GROUND-LEVEL OZONE:
OCCURRENCE AND TRANSPORT
IN EASTERN NORTH AMERICA
A Report by the
Canada-United States Air Quality Committee
Subcommittee 1:
Program Monitoring and Reporting
March, 1999

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TABLE OF CONTENTS
1.	INTRODUCTION
Foundation for the Transborder Ozone Issue in Eastern North America
Joint Plan of Action for Addressing Transboundary Air Pollution
Joint Workplan
2.	AIR QUALITY DATA ANALYSIS
Air Quality Snapshot
Ozone Episodes
Factors that Influence Ozone Concentrations
Air Quality Data Analysis Conclusions
3.	AIR QUALITY MODELLING
Model Setup and Episodes
Analysis of Modelling Results
Air Quality Modelling Conclusions
4.	POLICY CONCLUSIONS RELEVANT TO THE CONSIDERATION OF AN OZONE ANNEX
BY THE AIR QUALITY COMMITTEE
5.	REFERENCES
* Note: Canadian spelling is used throughout.
"This is a policy document that provides a summary of information as a basis for decision by the Air
Quality Committee."

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1. INTRODUCTION
This report presents results of co-operative efforts set in motion in April 1997 to describe
ground-level ozone1 concentrations and transport in the border region of the eastern United
States and Canada. It is intended to provide a foundation for a recommendation to
governments on the means to jointly address the transboundary ozone issue.
Foundation for the Transborder Ozone Issue in Eastern North
America
Ozone has long been recognised as an important health and ecosystem-related air quality
concern in the United States and Canada. Recent health and environmental studies in both
countries indicate that adverse effects result from ozone exposures at concentrations much
lower than previously thought. The United States has recently revised the ozone air quality
standards and Canada has a process underway to examine its ozone-related objectives and
standards. Both countries have committed to addressing the ozone air quality problem within
their own territories. The status of ambient air quality standards and objectives for ozone in
Canada and the United States are summarised in Table 1.
TABLE 1. AMBIENT AIR QUALITY OBJECTIVES AND STANDARDS FOR OZONE

