The Nature of the Ozone Air Quality Problem

in the Ozone Transport Region:

A Conceptual Description

Prepared for the Ozone Transport Commission

Prepared by NESCAUM

Boston, MA

Final

October 2006

Contributing Authors

Tom Downs, Maine Department of Environmental Protection

Richard Fields, Massachusetts Department of Environmental Protection

Prof. Robert Hudson, University of Maryland

Iyad Kheirbek, NESCAUM

Gary Kleiman, NESCAUM

Paul Miller, NESCAUM

Leah Weiss, NESCAUM
Acknowledgements

NESCAUM thanks the Mid-Atlantic Regional Air Management Association for

providing the foundational basis of this report.

NESCAUM also thanks the following people for their comments and input during the

development of this report:

Tad Aburn, Maryland Department of the Environment

Michael Geigert, Connecticut Department of Environmental Protection

Kurt Kebschull, Connecticut Department of Environmental Protection

Tonalee Key, New Jersey Department of Environmental Protection

Mohammed A. Majeed, Delaware Department of Natural Resources and Environmental

Conservation

Charles Pietarinen, New Jersey Department of Environmental Protection

Jeff Underhill, New Hampshire Department of Environmental Services

David Wackter, Connecticut Department of Environmental Protection

Martha Webster, Maine Department of Environmental Protection

Danny Wong, New Jersey Department of Environmental Protection

Jung-Hun Woo, NESCAUM

Michael Woodman, Maryland Department of the Environment

ii
TABLE OF CONTENTS

Executive Summary.............................................................................................................v

 1.Introduction ....................................................................................................................... 1

 1.1.Background ................................................................................................................ 1

 1.2.Ozone formation ........................................................................................................ 2

 1.3.Spatial pattern of ozone episodes in the OTR ............................................................ 3

 1.4.The regional extent of the ozone problem in the OTR .............................................. 4

 1.5.Ozone trends in the OTR ........................................................................................... 6

 1.6.History of ozone transport science ............................................................................. 7

 1.6.1.From the 1970s to the National Research Council report, 1991 ......................... 7

 1.6.2.Ozone Transport Assessment Group (OTAG) 1995-1997 ................................. 8

 1.6.3.Northeast Oxidant and Particle Study (NE-OPS) 1998-2002 ............................. 9

 1.6.4.NARSTO 2000 .................................................................................................. 11

 1.6.5.New England Air Quality Study (NEAQS) 2002-2004 .................................... 13

1.6.6.Regional Atmospheric Measurement, Modeling, and Prediction Program

 (RAMMPP) 2003 ....................................................................................................... 14

 1.7.Summary .................................................................................................................. 14

 2.Meteorology and Evolution of Ozone Episodes in the Ozone Transport Region ............. 1

 2.1.Large-scale weather patterns ...................................................................................... 1

 2.2.Meteorological mixing processes .............................................................................. 2

 2.2.1.Nocturnal inversions ........................................................................................... 3

 2.2.2.Subsidence inversions ......................................................................................... 3

 2.3.Meteorological transport processes ............................................................................ 3

 2.3.1.Introduction ......................................................................................................... 3

 2.3.2.Ground level winds ............................................................................................. 5

 2.3.3.Mid-level winds: Nocturnal low level jets .......................................................... 7

 2.3.4.Upper level winds: Ozone and precursors aloft .................................................. 9

 2.4.Atmospheric modeling of regional ozone transport ................................................. 11

 2.5.Summary .................................................................................................................. 14

 3.Ozone-forming Pollutant Emissions ................................................................................. 1

 3.1.Emissions inventory characteristics in the OTR ........................................................ 1

 3.1.1.Volatile organic compounds (VOCs) .................................................................. 1

 3.1.2.Oxides of nitrogen (NOX) .................................................................................. 2

 3.2.Emissions inventory characteristics outside the OTR ............................................... 5

 3.3.Are NOX or VOC control strategies most effective at reducing ozone? ................... 7

 3.4.Summary .................................................................................................................... 7

 4.What Will It Take to Clean the Air? – Linking the Science to Policy .............................. 1

 4.1.The three phases of a bad ozone day and the ozone reservoir ................................... 1

 4.2.Chronology of an ozone episode – August 2002 ....................................................... 3

 4.3.Clean Air Act provisions ........................................................................................... 9

 4.4.Past regional efforts ................................................................................................. 10

 4.5.Summary: Building upon success ............................................................................ 11

 Appendix A:USEPA Guidance on Ozone Conceptual Description .................................... 1

 Appendix B:Ozone pattern classifications in the OTR ........................................................ 1

 Appendix C:Exceedance days by monitor in the OTR ........................................................ 1

 Appendix D:8-hour ozone design values in the OTR, 1997-2005 ..................................... 17

iii
 Appendix E:The sea breeze and flow over the ocean in-depth ............................................ 1

 Appendix F:Observed nocturnal low level jet across the OTR, July 2002 .......................... 1

 Appendix G:Contributions to the ozone reservoir ............................................................... 1

FIGURES

Figure 1-1. Conceptual picture of ozone formation in the atmosphere............................... 3

Figure 1-2. Map of 8-hour ozone baseline design values in the OTR................................. 5

Figure 1-3. Trends in 8-hour ozone in the OTR 1997-2005................................................6

Figure 1-4. Conceptual picture of different transport regimes contributing to ozone

episodes in the OTR...........................................................................................................12

Figure 2-5. Temperature profile taken over Albany, NY, on September 1, 2006 at 7 a.m.

eastern standard time............................................................................................................2

Figure 2-6. Schematic of a typical weather pattern associated with severe ozone episodes

in the OTR............................................................................................................................4

Figure 2-7. Illustration of a sea breeze and a land breeze....................................................5

Figure 2-8. Average 2000 – 2002 wind direction frequency associated with elevated onehour ozone levels in coastal Maine......................................................................................6

Figure 2-9. Ozonesonde measurements on August 5, 2005 of elevated ozone

concentrations in a nocturnal low level jet above Beltsville, MD ...................................... 9

Figure 2-10. Altitude profiles for ozone, carbon monoxide, NOY, and SO2 taken on

July 15, 1995......................................................................................................................10

Figure 2-11. Observed vertical ozone profile measured above Poughkeepsie, NY at about

4 a.m. EST on July 14, 1995..............................................................................................11

Figure 3-12. 2002 MANE-VU state VOC inventories in the OTR..................................... 2

Figure 3-13. State level nitrogen oxides emissions............................................................. 3

Figure 3-14. Plot of monitored NOX trends in OTR during 1997-2005............................. 4

Figure 3-15. 2002 MANE-VU state NOX inventories in the OTR..................................... 5

Figure 4-16. Median ozone profiles for morning and afternoon flights from 1996 – 2003 1

Figure 4-17. Hourly ozone profiles in the southern OTR, August 12, 2002....................... 2

Figure 4-18. Hourly ozone profiles in the northern OTR, August 12, 2002........................3

Figure 4-19. Surface weather maps for August 9-16, 2002.................................................6

 Figure 4-20. HYSPLIT 72-hour back trajectories for August 9-16, 2002..........................7

Figure 4-21. Spatially interpolated maps of maximum 8-hour surface ozone

concentrations August 9 – 16, 2002.....................................................................................8

TABLES

Table 2-1. USEPA CAIR modeling results of percent contribution to 8-hour ozone

nonattainment in OTR counties in 2010 due to transport from upwind states.................. 12

Table 2-2. USEPA CAIR modeling results of upwind states that make a significant

contribution to 8-hour ozone in downwind OTR nonattainment counties........................ 13

Table 3-3. Eastern U.S. RPOs and their state members.......................................................6

Table 3-4. VOC emissions in eastern RPOs........................................................................ 6

Table 3-5. NOX emissions in eastern RPOs........................................................................7

iv
Executive Summary

The Ozone Transport Region (OTR) of the eastern United States covers a large

area that is home to over 62 million people living in Connecticut, Delaware, the District

of Columbia, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York,

Pennsylvania, Rhode Island, Vermont, and northern Virginia. Each summer, the people

who live within the OTR are subject to episodes of poor air quality resulting from

ground-level ozone pollution that affects much of the region. During severe ozone events,

the scale of the problem can extend beyond the OTR’s borders and include over

200,000 square miles across the eastern United States. Contributing to the problem are

local sources of air pollution as well as air pollution transported hundreds of miles from

distant sources outside the OTR.

To address the ozone problem, the Clean Air Act Amendments require states to

develop State Implementation Plans (SIPs) detailing their approaches for reducing ozone

pollution. As part of this process, states are urged by the U.S. Environmental Protection

Agency (USEPA) to include in their SIPs a conceptual description of the pollution

problem in their nonattainment areas. This document provides the conceptual description

of the ozone problem in the OTR states, consistent with the USEPA’s guidance.

Since the late 1970s, a wealth of information has been collected concerning the

regional nature of the OTR’s ground-level ozone air quality problem. Scientific studies

have uncovered a rich complexity in the interaction of meteorology and topography with

ozone formation and transport. The evolution of severe ozone episodes in the eastern U.S.

often begins with the passage of a large high pressure area from the Midwest to the

middle or southern Atlantic states, where it assimilates into and becomes an extension of

the Atlantic (Bermuda) high pressure system. During its passage east, the air mass

accumulates air pollutants emitted by large coal-fired power plants and other sources

located outside the OTR. Later, sources within the OTR make their own contributions to

the air pollution burden. These expansive weather systems favor the formation of ozone

by creating a vast area of clear skies and high temperatures. These two prerequisites for

abundant ozone formation are further compounded by a circulation pattern favorable for

pollution transport over large distances. In the worst cases, the high pressure systems stall

over the eastern United States for days, creating ozone episodes of strong intensity and

long duration.

One transport mechanism that has fairly recently come to light and can play a key

role in moving pollution long distances is the nocturnal low level jet. The jet is a regional

scale phenomenon of higher wind speeds that often forms during ozone events a few

hundred meters above the ground just above the stable nocturnal boundary layer. It can

convey air pollution several hundreds of miles overnight from the southwest to the

northeast, directly in line with the major population centers of the Northeast Corridor

stretching from Washington, DC to Boston, Massachusetts. The nocturnal low level jet

can extend the entire length of the corridor from Virginia to Maine, and has been

observed as far south as Georgia. It can thus be a transport mechanism for bringing ozone

and other air pollutants into the OTR from outside the region, as well as move locally

formed air pollution from one part of the OTR to another.

v
Other transport mechanisms occur over smaller scales. These include land, sea,

mountain, and valley breezes that can selectively affect relatively local areas. They play a

vital role in drawing ozone-laden air into some areas, such as coastal Maine, that are far

removed from major source regions.

With the knowledge of the different transport scales into and within the OTR, a

conceptual picture of bad ozone days emerges. After sunset, the ground cools faster than

the air above it, creating a nocturnal temperature inversion. This stable boundary layer

extends from the ground to only a few hundred meters in altitude. Above this layer, a

nocturnal low level jet can form with higher velocity winds relative to the surrounding

air. It forms from the fairly abrupt removal of frictional forces induced by the ground that

would otherwise slow the wind. Absent this friction, winds at this height are free to

accelerate, forming the nocturnal low level jet. Ozone above the stable nocturnal

inversion layer is likewise cut off from the ground, and thus it is not subject to removal

on surfaces or chemical destruction from low level emissions. Ozone in high

concentrations can be entrained in the nocturnal low level jet and transported several

hundred kilometers downwind overnight. The next morning as the sun heats the Earth’s

surface, the nocturnal boundary layer begins to break up, and the ozone transported

overnight mixes down to the surface where concentrations rise rapidly, partly from

mixing and partly from ozone generated locally. By the afternoon, abundant sunshine

combined with warm temperatures promotes additional photochemical production of

ozone from local emissions. As a result, ozone concentrations reach their maximum

levels through the combined effects of local and transported pollution.

Ozone moving over water is, like ozone aloft, isolated from destructive forces.

When ozone gets transported into coastal regions by bay, lake, and sea breezes arising

from afternoon temperature contrasts between the land and water, it can arrive highly

concentrated.

During severe ozone episodes associated with high pressure systems, these

multiple transport features are embedded within a large ozone reservoir arriving from

source regions to the south and west of the OTR. Thus a severe ozone episode can

contain elements of long range air pollution transport from outside the OTR, regional

scale transport within the OTR from channeled flows in nocturnal low level jets, and

local transport along coastal shores due to bay, lake, and sea breezes.

From this conceptual description of ozone formation and transport into and within

the OTR, air quality planners need to develop an understanding of what it will take to

clean the air in the OTR. Weather is always changing, so every ozone episode is unique

in its specific details. The relative influences of the transport pathways and local

emissions vary by hour and day during the course of an ozone episode and between

episodes. The smaller scale weather patterns that affect pollution accumulation and its

transport underscore the importance of local (in-state) controls for emissions of nitrogen

oxides (NOX) and volatile organic compounds (VOCs), the main precursors of ozone

formation in the atmosphere. Larger synoptic scale weather patterns, and pollution

patterns associated with them, support the need for NOX controls across the broader

eastern United States. Studies and characterizations of nocturnal low level jets also

support the need for local and regional controls on NOX and VOC sources as locally

generated and transported pollution can both be entrained in nocturnal low level jets

vi
formed during nighttime hours. The presence of land, sea, mountain, and valley breezes

indicate that there are unique aspects of pollution accumulation and transport that are

area-specific and will warrant policy responses at the local and regional levels beyond a

one-size-fits-all approach.

The mix of emission controls is also important. Regional ozone formation is

primarily due to NOX, but VOCs are also important because they influence how

efficiently ozone is produced by NOX, particularly within urban centers. While reductions

in anthropogenic VOCs will typically have less of an impact on the long-range transport

of ozone, they can be effective in reducing ozone in urban areas where ozone production

may be limited by the availability of VOCs. Therefore, a combination of localized VOC

reductions in urban centers with additional NOX reductions across a larger region will

help to reduce ozone and precursors in nonattainment areas as well as downwind

transport across the entire region.

The recognition that ground-level ozone in the eastern United States is a regional

problem requiring a regional solution marks one of the greatest advances in air quality

management in the United States. During the 1990s, air quality planners began

developing and implementing coordinated regional and local control strategies for NOX

and VOC emissions that went beyond the previous emphasis on urban-only measures.

These measures have resulted in significant improvements in air quality across the OTR.

Measured NOX emissions and ambient concentrations have dropped between 1997 and

2005, and the frequency and magnitude of ozone exceedances have declined within the

OTR. To maintain the current momentum for improving air quality so that the OTR states

can meet their attainment deadlines, there continues to be a need for more regional NOX

reductions coupled with appropriate local NOX and VOC controls.

vii

 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 1

1.INTRODUCTION

1.1.Background

Ground-level ozone is a persistent public health problem in the Ozone Transport

Region (OTR), a large geographical area that is home to over 62 million people living in

Connecticut, Delaware, the District of Columbia, Maine, Maryland, Massachusetts, New

Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and northern

Virginia. Breathing ozone in the air harms lung tissue, and creates the risk of permanently

damaging the lungs. It reduces lung function, making breathing more difficult and

causing shortness of breath. It aggravates existing asthmatic conditions, thus potentially

triggering asthma attacks that send children and others suffering from the disease to

hospital emergency rooms. Ozone places at particular risk those with preexisting

respiratory illnesses, such as emphysema and bronchitis, and it may reduce the body’s

ability to fight off bacterial infections in the respiratory system. Ground-level ozone also

affects otherwise healthy children and adults who are very active, either at work or at

play, during times of high ozone levels (USEPA, 1999). In addition, recent evidence

suggests that short-term ozone exposure has potential cardiovascular effects that may

increase the risk of heart attack, stroke, or even death (USEPA, 2006).

The Clean Air Act requires states that have areas designated “nonattainment” of

the ozone National Ambient Air Quality Standard (NAAQS) to submit State

Implementation Plans (SIPs) demonstrating how they plan to attain the ozone NAAQS.

The SIPs must also include regulations that will yield the necessary emission reductions

to attain the national ozone health standard. As part of the SIP process, the U.S.

Environmental Protection Agency (USEPA) urges states to include a conceptual

description of the pollution problem in their nonattainment areas. The USEPA has

provided guidance on developing a conceptual description, which is contained in

Chapter 8 of the document “Guidance on the Use of Models and Other Analyses in

Attainment Demonstrations for the 8-hour Ozone NAAQS” (EPA-454/R-05-002,

October 2005) (Appendix A of this report reproduces Chapter 8 of the USEPA guidance

document).a This document provides the conceptual description of the ozone problem in

the OTR states, consistent with the USEPA’s guidance. In the guidance, the USEPA

recommends addressing three questions to help define the ozone problem in a

nonattainment area: (1) Is regional transport an important factor? (2) What types of

meteorological episodes lead to high ozone? (3) Is ozone limited by availability of

volatile organic compounds, nitrogen oxides, or combinations of the two, and therefore

which source categories may be most important to control? This report addresses these

questions, as well as provides some in-depth data and analyses that can assist states in

developing conceptual descriptions tailored to their specific areas, where appropriate.

a

 At the time of this writing, the USEPA was incorporating Section 8 of the 8-hour ozone guidance into a

new USEPA guidance document covering ozone, PM2.5, and regional haze. The new guidance is in

Section 11 of Draft 3.2 “Guidance on the Use of Models and other Analyses for Demonstrating Attainment

of Air Quality Goals for Ozone, PM2.5, and Regional Haze,” U.S. EPA, (Draft 3.2 – September 2006),

available at http://www.epa.gov/ttn/scram/guidance_sip.htm#pm2.5 (accessed Oct. 5, 2006). The newer

guidance, when finalized, may differ in some respects from the text given in Section 8 of the earlier ozone

guidance.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 2

1.2.Ozone formation

Ground-level ozone is formed in the atmosphere through a series of complex

chemical reactions involving sunlight, warm temperatures, nitrogen oxides (NOX) and

volatile organic compounds (VOCs). Figure 1-1 is a conceptual picture of the emission

sources and conditions contributing to ozone formation in the atmosphere. There are

natural (biogenic) sources of NOX, such as formation by soil microbes, lightening, and

forest fires, but the dominant NOX sources in the eastern United States arise from human

activities, particularly the burning of fossil fuels in cars, trucks, power plants, and other

combustion sources (MARAMA, 2005).

In contrast to NOX sources, there are significant biogenic sources of VOCs in the

eastern United States that can play an important contributing role in ozone formation.

Isoprene, a highly reactive natural VOC emitted typically by deciduous trees such as oak,

is an important ozone precursor across large parts of the East. Isoprene emissions

typically increase with temperature up to a point before high temperatures tend to shut off

emissions as leaf stomata (pores) close to reduce water loss. The tendency for increasing

isoprene emissions with increasing temperatures (up to a point) coincides with the

temperature and sunlight conditions favorable for increased ozone production

(MARAMA, 2005).

Human-caused (anthropogenic) VOC emissions are important and may dominate

the VOC emissions by mass (weight) in an urban area, even though natural sources

dominate in the overall region. Some anthropogenic VOCs, such as benzene, are toxic,

and may increase risks of cancer or lead to other adverse health effects in addition to

helping form ozone (MARAMA, 2005). 
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 3

Figure 1-1. Conceptual picture of ozone formation in the atmosphere

Picture provided by the Maryland Department of the Environment.

The relationship between the relative importance of NOX and VOC emissions in

producing ozone is complex. The relative ratio of NOX and VOC levels in the local

atmosphere can affect the efficiency of local urban ozone production, and this can vary

by time (hour or day) at the same urban location, as well as across locations within the

same urban area. High NOX concentrations relative to VOC levels may hinder ozone

production through the destruction of ozone by NOX (sometimes called “NOX

scavenging”). The same NOX, however, when diluted relative to VOCs through the

downwind transport and dispersal of a pollution plume, will promote ozone formation

elsewhere.

1.3.Spatial pattern of ozone episodes in the OTR

The day-to-day pattern of ground-level ozone varies according to meteorological

variables that include, but are not limited to, sunlight, air temperature, wind speed, and

wind direction. Generally within the OTR, one would expect elevated ozone to occur

more frequently in southernmost areas, where solar elevation angles are greater and cold

frontal passages are fewer. A glance at monthly composite maps (for example, JulyAugust 2002) at the USEPA AIRNOW website seems to confirm this

(http://www.epa.gov/airnow/nemapselect.html). On some days, however, one notes that

the highest ozone levels shift northward to mainly affect the northern part of the OTR.

Other shifts are apparent between coastal and interior areas.

This variability of the daily ozone pattern is tied to variations in the atmosphere’s

circulations over a range of scales, and how geographic features influence these
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 4

circulations. These features can include boundaries between land and sea, and the

influence of the Appalachian Mountains on winds to their east over the Atlantic Coastal

Plain.

For the OTR, Stoeckenius and Kemball-Cook (2005) have identified five general

ozone patterns: (1) high ozone throughout the OTR; (2) high ozone confined to the

extreme southeastern OTR; (3) high ozone along the I-95 corridor and northern New

England; (4) high ozone in the western OTR; and (5) generally low ozone throughout the

OTR. However, not all ozone episodes necessarily neatly fit into one of the five general

patterns as daily conditions will vary and a given ozone episode may have characteristics

that fall across several class types. These five general patterns, however, are a useful

classification scheme for characterizing how representative an historical ozone episode is

for possible use in air quality planning efforts. Appendix B presents the descriptions of

the five general ozone patterns and their meteorological attributes as developed by

Stoeckenius and Kemball-Cook (2005).

1.4.The regional extent of the ozone problem in the OTR

Air monitoring demonstrates that areas with ozone problems in the OTR do not

exist in isolation. The map of Figure 1-2 shows an extensive pattern of closely adjacent

ozone nonattainment in areas throughout the OTR. The 8-hour ozone baseline design

values (defined in the figure caption) at the monitoring sites shown in the figure indicate

extensive areas throughout the OTR with many monitors having values above the 8-hour

ozone NAAQS of 0.08 ppm. In practice, this corresponds to levels equal to or greater

than 0.085 ppm (equivalent to 85 ppb). The map also shows that many monitors outside

the designated nonattainment areas of the OTR also record elevated ozone concentrations

approaching the 8-hour ozone NAAQS (i.e., 75-84.9 ppb), even if not violating it. The

many monitoring locations across that OTR measuring elevated ozone levels that

approach or exceed the 8-hour ozone NAAQS give a strong indication of the regional

nature of the OTR’s ozone problem.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 5

Figure 1-2. Map of 8-hour ozone baseline design values in the OTR

Note: A monitor’s baseline design value is the average of the three design values (3-year averages of the 4th maximum 8-hour ozone level) for the set of years 2000-2002, 2001-

2003, and 2002-2004. The figure shows the regional nature of ozone levels in the OTR, with a number of closely adjacent nonattainment areas (baseline design values ≥ 85 ppb)

along with a broader region of elevated regional ozone (e.g., baseline design values ≥ 75 ppb) (figure by Michael Geigert, Connecticut Department of Environmental Protection).
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 6

1.5.Ozone trends in the OTR

The number of 8-hour ozone exceedance days vary year-to-year in the OTR,

which is largely driven by variations in meteorology. During warmer summers conducive

for ozone formation, the number of exceedance days at individual monitors in

nonattainment areas of the OTR has been frequent, typically with 10 or more days above

the 8-hour ozone NAAQS during the course of the summer. Figure 1-3 displays the

variation in exceedance days when collectively considering all monitoring sites across the

OTR since 1997. The figure also includes a line indicating the trend in the maximum 8-

hour ozone concentrations observed in the OTR each year. The variation in exceedance

days from year-to-year makes it difficult to discern a clear trend, although there is some

hint that the number of exceedance days may be declining in recent years. There appears

to be a stronger indication of a declining maximum 8-hour ozone concentration in the

OTR since 1997, although the maximum concentration remains well above the 8-hour

ozone NAAQS. This reflects the impact of numerous control strategies implemented

locally, regionally, and nationally to reduce emissions of the precursor pollutants that

contribute to ozone formation in the atmosphere.

Figure 1-3. Trends in 8-hour ozone in the OTR 1997-2005

1997-2005 OZONE SEASON 8-HOUR OZONE EXCEEDANCE DAYS AND MAXIMUM 8-hr

OZONE CONCENTRATION TRENDS IN THE OTR

0

10

20

30

40

50

60

70

80

90

1997 1998 1999 2000 2001 2002 2003 2004 2005

YEAR

# 8-hr OZONE EXCEEDANCE DAYS 

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

0.14

0.15

0.16

8-HOUR CONCENTRATION (pp

m)

# EXCEEDANCE DAYS MAXIMUM 8-hr OZONE

8-hour ozone NAAQS level

0.085

1997-2005 OZONE SEASON 8-HOUR OZONE EXCEEDANCE DAYS AND MAXIMUM 8-hr

OZONE CONCENTRATION TRENDS IN THE OTR

0

10

20

30

40

50

60

70

80

90

1997 1998 1999 2000 2001 2002 2003 2004 2005

YEAR

# 8-hr OZONE EXCEEDANCE DAYS 

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

0.11

0.12

0.13

0.14

0.15

0.16

8-HOUR CONCENTRATION (pp

m)

# EXCEEDANCE DAYS MAXIMUM 8-hr OZONE

8-hour ozone NAAQS level

0.085
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 7

Note: The bars correspond to the number of 8-hour ozone exceedance days per year. The upper blue line indicates

the trend in maximum 8-hour ozone concentrations in the OTR during 1997-2005. The lower red horizontal line

indicates the level of the 8-hour ozone NAAQS (functionally 0.085 ppm). (Figure created by Tom Downs, Maine

Dept. of Environmental Protection.)

