A!?, Qli-i.ITY TRENDS IN THE NATION'S LARGEST
URBANIZED AREAS
Monitoring and Reports Branch
Monitoring and Data Analysis Division
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
March 31, 1978
-------
AIR QUALITY TRENDS IN THE NATION'S LARGEST URBANIZED AREAS
1. INTRODUCTION AMD 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
o
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
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 magnitude. 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
monoxide
(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 STANDARDS3
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
3
10 mg/m (9 ppm)
maximum 8-hr
40 mg/m3 (35 ppm)
maximum 1-hr
160 yg/m3 (0.08
ppm) maximum
1-hr
Secondary0
3
60 yg/m annual
geometric mean
150 yg/m maxi-
mum 24-hr
1300 yg/m3
(0.5 ppm
maximum
3-hr)
Same as primary
Same as primary
yg/m = micrograms per cubic meter; mg/m = milligrams 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.
Primary - necessary to protect the public health.
Secondary - necessary to protect the public welfare.
-------
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.
-------
3
2. TRENDS IN TOTAL SUSPENDED PARTICULATES
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 ?
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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. TREND IN TOTAL SUSPENDED PARTICIPATE ANNUAL AVERAGE AND PEAK CONCENTRATIONS FOR 50 LARGEST URBANIZED AREAS IN U.S. FOR1971/73 AND 1974/76
Urbanized areas a
Akron, OH
Albany-Schenectady-Troy, NY
Atlanta, GA
Salti more, HD
Birmingham, AL
Boston, MA
Buffalo, NY
Chicago, IL-Northwestern Indiana
Cincinnati, OH-KY
Cleveland, OH
Columbus, OH
Dallas, TX
Dayton, OH
Denver, CO
Detroit, MI
Ft. Lauderdale-Hollywood, FL
Ft. Worth, TX
Houston, TX
Indianapolis, IN
Jacksonville, FL
Kansas City, MO-Kans.
Los Angeles-Long Beach, CA
Louisville, KY-IN
[•'.cniphis, TN-HS
MiaTi, FL
Milwaukee, WI
Minneapolis-St. Paul, MN
ticv; Orleans, LA
Ncft York, NY-Northeastern NJ
Norfolk-Portsmouth, VA
Oklahoma City, OK
' t ' *
No. of b
monitors
12
17
2
25
20
20
44
85
42
37
•fr
13
16
19
33
9
10
31
16
11
18
21
10
15
6
16
16
1
76
7
6
3-year averages
ug/m3
1971/73
79
62
55
63
104
56
73
79
78
88
+
66
63
90
83
49
61
67
75
45
66
100
75
74
69
59
67
78
66
66
54
1974/76
67 "
52
45
58
87
49
63
76
69
80
*
58
62
82
56
52
59
68
72
.45
69
97
62
67
52
49
60
68
53
53
51
Percent
change
-16
-16
-19
-8
-16
-12
-14
-4
-12
-12
*
-12
-2
-9
-32
6
-4
2
-4
0
4
-4
-17
-10
. -25
-16
-10
-13
-12
-12
-5 .
Trend c
Po'.-m
Down
Do;-;;-,
Down
Down
Down
Down
Unchanged
Down
Down
*
Down
Unchanged
Down
Down
Up
Unchanged
Unchanged
Unchanged
Unchanged
Unchanged
Unchanged
Down
Down
Down
Down
Down
Down
Down
Down
Down
Average maximum 24-hour
values, pg/m3
1971/73
179
191
179
203
343
162
206
268
178
248
*
314
176
309
249
147
269
251 .
