exposures of

High School Students: A Columbia/Harvard

Study) is addressing PM2.5 and air toxic exposures among racial/ethnic minority high

school students in New York City and Los

Angeles (110). The RIOPA (Relationships of

Indoor, Outdoor and Personal Air) study is

currently investigating indoor, outdoor and

personal air concentrations of VOCs, aldehydes, and PM2.5 in 100 residences in Los

Angeles; Elizabeth, New Jersey; and Houston,

Texas (111). Lioy et al. have reported data on

toxic metal exposures in New Jersey urban

areas (112). Although the data from these

studies are not representative for the general

population, they are providing needed information on personal exposures to air pollutants, particularly some of the HAPs. Except

for the RIOPA study, these studies do not

include individual-level data about SES, thus

making it difficult to draw conclusions

regarding differential exposures by SES. 

Time, budget, and travel behavior studies

consistently show that role-related characteristics, particularly employment status and

gender, have strong influences on travel/activity patterns of individuals (113). Work status

appears to explain most of the differences in

traditional measures of activity patterns.

Thus, factors contributing to exposure will

likely differ for those who do and do not

work outside the home. Nonworkers spend

significantly more time at home (i.e., between

4 and 6 hr, on average), but only half as

much time in travel as workers. Men spend

about twice as much time traveling and being

outdoors as women. Among adults, activity

patterns do not differ based on age (over or

above 60 or 65 years) once work status has

been controlled (113). Clearly, children’s outdoor exposure is determined by school schedules during much of the year.

To date, little of the time–activity data

from air pollution exposure studies have been

analyzed for differences by SES. Research

shows, however, differences based on education and/or income in the uses of discretionary time and the amount of travel.

Specifically, higher SES groups tend to spend

more time in active and away-from-home

activities than lower SES groups. The implications of this difference for current patterns

of exposure to air pollutants are not clear.

Lower SES groups also spend less time traveling and travel shorter distances. Much of the

difference in travel behavior among income

groups has been attributed to differential rates

of automobile ownership. 

Several researchers have investigated the

potential for differences in in-home air

pollution concentrations and personal

exposures across groups defined by socioeconomic and demographic characteristics.

Two different studies found that, despite

differences in time at home and in travel, there

are few statistically significant differences in

levels of personal exposure to carbon monoxide (Washington, DC, area) and nitrogen

dioxide (Los Angeles Basin) between workers

and nonworkers (113,114). On the other

hand, these analyses did show differences

among gender and work-status groups in the

contribution of different sources to the total

exposure. In addition, another study found

that being male, Hispanic, employed, and/or

middle-aged were positively associated with

personal exposures to various VOCs, even after

proximity to sources was considered (115).

Geographic analyses suggest systematic

differences in exposure by community. For

instance, indoor levels of carbon monoxide in

the Washington, DC, area and nitrogen dioxide in the Los Angeles Basin are higher in

central-city areas than in the suburbs

(116,117). Models of exposure based on both

activity patterns (i.e., indoor vs outdoor time,

exertion level, and mobility) and ambient

monitoring show that low-income groups,

racial minorities, and children are exposed to

the highest levels of ozone and particulates in

the South Coast Air Quality Management

District of California (118). Kinney and colleagues recently reported results of a study of

small-scale spatial variations in PM2.5 and elemental carbon in the Harlem neighborhood

of New York City (119). Another recent

study reported a correlation between residential indoor polycyclic aromatic hydrocarbon

concentrations and local traffic density (120).

These limited data suggest that ambient concentration differentials can exist in urban

areas due to traffic sources. 

Using modeling to evaluate exposures in

urban areas. Air-monitoring data can contribute to our understanding of community

exposures. Because of financial, technologic,

or logistical constraints, however, airmonitoring data may be unavailable or of

limited scope geographically or temporally.

Air quality modeling can help to fill in the

gaps over both space and time. To have valid

models, good data are needed on source locations and emission rates in the community, as

well as meteorologic conditions such as wind

direction and speed. Wind flow through

urban street canyons is complex and difficult

to model. Air pollution concentration gradients should be modeled in three dimensions,

as vertical gradients may be important for

personal exposures. Depending on the level of

detail of the model and emissions inventory,

estimated ambient concentrations of air pollutants from modeling can provide information on a large scale to screen for potential

adverse impacts on health, or more precise

estimates can be used to assess geographic

variations in risk. 

For example, the CEP estimates longterm outdoor concentrations of 148 of the

188 HAPs listed in the Clean Air Act for

every census tract (60,803) in the contiguous

United States for 1990. Concentration estimates were based on emissions rates of the

HAPs, frequencies of various meteorologic

conditions, and effects of atmospheric

processes such as decay, secondary formation,

and deposition. This assessment provides

information for every community in the

United States and can be used to assess priorities on important areas and pollutants in a

community, but need to be supplemented

with local information prior to making policy

or community decisions.

An example of how large-scale modeling

can be combined with local information is the

Chicago Cumulative Risk Initiative for Cook

County, Illinois, and Lake County, Indiana,

an evaluation of potential environmental

impacts of air pollution in the Chicago area.

This is a joint project between U.S. EPA

Region 5, local community activists, and

researchers and was initiated by concerns from

the community over high concentrations of

HAPs in their neighborhoods (121). The project draws upon a variety of data sources,

including the Toxics Release Inventory, local

emission inventories, and ambient concentrations, which are used to describe local conditions in terms of air quality, health outcomes,

and demographic makeup of the communities

in the Chicago area. 

Summary

The knowledge gaps in collective data on

health effects of air pollution require additional research, particularly on the specific

mechanisms for mortality and morbidity from

increased PM exposure. The adverse health

effects of air pollution among urban communities are even less well understood. Existing

research specific to urban populations has

clearly shown a disproportionate burden of

exposure to air pollutants in low-income and

racial/ethnic minority communities. These

communities are also subject to higher risks of

health problems associated with air pollution,

at levels beyond those expected with the

higher levels of exposure. Numerous host and

environmental susceptibility factors in urban

populations play roles in the observed

increased burden of disease. Although the

higher air pollutant exposure levels in urban

areas can be mitigated through changes in

policies and regulations, more data are needed

on the health effects of air pollution in urban

communities and the factors within these

populations that lead to the observed

inequities in health risks. In addition, exposure assessment, air quality monitoring, and

air quality modeling are areas that should be

addressed in future research and current

Environmental Health Perspectives • VOLUME 109 | SUPPLEMENT 3 | June 2001 363
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364 VOLUME 109 | SUPPLEMENT 3 | June 2001 • Environmental Health Perspectives

actions aimed at resolving urban health

inequities. Biomarkers are other potentially

useful tools that could provide insights.

Recommendations follow for air quality data

collection and exposure assessment, health

effects research, community-based intervention, and public policy.