The tables in Appendix C contain the frequency of ozone exceedance days for

individual monitors in the OTR states from 1997 to 2005. Appendix D contains tables for

the 8-hour ozone design values recorded at ozone monitors in the OTR during 1997-

2005. These tables give an indication of the number of monitors in the OTR since 1997

that have exceeded the 8-hour NAAQS of 85 ppb (equal to 0.085 ppm in the tables of

Appendix D) at some point in time.

1.6.History of ozone transport science

1.6.1.From the 1970s to the National Research Council report, 1991

Research studies conducted in the 1970s gave some of the earliest indications that

pollution transport plays an important role in contributing to air pollution problems in the

OTR. An aircraft study in the summer of 1979 tracked a mass of ozone-laden air and its

precursors leaving central Ohio, crossing the length of Pennsylvania, and entering the

Northeast Corridor where it contributed upwards of 90 ppb to early morning ozone

concentrations in the OTR prior to local ozone formation from local emissions (Clarke &

Ching, 1983). Wolff and Lioy (1980) described a “river of ozone” extending from the

Gulf Coast through the Midwest and into New England. A number of early studies also

documented the role of large coal-fired power plants in forming significant amounts of

ozone pollution that traveled far downwind from the power plant source and contributed

to a large elevated background of regional ozone (Davis et al., 1974; Miller et al., 1978;

Gillani & Wilson, 1980; Gillani et al., 1981; White et al., 1983). Section 2 below

describes in more depth the observed meteorological processes identified as the ozone

transport mechanisms important for the OTR.

On a regional scale, NOX emissions within areas of high VOC emissions, such as

forested regions rich in isoprene, will produce elevated levels of ozone. A number of

studies have now established that regional ozone formation over the eastern United States

is limited primarily by the supply of anthropogenic NOX, with anthropogenic VOCs

having less regional influence compared to their potential urban influence. This is due to

the presence of significant amounts of natural VOCs across broad areas of the eastern

United States (Trainer et al., 1987; Chameides et al., 1988; Sillman et al., 1990; McKeen

et al., 1991; Chameides et al., 1992; Trainer et al., 1993; Jacob et al., 1993).
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 8

The presence of dispersed NOX emissions sources, such as coal-fired power

plants, in rural regions rich in isoprene and other natural VOC emissions from trees and

other vegetation often leads to elevated regional ozone during the summer months. This

ozone can then be transported into urban areas where it contributes to high background

concentrations during the early morning hours before local production of ozone occurs

from local precursor emissions (both NOX and VOCs).

In 1991, a National Research Council (NRC) committee, synthesizing the best

available information at the time on ozone formation and transport in the eastern United

States, reported (NRC, 1991):

High ozone episodes last from 3-4 days on average, occur as many as 7-10 times a year,

and are of large spatial scale: >600,000 km2. Maximum values of non-urban ozone

commonly exceed 90 ppb during these episodes, compared with average daily maximum

values of 60 ppb in summer. An urban area need contribute an increment of only 30 ppb

over the regional background during a high ozone episode to cause a violation of the

National Ambient Air Quality Standard (NAAQS) in a downwind area. ... Given the

regional nature of the ozone problem in the eastern United States, a regional model is

needed to develop control strategies for individual urban areas. 

[Note: The NRC discussion was in the context of the ozone NAAQS at the time of the

NRC report, which was 0.12 ppm (120 ppb) averaged over one hour.]

The observed ozone spatial scale of >600,000 km2 (>200,000 square miles) is

comparable to the combined size of Kentucky, Ohio, West Virginia, Pennsylvania,

Maryland, New York, and New Jersey. Additional field studies and modeling efforts

since the NRC report (described below) have reinforced its basic findings and provide a

consistent and coherent body of evidence for transport throughout the eastern United

States.

1.6.2.Ozone Transport Assessment Group (OTAG) 1995-1997

The increasing regulatory focus on broader regional approaches to ozone control

beyond the OTR began with the Ozone Transport Assessment Group (OTAG) in 1995.

OTAG was a partnership between the USEPA, the Environmental Council of the States

(ECOS), state and federal government officials, industry organizations, and

environmental groups. OTAG’s goal was “to develop an assessment of and consensus

agreement for strategies to reduce ground-level ozone and its precursors in the eastern

United States” (OTAG, 1997a). The effort assessed transport of ground-level ozone

across state boundaries in the 37-state OTAG region and developed a set of

recommendations to the USEPA. OTAG completed its work in 1997.

OTAG supported a significant modeling effort of four regional ozone episodes

across the eastern United States. OTAG’s Regional and Urban Scale Modeling

Workgroup found that on a regional scale, modeled NOX reductions produced widespread

ozone decreases across the eastern United States with limited ozone increases generally

confined to some urban areas. Also on a regional scale, VOC reductions resulted in

limited ozone decreases generally confined to urban areas (OTAG, 1997b). 
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 9

The OTAG Air Quality Analysis Workgroup provided additional observational

and other analytical results to inform model interpretation and the development of OTAG

recommendations. Among its many finding, this Workgroup observed:

Low wind speeds (< 3 m/sec) enable the accumulation of ozone near local source areas. High

winds (> 6 m/sec) reduce the concentrations but contribute to the long-range transport of ozone.

The average range of ozone transport implied from an array of diverse methods is between 150

miles and 500 miles. However, the perceived range depends on whether one considers the average

concentrations (300–500 miles) or peak concentrations (tens of miles at 120 ppb). The relative

importance of ozone transport for the attainment of the new 80 ppb 8-hour standard is likely to be

higher due to the closer proximity of nonattainment areas. (OTAG, 1997c)

Based on the variety of technical work performed by multiple stakeholders during

the process, OTAG reached a number of major conclusions (OTAG, 1997d), including:

• Regional NOX reductions are effective in producing ozone benefits; the more NOX reduced, the

greater the benefit.

• Ozone benefits are greatest in the subregions where emissions reductions are made; the benefits

decrease with distance.

• Both elevated (from tall stacks) and low-level NOX reductions are effective.

• VOC controls are effective in reducing ozone locally and are most advantageous to urban

nonattainment areas.

• Air quality data indicate that ozone is pervasive, that ozone is transported, and that ozone aloft is

carried over and transported from one day to the next. 

The technical findings of OTAG workgroups were consistent with the modeling

and observational studies of regional ozone in the eastern United States already appearing

in the scientific literature at that time.

Through its work, OTAG engaged a broad group outside of the scientific

community in the discussion of ozone transport. This brought a greater understanding of

the role of ozone transport across the eastern United States that was then translated into

air quality policy with the creation of a regional ozone control strategy focusing on the

reduction of NOX emissions from power plants.

1.6.3.Northeast Oxidant and Particle Study (NE-OPS) 1998-2002

The Northeast Oxidant and Particle Study (NE-OPS) began in 1998 as a USEPA

sponsored project to study air quality issues in the Northeast. The study undertook four

major field programs at a field site in northeastern Philadelphia during the summers of

1998, 1999, 2001, and 2002. It involved a collaborative effort among research groups

from a number of universities, government laboratories, and representatives of the

electric power industry in an investigation of the interplay between the meteorological

and chemical processes that lead to air pollution events in the Northeast. A suite of

measurement techniques at and above the earth’s surface gave a three-dimensional

regional scale picture of the atmosphere. The studies found that horizontal transport aloft

and vertical mixing to the surface are key factors in controlling the evolution and severity

of air pollution episodes in the Northeast (Philbrick et al., 2003a).

At the conclusion of the 2002 summer field study, the NE-OPS researchers were

able to draw several conclusions about air pollution episodes in Philadelphia and draw

inferences from this to the conditions in the broader region. These include (Philbrick

et al., 2003b):
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 10

• Transported air pollution from distant sources was a major contributor to all of the major summer

air pollution episodes observed in the Philadelphia area.

• Regional scale meteorology is the major factor controlling the magnitude and timing of air

pollution episodes.

• Knowledge of how the planetary boundary layer evolves over the course of a day is a critical input

for modeling air pollutant concentrations because it establishes the mixing volume.

• Remote sensing and vertical profiling techniques are critical for understanding the processes

governing air pollution episodes.

• Ground-based sensors do not detect high levels of ozone that are frequently trapped and

transported in layers above the surface.

• Horizontal and vertical nighttime transport processes, such as the nocturnal low level jets and

“dynamical bursting”b events, are frequent contributors of pollutants during the major episodes. 

• Specific meteorological conditions are important in catalyzing the region for development of

major air pollution episodes. 

• Tethered balloon and lidar measurements suggest a very rapid down mixing of species from the

residual boundary layer during the early morning hours that is too large to be accounted for on the

basis of NOX reactions alone.

• Summer organic aerosols in Philadelphia consist of a relatively constant level of primary organic

particulate matter, punctuated by extreme episodes with high levels of secondary organic aerosol

during ozone events. Primary organic particulate matter is both biogenic and anthropogenic in

nature, with the relative importance fluctuating from day to day, and possibly associated more

strongly with northwest winds. Secondary aerosol formation events may be responsible for

dramatic increases in particulate organic carbon, while the relatively constant contribution of

primary sources could make a greater contribution to annual average particulate levels. More

research is needed to sort out the relative contributions of anthropogenic and biogenic sources.

The findings on nocturnal low level jets occurring in concert with ozone pollution

episodes are particularly salient for air quality planning for the OTR. In 19 of 21 cases

where researchers observed nocturnal low level jets during the NE-OPS 2002 summer

campaign in the Philadelphia area, they also saw peak 1-hour ozone levels exceeding

100 ppbv. The nocturnal low level jets were capable of transporting pollutants in air

parcels over distances of 200 to 400 km. The field measurements indicating that these jets

often occur during periods of large scale stagnation in the region demonstrate the

important role nocturnal low level jets can play in effectively transporting air pollutants

during air pollution episodes (Philbrick et al., 2003b).

The upper air observations using tethered balloons and lidar indicated the

presence of high pollutant concentrations trapped in a residual layer above the surface,

thus preserving the pollutants from destruction closer to the surface. Ozone, for example,

when trapped in an upper layer during nighttime hours is not subject to destruction by

NOX scavenging from low-level emission sources (i.e., cars and trucks) or deposition to

surfaces like vegetation, hence it is available for horizontal transport by nocturnal low

level jets. The following day, it can vertically transport back down to the surface through

“bursting events” and daytime convection. When involving an upper layer of ozone-laden

air horizontally transported overnight by a nocturnal low level jet, downward mixing can

increase surface ozone concentrations in the morning that is not the result of local ozone

production (Philbrick et al., 2003b).

b

 “Dynamical bursting” events occur in the early morning hours due to instabilities in the lower atmosphere

caused by differences in wind speeds at different altitudes below the layer of maximum winds. Bursting

events can vertically mix air downwards to the surface (see Philbrick et al., 2003b at p. 36).
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 11

1.6.4.NARSTO 2000

NARSTO (formerly known as the North American Research Strategy for

Tropospheric Ozone) produced “An Assessment of Tropospheric Ozone Pollution – A

North American Perspective” in 2000 to provide a policy-relevant research assessment of

ozone issues in North America (NARSTO, 2000). While the NARSTO Assessment is

continental in scope, it encompasses issues relevant to the OTR, including results from a

NARSTO-Northeast (NARSTO-NE) field campaign.

Several policy-relevant findings from the NARSTO Assessment are of relevance to the

OTR (NARSTO, 2000):

• Available information indicates that ozone accumulation is strongly influenced by extended

periods of limited mixing, recirculation of polluted air between the ground and aloft, and the longrange transport of ozone and its precursors. As a result, air quality management strategies require

accounting for emissions from distant as well as local sources.

• Local VOC emission reductions may be effective in reducing ozone in urban centers, while NOX

emission reductions become more effective at distances removed from urban centers and other

major precursor emissions.

• The presence of biogenic emissions complicates the management of controllable precursor

emissions and influences the relative importance of VOC and NOX controls.

• The effectiveness of VOC and NOX control strategies is not uniquely defined by the location or

nature of emissions. It is now recognized that the relative effectiveness of VOC and NOX controls

may change from one location to another and even from episode to episode at the same location.

The NARSTO Assessment identified the stagnation of synoptic scale (>1000 km2)

high pressure systems as a commonly occurring weather event leading to ozone pollution

episodes. These systems are warm air masses associated with weak winds, subsiding air

from above, and strong inversions capping the planetary boundary level in the central

region of the high. The warm air mass can settle into place for days to more than a week,

and in the eastern U.S. tend to slowly track from west to east during the summer. These

conditions result in the build up of pollution from local sources with reduced dispersion

out of the region. In terms of air quality, the overall appearance of such systems is the

presence of numerous local or urban-scale ozone pollution episodes embedded within a

broader regional background of elevated ozone concentrations (NARSTO, 2000 at p. 3-

34).

While stagnation implies little movement, the NARSTO Assessment found that a

variety of processes can lead to long-range transport of air pollutants that initially

accumulated in these large-scale stagnation events. Over time, pollution plumes meander,

merge, and circulate within the high pressure system. Because of the difference in

pressures, pollutant plumes that eventually migrate to the edges of a high pressure system

get caught in increasing winds at the edge regions, creating more homogeneous regional

pollution patterns. Stronger winds aloft capture the regional pollutant load, and can

transport it for hundreds of kilometers downwind of the stagnated air mass’s center

(NARSTO, 2000 at p. 3-34). For example, air flow from west to east over the

Appalachian Mountains can move air pollution originating within the Ohio River Valley

into the OTR. 

Studies undertaken by the NARSTO-NE field program also observed several

regional scale meteorological features arising from geographical features in the eastern
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 12

U.S. that affect pollutant transport. One important feature is the channeled flow of a

nocturnal low level jet moving air pollution from the southwest to the northeast along the

Northeast Corridor during overnight hours. The NARSTO-NE field program observed

nocturnal low level jets on most nights preceding regional ozone episodes in the OTR,

consistent with the observations of the NE-OPS campaign.

Another important smaller scale transport mechanism is the coastal sea breeze

that can sweep ashore pollutants originally transported over the ocean parallel to the

coastline. An example of this is the high ozone levels seen at times along coastal Maine

that move in from the Gulf of Maine after having been transported in pollution plumes

from Boston, New York City, and other Northeast Corridor locations (NARSTO, 2000 at

pp. 3-34 through 3-37).

As a result of the NARSTO-NE field program, a conceptual picture of pollution

transport into and within the OTR is possible. It consists of a combination of large-scale

synoptic flow from the Midwest interacting with various regional and smaller-scale

transport and meteorological features within the OTR, as illustrated in Figure 1-4.

Synoptic-scale transport from west to east across the Appalachian Mountains occurs with

the slow-moving stagnant high pressure systems that foster large regional ozone episodes

across eastern U.S. Regional-scale channeled flows, specifically nocturnal low level jets

from the southwest to the northeast along the Atlantic Coastal Plain, can occur within the

synoptic system. In addition, daytime sea breezes can significantly affect bay and coast

line air pollution levels within the OTR (NARSTO, 2000 at 3-36 and 3-37, citing

Blumenthal et al., 1997).

Figure 1-4. Conceptual picture of different transport regimes contributing to ozone

episodes in the OTR
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 13

Long-range (synoptic scale) transport occurs from west to east across the Appalachian Mountains.

Regional scale transport in channeled flows also occurs from west to east through gaps in the

Appalachian Mountains and in nocturnal low level jets from southwest to northeast over the Northeast

Corridor. Daytime sea breezes can affect local coastal areas by bringing in air pollution originally

transported near the surface across water parallel to the coast (e.g., along the Maine coastline). Figure

from NARSTO, 2000, citing Blumenthal et al., 1997.

1.6.5.New England Air Quality Study (NEAQS) 2002-2004

The New England Air Quality Study (NEAQS) has to date conducted field

campaigns during the summers of 2002 and 2004 to investigate air quality on the Eastern

Seaboard and transport of North American emissions into the North Atlantic (NEAQS,

2002). Transport of air pollution into the Gulf of Maine and subsequently into coastal

areas of northern New England received extensive attention.

High ozone levels in northern New England occur with light to moderate winds

from source regions in the Northeast urban corridor, rather than under locally stagnant

conditions. The most important transport pathways leading to high ozone in coastal New

Hampshire and Maine are over water rather than over land. Transport over water is

particularly important in this northern region of the OTR for several reasons. First, there

is a persistent pool of cooler water in the northern and eastern Gulf of Maine and Bay of

Fundy. This creates a smoother transport surface for air pollutants relative to land

transport, with a decrease in convective (vertical) mixing. Second, deposition of

pollutants to the water surface is very small compared to the more rapid deposition

occurring on land. Third, the lack of convective mixing allows pollution to be transported

in different directions in layers at different heights in the atmosphere (Angevine et al.,

2004).

During the summer of 2002, researchers observed two transport events into

coastal northern New England. The first occurring on July 22 through July 23 involved

large-scale synoptic transport in a 400-600 m layer over the Gulf of Maine that was in

contact with the water’s surface. The southwesterly flow brought ozone pollution up from

the New York City, Boston and other northeastern urban locations into coastal northern

New England. Ozone monitors on Maine’s coast extending from the New Hampshire

border to Acadia National Park recorded elevated 1-hour average ozone levels between

88 and 120 ppb during this period. In a later episode during August 11-14, ozone and

wind observations indicated the role of local-scale transport via a sea breeze

(southeasterly flow) bringing higher ozone levels into coastal New Hampshire from a

polluted layer originally transported off shore in the Gulf of Maine in a southwesterly

flow arising out of the Northeast urban corridor. Transport in an elevated layer also

occurred with higher ozone recorded at a monitor on Cadillac Mountain in Acadia

National Park relative to two monitors located at lower elevations in the park (Angevine

et al., 2004). 

The results of NEAQS indicate the important conditions contributing to ozone

transport along the northern New England coast. The cool waters of the Gulf of Maine

allow for transport of air pollutants over distances of 20-200 km in stable layers at the

water’s surface with little pollutant deposition or dilution. Sea breezes can modify largescale synoptic transport over the ocean and bring high ozone levels into particular sites
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 14

located on the coast. Transport within higher layers above the Gulf of Maine can carry

pollutants over much greater distances, 200-2000 km (Angevine et al., 2004). 

1.6.6.Regional Atmospheric Measurement, Modeling, and Prediction

Program (RAMMPP) 2003

The Regional Atmospheric Measurement, Modeling, and Prediction Program

(RAMMPP) is a program led by researchers at the University of Maryland. Its focus is

developing a state-of-the-art scientific research tool to improve understanding of air

quality in the mid-Atlantic region of the United States. It has a number of facets,

including ozone and PM2.5 pollutant level forecasting, aircraft, and surface measurements,

real-time weather forecasting, and chemical transport modeling.

During the August 2003 electrical blackout in the eastern United States, one of the

largest in North American history, scientists with RAMMPP were able to obtain airborne

measurements that directly recorded changes in air pollution due to the virtual shutdown

of numerous coal-fired power plants across a large part of this region (Marufu et al.,

2004). Initially, aircraft measurements were collected early in the day on August 15, 2003

above western Maryland, which was outside the blackout region. These measurements

were compared with aircraft measurements taken later that day over central Pennsylvania,

about 24 hours into the blackout. The comparison indicated a decrease in ozone

concentrations of ~50 percent within the blackout region (as well as >90 percent decrease

in SO2 and ~70 percent reduction in light scattered by particles). These reductions were

also consistent with comparisons to measurements obtained over central Pennsylvania the

previous year during a period of similar synoptic patterns as occurred during the

blackout. Forward trajectories indicated that the decrease in air pollution during the

blackout benefited much of the eastern United States. The decrease in ozone was greater

than expected based on estimates of the relative contribution of power plant NOX

emissions to ozone formation in the region. The researchers suggested that this could be

due to underestimation of power plant emissions, poor representation of power plant

plumes in emission models, or an incomplete set of atmospheric chemical reactions in

photochemical models. This accidental “real world” experiment indicates that ozone

formation across a large part of the eastern United States is sensitive to power plant NOX

emissions, and may be even more sensitive to NOX reductions from these sources than

currently predicted by air quality modeling.

1.7.Summary

The chemistry of ozone formation in the atmosphere involves reactions of NOX

and VOC emissions from numerous sources during periods of warm temperatures and

abundant sunshine. The day-to-day pattern of ground-level ozone in the OTR varies

according to a number of meteorological variables, such as sunlight, temperature, wind

speed, and wind direction. High levels of ozone within the OTR do not occur in isolation,

indicating a broad regional air quality problem. Trends in 8-hour ozone levels since 1997

indicate improvement in air quality, a reflection of numerous control strategies

implemented locally, regionally, and nationally to reduce emissions of the pollutants that

contribute to ozone formation.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 15

The scientific literature prior to 1985 contains a number of peer reviewed papers

describing observed episodes of ozone and precursor pollutant transport. In 1991, a

National Research Council report summarized the state-of-the-science, which further

highlighted the broad regional nature of the ozone problem in the eastern U.S. Since then,

multiple collaborative efforts and field campaigns have further investigated specific

aspects of the regional ozone problem affecting the OTR, and these provide a significant

foundational basis for informed policy decisions to improve air quality.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 16

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 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 1

2.METEOROLOGY AND EVOLUTION OF OZONE

EPISODES IN THE OZONE TRANSPORT REGION

The following sections describe current knowledge of the factors contributing to

ozone episodes in the OTR. The general description of weather patterns comes mainly

from the work of Ryan and Dickerson (2000) done for the Maryland Department of the

Environment. Further information is drawn from work by Hudson (2005) done for the

Ozone Transport Commission and from a mid-Atlantic regional air quality guide by

MARAMA (2005). The regional nature of the observed ozone episodes in the OTR is

reinforced in modeling studies by the USEPA for the Clean Air Interstate Rule.

2.1.Large-scale weather patterns

Ryan and Dickerson (2000) have described the general meteorological features

conducive to ozone formation and transport that are pertinent to the OTR. On the local

scale, meteorological factors on which ozone concentrations depend are the amount of

available sunlight (ultraviolet range), temperature, and the amount of space (volume) in

which precursor emissions mix. Sunlight drives the key photochemical reactions for

ozone and its key precursors and the emissions rates of many precursors (isoprene for

example) are temperature dependent. Emissions confined within a smaller volume result

in higher concentrations of ozone. Winds in the lowest 2 km of the atmosphere cause

horizontal mixing while vertical temperature and moisture profiles drive vertical mixing.

High ozone is typically associated with weather conditions of few clouds, strong

temperature inversions, and light winds. 

The large-scale weather pattern that combines meteorological factors conducive

to high ozone is the presence of a region of upper air high pressure (an upper air ridge)

with its central axis located west of the OTR. The OTR east of the axis of the highpressure ridge is characterized by subsiding (downward moving) air. This reduces

upward motion necessary for cloud formation, increases temperature, and supports a

stronger lower level inversion. While the upper air ridge is located west of the OTR,

surface high pressure is typically quite diffuse across the region. This pattern occurs

throughout the year but is most common and longer lived in the summer months (Ryan

and Dickerson, 2000).

The large, or synoptic, scale, weather pattern sketched above has important

implications for transport into and within the OTR. First, the persistence of an upper air

ridge west of the OTR drives generally west to northwest winds that can carry ozone

generated outside the OTR into the OTR. A key point from this wind-driven transport

mode is that stagnant air is not always a factor for high ozone episodes in the OTR.

Second, the region in the vicinity of the ridge axis, being generally cloud free, will

experience significant radiational cooling after sunset and therefore a strong nocturnal

inversion will form. This inversion, typically only a few hundred meters deep, prevents

ozone and its precursors from mixing downward overnight. Above the inversion layer,

there is no opportunity for destruction of the pollutants by surface deposition, thus

increasing the pollutants’ lifetimes aloft and consequently their transport distances. Third,

with diffuse surface high pressure, smaller scale effects can become dominant in the
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 2

lowest layers of the atmosphere. These include bay and land breezes, the Appalachian lee

side trough, and the development of the nocturnal low level jet. Nocturnal low-level jets

are commonly observed during high ozone events in the OTR (Ryan and Dickerson,

2000).

As previously mentioned in Section 1, Stoeckenius and Kemball-Cook (2005)

have identified five ozone patterns in the OTR as a guide to an historical ozone episode’s

representativeness for air quality planning purposes. They also described the

meteorological conditions that are generally associated with each of these patterns.

Appendix B presents the five types with the additional meteorological detail.

2.2.Meteorological mixing processes

An important element in the production of severe ozone events is the ability of the

atmosphere through temperature inversions to inhibit the mixing processes that under

normal conditions would lead to dilution of the emitted pollutants. For the purposes of

this discussion, we focus on two major classes of temperature inversions, (1) nocturnal

(radiative) and (2) subsidence.

Figure 2-5 shows an example of nocturnal and subsidence inversions in a

temperature profile taken over Albany, NY, on September 1, 2006 at 7 a.m. eastern

standard time. The figure shows two distinct temperature inversions – the ground-based

nocturnal inversion and an inversion at about 1600 meters caused by the sinking motion

(subsidence) of the atmosphere in a high pressure system.

