EVALUATION OF REGIONAL OZONE MONITORING NETWORK AND ANALYSIS

OF DATA TO DETERMINE TRENDS

Final Report STI-909049-3811-FR

By: Michael C. McCarthy

Joshua P. Shiffrin Theresa E. O’Brien

Hilary R. Hafner Sonoma Technology, Inc.

1455 N. McDowell Blvd., Suite D Petaluma, CA 94954-6503

Prepared for: Capital Airshed Partnership

P.O. Box 4379 Edmonton AB T6E 4T5

March 11, 2010

iii

TABLE OF CONTENTS

Section Page LIST OF FIGURES .........................................................................................................................v LIST OF TABLES......................................................................................................................... vi

1. INTRODUCTION.............................................................................................................. 1-1

2. GENERIC OZONE CONCEPTUAL MODEL ................................................................. 2-1

3. ANALYSIS RESULTS...................................................................................................... 3-1 3.1 Maximum Ozone Concentration Spatial Maps......................................................... 3-3 3.2 Analysis of Ozone Titration by NO.......................................................................... 3-8 3.3 Wind and Pollution Roses ...................................................................................... 3-10 3.4 Seasonality in Ozone Episodes............................................................................... 3-16 3.5 Ozone, NOx, and VOC Trends Analysis ................................................................ 3-17 3.6 Ratios of NMHC to NOx......................................................................................... 3-23 3.7 Ozone Episode Meteorology and Pollution Analysis............................................. 3-25

4. SUMMARY OF RESULTS............................................................................................... 4-1

5. FINAL RECOMMENDATIONS ...................................................................................... 5-1

APPENDIX A: Supplementary Plots and Tables of Ozone and NOx ....................................... A-1

v

LIST OF FIGURES

Figure Page

2-1. Typical ozone isopleths used in U.S. EPA’s Empirical Kinetics Modeling Approach.......................................................................................................................... 2-2

3-1. Average number of days per year on which the maximum daily 1-hr average ozone concentration exceeded 72 ppb from April through September 2004-2008.................... 3-4

3-2. Average number of days per year on which the maximum daily 8-hr average ozone concentration exceeded 58 ppb from April through September 2004-2008.................... 3-5

3-3. Relative proportion of 1-hr ozone concentrations above or below 25 ppb for all days from 2004 through 2008 .......................................................................................... 3-9

3-4. Example wind rose......................................................................................................... 3-11

3-5. April through June 6 a.m. to 6 p.m. wind roses for the years 2004 to 2008 in the Edmonton region............................................................................................................ 3-12

3-6. July through September 6 a.m. to 6 p.m. wind roses for the years 2004 to 2008 in the Edmonton region...................................................................................................... 3-13

3-7. April through June daytime (6 a.m. to 6 p.m.) NOx pollution roses (ppb) for the years 2004 to 2008 in the Edmonton region. ................................................................. 3-14

3-8. July through September daytime (6 a.m. to 6 p.m.) NOx pollution roses (ppb) for the years 2004 to 2008 in the Edmonton region. ........................................................... 3-15

3-9. Ozone episode occurrence frequency (days with 8-hr ozone maximum concentration >58 ppb) by month at Edmonton region monitoring sites ...................... 3-17

3-10. Notched box whisker plots of daily maximum 1-hr ozone concentrations (ppb) for April through September 1998-2009 ............................................................................. 3-20

3-11. Notched box whisker plot of April through September morning (0500-0800) NOx concentrations (ppb) at Edmonton Central for 1998-2005. ........................................... 3-22

3-12. Notched box whisker plot of summer, 24-hr average, every 6th day ethylene concentrations (ppbC) at Edmonton Central for 1996–2009......................................... 3-23

3-13. Ratio of NMHC/NOx in units of ppbC/ppb at the Lamont County site from 2003 through 2008 for summer days between 5 a.m. and 8 a.m. LST. .................................. 3-24

3-14. Wind roses for summertime 6 a.m. to 6 p.m. days where at least one monitor reported a 1-hr ozone concentration above 65 ppb from 2004 through 2008................ 3-26

vi

LIST OF FIGURES

Figure Page

3-15. Wind roses for summertime 6 a.m. to 6 p.m. days where at least one monitor reported an 8-hr ozone concentration above 58 ppb from 2004 through 2008.............. 3-27

3-16. NOx pollution roses for summertime 6 a.m. to 6 p.m. days where at least one monitor reported a 1-hr ozone concentration above 65 ppb from 2004 through 2008................................................................................................................................ 3-28

3-17. NOx pollution roses for summertime 6 a.m. to 6 p.m. days where at least one monitor reported an 8-hr ozone concentration above 58 ppb from 2004 through 2008................................................................................................................................ 3-29

LIST OF TABLES

Table Page

3-1. Data available for key pollutants for the ozone network assessment .............................. 3-2

3-2. Number of days on which the site had the highest ozone concentration when the peak 1-hr ozone concentration anywhere in the network was above 72 ppb................... 3-6

