450R78105
              AIR QU-_ITY TRENDS  IN TH£  
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U,S. Environmental Protection Agency

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 AIR QUALITY TRENDS IN THE NATION'S LARGEST URBANIZED AREAS

1.    INTRODUCTION AND OVERVIEW
      The 1970's have seen general improvements in the Nation's air
quality for Total Suspended Particulate, Sulfur Dioxide, and Carbon
Monoxide, but Ozone remains a general problem with no clear pattern
                          1 2
of nationwide improvement. '   A general discussion of these trends
is contained in EPA's National Air:Quality and  Emissions Trends
Report, 1976. .   This present report focuses on air quality trends
in the Nation's fifty largest urbanized areas during the 1971-1976
time period.  These fifty areas were selected on the basis of the
U.S. Department of Commerce's 1970 Census of Population, Number of
                                    •y
Inhabitants, United States Summary.
      Results are presented for Total Suspended Particulate, Sulfur
Dioxide, Ozone, and Carbon Monoxide.  The National Ambient Air Quality
                                                           4
Standards (NAAQS) for these pollutants are shown in Table 1. Historical
data for Ozone is limited to certain areas and therefore the Ozone
discussion  highlights trends in only a few areas, but also includes
a general overview of observed levels in the Nation's 'largest cities.
Data for Nitrogen Dioxide are even more limited and are not yet
sufficient  to establish any general  trend patterns.   Therefore, no
discussion  is included for this pollutant.
      The primary purpose of the Tables contained in this report is
to  indicate trends.  They are not  intended to reflect the status of
particular  areas with respect to the NAAQS.  A comprehensive listing
of  the attainment status of these  areas has recently been published
                       c
by  EPA for  this purpose  .   It should also be noted that caution should
be  used  in  making comparisons between cities based upon the results
presented here.  Sufficient flexibility is allowed in the placement
of  local monitoring networks so that the results should be viewed in
terms of relative change rather than absolute "laqnitude.  One  reason
for this caution is that one city  may choose to place monitors only
in  high  concentration areas while  another city may also place monitors
in  low concentration areas to assess the impact of growth.  This problem

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  TABLE  1.   NATIONAL AMBIENT AIR QUALITY  STANDARDS  FOR MAJOR  POLLUTANTS
Pollutant
Particulate
matter
(TSP)
Sulfur oxides
(sulfur
dioxide)

Carbon
monoxi de
(CO)
Photochemical
oxidants
(expressed
as ozone)
Description
Solid and liquid particles
in the atmosphere, in-
cluding dust, smoke
mists, fumes, and spray
from many sources
Heavy, pungent, colorless
gas formed from combus-
tion of coal , oil , etc.

Invisible, odorless gass
formed from combustion
of gasoline, coal, etc.,
largest man-made frac-
tion combes from auto-
mobiles.
Pungent, colorless toxic
gas; one component of
photochemical smog.
POLLUTANT STANDARDS*
Primary
3
75 yg/m annual
geometric mean
3
260 yg/m maxi-
mum 24-hr
80 yg/m3 (0.03
ppm) annual
arithmetic
mean
365 yg/m3 (0.14
ppm) maximum
24-hr
10 mg/m (9 ppm)
maximum 8-hr
3
40 mg/m (35 ppm)
maximum 1-hr
160 yg/m3 (0.08
ppm) maximum
1-hr
Secondary0
3
60 yg/m annual
geometric mean
3
150 yg/m maxi-
mum 24-hr
1300 yg/m3
(0.5 ppm
maximum
3-hr)

Same as primary
Same as primary
t
51



B_
•_ i
t
63                                   ^
m yg/m  = micrograms per cubic meter; mg/m  = mi Hi grams per cubic meter;  ppm =
parts per million, the number of parts of a given substance in  a  million parts
of air.  Short-term standards for 1-, 3-, 8-, or 24-hour averages may not  be
exceeded more than once per year.


b Primary - necessary to protect the public health.

  Secondary - necessary to protect the public welfare.