Figure 2-5. Temperature profile taken over Albany, NY, on September 1, 2006 at

7 a.m. eastern standard time

-40 -30 -20 -10 0 10 20 30 40

1000

925

850

700

500

Subsidence

Inversion

Nocturnal

Inversion

Temperature oC (red line)

Note: Blue line is dew point sounding

Altitude

m

b

1600 m

3200 m

850 m

-40 -30 -20 -10 0 10 20 30 40

1000

925

850

700

500

Subsidence

Inversion

Nocturnal

Inversion

Temperature oC (red line)

Note: Blue line is dew point sounding

Altitude

m

b

-40 -30 -20 -10 0 10 20 30 40

1000

925

850

700

500

Subsidence

Inversion

Nocturnal

Inversion

-40 -30 -20 -10 0 10 20 30 40

1000

925

850

700

500

-40 -30 -20 -10 0 10 20 30 40

1000

925

850

700

500

Subsidence

Inversion

Subsidence

Inversion

Nocturnal

Inversion

Nocturnal

Inversion

Temperature oC (red line)

Note: Blue line is dew point sounding

Altitude

m

b

1600 m

3200 m

850 m
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 3

2.2.1.Nocturnal inversions

Land surfaces are far more efficient at radiating heat than the atmosphere above,

hence at night, the Earth’s surface cools more rapidly than the air. That temperature drop

is then conveyed to the lowest hundred meters of the atmosphere. The air above this layer

cools more slowly, and a temperature inversion forms. The inversion divides the

atmosphere into two layers that do not mix. Below the nocturnal surface inversion, the

surface winds are weak and any pollutants emitted overnight accumulate. Above the

inversion, winds continue through the night and can even become stronger as the

inversion isolates the winds from the friction of the rough surface.

In the morning, the sun warms the Earth’s surface, and conduction and convection

transfer heat upward to warm the air near the surface. By about 10:00 – 11:00 a.m., the

temperature of the surface has risen sufficiently to remove the inversion. Air from above

and below the inversion can then mix freely. Depending on whether the air above the

inversion is cleaner or more polluted than the air at the surface, this mixing can either

lower or increase air pollution levels.

2.2.2.Subsidence inversions

Severe ozone events are usually associated with high pressure systems. In the

upper atmosphere, the winds around a high pressure system move in a clockwise

direction. At the ground, friction between the ground and the winds turns the winds away

from the center of the system and “divergence” occurs, meaning that air at the surface

moves away from the center. With the movement of air horizontally away from the center

of the high at the surface, air aloft moves vertically downward (or “subsides”) to replace

the air that left. Thus, the divergence away from the high pressure system gives rise to

subsidence of the atmosphere above the high. The subsiding motion causes the air to

warm as it moves downward and is compressed. As the warmer air meets the colder air

below, it forms an inversion. A subsidence inversion is particularly strong because it is

associated with this large scale downward motion of the atmosphere. The subsidence

inversion caps pollution at a higher altitude in the atmosphere (typically from 1200 to

2000 meters), and it is far more difficult to break down than the nocturnal inversion.

Hence the subsidence inversion limits vertical mixing in the middle of the day during an

air pollution episode, keeping pollutants trapped closer to the ground.

2.3.Meteorological transport processes

2.3.1.Introduction

Figure 2-6 shows the classic synoptic weather pattern at the Earth’s surface

associated with severe ozone episodes within the OTR. A quasi-stationary high pressure

system (the Bermuda high) extends from the Atlantic Ocean westward into interior

southeastern U.S., where a second weaker high is located. Surface winds, circulating

clockwise around the high, are especially light in the vicinity of the secondary high.

Farther north, a southwesterly flow strengthens toward New York and southern New

England. This situation illustrates two circulation regimes often existing in OTR ozone

episodes: more stagnant conditions in southern areas and a moderate transport flow in the

OTR from southwest to northeast. In addition, as discussed previously, high pressure
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 4

systems exhibit subsidence, which results in temperature inversions aloft, and cloud free

skies. 

Closer to the surface, the Appalachian Mountains induce changes in the wind

field that also play important roles in the formation and transport of ozone in the OTR.

The mountains act as a physical barrier confining, to some degree, pollution to the coastal

plain. They also induce local effects such as mountain and valley breezes, which, in the

case of down-slope winds, can raise surface temperatures thereby increasing chemical

reactivity. In addition, mountains create a lee side trough, which helps to channel a more

concentrated ozone plume, and contribute to the formation of nocturnal low level jets, the

engine of rapid nighttime transport. 

The Atlantic Ocean also plays a strong role during ozone episodes where sea

breezes can draw either heavily ozone-laden or clean marine air into coastal areas.

Figure 2-6. Schematic of a typical weather pattern associated with severe ozone

episodes in the OTR

Meteorological processes that transport ozone and its precursors into and within

the OTR can roughly be broken down into three levels: ground, mid and upper. The

following sections discuss the three wind levels associated with meteorological transport

processes in more detail.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 5

2.3.2.Ground level winds

Land, sea, mountain, and valley breezes

In the OTR, land and sea breezes, and mountain and valley breezes can have an

important influence on local air quality. These local winds are driven by a difference in

temperature that produces a difference in pressure. Figure 2-7 shows a schematic of the

formation of a sea breeze. The sea breeze forms in the afternoon when the land is

considerably hotter than the ocean or bay. Air then flows from the high pressure over the

ocean toward the low pressure over land. At night, the opposite may happen as the land

cools to below the ocean’s temperature, and a land breeze blows out to sea. Because the

nighttime land and water temperature differences are usually much smaller than in the

day, the land breeze is weaker than the sea breeze. Sea breezes typically only penetrate a

few kilometers inland because they are driven by temperature contrasts that disappear

inland.

Figure 2-7. Illustration of a sea breeze and a land breeze

a) Sea Breeze b) Land Breeze

Figure from Lutgens & Tarbuck, 2001.

Along coastlines, such as coastal New England, sea breezes bring in air pollution

transported near the surface over water from urban locations located to the southwest.

Figure 2-8 shows the average 2000-2002 wind direction frequency for elevated 1-hour

ozone in the vicinity of the Kennebec and Penobscot Rivers in Maine. There is a clear

maximum of pollution in the direction of the sea breeze. These sites are located many

miles upriver from the coast, and receive ozone transported over water from the sea up

through the coastal bays and rivers.

In other cases, sea breezes can affect air quality in coastal cities because, under

stagnant synoptic-scale winds, a city’s emissions may be recirculated or pushed back

over land after having drifted out over the sea earlier. Before sea breeze circulation

begins, air pollution from a coastal city can move out over the water. In the absence of a

shift in winds due to a sea breeze, the city’s air pollution will be blown away. When a sea

breeze circulation sets up, however, the polluted air is pushed back toward the city. The

sea breeze only pushes a few miles inland, which is where the barrier to mixing lies.

Later in the day, the air may be quite clean on the ocean side of the city, but the air is
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 6

usually quite dirty on the inland side. The city suffers from its own recirculated pollution,

and also from the sea breeze that does not allow pollution from the city to flow away

from it. Appendix E presents more detailed information on sea breezes and flow over the

ocean that contribute to ozone transport in parts of the OTR.

Figure 2-8. Average 2000 – 2002 wind direction frequency associated with elevated

one-hour ozone levels in coastal Maine

The bay breeze is a shallow circulation over large inland bays, and may only

extend a couple hundred meters above the surface. For example, bay breezes from the

Chesapeake Bay often make Baltimore’s summertime air quality particularly poor. Air

from the city cannot escape directly across the Bay. On the other hand, a few miles closer

to the Bay, conditions are often considerably cleaner, since no fresh emissions have

gotten into the air there since earlier that morning. Polluted air from the west side of the

Bay can still mix upward, where it meets the stronger winds aloft, pass over the Bay

breeze circulation and come back down on the east side of the Bay.

Mountain and valley breezes are also driven by a temperature contrast. In the

daytime, the side of the mountain will heat up more quickly than the valley, and hence a

flow from the valley to the mountain results. At night this flow is reversed as the

mountain side cools more quickly than the valley. As a result of these differences in

cooling and heating, during the day, warm winds blow up toward the peaks from the

valley below, while at night, cool air sinks and flows down the valley, settling in the

lowest points. Local topography is very important in generating this phenomenon,

making the breeze unique to a particular area.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 7

Mountains and valleys also serve to isolate air in the valleys, while air at the

mountaintops may be coming from very far away. Mountain winds, inversions, and

mixing are quite complex. On a quiet night, the mountaintop may be in the free

troposphere, open to long-range transport, while the valley below is usually capped by a

nocturnal inversion, isolating pollution in the valley. Air quality measurements taken

during plane flights in the Shenandoah River Valley have shown that the air pollutants in

the valley may be rather different from the air at the nearby peaks. Cities on the western

side of the mountains will find that the Appalachians are capable of damming pollution

up against them (MARAMA, 2005 at pp. 42-43).

Appalachian lee side trough

The Appalachian lee side trough forms on the leeward (downwind) side of the

Appalachian Mountains. In a sense, it is the daytime companion to the nocturnal low

level jet, discussed below, because it forms under similar stagnant conditions; however,

the mechanism for its formation is different. In the OTR, a lee side trough forms when

winds blow over the Appalachian Mountains and down the lee side of the mountain range

to the coastal plain. As the column descends down the lee side, it stretches vertically and

spins faster, pulling up air and creating low pressure, thus rotating the winds to the

southwest. Because the air is typically rather dry, and the trough itself is rather weak, it

does not usually lead to showers and thunderstorms the way a trough associated with

other weather systems would. It does cause winds to shift their direction, so a wind that

comes over the mountains from the west will turn and blow from the southwest along the

coastal plain. Therefore, when surface winds on the coastal plain are from the southwest,

if the Appalachian lee side trough is in place, it may be that the air actually came from

the west, descended, and turned. The implication for air quality policy is straightforward.

Pollution making its way over the mountains from the west will turn once it reaches the

coastal plain and come from the southwest. Because surface winds are then from the

southwest, when the Appalachian lee side trough is in place, the limits of a nonattainment

area’s airshed will be expanded farther south and west than they might otherwise be

(MARAMA, 2005 at pp. 41-42). Studies have observed high ozone levels in the OTR

associated with a lee side trough east of the Appalachian Mountains and aligned with the

Northeast Corridor (Gaza, 1998; Kleinman et al., 2004).

2.3.3.Mid-level winds: Nocturnal low level jets

The nocturnal low levelc jet is a localized region of rapid winds in the lower

atmosphere (typically 500-1500 m above the ground level) that form at night under the

same calm conditions often present in a pollution episode. Forming just above the

nighttime temperature inversion mentioned previously, the nocturnal low level jet

depends on the isolation from the surface provided by the inversion. It is primarily a

nocturnal phenomenon that occurs more frequently during the spring and summer

seasons. 

A nocturnal low level jet is generally found where a range of mountains meets a

flat plain. There is a particularly strong nocturnal low level jet in the Great Plains of the

c

 “Low level” in this instance is relative to upper level jets occurring in the upper troposphere to lower

stratosphere at heights of 10-15 km above the ground level. It is not a “ground level” phenomenon of the

types described in the previous section.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 8

central United States on the eastern side of the Rocky Mountains. On the Eastern

Seaboard, nocturnal low level jets develop along the Atlantic Coastal Plain located to the

east of the Appalachian Mountains and to the west of the Atlantic Ocean. While the

typical wind speed minimum of a nocturnal low level jet is often defined as more than

12 meters per second (m s

-1), Ryan (2004) has proposed a weaker minimum speed

criterion of 8 m s

-1

 in the East because of the expected weaker terrain-induced forcing in

this region. The mid-Atlantic nocturnal low level jet has a width of 300-400 km (to its

half peak value) and a length scale of more than 1500 km, following closely the

orientation of the Appalachian Mountains.

The nocturnal low level jet forms when fronts and storm systems are far away.

Surface winds are parallel to the terrain, which in the case of the OTR is southwest

running over the Atlantic Coastal Plain in front of the Appalachian Mountains. The

nocturnal low level jet forms because land cools quicker than the air above it at night.

The quickly cooling land results in the air closest to the surface cooling quicker than the

air higher above. This creates a temperature inversion that separates the atmosphere into

layers. The warmer air above the inversion layer (~200-800 m above ground) loses the

frictional effect of the surface and increases in speed. In the eastern United States, the

nocturnal low level jet has been observed in Georgia, the Carolinas and Virginia

(Weisman, 1990; Sjostedt et al., 1990) in addition to the OTR (NARSTO, 2000).

Appendix F describes a specific example of an observed nocturnal low level jet occurring

over the length of the OTR during a period of high ozone in July 2002.

Upper air studies have observed ozone being transported overnight in nocturnal

low level jets in the OTR (Woodman et al., 2006). The Maryland Department of the

Environment (MDE) operates an upper air profiler at the Howard University (HU) site

located in Beltsville, Maryland. On August 5, 2005, two helium-filled balloons carrying

ozone sensors (called “ozonesondes”) were launched at the HU – Beltsville site in the

early morning hours. Using the upper air profiler, a nocturnal low level jet of 15 m s

-1

was observed between approximately midnight and 7:30 a.m. One ozonesonde was

launched at 3:30 a.m. and measured an ozone concentration of approximately 95 ppb at

about 600 meters, which is within the nocturnal low level jet. Another ozonesonde was

launched at 7:30 a.m. and measured an ozone concentration of approximately 90 ppb at

about 1,000 meters (Figure 2-9). Each of the ozone concentrations was observed at

approximately the same height as the nocturnal temperature inversion as indicated by the

kink in the temperature profile. The observations indicated that elevated ozone

concentrations are within the nocturnal low level jet.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 9

Figure 2-9. Ozonesonde measurements on August 5, 2005 of elevated ozone

concentrations in a nocturnal low level jet above Beltsville, MD 

2.3.4.Upper level winds: Ozone and precursors aloft

Theoretical and numerical model simulations have suggested for some time that

there is a strong regional component to urban air quality in the northeastern United States

(Liu et al., 1987; Sillman et al., 1990; McKeen et al., 1990). Since 1992, over 300

aircraft flights have been made to measure vertical profiles of ozone, the nitrogen oxides,

carbon dioxide, sulfur dioxide, and more recently aerosol particles during high ozone

episodes.dFigure 2-10 shows the results of profiles taken over central Virginia on July

15, 1995, at about 9:00 am on the last day of a four day severe ozone episode. During this

episode, winds measured at Sterling, Virginia (IAD) in the 500-3000 m layer, where

ozone was at a maximum, were consistently from the west to the north. This was

particularly true on July 15. There were no periods of stagnation or reversal of wind

direction during this period. Figure 2-10 shows that the ozone mixing ratio above the

boundary layer is much larger than that at the ground, peaking at about 1200 meters.

An examination of the various pollutant data in Figure 2-10 helps to identify

possible sources of the elevated ozone. It should be noted that while both automobiles

and power plants emit NOX, automobiles emit carbon monoxide (CO) but not sulfur

dioxide (SO2), while power plants emit SO2 but not CO. The CO profile is not correlated

well with the ozone data, indicating that the source of the ozone is not from local sources,

i.e., automobiles. The peak in the NOY

e

 profile at around 800 meters is an indication of

“aged air” (hence transport) as a number of studies have found a strong relationship

between increasing ozone and NOY in photochemically aged air masses (Trainer et al.,

1993; Kleinman et al., 1994; Olszyna et al., 1994). Finally, the peak in the SO2 profile,

d

 These measurements were made as part of the University of Maryland’s RAMMPP (Regional

Atmospheric Measurement, Modeling, and Prediction Program) under the sponsorship of ARMA,

MARAMA (Mid-Atlantic Regional Air Management Association), VADEQ (Virginia Department of

Environmental Quality), and NCDEQ (North Carolina Department of Environmental Quality).

e

 NOY = NO + NO2 + all other oxidized nitrogen products of NOX, excluding N2O.

7:30 AM

AM

3:30 AM 

AM
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 10

which occurs above the nocturnal inversion, is unlikely to come from local sources.

Indeed the presence of the SO2 leads to the conclusion that the air is coming from power

plants west of the Appalachian Mountains.

Figure 2-10. Altitude profiles for ozone, carbon monoxide, NOY, and SO2 taken on

July 15, 1995

During the same July 1995 period, measurements aloft in other parts of the OTR

also recorded high ozone overnight in layers 500 m or higher above the surface. Ozone

aloft concentrations above Poughkeepsie, NY and New Haven, CT approached levels of

120 ppb or greater on the night of July 14 (Zhang & Rao, 1999). Figure 2-11 displays the

aircraft measurements above Poughkeepsie, NY around 4 a.m. EST.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 11

Figure 2-11. Observed vertical ozone profile measured above Poughkeepsie, NY at

about 4 a.m. EST on July 14, 1995

0 20 40 60 80 100 120 140

Ozone (ppb)

1600

1200

800

400

Altitude (meters)

8-hour standard

Observed ozone

0 20 40 60 80 100 120 140

Ozone (ppb)

1600

1200

800

400

Altitude (meters)

8-hour standard

Observed ozone

Note: The figure includes a vertical line at 85 ppb for comparing aloft measurements with the

8-hour ozone NAAQS (observed ozone data from Zhang & Rao, 1999). 

The aircraft measurements since 1992 reinforce the previously mentioned

observations by Clarke and Ching (1983) during the summer of 1979, in which aircraft

measurements recorded aloft ozone concentrations of about 90 ppb transported overnight

from eastern Ohio and entering into the Northeast Corridor over a region stretching from

the lower Hudson River Valley north of New York City down across eastern

Pennsylvania and into Maryland just west of Baltimore. The measurements also observed

NOX aloft during the overnight hours that could contribute to additional ozone formation

in the OTR as it mixed down to the surface in the morning.

The presence of high levels of ozone and precursors aloft across a large spatial

region gives rise to the concept of an “ozone reservoir” existing at night just above the

nocturnal inversion boundary. The pollutants in this reservoir are not subject to

destruction at the surface, and can be transported long distances in the wind flows created

by the synoptic scale weather patterns conducive to ozone formation and transport.

2.4.Atmospheric modeling of regional ozone transport

Modeling results by the USEPA for the Clean Air Interstate Rule (CAIR) further

underscore the regional nature of ozone transport into and within the OTR through the
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 12

various pathways described in the above sections. Based on ozone air quality modeling

results, the USEPA tabulated the percent contribution to 8-hour ozone nonattainment in a

number of OTR counties. The USEPA modeled the contributions for the base year 2010,

which included implementation of the NOX SIP Call and other existing and promulgated

control programs. Table 2-1 shows the CAIR results for the OTR counties (USEPA,

2005, from Table VI-2).

Table 2-1. USEPA CAIR modeling results of percent contribution to 8-hour ozone

nonattainment in OTR counties in 2010 due to transport from upwind states

2010 Base

Nonattainment

Counties

2010 Base

8-Hour Ozone (ppb)

Percent of 8-Hour

Ozone due to

Transport

Fairfield CT 92 80 %

Middlesex CT 90 93 %

New Haven CT 91 95 %

Washington DC 85 38 %

Newcastle DE 85 37 %

Anne Arundel MD 88 45 %

Cecil MD 89 35 %

Harford MD 93 31 %

Kent MD 86 47 %

Bergen NJ 86 38 %

Camden NJ 91 57 %

Gloucester NJ 91 62 %

Hunterdon NJ 89 26 %

Mercer NJ 95 36 %

Middlesex NJ 92 62 %

Monmouth NJ 86 65 %

Morris NJ 86 63 %

Ocean NJ 100 82 %

Erie NY 87 37 %

Richmond NY 87 55 %

Suffolk NY 91 52 %

Westchester NY 85 56 %

Bucks PA 94 35 %

Chester PA 85 39 %

Montgomery PA 88 47 %

Philadelphia PA 90 55 %

Kent RI 86 88 %

Arlington VA 86 39 %

Fairfax VA 85 33 %

From USEPA, 2005 (Table VI-2)

The CAIR modeling by the USEPA also provides information on the upwind

areas (by state) contributing to downwind nonattainment in the OTR counties. Table 2-2

presents the upwind states significantly contributing to 8-hour ozone nonattainment in

counties within the OTR, according to significance criteria used by the USEPA (USEPA,

2005, from Table VI-5). The states listed in the table as significantly contributing to
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 13

downwind ozone nonattainment in the OTR counties include states outside of the OTR,

indicating the broad regional scale of the ozone transport problem.

Table 2-2. USEPA CAIR modeling results of upwind states that make a significant

contribution to 8-hour ozone in downwind OTR nonattainment counties

Downwind

State/County Upwind States

CT Middlesex MA NJ NY OH PA VA

CT New Haven MD/DC NJ NY OH PA VA WV

CT Fairfield MD/DC NJ NY OH PA VA WV

District of Columbia MD/DC OH PA VA

DE New Castle MD/DC MI NC OH PA VA WV

MD Harford NC OH PA VA WV

MD Kent MI NC OH PA VA WV

MD Cecil MI OH PA VA WV

MD Anne Arundel MI NC OH PA VA WV

NJ Ocean DE MD/DC MI NY OH PA VA WV

NJ Bergen MD/DC MI OH PA VA WV

NJ Gloucester DE MD/DC MI OH PA VA WV

NJ Morris DE MD/DC MI NY OH PA VA WV

NJ Middlesex DE MD/DC MI NY OH PA VA WV

NJ Hunterdon DE MD/DC OH PA VA WV

NJ Camden DE MD/DC MI OH PA VA WV

NJ Mercer DE MD/DC MI NY OH PA VA WV

NJ Monmouth DE MD/DC MI NY OH PA VA WV

NY Erie MD/DC MI NJ PA VA WI

NY Westchester MD/DC NJ OH PA VA WV

NY Richmond MD/DC MI NJ PA VA WV

NY Suffolk CT DE MD/DC MI NC NJ OH PA VA WV

PA Montgomery DE MD/DC NJ OH WV

PA Philadelphia DE MD/DC MI NJ OH VA WV

PA Chester DE MD/DC MI NJ OH VA WV

PA Bucks DE MD/DC MI NJ OH VA WV

RI Kent CT MA NJ NY OH PA VA

VA Arlington MD/DC OH PA

VA Fairfax MD/DC OH PA WV

From USEPA, 2005 (Table VI-5). States are listed alphabetically and not according to order of influence.

While the USEPA modeled 40 eastern U.S. counties as in nonattainment of the 8-

hour ozone NAAQS in the 2010 base year (including counties not in the OTR), it

projected that only three of those 40 counties would come into attainment by 2010 with

the additional NOX reductions of CAIR (USEPA, 2005, p. 58). The USEPA modeling

does predict that ozone will be lower in the remaining nonattainment counties by 2010

due to CAIR, with additional counties coming into attainment by 2015. The CAIR

reductions, therefore, will bring the OTR nonattainment counties closer to attainment by

2010, but will not result in attainment for a large majority of OTR counties predicted to

be in nonattainment in 2010 prior to implementation of CAIR.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 14

2.5.Summary

This section has summarized current knowledge of the meteorological processes

that affect local ozone levels within the OTR. A conceptual description of transport

within the OTR can be divided into three principle components: ground level transport at

the surface, transport by the nocturnal low level jet, and transport aloft. All three modes

of transport depend on the location of the high pressure system. Ground level transport is

the result of interaction between the synoptic flow and local effects, such as the sea

breeze and the Appalachian lee side trough. Transport within the OTR can occur by the

nocturnal low level jet that forms late at night or in the very early morning hours. This

phenomenon is a result of the differential heating of the air between the Appalachian

Mountains and the Atlantic Ocean. It has been observed throughout the Eastern Seaboard

from Georgia to Maine. The nocturnal low level jet can transport ozone that formed

within the OTR or was transported into the OTR from outside the region. Transport aloft

is dominated by the anti-cyclonic flow around a high pressure system, which can lead to

transport of an ozone reservoir into the OTR created by emissions in areas that lie outside

the OTR. Local emissions within the OTR add to the polluted air mixing down from

above that arrived from more distant locations.

Atmospheric modeling by the USEPA underscores the observations that the

OTR’s ozone problem has contributions from outside and upwind of the region. Pollution

sources in the Ohio River Valley and the Southeast significantly contribute to ozone

nonattainment problems in various portions of the OTR.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 15

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implications for regional and global ozone distributions.” J. Geophys. Res. 92, 4191–

4207, 1987.

Lutgens, F., and E. Tarbuck. The Atmosphere: An Introduction to Meteorology, 8th ed.,

512 pp., Prentice Hall, Upper Saddle River, New Jersey, 2001.

MARAMA (Mid-Atlantic Regional Air Management Association). A guide to midAtlantic regional air quality. MARAMA. Baltimore, MD, pp. 2-3, 2005 (available online at www.marama.org/reports).

McKeen, S. A., M. Trainer, E. Y. Hsie, R. K. Tallamraju, and S. C. Liu. “On the indirect

determination of atmospheric OH radical concentrations from reactive hydrocarbon

measurements.” J. Geophys. Res. 95, 7493–7500, 1990.

NARSTO. An Assessment of Tropospheric Ozone Pollution. NARSTO, July 2000.

Olszyna, K.J., E.M. Bailey, R. Simonaitis and J.F. Meagher. “O3 and NOy Relationships

at a Rural Site.” J. Geophys. Res. 99, 14,557-14,563, 1994.

