&EPA
United States
Environmental Protection
Agency
-------
EPA454/K-04-OOI
April 2004
The Ozone Report
Measuring Progress through 2003
Contract No. 68-D-02-065
Work Assignment No. 2-01
U.S. Environmental Protection Agency
Office of Air Quality Planning and Standards
Emissions, Monitoring, and Analysis Division
Research Triangle Park, North Carolina
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Contents
Introduction
A Look at 2003 4
Measuring Progress 8
A Closer Look 11
Ozone by EPA Region 11
Meteorological Adjustment 13
Emission Trends by EPA Region 14
A New Look at Patterns in Ozone Trends 15
National Parks and Other Federal Lands 16
Looking Toward the Future 17
Summary 18
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The Ozone Report: Measuring Progress through 2003
The Formation of Ozone
Ozone is a gas composed of three oxygen atoms. It occurs naturally in the stratosphere
approximately 10 to 30 miles above the earth's surface and forms a layer that protects
life on earth from the sun's harmful rays. Ozone is also formed at ground level by a
chemical reaction of various air pollutants combined with sunlight. "Ground-level" ozone
is an air pollutant that damages human health and the environment.
VOC + NOX + Sunlight = Ozone
Ozone is rarely emitted directly into the air. The pollutants that contribute to ozone
formation are oxides of nitrogen (NOX) and volatile organic compounds (VOCs). Some of
the major sources of these pollutants are vehicle and engine exhaust, emissions from
industrial facilities, combustion from electric utilities, gasoline vapors, chemical solvents,
and biogenic emissions from natural sources. Intense sunlight, which usually occurs in the
summer, causes ground-level ozone to form in harmful concentrations in the air. Many
urban areas tend to have higher levels of ozone, but even rural areas with relatively low
amounts of local emissions may experience high ozone levels because the wind transports
ozone and the pollutants that form it hundreds of miles away from their original sources.
Throughout this report, the ozone discussed is ground-level ozone.
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Introduction
In 2003, ozone levels nationwide were the lowest they
have been since 1980. Yet ozone continues to be a
pervasive air pollution problem, affecting many areas
across the country and, at times, harming millions of
people, sensitive vegetation, and ecosystems. This
report analyzes ozone levels in 2003, summarizes the
progress we have made in reducing levels of ozone
since 1980, investigates how we have made progress,
and looks at our current challenges and long-term
prospects for continuing to reduce ground-level
ozone. This report does not provide all of the
answers, but may bring us closer to understanding the
ozone problem, including the links between emission
reduction programs, changes in emissions and meteo-
rology, and ozone air quality.
Major Findings
• Ozone levels have decreased over the past 10 to 25
years, and these reductions resulted from emission
control programs. In 2003, the improved air quality
resulted mainly from favorable weather conditions
and continuing reductions in emissions.
• Ozone is at its lowest level nationally since 1980,
but the downward trend is slowing. One-hour
levels have been reduced by 29% and 8-hour
levels by 21%. Ozone levels are still decreasing
nationwide, but the rate of decrease for 8-hour
levels has slowed since 1990.
• The VOC and NOX emissions that contribute
to the formation of ground-level ozone have
decreased 54% and 25%, respectively, since 1970
despite significant increases in vehicle miles
traveled (VMT) (155%), population (39%), energy
consumption (45%), and the economy (176%).
These emissions declined during the 1980s and
1990s and showed continued reductions in 2003.
• Looking at 2003 alone, more than 100 million
people lived in the 209 counties with poor ozone
air quality based on the nation's 8-hour ozone
standard. Most of these counties are located in the
Northeast, Mid-Atlantic, Midwest, and California,
with smaller numbers of areas in the South and
south-central United States.
The most consistent and substantial improvements
in 8-hour ozone levels occurred in the Northeast
and southern West Coast. In other areas, where
regional transport of emissions is significant,
ozone trends appear flatter, indicating the need
for greater attention to sources of long-range
transported pollutants.
Meteorologically adjusted trends in many eastern
U.S. cities reveal interesting patterns in similar
ozone behavior. Many eastern cities exhibited
increases in ozone levels during the mid-1990s
followed by improvements since the late 1990s.
Improvements in eastern ozone air quality since
the mid-1990s coincide with continued decreases
in VOCs together with NOX emission reductions
from the Acid Rain Program and vehicle emis-
sion reduction programs. EPA recently proposed
rules to reduce transported precursors of ozone
and particulate pollution from stationary sources.
These rules, along with rules on vehicles and
off-road engines, will provide additional NOX
emission reductions.
Since 1990, most eastern national parks and
other federal lands experienced generally
improving ozone air quality. However, air quality
in western parks appeared to degrade. Ozone
trends in eastern national parks/federal lands
appear to closely track air quality changes in
nearby urban areas.
Over the next 10 to 15 years, scheduled regional
emission reductions are expected to result in
significantly fewer areas with unhealthy ozone.
However, in several highly populated sections of
the country, supplemental local emission control
measures will be needed to attain the national air
quality standards for ozone. Existing emission
control measures are not expected to achieve
attainment in those areas even as late as 2015.