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                              2
has been previously discussed and the designation of a standardized
network of national trend sites has been proposed as a solution.
This national network would result in a standardized and consistent
historical data base for future trend assessments.

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                              3
2.     TRENDS IN TOTAL SUSPENDED PARTICIPATES
      This section discusses trends in TSP for the Nation's 50 largest
urban areas.  In addition, it presents a more detailed discussion for
three areas.

2.1   TRENDS IN TSP FOR THE 50 LARGEST URBAN AREAS
      The general improvement in ambient air quality with respect to
                                                     1 o
Total Suspended Particulate (TSP) discussed elsewhere '  can be seen
in most of the Nation's 50 largest urbanized areas (Table 2).  The
TSP data for each urbanized area were divided into two time periods,
1971-73 and 1974-76.  Only those air monitoring sites with at least
a year of data in both time periods were included in the analysis.
It should be noted that several urbanized areas had only a limited
number of monitoring sites with sufficient data to meet this criterion.
Trends in data from only one or two monitors should be viewed with
considerable caution since TSP air quality is known to vary considerably
from place to place within urban areas.
      Two statistics for the two time periods are compared, 3-year
annual averages and average maximum 24-hour values.  For each of the
statistics, a trend is defined as  (1) "down," if the percent decrease
between the base periods is more than or equal to 5 percent; (2) "up,"
if the increase is greater than or equal to 5 percent; or (3) "unchanged,"
if the percent change falls between -5 and +5 percent.
      An examination of the 3-year averages (Table 2) shows a downward
trend in 30 urbanized areas (5 to 32%), no change in 17 areas, and an
upward trend in 2 areas (6 to 8%).  These results correspond reasonably
well with the trend in average maximum 24-hour values, which show a
downward trend in 33 urbanized areas, no change in 8 areas, and an
upward trend in 8 areas.  One factor affecting short-term TSP trends     ,
has been the drought conditions occurring in various areas of the country.
Extremely dry soil conditions increase the likelihood of wind-blown dust
contirbuting to ambient TSP levels.  It should be noted that while no
data is shown for Columbus, Ohio in Table 2 this is due to an absence
of historical data and more recent TSP data is available for this area.

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                              4
2.2   TRENDS IN POPULATION EXPOSURE TO TSP IN THREE METROPOLITAN
      AREAS
      Detailed trends analyses of TSP were conducted for three
metropolitan areas - New York, New York-Northeastern New Jersey
urbanized area, City of Chicago and Metropolitan Denver.   The
improvements in air quality were measured in terms of the change
in the number of people exposed to levels above the annual primary
standard of 75 yg/m3.
      The greatest long-term improvement occurred in the New York-
New Jersey-Connecticut Air Quality Control Region, where the proportion
of the population exposed to concentrations in excess of the annual
primary health standard of 75 yg/m3 decreased from 66 percent to 0
between 1970 and 1976.  Considerable progress was also seen in
Chicago; the proportion of the population exposed to TSP levels greater
than the annual primary standard fell from 100 percent in 1970 to 64
percent in 1976.  In Denver, the percentage of the exposed population
dropped from 83 percent in 1970 to 74 percent in 1975.

2.2.1 TSP Trends in New York, New York-Northeastern New Jersey
      The change in number of people exposed to total suspended particu-
late (TSP) matter in the Mew York-New Jersey-Connecticut AQCR was
examined for the period from 1970 to 1976.  Overall, significant
progress has been made in reducing population exposure to annual
average TSP levels within the AQCR.  Switching to cleaner fuels and
implementing particulate control measures has reduced annual concen-
tration levels by 30 percent.  This improvement means that no one
lives in areas exposed to concentrations  in excess of the annual
primary health standard of 75 yg/m3.
      Isopleths of average TSP in the New York area during 1970, 1973
and 1976 are shown in Figure 1.  In 1970, approximately 21 percent of
the region had TSP concentrations greater than the primary NAAQS.  The
affected areas included New York City and adjacent populated parts of
Mew Jersey, New York State and Connecticut.  At the same time, 51 per-
cent of the land area exhibited TSP concentrations over the secondary

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                                              AREA WHERE TOTAL SUSPENDED

                                              PARTICULATE CONCENTRATION
                                              IS:
                                                       ^=60 ^ig/
                                                       50-75 j
            1975
Figure  1 -  Isopleth of annual geometric mean concentrations of tota! suspended
particulate in 1970, 1973, 1976.