Ryan, W.F. and R.R. Dickerson. “Regional transport of pollutants and implications for 8-

hour ozone non-attainment areas in Maryland.” Report prepared for the Maryland

Department of the Environment, Final version 2.2, 2000.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 16

Ryan, W.F. “The low level jet in Maryland: Profiler observations and preliminary

climatology.” Report prepared for the Maryland Department of the Environment, Air and

Radiation Administration, 2004.

Sillman, S., J. A. Logan, and S. C. Wofsy. “A regional scale model for ozone in the

United States with subgrid representation of urban and power plant plumes.” J. Geophys.

Res. 95, 5731–5748, 1990.

Sjostedt, D.W., J.T. Sigmon, and S.J. Colucci. “The Carolina nocturnal low-level jet:

Synoptic climatology and a case study.” Weather and Forecasting. 5, 404-415, 1990.

Stoeckenius, T. and Kemball-Cook, S. “Determination of representativeness of 2002

ozone season for ozone transport region SIP modeling.” Final Report prepared for the

Ozone Transport Commission, 2005.

Trainer, M., D.D. Parrish, M.P. Buhr, R.B. Norton, F.C. Fehsenfeld, K.G. Anlauf, J.W.

Bottenheim, Y.Z. Tang, H.A. Wiebe, J.M. Roberts, R.L. Tanner, L. Newman, V.C.

Bowersox, J.F. Meagher, K.J. Olszyna, M.O. Rodgers, T. Wang, H. Berresheim, K.L.

Demerjian, and U.K. Roychowdhury. “Correlation of Ozone with NOy in

Photochemically Aged Air.” J. Geophys. Res. 98, 2917-2925, 1993.

Weisman, R.A. “An observational study of warm season southern Appalachian lee

troughs. Part I: Boundary layer circulation.” Monthly Weather Review. 118, 950-962,

1990.

Woodman, M.F., D.T. Nguyen, D.J. Krask, E. Joseph, V. Davis, R. Hoff, R. Rogers,

M.G. Seybold. “Maryland Ozonesonde Campaign 2005.” Poster at EPA National Air

Quality Conference, San Antonio, TX, 2006.

Zhang J. and S.T. Rao. “The role of vertical mixing in the temporal evolution of groundlevel ozone concentrations.” J. Applied Meteor. 38, 1674-1691, 1999.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 1

3.OZONE-FORMING POLLUTANT EMISSIONS

The pollutants that affect ozone formation are volatile organic compounds

(VOCs) and nitrogen oxides (NOX). The emissions dataset presented for the OTR in the

first section below is from the 2002 MANE-VU (Mid-Atlantic/Northeast Visibility

Union) Version 2 regional haze emissions inventory. MANE-VU is the regional planning

organization (RPO) for the mid-Atlantic and Northeast states coordinating regional haze

planning activities for the region. While the context of the MANE-VU inventory is

regional haze, it includes inventories of NOX and VOCs that also inform air quality

planners on sources important to ozone formation.f To provide a fuller context of

precursor emissions contributing to regional ozone affecting the OTR, the section

following the MANE-VU information presents NOX and VOC emissions information

from the 2002 National Emissions Inventory (NEI) for states in adjacent RPOs.

3.1.Emissions inventory characteristics in the OTR

3.1.1.Volatile organic compounds (VOCs)

Existing emission inventories generally refer to VOCs as hydrocarbons whose

volatility in the atmosphere makes them particularly important in enhancing ozone

formation in the presence of NOX.

As shown in Figure 3-12, the VOC inventory for the OTR is dominated by mobile

and area sources. Most VOC emissions in the OTR, however, come from natural sources,

which are not shown in the figure. Among the human-caused VOC emissions, on-road

mobile sources of VOCs include exhaust emissions from gasoline passenger vehicles and

diesel-powered heavy-duty vehicles as well as evaporative emissions from transportation

fuels. VOC emissions may also originate from a variety of area sources (including

solvents, architectural coatings, and dry cleaners) as well as from some point sources

(e.g., industrial facilities and petroleum refineries).

Naturally occurring (biogenic) VOC emissions are caused by the release of

natural organic compounds from plants in warm weather. Many natural VOCs that

contribute to ozone formation are highly reactive. Isoprene, for example, is a highly

reactive five-carbon natural VOC emitted from mostly deciduous trees (e.g., oaks) that

plays an important role in enhancing regional ozone formation across the eastern U.S.

(Trainer et al., 1987; Chameides et al., 1988). Because biogenic VOC emissions are large

and reactive, they are the most important part of the VOC inventory for understanding

and predicting ozone formation. Biogenic VOCs are not included in Figure 3-12, but

nationally, they represent roughly two-thirds of all annual VOC emissions (USEPA,

2006a). Modeling biogenic emissions can be difficult as it requires simulating biological

responses to a range of environmental conditions, such as leaf temperature and the

amount of sunlight reaching a leaf surface.

f

 The description of OTR state inventories discussed in the first section does not include the portion of

Virginia in the Washington, DC metropolitan area. Information for Virginia is in the following section and

comes from the 2002 National Emissions Inventory.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 2

Figure 3-12. 2002 MANE-VU state VOC inventories in the OTR

0%

25%

50%

75%

100%

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

million t/y

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

AREA NONROAD ONROAD POINT Emission

Figure key: Bars = Percentage fractions of four source categories; Circles = Annual

emissions amount in 106 tons per year. The Virginia portion of the Washington, DC

metropolitan area is not shown in the figure.

3.1.2.Oxides of nitrogen (NOX)

NOX emissions are a fundamental necessity for the atmospheric formation of

ozone. Without NOX, ozone formation during warm summer days would virtually cease,

regardless of the amount of reactive VOCs present. By contrast, without VOCs, NOX

would still produce ozone in the presence of sunlight, albeit at a much diminished

efficiency.

Figure 3-13 shows NOX emissions in the OTR at the state level. Since 1980,

nationwide emissions of NOX from all sources have shown little change. In fact,

emissions increased by 2 percent between 1989 and 1998 (USEPA, 2000). This increase

is most likely due to industrial sources and the transportation sector, as power plant

combustion sources have implemented modest emissions reductions during the same time

period. Most states in the OTR experienced declining NOX emissions from 1996 through

2002, except Massachusetts, Maryland, New York, and Rhode Island, which show an

increase in NOX emissions in 1999 before declining to levels below 1996 emissions in

2002.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 3

Figure 3-13. State level nitrogen oxides emissions

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

million t/y

NEI 1996

NEI 1999

MV 2002 v.2

Monitored ambient NOX trends during the summer from 1997 to 2005 corroborate

the downward trend in NOX emissions seen in the emissions inventories for the OTR. As

seen in Figure 3-14, the 24-hour (lower trend lines) and 6 a.m.-8 a.m. (upper trend lines)

NOX concentrations indicate decreases in NOX over this time period in the OTR. The

NOX reductions likely come from decreasing vehicle NOX emissions due to more

stringent motor vehicle standards as well as NOX reductions from the OTR NOX Budget

Program and the NOX SIP Call (mainly power plants).
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 4

Figure 3-14. Plot of monitored NOX trends in OTR during 1997-2005

JUNE, JULY & AUGUST 1997-2005 OTC AVERAGE NOx CONCENTRATIONS

10

15

20

25

30

35

40

45

50

199719981999200020012002200320042005199719981999200020012002200320042005199719981999200020012002200320042005

Average Concentration (ppb) .

JUN (all hrs)

JUL (all hrs)

AUG (all hrs)

JUN (06-08 EST)

JUL (06-08 EST)

AUG (06-08 EST)

Note: Upper trend lines correspond to ambient NOX measured from 0600-0800 EST in the morning. Lower

trend lines correspond to NOX measured over entire day (created by Tom Downs, Maine Department of

Environmental Protection).

Power plants and mobile sources generally dominate state and national NOX

emissions inventories. Nationally, power plants account for more than one-quarter of all

NOX emissions, amounting to over six million tons. The electric sector plays an even

larger role, however, in parts of the industrial Midwest where high NOX emissions have a

particularly significant power plant contribution. By contrast, mobile sources dominate

the NOX inventories for more urbanized mid-Atlantic and New England states to a far

greater extent, as shown in Figure 3-15. In these states, on-road mobile sources — a

category that mainly includes highway vehicles — represent the most significant NOX

source category. Emissions from non-road (i.e., off-highway) mobile sources, primarily

diesel-fired engines, also represent a substantial fraction of the inventory.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 5

Figure 3-15. 2002 MANE-VU state NOX inventories in the OTR

0%

25%

50%

75%

100%

Connecticut

Delaware

District of Columbia

Maine

Maryland

Massachusetts

New Hampshire

New Jersey

New York

Pennsylvania

Rhode Island

Vermont

million t/y

0.0

0.3

0.6

0.9

AREA NONROAD ONROAD POINT Emission

Figure key: Bars = Percentage fractions of four source categories; Circles = Annual

emissions amount in 106 tons per year. The Virginia portion of the Washington, DC

metropolitan area is not shown in the figure.

3.2.Emissions inventory characteristics outside the OTR

NOX and VOC emissions in the OTR are only one component of the emissions

contributing to ozone affecting the OTR. As regional modeling for the NOX SIP Call and

CAIR have shown, emission sources, primarily of NOX, located outside the OTR can

significantly contribute to ozone transported into the OTR. Here we present regional

emissions information grouped by the three eastern RPOs – MANE-VU, VISTAS

(Visibility Improvement State and Tribal Association of the Southeast), and the MWRPO

(Midwest RPO). Table 3-3 lists the states in each RPO.

The inventory information is extracted from the USEPA final 2002 National

Emissions Inventory (NEI). For consistency, the MANE-VU information here also comes

from the 2002 NEI rather than from the MANE-VU Version 2 regional haze emissions

inventory described above. The differences between the inventories are not great, as the

NEI and the MANE-VU Version 2 inventory are both based on the same inventory

information provided by the states.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 6

Table 3-3. Eastern U.S. RPOs and their state members

RPO State

MWRPO Illinois

MWRPO Indiana

MWRPO Michigan

MWRPO Ohio

MWRPO Wisconsin

MANE-VU Connecticut

MANE-VU Delaware

MANE-VU District of Columbia

MANE-VU Maine

MANE-VU Maryland

MANE-VU Massachusetts

MANE-VU New Hampshire

MANE-VU New Jersey

MANE-VU New York

MANE-VU Pennsylvania

MANE-VU Rhode Island

MANE-VU Vermont

VISTAS Alabama

VISTAS Florida

VISTAS Georgia

VISTAS Kentucky

VISTAS Mississippi

VISTAS North Carolina

VISTAS South Carolina

VISTAS Tennessee

VISTAS Virginia

VISTAS West Virginia

Table 3-4 presents VOC emissions by source sector and RPO for the eastern

United States. The NOX emissions by source sector and RPO are presented in Table 3-5.

Regionally, NOX emissions are more important with respect to regional ozone formation

and transport. NOX emissions in combination with abundant naturally occurring VOC

emissions from oaks and other vegetation have been shown to be important sources of

regional ozone in the eastern U.S. (Trainer et al. 1987; Chameides et al. 1988).

Table 3-4. VOC emissions in eastern RPOs

RPO Point Area On-road Non-road Total

MWRPO 234,938 1,182,186 660,010 492,027 2,569,160

MANE-VU 93,691 1,798,158 793,541 494,115 3,179,504

VISTAS 458,740 2,047,359 1,314,979 609,539 4,430,617
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 7

Table 3-5. NOX emissions in eastern RPOs

RPO Point Area On-road Non-road Total

MWRPO 1,437,284 184,790 1,290,178 723,844 3,636,096

MANE-VU 680,975 268,997 1,297,357 534,454 2,781,783

VISTAS 2,094,228 266,848 2,160,601 812,615 5,334,293

3.3.Are NOX or VOC control strategies most effective at reducing

ozone?

The effectiveness of a NOX-focused or VOC-focused control strategy to reduce

ozone is not constant by location or emissions; rather it is a changing chemical

characteristic of an air parcel affecting a particular location. As a result, the effectiveness

of a NOX or VOC-focused control strategy can vary within an air parcel as it dynamically

evolves over time with transport, dispersion, and photochemical aging (NARSTO, 2000).

On a regional basis, OTAG, CAIR and other modeling studies have consistently

shown that NOX reductions have the greatest impact on regional ozone concentrations,

while VOC reductions have more local impacts. This is largely a result of significant

naturally occurring VOC emissions (especially isoprene) in large forested regions of the

eastern U.S. Real-world results from regional NOX reductions at power plants (i.e., the

NOX SIP Call) are now indicating that significant ozone reductions are occurring on a

regional basis as a result of regional NOX strategies. A recent USEPA report finds a

strong association between areas with the greatest NOX emission reductions due to the

NOX SIP Call and downwind sites exhibiting the greatest improvement in ozone in 2005

(USEPA, 2006b).

As a general rule, VOC reductions may be effective at reducing urban-scale ozone

pollution in lieu of or in combination with local NOX reductions, while regional NOX

controls are most effective at reducing regional ozone. While a general rule can be

outlined in evaluating the potential effectiveness of NOX and VOC-focused control

strategies, the optimal strategy for a specific location will depend on the particular

circumstances of that location. Exceptions to a VOC-only strategy for an urban area can

occur when the urban area has large natural VOC emissions, ozone is transported from

upwind, or there is recirculation of aged local pollution (e.g., sea breeze effect).

Furthermore, because the conditions causing individual ozone episodes can vary, a given

urban area may change in sensitivity between a NOX and VOC-focused strategy

depending on a particular episode’s conditions (NARSTO, 2000). Therefore, the

appropriate combination of VOC and NOX controls at the local level depends on local

circumstances with the realization that a single approach focusing on NOX or VOC-only

controls is not necessarily effective for all episode types. It is clear, however, that

regional NOX reductions provide regional ozone reductions, and this will influence ozone

levels being transported into local urban areas.

3.4.Summary

There are large emissions of VOCs and NOX within and outside the OTR that

contribute to local and regional ozone problems. Naturally occurring VOC emissions play

an important role in combination with human-caused NOX emissions in forming regional
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 8

ozone across large sections of the eastern U.S. Regional NOX control strategies are

demonstrating success in reducing regional ozone. On a more local scale, some

combination of VOC and NOX controls may be needed, with the specific combination

dependent upon local circumstances.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 9

References

Chameides, W.L., R.W. Lindsay, J. Richardson, and C.S. Kiang. “The role of biogenic

hydrocarbons in urban photochemical smog: Atlanta as a case study.” Science 241, 1473-

1475, 1988.

NARSTO. An Assessment of Tropospheric Ozone Pollution. NARSTO, July 2000.

Trainer, M., E.J. Williams, D.D. Parrish, M.P. Buhr, E.J. Allwine, H.H. Westberg, F.C.

Fehsenfeld, and S.C. Liu. “Models and observations of the impact of natural

hydrocarbons on rural ozone.” Nature 329, 705-707, 1987.

USEPA. National Air Quality and Emission Trends Report, 1998, EPA 454/R-00-003,

available online: http://www.epa.gov/oar/aqtrnd98/, 2000.

USEPA. 2002 Final National Emissions Inventory (NEI), available online:

ftp://ftp.epa.gov/EmisInventory/2002finalnei/, 2006a (accessed October 10, 2006) [The

2002 NEI reports national annual emissions for total anthropogenic VOC emissions as

16.8 million tons, and total biogenic VOC emissions as 41.8 million tons].

USEPA. NOX Budget Trading Program 2005 Compliance and Environmental Results,

EPA430-R-06-013, available online: http://www.epa.gov/airmarkets/fednox/, 2006b.

 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 1

4.WHAT WILL IT TAKE TO CLEAN THE AIR? – LINKING

THE SCIENCE TO POLICY

4.1.The three phases of a bad ozone day and the ozone reservoir

With the atmospheric chemistry, meteorology, and air emission inventory

elements presented in the previous sections, a conceptual description emerges of ozone

problem in the OTR. Consider a typical “day,” defined as starting at sunset, for a severe

ozone event associated with a high pressure system. Conceptually, a bad ozone day can

be considered as occurring in three phases. During phase one, a nocturnal inversion forms

as the temperature of the earth drops following sunset, isolating the surface from stronger

winds only a few hundred feet overhead. Ozone near the surface cannot mix with ozone

above and is destroyed as it reacts with the Earth’s surface. In a city, fresh NOX emissions

react with ozone, further reducing its concentration, so that by morning, very little ozone

is left below the nocturnal inversion. At this time, the nocturnal inversion is at its

strongest, and winds at the surface are typically calm.

Above the nocturnal inversion, the situation is quite different. Ozone and its

precursors, both from the previous day’s local emissions and from transport, remain

largely intact. There are no surfaces to react with the ozone and a large reservoir of ozone

remains above the inversion. During phase two of a bad ozone day, the nocturnal

inversion breaks down at mid-morning, with the result that the ozone and precursors

above the inversion can now mix with the air near the surface. The result of this mixing is

a sudden change in ozone. Figure 4-16 shows median ozone profiles for morning and

afternoon aircraft flights from 1996 – 2003. One can clearly see the breakdown of the

nocturnal inversion throughout the day (Hudson, 2005).

Figure 4-16. Median ozone profiles for morning and afternoon flights

from 1996 – 2003

O3 median profiles for morning and afternoon flights

(1996 - 2003)

0

500

1000

1500

2000

2500

3000

3500

0 20 40 60 80 100 120

Median O3 (ppb) with 25th and 75

th percentiles

Pressure derived altitude (m)

median

am (254)

median

pm (293)

q25 am

q75 am

q25 pm

q75 pm

AM PM
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 2

In phase three of a bad ozone day, ozone concentrations reach their highest levels

in the afternoon through the combined accumulation of local pollution produced that day

mixed with the transported regional pollution load brought in overnight from the ozone

reservoir. Figure 4-17 shows this graphically for the southern OTR. The ozone monitor at

Methodist Hill, PA is a high elevation site located at 1900 ft in altitude in south central

Pennsylvania, and is above the nocturnal inversion. In the early morning hours of August

12, 2002 (e.g., 5 a.m.), it recorded ozone concentrations above 80 ppb, which was much

higher than what other lower elevation monitors in the region were recording (e.g., Little

Buffalo State Park, PA, South Carroll County, MD, Frederick, MD, Ashburn, VA, Long

Park, VA). Due to the lack of sunlight necessary to produce ozone photochemically

during nighttime hours, the high ozone levels seen at Methodist Hill, PA indicate the

presence of a significant ozone reservoir above the nocturnal inversion layer produced

during daylight hours at some earlier point in time and transported into the region. With

the break up of the nocturnal inversion after sunrise (e.g., starting about 7 a.m.), ozone

concentrations at the lower elevation monitors show a rapid increase. This reflects the

mixing down of the ozone reservoir from higher altitude to the surface in combination

with local ozone production near the surface now that the sun has begun inducing its

photochemical production.

Figure 4-17. Hourly ozone profiles in the southern OTR, August 12, 2002

0

20

40

60

80

100

120

140

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

Hour (EST)

Ozone (ppb)

South Carroll, MD

Frederick, MD

Methodist Hill, PA

Little Buffalo SP, PA

Ashburn, VA

Long Park, VA

The ozone reservoir extends across the OTR, as seen on the same night in high

elevation ozone monitoring sites in the northern OTR. Figure 4-18 shows the hourly

ozone concentrations measured on August 12, 2002 at Mohawk Mountain, CT, Cadillac

Mountain, ME, Mt. Greylock, MA, Mt. Monadanock, NH, Mt. Washington, NH, and
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 3

Whiteface Mountain, NY. As with Methodist Hill, PA on this day, these sites show

elevated ozone concentrations during nighttime hours, as compared to lower elevation

sites below the nocturnal inversion (e.g., Danbury, CT). By mid-day, however, the

nocturnal boundary layer has broken down, mixing the transported ozone from the

reservoir above into the locally produced ozone below. Appendix G provides more detail

on contributions to the ozone reservoir within and outside the OTR.

Figure 4-18. Hourly ozone profiles in the northern OTR, August 12, 2002

0

20

40

60

80

100

120

140

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

Hour (EST)

Ozone (ppb)

Mohawk Mtn., CT

Mt. Monadanock, NH

Mt. Greylock, MA

Mt. Washington, NH

Whiteface Mtn., NY

Cadillac Mtn., ME

Danbury, CT

Data provided by Tom Downs, Maine Department of Environmental Protection.

4.2.Chronology of an ozone episode – August 2002

The chronology of an historical ozone episode occurring in the OTR from August

8 to August 16, 2002 provides a real-world example that pieces together the elements of

the ozone conceptual description given in this document. Surface maps from the period

provide a synoptic overview of major weather systems that were influencing air quality

across the OTR during that time. Meteorological insights combined with ozone

concentration information provide a picture of the evolving ozone episode on a day-byday basis. Figure 4-19, Figure 4-20, and Figure 4-21, respectively, show eight-panel

displays of surface weather maps, back trajectories, and 8-hour maximum ozone

concentrations from each day. The daily progression shows the formation of high ozone

that shifts from west to east, and ultimately northward, during successive days of the

episode according to local ozone formation and transport shaped by wind patterns within

and outside of the OTR.

The August 2002 episode began with a slow-moving high pressure system

centered over the Great Lakes initiating a northerly flow over the OTR on August 8. Over
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 4

the next several days, the high drifted southeastward and became extended across a large

part of the eastern U.S., bringing high temperatures to the region. Calm conditions west

of the OTR on August 10 were pivotal for the formation of ozone, which first began

building in the Ohio River Valley. Over the next four days, 8-hour ozone concentrations

climbed well above the 85 ppb (0.08 ppm) NAAQS over a wide area of the OTR. Large

parts of the heavily populated Northeast Corridor experienced 8-hour ozone levels above

100 ppb during the height of the episode, which far exceeded the 85 ppb NAAQS.

The following chronology provides a day-by-day evolution of the August 2002

ozone episode. Parts of this description are taken from Ryan (2003).

August 8: A high pressure system over the Great Lakes produces NW-N

prevailing surface winds (~4-8 mph) throughout the region. Maximum daily temperatures

approach or exceed 80o F.

August 9: Wind speeds fall off but the direction remains NW-N as the high

moves into the Pennsylvania-New York region. Temperatures rise as cloud cover

declines. Background ozone levels begin to build in the Ohio River Valley with 8-hour

maximum concentrations reaching the 60-80 ppb range.

August 10: High pressure is directly over the mid-Atlantic. With dew points still

in the mid-50o’s F, the skies are extraordinarily clear throughout the day. Temperatures

(except in northern-most areas) approach 90o F while surface-level winds turn to more

southerly directions. With high pressure overhead, the back trajectories suggest very light

winds and recirculation. Calm conditions through the morning hours in the lower Ohio

River Valley promote increasingly higher levels of ozone noted in surface observations –

now reaching above the 85 ppb 8-hour ozone NAAQS over much of Indiana, Ohio, and

other states along the Ohio River, as well as states around Lake Michigan and large

portions of the southeastern U.S. Ozone levels above the 8-hour NAAQS now begin

appearing for the first time in the western and southern parts of the OTR.

August 11: Surface high pressure drops slowly southeastward across the midAtlantic with the center in western North Carolina drifting to coastal South Carolina

during the day. The upper level ridge has also moved east and is located over the midAtlantic. Circulation around the high becomes well established. A surface-level trough

descends from north of the Great Lakes during the day, passes eastward through the Ohio

River Valley and stalls over the Allegheny Mountains and southward. Peak temperatures

are in the low to mid-90o’s F. Morning winds are low-to-calm in the area east of the

Mississippi – the area of ozone now reaches from eastern Wisconsin to Tennessee and

eastward to Georgia up through the Carolinas into the OTR, covering most of

Pennsylvania, New York, New Jersey, Connecticut, Rhode Island and Massachusetts.

Winds are generally south to southwest as is reflected in the boundary layer back

trajectories. The key factor driving local ozone production appears to be a very stable

boundary layer. The 8 a.m. sounding at the Washington-Dulles airport shows a very

strong low-level inversion from 950-900 mb with a deep residual layer beneath a

continuing strong subsidence inversion – now based at 760 mb.

August 12: The upper level ridge remains quasi-stationary with its axis over the

mid-Atlantic. The center of high pressure at 850 mb is over North Carolina and Georgia.

At the surface, the characteristic Appalachian lee side trough forms. Temperatures exceed
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 5

90o F throughout the OTR except in coastal Maine. Winds are fairly strong from the

northwest. This is reflected in the back trajectories that show a shift to westerly transport.

Elevated upwind ozone concentrations at 11 a.m. on August 11 occur in the vicinity of

the origin of the back trajectories, on the order of 78-86 ppb. Ozone concentrations fall

this day west of the Appalachians but increase markedly across the mid-Atlantic. The

area of highest ozone has pushed eastward and now extends from southern Maine across

central Pennsylvania down through Maryland into the Carolinas, Georgia, and eastern

Tennessee. Ozone builds throughout the day as circulation forces it to channel northeast

between the stalled trough and a cold front approaching from the Midwest. Some of the

highest 8-hour concentrations occur through the central to southern OTR on this day.