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Health and Ecological Effects of Ozone
Exposure to ozone has been linked to a number of health effects, including
significant decreases in lung function, inflammation of the airways, and
increased respiratory symptoms, such as cough and pain when taking a
deep breath. Exposure can also aggravate lung diseases such as asthma,
leading to increased medication use and increased hospital admissions and
emergency room visits. Active children are the group at highest risk from
ozone exposure because they often spend a large part of the summer
playing outdoors. Children are also more likely to have asthma, which
may be aggravated by ozone exposure. Other at-risk groups include adults
who are active outdoors (e.g., some outdoor workers) and individuals with
lung diseases such as asthma and chronic obstructive pulmonary disease.
In addition, long-term exposure to moderate levels of ozone may cause
permanent changes in lung structure, leading to premature aging of the
lungs and worsening of chronic lung disease.
Ozone also affects vegetation and ecosystems, leading to reductions in
agricultural crop and commercial forest yields, reduced growth and surviv-
ability of tree seedlings, and increased plant susceptibility to disease, pests,
and other environmental stresses (e.g., harsh weather). In long-lived
species, these effects may become evident only after several years or even
decades and may result in long-term effects on forest ecosystems. Ground-
level ozone injury to trees and plants can lead to a decrease in the natural
beauty of our national parks and recreation areas.
The National Ozone Standards
In 1997, EPA revised the primary (health) and secondary (welfare) National
Ambient Air Quality Standards (NAAQS) for ozone by establishing 8-hour
standards. One-hour standards have been in place since 1979. The 1-hour
standards are met when the expected number of days per calendar year
with maximum hourly average concentrations above 0.12 ppm is equal to
or less than 1. The 8-hour standards are met when the 3-year average of
the annual fourth highest daily maximum 8-hour average concentration
is less than 0.08 ppm. EPA expects to revoke the 1-hour standards 1 year
after an area is designated under the 8-hour standards.
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A Look at 2003
Nationally, 2003 was a good year for ozone air quality.
Much of the good news can be attributed in part to
favorable weather conditions across many parts of the
nation. Most metropolitan areas experienced fewer
poor ozone air quality days (i.e., days with ozone
levels above the national standard) in 2003 compared
to an average of poor ozone air quality days over the
previous 5 years (1998-2002). Figure 1 shows the
results for selected metropolitan areas, and Figure 2
compares temperature and precipitation levels of 2003
with historical levels. For the eastern half of the country,
the height of the ozone season (June through August)
L
Sacramento, CA
San Jose, CA
L
Salt Lake City, UT
Denver, CO
Los Angeles, CA
Minneapolis, MN
Chicago, IL
Kansas City, MO
L
L
New York, NY
Atlanta, GA
Washington, DC
FortWorth,TX
5-year average
2003
k
Houston,TX
Figure 1. Comparison of Days with Ozone Levels above the National Standard, 2003 versus Average 1998-2002.
Note: In this graphic and throughout this report, metropolitan statistical area (MSA) boundaries, as defined by the U.S. Census
Bureau, are used.
Record Much
Coldest Below
Normal
Below Near
Normal Normal
Above
Normal
Much Record
Above Warmest
Normal
Record
Driest
Much Below Near Above
Below Normal Normal Normal
Normal
Much Record
Above Wettest
Normal
Figure 2. June-August 2003 Statewide Ranks of Temperature and Precipitation Compared to Past 109 Years (National Climatic
Data Center/NESDIS/NOAA).
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•was cooler and wetter than normal; therefore, it was
less conducive to the formation of ozone than in past
years. Despite being warmer than normal between
June and August, California experienced a wetter-
than-normal summer, which likely contributed to
lower ozone levels. Some areas, such as Denver, where
the weather in 2003 was warmer and drier than usual,
had more poor air quality days in 2003 than they did
on average during each of the previous 5 years.
Not only were weather conditions generally good last
year, but emissions of ozone precursors were also
lower in 2003. Trends show that VOCs and NOX, the
pollutants that contribute to ozone formation, were at
their lowest levels since 1970 (see "Measuring
Progress" on page 8). Determining exactly how much
of the improvement in ozone air quality is a result of
•weather conditions rather than lower emissions is
difficult because the formation of ozone is such a
complex process. This question is explored further in
later sections of this report.
The number of counties with poor ozone air quality
•was also lower in 2003. In fact, the number of coun-
ties with poor air quality in 2003 was the lowest for
both the 1-hour standard and the 8-hour standard
compared to the previous 5 years, as shown in Figure
3. By comparison, in 2002, a large number of counties
reported measuring poor ozone air quality, in part
because of •warm, dry conditions that were conducive
to ozone formation.
Number of Counties Above the Level of the 1-hour NAAQS
94 100
38
1998 1999 2000 2001 2002 2003
Number of People (in millions) Living in Counties Above
the Level of the 1-hour NAAQS
59 61
1998 1999 2000 2001 2002 2003
Number of Counties Above the Level of the 8-hour NAAQS
387
404
403
1998
1999
2000
2001
2002
2003
Number of People (in millions) Living in Counties Above
the Level of the 8-hour NAAQS
146
1998
1999
2000
2001
2002
2003
Figure 3. Annual Counts of Counties with Ozone Values Above the Level of the National Ozone Standards and Number of People Living
in Those Counties.