202
142
204
347
185
215
186
217
229
225
197
230
264
1974/7*
160
154
132
183
286
146
170
256
174
245
*
163
169
270
191
177
462
212
226
110
188
270
155
181
137
155
226
141
176
188
209
e
Percent
change
-10
-20
-26
-10
-17
-10
-18
-4
-2
-10
*
-48
-4
-13
-23
20
72
-15
12
-23
-8
-22
-16
-16
-25
-29
-1
-37
-10
-18
-21
Trend0
Down
Down
Down
Down
Down
Down
Down
Unchanged
Unchanged
Down
+
Down
. Unchanged
Down
Down
Up
Up
Down
Up
Down
Down
Down
Down
Down
Down
Down
Unchanged
Down
Down
Down
Down
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Table 2 (CONTINUED)
No. of
Urbanized areas monitors
Omaha, NE-IA
Philadelphia, PA-NJ
Phoenix, AR
Pittsburgh, PA
Portland, OR
Providence-Pawtucket-Warwick, RI-MA
Riverside-San Bernadino, CA
Rochester, NY
Sacramento, CA
St. Louis, MO-IL
Ta;upa-St. Petersburg FL
San Antonio, TX
San Diego, CA
San Francisco-Oakland, CA
San Jose
Seattle-Everett, WA
Springf ield-Chicopee-Holyoke, MA-CT
Toledo, OH-MI
Washington, D.C.-ND-VA
aUrbanized areas are taken from
10
19
3
25
13
12
1
16
2
28
17
3
3
13
1
10
3
19
42
the U.S.
3-year averages
ug/m3
1971/73 1974/76 Change
74
62
133
101
49
51
122
52
63
09
50
43
80
50
60
52
60
70
53
Dept. of
76
62
120
93
45
51
125
43
63
82
49
50
72
51
65
47
61
63
51
Commerce
3
0
-13
-8
-9
0
3
-17
0
-8
-1
4
-10
3
8
-9
-10
-11
-4
publication:
e
Trendc
Unchanged
Unchanged
Down
Down
Down
Unchanged
Unchanged
Down
Unchanged
Down
Unchanged
Unchanged
Down
Unchanged
Up
Down
Down
Down
Unchanged
1970 Census of
Average maximum 24-hour
values, pg/m3
1971/73
187'
183
360
308
182
216
402
131
173
230
151
253
233
135
132
179
227
202
152
Population,
19.74/76
248
132
332
317
171
132
^02
110
191
238
115
289
181
155
143
149
182
172
183
PS(1)-A1 U.S.
e
Percent
change Trend
33
0
-8
3
-6
-39
0
-16
10
3
-23
14
-22
15
8
-16
-20
-15
-20
Summary,
Up
Unchanged
Down
Unchanged
Down
Down
Unchanged
Down
Up
Unchanged
Down
Up
Down
Up
Up
Down
Down
Down
Down
December, 1971.
Ho. of monitors are the number of monitors within the urbanized area meeting the trends criteria of having at least 1 year of data in the
period 1970-72 and 1 year of data in the period 1973-75.
CA trend is defined as 'Down1 if the change is <_ 5.0%, 'Up' 1f it is _> 5.0%, and 'Unchanged' 1f it Is > -5.0%, but < +5.OX.
dNo trend data.
ePercent change based on unrounded averages
-------
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 ug/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 ug/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-
lats (TSP) matter in the New 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 ug/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
New 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
PARTICIPATE CONCENTRATION
IS:
I I
60-
1976
Figure 1. Isopleth of annual geometric mean concentrations of total suspended
particulate in 1970, 1973, 1976.
-------
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 Mew 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 35 percent fewer
people exposed to annual TSP levels above the annual primary health
standard of 75 ug/m3.
Isopleths of average TSP during 1970 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.
-------
AREA WHERE ANNUAL MEAN
TOTAL SUSPENDED PARTICU-
LATE CONCENTRATION !S:
r?w?S3 75-90 pg/m3
HEl 90-105 /ug/m3
60
105
1970 1976
Figure 2 Annual mean TSP in the city of Chicago, 1970, 1976.
90
-------
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 central
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.
-------
75
AREA WHERE ANNUAL
MEAN TOTAL SUSPENDED
PARTICULATE CONCEN-
TRATION IS:
< 75 ,u o/m
75-90 ;ug/m3
90-105 pg/
1975
-------
7
3. TRENDS IN SULFUR DIOXIDES
The Nationwide improvement in Sulfur Dioxide (S0?) concentrations
22
reported previously ' can be seen in the Nation's 50 largest urbanized
areas (Table 3). The S02 data for each urbanized areas were divided
into two time periods 1971-73 and 1974-76.