August 13: Calm conditions prevail as the trough reaches coastal New Jersey by

8 a.m. Generally clear skies allow temperatures to reach the mid-90o’s F everywhere

except in coastal Maine. Dew points, which had been rising since August 8, reach the

upper 60o’s F. A morning sounding at the Washington-Dulles airport showed a

continuing strong low level inversion with a residual mixed layer to 850 mb ending just

beneath a weak secondary inversion. The cap aloft has lifted to ~ 630 mb and the

sounding is more unstable compared to previous day’s between the two inversion layers.

The Appalachian lee side trough continues in place from late on August 12. As is

typically the case, the highest ozone concentrations are found in proximity to this

boundary. The highest 8-hour ozone concentrations are along the eastern portions of the

OTR from northeastern Virginia through New Jersey, Long Island, Connecticut, and into

eastern Massachusetts. By 8 p.m., showers associated with the approaching cold front

have reached into Ohio.

August 14: By 8 a.m., the trough has dissipated and the high is moving offshore,

resulting in an increasing southerly wind component, which pushes maritime air

northward. Dew points remain in the upper 60o’s F and peak temperatures reach into the

90o’s F everywhere and top 100o F in several locations. Ozone concentrations build again,

with the highest levels concentrated in the central OTR from eastern Pennsylvania across

to Massachusetts. A “hotspot” of ozone appears in upstate New York at the eastern end of

Lake Ontario, and may be the result of transport from the west across the lake. Ozone

concentrations decrease south and west of Baltimore and along coastal New Jersey as

cleaner maritime air pushes in from the south.

August 15: This episode ends in a very different manner than the standard high

ozone episode. Instead of the passage of a sharp cold front, this episode ends gradually as

cleaner air sweeps north, winds increase, and the atmosphere steadily destabilizes. Ozone

concentrations fall across the middle and lower OTR as low level flow becomes more

southeast and the Bermuda high fills in westward. The highest levels, still exceeding the

8-hour ozone NAAQS, now occur in the northern reaches of the OTR in upstate New

York, Vermont, New Hampshire, and Maine.

August 16: Cloud cover spreads over the region with ozone falling further. The

new high building into the upper Midwest pushes the remains of the showers out of the

Northeast. A spot of high ozone persists in central New Jersey. This is the last

exceedance day in a string of seven exceedance days within the OTR during this

extended episode.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 6

Figure 4-19. Surface weather maps for August 9-16, 2002

August 9, 8:00AM EDT August 10, 8:00 AM EDT

August 11, 8:00 AM EDT August 12, 8:00 AM EDT

August 13, 8:00 AM EDT August 14, 8:00 AM EDT

August 15, 8:00 AM EDT August 16, 8:00 AM EDT
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 7

 Figure 4-20. HYSPLIT 72-hour back trajectories for August 9-16, 2002

Aug 9, 2002 8 , 2002 8 am EDT Aug 10, 2002 8 am EDT

Aug 11, 2002 8 am EDT Aug 12, 2002 8 am EDT

Aug 13, 2002 8 am EDT Aug 14, 2002 8 am EDT

Aug 15, 2002 8 am EDT Aug 16, 2002 8 am EDT
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 8

Figure 4-21. Spatially interpolated maps of maximum 8-hour surface ozone concentrations August 9 – 16, 2002
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 9

4.3.Clean Air Act provisions

As is evident from the myriad source regions and transport pathways affecting the

OTR, the regional ozone nonattainment problem presents a significant challenge to air

quality planners. To improve air quality, emission reductions of the appropriate pollutants

must occur at the appropriate levels (i.e., stringency of controls) and over the appropriate

geographic extent. States have primary responsibility for achieving the goals of the Clean

Air Act, as they are responsible for developing State Implementation Plans and

implementing and enforcing emission reduction programs to meet the health-protective

National Ambient Air Quality Standards (NAAQS). 

When Congress passed the Clean Air Act Amendments of 1990, it recognized that

air pollution transcends political boundaries and that tools for addressing transport must

be made available to state and federal governments. Accordingly, several Clean Air Act

provisions deal with transported pollution, including: (1) prohibiting the USEPA from

approving State Implementation Plans that interfere with another state’s ability to attain

or maintain a NAAQS; (2) requiring the USEPA to work with states to prevent emissions

that contribute to air pollution in a foreign country; (3) allowing states to form ozone

transport regions; (4) requiring states in ozone transport regions to adopt a prescribed set

of controls in order to achieve a minimum level of regional emission reductions; and (5)

allowing states to petition the USEPA for timely relief from stationary source emissions

that interfere with attainment or maintenance of a NAAQS, and requiring the USEPA to

act on such petitions within a very short, prescribed timeframe. Taken together, these

provisions provide a framework for air quality planning. Its inherent principles are:

• Timely action is critical in order to protect public health;

• States must act locally to address air pollution;

• While acting locally, states must also consider their impacts downwind in addition

to in-state impacts when developing state implementation plans (SIPs), and

ameliorate such impacts through SIPs;

• Regional actions have been and can continue to be effective;

• To be effective on a regional level, states working together must work off of a

level playing field.

What the science tells us of the nature of the ozone problem in the OTR supports

this framework. The smaller scale weather patterns that affect pollution accumulation and

transport underscore the importance of local (in-state) controls for NOX and VOC

emissions. Larger synoptic scale weather patterns, and pollution patterns associated with

them, support the need for NOX controls across the eastern United States. Studies and

characterizations of nocturnal low level jets (i.e., channeled transport) also support the

need for local and regional controls on NOX and VOC sources as local and transported

pollution from outside the OTR can be entrained in nocturnal low level jets formed

during nighttime hours within the OTR. Land, sea, mountain, and valley breezes indicate

that there are unique aspects of pollution accumulation and transport that are area-specific

and will warrant policy responses at the local and regional levels beyond a one-size-fitsall approach.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 10

The mix of emission controls is also important for states to consider. While longrange transport of ozone is primarily due to NOX, VOCs are important because they

contribute to ozone formation by influencing how efficiently ozone is produced by NOX,

particularly within urban centers. While reductions in anthropogenic VOCs will typically

have less of an impact on the long-range transport of ozone, they can be effective in

reducing ozone in those urban areas where ozone production may be limited by the

availability of VOCs. Therefore, a combination of localized VOC reductions in urban

centers with additional NOX reductions (from both mobile and point sources) across a

larger region will help to reduce ozone and precursors in nonattainment areas as well as

their downwind transport across the entire region (NESCAUM, 1997). 

4.4.Past regional efforts

While states are somewhat limited in their ability to directly affect emissions

reductions beyond their own geo-political boundaries, over the past 15-20 years, the

Northeast states have acted regionally with tremendous success. Such efforts have

included:

• In 1989, regional low volatility gasoline (i.e., Reid Vapor Pressure pf 9.0 psi) was

introduced into the NESCAUM region, resulting in significant VOC reductions;

• In 1994, the California Low Emission Vehicle (LEV) program commenced in the

Northeast Corridor as regulations were adopted by Maine, Massachusetts, New

York, and Vermont. To date, four additional states have joined the program,

which continues to yield reductions in NOX, VOC, CO, and air toxics.

• In 1994, the states of the Ozone Transport Commission agreed to promulgate

regional NOX RACT controls and a NOX cap-and-trade program. The adopted

regional RACT deadline was 1995. By 1999, the NOX Budget Program was

implemented over the 12-state region from Maine to Washington, DC. In 2002,

the USEPA reported that the NOX Budget sources “emitted at a level

approximately 12 percent below 2001 allocations” (USEPA, 2002). Progress

continues with a more stringent cap taking effect in 2003.

• In 1997, eight OTR states petitioned the USEPA under section 126 of the Clean

Air Act, requesting NOX emissions reductions on certain stationary sources in the

Eastern U.S. In 1999, four more OTR members filed section 126 petitions. The

USEPA granted four of the initial eight state petitions in 2000.g

• In 2001, the states of the Ozone Transport Commission agreed to support a suite

of model rules for inclusion in SIPs as appropriate to address 1-hour ozone

problems. The model rules included controls for: (1) architectural and industrial

maintenance coatings; (2) portable fuel containers; (3) consumer products; (4)

solvent cleaning; (5) mobile equipment repair and refinishing; and (5) additional

NOX controls for industrial boilers, cement kilns, stationary reciprocating engines,

and stationary combustion engines.

g

 The initial eight section 126 OTR states were Connecticut, Maine, Massachusetts, New Hampshire, New

York, Pennsylvania, Rhode Island, and Vermont. The additional four OTR members filing section 126

petitions were Delaware, the District of Columbia, Maryland, and New Jersey. The four granted petitions

were from Connecticut, Massachusetts, New York, and Pennsylvania.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 11

These regional efforts have led the way for similar broader regional and national

programs. For mobile sources, the USEPA promulgated its federal Reformulated

Gasoline Program in 1995 and the National LEV program in 1998. For stationary

sources, the USEPA announced in 1997 that it would expand the OTR NOX Budget

Program through the NOX SIP Call, which included 22 states and NOX caps in place by

2003. The NOX SIP Call also served as a response to the states’ Section 126 petitions

under the Clean Air Act.

In 2005, the USEPA took a further step to address the regional ozone problem by

issuing the Clean Air Interstate Rule (CAIR), which requires additional NOX reductions

in 25 eastern states and the District of Columbia. The USEPA projects that CAIR will

achieve NOX reductions of 2 million tons in 2015, a 61% decrease from 2003 levels. This

will be a significant step forward in improving air quality, but the time allowed to achieve

these reductions is later than the deadline many eastern states are facing to meet the

current 8-hour ozone NAAQS. This, therefore, only partially provides the OTR with a

regional measure that helps achieve the Clean Air Act’s goal of attaining the ozone air

quality health standard within the Act’s mandatory deadlines.

4.5.Summary: Building upon success

A conceptual understanding of ozone as a regional problem in the OTR and

throughout the eastern U.S. is now well established. With this evolution in understanding,

regional approaches to the ozone problem are now underway, starting with the 1990

Clean Air Act Amendments that created the Ozone Transport Region. This initial

regional approach, however, did not include large source regions outside of the OTR

containing many large coal-fired power plants and other pollution sources contributing to

the long-range transport of ozone into the OTR. 

In 1998, the USEPA took another step in addressing the regional problem by

finalizing the NOX SIP Call, which covered emissions of NOX, the main precursor of

regional ozone, in additional parts of the East. Even with these reductions, air quality

modeling has projected continuing significant contributions from upwind sources in outof-state regions. As a result, the USEPA promulgated a further round of regional NOX

reductions in the East with the adoption of CAIR in 2005. With the modeling foundation

for CAIR, the USEPA has presented a compelling technical case on the need for

additional regional NOX reductions in the eastern U.S. to reduce ozone levels and protect

public health. While states in the Northeast disagree with the extent of NOX reductions

and the timeline for those reductions to occur, the program is an excellent next step

toward reducing ozone in the OTR. 

There is a tendency to characterize the nonattainment problems persisting after

implementation of the USEPA’s Clean Air Interstate Rule and other federal programs as

“residual,” but care must be taken in assessing these continuing nonattainment problems.

A “residual” ozone problem is better characterized as a persistent nonattainment problem

that still requires broad regional responses coupled with local controls. As this conceptual

description points out, one of the great lessons and successes seen in the history of air

quality policy was the shift from urban-only air pollution control strategies to broader

regional approaches in the East at the end of the 1990s (e.g., NOX SIP Call). The danger
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 12

exists, however, that the perception of a “residual” ozone problem as being only a local

issue will ignore the lessons learned from effective regional approaches.

The current suite of local and regional controls have a proven track record of

success, and have helped to significantly lower NOX, VOC, and ozone levels across the

eastern U.S. As described earlier in this report, monitored NOX emissions and ambient

concentrations have dropped between 1997 and 2005, and the frequency and magnitude

of ozone exceedances have declined within the OTR. To maintain the current momentum

for improving air quality so that the OTR states can meet their attainment deadlines, there

continues to be a need for more regional NOX reductions coupled with appropriate local

NOX controls and regional and local VOC controls.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 13

References

Hudson, R. “A Conceptual Model for Ozone Transport.” University of Maryland, Dept.

of Atmospheric and Oceanic Science. Prepared for the Ozone Transport Commission.

Draft Nov. 29, 2005.

NESCAUM. The Long Range Transport of Ozone and Its Precursors in the Eastern

United States. NESCAUM, Boston, MA, p.6, 1997.

Ryan, W.F. Air Quality Forecast Report Philadelphia Forecast Area 2002. The

Pennsylvania State University, Department of Meteorology, University Park, PA, March

2003 (available on-line at

http://www.meteo.psu.edu/~wfryan/phl_2002_final_report.htm).

USEPA. OTC NOX Budget Program Compliance Report 2001. U.S. Environmental

Protection Agency, Washington, DC, p. 1, 2002.

 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 1

Appendix A:USEPA Guidance on Ozone

Conceptual Description

From “Guidance on the Use of Models and Other Analyses in Attainment

Demonstrations for the 8-hour Ozone NAAQS,” U.S. Environmental Protection Agency,

EPA-454/R-05-002, Section 8, October 2005.

Note: At the time of this writing, the USEPA was incorporating Section 8 of the 8-hour

ozone guidance into a new USEPA guidance document covering ozone, PM2.5, and

regional haze. The new draft guidance is in Section 11 of Draft 3.2 “Guidance on the Use

of Models and other Analyses for Demonstrating Attainment of Air Quality Goals for

Ozone, PM2.5, and Regional Haze,” U.S. EPA, (Draft 3.2 – September 2006), available at

http://www.epa.gov/ttn/scram/guidance_sip.htm#pm2.5 (accessed Oct. 5, 2006). The

newer guidance, when finalized, may differ in some respects from the text given in

Section 8 of the earlier ozone guidance.

Excerpt of Section 8 from EPA 8-hour ozone NAAQS guidance document:

8.0 How Do I Get Started? – A “Conceptual Description”

8.1 What Is A “Conceptual Description”?

8.2 What Types Of Analyses Might Be Useful For Developing And Refining

A Conceptual Description?

8.2.1. Is regional transport an important factor affecting the

nonattainment area?

8.2.2. What types of meteorological episodes lead to high ozone?

8.2.3. Is ozone limited by availability of VOC, NOX or combinations of

the two? Which source categories may be most important?
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 2

Appendix A: USEPA Guidance on Ozone Conceptual

Description

8.0 How Do I Get Started? - A “Conceptual Description”

A State/Tribe should start developing information to support a modeled attainment

demonstration by assembling and reviewing available air quality, emissions and

meteorological data. Baseline design values should be calculated at each ozone

monitoring site, as described in Section 3. If past modeling has been performed, the

emission scenarios examined and air quality predictions may also be useful. Readily

available information should be used by a State/Tribe to develop an initial conceptual

description of the nonattainment problem in the area which is the focus of a modeled

attainment demonstration. A conceptual description is instrumental for identifying

potential stakeholders and for developing a modeling/analysis protocol. It may also

influence a State’s choice of air quality model, modeling domain, grid cell size, priorities

for quality assuring and refining emissions estimates, and the choice of initial diagnostic

tests to identify potentially effective control strategies. In general, a conceptual

description is useful for helping a State/Tribe identify priorities and allocate resources in

performing a modeled attainment demonstration.

In this Section, we identify key parts of a conceptual description. We then present

examples of analyses which could be used to describe each of these parts. We note that

initial analyses may be complemented later by additional efforts performed by those

implementing the protocol.

8.1 What Is A “Conceptual Description”?

A “conceptual description” is a qualitative way of characterizing the nature of an

area’s nonattainment problem. It is best described by identifying key components of a

description. Examples are listed below. The examples are not necessarily comprehensive.

There could be other features of an area’s problem which are important in particular

cases. For purposes of illustration later in the discussion, we have answered each of the

questions posed below. Our responses appear in parentheses.

1. Is the nonattainment problem primarily a local one, or are regional factors

important?

(Surface measurements suggest transport of ozone close to 84 ppb is likely. There

are some other nonattainment areas not too far distant.)

2. Are ozone and/or precursor concentrations aloft also high?

(There are no such measurements.)
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 3

3. Do violations of the NAAQS occur at several monitoring sites throughout the

nonattainment area, or are they confined to one or a small number of sites in

proximity to one another?

(Violations occur at a limited number of sites, located throughout the area.)

4. Do observed 8-hour daily maximum ozone concentrations exceed 84 ppb

frequently or just on a few occasions?

(This varies among the monitors from 4 times up to 12 times per year.)

5. When 8-hour daily maxima in excess of 84 ppb occur, is there an

accompanying characteristic spatial pattern, or is there a variety of spatial

patterns?

(A variety of patterns is seen.)

6. Do monitored violations occur at locations subject to mesoscale wind patterns

(e.g., at a coastline) which may differ from the general wind flow?

(No.)

7. Have there been any recent major changes in emissions of VOC or NOX in or

near the nonattainment area? If so, what changes have occurred?

(Yes, several local measures [include a list] believed to result in major reductions

in VOC [quantify in tons per summer day] have been implemented in the last five

years. Additionally, the area is expected to benefit from the regional NOX

reductions from the NOX SIP call.)

8. Are there discernible trends in design values or other air quality indicators

which have accompanied a change in emissions?

(Yes, design values have decreased by about 10% at four sites over the past [x]

years. Smaller or no reductions are seen at three other sites.)

9. Is there any apparent spatial pattern to the trends in design values?

(No.)

10. Have ambient precursor concentrations or measured VOC species profiles

changed?

(There are no measurements.)
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 4

11. What past modeling has been performed and what do the results suggest?

(A regional modeling analysis has been performed. Two emission scenarios were

modeled: current emissions and a substantial reduction in NOX emissions

throughout the regional domain. Reduced NOX emissions led to substantial

predicted reductions in 8-hour daily maximum ozone in most locations, but

changes near the most populated area in the nonattainment area in question were

small or nonexistent.)

12. Are there any distinctive meteorological measurements at the surface or aloft

which appear to coincide with occasions with 8-hour daily maxima greater than

84 ppb?

(Other than routine soundings taken twice per day, there are no measurements

aloft. There is no obvious correspondence with meteorological measurements

other than daily maximum temperatures are always > 85 F on these days.)

Using responses to the preceding questions in this example, it is possible to

construct an initial conceptual description of the nonattainment area’s ozone problem.

First, responses to questions 1 and 11 suggest there is a significant regional component to

the area’s nonattainment problem. Second, responses to questions 3, 4, 7, 8, and 11

indicate there is an important local component to the area’s nonattainment problem. The

responses to questions 4, 5 and 12 indicate that high ozone concentrations may be

observed under several sets of meteorological conditions. The responses to questions 7, 8,

and 11 suggest that ozone in and near the nonattainment area may be responsive to both

VOC and NOX controls and that the extent of this response may vary spatially. The

response to question 6 suggests that it may be appropriate to develop a strategy using a

model with 12 km grid cells.

The preceding conceptual description implies that the State/Tribe containing the

nonattainment area in this example will need to involve stakeholders from other, nearby

States/Tribes to develop and implement a modeling/analysis protocol. It also suggests

that a nested regional modeling analysis will be needed to address the problem. Further, it

may be necessary to model at least several distinctive types of episodes and additional

analyses will be needed to select episodes. Finally, sensitivity (i.e., diagnostic) tests, or

other modeling probing tools, will be needed to assess the effects of reducing VOC and

NOX emissions separately and at the same time.

It should be clear from the preceding example that the initial conceptual

description of an area’s nonattainment problem may draw on readily available

information and need not be detailed. It is intended to help launch development and

implementation of a modeling/analysis protocol in a productive direction. It will likely be

supplemented by subsequent, more extensive modeling and ambient analyses performed

by or for those implementing the modeling/analysis protocol discussed in Section 9.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 5

8.2 What Types Of Analyses Might Be Useful For Developing And

Refining A Conceptual Description?

Questions like those posed in Section 8.1 can be addressed using a variety of

analyses ranging in complexity from an inspection of air quality data to sophisticated

mathematical analyses. We anticipate the simpler analyses will often be used to develop

the initial conceptual description. These will be followed by more complex approaches or

by approaches requiring more extensive data bases as the need later becomes apparent. In

the following paragraphs, we revisit key parts of the conceptual description identified in

Section 8.1. We note analyses which may help to develop a description of each part. The

list serves as an illustration. It is not necessarily exhaustive.

8.2.1. Is regional transport an important factor affecting the nonattainment

area?

- Are there other nonattainment areas within a day’s transport of the nonattainment area?

- Do “upwind” 8-hour daily maximum ozone concentrations approach or exceed 84 ppb

on some or all of the days with observed 8-hour daily maxima > 84 ppb in the

nonattainment area?

- Are there major sources of emissions upwind?

- What is the size of the downwind/upwind gradient in 8-hour daily maximum ozone

concentrations compared to the upwind values?

- Do ozone concentrations aloft but within the planetary boundary layer approach or

exceed 84 ppb at night or in the morning hours prior to breakup of the nocturnal surface

inversion?

- Is there a significant positive correlation between observed 8-hour daily maximum

ozone concentrations at most monitoring sites within or near the nonattainment area?

- Is the timing of high observed ozone consistent with impacts estimated from upwind

areas using trajectory models?

- Do available regional modeling simulations suggest that 8-hour daily maximum ozone

concentrations within the nonattainment area respond to regional control measures?

- Does source apportionment modeling indicate significant contributions to local ozone

from upwind emissions?

8.2.2. What types of meteorological episodes lead to high ozone?

- Examine the spatial patterns of 8-hour daily maxima occurring on days where the ozone

is > 84 ppb and try to identify a limited number of distinctive patterns.

- Review synoptic weather charts for days having observed concentrations > 84 ppb to

identify classes of synoptic scale features corresponding to high observed ozone.

- Perform statistical analyses between 8-hour daily maximum ozone and meteorological

measurements at the surface and aloft to identify distinctive classes of days

corresponding with observed daily maxima > 84 ppb.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 6

8.2.3. Is ozone limited by availability of VOC, NOX or combinations of the

two? Which source categories may be most important?

- What are the major source categories of VOC and NOX and what is their relative

importance in the most recent inventory?

- Review results from past modeling analyses to assess the likelihood that ozone in the

nonattainment area will be more responsive to VOC or NOX controls. Do conclusions

vary for different locations?

- Apply modeling probing tools (e.g., source apportionment modeling) to determine

which source sectors appear to contribute most to local ozone formation.

- Apply indicator species methods such as those described by Sillman (1998, 2002) and

Blanchard (1999, 2000, 2001) at sites with appropriate measurements on days with 8-

hour daily maximum ozone exceedances. Identify classes of days where further ozone

formation appears limited by available NOX versus classes of days where further ozone

formation appears limited by available VOC. Do the conclusions differ for different

days? Do the results differ on weekdays versus weekends?

- Apply receptor modeling approaches such as those described by Watson (1997, 2001),

Henry (1994) and Henry (1997a, 1997b, 1997c) to identify source categories contributing

to ambient VOC on days with high observed ozone. Do the conclusions differ on days

when measured ozone is not high?

Additional analyses may be identified as issues arise in implementing a

modeling/analysis protocol. These analyses are intended to channel resources available to

support modeled attainment demonstrations onto the most productive paths possible.

They will also provide other pieces of information which can be used to reinforce

conclusions reached with an air quality model, or cause a reassessment of assumptions

made previously in applying the model. As noted in Section 4, corroboratory analyses

should be used to help assess whether a simulated control strategy is sufficient to meet

the NAAQS.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 7

References

Blanchard, C.L., F.W. Lurmann, P.M. Roth, H.E. Jeffries and M. Korc. “The use of

ambient data to corroborate analyses of ozone control strategies.” Atmos. Envt. 33, 369-

381, 1999.

Blanchard, C. L. “Ozone process insights from field experiments – Part III: Extent of

reaction and ozone formation.” Atmos. Envt. 34, 2035-2043, 2000.

Blanchard, C. L., and T. Stoeckenius. “Ozone response to precursor controls: comparison

of data analysis methods with the predictions of photochemical air quality simulation

models.” Atmos. Envt. 35, 1203-1216, 2001.

Henry, R.C., C.W. Lewis, and J.F. Collins. “Vehicle-related hydrocarbon source

compositions from ambient data: The GRACE/SAFER Method.” Envtl. Sci. & Technol.

28, 823-832, 1994.

Henry, R.C. “Receptor Model Applied to Patterns in Space (RMAPS) Part I. Model

description.” J. Air & Waste Mgmt. Assoc. 47, 216-219, 1997a.

Henry, R.C. “Receptor Model Applied to Patterns in Space (RMAPS) Part II.

Apportionment of airborne particulate sulfur from Project MOHAVE.” J. Air & Waste

Mgmt. Assoc. 47, 220-225, 1997b.

Henry, R.C. “Receptor Modeling Applied to Patterns in Space (RMAPS) Part III.

Apportionment of airborne particulate sulfur in western Washington State.” J. Air &

Waste Mgmt. Assoc. 47, 226-230, 1997c.

Sillman, S. “Evaluating the Relation between Ozone, NOX and Hydrocarbons: The

Method of Photochemical Indicators.” EPA/600R-98/022, http://wwwpersonal.engin.umich.edu/~sillman/publications.htm, 1998.

Sillman, S., and D. He. “Some theoretical results concerning O3-NOX-VOC chemistry

and NOX-VOC indicators.” J. Geophys. Res. 107, 4659-4673, 2002.