Note: These graphs illustrate ozone trends on an annual basis rather than the multi-year period used in determining compliance
with the 1-hour and 8-hour standards. Only counties containing at least one ozone monitor are included. Ozone nonattainment
designations generally include counties with violating monitors and the nearby counties that contribute to those violations.
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Still, in 2003 alone, more than 100 million people
lived in 209 counties with poor ozone air quality
based on the 8-hour ozone standard. Most of these
counties are located in the Northeast, Mid-Atlantic,
Midwest, and California, with smaller numbers of
areas in the South and south-central United States
(Figure 4). For the 1-hour standard, unhealthy ozone
levels in 2003 occurred in 38 counties, where
37 million people live, primarily in the Northeast,
Midwest, south-central United States, and California
(Figure 5). Although 2003 was generally a good year
in terms of ozone air quality, clearly more remains
to be done to address this persistent health and
environmental problem.
Figure 4. Counties Where Fourth Highest Daily Maximum 8-Hour Ozone Concentration Is Above the Level of the 8-Hour Standard
in 2003.
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L^
Figure 5. Counties Where Second Highest Daily Maximum 1 -Hour Ozone Concentration Is Above the Level of the 1 -Hour Standard
in 2003.
Note: Figures 4 and 5 show single-year measurements for 2003. EPA's air quality standards for ozone are based on a 3-year average.
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8-hour Ozone Designations
On April 15, 2004, EPA identified, or designated, areas as
"attainment" or "nonattainment" for the more protective
national air quality standard for 8-hour ozone. EPA designates
an area as nonattainment if it has violated the national 8-hour
ozone standard (assessed over a 3-year period) or has contributed
to violations of this standard. The designations take effect on
June 15, 2004. They are a crucial first step in state, tribal, and
local governments' efforts to reduce ground-level ozone.
The map below shows the 8-hour ozone nonattainment areas.
These 126 areas include 474 counties and are home to 159 million
people. These 474 counties are comprised of those with monitors
violating the standard between 2000 and 2003 and others that
contribute to the areas' ozone problems. In addition to metropol-
itan areas, some of our national parks, including Great Smoky
Mountains in Tennessee and North Carolina, Shenandoah in
Virginia, and Point Reyes National Seashore in California, are not
meeting the 8-hour ozone standards. Nonattainment areas must
take actions to improve their ozone air quality on a certain time-
line. For more details on 8-hour ozone designations, visit
www.epa.gov/ozonedesignations.
fj Attainment or Unclassifiable Areas
(2,668 counties)
D Nonattainment Areas (432 entire counties)
D Nonattainment Areas (42 partial counties)
Smoothing Out the Trends
Trends in ozone concentrations can be difficult to discern because
of the year-to-year variability of the data. By using a rolling 3-year
time period, we can smooth out the "peaks" and "valleys" in the
trend, making it easier to read without changing the overall trend
statistic. Three years is consistent with the 3-year period used to
assess compliance with the ozone standards. For the 1-hour trends
in this report, we use the fourth highest daily maximum over a
3-year period to be consistent with the 1-hour ozone standard. For
the 8-hour trends in this report, we use a 3-year average of the
fourth highest daily maximum in each year to be consistent with
the 8-hour ozone standard.
The 3-year statistic is assigned to the last year in each 3-year
period. For example, 1990 is based on 1988-1990, and 2003 is
based on 2001-2003. Thus, when endpoint comparisons are used
in this report to describe long-term changes (1980-2003 or
1990-2003), they are based on the first 3-year period and the
last 3-year period.
0.20
Year-to-Year Versus Rolling Average
National 8-Hour Ozone Trends, 1980-2003
82 84
86 88 90
Year-to-year
92
94 96 98
Rolling
00 02
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Measuring Progress
In addition to comparing 2003 ozone levels with
levels for recent years, EPA has been evaluating
longer-term trends in ozone using data collected from
a nationwide network of monitoring sites. From these
data, EPA has developed 1-hour and 8-hour ozone
trends for the periods 1980-2003 and 1990-2003.
Nationally, 2003 levels were 29% lower than 1980
levels and 16% lower than 1990 levels for the 1-hour
ozone standard. For the 8-hour standard, 2003 ozone
levels were 21% lower than 1980 levels and 9% lower
than 1990 levels (Figures 6-9). Ozone levels are still
decreasing nationwide, but the rate of decrease for
8-hour levels has slowed since 1990.
0.20
E 0.15
CL
cf
Q
'g 0.10
'c
0)
o
c
O 0.05
0.00
90th percentile
155 Monitoring Sites
National Standard
10th percentile
1980-2003:-29%
80 82 84 86 88 90 92 94 96 98 00 02
0.20
c
g
'g 0.10 ;
'c
0)
o
c
O 0.05 -
0.00
480 Monitoring Sites
90th percentile
National Standard
T
10th percentile
Mean
1990-2003:-16%
90 91 92 93 94 95 96 97 98 99 00 01 02 03
Figure 6. One-Hour Ozone Air Quality Trend, 1980-2003, Based
on Running Fourth Highest Daily Maximum 1-Hour Ozone Value
over 3 Years.