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                              5
TSP "welfare" standard of 60 yg/m3.
      By 1973, substantial reductions in TSP could be seen.   The
land area exposed to concentrations in excess of the annual  primary
standard has been reduced to 2 percent of the Air Quality Control
Region.  The affected areas were mostly in the central portion of
the region consisting of parts of New York City and adjacent New Jersey.
The area with concentrations above the secondary standard was also
reduced; the affected area constituted about 15 percent of the AQCR.
      In 1976, only one TSP monitoring site in Jersey City,  N.J.,
produced an annual TSP concentration above the primary standard.  The
reported concentration was 78 ug/m3. Because this monitor was adjacent
to monitors measuring lower concentrations, Figure 1 does not show
any areas above  the primary standard.  The land area subjected to
concentrations above the  secondary standard has also continued to
shrink.  The affected area is less than 7 percent of the AQCR.

2.2.2 TSP Trends in City  of Chicago
      The change in the number of  people exposed to total suspended
particulate matter in the City of  Chicago was examined for the period
from 1970 to 1976.  The analysis showed an overall reduction in average
TSP levels of 26 percent.  The improvement resulted in 36 percent fewer
people  exposed to annual  TSP levels  above the annual primary health
standard of  75 pg/m3.
       Isopleths  of average TSP during 197Q and 1976 are shown in
Figure  2.   In 1970, the entire city  was above the TSP primary NAAQS.
The highest  TSP  concentrations are found in the highly industrialized
Calumet region of Southeast Chicago.  High concentrations are also
found  in downtown Chicago, extending westward into the adjoining
industrial  areas.
       In the 1976 isopleths, a substantial city-wide decrease in TSP
levels  can  be seen.  About one-third of the city is now below the
primary TSP  NAAQS.  These areas  include the North and South Central
parts  of Chicago. Both are areas  of moderate population density.

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2.2.3 TSP Trends in Metropolitan Denver
      The change in the number of people exposed to total  suspended
particulate matter in the Metropolitan Denver area was  examined for
the period from 1970 to 1975.  The analysis showed an overall  improvement
of 10 percent in the exposure to annual average TSP.
      Isopleths of average TSP during 1970 and 1975 are shown  in Figure
3,  In 1970 most of the study area was exposed to annual TSP above the
primary NAAQS.  The highest TSP concentrations are found in the centra]
City of Denver and extend northward down the Platte River Valley.  Most
of the areas with levels below the primary NAAQS were in the south-
eastern part of Denver County and suburban areas of Arapahoe County.
A moderate decrease in TSP levels was observed throughout the region.
The areas below the primary NAAQS in 1975 have grown to include more
of the eastern portions of Jefferson County.

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 ,,;!]]!! ill ill 'I1!!!! 1 !|i;,,*-7~7

ym^mmxwm±
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StiSiiiiillliis1

                          AREA WHERE ANNUAL
                          MEAN TOTAL SUSPESiDED
                          PARTICULATE CONCEN-
                          TRATION IS:

