United States
                    Environmental Protection
                    Agency
Environmental Monitoring Systems
Laboratory
Research Triangle Park NC 27711
                    Research and Development
EPA-600/S4-83-025 Aug. 1983
&EPA         Project  Summary
                    Carbon  Monoxide Concentrations
                    in   Four  U.S.  Cities  During  the
                    Winter  of  1981
                    David Holland and David Mage
                     Portable monitors were used to meas-
                    ure time averaged personal exposures
                    (10 to 30 min) to carbon monoxide.
                    Data  were collected from January
                    through March  1981  in four cities
                    where carbon monoxide ambient levels
                    in excess of National Ambient Air Quali-
                    ty Standards have been reported: Stam-
                    ford, CT; Los Angeles, CA; Phoenix, AZ;
                    and Denver, Co. In each city, personal
                    exposures were measured in three ty-
                    pical microenvironment types: indoor,
                    commuting, and residential driving.
                    These measurements were made in
                    the vicinities of fixed monitoring sta-
                    tions that recorded ambient levels of
                    carbon monoxide.
                     The highest indoor personal expo-
                    sures were recorded  in Denver (arith-
                    metic mean value of 6.1 ppm).  The
                    highest commuting  and residential
                    driving exposures were recorded in
                    Los Angeles (11.4 ppm and 7.6 ppm,
                    respectively). Except in Stamford, per-
                    sonal exposures during commuting
                    and residential driving activities were
                    higher than fixed-site ambient concen-
                    trations. Indoor exposures were lower
                    than fixed-site concentrations in all
                    cities except Denver.
                     For the four cities, the linear relation-
                    ships between simultaneous fixed-site
                    and personal exposure measurements
                    were  inconclusive. Any relationship
                    that may exist between these two types
                    of measurements is probably very com-
                    plex. The exposure vs. fixed-site linear
                    relationships were further complicated
                    in this study by the large distances
                    separating many measurements of the
                    personal exposures and fixed-site con-
                    centrations.
  Ambient concentrations were high-
est during the morning (7 to 8 a.m.)
and evening (4 to 6 p.m.) hours, with
average hourly peak levels of approxi-
mately 6 ppm. An exception to this
pattern  was observed in Stamford
where average levels of 10 to 12 ppm
were recorded at one fixed site.
  This Project Summary was developed
by the Environmental Monitoring Sys-
tems Laboratory,  Research Triangle
Park, NC, to announce key findings of
the research project that is fully doc-
umented in a separate report of the
same title (see Project Report ordering
information at back).

Introduction
  Ambient levels of carbon monoxide (CO)
are regulated according  to the National
Ambient Air Quality Standards (NAAQS).
The Office of Mobile Sources is responsible
for regulating motor vehicle emissions --
the  major source of CO in the urban
environment. When the NAAQS for CO are
violated, the states  involved must effect
State Implementation Plans (SIPs) to re-
duce the ambient levels to meet the NAAQS
The fundamental premise is that when a
CO standard is violated at an urban moni-
toring station, the people in the area sur-
rounding the station also are exposed to
CO levels above the NAAQS, therefore, a
SIP is necessary. However, actual human
CO exposures in various indoor and out-
door activity patterns are affected by highly
localized phenomena and may be signifi-
cantly different  from ambient CO levels
recorded at fixed stations that are sparsely
distributed in urban areas. These phe-
nomena include vehicle emissions, smok-
ing, and indoor ventilation conditions. Ac-

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cordingly, the "CO Winter Studies" were
designed to collect personal CO exposures
in microenvironments located in the vicinity
of fixed monitoring stations. The data from
the  two types of  measurements were
compared to determine if individuals were
exposed to the CO levels indicated by the
fixed monitoring stations. For the purposes
of this study, microenvironments are de-
f i ned to be specific locations with air space
of homogeneous CO concentration. Micro-
environment types  are groups of similar
microenvironments.