United States
Canada
Averaging
time
National Ambient Air Quality
Standards
National Ambient Air
Quality Objective
Proposed Canada-wide
Standard
1-hour
120 parts per billion (ppb)
(std. being replaced by 8-hr)
82 ppb
—
8-hours*
80 ppb
(Revised standard)
—
60-70 ppb
""4th highest 8-hours averaged over 3 years
Recognition of the effects of ozone has been accompanied by considerable monitoring and
analyses of the spatial pattern of ozone in the two nations. Large-scale summertime smog
episodes occur in the eastern half of both countries, with events that transcend political borders.
In Canada, exceedences of the current 1-hour 82 ppb (parts per billion) air quality objective are
regional in nature, with areas of concern in southern British Columbia in the West, and
throughout the Windsor-Quebec City Corridor and the Southern Atlantic Region in the East. A
similar pattern of regionally elevated ozone occurs in the United States; nationally, a number of
areas in California and the Gulf Coast, as well as numerous locations in the eastern portion of
the nation exceed the U.S. standards.
The Canadian effort to address ozone exceedences began in 1990 with all governments co-
operating to develop the first phase of a management program to reduce precursor emissions
of ozone - nitrogen oxides (NOx) and volatile organic compounds (VOC) (CCME, 1990). Since
1990, while the management program has continued to be further refined and implemented, a
comprehensive science assessment has defined the nature and extent of the ozone problem in
Canada and established the scientific foundation for management options (Multistakeholder,
1990).
1 The term ground-level ozone, which includes smog-related ozone found in the lower troposphere, is
used to make a clear distinction from beneficial stratospheric ozone. Hereafter, the report refers to
ground-level or smog ozone simply as ozone.
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In the United States, the need to improve upon the effectiveness of ozone implementation
programs led to the new classification system, mandatory requirements, and additional mobile
source controls embodied in Titles I and II of the 1990 Clean Air Act Amendments. In the
process of implementing these requirements, it became clear that expanded regional, as well
as local control approaches were essential to meet clean air standards. As a result, 37 eastern
states formed the Ozone Transport Assessment Group (OTAG). The OTAG effort produced
substantial documentation on the nature of regional ozone transport and alternative strategies
(OTAG, 1997). This led directly to promulgation of a major new regional regulatory program to
reduce emissions responsible for such transport. The U.S. Environmental Protection Agency
(EPA) promulgated this ozone transport rule on October 27, 1998 (EPA, 1998). Since it calls
on states to develop implementation plans (SIPs) to address NOx emissions, the rule is known
as the NOx SIP call.
Canadian and international studies have reached similar conclusions. In addition to the OTAG
Air Quality Analysis Workgroup section of the OTAG final report (OTAG, 1997), the Canadian
1996 NOxA/OC Science Assessment reports (Multistakeholder, 1997) have demonstrated that
ozone concentrations locally, sub-regionally, and regionally are influenced by background
concentrations, locally generated ozone, and transported ozone. The contribution of
transported ozone and its precursor emissions occurs over distances of many hundreds of
kilometres in the eastern United States and Canada. Recent reports by the Commission on
Environmental Cooperation (CEC, 1997) and the International Joint Commission (IJC, 1998)
have also highlighted the significance of the transboundary transport of ozone and its
precursors to air quality management programs in the United States and Canada.
Joint Plan of Action for Addressing Transboundary Air Pollution
In 1991, Canada and the United States signed the Air Quality Agreement, which codified the
principle that countries are responsible for the effects of their air pollution on one another.
While the Agreement initially addressed acid rain, it also confirmed the commitment of the
United States and Canada to consult and develop the means to deal with any existing
transboundary air pollution problems.
The increasing evidence on regional transport of ozone outlined above led to a recognition that
ground-level ozone would be an appropriate issue to consider for the Canada-U.S. Air Quality
Agreement as early as 1994 (AQC, 1994). Members from both countries met in 1995 to outline
a Canada-U.S. Regional Ozone Study Area (ROSA) project. Under this program, the countries
initiated regional modelling to evaluate the relative effectiveness of regional controls for ozone
pollution in a broad transboundary area in eastern North America. Both counties are also
participating in a coordinated program of scientific research and assessment of ozone and
particulate matter under NARSTO. This transboundary work occurred in parallel with the
domestic OTAG and NOxA/OC Science Assessment activities. Collectively, these endeavours
formed the basis of discussions of policy-makers from both countries.
In April 1997, President Clinton and Prime Minister Chretien's meeting reinforced the
importance of Canada-U.S. cooperation to protect North American air quality. As part of the
President-Prime Minister meeting agenda, U.S. EPA Administrator Carol Browner and
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Canadian Minister of the Environment Sergio Marchi signed a "Commitment to Develop a Joint
Plan of Action for Addressing Transboundary Air Pollution on April 7, 1997." The commitment
was to address jointly shared air pollution problems with ground-level ozone identified as the
next priority. In June 1998, EPA Administrator Browner and Canadian Minister of the
Environment Christine Stewart signed a report on progress in developing the Joint Plan of
Action. The Progress Report set targets and schedules for governments in working toward a
negotiated ozone annex to the Air Quality Agreement. The report identified a strategy of
cooperation and joint work, and called for delivery, by April 1999, of a recommendation on
negotiation of an ozone annex to the Canadian Minister of the Environment and the U.S. EPA
Administrator.
Joint Workplan
The following technical analyses, described in some detail in this document, enable conclusions
regarding the transport of ozone in the border regions of the eastern United States and
Canada:
•	Air quality data analyses using integrated Canadian and U.S. data for the years 1989-1996
to determine how, when, and where transboundary transport of ozone and precursor
emissions occurs within the region and the regional extent of elevated 8-hour ozone levels;
•	Analyses of factors affecting ozone formation and transport to identify major source regions
within the transboundary region; and
•	Joint modelling using Canadian and U.S. data and forecasts of planned reduction