Recommendations

Air Quality Data Collection 

and Exposure Assessment

Improved monitoring and modeling of urban

air quality. In assessing the impact of ambient air pollution in urban areas, it is critical

to characterize the pollutants, both in terms

of species and concentrations, as well as

exposures to both susceptible and nonsusceptible populations. The existing databases

have been designed primarily for regulatory

purposes and are not necessarily well suited

for answering questions relating to exposure

and health inequities. Pollutant levels can

vary both horizontally and vertically, particularly in urban settings. Traffic patterns may

result in pollutant levels very different in

areas just blocks apart. In addition, building

characteristics, which may be related to

socioeconomic factors, can affect the movement of ambient air pollution into indoor

spaces and resulting personal exposures.

Along with the need to better characterize

pollutant concentrations and exposures in

urban environments, access to this information by communities, researchers, and

decision makers needs to be ensured.

Equally as important as the types of data

collected are the locations for monitoring

urban pollution. Current monitoring sites are

not always located to reveal urban inequities.

For the most part there is insufficient spatial

and temporal detail to answer exposurerelated questions in urban environments. The

current monitoring locations may or may not

include hot spots and represent the entire

exposure area. Dispersion modeling can be

used to identify where these monitors may

best be located, but a sufficient number of

monitors is needed to assure that highconcentration areas are found. 

Hot spots are currently defined by air

quality data alone. More holistically, health

and psychosocial stressors should be included

in the modeling and hot spots redefined to

include areas of significant health inequity.

Siting of air pollution monitors should

include site selection based on health hot

spots and proximity to facilities and intersections of concern likely to increase exposures.

Expansion and better targeting of existing

air-monitoring systems would require a concerted effort of local, state, and federal agencies, along with participation by academia

and community interests. Federal partners in

monitoring would include the U.S. EPA, the

National Institute for Environmental Health

Sciences, the U.S. Department of Energy,

the U.S. Department of the Interior, and the

U.S. Centers for Disease Control and

Prevention. 

Although the State Implementation Plans

(SIPs) required under the Clean Air Act often

use dispersion modeling of criteria pollutants

to identify high-concentration locations,

analyses of toxic chemicals remain quite limited, particularly at the level of specificity

needed to distinguish exposures in one community from those in another. The U.S. EPA

made a first attempt to quantify and locate

the highest concentrations of a series of toxic

chemicals in the CEP. Because of the national

scope of this study, it was not possible to

develop the detailed local level data necessary

to identify hot spots. The study was designed

to estimate average concentrations for each

census tract and not to identify peak concentrations that might occur inside a census

tract. Urban areas need to be reevaluated,

using more detailed information and knowledge of the communities, to identify high

concentration areas in order to appropriately

evaluate the relationship between hot spots

and inequity issues.

Continued application of refined modeling

to the cumulative impacts from various sources

on a neighborhood scale would also contribute

to more appropriate analyses of inequity issues.

Modeling analysis could be refined by including additional parameters such as the refined

deposition properties of pollutants and robust

simulations of chemical reactions and the

decay of hazardous air pollutants.

California is a leading state in obtaining

ambient data for criteria and toxic pollutants

and in modeling the emissions from urban air

pollutants. As other states increase their abilities to obtain ambient data and improve their

modeling capabilities, they could learn from

the changes that California is making to its

approach. A report of lessons learned from

California that includes the perspectives of

regulators and communities would be a very

useful resource. Finally, modeling and monitoring need to be translated into public policy. Data, once gathered and analyzed, must

be acted upon, not further debated.

Adoption of an interdisciplinary approach

to data collection and analysis. Existing data

sources from other sectors can be used to learn

more about health variations in urban populations. Several potential sources of valuable data

for secondary use are available from administrative record systems, including vital events

registries, hospital admissions, emergency

department visits, Health Care Finance

Administration records, health maintenance

organizations, and the Department of Veterans

Affairs medical system. Supplemental analyses

of previous epidemiologic studies with

individual-level data, including the Harvard

Six Cities Studies (27), the Harvard 24 Cities

Study (34,122), and the NCICAS (71,123),

could also add to our understanding of urban

health inequities.

An interdisciplinary approach to analyses

of the available data is also needed. Health

departments should play a more central role

in analyzing and using air quality data, and

there should be local annual reports on air

quality, with public meetings coordinated by

the appropriate health and environmental

agencies. Community environmental health

advisory boards should be established that are

trained and educated to interact with communities and to guide this ongoing effort. 

Collection of air pollution data can be

made much more informative through an

interdisciplinary approach. One example is

by expanding the use of geographic information systems technology in the construction

of air-monitoring databases. Data on air pollutant levels and traffic patterns could be

overlaid with data on other risk factors such

as specific pollution sources, crowding, and

poverty. It appears that psychosocial stressors, including but not limited to SES, may

act as environmental toxicants independent

from, but synergistic with, air pollutants.

Current analytic methodologies and associated databases regarding air pollution and

health in urban environments are incomplete, in that they do not include many

health indicators such as psychosocial and

related stressors, which are increasingly

understood to affect individual biologic

function on a number of levels. 

The term “biopsychosocial model” characterizes the nested, interactive ecology of biology, mental function, and social status and

relations in a range of human pathologies

(124–128). The biopsychosocial model has

not yet been widely applied to understanding

the effects of air pollutants. According to this

model, the effects of airborne or other toxic

substances can be understood in the context of

individual biology only when socioeconomy

and personal and perhaps community history,

which also profoundly affect that biology, are

also considered. The approach implies that our

understanding of the effects of toxic exposures

must take place in the context of the multiplicative, synergistic impacts of the many other

physiologic, psychologic, and social stressors

that constrain, and indeed largely define, life in

marginalized urban neighborhoods. 

Existing pollution models can be

expanded to incorporate the biopsychosocial

model by including indices derived from the

many administrative data sets available from

government agencies, using standard tools

available from population and community

ecology. These data range from the decennial
Urban air pollution and health inequities

U.S. census to annual school achievement

indices, housing inspection information,

monthly or even daily demand for law

enforcement, fire extinguishment, and other

emergency services. Standard ecosystem index

methods can be applied to create local indices

of psychosocial stress from such data.

Incorporation of these indices with existing

pollution models and data would permit tests

of synergistic models against health status

data available from various agencies on

different scales. 

Community access to information.

Residents of low-income areas and communities of color recognize that air pollution

exacerbates asthma and other respiratory diseases. In this context, databases and monitoring can be important tools for community

education and for affecting public policy

change. Making these data both accessible

and understandable to community members,

however, is a major challenge. The rapid

development of technology and resources

such as the Internet make accessibility possible, but only to the extent that computers are

available. For example, the Internet is already

being used for United States–Mexico border

air quality information (129). In addition to

accessibility, there is the need to develop

ongoing relationships between governmental

agencies and communities, perhaps through

the development of regional centers or

regional meetings, such that problems and

issues can be approached from a long-term

perspective as opposed to multiple ad hoc

solutions. Communities have not been

actively included in the development and use

of databases. Reports on data should be prepared quarterly in lay language and explained

in public meetings where communities can

bring their own expert resource persons.

Most low-income areas are widely served by

local community- and church-based organizations. These organizations are important

resources for community access to information and advice on appropriate local

responses to the information.