Procedure
  The study was conducted  during an 8-
wk period in the winter (January to March)
of 1 981  in four U.S. cities where ambient
CO levels above  the  NAAQS had been
observed. Miniature portable monitors
were used to measure time averaged ex-
posures  to  CO for  10  to 30 min time
periods. In each city, personal exposures
were measured in three common micro
environment types: Indoor, commuting,
and residential driving. The cities and the
contractors that performed the monitoring
were: Stamford, CT (GCA Corp., Tech-
nology Division); Los Angeles, CA (Science
Applications, Inc.); Phoenix, AZ(Systems,
Science and Software, Inc.), and  Denver,
CO(PEDCo Environmental, Inc.). Stamford
was selected because of the high occur-
rence of CO fixed-site measurements  in
excess of the 8-h IMAAQS standard  of 9
ppm. These measurements are caused by
the monitors' location near a busy inter-
section.  Los Angeles was chosen beause
the average commute time is greater  than
the national average of about 20 mm. Also,
a 9-person pilot study using personal ex-
posure monitors has been conducted  in
Los Angeles. Phoenix was chosen because,
unlike most cities, the highest CO ambient
levels are measured during the  evening
hours. These CO levels may be a result of
evening atmospheric inversions that occur
before the evening rush hour traffic period.
Denver was selected because of its high
elevation  above sea  level. At  Denver's
altitude, more automobile exhaust may be
released into the air  due to  inadequate
adjustment of vehicle engines to the lower
levels of oxygen available for fuel combus-
tion.

Results
  Descriptive statistics  for each  micro-
environment type  within  each city are
presented in Table 1.  The personal ex-
posures within each  microenvironment
type were matched by time to the concen-
tration recorded at the nearest fixed site in
each city. For Stamford, summary statistics
are provided for each of the two fixed sites.
For Los Angeles, the personal exposures
are matched to the nearest fixed site. For
Phoenix and Denver, the indoor and com-
muting personal exposures are compared
Table 1.    Summary Statistics:  Personal Exposures and Fixed-Site Concentrations by Microenvironment Type for Four U.S. Cities

                                                                        Data source3
Microenvi-
ronment
type
Indoor









Commut-
ing








Residen-
tial
driving







Statistic
Sample size
Geometric mean
Arithmetic
mean
Standard
deviation
Median
Range
Correlation
coefficient
Sample size
Geometric mean
Arithmetic
mean
Standard
deviation
Median
Range
Correlation
coefficient
Sample size
Geometric mean
Arithmetic
mean
Standard
deviation
Median
Range
Correlation
coefficient
Stamford11
Personal
Exposure
659
3.0

5.6

8.0
2.7
0-61

0.14
1341
4.9

6.3

4.7
5.2
0-38

0.12
577
1.8

2.6

2.9
2.0
0-39

0.08
Fixed
Site 1
659
5.0

6.4

3.8
6.8
0-25

0.03
1341
6.6

9.3

5.7
9.6
0-25

0.27
577
4.9

6.2

3.8
6.3
0-29

0.26
Fixed
Site 2
659
1.3

2.0

2.2
1.0
0-12


1341
1.8

2.8

2.9
1.9
0-16


577
1.3

2.0

2.0
1.0
0-8


Los Angelesc
Personal Fixed
Exposure Site
1239
2.3

3.2

2.5
2.6
0-18

0.47
96
15.2

16.4

6.2
15.5
3-42

-0.06
807
6.2

7.6

5.0
7.0
1-38

0.41
1239
3.3

4.2

3.2
3.0
1-21


96
4.0

5.2

4.0
4.0
1-21


807
3.1

4.0

2.9
3.0
1-16


Phoenixd
Personal Fixed
Exposure Site
380
0.3

2.0

2.2
1.5
0-17

0.48
839
4.7

6.4

4.7
5.3
0-50

0.47
58
5.3

6.3

3.1
6.4
0-14

0.34
380
1.6

2.7

2.5
2.0
0-13


839
2.6

3.7

3.0
2.5
0-16


58
1.1

3.1

2.4
3.6
0-9


Denver1*
Personal
Exposure
1953
4.2

6.1

4.8
5.0
0-58

0.33
3584
7.9

10.7

7.6
9.0
0-55

0.24
526
4.2

6.0

5.1
4.5
0-45

0.02
Fixed
Site
1953
4.2

5.0

3.3
4.0
1-24


3584
5.5

6.4

3.9
5.7
1-27


526
2.0

2.9

2.2
2.4
0-10


aAveraging times of personal exposure and fixed data are not equal.
bSummary statistics are provided for each of the two fixed sites.
cPersonal exposures are matched to the nearest fixed site.
dlndoor and commuting personal exposures are compared to data from the urban fixed site.
 Residential driving exposures are compared to the urban-residential fixed site.