Figure 7. One-Hour Ozone Air Quality Trend, 1990-2003, Based
on Running Fourth Highest Daily Maximum 1-Hour Ozone Value
over 3 Years.
E 0.15
CL
CL
.g
"c
0 0.05
n nn
155 Monitoring Sites
90th percentile
~" ^^
National Standard >
/
10th percentile Mean
1980-2003: -21%
E 0.15
Q.
g
Q 0.10
'c
o
c
0 0.05
n nn
480 Monitoring Sites
90th percentile
— - \
National Standard .
/ ^
/ Mean
10th percentile
1990-2003: -9%
i i i i i i i i i i i i
80 82 84 86
90 92 94 96 98 00 02
Figure 8. 8-Hour Ozone Air Quality Trend, 1980-2003, Based
on 3-Year Rolling Averages of Annual Fourth Highest Daily
Maximum 8-hour Ozone Concentrations.
90 91 92 93 94 95 96 97 98 99 00 01 02 03
Figure 9. 8-Hour Ozone Air Quality Trend, 1990-2003, Based on
3-Year Rolling Averages of Annual Fourth Highest Daily
Maximum Ozone Concentrations.
Note: There are 480 monitoring sites with sufficient data for measuring trends from 1990 to 2003. There are fewer sites with
sufficient data for longer trend periods because some began monitoring in the mid-1980s, some had gaps in middle years, and some
discontinued monitoring at some point. There are 155 monitoring sites with sufficient data for trends from 1980 to 2003.
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200%
150% -
100% -
50% -
0%
-50% -
Gross Domestic Product
Vehicle Miles Traveled
.^ Energy Consumption
Population
NOV Emissions
VOC Emissions
70 80 90 95 96 97 98 99 00 01 02 03
Figure 10. Comparison of Growth Areas and Emissions. Between 1970 and 2003, gross domestic product increased 176%
VMT increased 155%, energy consumption increased 45%, and population increased 39%. At the same time, emissions of NOX
decreased 25% and VOC decreased 54%.
Over the past 30 years, EPA, in conjunction with state
and local agencies, has instituted various programs to
reduce NOX and VOC emissions that contribute to
ozone formation. These emission reductions occurred
at the same time the nation's economy, energy
consumption, and population were growing. For
example, between 1970 and 2003, gross domestic
product increased approximately 176%; VMT, 155%;
energy consumption, 45%; and population, 39%,
whereas emissions of NOX and VOCs decreased
approximately 25% and 54%, respectively (Figure 10).
The ratio of NOX and VOC emissions to population
has also dropped since 1970 (Figure 11).
70 80 90 95 96 97 98 99 00 01 02 03
Figure 11. NOX and VOC Emissions Per Capita, 1970-2003.
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Figure 12 shows the trends in NOX emissions for
the period 1970-2003. After 1980, NOX emissions
decreased approximately 27%, and, after 1990, NOX
emissions decreased approximately 22%. Most of the
NOX emission reductions since the Clean Air Act was
enacted in 1970 have occurred since 1990, during
•which time NOX emissions have decreased by 5.5
million tons. Most of this decrease (89% of all NOX
reductions) has come from two sectors: on-road
motor vehicles, which have reduced emissions by
2.5 million tons (a 26% reduction since 1990), and
electric utilities, which have reduced emissions by
2.4 million tons (a 36% reduction since 1990).
Figure 13 shows the trends in VOC emissions for
the period 1970-2003. VOC emissions have declined
steadily, dropping approximately 48% since 1980 and
32% since 1990. Since 1990, most of this decrease
(92% of all VOC reductions) has come from two
sectors: on-road motor vehicles, which reduced
emissions by over 5 million tons (a 55% reduction
since 1990), and solvent utilization, which reduced
emissions by more than 1 million tons (a 20%
reduction since 1990). Table 1 lists the major
emission control programs that have contributed
to NCL and VOC reductions since 1990.
Fuel Combustion D Industrial Processes
D Transportation D Miscellaneous
20,000
15,000
10,000
5,000
0
ja-- In 1985, EPA refined its methods I
^0*^^^^* •"naGa^^^-T" for estimating emissions.
>~^__^
^^ ^_
70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00 02
Figure 12. National Trends in NOX Emissions, 1970-2003.
• Fuel Combustion
D Transportation
D Industrial Processes
D Miscellaneous
In 1985, EPA refined its methods
for estimating emissions.
70 72 74 76 78 80 82 84 86 88 90 92 94 96 98 00 02
Figure 13. National Trends in VOC Emissions, 1970-2003.
Table 1. Emission Control Programs Contributing to NOxand VOC Emission Reductions Since 1990
Sector
Electric Utilities
Electric Utilities
Electric Utilities
Chemical
Manufacturing
Other Stationary Source
Mobile Sources
Mobile Sources
Mobile Sources
Mobile Sources
Mobile Sources
Mobile Sources
Program
Acid Rain Program
Ozone Transport Commission NOX Program
NOX State Implementation Plan Call
Synthetic Organic Chemical Manufacturing
Maximum Achievable Control Technology
Clean Air Act Solvent and Coating Controls
Tier I Emission Standards
Reformulated Gasoline
National Low Emission Vehicle Program
Inspection/Maintenance Programs
Reid Vapor Pressure Controls
Evaporative Controls
NOX
Reductions
X
X
X
X
X
X
X
VOC
Reductions
X
X
X
X
X
X
X
X
10
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A Closer Look
Ozone by EPA Region
The national trends presented so far do not
completely describe the ozone story. Because weather
patterns and emission changes are variable throughout
the United States, it is important to examine ozone
trends on a more detailed basis, such as regionally.