Watson, J.G. “Observational Models: The Use of Chemical Mass Balance Methods.”

Prepared for the U.S. EPA Source Attribution Workshop, Research Triangle Park, NC,

July 16-18, 1997, available at http://www.epa.gov/ttn/faca/stissu.html, Source Attribution

Workshop Materials, 1997.

Watson, J.G., J.C. Chow, and E.M. Fujita. “Review of volatile organic compound source

apportionment by chemical mass balance.” Atmos. Envt. 35, 1567-1584, 2001.

 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 1

Appendix B:Ozone pattern classifications

in the OTR
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 2

Appendix B: Ozone pattern classifications in the OTR 

The following five types of ozone patterns in the OTR are taken from: Stoeckenius, T.

and Kemball-Cook, S. “Determination of representativeness of 2002 ozone season for

ozone transport region SIP modeling.” Final Report prepared for the Ozone Transport

Commission, 2005. Figure B-1 shows the 850 mb height and wind fields and Figure B-2

shows the surface temperatures and 10 meter wind fields for the five patterns (reproduced

from Figures 3-2 and 3-5 of Stoeckenius & Kemball-Cook, 2005).

“Type A” – High ozone throughout the OTR. This pattern is characterized by strong high

pressure over the southeastern states extending from the surface to 500 mb with high

temperatures extending into New England and southwest surface winds throughout the

OTR. The 850 mb temperatures and heights, and surface temperatures are above average

at all locations except Washington DC; winds are southwest to west throughout the OTR

except more variable at LaGuardia and magnitudes of resultant wind vectors are higher

than average (indicative of a fairly steady, well defined flow regime), east-west surface

pressure gradients are near neutral but southwest-northeast gradients along the I-95

corridor and in the west (Pittsburgh to Buffalo) are positive, which is consistent with the

southwest flow. The stable air mass and high temperatures promote ozone formation

throughout the OTR under these conditions.

“Type B” – High ozone confined to the extreme southeastern OTR. This pattern is

characterized by an upper-level trough offshore of the OTR and a surface high centered

over Kentucky. This results in cooler air advection over nearly all of the OTR with

northwest flow aloft and a more westerly flow at the surface. The 850 mb heights are

lower than average (especially in New England) and surface winds are more frequently

from the northwest along the I-95 corridor than under Type A. Temperatures at 850 mb

along the I-95 corridor are only slightly cooler than under Type A but inland

temperatures, especially in the north, are much cooler (e.g., at Buffalo); similarly, surface

temperatures along the I-95 corridor are about the same as under Type A but

temperatures are cooler in Buffalo and Albany. Type B events have the strongest positive

west-east surface pressure gradients of any category, consistent with the northwest winds

but gradients from Washington to New York and Boston are positive. The cooler air over

the western OTR and westerly to northwesterly flow result in the higher ozone levels

being confined to just the extreme southern portion of the OTR under this pattern.

“Type C” – High ozone along the I-95 corridor and northern New England. This pattern

is characterized by an extension of the semi-permanent Bermuda high into the

southeastern U.S. and an area of high surface and 850 mb temperatures extending from

Maryland to Maine; the 500 mb pattern is nearly zonal (east-west flow) while flow at the

surface is generally from the southwest. The 850 mb heights are intermediate between

Type A and Type B but 850 mb temperatures are very high along the I-95 corridor and

slightly cooler further inland. Winds are more consistently south - southwest at all sites

than under other episode types and almost no northwest-north-northeast winds are seen at

LaGuardia in contrast to other types. Resultant wind vector magnitudes are much higher
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 3

than average, consistent with the steady southwest flow. Southwest – northeast pressure

gradients along the I-95 corridor and from Pittsburgh to Buffalo are positive, consistent

with the southwest flow. Average east-west pressure gradients are near zero. These

conditions result in above average ozone levels all along the I-95 corridor with advection

north into coastal and interior New England. Ozone levels are slightly below average in

the extreme southeastern and western OTR.

“Type D” – High ozone in the western OTR. This pattern is characterized by an area of

mean upper level divergence with associated cut-off low at 850 mb off the Outer Banks

of North Carolina. A relatively vigorous mean low pressure center can be seen at the

surface. An east-west temperature gradient across the OTR is evident at 850 mb. Surface

temperatures along the I-95 corridor and in Albany are below average but surface

temperature is above average at Buffalo. The 850 mb heights are the highest of any

episode type due to a strong ridge over New England. Surface winds are mostly eastnortheast along the I-95 corridor from DC to New York but more variable further north.

In contrast to episode types A, B, or C, the southwest-northeast pressure gradients along

the I-95 corridor are negative, consistent with the northeast surface winds. West-east

pressure gradients are flat. These conditions result in below average ozone in the eastern

OTR due to the on-shore flow in the north and cyclonic conditions in the south but above

average ozone levels in the western OTR due to stable, warm conditions with light winds.

“Type E” – Generally low ozone throughout the OTR. This category includes days with

moderately low to lowest average ozone readings of all OTR exceedance days used in the

characterization scheme. The Bermuda high is shifted east relative to the other types and

flow over the southeastern U.S. is only weakly anti-cyclonic with a nearly zonal flow

pattern at the 850 and 500 mb levels over the OTR. Temperatures at the surface and aloft

are the coolest of any episode type. While winds aloft are nearly westerly, surface winds

are generally south-southeast over most of the OTR. The southwest-northeast pressure

gradients are negative along the I-95 corridor and east-west gradients are positive,

consistent with the southeast flow. These conditions result in below average ozone

throughout the OTR due to the relatively low temperatures and southeasterly onshore

flow at coastal locations.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 4

Figure B-1. Average 850 mb height and wind fields for each episode (pattern) type identified by

Stoeckenius and Kemball-Cook (pattern numbers refer to the episode types listed in text): Pattern 1 =

Episode Type E, 2 = B, 3 = A, 4 = D, 5 = C) (Figure 3-2 of Stoeckenius & Kemball-Cook (2005)).
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 5

Figure B-2. Average surface temperature and 10 m wind fields for each episode (pattern) type identified by

Stoeckenius and Kemball-Cook (pattern numbers refer to the episode types listed in text): Pattern 1 =

Episode Type E, 2 = B, 3 = A, 4 = D, 5 = C) (Figure 3-5 of Stoeckenius & Kemball-Cook (2005)).

 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 1

Appendix C:Exceedance days by monitor

in the OTR
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 2

Appendix C: Exceedance days by monitor in the OTR

Tables of the number of 8-hour ozone NAAQS exceedance days recorded at individual monitors in the OTR nonattainment/attainment

areas for the 1997-2005 ozone seasons. Hourly data were downloaded in January 2006 from the USEPA Air Quality System (AQS)

database. The number of 8-hour ozone exceedance days were calculated using procedures specified in USEPA’s “Guideline on Data

Handling Conventions for the 8-hour Ozone NAAQS” (OAQPS, EPA-454/R-98-017, Dec. 1998) with flagged data (due to a regional

forest fire smoke event) eliminated from the analysis. While these tables are derived from the publicly available data in the USEPA

AQS database, states may have monitoring data that differ from these. For example, the tables contain state-specific data provided by

the Maryland Department of the Environment and the New Jersey Department of Environmental Protection that differ from the

USEPA AQS database at the time the data were downloaded in January 2006. “***” indicates years during which a monitor was not

in operation or had less than 75 percent data collection during the ozone season. 

Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

100010002 Kent Killens Pond DE 14 17 13 5 8 10 3 0 2

100031003 New Castle Bellefonte DE 6 8 10 5 5 11 *** *** ***

100031007 New Castle Lums Pond DE 15 12 12 5 9 9 4 0 6

100031010 New Castle Brandywine Creek DE 17 17 16 7 15 18 3 3 3

100031013 New Castle Wilmington (Bellefonte2) DE *** *** *** *** *** 8 3 1 4

100051002 Sussex Seaford DE 14 16 17 5 4 10 4 0 3

100051003 Sussex Lewes DE *** 17 17 6 10 14 4 2 7

240150003 Cecil Fairhill MD 19 20 20 18 16 17 6 3 9

340010005 Atlantic Nacote Creek NJ 18 24 14 4 9 11 4 0 3

340070003 Camden Camden Lab NJ 12 15 16 6 19 19 4 3 5

340071001 Camden Ancora NJ 23 29 25 10 17 27 9 6 12

340110007 Cumberland Millville NJ 14 17 17 6 14 20 6 2 4

340150002 Gloucester Clarksboro NJ 19 22 21 8 17 24 6 4 6

340210005 Mercer Rider Univ. NJ 16 17 24 11 15 26 7 1 7

340290006 Ocean Colliers Mills NJ 21 28 23 11 21 30 9 8 14

420170012 Bucks Bristol PA 14 17 24 14 16 17 9 2 7

420290050 Chester West Chester PA *** *** *** *** 20 19 4 *** ***
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 3

Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420290100 Chester New Garden PA *** *** *** *** 17 23 4 5 8

420450002 Delaware Chester PA 19 17 19 7 12 16 3 2 4

420910013 Montgomery Norristown PA 19 17 20 11 18 12 4 1 8

421010004 Philadelphia Philadelphia - Downtown PA 0 1 2 1 0 0 2 0 0

421010014 Philadelphia Philadelphia - Roxborough PA 10 7 *** 4 10 13 2 0 3

421010024 Philadelphia Philadelphia - NE Airport PA 17 15 *** 5 13 22 4 6 8

421010136 Philadelphia Philadelphia - Elmwood PA 0 4 12 3 5 13 2 0 ***

Baltimore, MD (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

240030014 Anne Arundel Davidsonville MD 20 42 31 7 14 25 5 4 9

240030019 Anne Arundel Fort Meade MD 24 25 27 10 19 20 3 5 ***

240051007 Baltimore Padonia MD 10 7 14 3 9 19 2 1 2

240053001 Baltimore Essex MD 10 11 11 3 10 14 3 2 6

240130001 Carroll South Carroll MD 9 18 16 5 10 10 2 1 5

240251001 Harford Edgewood MD 18 17 17 11 20 25 7 6 11

240259001 Harford Aldino MD 20 12 17 8 18 22 4 3 10

245100053 Baltimore (City) Baltimore-Ponca St MD *** *** *** *** *** 8 *** *** ***

245100050 Baltimore (City) Baltimore-0050 MD 16 *** *** *** *** *** *** *** ***

245100051 Baltimore (City) Baltimore-0051 MD 9 5 7 *** *** *** *** *** ***

New York-N. New Jersey-Long Island, NY-NJ-CT (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

90010017 Fairfield Greenwich CT 13 8 14 3 13 18 7 1 8

90011123 Fairfield Danbury CT 14 9 17 7 9 17 4 4 11

90013007 Fairfield Stratford CT 17 11 9 4 10 20 8 2 8

90019003 Fairfield Westport CT 15 13 13 3 15 19 6 2 10
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 4

New York-N. New Jersey-Long Island, NY-NJ-CT (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

90010113 Fairfield Bridgeport CT 6 *** *** *** *** *** *** *** ***

90070007 Middlesex Middletown CT 12 5 15 6 11 16 7 1 7

90091123 &

90090027

New Haven New Haven CT 7 3 5 *** *** *** *** 1 2

90093002 New Haven Madison CT 19 9 16 6 11 19 9 2 8

90099005 New Haven Hamden CT *** *** 11 2 9 14 7 *** ***

340030005 Bergen Teaneck NJ *** *** *** 2 10 18 4 2 8

340030001 Bergen Cliffside Park NJ 5 *** *** *** *** *** *** *** ***

340130011 &

340130016 Essex Newark Lab NJ 6 5 6 *** *** 6 *** *** ***

340170006 Hudson Bayonne NJ 9 7 17 3 6 6 2 1 6

340190001 Hunterdon Flemington NJ 18 21 23 9 12 19 7 6 13

340230011 Middlesex Rutgers Univ. NJ 16 15 23 10 17 26 5 2 10

340250005 Monmouth Monmouth Univ. NJ 12 20 12 5 8 17 10 2 8

340273001 Morris Chester NJ 13 22 21 6 15 27 5 0 3

340315001 Passaic Ramapo NJ *** 8 16 1 9 13 2 2 8

340390008 Union Plainfield NJ 5 *** *** *** *** *** *** *** ***

360050080 Bronx NYC-Morrisania Center NY 5 1 5 *** *** *** *** *** ***

360050083 Bronx NYC-200th St & Southern

Blvd NY 5 0 8 1 1 6 2 1 0

360050110 Bronx NYC-IS52 NY *** *** *** 1 *** 6 2 0 1

360610010 New York NYC-Mabel Dean HS NY *** 2 3 0 *** *** *** *** ***

360610063 New York NYC-Roof WTC NY 16 22 18 5 12 *** *** *** ***

360810004 Queens NYC-Queens College NY 10 *** *** *** *** *** *** *** ***

360810097 Queens NYC-QBORO NY *** *** 10 3 3 *** *** *** ***

360810098 Queens NYC-College Pt NY *** *** *** 1 1 1 1 0 0

360810124 Queens NYC-Queens NY *** *** *** *** *** 7 4 0 4

360850067 Richmond NYC-Susan Wagner HS NY 21 12 17 11 10 19 5 2 8

361030002 Suffolk Babylon NY 8 10 11 4 2 9 6 2 6

361030004 Suffolk Riverhead NY 11 9 16 4 3 6 3 *** 6

361030009 Suffolk Holtsville NY *** *** *** 4 8 18 6 2 ***
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 5

New York-N. New Jersey-Long Island, NY-NJ-CT (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

361192004 Westchester White Plains NY 11 6 12 2 8 15 4 0 9

Washington, DC-MD-VA (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

110010025 District of Columbia (all) Takoma DC 11 18 15 5 7 13 3 2 1

110010041 District of Columbia (all) River Terrace DC 12 11 16 2 7 12 2 0 1

110010043 District of Columbia (all) McMillian Reservoir DC 18 20 22 2 12 21 3 3 5

240090010 &

240090011 Calvert Calvert MD 4 10 10 5 5 *** *** *** 2

240170010 Charles S. Maryland MD 17 30 31 5 9 15 6 1 6

240210037 Frederick Frederick Municipal Airport MD *** *** 19 4 14 13 3 1 1

240313001 Montgomery Rockville MD 13 22 16 2 11 11 3 2 3

240330002 Prince George's Greenbelt MD 24 24 23 7 19 15 3 *** ***

240338001 Prince George's Suitland MD 14 25 18 3 14 *** *** *** ***

240338003 Prince George's Equestrian Center MD *** *** *** *** *** 15 4 5 5

510130020 Arlington Co Aurora Hills VA 17 10 21 3 12 18 4 4 5

510590005 Fairfax Chantilly (Cub Run) VA 2 16 6 2 9 12 2 3 0

510590018 Fairfax Mount Vernon VA *** 17 16 4 10 16 5 6 8

510590030 Fairfax Franconia VA *** *** 19 0 14 18 5 5 6

510591004 &

510591005 Fairfax Seven Corners &Annandale VA 10 17 9 2 *** 20 3 4 4

510595001 Fairfax McLean – Lewinsville VA 3 7 6 2 8 7 3 3 2

511071005 Loudoun Ashburn VA *** 17 7 1 9 23 3 2 ***

511530009 Prince William James S. Long Park VA 4 13 9 2 6 7 4 1 0

515100009 Alexandria (City) Alexandria VA 5 10 10 2 6 10 3 3 2

Jefferson Co., NY (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 6

360450002 Jefferson Perch River NY 8 4 6 1 17 13 9 2 3

Greater Connecticut, CT (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

90031003 Hartford East Hartford CT 7 2 11 2 8 10 0 1 5

90050005 Litchfield Cornwall (Mohawk Mt) CT *** *** *** *** *** 13 4 2 8

90050006 Litchfield Torrington CT 9 10 12 4 *** *** *** *** ***

90110008 New London Groton CT 17 3 11 3 7 7 5 1 4

90131001 Tolland Stafford CT 10 8 12 1 10 13 1 2 8

Boston-Lawrence-Worcester (E. MA), MA (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

250010002 Barnstable Truro MA 17 2 12 3 13 9 8 3 7

250051002 Bristol Fairhaven MA 12 2 8 3 8 5 8 1 1

250051005 Bristol Easton MA 7 7 3 0 14 *** *** *** ***

250070001 Dukes Wampanoag Laboratory –

Martha’s Vineyard MA *** *** *** *** *** *** *** 0 4

250095005 Essex Lawrence-Haverhill MA 2 1 1 0 0 6 *** *** 0

250092006 Essex Lynn MA 6 7 6 1 11 13 3 2 6

250094004 Essex Newbury MA 6 6 6 0 8 9 2 1 0

250170009 Middlesex USEPA Region 1 Lab –

Chelmsford MA *** *** *** *** *** *** *** *** 2

250171102 Middlesex Stow MA *** 5 8 1 12 8 0 1 2

250171801 Middlesex Sudbury MA 6 4 *** *** *** *** *** *** ***

250174003 Middlesex Waltham MA 6 7 5 *** *** *** *** *** ***

250213003 Norfolk E Milton (Blue Hill) MA *** *** *** *** *** 17 5 2 4

250250041 Suffolk Boston-Long Island MA *** *** 4 0 9 10 1 1 5

250250042 Suffolk Boston-Roxbury MA *** *** 0 0 2 2 1 1 1

250251003 Suffolk Chelsea MA 2 4 3 *** *** *** *** *** ***

250270015 Worcester Worcester MA 5 6 8 1 6 *** 1 0 5
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 7

Providence (All RI), RI (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

440030002 Kent W Greenwich RI 10 4 7 5 13 12 1 2 5

440071010 Providence E Providence RI 3 2 2 2 10 9 4 2 4

440090007 Washington Narragansett RI *** 1 11 4 11 8 8 4 5

Springfield (Western MA), MA (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

250034002 Berkshire Adams MA *** *** 1 *** 16 4 2 1 6

230130003 Hampden Agawam MA 9 1 1 1 2 6 *** *** ***

250130008 Hampden Chicopee MA 7 5 7 1 9 10 3 1 8

250150103 Hampshire South Hadley (Amherst) MA 2 2 3 1 3 4 0 1 1

250154002 Hampshire Ware MA 9 6 9 2 12 10 0 3 8

Poughkeepsie, NY (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

360270007 Dutchess Millbrook NY 7 8 8 2 8 8 0 1 3

360715001 Orange Valley Central NY 6 6 8 1 12 4 4 2 7

360790005 Putnam Mt Ninham NY 7 8 15 1 10 19 2 1 7

Boston-Manchester-Portsmouth (SE), NH (Classification: MODERATE)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

330110016 &

330110019 &

330110020

Hillsborough Manchester NH 3 0 *** 0 *** 4 0 1 0

330111010 &

330111011 Hillsborough Nashua NH 4 3 8 1 7 5 1 2 1
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 8

330150009 &

330150015 &

330150014

Rockingham Portsmouth NH 5 3 5 0 *** 8 0 1 0

330150013 Rockingham Brentwood NH *** 0 1 0 4 10 *** *** ***

330150012 &

330150016 Rockingham Rye NH 9 4 3 0 7 7 0 1 0

330173002 Strafford Rochester NH 1 0 2 0 1 6 0 *** ***

Kent and Queen Anne’s Cos., MD (Classification: MARGINAL)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

240290002 Kent Millington MD 19 16 22 6 13 17 4 1 3

Lancaster, PA (Classification: MARGINAL)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420710007 Lancaster Lancaster PA 21 27 18 5 15 18 3 1 6
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 9

Portland, ME (Classification: MARGINAL)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

230050027 Cumberland Portland ME *** *** *** *** *** *** *** 0 0

230052003 Cumberland Cape Elizabeth ME 6 5 2 0 8 5 0 0 0

230230003 &

230230004 Sagadahoc Phippsburg/Georgetown(Reid State Park) ME 7 4 4 1 *** 5 1 0 0

230313002 York Kittery ME 7 4 4 0 4 12 2 1 0

230312002 York Kennebunkport ME 5 5 5 1 8 10 2 1 0

230310037 &

230310038 York Hollis ME 2 0 1 0 *** 3 0 0 0

Buffalo-Niagara Falls, NY (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

360290002 Erie Amherst NY 0 13 6 4 10 21 7 0 5

360631006 Niagara Middleport NY 1 6 7 3 10 16 6 0 4

Youngstown-Warren-Sharon, OH-PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

390990009 &

390990013 Mahoning Youngstown - Oakhill OH 3 15 7 1 5 14 4 1 2

391550008 &

391550011 Trumbull Warren-Trumbull County OH 8 19 10 2 12 24 5 2 5

391550009 Trumbull Kinsman OH 7 15 10 2 5 16 4 0 2

420850100 Mercer Farrell PA 9 24 8 2 15 20 6 1 4
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 10

Pittsburgh-Beaver Valley, PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420030008 Allegheny Lawrenceville PA 7 14 10 3 4 16 5 0 1

420030010 Allegheny Pittsburg PA *** 6 16 4 9 25 5 0 4

420030067 Allegheny South Fayette PA 8 24 15 4 7 17 4 1 4

420030088 Allegheny Penn Hills PA 5 16 11 4 *** *** *** *** ***

420031005 Allegheny Harrison Township PA 12 18 14 4 8 14 2 0 6

420050001 Armstrong Kittanning PA *** 21 18 2 16 15 5 1 4

420070002 Beaver Hookstown PA 4 11 9 1 9 19 6 0 5

420070005 Beaver Brighton Township PA 3 15 11 1 8 23 3 0 4

420070014 Beaver Beaver Falls PA 5 10 6 3 4 9 3 0 2

421250005 Washington Charleroi PA 14 34 11 3 7 14 4 0 2

421250200 Washington Washington PA 6 15 11 3 6 9 5 0 4

421255001 Washington Florence PA 4 11 9 2 7 17 3 0 4

421290006 Westmoreland Murrysville PA 4 3 5 2 1 9 2 0 4

421290008 Westmoreland Greensburg PA *** *** 16 3 3 10 4 0 2

Jamestown, NY (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

360130006 Chautauqua Dunkirk NY *** *** 12 5 11 23 7 4 6

360130011 Chautauqua Westfield NY 4 11 8 3 4 18 4 0 2
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 11

Hancock, Knox, Lincoln & Waldo Cos., ME (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

230130004 Knox Port Clyde ME 6 3 2 0 6 5 3 0 1

230090401 Hancock Schoodic Point ME *** *** *** *** *** *** 1 0 ***

230090001 Hancock Seawall ME *** *** *** 0 4 *** *** *** ***

230090101 &

230090103 Hancock Acadia National Park –McFarland Hill ME 1 4 5 0 9 6 2 0 0

230090102 Hancock Acadia National Park –

Cadillac Mtn. ME 5 8 4 3 9 8 3 0 3

Franklin Co., PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420550001 Franklin Methodist Hill PA 7 22 20 4 15 27 3 0 0

Erie, PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420490003 Erie Erie PA 6 12 13 2 4 17 4 0 4

Essex Co. (Whiteface Mtn.), NY (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

360310002

360310003

Essex (Whiteface

Mountain above 1,900

foot elevation )

Whiteface Mountain

Summit NY 2 1 3 2 5 12 7 0 ***

Whiteface Mtn. Base NY 1 2 3 0 3 11 5 0 1
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 12

Allentown-Bethlehem-Easton, PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420770004 Lehigh Allentown PA 12 18 19 5 9 16 4 3 6

420950025 Northampton Freemansburg PA 0 5 22 6 14 12 4 6 5

420950100 &

420958000 Northampton Easton PA 11 8 12 2 11 13 3 1 1

Reading, PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420110001 Berks Kutztown PA 6 14 12 2 7 11 1 *** ***

420110009 &

420110010 Berks Reading PA 10 16 14 3 8 13 3 1 4

Clearfield and Indiana Cos., PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420630004 Indiana Strongstown PA *** *** *** *** *** *** *** *** 5

420334000 Clearfield Moshannon PA 12 16 1 2 8 13 4 0 4

Greene Co., PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420590002 Greene Holbrook PA *** *** 21 6 12 9 3 0 5

York, PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 13

1997 1998 1999 2000 2001 2002 2003 2004 2005

420010002 Adams Biglerville PA *** *** *** *** *** 7 2 0 1

421330008 York York PA 13 18 10 6 8 12 3 1 6

Rochester, NY (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

360551004 &

360551007 Monroe Rochester NY 4 1 *** 1 3 12 3 0 0

361173001 Wayne Williamson NY 4 4 7 1 5 10 2 0 0

Albany-Schenectady-Troy, NY (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

360010012 Albany Albany – Loudonville NY 2 1 3 1 6 6 2 2 3

360830004 Rensselaer Grafton State Park NY *** *** *** *** *** 16 2 2 2

360910004 Saratoga Stillwater NY 3 2 6 1 7 6 5 2 3

360930003 &

360930093 Schenectady Schenectady NY 1 0 2 1 1 3 2 0 0

Harrisburg-Lebanon-Carlisle, PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420430401 Dauphin Harrisburg PA 3 22 15 3 7 11 2 1 3

420431100 Dauphin Hershey PA 9 9 15 5 12 13 2 0 4

420990301 Perry Little Buffalo State Park PA 7 8 13 2 10 7 3 0 1

Johnstown, PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420210011 Cambria Johnstown PA 7 13 11 5 5 6 2 0 1
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 14