programs to demonstrate the likely impact of emission control scenarios within the
transboundary region.
This document and its conclusions on ozone transport in the border region fulfils the
requirement to account, by April 1999, to the Canada-U.S. Air Quality Committee whose
mandate is to implement the Air Quality Agreement. Further, the conclusions of this report
provide support for drafting of possible elements for an ozone annex pursuant to the Air
Quality Agreement.
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2. AIR QUALITY DATA ANALYSIS
Ozone is a photochemical oxidant formed from reactions involving nitrogen oxides (NOx) and
volatile organic compounds (VOC) in the presence of sunlight. In order to understand the
nature of ozone levels and transboundary flows of ozone and precursor emissions in the
border region, this section presents highlights of several existing analyses, assessments, and
publications of air quality and meteorology. This work includes the existing and currently
ongoing Canadian Multistakeholder NOxA/OC Science Assessment reports (Multistakeholder,
1997) and the OTAG final report (OTAG, 1997). In addition, new analyses that extend these
data and analytical techniques into the Canada-U.S. transboundary region were developed for
this report and are summarised below (Dann, 1999, Husaret al., 1999; Schichtel and Husar,
1999).
The sections presented here include: a snapshot of current ozone levels, regional maps
showing episodic flows in the border region, emissions information, and an overview and
analysis of meteorological factors affecting ozone concentrations and transport.
Air Quality Snapshot
The air quality snapshot depicts the regional extent of elevated ozone concentrations in the
Canada-U.S. border area based on analysis and maps in an Environment Canada report
(Dann, 1999). Data from 100 Canadian sites and 122 U.S. sites for the ozone season (May to
September) for the period 1994 to 1996 were used to demonstrate regional patterns in ozone
concentrations. Ozone concentrations were computed for running 8-hour periods and
maximum 8-hour concentrations by day were determined. The maximum and the fourth
highest daily maximum 8-hour ozone values were then computed by site by year.
Figure 1 shows the distribution of fourth highest daily maximum 8-hour ozone concentrations
by monitoring site within each region using data for 1994 to 1996. The boxplot figure provides
the median, the 95th, 75th, 25th and 5th percentile site ozone concentrations.2 Figure 2 maps the
4th highest daily maximum 8-hour ozone concentration for the north-eastern portion of North
America averaged over the years 1994-1996. Figure 3 provides similar information but uses
the average highest daily maximum 8-hour ozone value.
2 The 95th percentile value shows, for example, that 5% of the monitoring sites in that monitoring region have ozone
concentrations that are equal to or higher than that level.
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Figure 2. Average of the 4th Highest Daily 8h Maximum Ozone Concentration (ppb) for
1994 to 19964.
Highest daily 8h Max. Ozone
Figure 3. Average of the Highest Daily 8h Maximum Ozone Concentration for 1994 to
19964.
4 Figures 2 and 3 were created using the U.S. EPA sponsored Map Generator program (MCNC-Morth Carolina
Supercomputing Center) and incorporates data from 271 ozone monitoring sites that had at least two years of
observations in the 1994-1996 period. The contours were generated using inverse distance weighting interpolation.
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Ozone Episodes
Widespread regional episodes are a common feature of eastern North America and have the
potential to contribute to exceedences of air quality objectives and standards. To illustrate how
a regional episode develops and flows within the region of interest, measured ozone
concentration data were compiled from monitoring sites located in eastern United States and
eastern Canada for two regional ozone episodes and then mapped. The episode years, 1988
and 1995 were chosen because they show clearly ozone transport within the region of interest
over the duration of the episodes. The 1988 episode illustrates ozone transport in both
directions across the Canada-U.S. border whereas the 1995 episode illustrates a good example
of transport from the United States to Canada. Both episodes were also used in the joint
modelling scenarios presented later in this report.
During the summers of 1988 and 1995, ozone-rich plumes were transported across all of
eastern North America. Many sites recorded multiple hours and days with ozone
concentrations greater than the Canadian and U.S. air quality criteria. The following series of
maps (Figures 4, 5 and 6) depict the levels of ozone concentrations in eastern United States
and Canada at four progressively later hours in a day during an episode. The maps provide
the magnitude and extent of high concentrations while demonstrating movement of ozone over
time through the region.
These figures illustrate that essentially all areas of eastern Canada and most areas of the
eastern United States experience high concentrations of ozone. Although some areas
experience very high 8-hour concentrations, widespread areas experience concentrations
ranging from 60-80 ppb and from 80-100 ppb over 8 hours. The following section will discuss
what factors contribute to high ozone concentrations locally and regionally.
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Figure 4. Ozone Transport on July 13,1995 10AM - 8PM. The first frame shows a regionally uniform pattern of ozone levels.
Transport generally followed a north-easterly path, across the heavily industrialised and urbanised area of the U.S. Midwest, then
across the Great Lakes (frame 2) into southern Ontario and out to the coast. After picking up local emissions, transport continues
west along the St. Lawrence river basin (frame 3) and finally out to the North Atlantic.
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Figure 5. Ozone Transport on July 7 1988,10AM - 7PM...These frames show fewer urban-industrial peaks and an elevated non-
urban pattern extending across most of eastern North America. Both characteristics are evidence of regional scale transport.
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Figure 6. Ozone transport on July 10,1988,10AM -11 PM. Figure 6 shows night time flows into eastern Canada when
concentrations greater than 82 ppb occur late in the evening in the southern Atlantic region (frame 4) after high ozone
concentrations have moved across the Northeast region (IND, WV, VA, OH, PA, ON) and along the Atlantic seaboard.
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The spatial patterns of NOx emission sources in Canada and the United States are shown in
Figures 10 and 11. The figures show high NOx emission densities in urban-industrialised
areas, although the order of magnitude is different from Canada to the United States.