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                              7
3.    TRENDS IN SULFUR DIOXIDES
      The Nationwide improvement in Sulfur Dioxide (SOo) concentrations
                   22
reported previously '  can be seen in the Nation's 50 largest urbanized
areas (Table 3).  The SC^ data for each urbanized areas were divided
into two time periods 1971-73 and 1974-76.
      The most complete historical SC^ data base exists for the t-Jest-
Gaeke bubbler.  Although this monitoring method may underestimate SO;?
concentrations, if the temperature in the instrument's environment
is uncontrolled, changes in the annual averages should be a reasonable
indicator of trends.
      An examination of 3-year averages (Table 3) shows a downward
trend in 14 urbanized areas, no change in 5 areas and an upward trend
in 4 areas.  For the 3-year averages, a trend is defined as "down"
if the percent decrease between the 1971-73 and 1974-76 base periods
is more than or' equal to 5 percent and "up" if the increase is greater
than or equal to 5 percent.  If the percent change falls between -5
percent and +5 percent, the trend is  defined as "unchanged."  Fifteen
areas had insufficient data to determine  trends, and 12 areas reported
3-year averages below one-half of the minimum detectable measurement
(13 yg/m3) for both time periods.  No trend was indicated when the
average in both years fell below  13 ug/m3.

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•TABLE  3.    TREND  IN SULFUR DIOXIDE  ANNUAL AVERAGE  (WEST-GAEKE  BUBBLERS)
            CONCENTRATIONS FOR  50 LARGEST METROPOLITAN AREAS  II! U.S.
            FOR  1971-73  and  1974-76.
                                              3-year average
 Metropolitan Area

Akron, OH
Albany-Schenectady-
    Troy, NY
Atlanta, GA
 Baltimore, MD
 Birmingham, AL
 Boston, MA
 Buffalo, NY
 Chicago, IL-Northwest-
      ern, IN
 Cincinnati, OH-KY
 Cleveland, OH
 Columbus, OH
 Dallas, TX
 Dayton, OH
 Denver, CO
 Detroit, MI
 Ft. Lauderdale-Hollywood,
      FL
 Forth Worth, TX
 Houston, TX
 Indianapolis,  IN
 Jacksonville,  FL
 Kansas  City, MO-KS
 Los Angeles-Long  Beach, CA
 Louisville,  KY-IM
 Memphis, TN-MS
 Miami,  FL
No. of
monitors
6
2
*
12
11
19
5
46
15
22
*
4
8
*
6
1
1
20
11
10
8
11
11
*
yg/m3
' ' 1971-73
54
69
*
13
13
25
84
37
16
64
*
3
24
*
25
3
2
9
29
12
10
16
33
*

1974^75
42
66
*
15
10
19
42
25
20
56
*
2
18
*
16
3
2
4
28
12
6
15
38
*
Percent
change
-22
-4
*
13
-25
-24
-50
-33
25
-13
*

-27
*
-35



-2


-7
-1
*
Trend
Down
Unchanged
*
Up
Down
Down
Down
Down
UP
Down
*
a
Down
*
Down
a
a
a
Unchanged
a
a
Down
Unchanged
*

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            TREfiD IN SULFUR DIOXIDE ANNUAL AVERAGE (K'EST-GAEKE BUBBLERS)
            CONCENTRATIONS FOR 50 LARGEST METROPOLITAN AREAS IN U.S.
            FOR  1971-73 and 1974-76.

                                              3-year average
Metropolitan Area
Milwaukee, WI
Minneapolis, -St. Paul ,MN
New Orleans, LA
New York, NY-Northeastern, f!J
Norfolk-Portsmouth,VA
Oklahoma City, OK
Omaha, NE-IA
Philadelphia, PA-NJ
Phoenix, AZ
Pittsburgh, PA
'Portland, OR
Providence-Pawtucket-Warwick
RI-MA
Riverside-San Bernardino, CA
Rochester, NY
Sacramento, CA
St. Louis, MO-IL
San Antonio, TX
San Diego, CA
San Francisco-Oakland, CA
San Jose, CA
Seattle-Everett, WA
Sprinafield-Chicooee-
Holyoke, MA-CT '
'Tampa-St. Petersburg, FL
Toledo, OH
'Washington, DC-MD-VA
No. of
monitors
*
7
2
10
6
T
*
*
*
*
*
f
11
1
7
*
*
1
1
2
*
*
5
10
2
16
yg/m3
1971-73
*
36
8
28
22
4
*
*
*
*
*