Scranton-Wilkes-Barre, PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420690101 Lackawanna Peckville PA 6 5 11 1 5 14 2 0 2

420692006 Lackawanna Scranton PA 4 5 11 1 5 8 2 0 1

420791100 Luzerne Nanticoke PA 0 2 4 1 5 6 3 0 0

420791101 Luzerne Wilkes-Barre PA 8 7 9 1 7 7 2 0 1

State College, PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420270100 Centre State College PA *** *** *** 2 5 8 3 0 1

420274000 Centre Penn Nursery PA 7 8 4 2 1 12 4 0 ***

Tioga Co., PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

421174000 Tioga Tioga PA *** *** *** 2 3 8 3 0 0

Altoona, PA (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420130801 Blair Altoona PA 7 17 6 2 3 9 3 0 1

Washington Co. (Hagerstown), MD (Classification: SUBPART 1 EARLY ACTION COMPACT)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

240430009 Washington Hagerstown MD *** *** 11 2 5 17 3 1 2
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 15

New York (Classification: ATTAINMENT)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

360150003 Gloucester Elmira NY 0 2 2 1 2 4 1 0 0

360410005 Hamilton Piseco Lake NY 1 1 1 1 2 4 2 0 1

360430005 Herkimer Nicks Lake NY 0 0 0 1 0 1 2 0 0

360530006 Madison Camp Georgetown NY 0 2 1 1 2 5 2 0 0

360650004 Oneida Camden NY 0 1 1 1 3 5 2 0 0

360671015 Onondaga East Syracuse NY 2 3 4 1 4 9 2 0 2

360750003 Oswego Fulton NY *** *** *** *** *** *** 5 0 2

361111005 Ulster Belleayre Mountain NY 4 1 3 1 3 1 3 0 0

Maine (Classification: ATTAINMENT)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

230112005 Kennebec Gardiner ME 2 3 1 0 3 4 1 0 0

230090301 Hancock Castine ME *** *** *** *** *** 3 1 0 0

230210003 Piscataquis Dover-Foxcroft ME *** 0 1 0 0 *** *** *** ***

230194008 Penobscot Holden ME 0 2 0 *** 6 4 1 0 0

230173001 Oxford North Lovell ME 0 0 0 0 0 1 0 0 0

CC0040002 NB CAN Roosevelt-Campobello IP NB 0 1 0 0 0 0 0 0 0

230194007 Penobscot Howland ME 0 0 1 0 0 1 0 0 0

230038001 Aroostook Ashland ME 0 0 0 0 0 1 0 0 0
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 16

Pennsylvania (Classification: ATTAINMENT)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

420730015 Lawrence New Castle PA 4 2 5 0 1 6 2 0 1

420810100 Lycoming Montoursville PA *** *** *** *** *** 7 3 0 3

420810403 Lycoming Williamsport PA 0 1 0 1 1 *** *** *** ***

420814000 Lycoming Tiadaghton PA 0 3 0 1 1 3 2 0 ***

Vermont (Classification: ATTAINMENT)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

500030004 Bennington Bennington VT 2 0 3 1 2 4 0 2 0

500070007 Chittenden Underhill VT 0 0 1 0 0 3 0 0 0

New Hampshire (Classification: ATTAINMENT)

AQS MONITOR ID COUNTY MONITOR NAME ST 8-hr Ozone exceedance days

1997 1998 1999 2000 2001 2002 2003 2004 2005

330012003 &

330012004 Belknap Laconia NH 1 0 0 *** 2 3 0 0 0

330031002 Carroll Conway NH 0 0 0 0 0 1 *** *** ***

330050007 Cheshire Keene NH 1 1 1 1 1 1 0 0 0

330074002 Coos Mt Washington Base NH *** *** *** *** *** 0 0 1 0

330074003 Coos Pittsburg NH *** *** *** *** *** *** 0 0 0

330090008 &

330092005 Grafton Haverhill-Lebanon NH 0 0 0 0 0 1 0 0 0

330115001 Hillsborough

Peterborough (Miller State

Park) NH *** *** *** *** *** *** 0 1 3

330170007 &

330171007 Strafford Concord NH 1 0 0 0 1 4 0 1 0

330190003 Sullivan Claremont NH 1 0 0 1 0 3 0 1 0
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 17

Appendix D:8-hour ozone design values in the OTR, 1997-2005
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 18

Appendix D: 8-hour ozone design values in the OTR, 1997-2005

Tables of the valid 8-hour ozone design values (3-year averages of the ozone season 4th maximum 8-hour ozone concentrations)

recorded at individual monitors in OTR nonattainment/attainment areas for the 1997-2005 ozone seasons. Hourly data were

downloaded from the USEPA Air Quality System (AQS) database in January 2006. The 8-hour averages and design values were

calculated using procedures specified in EPA’s “Guideline on Data Handling Conventions for the 8-hour Ozone NAAQS” (OAQPS,

EPA-454/R-98-017, Dec. 1998) with flagged data (due to a regional forest fire smoke event) eliminated from the analysis. “***”

indicates years during which a monitor was not in operation or had less than 90 percent data collection (with a design value less than

85 ppb) for the respective 3-year period. Red shading indicates averages ≥ 85 ppb (violating the 8-hr ozone NAAQS), orange shading

indicates averages between 80 and 84 ppb, yellow shading indicates average between 75 and 79 ppb and green shading indicates

averages < 75 ppb. While these tables are derived from the publicly available data downloaded in January 2006 from the USEPA AQS

database, states may have monitoring data that differ from these. For example, design values for New Jersey were provided by the

New Jersey Department of Environmental Protection and differ in some instances from the derived values based on the USEPA AQS

database.

Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

100010002 Kent Killens Pond DE 99 97 93 92 89 84 80

100031003 New Castle Bellefonte DE 90 91 91 92 *** *** ***

100031007 New Castle Lums Pond DE 100 97 97 96 93 84 80

100031010 New Castle Brandywine Creek DE 99 96 95 96 93 89 82

100031013 New Castle Wilmington (Bellefonte2) DE *** *** *** *** 90 85 82

100051002 Sussex Seaford DE 99 98 95 94 91 85 82

100051003 Sussex Lewes DE *** 95 90 87 88 85 84

240150003 Cecil Fairhill MD 110 106 106 104 98 91 89

340010005 Atlantic Nacote Creek NJ 101 94 95 91 91 85 82

340070003 Camden Camden Lab NJ 104 101 104 101 102 93 85

340071001 Camden Ancora NJ 111 106 108 104 102 96 92

340110007 Cumberland Millville NJ 104 101 102 98 98 91 86

340150002 Gloucester Clarksboro NJ 106 105 105 104 100 94 88

340210005 Mercer Rider Univ. NJ 112 109 112 102 99 91 85
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 19

Philadelphia-Wilmington-Atlantic City, PA-NJ-MD-DE (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

340290006 Ocean Colliers Mills NJ 113 114 115 113 109 99 94

420170012 Bucks Bristol PA 103 102 105 104 100 93 86

420290050 Chester West Chester PA *** *** *** *** 95 *** ***

420290100 Chester New Garden PA *** *** *** 95 98 91 87

420450002 Delaware Chester PA 100 96 94 95 92 88 82

420910013 Montgomery Norristown PA 104 102 100 97 92 88 86

421010004 Philadelphia Philadelphia – Downtown PA 72 72 71 74 75 68 63

421010014 Philadelphia Philadelphia – Roxborough PA 90 87 88 93 93 86 81

421010024 Philadelphia Philadelphia – NE Airport PA *** *** *** 98 97 95 90

421010136 Philadelphia Philadelphia – Elmwood PA 86 89 88 87 84 80 ***

Baltimore, MD (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

240030014 Anne Arundel Davidsonville MD 109 107 103 102 98 94 89

240030019 Anne Arundel Fort Meade MD 107 100 100 101 97 93 ***

240051007 Baltimore Padonia MD 95 92 93 92 89 85 77

240053001 Baltimore Essex MD 99 93 93 93 93 88 83

240130001 Carroll South Carroll MD 95 94 93 92 89 85 82

240251001 Harford Edgewood MD 105 100 104 104 103 94 91

240259001 Harford Aldino MD 106 97 98 100 98 93 86

245100053 Baltimore (City) Baltimore-Ponca St MD *** *** *** *** *** *** ***

245100050 Baltimore (City) Baltimore-0050 MD *** *** *** *** *** *** ***

245100051 Baltimore (City) Baltimore-0051 MD 90 *** *** *** *** *** ***

New York-N. New Jersey-Long Island, NY-NJ-CT (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

90010017 Fairfield Greenwich CT 99 93 96 95 100 92 87

90011123 Fairfield Danbury CT 101 96 97 98 96 93 91

90013007 Fairfield Stratford CT 98 94 96 98 102 95 90
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 20

New York-N. New Jersey-Long Island, NY-NJ-CT (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

90019003 Fairfield Westport CT 103 94 97 93 97 92 89

90010113 Fairfield Bridgeport CT *** *** *** *** *** *** ***

90070007 Middlesex Middletown CT 99 95 99 97 98 92 90

90091123 &

90090027

New Haven New Haven CT 86 *** *** *** *** *** ***

90093002 New Haven Madison CT 103 96 97 98 102 95 90

90099005 New Haven Hamden CT *** *** 95 94 98 *** ***

340030005 Bergen Teaneck NJ *** *** *** 92 95 89 86

340030001 Bergen Cliffside Park NJ *** *** *** *** *** *** ***

340130011 &

340130016 Essex Newark Lab NJ 93 *** *** *** *** *** ***

340170006 Hudson Bayonne NJ 107 99 100 86 87 82 84

340190001 Hunterdon Flemington NJ 106 103 104 97 97 92 90

340230011 Middlesex Rutgers Univ. NJ 113 109 111 101 98 89 86

340250005 Monmouth Monmouth Univ. NJ 100 102 101 97 97 93 89

340273001 Morris Chester NJ 102 100 101 98 98 90 82

340315001 Passaic Ramapo NJ *** 89 94 88 88 84 81

340390008 Union Plainfield NJ *** *** *** *** *** *** ***

360050080 Bronx NYC-Morrisania Center NY 84 *** *** *** *** *** ***

360050083 Bronx NYC-200th St & Southern Blvd NY 88 80 83 81 84 83 75

360050110 Bronx NYC-IS52 NY *** *** *** *** *** 80 76

360610010 New York NYC-Mabel Dean HS NY *** 69 *** *** *** *** ***

360610063 New York NYC-Roof WTC NY 106 98 98 *** *** *** ***

360810004 Queens NYC-Queens College NY *** *** *** *** *** *** ***

360810097 Queens NYC-QBORO NY *** 88 86 *** *** *** ***

360810098 Queens NYC-College Pt NY *** *** 68 74 75 72 69

360810124 Queens NYC-Queens NY *** *** *** *** *** *** ***

360850067 Richmond NYC-Susan Wagner HS NY 105 96 98 96 94 89 87

361030002 Suffolk Babylon NY 97 91 87 92 95 94 91

361030004 Suffolk Riverhead NY 98 94 91 85 *** *** ***

361030009 Suffolk Holtsville NY *** *** *** 97 100 94 ***
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 21

New York-N. New Jersey-Long Island, NY-NJ-CT (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

361192004 Westchester White Plains NY 98 92 92 90 94 90 88

Washington, DC-MD-VA (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

110010025 District of Columbia

(all) Takoma DC 95 96 93 93 88 85 78

110010041 District of Columbia

(all) River Terrace DC 91 88 88 91 92 84 77

110010043 District of Columbia

(all) McMillian Reservoir DC 100 96 94 95 94 89 82

240090010 &

240090011 Calvert Calvert MD 90 91 89 *** *** *** ***

240170010 Charles S. Maryland MD 104 101 96 94 94 91 88

240210037 Frederick Frederick Municipal Airport MD *** 92 91 91 88 83 78

240313001 Montgomery Rockville MD 95 90 89 89 88 83 80

240330002 Prince George's Greenbelt MD 106 99 97 95 93 *** ***

240338001 Prince George's Suitland MD 99 94 93 *** *** *** ***

240338003 Prince George's Equestrian Center MD *** *** *** *** *** 94 91

510130020 Arlington Co Aurora Hills VA 97 92 92 96 99 95 87

510590005 Fairfax Chantilly (Cub Run) VA 91 91 88 88 89 84 79

510590018 Fairfax Mount Vernon VA 96 97 95 97 97 96 91

510590030 Fairfax Franconia VA *** 90 89 92 97 96 89

510591004 &

510591005 Fairfax Seven Corners & Annandale VA 95 90 *** *** *** 94 86

510595001 Fairfax McLean – Lewinsville VA 86 86 86 90 88 86 79

511071005 Loudoun Ashburn VA *** 89 86 90 92 88 ***

511530009 Prince William James S. Long PARK VA 91 88 85 85 87 83 79

515100009 Alexandria (City) Alexandria VA 91 89 88 90 92 88 81

Jefferson Co., NY (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 22

360450002 Jefferson Perch River NY 90 82 87 91 97 86 81

Greater Connecticut, CT (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

90031003 Hartford East Hartford CT 91 84 88 90 90 84 80

90050005 Litchfield Cornwall (Mohawk Mt) CT *** *** *** *** *** 89 87

90050006 Litchfield Torrington CT 97 93 *** *** *** *** ***

90110008 New London Groton CT 94 87 90 89 93 88 85

90131001 Tolland Stafford CT 95 89 90 94 95 88 86

Boston-Lawrence-Worcester (E. MA), MA (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

250010002 Barnstable Truro MA 95 89 96 93 95 88 86

250051002 Bristol Fairhaven MA 91 87 93 90 95 88 86

250051005 Bristol Easton MA 88 81 84 *** *** *** ***

250070001 Dukes Wampanoag Laboratory –

Martha’s Vineyard MA *** *** *** *** *** *** ***

250095005 Essex Lawrence-Haverhill MA 74 68 63 70 *** *** ***

250092006 Essex Lynn MA 93 86 86 90 93 87 83

250094004 Essex Newbury MA 87 82 83 86 89 83 78

250170009 Middlesex USEPA Region 1 Lab –

Chelmsford MA *** *** *** *** *** *** ***

250171102 Middlesex Stow MA *** 86 88 89 89 79 75

250171801 Middlesex Sudbury MA *** *** *** *** *** *** ***

250174003 Middlesex Waltham MA 93 *** *** *** *** *** ***

250213003 Norfolk E Milton (Blue Hill) MA *** *** *** *** *** 91 85

250250041 Suffolk Boston-Long Island MA *** *** 84 89 91 86 81

250250042 Suffolk Boston-Roxbury MA *** *** 66 72 76 71 68

250251003 Suffolk Chelsea MA 82 *** *** *** *** *** ***

250270015 Worcester Worcester MA 94 88 85 85 86 *** 79

Providence (All RI), RI (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 23

440030002 Kent W Greenwich RI 92 88 94 97 95 87 84

440071010 Providence E Providence RI *** *** 87 91 93 *** 82

440090007 Washington Narragansett RI *** 85 92 93 95 90 89

Springfield (Western MA), MA (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

250034002 Berkshire Adams MA *** *** *** *** 87 *** ***

230130003 Hampden Agawam MA 84 77 77 83 *** *** ***

250130008 Hampden Chicopee MA 91 86 85 92 94 90 84

250150103 Hampshire South Hadley (Amherst) MA 82 76 77 78 77 69 67

250154002 Hampshire Ware MA 99 89 89 89 87 84 82

Poughkeepsie, NY (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

360270007 Dutchess Millbrook NY 90 87 87 93 94 89 79

360715001 Orange Valley Central NY 90 86 87 84 87 83 84

360790005 Putnam Mt Ninham NY 94 89 89 92 93 89 86

Boston-Manchester-Portsmouth (SE), NH (Classification: MODERATE) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

330110016 &

330110019 &

330110020

Hillsborough Manchester NH *** *** *** *** *** 75 70

330111010 &

330111011 Hillsborough Nashua NH 89 81 83 85 87 84 80

330150009 &

330150015 &

330150014

Rockingham Portsmouth NH 87 80 *** *** *** 80 75

330150013 Rockingham Brentwood NH *** 69 76 80 *** *** ***

330150012 &

330150016 Rockingham Rye NH 90 79 81 83 84 78 73

330173002 Strafford Rochester NH 81 76 75 77 80 *** ***
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 24

Kent and Queen Anne’s Cos., MD (Classification: MARGINAL) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

240290002 Kent Millington MD 100 101 100 102 95 89 82

Lancaster, PA (Classification: MARGINAL) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420710007 Lancaster Lancaster PA 101 97 96 94 92 86 83

Portland, ME (Classification: MARGINAL) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

230050027 Cumberland Portland ME *** *** *** *** *** *** ***

230052003 Cumberland Cape Elizabeth ME 89 77 80 86 88 79 71

230230003 &

230230004 Sagadahoc

Phippsburg/Georgetown (Reid

State Park) ME 92 84 *** *** *** 79 70

230313002 York Kittery ME 88 81 81 84 88 84 77

230312002 York Kennebunkport ME 92 82 86 90 91 84 74

230310037 &

230310038 York Hollis ME 76 72 *** *** *** 75 73

Buffalo-Niagara Falls, NY (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

360290002 Erie Amherst NY 85 89 92 97 99 91 86

360631006 Niagara Middleport NY 86 85 87 91 95 89 86

Youngstown-Warren-Sharon, OH-PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

390990009 &

390990013 Mahoning Youngstown - Oakhill OH 91 89 86 87 89 85 80
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 25

391550008 &

391550011 Trumbull Warren-Trumbull County OH 95 91 88 90 95 91 86

391550009 Trumbull Kinsman OH 95 91 87 87 90 87 83

420850100 Mercer Farrell PA 96 92 88 92 94 88 83

Pittsburgh-Beaver Valley, PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420030008 Allegheny Lawrenceville PA 91 88 85 89 92 87 81

420030010 Allegheny Pittsburg PA *** 91 92 93 93 86 84

420030067 Allegheny South Fayette PA 99 96 90 90 91 87 82

420030088 Allegheny Penn Hills PA 92 91 88 *** *** *** ***

420031005 Allegheny Harrison Township PA 101 94 92 95 92 87 81

420050001 Armstrong Kittanning PA 86 93 92 91 93 88 84

420070002 Beaver Hookstown PA 92 89 88 90 94 90 84

420070005 Beaver Brighton Township PA 91 90 89 90 92 87 81

420070014 Beaver Beaver Falls PA 90 89 85 88 86 81 75

421250005 Washington Charleroi PA 101 94 87 86 89 84 80

421250200 Washington Washington PA 91 88 86 86 88 82 81

421255001 Washington Florence PA 91 90 88 88 87 82 78

421290006 Westmoreland Murrysville PA 85 81 80 81 84 81 80

421290008 Westmoreland Greensburg PA *** *** 86 86 91 87 82

Jamestown, NY (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

360130006 Chautauqua Dunkirk NY *** *** 89 92 94 93 89

360130011 Chautauqua Westfield NY 89 88 85 87 89 85 79

Hancock, Knox, Lincoln & Waldo Cos., ME (Classification: SUBPART 1)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

230130004 Knox Port Clyde ME 82 76 80 83 87 81 77

230090401 Hancock Schoodic Point ME *** *** *** *** *** *** ***
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 26

230090001 Hancock Seawall ME *** *** *** *** *** *** ***

230090101 &

230090103 Hancock Acadia National Park -McFarland Hill ME 85 83 85 84 87 80 75

230090102 Hancock Acadia National Park -

Cadillac Mtn. ME 89 87 89 93 94 88 82

Franklin Co., PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420550001 Franklin Methodist Hill PA 97 95 92 94 93 85 75

Erie, PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420490003 Erie Erie PA 93 90 87 88 92 87 83

Essex Co. (Whiteface Mtn.), NY (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

360310002

360310003

Essex (Whiteface

Mountain above 1,900

foot elevation )

Whiteface Mountain Summit NY 80 *** *** 87 91 89 ***

Whiteface Mtn. Base NY 79 76 78 82 88 83 77
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 27

Allentown-Bethlehem-Easton, PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420770004 Lehigh Allentown PA 100 97 96 93 91 88 85

420950025 Northampton Freemansburg PA 87 95 97 92 90 88 87

420950100 &

420958000 Northampton Easton PA 93 90 91 89 89 86 82

Reading, PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420110001 Berks Kutztown PA 92 89 90 87 84 *** ***

420110009 &

420110010 Berks Reading PA 96 92 95 92 91 83 80

Clearfield and Indiana Cos., PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420630004 Indiana Strongstown PA *** *** *** *** *** *** ***

420334000 Clearfield Moshannon PA 93 87 83 87 90 85 82

Greene Co., PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420590002 Greene Holbrook PA 97 96 92 90 89 84 81

York, PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420010002 Adams Biglerville PA *** *** *** *** *** 80 76

421330008 York York PA 94 93 90 92 89 86 82

Rochester, NY (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 28

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

360551004 &

360551007 Monroe Rochester NY *** *** *** 85 88 79 73

361173001 Wayne Williamson NY 86 81 81 83 88 81 71

Albany-Schenectady-Troy, NY (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

360010012 Albany Albany - Loudonville NY 80 77 80 83 86 80 76

360830004 Rensselaer Grafton State Park NY *** *** *** *** *** 86 80

360910004 Saratoga Stillwater NY 84 80 84 *** 87 84 82

360930003 &

360930093 Schenectady Schenectady NY 75 71 75 76 81 76 74

Harrisburg-Lebanon-Carlisle, PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420430401 Dauphin Harrisburg PA 92 90 86 87 86 82 78

420431100 Dauphin Hershey PA 94 93 94 91 88 81 78

420990301 Perry Little Buffalo State Park PA 90 85 84 83 87 80 78

Johnstown, PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420210011 Cambria Johnstown PA 93 91 88 88 87 80 77
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 29

Scranton-Wilkes-Barre, PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420690101 Lackawanna Peckville PA 90 87 86 85 85 80 75

420692006 Lackawanna Scranton PA 88 84 84 83 84 79 76

420791100 Luzerne Nanticoke PA 82 81 82 83 84 78 73

420791101 Luzerne Wilkes-Barre PA 92 84 84 84 86 81 77

State College, PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420270100 Centre State College PA *** *** *** 85 86 82 79

420274000 Centre Penn Nursery PA 90 84 80 82 88 84 ***

Tioga Co., PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

421174000 Tioga Tioga PA *** *** *** 84 86 85 81

Altoona, PA (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420130801 Blair Altoona PA 95 89 84 84 85 81 77

Washington Co. (Hagerstown), MD (Classification: SUBPART 1) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

240430009 Washington Hagerstown MD *** *** 85 87 86 83 78
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 30

New York (Classification: ATTAINMENT) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

360150003 Gloucester Elmira NY 79 79 79 81 83 77 70

360410005 Hamilton Piseco Lake NY 79 77 77 79 81 76 73

360430005 Herkimer Nicks Lake NY 72 70 72 74 76 72 69

360530006 Madison Camp Georgetown NY 79 78 78 80 82 77 73

360650004 Oneida Camden NY 76 73 76 78 83 78 72

360671015 Onondaga East Syracuse NY 82 80 81 83 85 *** 74

360750003 Oswego Fulton NY *** *** *** *** *** *** 82

361111005 Ulster Belleayre Mountain NY 83 80 81 81 83 80 79

Maine (Classification: ATTAINMENT) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

230112005 Kennebec Gardiner ME 77 73 75 78 80 76 70

230090301 Hancock Castine ME *** *** *** *** *** 75 70

230210003 Piscataquis Dover-Foxcroft ME *** 62 65 *** *** *** ***

230194008 Penobscot Holden ME 75 *** 76 *** 83 75 68

230173001 Oxford North Lovell ME 59 58 61 60 62 60 61

CC0040002 NB CAN Roosevelt-Campobello IP NB 62 60 61 60 61 54 54

230194007 Penobscot Howland ME 71 68 69 68 68 64 61

230038001 Aroostook Ashland ME 65 62 64 65 64 63 60

Pennsylvania (Classification: ATTAINMENT) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

420730015 Lawrence New Castle PA 83 78 78 78 80 77 73

420810100 Lycoming Montoursville PA *** *** *** *** *** 82 79

420810403 Lycoming Williamsport PA 74 71 71 *** *** *** ***

420814000 Lycoming Tiadaghton PA *** 77 76 79 80 77 ***

Vermont (Classification: ATTAINMENT) 8-hr Ozone DESIGN VALUE (ppb)
 DRAFT – The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 31

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

500030004 Bennington Bennington VT 80 76 79 80 80 78 73

500070007 Chittenden Underhill VT 74 74 75 77 78 76 71

New Hampshire (Classification: ATTAINMENT) 8-hr Ozone DESIGN VALUE (ppb)

AQS MONITOR ID COUNTY MONITOR NAME ST 1997-

1999

1998-

2000

1999-

2001

2000-

2002

2001-

2003

2002-

2004

2003-

2005

330012003 &

330012004 Belknap Laconia NH 68 *** *** *** 78 75 73

330031002 Carroll Conway NH 67 64 66 67 *** *** ***

330050007 Cheshire Keene NH 75 71 72 73 76 74 71

330074002 Coos Mt Washington Base NH *** *** *** *** *** *** 67

330074003 Coos Pittsburg NH *** *** *** *** *** *** 60

330090008 &

330092005 Grafton Haverhill-Lebanon NH 70 70 69 68 72 72 71

330115001 Hillsborough Peterborough (Miller State

Park) NH *** *** *** *** *** *** 77

330170007 &

330171007 Strafford Concord NH 74 71 70 74 75 75 71

330190003 Sullivan Claremont NH 73 70 72 73 75 77 72

 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 1

Appendix E:The sea breeze and flow over

the ocean in-depth
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 2

Appendix E: The sea breeze and flow over the ocean in-depth

Figure E-1 displays a general description of ozone transport in coastal New

England. This figure shows 90th percentile ozone concentration wind direction plots at

four sites along the coast. For the first site, Lynn, MA, high ozone days are affected

mainly by winds from the southwest bringing ozone up the coast to the site. At the

second site, Newbury, MA, winds arrive to the site from two directions, up the coast, in a

similar pattern seen at Lynn, but also from the ocean. The high ozone days therefore can

result from ozone and its precursors coming from inland or from the ocean in the sea

breeze. At the two northern sites in Maine, Cape Elizabeth and Acadia National Park,

winds on high ozone days come mostly off the ocean. This is mainly due to the

orientation of the Maine coastline, as summertime winds generally come from the

southwest, therefore traveling over the ocean before arriving to these sites.