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NOx EMISSIONS DENSITIES >
Figure 9. 1995 NOx Emission Densities (in kg/km2) for Eastern Canada.
Source: Environment Canada Pollution Data Branch.
Figure 10. NOx Emission Densities (in tons/hr/grid) in the Eastern United States and
Canada. The emissions included on this map for the U.S. reflect the 1995/96 base year
emissions that were used in the NOx SIP Call. The emissions for Canada are the 1990
emissions that were used by OTAG.
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In the transborder region, the areas of highest emission densities are along the Canada-U.S.
border and along the Atlantic coast in the United States. Taken together, these twin corridors
of dense population and precursor emissions run from the Southwest to the Northeast, in
parallel to weather patterns that frequently occur in the summer. The metropolitan areas along
the Canada-U.S. border also have high emission densities of ozone precursors. The following
sections present data on transport meteorology, and show the relationship between transport
and ozone concentrations within the region.
Ozone as a Function of Wind Speed and Direction
Analysis of ozone a function of wind speed and direction can help provide insight into the
relative importance of local and distant sources under varying meteorological conditions.
Previous analyses, including those done for OTAG (OTAG, 1997) and for the Canadian
Multistakeholder NOxA/OC Science Assessment (Multistakeholder, 1997) indicate that these
factors are important influences on the transport of ozone. The series of analyses for the
OTAG region has been extended for this report to include Canada to provide more specific
insights into transboundary issues (Husar et al., 1999).
In order to analyse the effects of wind speed and direction on ozone concentrations, analysts
sorted 11 years of measured ozone concentrations (1989-1996) and averaged for specific
wind direction and speed ranges. The average ozone concentration was computed for each
wind direction range in 90° increments, starting with 0-90°, i.e. when the wind blew from the
North or Northeast. This resulted in four wind directional concentration bins. The average
concentrations for each directional bin were further classified by wind speed, ranging between
0-2, 2-4, 4-6, 6-8 metre/second (m/s) increments. Thus, there were four directional and four
wind speed bins, yielding a total of 16 concentration bins.
The results of this analysis are presented in maps of average ozone concentration for the four
wind directions and three wind speeds - low, medium and high (Figures 11, 12, 13). The
detailed results are discussed in a supporting technical paper (Husar et al., 1999).
In summary, average ozone concentration maps at low wind speeds (<3 m/s, Figure 11) show
elevated levels of ozone throughout the eastern North American domain. Ozone concentration
hot-spots appear over the major metropolitan areas in the United States and the Ohio River
Valley but the concentrations are virtually the same regardless of the wind direction. Ozone
concentrations in metropolitan areas of Canada are similar to surrounding sites. At
intermediate wind speeds (3-6 m/s, Figure 12) the overall concentrations are lower, and the
higher ozone concentrations appear to be displaced up to 500 km downwind of the major
source areas. At high wind speeds (>6 m/s, Figure 13) most metropolitan source areas do not
cause elevated ozone in their own vicinity. Rather, higher concentrations appear in the
downwind corners of the eastern North American domain, up to 1000 km from the domain
centre.
The ozone concentration pattern at different wind directions and speeds are consistent with an
atmospheric ozone lifetime of about one day and a corresponding transport distance of 200,
500 and 800 km at 2, 5, and 8 m/s respectively. Therefore, at low wind speeds, ozone
accumulates near precursor emission source areas. Higher wind speeds cause increased
dilution of local concentrations and increased transport from one source region to another.
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Wind Dir: 1B0-270; Speed 0-3 m.'s|
Miinl Dii iiliini
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Figure 11. Maps of average ozone concentration at low (<3 m/s) wind speed, a) 270-360 degrees, b) 0-90 degrees, c) 90-180
degrees, d) 180-270 degrees. At low wind speeds, ozone concentrations tend to be somewhat higher just downwind of urban
areas. Concentrations tend to be fairly similar, regardless of wind direction. In such cases, local sources likely dominate ozone
formation.
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Wind Dir: 1B0-27O; Speed 3-6 m/s
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Figure 12. Maps of average ozone concentration at intermediate (3-6 m/s) wind speed, a) 270-360 degrees, b) 0-90 degrees,
c) 90-180 degrees, d) 180-270 degrees...At intermediate wind speeds, there are substantial differences between the maps
depending on the wind direction. Northerly flows (frames a and b) show low concentrations throughout Canada and the northern
United States. Southerly flows result in higher concentrations in the north, especially in the Michigan/Ontario/New York region.
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Surface Windy HE-fir,
Wind Diir; 00- 90; Speed >6 m/s
ind Oir; 270-360; 5
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Figure 13. Maps of average ozone concentration at high (>6 m/s) wind speed, a) 270-360 degrees, b) 0-90 degrees, c) 90-
180 degrees, d) 180-270 degrees. At high wind speeds, the eastern North American domain appears as a regional domain,
although there are still some near-urban areas of elevated ozone.
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Transport During High and Low Ozone Days
Ozone transport on days of regionally high and low ozone concentrations was also investigated
in the analyses conducted for this report. Ozone transport, precursor emissions, and the
influence of wind were examined in two ways. First, from the transport climatology, regions
were identified where transport conditions are conducive to the accumulation of ozone from
local or sub-regional sources, as well as where influence by regional scale transport can be
seen. Second, by contrasting the transport conditions during periods of high and low ozone
concentrations, unique transport pathways for a given region, as well as common pathways for
multiple regions, were identified. The results of this analysis are summarised below and
presented fully in a background paper (Schichtel and Husar, 1999).
Transport conditions were established for regionally high (90th percentile) and low (10th
percentile) daily maximum 1-hour ozone concentrations. Figure 15 shows source regions of
influence (SRI) overlaid with transport wind vectors. The wind vectors convey the direction and
magnitude of the air mass transport while the SRIs represent the area encompassing the
source impact and resultant air mass transport direction and speed. The SRIs are for the
nearest modelled regions to Atlanta, Houston, Chicago, the Ohio River Valley, and New York
City. At each source region, the highest and lowest daily maximum ozone values usually
occurred on different days. Therefore, the transport conditions at each source region represent
transport over different time periods.
Regionally high ozone days (Figure 15A) were associated with slow meandering or recirculating
transport over Kentucky, Tennessee, and West Virginia, with strong clockwise transport around
this region. It is clear that transport from sources in the southern Great Lakes border region
