United States
Environmental Protection
Agency
Environmental Monitoring
Systems Laboratory
Research Triangle Park NC 27711
Research and Development
EPA-600/S4-84-034 May 1984
Project Summary
Final Sampling Report for the
Study of Personal CO Exposure
Roy W. Whitmore, Shelton M. Jones, and Martin S Rosenzweig
This report describes the sampling
design phase of a study funded by the
EPA and conducted by the Research
Triangle Institute in 1982 and 1983 to
evaluate methodology for collecting
representative personal exposure
monitoring (PEM) CO and correspond-
ing activity data in an urbanized area.
This involved telephone screening of
households and sample selection of
respondents in the metropolitan areas
in and around Denver, Colorado and
Washington, DC. Data on CO breath
levels were also collected in
Washington, DC. (PEDCo Environ-
mental conducted the field work in
Denver.) The target population in both
cities consisted of the non-institutional-
ized, non-smoking adults (ages 18 to
70) of these metropolitan areas. The
sampling design in each city was a
stratified three stage design. Area
segments were selected at the first
stage; households were selected at the
second stage; and individuals were
selected for monitoring at the third
stage.
Based on the experience gained
during the study, the methodology
developed, with some modifications,
may be used effectively in other areas of
the country for collecting PEM data.
Modifications of the sampling design
should make the methodology more
cost effective and improve the response
rate.
This Project Summary was developed
by EPA's Environmental Monitoring
Systems Laboratory, Research Triangle
Park. NC. to announce key findings of
the research project that is fully docu-
mented in a separate report of the same
title (see Project Report ordering infor-
mation at back).
Introduction
As the control of emissions increases,
the burden of proof on EPA to show that a
particular level of emission control is
justified also increases. It has become
more and more important to show that a
given level of control is justified for each
air pollutant with the relative risk of
public health approximately comparable
for each pollutant controlled.
A critical factor in determining the
degree of risk to the population is the
exposure of members of the population.
In the past, monitoring of airborne pollu-
tants has necessarily been based on the
assumption that fixed-site monitoring is
representative of concentrations sur-
rounding the site, since monitoring
techniques were generally not developed
for determining personal exposures.
Then to obtain estimates of population
exposure, techniques such as computer
simulation or overlaying isopleths of
pollution concentrations measured at
fixed sites on population density maps
have been used. For some pollutants,
these techniques may be reasonable
approximations; however, recent work
has shown that many pollutant
concentrations are not homogeneous and
that activity patterns play an important
role in an individual's actual exposure.
Therefore, data from ambient fixed sites
often differ significantly from the concen-
trations with which people actually come
into contact.
Accordingly, RTI and EPA formulated a
study plan to develop and field test a pop-
ulation exposure methodology using CO
while making sure that the methodology
was broad enough to accommodate other
pollutants of concern. The specific objec-
tives of this study were the following:
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To develop a methodology for meas-
uring the distribution of carbon
monoxide (CO) exposures of a
representative population of an
urban area for assessment of the risk
to the population.
To test, evaluate, and validate this
methodology by employing it in the
execution of pilot field studies in
Denver, Colorado, and in Washing-
ton, DC.
' To obtain an activity-pattern data
base related to CO exposures.
Carbon monoxide was selected for
primary emphasis in the current study
because:
• Accurate and portable field tested
instruments now are available for
CO.
• Most of the CO to which the public is
exposed can be attributed to
motor vehicles.
• It appears that CO is a good "indica-
tor" (i.e., surrogate) pollutant for esti-
mating exposures to several other
motor vehicle pollutants of interest.
• Because CO is a nonreactive air pol-
lutant, it is simpler to treat
analytically.
• The health effects of CO are reason-
ably well documented, and NAAQS
based on these effects have been
promulgated.
• Considerable data exist showing that
CO varies spatially and that many
locations in cities have concentra-
tions that differ from those reported
at fixed air monitoring stations.
The study was carried out in Washing-
ton, DC and Denver, Colorado during the
winter of 1982-83 (the period of the year
with maximum ambient CO concentra-
tions). The population exposure
profile was determined by direct
measurement of CO with personal
exposure monitors (PEMs) through the
use of statistical inference from the
statistically drawn sample. The study
provided sufficient data to determine
exposure as a function of concentrations
within significant microenvironments
(home, in-transit, work, and leisure) and
individual activity patterns.