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 to data from the  urban fixed  site;  the
 residential  driving exposures  are  com-
 pared to the urban-residential fixed site.
   The majority of the personal exposures
 were not continuous mtime. However, the
 fixed site monitors usually recorded con-
 tinuous 1-h averages. Thus, the summary
 statistics  presented in Table 1  were ob-
 tained by comparing personal exposures
 that were averaged over a portion of a
 given  hour to hourly averages. This pro-
 cedure introduces  a fictitious replication
 into the analysis because a given  fixed
 hourly average is repeated for every per-
 sonal  exposure. Any possible effects of
 this replication should be negligible  when
 comparing the arithmetic means of each
 type of measurement because of the large
 number of personal exposures  in  each
 microenvironment type (see sample sizes
 in Table 1). However, it is important when
 comparing ranges and standard deviations
 that the averaging time be held  constant
 due to the potential for CO levels to rapidly
 increase or  decrease under conditions
 found in urban environments. Thus, some
 of the statistical results from comparing
 personal exposures that usually  included
 only a portion of a given hour to hourly
 averages should be viewed with caution.
 Except  for Stamford, each  personal  ex-
 posure arithmetic mean was higher than
 the corresponding fixed-site mean during
 commuting and residential driving. In ad-
 dition,  the  indoor  mean  for  Denver is
 higher than the fixed-site mean. The  arith-
 metic means and median values indicate
 that the highest indoor exposures  were
 measured in Denver. As expected, the
 highest commuting and residential driving
 exposures were measured in Los Angeles.
 Stamford fixed monitoring station 1, which
 is located near heavy construction activity,
 recorded the highest fixed-site concentra-
 tions.
  The sample correlation coefficients, which
 provide an empirical measure of the linear
 association between the personal exposure
 and fixed-site measurements, are very low
 (<0.5). The square  of the correlation co-
 efficient multiplied  by  100  provides a
 percentage measure of the total  sample
variation that is accounted for in the linear
 relationship. As measured by the square of
the correlation, none of the linear relation-
 ships are strong within any of the micro-
environment types.  Any relationship that
 may exist between these two  types of
 measurements is  probably very complex
 and cannot be adequately described by a
 simple linear relationship. The exposure
vs.  fixed-site relationships were further
complicated  in this  study by the  large
distances separating many of the personal
exposures and fixed-site measurements.
  Plots of the hourly fixed-site arithmetic
means vs. hour of day (Figures 1 through
5) indicate that the highest CO concentra-
tions occurred in the morning and evening
hours. The morning peak occurred at ap-

       12  -\
       11  -

       10  -
                                   proximately 8:00 am.  and the evening
                                   peak varied from city to city. As expected,
                                   the evening peak occurred much later in
                                   Phoenix (around 10 p.m.). Also, the Phoenix
                                   evening peak concentration exceeded that
                                   of the morning  peak, unlike the pattern
                                   observed in the other cities. Again, Stam-
 I
O
O
 
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to
                      68     10    12    14    16   18    20    22    24
                                Time of day
     024


Figure 3.    Hourly arithmetic means recorded at 10 fixed-site monitoring stations in Los Angeles
    6  -
                                                                          24
Figure 4.    Hourly arithmetic means recorded at the urban fixed-site monitoring station in
           Phoenix
ford monitoring  station  1  recorded the     An indirect approach was used to esti-
highest hourly mean concentrations. The   mate the exposure of a typical commuting
morning  and evening peak levels  were   office worker. A time-weighted average
approximately 6  ppm in the other three   exposure (equation 1) was calculated for
cities.                                   the following activities: morning commute
to office, work at office, midday eating and
shopping, and evening commute to home.
The time periods used to determine average
estimates for each activity were 8-12 a. m.
and 1-5 p.m. for work at the office, 7-9
am. for the morning commute, and 4-6
p. m. for the evening commute. The midday
hours used for the eating  and shopping
activities varied from city to city due to the
different monitoring procedures used  in
each city. Although the morning and eve-
ning commute time periods overlap the
assumed office hours, these times were
used to provide a representative estimate
of the average CO levels of these activities.

                     n
                     Z  CO,    t,
 time  weighted _  i = 1	
 average exposure    n

                    i=1   '        (1)

where       n = number of measurements
                recorded  during  an ac-
                tivity time period for the
                entire study
            t, = averaging time of expo-
                sure (min)
          CO, = average  exposure for
                averaging time t,