35
5
36
*
*
2
5
6
*
*
26
27
16
13

1974^76
*
15
7
2B
34
4
*
*
*
*
*

27
4
27
*
*
2
6
4
*
*
20
17
16
15
Percent
change
*
-58

0
53
*
*
*
*
*
*

-22

-24
*
*



*
*
-22
-37
0
18
Trend
*
Down
a
Unchanged
Up
a
*
*
*
*
*

Down
a
Down
*
*
a
a
a
*
*
Down
Down
Unchanged
Up
* Insufficient Trend Data

a Annual Average <13yg/m  in both time periods

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                              8
4.    TRENDS IN OXIDANTS
      Due to the lack of sufficient photochemical  oxidants data in
the 1971-73 period for urban areas outside of California, the trend
Tables presented for the other pollutants will not be presented
here.  Oxidant trends will be discussed specifically only for the
Los Angeles-Long Beach, California and San Francisco-Oakland, Cali-
fornia areas.  Table 4   is presented to show the recent status and
extent of the urban photochemical oxidant air pollution problem.  The
maximum second highest hour in a year during the period 1974-76 is
shown for the 50 urban areas discussed previously.  All 50 of the
areas violated the photochemical oxidant standard of 160 yg/m3 during
this time period.  The highest measured concentrations of photochemical
oxidants occurred in the adjacent southern California urban areas of
Riverside-San Bernardino  (764 yg/m3) and Los Angeles-Long Beach (725
yg/m3).

4.1   OXIDANT TRENDS IN LOS ANGELES - LONG BEACH, CALIFORNIA
      URBANIZED AREA
      An analysis similar  to that for the New York, Chicago and
Denver areas was made  to  examine the change  in population exposure
to oxidants  in the Los Angeles - Long Beach  urbanized area.   Air
quality data collected from 1965 through 1976 were grouped into
2-year intervals to preserve historical continuity among the trend
sites.  The  analysis showed a considerable reduction in  the percent
of days on which the 1-hour primary health standard for  oxidant was
violated.  People in the  area were exposed to a concentration above
the  standard on an average of  175 days per year in 1965  and 1965,  144
days per year  in 1969  and  1970,  and 112 days  per year in 1975 and  1976.
      Daily  exposure patterns are displayed  on isopleth  maps to
indicate areas of the  region that exceed the 1-hour oxidant standard
of 160 ug/m3 for a given  percent of the days  (Figure 4).  A long-tern
improvement  can be seen over the  12-year period from 1965 through  1976.
In 1965 and  1966, more than half of the Los  Angeles Basin violated the
standard more  than 50  percent  of  the days and the rest of the region

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TABLE 4. SECOND HIGHEST HOUR OF PHOTOCHEMICAL OXIDANT CONCENTRATIONS IN A YEAR
         DURING THE PERIOD  1974-76  IN THE 50 LARGEST URBANIZED AREAS IN U.S.
                                                            2nd HIGHEST
                    URBANIZED AREAS                     HOUR IN YEAR (yg/m3)

         Akron, OH                                          298
         Albany-Schenectady-Troy, NY                        272
         Atlanta, GA                                        324
         Baltimore, MD                                      510
         Birmingham, AL                                     268
         Boston, MA                                         392
         Buffalo, MY                                        404
         Chicago, IL - Northwestern  Indiana                 457
         Cincinnati, OH-KY                                  412
         Cleveland, OH                                      341
         Columbus, OH                                       316
         Dallas, TX                                         367
         Dayton, OH                                         353
         Denver, CO                                         490
         Detroit, MI                                        455
         Ft.  Lauderdale-Hollywood,  FL                       196
         Ft.  Worth, TX                                      353
         Houston, TX                                        500
         Indianapolis,  IN                                   304
         Jacksonville,  FL                                   372
         Kansas City, MO-KS                                 294
         Los  Angeles-Long  Beach,  CA                         725
         Louisville, KY-IM                                  461
         Memphis, TN-MS                                     255