This initial regional assessment focuses on monitored
levels of 8-hour ozone by EPA Region. One-hour
ozone levels show similar patterns.
Not surprisingly, a closer look at trends in measured
ozone values by EPA Region shows differences in
the progress made since 1980 in different parts of
the country. Although all Regions have experienced
reductions in ozone concentrations, some have made
more substantial advances than others. For example,
EPA Regions 1,9, and 10 exhibited the most
significant improvement in ozone (20%, 37%, and
22% decreases, respectively), as shown in Figure 14.
In general, the greatest improvements occurred in
areas that had the highest ozone concentrations back
in the early 1980s. EPA Regions 2 and 5 exhibited
the least improvement (11% decreases).
Ozone trends in EPA Regions since 1990 (Figure 15)
show patterns similar to the 1980 trends. However,
progress in reducing ozone concentrations has slowed
nationally since 1990. Again, the Northeast (Region 1)
and the southern West Coast (Region 9) show the
most progress. Areas in the western portion of
the country (Regions 7 and 8) showed the least
improvement over the past 14 years.
10
.081
.063
.090
22%
.126
.080
37%
12%
.079
8
.095
.122
.097
*20%
.104
.093
•096^ .085
tn%
7
.079
.106
.091
17%
14%
.104
.090
.086
.078
17%
13%
The National Trend
.105
21%
.083
Figure 14. Trend in Fourth Highest Daily Maximum 8-Hour Ozone Concentration (ppm) by EPA Region, 1980-2003.
11
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.069
10
.104
10%
-062
.075
^072
4%
.090
.085
6%
.091
.097
.081
16%
8
.076
.076
no change
.087
.081
.085 _ nan
6%
The National Trend
.091
.083
9%
Figure 15. Trend in Fourth Highest Daily Maximum 8-Hour Ozone Concentration (ppm) by EPA Region, 1990-2003.
Although trends by EPA Region provide important
insights into different rates of improvement across
the country, even these depictions mask interesting
differences in air quality at more local levels. For
example, the significant downward trend in EPA
Region 9 (16% decrease) is largely influenced by
the improvements in Los Angeles and other southern
California metropolitan areas where VOC and
NOX emission control programs have had significant
impact on ozone concentrations. In other urban
areas within Region 9, ozone improvements have
been more modest or even different directionaUy
as illustrated in Figure 16. The concept of looking
at trends for a more localized area than EPA Regions
is explored further in "A New Look at Patterns in
Ozone Trends" on page 15.
16%
Figure 16. Difference in Trends in Fourth Highest Daily Maximum 8-Hour
Ozone Concentrations for Metropolitan Areas in Region 9, 1990-2003.
12
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Meteorological Adjustment
Ozone is formed through complex chemical reactions
of VOC and NOX emissions during periods of
conducive weather conditions. Ozone is more readily
formed when it is sunny and hot and the air is stag-
nant. Conversely, ozone production is more limited
when it is cloudy, cool, rainy, and windy. For these
reasons, ozone concentrations are generally the highest
during the summer.
To separate the effects of weather from those of VOC
and NOX emissions, measured ozone levels can be
adjusted to account for the impact of meteorology.
This meteorological adjustment technique helps us
understand how much of the year-to-year variability
of an ozone trend is due to the weather rather than
to the effects of emission control programs.
The number of summertime days above 90° is one
of the indicators of conditions conducive to ozone
formation. Figure 17 shows temperature data together
with the meteorologically adjusted trends
(1990-2003) for two example metropolitan areas.
For these eastern cities, the meteorological adjustment
generally lowers the measured ozone when the
summer is relatively hot. Similarly, when the summer
is cool, the adjusted value is usually increased. For
Atlanta, you can see these adjustments for the hot
summer of 1993 (where the meteorologically adjusted
value is lower) and the cool summer of 2003 (where
the adjusted ozone value is higher). These graphics
help explain how meteorologically adjusted trends
smooth out some of the year-to-year variability in
observed ozone levels.
Figure 18 presents trends in meteorologically adjusted
ozone levels by EPA Region from 1990 to 2003.
These results are based on summertime average daily
maximum 8-hour ozone and meteorological data for
35 selected eastern cities. (At the time of publication,
meteorologically adjusted data for western cities were
not available.) With these analyses, we can begin to
look at some of the influence of meteorology on
ozone. However, these analyses are based on a limited
number of cities in each EPA Region, so these
regional trends should not be compared directly to
the regional trends presented in the previous section.