AGED TRANSPORT

LONG RANGE 

TRANSPORT

90

th percentile 

Ozone concentration wind

direction frequency plots

Local and

transported 

ozone/precursors in

the land/seabreeze

recirculation pattern 

AGED TRANSPORT

LONG RANGE 

TRANSPORT

90

th percentile 

Ozone concentration wind

direction frequency plots

Local and

transported 

ozone/precursors in

the land/seabreeze

recirculation pattern 

AGED TRANSPORT

LONG RANGE 

TRANSPORT

90

th percentile 

Ozone concentration wind

direction frequency plots

Local and

transported 

ozone/precursors in

the land/seabreeze

recirculation pattern 

Figure E-1. 90th percentile ozone concentration wind direction frequency plots at four coastal sites in

northern New England (figure provided by Tom Downs, Maine Department of Environmental Protection).

Figure E-2 displays wind directions at Newbury, MA on June 29, 1997 where

hourly ozone concentrations ranged from 88 ppb to 107 ppb during the afternoon hours

and a sea breeze can be identified. The forward trajectory starting in Boston at 6 a.m.

shows winds pushing air from the Boston metro area out into the harbor throughout the
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 3

day. The hourly ozone wind rose at Newbury, MA shows the afternoon wind shift that

occurred on this day where vector direction indicates wind direction and magnitude

indicates ozone concentrations. Morning winds came from a west/northwesterly direction

when hourly ozone concentrations at the site ranged from 47 to 68 ppb. At 1 p.m., the

wind shifted direction, now coming off the ocean from the southeast, accompanied by a

20 ppb increase in hourly ozone. Hourly ozone levels then continued to increase in the

early afternoon, peaking at 107 ppb at 3 p.m. This increase in ozone levels accompanying

a shift in winds pushing air masses from the ocean to a coastal site illustrates how the sea

breeze can contribute to poor air quality along the coast. The poor air quality could be a

result of polluted air from Boston being pushed back to the site in the sea breeze. Sea

breezes, however, are not always associated with worsening air quality as the afternoon

sea breeze doesn’t always bring in polluted air.

0

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1 1 8 1 1 9 1 2 0 1 2 1 1 2 2 1 2 3 1 2 4 1 2 5 1 2 6 1 2 7 1 2 8 1 2 9

1 3 0 1 3 1 1 3 2 1 3 3 1 3 4 1 3 5 1 3 6 1 3 7 1 3 8 1 3 9 1 4 0 1 4 1 1 4 2 1 4 3 1 4 4 1 4 5 1 4 6 1 4 7 1 4 8 1 4 9 1 5 0 1 5 1 1 5 2

1 5 3 1 5 4 1 5 5 1 5 6 1 5 7 1 5 8 1 5 9 1 6 0 1 16 62 1 1 6 3 1 6 4 1 6166 5 1 6186 7 1 17 60 9 1 17 72 1 1 71617 75147 3 1 81017 79187 7

1 8 1

1 81518 84138 2 1 81918 8178 6 1 9 119 0 1 19 93 2 1 9159 4 1 9179 6 1 9 8 1 9 9 2 012 00 2 02 2 03 2 04 2 05 2 06 2 07 2 08 2 09

2 1 0 2 1 1 2 1 2 2 1 3 2 1 4 2 1 5 2 1 6 2 1 7 2 1 8 2 1 9 2 2 0 2 2 1 2 2 2 2 2 3 2 2 4 2 2 5 2 2 6 2 2 7 2 2 8 2 2 9 2 3 0 2 3 1 2 3 2

2 3 3 2 3 4 2 3 5 2 3 6 2 3 7 2 3 8 2 3 9

2 4 0 2 4 1 2 4 2 2 4 3 2 4 4

2 4 5 2 4 6 2 4 7 2 4 8

2 4 9 2 5 0 2 5 1

2 5 2

2 5 3 2 5 4 2 5 5

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3 1 0

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3 1 3 3 1 4

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3 2 0 3 2 1

3 2 2

3 2 3

3 2 4 3 2 5

3 2 6 3 2 7

3 2 8

3 2 9

3 3 0 3 3 1 3 3 2

3 3 3

3 3 4

3 3 5 3 3 6

3 3 7

3 3 8

3 3 9

3 4 0 3 43 14 2

3 4 3 3 4 4 3 4354 6

3 4374 8 3 4395 0 3 53 15 2

3 53353 45355 6

3 53735 58 93 6 0

6AM-12PM

1PM-5PM

Forward Trajectory from Boston

Start Time: 6AM

Boston, MA

Newbury, MA

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1 08 1 09

1 1 0

1 1 1 1 1 2 1 1 3

1 1 4 1 1 5 1 1 6 1 1 7

1 1 8 1 1 9 1 2 0 1 2 1 1 2 2 1 2 3 1 2 4 1 2 5 1 2 6 1 2 7 1 2 8 1 2 9

1 3 0 1 3 1 1 3 2 1 3 3 1 3 4 1 3 5 1 3 6 1 3 7 1 3 8 1 3 9 1 4 0 1 4 1 1 4 2 1 4 3 1 4 4 1 4 5 1 4 6 1 4 7 1 4 8 1 4 9 1 5 0 1 5 1 1 5 2

1 5 3 1 5 4 1 5 5 1 5 6 1 5 7 1 5 8 1 5 9 1 6 0 1 16 62 1 1 6 3 1 6 4 1 6166 5 1 6186 7 1 17 60 9 1 17 72 1 1 71617 75147 3 1 81017 79187 7

1 8 1

1 81518 84138 2 1 81918 8178 6 1 9 119 0 1 19 93 2 1 9159 4 1 9179 6 1 9 8 1 9 9 2 012 00 2 02 2 03 2 04 2 05 2 06 2 07 2 08 2 09

2 1 0 2 1 1 2 1 2 2 1 3 2 1 4 2 1 5 2 1 6 2 1 7 2 1 8 2 1 9 2 2 0 2 2 1 2 2 2 2 2 3 2 2 4 2 2 5 2 2 6 2 2 7 2 2 8 2 2 9 2 3 0 2 3 1 2 3 2

2 3 3 2 3 4 2 3 5 2 3 6 2 3 7 2 3 8 2 3 9

2 4 0 2 4 1 2 4 2 2 4 3 2 4 4

2 4 5 2 4 6 2 4 7 2 4 8

2 4 9 2 5 0 2 5 1

2 5 2

2 5 3 2 5 4 2 5 5

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3 4 3 3 4 4 3 4354 6

3 4374 8 3 4395 0 3 53 15 2

3 53353 45355 6

3 53735 58 93 6 0

6AM-12PM

1PM-5PM

Forward Trajectory from Boston

Start Time: 6AM

Boston, MA

Newbury, MA

0

0.02

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0.06

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6AM-12PM

1PM-5PM

Figure E-2. Example of a sea breeze effect occurring in Newbury, MA on June 29,

1997 (figure data provided by Tom Downs, Maine Department of Environmental

Protection).

At sites further north in Maine, the sea breeze effect is less dramatic due to the

orientation of the Maine coastline. Figure E-3 shows a similar ozone wind rose plot for

Cape Elizabeth, ME on the same day illustrated in Figure E-2. With the exception of the

winds at 6 a.m. that came from the northwest, the winds arrived to the site from the

southwest direction. There are some slight shifts in wind direction, particularly a shift

after 5 p.m. that began to bring winds from the inland side of the coast, but it is difficult

to determine whether these shifts are due to a sea breeze effect or if the evening shift is

due to the weakened sea breeze. Winds are generally moving up the coast, over water,
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 4

and winds in the same direction of the sea breeze can bring poor air quality. On this day,

ozone concentrations ranged between 89 and 102 ppb between 3 p.m. and 7 p.m.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 5

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Forward Trajectory from Boston

Start Time: 6AM

Cape Elizabeth, ME

Boston, MA

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Forward Trajectory from Boston

Start Time: 6AM

Cape Elizabeth, ME

Boston, MA

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Start Time: 6AM

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Forward Trajectory from Boston

Start Time: 6AM

Cape Elizabeth, ME

Boston, MA

0

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Figure E-3. Wind directions and ozone concentrations at Cape Elizabeth, ME on June 29,

1997 (figure data provided by Tom Downs, Maine Department of Environmental Protection).

Transport over the ocean is commonly observed downwind of the New York City

metropolitan area during the summer months due its proximity to the Atlantic Ocean and

the Long Island Sound. The four pollution rose plots presented in Figure E-4 represent

the frequency of wind direction on the highest 10 percentile ozone concentration days

from April 1 to October 31 during the years 1997 to 2005. The winds on the highest

ozone days point at the New York City metropolitan area at all locations along the

Connecticut shoreline. Going along the Connecticut shoreline to the east (towards

Groton), the predominant wind frequency direction shifts increasingly to the west,

tracking the upwind location of the New York City metropolitan area.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 6

Figure E-4. Wind rose plots along Connecticut shoreline for the time period April 1 to October 31 during

the years 1997 through 2005. The elongated red outlines pointing to the southwest to west are wind

directions on the highest 10 percentile ozone concentration days at four Connecticut coastal locations. For

comparison, the blue outlines are the wind rose plots for all days over the same period. The high ozone day

wind rose plots indicate pollution flow over Long Island Sound that tracks the upwind location of the New

York City metropolitan area (figure from Tom Downs, Maine Department of the Environment).

Each plot shows frequency

of high ozone increases as

the wind points up LIS 

towards emission-rich areas

of the Northeast corridor.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 1

Appendix F:Observed nocturnal low level jet

across the OTR, July 2002
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 2

Appendix F: Observed nocturnal low level jet across the OTR,

July 2002

An example of the nocturnal low level jet across the OTR can be seen on the

nights of July 22 through July 24, 2002, as night time winds at altitudes between 450 m

and 1500 m were observed at several coastal sites. Figure F-1 shows wind profiler data

on the night of July 22-July 23, 2002 for five sites along the east coast: Fort Meade, MD

(FME), Orange, MA (ORE), Stow, MA (STW), Appledore Island, ME (ADI), and Pease

Air Force Base, NH (PSE). These wind “barb” plots show wind direction (direction of

arrow indicating where wind is coming from), wind speed (wind barb color), time of day

(UTC time, x-axis), and altitude (meters, y-axis). The location of the nocturnal low level

jet appears within the circle in each wind barb plot of Figure F-1. The figure shows a

weak nocturnal low level jet at the southernmost site, Fort Meade, with wind speeds of 15

to 25 knots between 300 m and 500 m in the early part of the night. Further north, the

nocturnal low level jet is more pronounced with wind speeds between 500 m and 1500 m

above ground reaching 40 knots. Figure F-1 shows on this day the nocturnal low level jet

extending from Maryland up through southern Maine. In addition, the wind barb plots

show the northeasterly direction of the nocturnal low level jet. Above this jet, we see

slower winds coming from the west to all the sites.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 3

7.22.02-7.23.02

FME

ORE

STW

ADI

PSE

Direction of

LLJ

7.22.02-7.23.02

FME

ORE

STW

ADI

PSE

Direction of

LLJ

Figure F-1. Nocturnal low level jet on July 22 – 23, 2002. Note: Circles in the wind barb plots indicate the

location of the nocturnal low level jet.

Figure F-1 shows that throughout the night, the nocturnal low level jet travels in a

northeasterly direction along the east coast. The pollution implications of this nocturnal

low level jet episode can be seen in Figure F-2. The Cadillac Mountain ozone monitor is

located on the coast of Maine at an elevation of 466 m. At this elevated position, we can

see how the nocturnal low level jet affects overnight and early morning ozone levels.

Between midnight and 4 a.m. during the northeasterly nocturnal low level jet, hourly

ozone concentrations at Cadillac Mountain are between 70 ppb and 80 ppb. Ozone levels
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 4

had begun to increase early in the evening on July 22 and continued to increase

throughout the night and peak at 3 a.m. This increasing nighttime ozone at an elevated

position corresponds to the nocturnal low level jet channeling air up the coast during the

night. Conversely, at Cape Elizabeth, a ground level site relatively close to Cadillac

Mountain, night time ozone levels are much lower than on top of Cadillac Mountain. This

difference in ozone at upper and lower levels shows how the nocturnal inversion can

isolate air masses above and below the inversion.

ADI

PSE

Direction of

LLJ

Cadillac

Mountain

Cape

Elizabeth

0

20

40

60

80

100

120

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

7/22/2002 7/23/2002

Ozone Concentration (ppb)

Cadillac

Mountain

Cape

Elizabeth

Time of LLJ

ADI

PSE

Direction of

LLJ

Cadillac

Mountain

Cape

Elizabeth

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120

0:001:002:003:004:005:006:007:008:009:00

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0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

7/22/2002 7/23/2002

Ozone Concentration (ppb)

Cadillac

Mountain

Cape

Elizabeth

Time of LLJ

ADI

PSE

Direction of

LLJ

Cadillac

Mountain

Cape

Elizabeth

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20

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60

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0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

7/22/2002 7/23/2002

Ozone Concentration (ppb)

Cadillac

Mountain

Cape

Elizabeth

Time of LLJ

Figure F-2. Nocturnal low level jet with hourly ozone concentrations at Cadillac Mountain, ME and Cape

Elizabeth, ME on July 22 – 23, 2002. Note: Circles in the wind barb plots indicate the location of the

nocturnal low level jet.

The air mass affecting early morning ozone concentrations in Figure F-2 can be

roughly tracked using wind speed and wind direction information from Cadillac

Mountain, Pease, Appledore Island, and Orange. Assuming the nocturnal low level jet

occurs for five hours that night (based on neighboring wind barb plots), the air mass

arriving at Cadillac Mountain at 3 a.m. during peak ozone conditions was over central

Massachusetts around 11 p.m. on July 22 when the nocturnal low level jet began to form.

Tracking this farther back shows that the air mass affecting Cadillac Mountain was over

western Connecticut around 6 p.m. on July 22. Looking at ozone levels in Cornwall, CT,

we see that high ozone conditions existed in this region during the afternoon of July 22

with the average hourly ozone at 112 ppb between 4 p.m. and 7 p.m. Elevated ozone from

this region first slowly traveled up the coast in the evening. When the nocturnal low level
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 5

jet formed, it quickly pushed ozone up the coast affecting ozone levels at Cadillac

Mountain, an elevated site in the jet, in the early morning hours (~3 a.m.).

Figure F-3 shows wind profiler information for the next day, July 24, 2002. In this

case we see a stronger nocturnal low level jet between midnight and 8am that originates

further to the south. The Fort Meade and Rutgers (RUT) sites show the nocturnal low

level jet in the early part of the evening with flow in the northeasterly direction. At higher

altitudes slower winds from the west pass over the nocturnal low level jet. Further north,

a strong nocturnal low level jet can be seen at Stow, Appledore Island, and Pease. It is

difficult to determine if a nocturnal low level jet exists at Orange as high winds continue

at the upper altitudes and data are missing for the highest altitudes. Figure F-3

demonstrates an example of the nocturnal low level jet passing along the east coast as far

south as Maryland and as far north as southern Maine. 
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 6

Figure F-3. Nocturnal low level jet on July 23 – 24, 2002. Note: Circles in the wind barb plots indicate the

location of the nocturnal low level jet. Data are inconclusive for identifying a nocturnal low level jet at

Orange, MA.

FME

ORE

STW

ADI

PSE

RUT

Direction of

LLJ

FME

ORE

STW

ADI

PSE

RUT

Direction of

LLJ
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 7

Figure F-3 shows that the nocturnal low level jet occurred on the night of July 23-

24 as it did on the previous night. Figure F-4 shows ozone levels overnight on the

July 23-24 at Cadillac Mountain and Cape Elizabeth. In this case, we see that low ozone

is occurring at both sites during the early hours of July 24. Applying the same methods

utilized earlier, wind speed and wind direction information from Cadillac Mountain

indicate that the air arriving at Cadillac Mountain was also roughly over central

Massachusetts at 10 p.m. on July 23 (same wind direction and wind speed as previous

day). Wind profiler data show that winds moved this air mass from eastern New York

and western Connecticut in the late afternoon. Average ozone levels between 4 p.m. and

7 p.m. were 53 ppb at Cornwall, CT. Therefore, much like on the previous day, air

masses were tracked back to the western Connecticut area upwind. In this case, however,

low levels of ozone existed in the air mass.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 8

Figure F-4. Nocturnal low level jet with hourly ozone concentrations at Cadillac Mountain, ME and Cape

Elizabeth, ME on July 23 – 24, 2002. Note: Circles in the wind barb plots indicate the location of the

nocturnal low level jet. Data are inconclusive for identifying a nocturnal low level jet at Orange, MA.

Examining the wind profiler data from 4 p.m. to midnight on July 23 (Figure F-1

and Figure F-3), we see high winds at all altitudes developing throughout the region.

Figure F-5 shows that these high winds are part of a weather front that passed through the

region in the afternoon of July 23. This corresponds with the sharp drop in ozone levels at

Cornwall, CT, Cadillac Mountain, ME, and Cape Elizabeth, ME (Figure F-6) as the front

pushed ozone out of the region. This explains the low levels of ozone seen at Cadillac

Mountain during the nocturnal low level jet in the early hours of July 24. This example

demonstrates that not all nocturnal low level jets are associated with high ozone levels at

elevated sites. A necessary condition for the transport of ozone in a nocturnal low level

jet is the presence of upwind elevated ozone levels. The front that pushed through the

region on the previous day resulted in “clean” air being transported in the nocturnal low

level jet.

FME

ORE

STW

RUT

Direction of

LLJ

Cadillac

Mountain

Cape

Elizabeth

0

20

40

60

80

100

120

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

7/23/2002 7/24/2002

Ozone Concentration (ppb)

Cadillac

Mountain

Cape

Elizabeth

Time of LLJ

FME

ORE

STW

RUT

Direction of

LLJ

Cadillac

Mountain

Cape

Elizabeth

0

20

40

60

80

100

120

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

7/23/2002 7/24/2002

Ozone Concentration (ppb)

Cadillac

Mountain

Cape

Elizabeth

Time of LLJ

0

20

40

60

80

100

120

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

7/23/2002 7/24/2002

Ozone Concentration (ppb)

Cadillac

Mountain

Cape

Elizabeth

Time of LLJ
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 9

8AM 7.23.02 8PM 7.23.02

Figure F-5. Weather map displaying a front passing through the East on July 23, 2002.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 10

0

20

40

60

80

100

120

0:001:002:003:004:005:006:007:008:009:0010:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

Ozone Concentration (pp

b)

Cornwall CT

Cape Elizabeth, ME

Cadillac Mountain

Figure F-6. Hourly ozone concentrations on July 23, 2002 at three sites.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 1

Appendix G:Contributions to the ozone reservoir

 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 1

Appendix G: Contributions to the ozone reservoir

Contributions to the ozone reservoir can come from two sources. The first is from

the residual local ozone and precursors in the atmosphere at sunset. The second is from

transport of ozone and precursors from outside of the local region. To identify these

outside sources, Taubman et al. (2006) have made an analysis of the complete set of

aircraft flights undertaken by RAMMPP between 1992 and 2003. Initially, the data were

divided into morning and afternoon profiles to identify diurnal patterns. Little diurnal

variation was observed in the carbon monoxide and sulfur dioxide profiles. The ozone

values were greater in the afternoon than the morning, while ozone in the lower free

troposphere (i.e., above the boundary level), where long range transport is possible, was

consistently ~55 ppb. Transport patterns and source regions during summertime haze and

ozone episodes were analyzed with a cluster analysis of back trajectory data. Eight

clusters were identified, which were then divided into morning and afternoon profiles.

Table G-1 lists the characteristics of each cluster, and Figure G-1 shows the back

trajectories calculated for each profile divided by cluster at an altitude of 2000 meters.

The median profile values were calculated and statistical differences were determined

using a nonparametric procedure. When the greatest trajectory density lay over the

northern Ohio River Valley, which has large NOX and sulfur dioxide sources, the results

were large ozone values, a large SO2/CO ratio, large scattering particles, and high aerosol

optical depth over the mid-Atlantic U.S. In contrast, relatively clean conditions over the

mid-Atlantic occurred when the greatest trajectory density lay over the southern Ohio

River Valley and nearly missed many large NOX and SO2 sources. The greatest afternoon

ozone values occurred during periods of stagnation that were most conducive to

photochemical production. The least pollution occurred when flow from the northnorthwest was too fast for pollution to accumulate and when flow was from the north,

where there are few urban or industrial sources.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 2

Figure G-1: Maps of the 2 km, 48 hr HY-SPLIT back trajectory clusters for

mid-Atlantic region

Note: Cluster groupings are a) cluster 1, b) cluster 2, c) cluster 3, d) cluster 4, e) cluster 5, f) cluster

6, g) cluster 7, and h) cluster 8. Figure from Taubman et al., 2006.
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 3

Ozone transport over several hundred kilometers into the mid-Atlantic U.S. was

estimated by calculating the ratio of the residual layer ozone between 500 m and 2 km in

the upwind morning profiles to the downwind afternoon boundary layer values between

100 m and 2 km. The greatest level of transported ozone (69-82 percent) occurred when

the maximum trajectory density lay over the southern and northern Ohio River Valley

(clusters 1, 2, 4, and 6); ~59 percent of the total profiles). The least amount of transported

ozone (55-58 percent) was associated with fast southwesterly flow (cluster 8; ~3 percent

of the total profiles), fast north-northwesterly flow or clean northerly flow from regions

with relatively few urban or industrial pollution sources (clusters 5 and 7; ~6 percent of

the total profiles), and stagnant conditions within the mid-Atlantic conducive to greater

local ozone production (cluster 3; ~27 percent of the total profiles). The average amount

of ozone transported into the Baltimore-Washington urban corridor is 64 percent of the

total observed ozone in the afternoon boundary layer. If the background ozone is

removed, then this value is lowered to 55 percent.

When trajectory density plots were overlaid on maps with the largest annual NOX

and SO2 emitters, specific source regions were identified. The results indicate that the

areas of maximum trajectory density together with wind speed are effective predictors of

regional pollution and loadings. Additionally, due to the Lagrangian nature of the dataset,

the regionally transported contribution to the total afternoon boundary layer column

ozone content in each cluster could be quantified.

Table G-1. Cluster groups for air mass trajectories into mid-Atlantic Region

Cluster Description Upwind Region

1 Large ozone values, large SO2/CO ratio, large highly

scattering particles. Moderate northwesterly flow – aged

point source air.

Northern Ohio River Valley

2 Small ozone values, large SO2/CO ratio. Northwesterly

flow at higher wind speeds than Cluster 1 – aged point

source air.

Northern Ohio River Valley,

extending into the Great

Lakes region

3 Large ozone values, small SO2/CO ratio. Stagnant

conditions with light southerly flow.

Central mid-Atlantic region

4 Small ozone values, small SO2/CO ratio. Moderate

southwesterly flow, small pollution loading – fewer

point sources.

Southern Ohio River Valley

5 Fairly fast north-northwesterly flow. Flow too fast for

pollution to accumulate from source region.

Northern Great Lakes

6 Moderately large ozone values, SO2/CO ratio very

large, smaller less scattering particles. Northwesterly

flow, but faster wind speeds than Clusters 1 and 2.

Crosses several large SO2 and NOX sources.

Northern Ohio River Valley

7 Least pollution of any of the clusters. Flow is out of the

north. Relatively cool, dry continental air.

Eastern Ontario, western

Quebec

8 Small ozone values, small SO2/CO ratio. Fast southwest

flow. Very few trajectories.

Vicinity of Texas
 The Nature of the Ozone Air Quality Problem in the Northeast: A Conceptual Description Page 4

Reference

Taubman, B.F., J.C. Hains, A.M. Thompson, L.T. Marufu, B.G. Doddridge, J.W. Stehr,

C.A. Peity, and R.R. Dickerson. “Aircraft vertical profiles of trace gas and aerosol

pollution over the mid-Atlantic United States: Statistics and meteorological cluster

analysis.” J. Geophys. Res. 111, D10S07, doi:10.1029/2005JD006196, 2006.