Programs such as the Environmental

Monitoring for Public Access and

Community Tracking of the U.S. EPA

should be widely implemented (130) and

data made available for community-based

research (CBR) and analysis, as in “Holding

Our Breath” from the Communities for a

Better Environment (131). Agencies should

be certain that there are no barriers keeping

data and analytic results from affected communities, so that they may respond at the

health behavior level as well as political level.

Resources and tools for community-based

analyses should be expanded to increase participatory decision making and the likelihood of behavioral adaptation for better

health outcomes. 

Targeted exposure assessment. A more

comprehensive description of actual

exposures of urban populations would

significantly enhance the ability to characterize

risk from ambient concentrations. A potential step toward this end point is the use of

broad-brush evaluations, such as the

National Air Toxics Assessment of the U.S.

EPA, to better delineate what chemicals may

be present in different communities.

Monitoring of emissions and exposures

could then potentially be targeted toward

specific chemicals. The use and further

development of passive dosimeters, for

example, would provide a noninvasive

means of monitoring VOC and other HAP

exposures that is both easy and practical.

Because of their ease of use, passive monitors

are an excellent tool for direct involvement

of communities in monitoring ambient concentrations and personal exposures.

Along with a better description of urban

exposures, additional research is needed on

the following components of exposure assessment in urban settings:

• Time–activity patterns in specific community settings.

• Ventilation characteristics of urban apartment buildings. It is hypothesized that

vertical flow may favor influx of trafficpolluted air at ground level.

• Microscale variations in ambient concentrations of HAPs as they relate to local

sources. Studies are needed on vertical as

well as horizontal gradients in concentrations over small spatial scales.

• Indoor/outdoor HAP relationships.

• The relationship between the political,

social, and economic context on the one

hand and pollution source-siting decisions

on the other.

• Better air quality emissions inventories,

to include both emissions factors as well

as location information, or techniques for

better specifying locations in the case of

small dispersed sources. Other model

improvements that may be important in

specific urban areas include certain

unique features of urban areas, such as

terrain and building downwash. Models

and methods for making better use of

community-based source inventory data

sets should be developed.

Community-level capabilities for carrying out exposure studies. The current capacity for community-based studies of personal

air pollution exposures in urban areas is

quite limited. Few communities possess the

technical expertise to tackle such studies

independently, and few scientists have yet

become engaged. Addressing these gaps will

require the formation of participatory CBR

partnerships in the form of active collaborations between research and community

groups in the conceptualization, design,

staffing, execution, analysis, and reporting of

community studies. This type of research has

potential advantages over nonparticipatory

community-based research or communitydriven research, including enhanced enthusiasm and support for the research at the

community level, greater study enrollment

rates, availability of community interns for

field work, increased credibility of findings,

greater understanding and acceptance of

research findings by the community, and

improved tools for community advocacy. 

One challenge to overcome is the tension

that often exists between the goals of community advocates and those of research scientists.

Community groups usually are in the position of advocating policy changes. Scientists

are often uncomfortable working in such settings because of concerns about the effects on

the scientific process and the possibility that

media attention and overinterpretation will

affect the ability to publish the data in peerreviewed journals. Another challenge is that

available technology for air monitoring is

often limited in utility and accessibility for

addressing personal exposures. Ideal technology would be affordable, portable, and provide real-time monitoring of criteria pollutant

and air toxic concentrations. Most current

technology, however, is expensive and blunt

in terms of temporal resolution.

In spite of these limitations, air monitoring

has an important role to play in communitybased studies of air pollution exposures.

Based on the experience gained in several

existing research partnerships, it may be possible to develop a standardized, inexpensive

research tool kit that could be adapted by

community groups for their own studies.

Aspects of the kit might include forms, protocols, and equipment for traffic counting and

PM2.5 and nitrogen dioxide sampling.

Health Effects Research

Characteristics that affect health can be at

the individual, neighborhood, community,

or even national level. Consequently,

research approaches, as well as intervention

strategies, differ across the spectrum from

individual to national levels of organization.

Recommendations were developed with consideration of the various levels of interaction.

Consensus on pertinent health indicators.

Numerous health indicators have been studied, as summarized in Table 1, and require

further analysis, but others need to be considered as well. Chronic and acute health effects

need to be considered separately. Whereas the

prevalence rates of some chronic health conditions such as asthma, atopy, cardiovascular

disease, and cancer are well documented,

there is a lack of sufficient baseline information on prevalence rates at local or state levels,

Environmental Health Perspectives • VOLUME 109 | SUPPLEMENT 3 | June 2001 365
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366 VOLUME 109 | SUPPLEMENT 3 | June 2001 • Environmental Health Perspectives

as for conditions childhood asthma. Also

lacking is experience with newer, more

sensitive outcomes, including

• Average level and daily variation of physiologic measures such as bronchial hyperresponsiveness, heart rate, and heart rate

variability.

• Biologic markers of exposure to ambient

air pollutants such as DNA adducts to

polycyclic aromatic hydrocarbons.

• Incidence of subclinical events such as respiratory symptoms and discharges of

implanted automatic cardiac defibrillators.

New or novel pollutant indices are also

needed, such as 

• Estimates of spatial and temporal gradients or profiles of exposure on fine scales.

• Subjective impressions of exposure to traffic, as well as objective indicators such as

measured proximity to major traffic arteries and automobile and truck counts.

• Direct, ongoing measurements of ambient

air pollutants including nitrogen dioxide,

carbon monoxide, ultrafine particle

counts, particle acidity, and bioaerosols

and their interactions with ambient and

indoor air pollutants.

Indicators of health outcome events can

be broadly grouped as mortality, medical

morbidity measures, and physiologic parameters. Mortality, both total and cause-specific,

is routinely available and well studied in relation to air pollution. Although mortality statistics have well-known limitations for

specific diagnostic groupings, the overall mortality rate is a fundamental measure of public

health. The rate of death from COPD is a

useful indicator of the frequency of the disease in the population, and asthma deaths

should be considered sentinel events. 

A variety of medical morbidity indicators

are available, although quality and completeness may vary depending on the types of

health systems in place. The Health Care

Financing Administration data on Medicare

enrollees provide virtually complete coverage

of significant health events in persons 65

years of age and older. The data files are cumbersome, but information on both hospitalizations and outpatient visits can be obtained.

For example, Medicare hospital admissions in

Chicago were analyzed to identify predisposing conditions for increased risk from air pollution (132). A nearly 2-fold increase in

hospital admissions for cardiovascular diseases

associated with air pollution was found

among patients with concurrent respiratory

infections. Similarly, individuals with asthma

were twice as likely to be admitted for pneumonia associated with PM10 than those without asthma. Other potential indicators of

events might be obtained from administrative

databases associated with health systems, such

as general hospitalization rates, emergency

room visits, prescriptions filled, and medical

devices sold. School or work absence rates,

although rarely used, are an additional

indicator of adverse events. 