Before adjusting for weather, EPA Regions 3, 4, and 6
show improving air quality, with average reductions
in ozone levels of 9% to 21%. After adjusting for
•weather, however, each Region demonstrates a more
moderate decline. The most dramatic effect of the
meteorological adjustment is in Region 4, where the
adjusted trend shows a 4% decrease, compared with
a 21% decrease for the unadjusted trend. Region 6
shows the largest improvement, 9%, after adjusting for
meteorology. Ozone levels in the midwest and central
regions of the country show the same percent increase
in ozone both with and without the meteorological
adjustment. EPA Region 2 shows a larger increase
in ozone levels after the meteorological adjustment
is applied.
The current meteorological adjustment method does
not reflect all of the influences of meteorology on
ozone. For example, future analyses will try to better
account for year-to-year variations in ozone levels due
to regional transport.
Bridgeport, CT
Atlanta, GA
50
40
20
10
• HI ..I
80
70
60
50
40
90 91 92 93 94 95 96 97 98 99 00 01 02 03
100
80
g- 60
Q
40
20
I
luiluili
70
60
50
40
30
90 91 92 93 94 95 96 97 98 99 00 01 02 03
Unadjusted Ozone
Meteorologically Adjusted Ozone
Figure 17. Number of Days Daily Maximum Temperatures Exceed 90° (bar) Compared to Unadjusted Ozone (red line) and
Meteorologically Adjusted Ozone (blue line) for Bridgeport and Atlanta, 1990-2003. Ozone Concentrations are Annual Average Daily
Maximum 8-Hour Values between June and August.
13
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10
8
49%
42%
'42%'
J7%_-.-
43% 2
f 2%
T5%
f 2%
t9%
_j*^
f 15%
_f4%_
T2?%
Trend in average daily maximum 8-hour concentrations (ppm)
Meteorological-adjusted trend in average daily maximum 8-hour concentrations (ppm)
Figure 18. Trends in Unadjusted and Meteorologically Adjusted Ozone Levels by EPA Region, 1990-2003.
Emission Trends by EPA Region
We can now look at regional trends in VOC and
NOX emissions and make an initial comparison to the
meteorologically adjusted regional ozone trends
described previously. Regional emissions data are
currently available only since 1996 and are presented
in Figure 19. The declines over the past 7 years are
substantial. Regional VOC reductions varied from
11% to 27%. Regional NOX reductions varied from
14% to 25%. The largest reductions for VOCs and
NOX occurred in Regions 3, 4, and 5, which account
for more than half of the national decrease.
Improvements in ozone air quality in the eastern
United States since the mid-1990s generally coincide
with these VOC and NOX emission reductions.
Regions 3 and 4, where significant emission reduc-
tions occurred, also show progress in reducing ozone
levels. This is even more evident when the second
half of the 14-year ozone trend is examined. The
apparent absence of an associated ozone air quality
improvement in Region 5 may be due at least in
part to the location of the emission sources. Much
of the NOX emission reductions occurred at facilities
located in the Ohio Valley. Most of Region 5's
metropolitan areas are upwind of these emission
sources. However, emission reductions would be
expected in downwind areas because pollutants can
be transported hundreds of miles.
Regional emission reductions conform to phased
implementation of emission control programs during
the late 1990s, as described at the national level. For
example, relatively large NOX reductions occurred in
the Mid-Atlantic and Midwestern states (Regions 2,
3, and 5) during 1999 and in the Southeast (Region 4)
during 2000. These reductions correspond to imple-
mentation of the Acid Rain Program, as described
earlier. Several eastern Regions also had large NOX
reductions in 2003, which may be attributed in
part to implementation of the Ozone Transport
Commission's NOX Program and the NOX State
Implementation Plan (SIP) Call.
14
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« 4
.o
NO,
1996 1997 1998 1999 2000 2001 2002 2003
Region 1
Region 2
Region 3
Region 4
voc
1996 1997 1998 1999 2000 2001 2002 2003
• Region 5
• Region 6
Region 7
Region 8
Region 9
Region 10
Figure 19. NOX and VOC Emissions by EPA Region, 1996-2003.
Note: The large increase in VOC emissions in Region 10 from 1998 to 1999 is due to a change in methodology rather than
a true emission increase.
A New Look at Patterns in Ozone Trends
It is important to understand ozone trends as they
relate to NOX and VOC emission trends to properly
design programs to mitigate ozone and to assess the
nation's progress in reducing ozone. However, the
influence of weather makes it difficult to isolate the
specific changes in ozone concentrations that result
from VOC and NOX reductions. In addition, and as
previously indicated, assessing trends in ozone levels
nationally or by EPA Region may mask important
local differences that make it difficult to determine
direct influence of emission reductions. We begin to
address these factors by looking at meteorologically
adjusted ozone trends for selected metropolitan statis-
tical areas (MSAs) in the East. The results provide
some interesting patterns that may be useful in
defining regions of similar ozone concentration
behavior. Studying these regional patterns may lead
to insights into the underlying effects of changes in
emission levels and transport of emissions on ozone
air quality. A full explanation of this analysis of ozone
patterns can be found at www.epa.gov/airtrends/
ozonepatterns.html.