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                                                                              if
SECOND HIGHEST HOUR OF PHOTOCHEMICAL OXIDAMT CONCENTRATIONS IN  A YEAR          |
DURING THE PERIOD 1974-76 IN THE 50 LARGEST URBANIZED AREAS IN  U.S.            »
                                                     2nd HIGHEST
            URBANIZED AREAS                    HOUR IN YEAR (yg/m3)

Miami,  FL                                          196
Milwaukee, WI                                      504
Minneapolis-St.  Paul,  MN                           231
New  Orleans, LA                                    214
New  York, NY - Northeastern  NO                     365
Norfolk-Portsmouth,  VA                            280
Oklahoma City, OK                                 268
Omaha,  NE-IA                                       225
Philadelphia, OA-NJ                                625
Phoenix, AZ                                     ,   357
Pittsburgh, PA                                     416
Portland, OR                                       294
Providence-Pawtucket-Warwick, RI-MA                396
Riverside-San Bernadino,  CA                        764
Rochester, NY                                      259
Sacramento, CA                                     353
St.  Louis, MO-IL                                  451
San  Antonio, TX                                    347
San  Diego, CA                                      510
San  Francisco-Oakland, CA                         490
San  Jose                                           333
Seattle-Everett, WA                                255
Springfield-Chicopee-Holyoke, MA-CT                368
Tampa-St. Petersburg,  FL                           355
Toledo, OH-MI                                      294
Washington, D.C.-MD-VA                            451

a  Urbanized areas are  taken  from  the  U.S.  Department  of  Commerce publication:
   1970  Census of Population,PS(1)  - Al  U.S.  Summary,  December,  1971.

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o
CO
3
i—^

O
—H

0.
u
•<
in

O
13
 O
  D
  in
  o
  X

  51
  o
  3
  QJ
  u>

  CO
  X
  o
  (D
  CD
  a.
  C3
  CL

  o.
   c
   x

   ro
    CO
    CD
   -o
    CD
    a.
    o
    •a
    •o
     cc
     ui
                                                                                                                                                           i;
                                                                                                                                                           5
                                                                                                                                                           I

-------
at least 20 percent of the days.  The greatest overall improvement
was in 1973 and 1974 when the standard was violated more than 50
percent of the days only in a small area around Azusa.  In 1975 and
1976, areas around Burbank and San Bernardino also violated the
standard more than 50  percent of the days.  These same areas violated
the standard in excess of 45 percent of the days in 1973 and 1974.
An examination of days with poor dispersion shows an increase in the
1975/76 period over the 1973/1974 period.  This, in part, explains
the slight deterioration in oxidant air quality between the two time
periods.

4.2   OXIDANT TRENDS IN SAN FRANCISCO-OAKLAND, CALIFORNIA URBANIZED
      AREA.
      Figure 5 shows the trend  in the Bay Area Air Pollution Control
District (BAAPCD) of the average highest hour oxidant concentrations
for days with comparable temperature and inversion conditions.   By
just  lookimg at comparable days in terms of meteorology in this way,
the varying affects of meteorology from year to year are greatly re-
duced.  The BAAPCD average of six sites shows a fairly stable pattern
over  the 1970-1976 period varying from 157 \ic/m3 in 1970 to 118 vig/m3
in 1976.  The San Francisco and San Jose sites are also shown because
they  represent the lowest and highest oxidant sites in the Bay Area.
Both  of these sites generally follow the same overall pattern as the
6 site composite average except that the change in the average from
1973  to 1974 at San Jose is much more pronounced and the 1976 average
for the San Francisco  site shows an increase from the 1975 figure.

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  300
  Z50
  200
a.

z~
t 150
2 100
x
a
   so
O SAN JOSE. CALIF.

D SAN FRANSISCO, CALIF.

A SIX-SITE AVERAGE. BAAPCO
        1970
                1971
                          1972
                                   1973

                                  YEAR
                                            1974
                                                     1975
                                                              1976
   Figure   5.  Average daily maximum-hour oxidant concentrations
   for days in April-October (1970-1976) having comparable
   temperatures and inversions in Bay Area Air Pollution Control
   District (BAAPCD).