Mitigation of nongenetic susceptibility

factors. Nongenetic susceptibility factors

have not been well studied in the context of

air pollution health effects. Community-level

factors can be broadly classified as socioeconomic indicators; rates of disruptive and

dangerous behaviors, including violent crime

and drug use; and measures of the adequacy

of the community’s structure, including

housing quality and adequacy of essential

services. At the household or individual level,

there are a variety of potential susceptibility

indicators, some reflecting environmental

exposures and others personal and lifestyle

characteristics. Additionally, higher-level factors may also be relevant, such as medical

care access and quality. Some of these nongenetic susceptibility factors are potentially

amenable to intervention. Housing quality

can be improved, for example, and overcrowding can be addressed. Unfortunately,

income—a critical determinant—is not

readily amenable to direct intervention.

Development of a national asthma

surveillance system. With asthma morbidity

being one of the most common and visible

health effects from air pollution, a national

asthma surveillance system is clearly needed

(133). Any asthma surveillance system must

address incidence, morbidity, and mortality.

To date, an effective system for monitoring

the incidence of asthma has not been developed. An understanding of asthma incidence

is necessary to address changes in prevalence.

A model approach could be developed in several representative locations, including the

possibility of using preschool and schools to

capture incidence from the responses to questionnaires completed by parents. Morbidity

needs to be tracked to capture the face of the

disease in the population. Again using schools

as an example, it might be possible to track

the number of inhalers maintained by the

school nurse. Finally, mortality should be

more fully utilized in an asthma surveillance

system, as it represents a sentinel event that

should always prompt investigation. Each

asthma death provides an opportunity to learn

more about potentially remediable exposures,

and use of case-based investigations for all

asthma deaths is strongly recommended.

Overall recommendations. Overall recommendations for the next steps in health

research fall into three broad classes: further

research on effects of specific factors, intervention research, and intervention programs. 

Research on effects. Nongenetic susceptibility factors that require further research

include diet, respiratory infections, and community stability and other characteristics.

This is far from a comprehensive list, but

serves as an illustration of the range of factors

that needs to be considered. For diet, for

example, studies might be carried out to

assess modification of the health effects of air

pollution by antioxidant supplementation or

dietary change. 

Intervention research. Intervention

research is needed on how to best implement

programs directed at exposures with characterized health effects, including exposures to

allergens, combustion sources, and overcrowding. Intervention research should also

be directed at such factors as access to medical

care, level of health knowledge, and health

behaviors. With allergen exposures, for example, clinical trials or other intervention

research with evaluation would be warranted. 

Intervention programs. Intervention programs need to be developed on the basis of

evidence from research on the efficacy of

interventions. For some factors, intervention

programs are already warranted on the basis

of available evidence, as with smoking and

housing quality.

Community-Based Intervention

Community-based research. The compelling

evidence that health inequities exist in urban

environments raises important questions about

why the economically disadvantaged are at disproportionate risk from asthma and other

adverse effects of outdoor air pollution. CBR

can be applied in a number of ways to identify

and reduce health disparities arising from air

pollutants in urban populations. By including

an action component, CBR distinguishes itself

from more traditional basic or clinical science,

which does not have a direct and immediate

impact on the community. Improvements in

health and living conditions are a priority for

most community-based organizations, as is the

power to make their own decisions and to take

actions to protect their health. For this reason

many scientists who use traditional approaches

are not familiar with the positive aspects of

CBR. Among the attributes that communitybased approaches offer are

• Research efforts are more cost-effective,

with communities offering staff, facilities,

and other resources that can leverage the

traditional academic environment.

• Data collection is of better quality and

quantity, provided the staff is properly

trained and supervised.

• Recruitment and retention within studies

are better when community members are

more directly involved.

• Input from the community on what may

or may not be effective can result in

improved and novel hypotheses, study

designs, and evaluation methods.

• Knowledge and findings can be applied

more readily to intervention strategies.
Urban air pollution and health inequities

• Data on community-identified concerns

can be translated into action by the people affected.

• More successful translation of science to

policy will lead to more informed public

policy decisions.

• Health considerations can be inserted into

economic development dialogues.

• Interventions are more likely to be sustainable with community participation in

their development.

• Collaborations increase credibility, recognition, and trust for both community

members and academic researchers.

Despite these advantages, CBR remains

only a fraction of the total effort devoted to

population-based research. A number of barriers, some of which are intuitive, account for

the difficulties associated with developing and

promoting CBR on a broader scale:

• Academic recognition for CBR is not

always the same as that devoted to more

traditional public health research.

• Credibility for community members is

threatened when they risk becoming more

closely associated with academic scientists

rather than their grassroots colleagues.

• Credibility for scientists is questioned

when they risk becoming more closely

associated with advocacy groups.

• Expectations of the groups differ.

Communities may expect to have their

problems identified and solved. Scientists

may expect to publish a number of articles on an annual basis.

• Difficulty in establishing trust.

• Limited financial resources.

• Limited time.

A potential strategy to optimize CBR on

eliminating exposures contributing to health

risks requires understanding of the factors

leading to differential exposures. Recognizing

that community interests in resolving

inequities will differ, only a general discussion

of overarching strategies is presented. These

are organized along the lines of the primary

pathways to health inequities related to urban

air pollution: pollutant sources, education and

training, community infrastructure and services, and the planning and financing process.

Pollutant sources. Some communitybased strategies to address the disproportionate number of sources in highly affected

communities include

Source reduction. Local point sources like

bus and truck depots, dry cleaners, auto-body

shops, hair salons, and other polluting facilities are examples of common sources in urban

communities. These sources often affect

receptors both indoors and outdoors.

Community-based strategies to reduce

sources often are framed as the struggle for

environmental justice and take many different forms including political, legal, and

educational campaigns. Mobile sources in

particular are major contributors to air pollution in most urban communities. Strategies

to reduce traffic (e.g., campaigns to improve

public transit) are particularly important for

reducing health inequities. Stationary polluting facilities can significantly reduce air emissions by using best management practices. 

Cleaner fuels. Because mobile sources are

a major source of pollution in urban neighborhoods, using vehicles that emit lower pollution levels through the use of cleaner fuels is

one strategy for reducing air toxics in highly

affected communities. A community-driven

campaign for cleaner fuels in public bus and

truck fleets is one strategy toward that end. 

Cleaner products. Encouraging the use of

cleaner products in both businesses and

households is another strategy to reduce pollution sources and consequent health inequities

in urban communities. Chemical and toxic

products can add to urban air pollution.

When hair salons reduce their use of chemicals and households use less-toxic cleaners,

fewer toxics are released into the indoor and

outdoor environment. Educational campaigns for both businesses and residents are

one strategy to encourage the use of cleaner

products. Making cleaner products more

accessible and affordable in urban communities is another strategy. 

Education and training. The lack of

knowledge about the relationship between

pollution sources, receptors, and resulting

health effects is one of the root causes of

health inequities from air pollution.

Healthcare providers, residents in highly

affected areas, and regulators all lack the

information necessary to take real action.

Some community-based intervention strategies to address this lack of knowledge include

the following:

Healthcare provider education.