These patterns have two characteristics: the overall
direction of MSA ozone trends (i.e., increases, no
change, or decreases) and the shape of each trend's
pattern (i.e., when temporary increases or decreases
occur). Consistency in these patterns suggests that
groups of MSAs behave similarly, showing several
geographic clusters with consistent ozone trends. For
example, the trends across many eastern MSAs reveal
an overall improvement in ozone levels since 1990
and a temporary increase in ozone levels during the
mid-1990s, followed by decreases in ozone levels
beginning in 1998. The improvement in ozone levels
in the late 1990s coincides with reductions
in NOX emissions associated with the Acid Rain
Program. Figure 20 shows reductions in NOX
emissions for the states contributing most of the
reductions in NOX since 1996. The figure also shows
the coincidental decrease in meteorologically adjusted
ozone levels across three of the identified geographic
clusters. The NOX reductions occurred across many of
the midwestern states, with the ozone trends down-
wind reflecting the transport of ozone precursors. At
the same time, NOX and VOC reductions occurred
from mobile sources, which also influence ozone
concentrations. Further analysis is needed to sort
out the degree of influence from regional and local
sources of ozone precursors.
Although additional investigation and more complete
characterization of meteorological influences are
needed, these relatively consistent regional patterns
in the behavior of ozone may, after further study, offer
important insights into designing programs to reduce
ozone and to assess the nation's progress in that direc-
tion. First, the approach appears to define areas with
"similar" ozone behavior and thereby provide a
meaningful grouping of urban areas. Further, with
improved information on emissions on a more refined
geographic and temporal scale, these data-defined
regions may enhance our ability to understand and
explain changes in ozone concentrations in terms of
regional transport, varying meteorology, and changes
in emissions.
15
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Trends in NOX Emissions for Eastern States with
Largest Reductions in NOX from Electric Utilities
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1996 1997 1998 1999 2000 2001 2002 2003
Ozone Levels
Since 1990
A Hartford, CT
Pittsburgh, PA
Columbia, SC
Figure 20. Ozone Trends for Selected Urban Areas and Corresponding Regional Emission Trends.
Note: Visit www. epa.gov/airtrends/ozonepatterns.html to look at additional areas with regional patterns of similar
ozone trends.
National Parks and Other Federal Lands
Thirty-two national parks and federal lands located
outside urban areas, mostly in the western United
States, had sufficient monitoring data to assess trends
for the period 1990-2003. Most of the locations show
no net change in 8-hour ozone levels over this time
period. Levels at four locations increased slightly
between 1990 and 2003, while levels at four other
locations decreased slightly. No location has shown
significant improvement over the past 14 years. Six
locations experienced statistically significant increases
in ozone during this period: Great Smoky Mountains
(Tennessee) in the eastern United States and Mesa
Verde (Colorado), Rocky Mountain (Colorado),
Craters of the Moon (Idaho), Canyonlands (Utah),
and Yellowstone (Wyoming) in the West. Generally,
the locations with the most consistent and
pronounced upward trends are located in the West,
•where the last two summers have been warmer and
drier than average. In contrast, the locations showing
the largest improvements in ozone levels are found in
the East, where the summer of 2003 was cooler and
•wetter than normal. The obvious exception is the
Great Smoky Mountains National Park, for which
a significant upward trend has already been noted.
As Figure 21 illustrates, however, the overall trend
at Great Smoky Mountain National Park is driven
by an increase in ozone levels in the late 1990s, which
has been followed by consistent improvement over the
past several years.
Ozone trends for many national parks and federal
lands in the East and South are similar to those of
nearby urban areas, providing evidence of the regional
nature of the ozone problem. For example, as seen in
Figure 21, the federal land in South Carolina (Cape
Remain) reveals declining ozone levels since 1990 and
a temporary increase late in the period consistent with
the trends in the neighboring urban area (Columbia,
South Carolina). In addition, the ozone trend in
Brigantine, New Jersey, reflects the same direction and
pattern seen in the Mid-Atlantic region for areas such
as Philadelphia and Baltimore, whereas the trend in
Cape Cod mirrors those of New York and Hartford.
Knoxville, Nashville, and Great Smoky Mountains
National Park all show similar trends in ozone for the
period 1990—2003. Comparisons between national
parks and nearby urban areas are more readily
performed in the East and South, where physical
proximity between the two makes associations more
meaningful. Further exploration is needed to assess
trends and patterns in •western rural areas.
16
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I Looking Toward the
Future
Nashville
Great Smoky Mtn
Knoxville
Reductions in NOX and VOC emissions associated
with upcoming national and regional regulations
should result in major improvements in ozone levels
over the next 10 to 20 years. EPA estimates that regu-
lations for mobile and stationary sources will cut NOX
emissions by 7 million tons annually in 2015 from
2001 levels. VOC emissions will be cut by 3 million
tons annually in 2015 compared to 2001 levels. New
national mobile source regulations, which will reduce
both NOX and VOCs, will affect heavy-duty diesel
engines, highway vehicles, and other mobile sources.
As Figure 22 shows, most of the NOX and VOC
reductions for mobile sources are associated with
continuing improvements in on-road vehicles.
National and regional control programs to reduce
utility emissions, in particular the NOX SIP Call,
will reduce NOX emissions from electric generating
units and industrial boilers across the East. In fact,
reductions can already be seen in 2003, where NOX
emissions from electric utilities and on-road motor
vehicles are 1.4 million tons less than 2001 levels. For
VOCs, 2003 emissions from on-road motor vehicles
are nearly 1 million tons less than 2001 levels.