moves from the United States into Canada, over the most dense emission regions of Southern
Ontario, and back into New York and the New England States. This flow pattern is consistent
with that of a large high-pressure system over eastern North America. The regionally low
ozone days (Figure 15B) had northerly flow into Canada from Wisconsin and Michigan that
converged over Kentucky and Tennessee with swift westerly-southwesterly flow in the
Southeast. In New England, substantial transport occurred in all directions with resultant mass
transport to the East.
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Jum - August. 1981 - 95; One Day Lifetime
Jmm - August. 1991 - 95; One Djy Lifetime
Transport Wind Vectors & Regions of Influence
_ Low (10%-He) Regional Ozone Days
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Transport Wind Vectors & Regions of Influence
High (90%^lle) Regional Ozone Days
Figure 15. Transport wind vectors and source regions of influence for the highest (A)
and lowest (B) 10% of regional ozone days during June - August, 1991 -1995. Transport
vectors in Figure A, regionally high ozone days, show wind speed and directions consistent with
regional-scale episode, i.e., strong clockwise transport. There is substantial transport into
southern Ontario, particularly from the Chicago source region. Figure B, low regional ozone
days, show transport vectors from the Great Plains into the Prairie provinces, east towards
southern Ontario and south into the New England states. The New York source region shows
substantial transport in all directions, while transport is primarily south in the Chicago source
region.
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Air Quality Analysis Conclusions
Ozone is not emitted directly, but produced in photochemical reactions involving NOx and VOC
emissions. High ozone concentrations occur in and around many of the urban-industrialised
areas in the transboundary region in both countries, resulting in frequent exceedences of
current and proposed air quality objectives and standards. Elevated concentrations also occur
over areas several hundred kilometres downwind of urban areas, causing exceedences of the
objectives and standards in relatively less populated non-industrial areas. Some of these
exceedences can occur at night as a result of ozone transport.
Transport of ozone and precursors has no boundaries. Polluted air masses can travel across
states and provinces and between the United States and Canada. High ozone concentrations
are typically located downwind of areas with the highest emissions. In the Canada-U.S.
transboundary region, a more uniform pattern of ozone concentrations occurs across the
region. The result is a regional "sea" of elevated ozone, extending east from the Mississippi
River to the Atlantic coast and north-northeast into the Windsor-Quebec City Corridor, New
Brunswick, and Nova Scotia, punctuated by "hot-spots" associated with dense emissions areas.
Emissions of NOx in the area were shown to form a boundary around the populated
transboundary region, with dense emissions in the Windsor-Quebec corridor, and along the
Atlantic coast from New Jersey to Massachusetts. The Ohio River Valley area, dense in
precursor emissions, sits at the "entrance" of these twin transboundary emission corridors.
Ozone transboundary flux data, presented in the section on wind speed and direction, illustrate
flows in both directions, but are consistent with greater transport of ozone from the United
States to Canada than from Canada to the United States. Concentrations along the Detroit-
Windsor-Quebec City corridor, and eastward, are increased when the wind blows from the
"entrance" of the corridor, both towards the northeast, and north-northeast around the Great
Lakes and out to the Atlantic.
Increasing wind speeds generally bring about reductions in locally produced ozone
concentrations in urban areas. Ozone concentrations in the northeast urban corridor, along the
Atlantic coast, are reduced when the ozone and precursor emissions are blown out to sea. For
border areas where local concentrations remain constant with wind speed, it appears that the
regional transport dominates ozone concentrations. This is observed in several of the urban
areas along the border (e.g., Detroit, Windsor, and Toronto) where ozone concentrations were
not reduced with increasing wind speeds.
Designing ozone control strategies is complicated because the effectiveness of strategies
depends on factors such as meteorological conditions, the absolute and relative amounts of
VOCs and NOx, the spatial and temporal distribution of anthropogenic and natural emissions,
and background concentrations. The air quality data analysis section discussed the
interrelationships between these factors and how each influences ozone concentrations. Some
general conclusions can be made, therefore, regarding the effectiveness of strategies in the
Canada-U.S. transborder region, based upon the conclusions from earlier reports and the
information presented in this report. In the urban areas, a combination of VOC and NOx
emission reductions are expected to lead to reductions in high ozone levels locally and
downwind. In the areas affected by transport of ozone and precursor emissions, the downwind
urban, suburban and rural areas, i.e. the Canada-U.S. transborder region, NOx reductions are
expected to be more effective.
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The next section presents the results of air quality modelling using Canadian and U.S. data and
forecasts of planned reduction program, focusing on NOx emission reductions to show the
likely impact of emission control scenarios in the transboundary region.
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3. AIR QUALITY MODELLING
EPA and Environment Canada worked jointly to develop an expanded air quality modelling
assessment for this report. The major purpose of this modelling was to evaluate the
effectiveness of combined illustrative NOx control strategies in reducing regional ozone
concentrations, with an emphasis on the transboundary region of concern. As discussed
previously, this modelling focuses on NOx controls because NOx reductions are generally more
effective in reducing ozone on a regional basis than VOC reductions. The modelling emphasis
on the effectiveness of example NOx control strategies is not intended to constrain the range of
control options to be discussed in any future negotiations on an ozone annex.
Model Setup and Episodes
The modelling for the assessment of regional strategies consisted of model runs using the
Variable Grid Urban Airshed Model (UAM-V). This model was chosen for several reasons.
This model has been widely used and generally accepted for policy applications in the U.S. In
addition, it was readily available to be adapted for the analyses done for this report. The inputs
needed to run the model (e.g., emissions and meteorological data) have been developed for a
domain that covers much of the portion of the Canada-U.S. border that is of primary interest. A
wide range of stakeholders reviewed these inputs. The configuration of the model used for this
report is the same as that used for OTAG. The OTAG final report (OTAG, 1997) describes this
in detail and addresses model performance and other issues related to application of the model
for purposes of evaluating regional transport.
Modelling was done using the OTAG modelling domain, which includes portions or all of 37
states and the District of Columbia and parts of three Canadian provinces: Ontario, Quebec,
and New Brunswick. The domain, therefore, incorporates some but not all areas of concern in