Specifically, there is a need to include curricula in both medical schools and continuing

medical education forums on the relationship between outdoor air quality and health

effects. By including this kind of curriculum

in medical schools, there is an opportunity to

train future doctors and healthcare providers

to recognize and explore the connections

between urban air pollution and health

inequities. Practitioners will be better

reached by continuing medical education

methods. Other means of educating healthcare providers about these issues include

grand rounds, peer education, and partnerships with community health workers.

Recruitment of scientists of color and

other ethnic minorities. Currently there are

few scientists of color and other ethnic

minorities working on public health issues.

By exposing young people from highly

affected communities to public health and

medical fields at an early age, there is an

opportunity to attract them to these careers.

Ultimately, this may lead to more scientists

concerned about and researching these issues.

Public health curricula in public schools,

medical and healthcare internship opportunities, and scholarships for scientific fields are

all strategies to engage and train ethnically

diverse scientists.

Patient/resident education. One strategy

to reach residents in highly affected communities is through patient groups where

patients suffering from similar diseases meet

regularly to discuss causes and management.

Another is through public schools. Curricula

on public health, specific diseases (like

asthma), and environmental issues can help

students of many levels understand the relationship between urban air pollution and

health effects. Curriculum materials and

information can then reach parents and families through the students. Working with

school nurses can be an excellent means of

reaching students who are highly affected by

urban air pollution. Because they see students

suffering from asthma regularly, they are in a

position to share information about the disease and possible environmental triggers with

both students and families. Once armed with

information about the relationship between

pollution sources, receptors, and health

effects, residents in highly affected areas can

use a number of strategies (e.g., community

organizing, political advocacy) to reduce pollution sources and health inequities.

Regulator education. Regulators also lack

adequate information on the relationship

between exposure and health effects, particularly in the context of exposure inequities.

Without this information it is extremely difficult to create regulatory strategies that effectively address health inequities. 

Community infrastructure and services.

One of the major root causes of health

inequities resulting from urban air pollution

is the lack of access in low-income communities and communities of color to quality

housing, transportation, healthcare, and other

social resources. Community-based interventions to address these social problems are

complicated. They include efforts to improve

• Quality of housing in highly affected

communities. Poor indoor environments

such as those with mold, dust mites,

rodents, or cockroaches can add to or

exacerbate health inequities resulting from

urban air pollution.

• Access to and quality of public transportation. This will not only help to reduce

traffic, but will facilitate access to quality

jobs and healthcare.

• Access to and quality of healthcare. Many

residents of low-income neighborhoods

and communities of color are forced to

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use emergency room care rather than

basic maintenance care to address health

problems. As a result, diseases like asthma

are much more serious and many more

people are hospitalized than in communities where disease management is more

adequate. 

• Other social concerns such as education

and job training. Without adequate education and employment, access to basic services such as healthcare is impaired. In

addition, scientific research is showing that

psychosocial stressors play a role in health

inequities from urban air pollution and

other environmental problems (134–136). 

Planning and financing process. The

process and opportunities by which disenfranchised communities become involved in planning and financing activities affecting their

lives should be improved. Often we find that

communities with inequitable exposures to air

pollutants also encounter poor housing, poor

schools, higher unemployment, and fewer

options for healthcare. Where these communities comprise more recent immigrants, they

tend to be disconnected from public participation because of language barriers and mistrust

of government. CBR strategies for addressing

these problems include the following:

Developing a code of “Best Practices for

Community-Based Research.” Such a code

should include guidance on how to more

fully incorporate community participation.

Negotiating among competing interests of

scientists, community activists, public agencies, and community members is often not an

explicit activity for CBR, but needs to

become so. 

Forming a multidisciplinary team of

investigators. Effective treatment of complex

societal problems requires not just epidemiologists, biostatisticians, and environmental scientists, but also others experienced in public

finance and administration, community organization, and social sciences, among other

specialties. CBR needs to be based in a capacity to assess underlying causes, not just overt

symptoms of inequities.

Recognizing that communities have

assets, not just problems. In order for our

academic institutions to play a meaningful

role in CBR, it is important to also acquire

the experiential sensitivity that comes from

those who have lived with inequities. Often

we find well-intentioned investigators who

have had all their formative education and

experiences shaped by middle-class American

values. Working with underserved urban

populations requires a reframing not easily

understood by many academic scientists. One

method of ensuring that both research and

interventions are adequate and address the

problem at hand is to involve community residents at all levels of research, intervention,

and policy development. Residents living in

communities suffering from health inequities

related to urban air pollution can provide

information and expertise that is vital to successful research, but often ignored. 

Developing competent staff and professionals from the ranks of racial/ethnic minority groups through training programs.

Funding agencies should recognize this as a

specific need and provide new categories of

training. A focus on CBR must be incorporated into individual and institutional training

programs in environmental health, especially

those in epidemiology. Moreover, although

separate funding is already available for

minority candidates for advanced scientific

training, funding is needed for internships for

high school and college students to work

directly on CBR. Targeted funding to develop

interest and experience among promising

young people will also help to bridge the sensitivity gap of investigators. An interest among

minorities for careers in environmental and

public health sectors should be cultivated by

exposing high school and college students

early on to the skills and knowledge required

of these professions. The mentoring that will

take place as these students work closely with

staff and investigators on CBR projects will

motivate educational choices. In addition, it is

critical that students are well advised on the

high school and college curricula that prepare

them for advanced studies.

CBR offers the opportunity to confront

disproportionate exposures and health effects

from a participatory, action-oriented framework that unites disparate groups, leverages

individual resources, and influences research,

intervention, and policy at all levels. Public

participation is fundamental to CBR and presents the best means of addressing health disparities in an effective and efficient manner.

To facilitate this process, long-term support

for community-based organizations and for

researchers conducting such work is required.

Coalitions among communities, scientists

and providers need to be fostered. In addition, similar partnerships among industries,

unions, and regulators can lead to enhanced

management practices. Finally, the underlying social environment and its contribution

to health inequities must be better understood at the time we address the physical

environment, thus requiring collaborations

among behavioral and biomedical scientists.

With contributions from all of these parties,

community-based strategies can be developed

to assess and reduce hazardous exposures and

to prevent adverse health effects.

Public Policy

Management of differential air pollution

exposures though public policy needs to be

viewed in the broader context of distributive

inequities across society. Under Executive

Order 12898 (6), federal environmental regulatory programs must address differential distributions of exposure. Early analysts of clean

air regulation recognized equity as a trade-off

between two competing forces. On one hand,

air pollution control measures had a regressive economic impact on low-income and

racial/ethnic minority communities, costing

those at the bottom of the economic ladder

much more than those at the top. On the

other hand, those same measures promised

greater net improvements as uniform standards took hold in these same disproportionately polluted communities (42 USC Sections

1857c-4, 1957c-5, reflecting the Clean Air

Act as passed in 1970, promised uniform pollution control “regardless of where...persons

reside” across the land) (137,138).