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                             10

5.     TRENDS IN CARBON MONOXIDE
      There has been general improvement in Carbon Monoxide (CO)
levels through 1976.   The majority of CO emissions are attributable
to transportation sources which account for 80 percent of the national
total.  However, in some areas, these sources may contribute as
much as 99 percent of the local CO emissions.  Any area with sufficient
traffic density may be viewed as having a potential CO problem.  The
problem may be very localized, perhaps at just a few street corners,
or it may be widespread throughout the center-city area and near major
commuter corridors.  The localized nature of the CO problem makes it
difficult to assess trends  in a particular city based upon data from
a few sites without adjustment for meteorology and possible changes
in local traffic patterns.  The results presented here are best viewed
in terms of an overall perspective of general trends on the national
level.
      Historical CO data are somewhat limited, although certain areas,
have had extensive monitoring networks operating for several years.
For this analysis, CO data  from EPA's National Aerometric Data Bank
were screened  to select sites  in the 50 largest urbanized areas with
current data.  Sites with 4000 or more hourly values (out of a possible
8760 per year) were considered to have a complete year of data.  All
sites with  three complete years of data beginning  in the 1971-73 period
were considered as  trend sites.  As shown  in Table 5 , 33 of the 50
largest urbanized areas had sites that could be used to assess CO trends.
Compared to  last year this  represents a 75 percent  increase in the
number of areas with sufficient trends data  and is  indicative of the
general expansion and improvement in State and local air monitoring
programs.   At  the present time, CO data is being collected in all 50
of  these cities.
      A primary concern  in  CO monitoring is  compliance monitoring
to  ensure  that standards are met.  An area with limited resources
may,  therefore, tend to move a monitor from  one location to another
to  determine  the area of peak  concentration.  Although such monitoring
does  not  lend  itself to  trend  assessment,  it is an  essential part of
a CO monitoring program.

-------
      As indicated in Table 5, the 90th percent!le of the 8-hour
average CO was used in the analyses.  This parameter is convenient
for trends purposes because it reflects peak concentrations  (only
10 percent of the values are higher) but is more stable than the
maximum or second-highest values.  In addition, the 8-hour average
primary CO standard is the one that is most frequently violated.
Nonparametric regression v/as used for the yearly values to assess
the sign of the trend and the statistical significance.  Net changes
of less than 5 percent were considered as no change.
      The results in Table 5 show general improvement with almost
all areas reporting progress.  This is consistent with national
emissions trends which show a 13 percent reduction in CO emissions
during this period.   These decreases are primarily attributable
to highway vehicle controls and  less burning of solid waste.  CO
emissions from other source categories have not changed appreciably.
The effect of motor vehicle emission controls is perhaps best evidenced
by areas, such as New Jersey, where ambient CO levels have continued
to improve despite increases in  gasoline consumption.

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 TABLE  5.   TRENDS IN CARBON MONOXIDE FOR 50 LARGEST URBANIZED  AREAS  IN  U.S.  FOR
           1971-73 and 1974-76 (90TH PEP.CENTILE  OF  8-HOUR VALUES)

Area
Akron, OH
Albany- Schenectadv-
Troy, NY
Atlanta, GA
Baltimore, MD
Birmingham, AL
Boston, MA
•Buffalo, NY
Chicago, IL-Northwest-
• ern>, IN
Cincinnati, OH-KY
Cleveland, OH
Columbus, OH
Dallas, TX
Dayton, OH
Denver, CO
Detroit, MI
Ft. Lauderdale-Hollywood,
FL
Fort Worth, TX
Houston, TX
Indianapolis, IN
Jacksonville, FL
•Kansas City, MO-KS
Los -Angeles-Long Beach, CA
Louisville, KY-IN
Memphis, TN-MS
Miami, FL
Number of
trend sites
*
2
1
2
*
5
2
5
1
1
*
*
•k
3
4
1
*
*
* •
*
3
15
2
*
*
90th percenti
1971-1973
*
4.4
5.6
3.7
*
7.9
5.4
5.7
4.8
6.0
*
*
*
6.9
3.1
5.8
*
*
*
*
4.2
8.9
7.4
*
*
le of 8-hour
1974-1976
*
2.9
4.9
3.8
*
6.1
4.9
3.8
3.8
3.9
*
*
*
6.6
2.7
5.9
*
*
*
*
3.4
7.7
6.1
*
*
values
Trend
*
Down
Down
Unchanged
*
Down
Down
Down
Down
Down
*
*
*
Down
Down
Unchanged
*
*
*
*
Down
Down
Down
*
*
* Insufficient Trenu Data

