United States
                     Environmental Protection
Environmental Monitoring
Systems Laboratory
Research Triangle Park NC 27711
                     Research and Development
EPA-600/S4-84-034  May 1984
&EPA          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
                      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
                      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).

  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:

    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

  • Accurate and portable field tested
    instruments now are  available for

  • 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

  • The health  effects of CO are reason-
    ably well documented, and NAAQS
    based  on  these  effects have been

  • 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

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-
  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 activitydiarydata. 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
jWith 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
33%     30%
 4%      6%
56%     71%
64%     25%
57%     78%
  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/
  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
                   f o u nd i n St udy 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 thef/na/
                   Samp/ing  Report  for  the  Study  of
                   Personal Exposure by Roy W. Whitmore,
                   et. al.

      Roy W. Whitmore, Shelton 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. PB 84-181 957; Cost: $11.50, subject to change) will be
       available only from:
             National Technical Information Service
             5285 Port Royal Road
             Springfield, VA22161
             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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