The report describes in detail the sam-
pling design employed, and recommen-
dations for improving the sampling
design for future monitoring studies of a
similar nature. It is extremely important
to note that the study not only developed
and tested methodology for measuring
the distribution of CO in an urban area but
also produced direct estimates of CO
exposure that apply to two large
metropolitan areas. In addition, a very
important product of this work is a unique
and valuable database on individual
exposures to CO and the corresponding
activities that led to these exposures.
Summary of Sampling Design
The target population consisted of the
non-institutionalized, non-smoking
adults (ages 18-70) in the metropolitan
areas in and around Denver, Colorado
and Washington, DC. A probability
sample of the target population was
selected in both cities. This sample was a
stratified, three-stage, probability-based
design. Area sample segments defined by
Census geographic variables were
selected at the first stage of sampling.
Households were selected at the second
stage, and a household member was
administered a short screening interview
covering all household members to
identify individuals with characteristics
believed to be positively correlated with
CO exposure. Household members with
these characteristics were oversampled
in the third stage. Donnelley Market
Corporation listings were used to help
select households for the screening
interview. The third stage sample was a
stratified sample of screened eligible
individuals (i.e., non-smoking, aged 18 to
70). The individuals in the third stage
sample were administered a Computer
Model Input Questionnaire and were
asked to carry a personal CO monitor and
an Activity Diary for 24 or 48 hours (for
Washington and Denver, respectively). A
breath sample was also requested from
these individuals and they were asked to
fill out a Household (Study) Questionnaire.
The third stage sample design also
allocated individuals to specific days
within the sampling period. A detailed
discussion of the sample design is given
in the report.
To carry out the sample design, RTI
developed the data collection instruments
and worked with EPA in obtaining OMB
approval for the study. An initial
telephone screening was carried out in
both Denver and Washington, DC by
using RTI's Computer Assisted
Telephone Interviewing (CATI) system.
This telephone screening was
supplemented by limited field screening
in both sites. Specific information
collected during this interview included:
time spent in regular commuting and
smoking status of each household
member, as well as presence of gas
appliances and attached garages in their
residences. After the initial screening
and the initial selection of potential
participants, another telephone interview
was conducted. The purpose of this call
was to contact the selected individual to
further explain the study and attempt to
enroll him (her) into the study. If the indi-
vidual agreed to be part of the study, an
appointment was established for a field
interview. In addition, during this call, a
Computer Model Input Questionnaire
was administered which collected addi-
tional data on commuting patterns,
demographics of household members,
and household characteristics.
Finally, participating individuals were
met at their home or other convenient
location and given all study materials.
These participants carried both a REM (a
model COED-1, which utilized a data
acquisition package supplied by Magnus,
Inc.) for the 24 hours of their participation
and an Activity Diary in which to record a
description of their activities. Participants
were requested to push a button on their
PEM every time they changed activities
and to record descriptions of the new
activities in their diaries. In addition, for a
small sample of participants, a GE/HP
PEM (which utilized a Hewlett-Packard
HP-41CV programmable calculator) was
used which allowed the participant to
also enter an activity code into the
monitor. Participants were also asked to
complete a self-administered Household
Questionnaire which provided
information on themselves and on their
home and work environments. The
telephone screening and sample
selection of individuals for both Denver
and Washington were carried out by RTI
as was the field work in Washington.
The results of the telephone screening
and field activities for the study are
described in detail in the report. Briefly,
8643 household screenings were
attempted by RTI in Washington, DC and
4987 were attempted in Denver,
Colorado. The successful screening rates
were 75.8 percent in Washington and
70.4 percent in Denver. From these
telephone and field screenings, 5418
eligible respondents were identified in
Washington and 2232 in Denver. From
this population of eligibles, 1987
individuals were selected for
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participation (i.e., to carry a PEM) in
Washington and 1139 in Denver. Of
these selected individuals, 58 percent
actually scheduled appointments to carry
a PEM in Washington. Finally, 35.8 per-
cent of the individuals in Washington
selected to participate contributed usable
CO monitor data. This represented 712
sample respondents. Instrument failure
was one of the major reasons for the low
response rate. Specifically, CO data was
not collected or was unusable for analysis
purposes for 232 respondents (22% loss
rate) due to monitor failure or malfunc-
tion. Usable CO breath data
corresponding to the usable CO monitor
data was collected on 659 sample re-
spondents.