The principal regulatory structure for

addressing ambient air pollution, the Clean

Air Act of 1970 (102), provides different control strategies for ambient air (or criteria) pollutants and HAPs (139–141). Although the

U.S. EPA is responsible for promulgating

ambient air quality standards for the criteria

pollutants, the states must develop SIPs to

attain and maintain these standards according

to time lines established in relation to the

baseline air quality of each state. Factored

into the planning process at the state level are

the U.S. EPA mobile source emissions standards, though some states, notably California

and several in the Northeast, have been

granted a statutory dispensation to develop

more stringent emissions standards. The

HAPs program was amended in 1990 to

require stationary sources of 189 specified

toxicants to effectuate 90% emissions reductions by the end of the decade, using existing

technologies (142). Any further reductions

after that time are to be based on an assessment of residual risks. In some states, regulation of stationary sources falls within the

jurisdiction of local air pollution control

agencies; in others, regulatory efforts are concentrated at the state level. 

Multiple opportunities exist to address

environmental justice concerns in the regulatory programs for criteria pollutants: a) standard-setting; b) establishing requirements for

monitoring, including siting criteria; c) developing and reviewing SIPs submitted by the

states; d ) reviewing permit decisions made by

state and local air pollution control agencies;

and e) imposing more stringent requirements

for public participation at all stages of the regulatory process, which would also be facilitated

by increasing data availability and transparency. The U.S. EPA could also apply the

latter two strategies to the HAPs program and

could, in addition, incorporate incentives for

reducing health inequities into the agency’s

cross-pollutant initiatives, such as the Urban
Urban air pollution and health inequities

Air Toxics Strategy (143) and the Economic

Incentives Program (144). The directives of

Executive Order 12898 could be invoked at

each level. We present several examples.

Air quality standard-setting. Ambient air

quality standards are to be set with a margin of

safety adequate to protect public health (140).

Such standards are not intended to provide

absolute protection to all individuals, but the

legislative history of the Clean Air Act makes it

clear that identifiable susceptible subgroups

such as persons with asthma should be protected. It could be argued that such recognition should be explicitly extended to large

subsets of susceptible subgroups. Such a subset

might include poor, urban, African Americans

with asthma who may be rendered more susceptible to the health impacts of air pollution

by suboptimal access to appropriate medical

care, widespread exposures to indoor aeroallergens and tobacco smoke, and a variety of other

psychosocial, nutritional, and environmental

stressors. Although it is still uncertain whether

such persons with asthma are differentially susceptible to the impacts of air pollution, such

concerns could be factored into the margin of

safety component of ambient air standards.

Under Executive Order 12898 this scenario, or

others representative of the urban poor, may

warrant consideration by the U.S. EPA.

Monitoring requirements and siting criteria. In principle, the states and local air districts, which are responsible for siting and

operation of air quality monitors, are required

to locate some monitors in hot spots as well

as in sites representing regional rather than

local pollutant concentrations (145). In many

jurisdictions, the vast majority of criteria air

pollutant monitors are sited away from hot

spots, as the latter are considered unrepresentative of regional population exposures. Thus,

an air basin or a state may be considered to be

in attainment with the federal ambient standard for a given pollutant even though substantial numbers of people residing, working,

or going to school near busy roads or stationary sources may be exposed to concentrations

exceeding the standard. Recent studies have

indicated that low-income and racial/ethnic

minority communities live in closer proximity to such hot spots than other population

groups (146,147).

Intense, localized monitoring efforts are

needed for hot spot identification and exposure reduction. The U.S. EPA should provide

specific guidelines to state and local authorities to monitor traffic-related and pointsource hot spots affecting substantial numbers

of people. There are also opportunities for

collaboration among community groups, university researchers, and regulatory agencies in

the identification and pilot air monitoring of

such hot spots. The results of hot spot monitoring should also be factored into criteria for

determining attainment with ambient air

quality standards.

Although the issue of hot spots highlights the difficulty of monitoring for

inequities across different spatial scales, lack

of long-term monitoring data pertinent to

many low-income and racial/ethnic minority

communities is an equally substantial obstacle to meaningful health interventions. The

decommissioning of monitoring networks

(due to urban economic crises over the last

20 years in cities like New York; Cincinnati,

Ohio; Gary, Indiana; and Detroit,

Michigan) has left inadequate data for many

inner-city communities to evaluate relationships between contemporary disease patterns

and historical air pollution trends. In the

interest of study design, major personal

exposure studies have omitted racial/ethnic

minority populations (27). Only recently

has there been renewed interest in understanding personal exposure in urban

communities (119,148).

State Implementation Plan review and

development. The NAAQS are set by the U.S.

EPA for carbon monoxide, lead, nitrogen

dioxide, ozone, PM, and sulfur dioxide, as

mandated under the Clean Air Act. Lowincome and racial/ethnic minority people live

in disproportionately high numbers in areas

out of attainment with the NAAQS and are

thus dependent on air quality policy and regulation for eventual relief (149,150). SIPs are

required for all such nonattainment areas and

embody a jurisdiction’s policy priorities for

clean air. These plans offer the structure

within which local and regional air quality is

regulated. The major concerns of urban communities are the equity implications of core

SIP provisions like emissions trading, transportation control measures, and other technologic or regulatory mandates. 

Emissions trading. In the name of economic efficiency, many economists and regulators have embraced the concept of

market-based emissions trading as a costeffective way to improve regional air quality.

For instance, large stationary sources may

contribute to vehicle buy-back programs

intended to remove older, more highly polluting vehicles from circulation. A local

source that has contributed to such a program may then receive credits against its own

emissions, allowing it to forego emissions

reductions that might otherwise be required.

This approach may lead to a net regional

reduction in air pollution while allowing

continued or increased exposures at the local

level. A number of state and local air pollution control districts have encouraged the

trading of VOCs or HAPs as a way of reducing regional ozone precursors, yet point

sources of these same pollutants may pose

even greater risks to local communities.

Undesirable distributional outcomes are an

inherent risk for any system developed primarily to ensure efficiency, and emissions

trading is no exception (151).

In many cases, emissions trading is a

compliance alternative available to local

authorities in lieu of specific SIP measures,

but verifiability and enforceability of trades

may be problematic. In the case of mobileto-stationary trades, vehicle scrapping programs may not achieve reductions above and

beyond normal obsolescence. In Los

Angeles, local officials have sought credit for

reductions in military flights completely

unrelated to air pollution control measures

(152). Such trades may not meet the legal

threshold of being surplus or above and

beyond what would normally have been

expected to happen. 

A number of environmental justice

groups, particularly in California, have suggested the elimination of emissions trading

(153), or at the very least, great caution in its

deployment. General criteria for limiting

trades have been proposed:

• Ensure no net increase in air pollution in

heavily affected communities, defined as

those currently in violation of ambient

standards for criteria pollutants or their

precursors (154). Specifically, in-trading

to such areas could be proscribed. Even

for communities currently below the

ambient standards, the potential cumulative health impacts in a community

should be considered in HAPs trading

when emissions are projected to increase

above existing baseline emissions. 

• Endow lower-income communities with

property rights within the trading system.