Table 2 shows the time-weighted average
exposures in each of the five activities and
the estimated  maximum  8-h average ex-
posure for a commuting  office worker  in
each city. The 8-h average value is a time-
weighted combination of the commuting
(maximum  of  the morning and evening
commute averages),  office,  store and
restaurant average exposures. These values
were computed by the following equation:
                                                                                 maximum 8-h
                                                                                        average =
                                                                                                     1/8 (maximum
                                                                                                         commuting
                                                                                                         exposure)
                                                                                                   + 6/8 (office
                                                                                                         exposure)
                                                                                                   + 1/16 (restaurant
                                                                                                          exposure +
                                                                                                          store  expo-
                                                                                                          sure)    (2)
                                                                                   This weighted combination assumes a
                                                                                 1 -h commuting time, 6 hours in the office,
                                                                                 1/2-h in a restaurant, and 1/2-h shopping
                                                                                 time during the total time period of 8-h.
                                                                                 Due to the high CO commuting levels, the
                                                                                 commuting office worker in Los Angeles
                                                                                 received  the  highest average exposure.
                                                                                 This exposure (8.2 ppm) is slightly under
                                                                                 the current 8-h standard The time-weighted
                                                                                 average indoor and commuting exposures
                                                                                 in Los Angeles also are considerably higher
                                                                                 than in the other three cities.
                                   4

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  S-\
Figure 5.   Hourly arithmetic means recorded at the urban-residential fixed-site monitoring
           station in Denver
Table 2.   Average Exposure of the Commuting Office Worker in Each City

                                  Average exposure (ppm)
City
Los Angeles
Denver
Stamford
Phoenix
Morning
Commute
17.8
13.9
6.8
10.9
Office
6.9
5.1
3.0
1.9
Restaurant
7.1
6.8
5.1
3.4
Store
5.8
5.2
2.4
1.6
Evening
Commute
15:2
11.5
6.0
6.9
Estimated
for 8-h
8.2
6.3
3.6
3.1
Conclusions
  The findings of this study of CO concen-
trations in Stamford, Los Angeles, Phoenix,
and Denver are summarized below:
    Except in Stamford, personal expo-
     sures during commuting and resi-
     dential driving were higher than fixed-
     site ambient concentrations (arith-
     metic mean values).
    Except in Denver, indoor exposures
     were lower than fixed-site ambient
     concentrations  (arithmetic mean
     values).
    The highest  indoor exposures were
     found in Denver (arithmetic mean
     value of 6.1  ppm).
    The highest commuting and resi-
     dential driving exposures were found
     in Los Angeles (arithmetic mean values
     of 16.4 ppm and 7.6  ppm, respec-
     tively).
    Hourly fixed-site arithmetic mean
     ambient concentrations in  all four
     cities were highest in the morning (7
     to 8 am.) and evening rush hours (4
     to 6 p.m.j. Except for a fixed monitor-
     ing station located near a construction
     site and busy intersection in Stamford,
     where peak  levels were 10 to  12
     ppm, morning and evening peak levels
     were approximately 6  ppm.
    In all four cities, regressing personal
     exposures on simultaneous fixed-site
     ambient concentrations resulted in
     inconclusive  linear relationships. Any
     relationship that  may exist between
     these two types of measurements is
     probably very complex and cannot
     be adequately described by a simple
     linear relationship.
    The highest estimated 8-h average
     exposure  for a  commuting office
     worker was  found in  Los Angeles
     (8.2 ppm).

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      The EPA authors David Holland (also the EPA contact, see below) and David
        Mage are with the Environmental Monitoring Systems Laboratory, Research
        Triangle Park. NC 27711.
      The complete report, entitled "Carbon Monoxide Concentrations in Four U.S.
        Cities During the Winter of 1981." (Order No. PB 83-224 907; Cost: $10.00.
        subject to change) will be available only from:
              National Technical Information Service
              5285 Port Royal Road
              Springfield, VA 22161
              Telephone: 703-487-4650
      David Holland can be contacted at:
              Environmental Monitoring Systems Laboratory
              U.S. Environmental Protection Agency
              Research Triangle Park. NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Postage and
Fees Paid
Environmental
Protection
Agency
EPA 335
Official Business
Penalty for Private Use $300
                                        .Ktfct

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