Sampling weights based upon the
probability of inclusion in the sample
were computed according to well-estab-
lished formulas. Analysis weights
adjusted for nonresponse were also
computed so that the weights could be
used to draw inferences to the target
populations. The sampling weights were
merged with the corresponding field data
on a computer file for analysis.
Detailed statistical analyses were
carried out using computer data files with
PEM CO and activity diary data. Estimates
computed during this analysis were
weighted estimates for the population of
inference—adult non-smokers in the
Washington, DC metropolitan area.
Standard errors of estimates were
produced by using specially written
software designed for analysis of data
from complex sample surveys.
Summary of Study Results
and Conclusions
Based on the experience gained during
the Washington, DC and Denver PEM CO
studies, the methodology developed, with
some modifications (see the detailed
report) may be used effectively in other
areas of the country for collecting PEM
data. Experience gained during this initial
study will improve the execution of such
similar studies. A modified sampling
design using the classified telephone
directory listings is recommended. The
modified design should be more cost
effective and improve the response rate.
Important new information was
learned for each of three sampling meth-
odology studies of the project: (1) It was
found that geographically classified
telephone directory listings can be used
in a cost-effective manner in association
with standard area household sampling
techniques for personal monitoring
studies like the current CO study. The
sampling design for the cost-effective use
of these telephone directory listings
differs substantially from the design used
for the CO study, however (details are
given in the report). (2) Sending lead
letters to individuals who were selected
for personal monitoring prior to calling to
schedule an appointment was found to be
an effective strategy. (3) The need for
person-day sampling for studies that
monitor personal exposure to airborne
pollutants is apparent. The CO study
gained valuable experience with this
technique. Further study, possibly even
another methodological study, is needed
to refine this technique.
Using the data collected in the Wash-
ington, DC and Denver metropolitan
areas with the Household Screening
Questionnaire, weighted estimates of
population characteristics were
computed. These estimates were based
on screening interviews in 4394
households in Washington and 2128
households in Denver. In particular, the
population estimate for the number of
households in the two areas are 953,714
for Washington and 345,163 for Denver.
Population estimates of percentages of
households with various characteristics
were as follows:
Washington Denver
Use Fireplace
Use Wood Stove
Use Gas Furnace
Use Gas Stove
Use Gas Hot Water
Have Attached Gar-
age or Multi-Family
Garage
33% 30%
4% 6%
56% 71%
64% 25%
57% 78%
22%
35%
In addition to household characteristics,
several estimates were also obtained for
individuals' characteristics in the two
areas. For example,
Washington Denver
Male 48% 47%
Smokers (13 years
or older) 33% 38%
Work (13 years or
older) 70% 72%
Travel >3 times/
weeks 84% 82%
Regarding estimates of CO exposure
for the winter of 1982-83 in Washington
DC, a data base was constructed from the
raw CO levels by activity data which con-
sisted of hourly CO values on 712
respondents, activity patterns and
corresponding CO levels on 705
respondents, and CO breath
measurement corresponding to the PEM
CO data on 659 respondents. These data
were used to obtain estimates of CO
exposure for the population of inference--
the adult (18 to 70 years old), non-
smokers in the urbanized portion of the
Washington, DC SMSA. The size of this
population was estimated to be 1.22
million individuals.
Detailed discussion of project results is
found in Study of Carbon Monoxide Expo-
sure of Residents of Washington, DC and
Denver. Colorado by T. D. Hartwell, et. al.
The sampling design employed for this
project is discussed in detail in the Final
Sampling Report for the Study of
Personal Exposure by Roy W. Whitmore,
et. al.
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Roy W. Whitmore, She/ton M. Jones, and Martin S. Rosenzweig are with
Research Triangle Institute, Research Triangle Park, NC 27709.
Gerald G. Akland is the EPA Project Officer (see below).
The complete report, entitled "Final Sampling Report for the Study of Personal CO
Exposure," (Order No. PB84-181 957; Cost: $11.50, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Environmental Monitoring Systems Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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