-------
TRENDS IN CARBON MONOXIDE FOR 50 LARGEST URBANIZED AREAS  IN  U.S.  FOR
1971-73 and 1974-76 (90TH PEPCENTILE OF 8-HOUR VALUES)

t,
Area . lj
Milwaukee, WI '
Minneapolis-St. Paul, MM
New Orleans, LA
New York, NY-Northeastern,
NJ
Norfolk -Portsmouth, VA
Oklahoma City, OK
Smaho, NE-IA
Philadelphia, PA-NJ
- Phoenix, A2
Pittsburgh, PA
Portland, OR
Providence-Pawtucket-War-
wick, RI-MA
x Riverside-San Bernardino,
CA
Rochester, NY
Sacramento, CA
St. Louis, MO-IL
San Antonio, TX
^an Diego, CA
San Francisco-Oakland, CA
San Jose, CA
Seattle-Everett, WA
Sprinfiel d-Chicopee-
• Hoi yoke, MA-CT
Tampa-St. Peterburg,FL
Toledo, OH
Washington, DC-MD-VA
Number of
trend sites
*
4
*

14
1
1
1
5
*
1
2

1

9
1
1
7
*
*
8
1
2

1
*
2
6
90th percen
1971-1973
*
5.8
*

11.0
3.1
' 6.8
5.5
6.5
*
12.6
10.7

6.0

6.4
3.6
2.9
5.2
*
*
4.7
8.3
8.6

9.0
*
6.9
4.1
tile of 8-hour
1974-1976
*
4.0
*

10.4
2.8
6.4
. 4.7
5. 6
*
8.0
7.6

5.2

5.2
3.6
3.0
4.9
*
*
4.2
6.9
6.5

7.3
*
4.3
3.5
values
Trend
*
Down
*

Down
Down
Down
Down
Down
*
Down
Down

Down

Down
Unchanged
Unchanged
Down
*
*
Down
Down
Down

Down
*
Down
Down

-------
                              12
6.     REFERENCES
1.    National Air Quality and Emissions Trends Report, 1976.  U.S.
      Environmental Protection Agency, Office of Air Quality Planning
      and Standards.  Research Triangle Park, N.C.  Publication No.
      EPA-450/1-77-002.

2.    Air Quality Trends in the Nation's Largest Urbanized Areas.
      U.S. Environmental Protection Agency, Office of Air Quality
      Planning and Standards.  Research Triangle Park, N.C. Publication
      Mo. EPA-450/2-77-011.  May, 1977.

3.    1970 Census of Population, Number of Inhabitants, United States.
      Summary, U.S. Department of Commerce, Bureau of the Census,
      Washington, D.C.  Publication Mo. PC(1)-A1, December, 1971.

4.    Federal Register, Volume 36, April 30, 1971, pp 8186-8201.

5.    Federal Register, Volume 43, March 3, 1978, pp 8962-9059.

6.    Air Monitoring Strategy for State Implementation Plans. U.S.
      Environmental Protection Agency, Office of Air Quality Planning
      and Standards.  Research Trianole Park, N.C.  Publication Mo.
      EPA-450/2-77-010.  June, 1977.

7.    Air Quality Past and Present in AQMP/Tech Memo 3, March, 1977.
      Bay Area Air Pollution Control District.  Berkeley, California.
               U.S. Environmental Protection Agency
               Region  V, Library
               230 South Dearborn Street
               Chicago, Illinois  60604

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