eastern Canada and in particular, leaves out the Southern Atlantic Region. Two episodes were
selected for evaluation: July 1-11, 1988 and July 7-18, 1995. These episodes were chosen
because they represent conditions that suggest interregional transport over the areas of
interest.
Emissions
EPA developed emissions for the United States and Environment Canada provided emissions
for the Canadian portion of the modelling domain. The U.S. base year emissions are the same
as those used for the development of the final rulemaking for the NOx SIP Call. These
emissions are based on continuous emissions monitoring data for utilities and OTAG emissions
for other sources and have been revised to reflect comments received during the public
comment period for the NOx SIP Call. The base emissions for Canada are taken from the
official Canadian 1990 National Emissions Inventory developed and compiled by the federal
and provincial/territorial governments.
Scenarios Modelled
Two scenarios were modelled: a projected 2007 base case and one control scenario. The base
case scenario is intended to represent conditions in 2007 if no emissions reductions occur in
either country beyond what is currently mandated. For the United States, the base
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case includes growth to 2007 and the application of Clean Air Act mandated controls as well as
certain Federal measures that have been or are expected to be promulgated. This base case is
described in detail in the final rulemaking for the NOx SIP Call (EPA, 1998). For Canada, the
base case includes growth to 2007 and the implementation of actual programs and measures
that are described in detail in the National Air Issues Coordinating Committee (NAICC) Base
Case Consensus Forecast (NAICC, 1996).
The control scenario was developed to represent potential additional NOx reductions. For the
United States, this includes the effects of the NOx SIP Call as shown in Table 2 and described
in detail in the final rulemaking for the NOx SIP Call.
TABLE 2. CONTROLS ASSUMED FOR SOURCES IN THE UNITED STATES.
Sources
Controls
Large Electricity Generating Units
0.15 lb NOx/mmBtu, implemented through a regional
trading program
Large Industrial Boilers and Turbines
60% reduction from uncontrolled levels
Large Glass Manufacturing Facilities
30% reduction from uncontrolled levels
Large Internal Combustion Engines
90% reduction from uncontrolled levels
For large electricity generating units, 1995 or 1996 heat input was grown to 2007 and the 0.15
lb NOx/mmBtu limit was applied. For the other categories listed in the table, emissions were
projected to 2007, any control efficiency that had been applied was removed, and the control
efficiency listed above was applied. For all other sources the control case is the same as the
base case.
Because the Canadian NOx reduction program is not yet completely defined, the Canadian
control scenario was developed as a "what if" case. The control scenario began from the basis
of a "25% across the board" emission reduction for the province of Ontario for all sectors for
both NOx and VOC from 1990 by 2007. In terms of the Ontario government Smog Plan
commitment to reduce NOx and VOC emissions by 45% from 1990 by 2015, an "across the
board" 25% reduction by 2007 was considered an appropriate scenario to model. The
application of the "25% across the board" premise resulted in emission reductions as shown in
Table 3.
TABLE 3. CONTROLS ASSUMED FOR SOURCES IN ONTARIO.
Category
% NOx Reduction from 1990
% VOC Reduction from 1990
Power Generation
25%
0% (Base Case used)
Industrial Sources
25%
25%
Fuel Combustion
25%
3.5% (Base Case used)
Incineration/other
0% (Base Case used)
25%
T ransportation
25%
29% (Base case used)
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Wherever a reduction in the Table differs from 25%, the base case scenario reduction was
used. The rationale for the use of the base case reduction was:
1)	few emissions of that pollutant are produced making a 25% reduction unrealistic (as in the
case of VOC emissions from power generation where the provincial total in 1990 was 0.4
kilotonnes);
2)	the base case forecast reduction for 2007 is already greater than 25% (as in the case of the
VOC emissions from the transportation sector); or
3)	an assessment was made that technology to meet a reduction of 25% is not available (as in
the case of a 25% reduction of VOC from the fuel combustion sector).
For the provinces of Quebec and New Brunswick, the same approach was used for the
transportation sector as for the province of Ontario. With respect to the other sectors, the
control case reductions were the same as the base case.
For the purpose of evaluating model results, the 2007 control case is compared to the 2007
base case. It is important to understand the difference in emissions between these two model
runs in order to analyse properly the model results. The application of the controls described
above translates to a 28% reduction in NOx emissions from the 2007 base case in the United
States and a 12% reduction in NOx emissions and a 14% reduction in VOC emissions from the
2007 base case in Canada. These overall percent reductions are influenced by two factors.
First, the reductions have been applied to some but not all sectors of the inventory in the United
States and Canada. Second, in Canada, the control scenario reductions are applied to the
1990 emissions so that when the 2007 control case scenario emissions are compared with the
2007 base case emissions, the level of the reduction is offset by growth and abatement
measures that are already incorporated in the base case scenario.
Analysis of Modelling Results
The impacts of emission controls were evaluated by comparing the results of the base case run
with the results of the control case run. Using the results in a comparative sense alleviates
some of the concerns with uncertainties in absolute predictions. The 1-hour and 8-hour base
case ozone predictions are shown in Figures 16 and 17, respectively. (These Figures and the
ones that follow have been cropped so that they do not show the entire OTAG modelling
domain but focus on the transboundary area of concern.) The change in the extent of values
above the standards or objectives indicates the improvements in air quality due to the reduction
in NOx emissions. This can be seen by looking at the difference in concentrations between the
base case and control case. Figures 18 and 19 show the composite decrease in ozone
concentrations throughout the area of interest. The decreases shown in these figures
represent the maximum reduction in each grid over the two episodes modelled. These figures
show that the controls assumed in the modelling runs result in a 2-10 ppb reduction in 1-hour
and 8-hour ozone concentrations over nearly the entire area. For a large portion of the domain,
particularly for the Ohio River Valley and surrounding areas in the United States, southern
Ontario, and Sudbury, Canada, the reductions in 1-hour and 8-hour ozone concentrations are
predicted to be greater than 14 ppb.
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130
115
100
85
70
55
40
PPB
FAME
by
MCNC
2007 Base Case
1-hr Episode Composite
8895
160 189
145
80
A
189
Figure 16. 2007 Base Case Episode Composite 1-hr Ozone Concentrations.
130
115
100
85
70
55
40
PPB
FAVE
by
MCNC
2007 Base Case
8-hr Episode Composite
8895
160 189
145
80
I
189
Figure 17. 2007 Base Case Episode Composite 8-hr Ozone Concentrations.
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Control Case — 2007 Base Case
1-hr Episode Composite Decrease
8895