The most complete historical S02 data base exists for the West-
Gaeke bubbler. Although this monitoring method may underestimate S0£
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 pg/m3.
-------
•TABLE 3. TREND IN SULFUR DIOXIDE ANNUAL AVERAGE (WEST-GAEKE BUBBLERS)
CONCENTRATIONS FOR 50 LARGEST METROPOLITAN AREAS IN U.S.
FOR 1971-73 and 1974-76.
3-year average
Metropolitan Area
Akron, OH
Albany-Sehenectady-
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
38
*
1974-76
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
*
-------
TREND IN SULFUR DIOXIDE ANNUAL AVERAGE (WEST-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
Mew Orleans, LA
Mew York, NY-Northeastern, HJ
Norf ol k-Portsmouth , VA
Oklahoma City, OK
Omaha, NE-IA
Philadelphia, PA-NJ
Phoenix, AZ
Pittsburgh, PA
Portland, OR
Provi dence-Pawtucket-Warwi ck
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-Chicopee-
Holyoke, MA-CT
Tampa-St. Petersburg, FL
Toledo, OH
Washington, DC-MD-VA
No. of
monitors
*
7
2
10
6
1
*
*
*
*
*
n
i
7
*
*
i
i
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-/6
.*>
15
7
28
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
-------
8
4. TRENDS IN OXIDAMTS
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
pg/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 v/ere 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 176 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 Mg/m3 for a given percent of the days (Figure 4). A long-term
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
-------
TABLE 4. SECOND HIGHEST HOUR OF PHOTOCHEMICAL OXIDANT CONCENTRATIONS IN A YEAR
DURING THE PERIOD 1974-75 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, NY 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-IN 461
Memphis, TN-MS 255
-------
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)
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, ME-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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mm 20-50%
>50%
1975/1976
Figure 4
Percent of days on which NAAQS for oxidant was
exceeded during six 2-year periods in Metropolitan Lo, ArVgeks.
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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 ng/m3 in 1970 to 118 yg/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
250
-I 200
a*
a.
150
2 100
SO
O SAM JOSE. CALIF.
D SAN FHANSISCO, CALIF.
A SIX-SITE AVERAGE. BAAPCO
1970
1971
1972
1973
YEAR
1974
1975
197S
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.
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n
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 was 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 PERCENTILE OF 8-HOUR VALUES)
Area
Akron, OH
Albany- Schenectady-
Troy, NY
Atlanta, GA
Baltimore, MD
Birmingham, AL
Boston, MA
Buffalo, NY
Chicago, IL-Northwest-
ernu 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
*
*
*
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 Trend Data
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TRENDS IN CARBON MONOXIDE FOR 50 LARGEST URBANIZED AREAS IN U.S. FOR
1971-73 and 1974-76 (90TH PERCENTILE OF 8-HOUR VALUES)
V
• Area • , !'J ' -
Milwaukee, VII '•"
Minneapolis-St. Paul, MN
New Orleans, LA
New York, NY-Northeastern,
M .
Norfolk-Portsmouth.VA
Oklahoma City, OK
Omaho, NE-IA
Philadelphia, PA-NJ
^ Phoenix, AZ
Pittsburgh 5PA
Portland, OR
Providence-Pawtucket-War-
wick, RI-MA
^ Riverside-San Bernardino,
CA
Rochester, NY
Sacramento, CA
St. Lou.is, MO-IL
San Antonio, TX
San Diego, CA
San Francisco-Oakland, CA
San Jose, CA
Seattle-Everett, WA
Sprinfiel d-Chicopee-
Holyoke, 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 percenti
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
le 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 ,.'r
Down
Down
Down
Down
*
Down
Down
Down
Down
Unchanged
Unchanged
Down
*
*
Down
Down
Dnwn
Down
*
Down
Down
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