3-3. Number of days on which the site had the highest ozone concentration when the peak 8-hr average ozone concentration anywhere in the network was above 58 ppb. .... 3-7

3-4. Qualitative summary of annual trends in ozone, NOx, and hydrocarbon data............... 3-18

1-1

1. INTRODUCTION

Sonoma Technology, Inc. (STI) contracted with the Alberta Capital Airshed Alliance (ACAA)1 on behalf of the Capital Airshed Partnership (CAP) to assess the suitability of the ozone monitoring network in the Edmonton area and analyze related trends in ozone and ozone precursors. CAP consists of members from Fort Air Partnership (FAP), Alberta Capital Airshed Alliance, West Central Airshed (WCAS), and Alberta Environment. The first objective is to determine whether the current air monitoring network is adequate for providing an understanding of ozone formation and transport in the Edmonton Census Metropolitan Area (CMA) and the surrounding areas. Factors in this determination include the suitability of measurements of ozone and key ozone precursors upwind, in source areas, and downwind of the Edmonton region. The second objective is to assess trends in ozone and/or ozone precursors to determine whether future exceedances of the Alberta Ambient Air Quality Objectives or the Canada-Wide Standard (CWS) for ozone are likely.

For this study, the STI team worked with the CAP technical team to understand the findings and implications of previous ozone studies and modeling work performed in the Edmonton area, developed a conceptual model of the ozone phenomena and the current monitoring network, identified potential gaps in the current network, and performed analyses built on past work to fill in knowledge gaps when possible. The results of this work provide a basis to decide whether additional monitoring or analyses are necessary to further refine a conceptual model of ozone formation and transport in the Edmonton CMA. Finally, we provide the CAP technical team with recommendations for modifications to the ozone network, as well as ideas for more comprehensive analyses that could be performed in the future to better understand ozone formation and transport in the Edmonton area.

The remainder of this report consists of four sections. In Section 2, we discuss generic ozone network design considerations based on the most-common ozone conceptual model. In Section 3, we discuss findings from our analyses and lay out options for the remaining analysis to be performed. Section 4 provides a summary of results and some small refinements to our ozone conceptual model for the Edmonton region. Finally, Section 5 lays out a series of network recommendations in priority order to help characterize and understand the extent and nature of the ozone problem in the Edmonton-area airsheds.

1 Through funding from Alberta Environment (AENV).

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2. GENERIC OZONE CONCEPTUAL MODEL

A conceptual model is a mental model of a phenomenon. In this case, the conceptual model describes the physical and chemical processes that form and transport ozone in general as they may apply to the Edmonton region. The conceptual model for the Edmonton-area airsheds is partly based on a generic ozone conceptual model developed as part of the U.S. Environmental Protection Agency’s (EPA) Photochemical Assessment Monitoring Stations (PAMS). We list some key components of a generic ozone conceptual model and methods for monitoring ozone transport and formation:

Ozone is present naturally in the atmosphere. In the lower 10 km of the atmosphere (i.e., the troposphere), ozone is a pollutant and harmful to human health. In the atmosphere 10 km to 50 km above the earth’s surface, ozone is beneficial because it helps block ultraviolet rays (i.e., the ozone layer in the stratosphere).

Natural northern hemisphere background ozone concentrations are typically 35 ± 10 ppb.2 Background concentrations typically peak in the springtime, known in the literature as “springtime maximum.” Given the Alberta Ozone Management Plan threshold trigger level of an 8-hr average ozone concentration of 58 ppb, background ozone can clearly be a substantial fraction of the ozone problem, assuming air transported into the Edmonton-area airsheds is typical of natural background conditions. This assumption is likely but may not be true. The 58 ppb level is an action threshold trigger set to initiate action to prevent a CWS exceedance. Note that springtime days during which background ozone is higher than 58 ppb do not count towards the trigger threshold and are removed from consideration by Alberta Environment.

High ozone concentrations can occur as a result of transport from areas of high pollution, stratospheric intrusions, or secondary production from nearby pollution sources.

Ozone is a secondary pollutant in the troposphere—it is created from photochemical reactions of other precursor pollutants rather than emitted directly. When nitrogen dioxide (NO2) is present in sunlight, it is photolyzed to create NO and O. The radical oxygen atom reacts with oxygen, O2, to create ozone, O3. Once formed, O3 can react with NO to reform O2 and NO2. The net reaction from this cycle is an equilibrium of O3, NO, and NO2 that depends on sunlight (i.e., clear skies).

The presence of volatile organic compounds (VOCs) in the atmosphere leads to production of ozone from additional hydroxyl radical reaction chemistry that goes beyond the depth of this memorandum.3 The relative levels of hydrocarbon and NOx (NO + NO2) in the atmosphere, along with the presence of solar radiation, will determine the ozone concentrations. While warm temperatures favor many of the chemical reactions that drive typical ozone chemistry, recent examples from Wyoming indicate that cold weather ozone formation is also possible4.