I
,0
NOV
VOC
• Area Sources D Industrial Sources
• Non-Road Sources • Electric Generating
D On-Road Sources
Sources
Figure 22. Expected Reductions in NOX and VOCs in 2015.
91 92 93 94 95 96 97 98 99 00 01 02 03
Figure 21. National Park/Federal Lands and Nearby Urban Area
Trends in Fourth Highest Daily Maximum 8-Hour Ozone from
1990-2003.
17
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Models predicting the effect of these emission reduc-
tions on air quality show that all areas in the eastern
United States will have lower ozone concentrations in
2015 relative to present-day conditions. In most cases,
the predicted improvement in ozone ranges from
10% to 20%. An estimated 274 counties violated the
8-hour ozone standard in 2002 (Figure 23), but only
34 of those counties are projected to violate the
8-hour standard by 2015 (Figure 24). Additional
NOX controls will be necessary to address the residual
ozone problem. Toward that end, EPA recently
proposed the Clean Air Interstate Rule, which would
reduce NOX emissions in 29 eastern states and the
District of Columbia by 1.8 million tons annually by
2015. This rule is projected to bring 8 of the 34
residual counties into attainment with the 8-hour
standard by 2015.
Summary
Figure 23. Counties (274) Violating the 8-Hour Ozone Standard
in 2002.
Figure 24. Remaining Counties (34) Likely to Violate the 8-Hour
Ozone Standard in 2015.
Ozone levels vary from year to year and location to
location. Meteorology, transport of ozone precursors,
and difficulties in estimating emissions make analysis
and interpretation of ambient ozone levels challeng-
ing. EPA will continue to measure and study ozone
concentrations, characterize and measure the reduc-
tions in VOC and NOX emissions, and assess the
nation's progress in attaining the ozone standards. This
information will help guide the country's air quality
program and help EPA to more accurately report the
status and progress of the program to the public.
The "state of ozone" can be summarized as follows:
• Ozone levels have decreased over the past 10
to 25 years, and these reductions resulted from
emission control programs.
• Ozone is at its lowest level nationally since 1980,
but the downward trend is slowing.
• Ozone trends vary by region: since 1980, the
Northeast and West/Southwest have shown the
greatest improvements, whereas other areas reveal
a flatter trend.
• Nationally, 2003 was one of the cleanest years on
record, due in part to meteorology.
• After the variability of meteorology is accounted
for, we are able to better assess regional ozone
trends and make initial comparisons to trends
in emissions.
• Ozone still threatens public health and the envi-
ronment in a number of areas around the country.
• Over the next decade, federal, state, and local
regulations are expected to further reduce ozone
precursor emissions, and, as a result, ozone levels
are expected to drop.
• Future analysis and continual tracking of ozone
trends across the nation will allow us to determine
the effectiveness of emission control programs and
•whether there is a sustained downward trend in
ozone across the United States.
• Areas of further investigation include regional
ozone air quality patterns, more detailed emission
estimates (including biogenics), meteorological
effects on ozone trends, and regional and
transcontinental transport of ozone and its
precursors.
• Additional information may be found at EPA's air
trends website at: www.epa.gov/airtrends.
18
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Acronyms
CAA Clean Air Act
EPA U.S. Environmental Protection Agency
MACT maximum achievable control technology
MSA metropolitan statistical area
NAAQS National Ambient Air Quality Standards
NOX oxides of nitrogen
ppm parts per million
SIP State Implementation Plan
VMT vehicle miles traveled
VOC volatile organic compound
For Further Information
Reference
U.S. Environmental Protection Agency. 1996. Air Quality Criteria for Ozone and Related
Photochemical Oxidants. EPA/600/P-93/004a-cF. Research Triangle Park, NC: U.S.
Environmental Protection Agency.
Web Sites
Bureau of Economic Analysis: www.bea.gov
Bureau of Transportation Statistics: www.bts.gov
Clean Air Interstate Rule: www.epa.gov/interstateairquality
Detailed Information of Air Pollution Trends: www.epa.gov/airtrends
Energy Information Administration: www.eia.doe.gov
Formation of Ozone: www.epa.gov/air/urbanair/ozone/what.html
Health and Ecological Effects:
www.epa.gov/airnow/health/smogl.htmW3
www.epa.gov/air/urbanair/ozone/hlth.html
National Park Service: www.nps.gov
Office of Air and Radiation: www.epa.gov/oar
Office of Air Quality Planning and Standards: www.epa.gov/oar/oaqps
Office of Atmospheric Programs: wwwepa.gov/air/oap.html
Office of Radiation and Indoor Air: www.epa.gov/air/oria.html
Office of Transportation and Air Quality: www.epa.gov/otaq
Online Air Quality Data: wwwepa.gov/air/data/index.html
Ozone Depletion: www.epa.gov/ozone
Ozone Designations: www.epa.gov/ozonedesignations
Real-Time Air Quality Maps and Forecasts: wwwepa.gov/airnow
Regional Patterns in Ozone: www.epa.gov/airtrends/ozonepatterns.html
Westar: www.westar.org/downloads.html
U.S. Census Bureau: www.census.gov
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