Regulatory authorities could allocate trading credits to heavily polluted communities, which would allow them to negotiate

with more distant intraregional point

sources to effectuate reductions locally

(e.g., through the purchase of low-emitting mass transit vehicles). 

• Assure verifiability and enforceability of

trading practices. Given the discretion

granted regulators and polluters in most

trading programs, higher standards of

accountability must be introduced to

ensure that trades that do occur in fact

lead to permanent reductions in the overall emissions inventory. 

Objective, reliable judgments about the

efficacy of these or other criteria would be

promoted by standardizing methods for

quantifying emissions reductions, which currently vary substantially among and, in some

cases, within jurisdictions (152). Such standardized methods should be promulgated at

the federal rather than at the state or local

level in order to achieve widespread uniformity and predictability in application. 

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Transportation control measures, and

other State Implementation Plan–based

policy initiatives. A wide range of initiatives

pertaining to infrastructure, mass transit,

regional planning, and technology change

(e.g., low-emission vehicles) is written into the

Clean Air Act Amendments of 1990 (142)

under the rubric of transportation control

measures. The emphasis placed on different

measures and the timing under which they

are introduced have significant implications

for the health and well-being of urban communities. New road usage fees and construction, new mass transit projects, and altered

planning priorities all offer the hope of reducing emissions. They also have the potential,

however, to disrupt the economic viability of

inner-city communities. In Los Angeles, for

example, analysis of plans had shown that the

new subway would have an adverse impact on

racial/ethnic minority bus riders while providing minimal service in their communities

(155). New road usage fees and stricter tail

pipe controls also have a disproportionate

impact on poorer commuters (156,157).

Stricter environmental controls on small

industries often threaten the livelihoods of

already marginal employees (158). These

issues can and should be considered and

addressed in the development and implementation of air pollution control strategies.

From an environmental justice perspective, the SIP is a two-edged sword. It is the

blueprint for a region’s compliance under the

Clean Air Act, but without environmental

justice stakeholder participation in its design

and close attention to the equity impacts of

its implementation, it can exacerbate environmental conditions in local communities.

Permitting and environmental justice.

One key mechanism of disproportionate

exposure may be the issuing of permits by

state and local regulatory agencies to facilities

in close proximity to vulnerable populations,

or the failing of the agencies to trigger permit

and/or new source review requirements. In

the latter case, the cumulative effect of a

number of small facilities may be enough to

create air pollution hot spots. Consequently,

the siting of permitted facilities has come

under increased scrutiny in recent years.

Title VI of the Civil Rights Act prohibits the

use of federal funding in activities that lead

to discriminatory outcomes (159). This provision has been invoked in recent times to

challenge local and state permitting processes

that may have led to a disproportionate local

pollution burden. Many complaints filed

under Title VI in the past few years have

been against air permitting programs (160).

Although at the time of this workshop the

U.S. EPA was still drafting guidelines for

permitting compliance with Title VI, state

and local agencies should consider Title VI

for preventing disproportionate siting of

noxious facilities in urban communities. 

Some facilities with significant local air

quality impacts may not fall under SIP permitting requirements, depending on the

jurisdiction. These include waste transfer

stations, bus depots, small industry, and new

commercial or residential development.

Nonattainment areas are, however, often

still required to account for such facilities

under federal, state, or local environmental

impact requirements. New York City, for

example, requires no individual permits for

over 270 transfer stations in its five boroughs. Many persistent local sources of air

pollution can only be addressed through

renewed attention to the environmental

review process at the facility level. A number

of tools exist to improve this process. For

example, several U.S. EPA regions and some

states and localities have added a cumulative

dimension to environmental impact reviews

to better contextualize the overall burden

faced by local communities. The addition of

performance standards for siting facilities

that otherwise comply with zoning codes

represents another innovative approach to

incorporating air quality concerns in land

use regulations. Finally, the environmental

review process itself needs to be taken more

seriously by local government and stakeholders. Clean air will not come as a result

of a “rubber-stamp” process. Environmental

review of siting and development decisions

often represents the only regulatory handle

available for bringing the bulk of a region’s

polluting activities into compliance. 

Public participation and increased data

availability. Substantive public participation

is a fundamental concept of environmental

justice. In principle, public participation is

already an administrative requirement in the

SIP process (102,142). Attempted notification of the public through newspaper

announcements alone, however, will not

reach large numbers of individuals who have

a legitimate stake in the process. The U.S.

EPA, as well as state and local regulatory

agencies, could expand public participation

requirements and practices consistent with

Executive Order 12898. For instance, active

local involvement in siting decisions could be

enhanced through specific outreach to

community-based organizations, churches

and other religious agencies, and possibly

directly to individual residents (161). 

To facilitate public participation, air quality and emissions data should be made widely

available, and all the steps leading to data

publication should be as transparent as possible. For example, agencies at local, state, and

federal levels could make relevant emissions,

monitoring, and modeling data readily accessible (e.g., on the Internet) in user-friendly

formats as soon as such data have received

appropriate internal reviews. In publishing

data electronically, agencies should also

ensure that underlying raw data (i.e., those

that have been subject to standard quality

assurance/quality control) can be accessed so

that users can derive reports useful to their

specific needs. Agencies should attempt to

give a context to such data to avoid unnecessary confusion while at the same time increasing their outreach to assist community

organizations to understand, evaluate, and

use the information. 

To remedy the historical underrepresentation of poor urban populations in environmental decision making, agencies should also

consider forming specialized stakeholder

groups for environmental justice. Such

groups can provide useful, direct policy feedback and can also help ensure broader participation in specific cases. New Jersey,

California, and New York are a few of the

states that presently have statewide committees advising decision makers on environmental justice policies. Local governments should

follow suit. 

Measures to address diesel emissions.

Within urban areas, fleets of diesel-powered

buses and trucks represent a significant source

of exposure to fine particles, VOCs, nitrogen

oxides, and other toxicants. Though some

transit agencies and school districts have considered the air quality impacts of their activities, others have continued to augment their

fleets with diesel technology. Several

approaches to reduce the urban burden of

diesel exposures include the following:

• Providing funding incentives to transit

agencies to purchase compressed natural

gas, electric, or other less-polluting vehicles.

• Providing federal guidance for stricter

interpretation of transportation conformity rules that govern the methods that

state and local agencies must follow in

preparing an emissions budget for transportation.

• Requiring diesel inspection and maintenance, if not emissions control retrofits,

for heavy- and medium-duty diesel vehicles as a part of the SIP process.

• Requiring the production and use of

cleaner, reformulated diesel fuels similar

to those used in Sweden, and the retrofit

of state-of-the-art pollution controls on

existing diesel fleet vehicles.

Odor control. Uncontrolled odors represent one of the major inequities of exposure

to stationary source pollution. With the

diminution of grossly visible pollution from

stationary sources, olfactory cues have

become more important in public perception

of air pollution. Exposure to unpleasant odors

can result in annoyance and interference with

one’s quality of life and may also produce
Urban air pollution and health inequities

headache and nausea and elicit respiratory

symptoms in some individuals with asthma

(162). In the 1970s the U.S. EPA opted

against developing any national strategy to

address odors (163). In the absence of

national regulatory guidance, local districts

rely on complaint-based systems for enforcement, which are variations of common-law

remedies for public nuisances. Numerous

institutional aspects of such complaint-based

systems impede resolutions satisfactory to the

surrounding communities (164).