A
189
Figure 18. Episode Composite Decrease in 1-hour Ozone Concentrations Between the
Base Case and the Control Case.
Control Case — 2007 Base Case
8-hr Episode Composite Decrease
8895
FAME
189
Figure 19. Episode Composite Decreases in 8-hour Ozone Concentrations Between the
Base Case and Control Case.
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In order to evaluate whether the reductions shown in Figures 18 and 19 are occurring in the
areas of concern, the predicted maximum decreases that occur in areas that are above
specified threshold levels in the base case were examined, along with predicted maximum
increases in these areas. Figures 20 and 21 show these results for the thresholds considered.
In these figures, the magnitude of decreases or increases is indicated using the colour scale
shown at the left of each figure. The white areas on the maps indicate areas where the base
case predicted ozone concentration is below the specified threshold. The grey areas indicate
areas where the predicted base case ozone concentration is above the threshold, but there are
no decreases or increases above 2 ppb. The thresholds chosen were 82 ppb for 1-hour values,
which is the level of the current Canadian objective and 85 ppb for 8-hour values, which is the
level of the current US 8-hour standard.
The results for the 1-hour 82 ppb and 8-hour 85 ppb thresholds are similar, although the
geographic extent of reductions is somewhat smaller. Decreases are in the range of 10-14 ppb
and higher in a broad area in both the United States and Canada. Increases are similar in
magnitude and location in both cases.
Air Quality Modelling Conclusions
The results of the model runs show that there are substantial benefits to controlling NOx
emissions in the United States and Canada. In the 2007 base case, without any additional
controls, predicted ozone concentrations exceed the Canadian 1-hour objective and the U.S. 8-
hour standard in a large portion of the modelling domain. The assumed reductions forecast for
2007 result in both 1- and 8-hour episode reductions of 6 to over 14 ppb ozone in a corridor
from Michigan/western Ohio/southwestern Ontario to New York and eastern Ontario.
Reductions of 2 to 6 ppb occur in New England states and Quebec. When the evaluation of the
results is restricted to only those areas that are above specific thresholds in the base case,
there are still benefits in the 6-14 ppb range and higher in many areas. The geographic extent
of the benefits that are seen depends on the threshold that is chosen.
The benefits tend to be larger in the United States. This may be due, in part, to the fact that the
emission reductions in the United States are larger both in term of percentage and total mass.
The NOx SIP call strategy that was modelled for the United States results in a 28% reduction in
NOx and the scenario modelled for Canada results in a 12% reduction in NOx and a 14%
reduction in VOC. A control scenario in Canada that resulted in higher percentage reductions
would increase the benefits that would be seen in Canada and the border region. Although the
results also show predicted increases in some areas, they are more limited in geographic extent
and are offset by the larger benefits. In fact, the benefits may be even greater than is indicated
because of the limitation of the modelling domain with respect to Canada's Southern Atlantic
Region and parts of the Windsor-Quebec City Corridor.
In addition, there are other non-ozone benefits that can be expected from widespread NOx
reductions. Decreases in NOx emissions will also decrease acid deposition, nitrates in drinking
water, excessive nitrogen loadings to aquatic and terrestrial ecosystems, and ambient
concentrations of nitrogen dioxide, particulate matter, and toxics.
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Control Case — 2007 Base Case
t-hr (Thresh=82 ppb) Episode Comp. Decrease
8895
—
18
1
,4

1.

G

2

-2

-
,

1

		.
-18
PPB

FAME

by
MCNC
80
189
B
n

1
,4

1.

G

2

-2

-
,
-
i
-14
_
-18
PPB

FAME

by
MCNC
18 189
80
45
Control Case — 2007 Base Case
1-hr fThresh=82 ppb) Episode Comp. Increase
8895
189
Figure 20. Predicted Maximum A) Decreases and B) Increases in 1-hr Ozone
Concentrations in Areas >= 82 ppb in the Base Case.
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A

18
14
10
6
2
-2
-6
-10
-14
-18
PPB
FAME
by
MCNC
Control Case — 2007 Base Case
8-hr (Thresh=85 ppb) Episode Comp. Decrease
8895
189
80
189
B
Control Case — 2007 Base Case
8-hr (Thresh=85 ppb) Episode Comp. Increase
8895
r AVE
MCNC
189
Figure 21. Predicted Maximum A) Decreases and B) Increases in 8-hr Ozone
Concentrations in Areas >= 85 ppb in the Base Case.
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4. POLICY CONCLUSIONS RELEVANT TO THE CONSIDERATION OF
AN OZONE ANNEX BY THE CANADA-U.S. AIR QUALITY COMMITTEE
In eastern North America, ozone levels that exceed established and proposed norms often
occur in large-scale regional episodes that do not respect political borders. Ozone is a reactive
respiratory irritant and is associated with decreases in lung function, aggravation of respiratory
disease, increases in hospital admissions and related health effects. Ozone also causes
damage to forested ecosystems and agriculture. Furthermore, precursors that form ozone
include substances that cause or contribute to acid rain and eutrophication of sensitive
estuaries as well as toxic organic air pollutants.
This document presents results of cooperative efforts to analyse ozone transport in eastern
North America. The approaches taken in the analyses represent an extension into the
transboundary area of concern of analytical techniques, methodologies, and tools already being
used in both countries to address domestic air pollution. They include integrated air quality
data analyses of patterns and episodes, consideration of emissions patterns together with
analyses of ozone as a function of changing meteorological conditions and transport
climatology, and finally, joint modelling of regional scale ozone transport and responses to
control scenarios.
These technical analyses clearly demonstrate the connections between emissions, transport,
and ozone occurrences on both sides of the border. These results strongly support the
common-sense conclusion that coordination of planning and execution of control strategies for
ozone precursors (NOx and VOC) for all source categories would be more beneficial than
individual initiatives.
The United States has made major steps forward in addressing air quality in general and ozone
in particular in recent years. Significant progress has been made in implementing the
provisions of the 1990 Clear Air Act Amendments with respect to ozone precursors. The U.S.
Air Quality Standards for ozone and particulate matter in air have been revised and tightened.
The Ozone Transport Assessment Group (OTAG) successfully completed intergovernmental
negotiations on ozone transport among 37 states. Finally, EPA has finalised a rule concerning
revisions to State Implementation Plans (SIPs) in 22 States and the District of Columbia to
respond to ozone transport through reductions in NOx emissions by 2007. Further actions are
planned with respect to fuel sulphur and vehicular emissions.
In Canada, there have been similar efforts on air quality and ozone. The first and second
phases of the NOxA/OC management program are complete with substantial programs for
major sources of NOx and VOC nationally and in key problem regions aimed at achieving the
current Canadian air quality objective of 1-hour 82 ppb. The Phase 3 Federal Smog Plan is
underway for both ozone and inhalable particles and the Ontario Smog Plan is being
implemented to reduce provincial emissions of NOx and VOC by 45% from 1990 levels by
2015. New sulphur in gasoline regulations are being promulgated and action on vehicular
emissions are planned. Finally, Canadian governments are now engaged in developing, for the
first time, Canada-Wide Standards and implementation plans for ozone and particulate matter
in air.
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The air quality data analyses conducted for this report focused on determining the pattern of
transport in the transboundary area of concern in the eastern United States and Canada. The
results indicate that long-range transport of ozone and its precursors significantly influences the
magnitude and persistence of high ozone concentrations in eastern North America. Air masses
from the United States contribute to high ozone concentrations in Ontario, Quebec, New
Brunswick and Nova Scotia. When winds blow from Canada, the southern shores of Lake Erie
and the eastern shores of Lake Ontario experience high ozone levels. Due to the relative
amounts of emissions in each country and the prevailing winds during the summer ozone
season, more ozone and precursors flow north-northeast from the United States into Canada
than south-southeast from Canada into the United States.
The extended regional air quality modelling conducted for this report demonstrates the
effectiveness of illustrative joint precursor emission reduction strategies on ozone
concentrations in the United States and Canada. The modelling indicates that there are
substantial transboundary regional benefits to controlling NOx emissions in the United States
and Canada. The assumed reductions forecast for 2007 result in both 1- and 8-hour episode
reductions of 6 to over 14 ppb ozone in a corridor from Michigan/western Ohio/southern Ontario
to New York and eastern Ontario. Reductions of 2 to 6 ppb occur in New England states and
Quebec. Although not part of the modelling domain, it can be expected that there would also
be reductions in ozone concentrations in the Southern Atlantic Region of Canada. While these
analyses did not attempt to examine reduced acid deposition, nutrient loadings, and particulate
matter levels that would accompany such strategies, these corollary improvements would
certainly add to the total benefits of these example strategies.
The spatial and temporal patterns exhibited in the analyses of empirical air quality and
emissions data are qualitatively consistent with the results of the air quality modelling analyses.
Taken together, these results offer clear evidence of the rationale for discussing an effective bi-
national approach for management of ozone and its precursors in eastern North America.
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5. REFERENCES
AQC, 1994. United States-Canada Air Quality Agreement: 1994 Progress Report, Air Quality
Committee. (This report is also known as the Canada-United States Air Quality Agreement:
1994 Progress Report.)
AQC, 1996. Canada-United States Air Quality Agreement: 1996 Progress Report, Air Quality
Committee. (This report is also known as the United States-Canada Air Quality Agreement:
1996 Progress Report.)
AQC, 1998. Canada-United States Air Quality Agreement: 1998 Progress Report, Air Quality
Committee. (This report is also known as the United States-Canada Air Quality Agreement:
1998 Progress Report.)
CCME, 1990. Management Plan For Nitrogen Oxides and Volatile Organic Compounds,
Canadian Council of Ministers of the Environment (CCME).
CCME, 1994. Management Plan: Status Report 1994,,Canadian Council of Ministers of the
Environment (CCME).
CEC, 1997. Continental Pollutant Pathways: An Agenda for Co-operation to Address Long
Range Transport of Air Pollution in North America,, Commission for Environmental Co-
operation.
Dann, T., 1999. Ozone, NOx and VOC Analysis 1989-1996,,Environment Canada,
Environmental Technology Centre.
EPA, 1998. "Finding of Significant Contribution and Rulemaking for Certain States in the Ozone
Transport Assessment Group Region for Purposes of Reducing Regional Transport of
Ozone," 63 FR 57356.
Husar, et al., 1999. Ozone as a Function of Local Wind Speed and Direction: Evidence of Local
and Regional Transport,,R.A. Husar, W.P. Renard, B.A. Schichtel,
http://capita.wustl.edu/CAPITA/CapitaReports/03FncQfWind/html/03asFncWnd.html.
IJC, 1998. Special Report on Transboundary Air Quality Issues,,International Joint
Commission.
Multistakeholder, 1997. Canadian 1996 NOxA/OC Science Assessment. Multistakeholder
NOx/VOC Science Program, Environment Canada.
Ground-Level Ozone and Its Precursors,, 1980-1993-Report of the Data Analysis Working
Group
Modelling Of Ground-Level Ozone in the Windsor-Quebec City Corridor and in the
Southern Atlantic Region - Report of the Windsor-Quebec City Corridor and Southern
Atlantic Region Modelling and Measurement Working Group
Modelling of Ground-Level Ozone in the Lower Fraser Valley - Report of the Lower Fraser
Valley Modelling and Measurement Working Group
Summary for Policy Makers: A Synthesis of the Key Results of the NOxA/OC Science
Program
NAICC, 1996. NAICC National Base Case Consensus Forecast,,presented to the NAICC in
May 1996. http://www2.ec.ac.ca/pdb.eft/eft.html.
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NRC, 1991. Rethinking the Ozone Problem in Urban and Regional Air Pollution,, National
Research Council.
OTAG, 1997. uOTAG Technical Supporting Document" http://www.epa.gpv/ttn/otaa/finalrpt.
Schichtel and Husar, 1999. Eastern North America Transport Climatology During Average, High
and Low Ozone Days,,B.A. Schichtel, R.B. Husar,
http://capita.wustl.edu/CAPITA/CapitaReports/NAMTrnsClim/html/NamTrnsClim.html.
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