Odor pollution can be addressed at both

the federal and local levels. For a selected number of common, well-characterized odorants,

the U.S. EPA could develop ambient exposure

standards to be enforced at the local level. As

this undoubtedly would take several years to

accomplish, local agencies could require

interim odor pollution prevention measures,

rather than emissions control technology.

Urban air toxics. The Urban Air Toxics

Strategy (143) is a program for cross-pollutant and cross-media toxics reduction. The

Economic Incentives Program (144) provides local and state agencies with a wide

array of economic tools for reducing air pollution. Both of these U.S. EPA programs

hold promise and risks. Failure of community members to participate in the Urban Air

Toxics Strategy process may lead to the

development of toxics reduction plans that

may not address the concerns of those communities most affected. The U.S. EPA could

take additional steps to give affected communities a formal stake in the process, such as

facilitating opportunities for early and

meaningful participation in regional deliberative processes. In the Economic Incentives

Program, low-income communities could be

endowed with credits that would allow

them to trade out high pollution levels.

Furthermore, Economic Incentives Programs

should prohibit trades that raise local hot

spot pollutant concentrations, and provide

incentives for trades that remove sources

from those communities.

Currently, there is no mandate for federal,

state, or local air permitting authorities to

consider siting issues while evaluating permit

applications. Failure to consider the aggregate

of localized emissions in this process has,

however, led to clustering of large stationary

sources in some communities. To remedy this

Environmental Health Perspectives • VOLUME 109 | SUPPLEMENT 3 | June 2001 371

Jonathan M. Samet (Chair)*

Department of Epidemiology

Johns Hopkins School of Public Health

Baltimore, Maryland

Allen Dearry*

National Institute of Environmental Health Sciences

National Institutes of Health

Research Triangle Park, North Carolina

Peyton A. Eggleston

Division of Immunology and Allergy

Department of Pediatrics

Johns Hopkins Hospital

Baltimore, Maryland

Jean Ford

Division of Pulmonary Medicine

Harlem Hospital Center

New York, New York

John Froines

Center for Occupational and Environmental Health

Department of Environmental Health Sciences

School of Public Health

University of California — Los Angeles

Los Angeles, California

Michel Gelobter

Graduate Department of Public Administration

Rutgers University

Newark, New Jersey

Henry Gong, Jr.*

Environmental Health Service

Rancho Los Amigos Medical Center

Downey, California

Patrick L. Kinney*

Department of Environmental Health Science

Columbia School of Public Health

New York, New York

George D. Leikauf

Departments of Environmental Health,

Physiology/Biophysics and Medicine

University of Cincinnati Medical Center 

Cincinnati, Ohio

Michael Lipsett

Department of Epidemiology and Biostatistics

School of Medicine

University of California, San Francisco

San Francisco, California

Jamson S. Lwebuga-Mukasa

Department of Medicine

Buffalo General Hospital

Buffalo, New York

David Mannino

National Center for Environmental Health

U.S. Centers for Disease Control and Prevention

Atlanta, Georgia

William McDonnell

Human Studies Facility

U.S. Environmental Protection Agency

Chapel Hill, North Carolina

Maria T. Morandi

Environmental Sciences

School of Public Health

University of Texas — Houston

Houston, Texas

Lucas M. Neas

Human Studies Facility

U.S. Environmental Protection Agency

Research Triangle Park, North Carolina

Carlos Porras

Communities for a Better Environment

Los Angeles, California

Shankar Prasad

California Environmental Protection Agency

Sacramento, California

Stephen Redd*

National Center for Environmental Health

U.S. Centers for Disease Control and Prevention

Atlanta, Georgia

Margo Schwab

Risk Sciences and Public Policy Institute

Johns Hopkins School of Public Health

Baltimore, Maryland

Tony Servin

California Air Resources Board

Sacramento, California

Peggy Shepard*

West Harlem Environmental Action

New York, New York

John D. Spengler

Environmental Science and Engineering Program

Department of Environmental Health

Harvard School of Public Health

Boston, Massachusetts

Jodi Sugerman-Brozan

Alternatives for Community and Environment

Roxbury, Massachusetts

Nicholas Targ

Office of Environmental Justice

U.S. Environmental Protection Agency

Washington, DC

Deborah Wallace

Center for Children’s Environmental Health

and Department of Sociomedical Sciences

Joseph L. Mailman School of Public Health

Columbia University

New York, New York

Rod Wallace

Epidemiology of Mental Disorders Research

Department

New York State Psychiatric Institute

New York, New York

Ronald H. White*

American Lung Association

Washington, DC

Tracey Woodruff

National Center for Environmental Economics

Office of Policy, Economics and Innovation

U.S. Environmental Protection Agency

Washington, DC

*Workshop Organizing Committee

Appendix. Workshop Participants.
American Lung Association

372 VOLUME 109 | SUPPLEMENT 3 | June 2001 • Environmental Health Perspectives

problem and avoid creating new hot spots, all

permit applications could be evaluated in

their site-specific context, including an assessment of potential cumulative health impacts

(e.g., cancers, acute and chronic effects)

within the affected community. 

In many states, evaluation of potential

cumulative and other health effects of exposure to air pollution is hampered to various

degrees by the institutional separation of public health and risk assessment expertise from

regulatory authority. Forging better organizational linkages between public health agencies

and those responsible for implementing air

pollution control strategies would likely be

helpful not only in siting and permitting

decisions, including the evaluation of environmental impact reports, but also in helping

to address other community concerns about

localized health impacts of air pollution.

Conclusions

The term environmental justice summarizes

an extraordinarily complex set of social,

political, economic, ethical, and scientific

issues in only two words. For urban air pollution, there are disproportionately greater

exposures to the poor and to minorities—a

problem of environmental justice—as made

clear by the available monitoring and modeling data, as well as by the experiences of

communities. This workshop explored the

environmental justice problem of urban air

pollution in depth, considering the tools

available to characterize the problem, the

needed research evidence to find solutions,

approaches through community-based

mechanisms to carry out the research, and

policy approaches to address inequities of

urban air pollution. Although the workshop

proceedings document a formidable

research problem, useful tools and research

approaches are already available, and the

participants set out a template for their

application. Pathways for gathering existing

evidence for policy development are also

proposed. However, success will not be

achieved without multidisciplinary research

groups that include communities as partners. A long-range, progressive research

agenda is needed, and funding agencies will

need to make the appropriate commitments. New pathways to policy formulation

may be needed, particularly to assure that

the disproportionately exposed communities are given sufficient voice in policy

development. 

This workshop offers many suggestions

for starting to address urban air pollution and

health inequities. The participants were optimistic that much can be accomplished to

reduce the risks of urban air pollution; it is

time to start a major, national program to

achieve that goal. 

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