2 Reid, N., A Review of Background Ozone in the Troposphere, 2007 http://www.ene.gov.on.ca/en/publications/air/6424e.pdf or Monks, 2000 3 See Seinfeld and Pandis, Atmospheric Chemistry and Physics, 2nd Ed. 1998, Chapter 5 for a complete description. 4 http://www.awma.org/proceedings/airqualityimpacts2009.html especially Session 5 The Basins: Challenges and Solutions – Wyoming Jonah/Pinedale series of presentations.

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VOCs are emitted from mobile sources, refineries, chemical plants, dry cleaning, and many other stationary sources that use or produce hydrocarbons. Nitrogen oxides (NO and NO2) come from combustion sources, including power plants, mobile sources, and fires.

Titration (i.e., lowering of ozone concentrations) occurs when nitrogen oxide (NO) reacts with ozone to form NO2 and oxygen. Ozone titration by NO is typical in the urban core of cities and downwind of large industrial combustion sources, where NO concentrations are often highest. One indicator of ozone titration by NO is that ozone concentrations are below the natural background levels.

The development of emission control strategies is based on assessments of whether an area is “VOC-limited” or “NOx-limited.” The ratio of VOCs to NOx in the morning is an important indicator for photochemical systems. This ratio characterizes the efficiency of ozone formation in air mixtures containing both VOCs and NOx. At low VOC/NOx ratios (e.g., < 4 or 5 ppbC/ppb), ozone formation is slow and inefficient (i.e., VOC-limited or VOC-sensitive chemistry). Decreasing NOx levels under VOC-sensitive conditions may increase ozone formation. At high VOC/NOx ratios (e.g., > 15 ppbC/ppb), ozone formation is limited by the availability of NOx rather than of VOCs (i.e., NOx-limited or NOx-sensitive chemistry). An example ozone isopleth plot is shown in Figure 2-1.

Figure 2-1. Typical ozone isopleths used in U.S. EPA’s Empirical Kinetics Modeling Approach (EKMA). The NOx-limited region is typical of locations downwind of urban and suburban areas, whereas the VOC-limited region is typical of highly polluted urban areas. Source: Adapted from Dodge, 1977, shown in Rethinking the Ozone Problem in Urban and Regional Air Pollution, National Academy Press, 1991.

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Conceptually, an ozone monitoring network is often comprised of four types of monitoring sites to characterize different parts of an airshed. These sites are classified as upwind, maximum (or representative) precursor emissions, maximum ozone concentration (downwind), and extreme downwind.

– Upwind sites are established to characterize ozone and precursor emissions being transported into the area. These sites should be located near the upwind edge of the photochemical grid model domain. They help characterize the extent of background influence on urban-scale concentrations of ozone and precursors.

– Maximum (or representative) precursor emissions sites are useful for characterizing the magnitude and type of precursor emissions representative of the urban area. This type of site will reap the most benefits from speciated VOC measurements. Fenceline monitors in an urban area may meet the criteria of a maximum precursor emissions site, although they may not be representative of the regional-scale mixture.

– Maximum ozone concentration sites are situated to monitor the highest ozone concentrations downwind of the maximum precursor emission area. These sites are typically located 15 to 45 km downwind of the fringe of the urban area. Downwind is the predominant direction daytime winds blow during ozone season. However, these distances and directions are sensitive to the meteorological conditions present during ozone episodes. If winds are stagnant or point in a different direction during episodes, maximum ozone concentration sites will require different siting criteria. Multiple sites may be needed to characterize the location of the maximum ozone concentrations if the meteorological conditions are split among a few large-scale meteorological regimes.

– Extreme downwind sites can be useful for characterizing the transported ozone well downwind, which may contribute to ozone concentrations in other jurisdictions. These sites should be located downwind of the predominant afternoon wind direction and may be near the downwind edge of the photochemical grid model domain.

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3. ANALYSIS RESULTS

STI used available monitoring data from the Edmonton airsheds (ACAA, FAP, and WCAS) to perform multiple separate analyses on the ozone monitoring network. These analyses are meant to explain the spatial, meteorological, and chemical characteristics of high ozone concentrations, as well as to identify common large-scale spatial and meteorological phenomena of ozone formation to help refine the preliminary Edmonton region ozone conceptual model developed in our previous technical memorandum.5 In this section, we give a brief overview of the available monitoring data and summarize the analysis methods and results from our analyses.

Table 3-1 provides an overview of the monitoring data available for these analyses. Sites with continuous ozone measurements were of primary importance. Additionally, we were interested in any sites measuring nonmethane hydrocarbons (NMHCs) or volatile organic compounds (VOCs)6 and NOx to help us assess the VOC or NOx sensitivity within the region and to assess trends in precursor concentrations over time. Note that while we indicate the first and last date that data were available for a given site, some sites did not monitor continuously throughout the entire time indicated. Of particular interest, no ozone measurements were available from Hightower Ridge from 2005 through 2007; thus analysis of data for spatial analyses from this high concentration ozone site was limited to years 2004 and 2008. Also note that additional historical data were available for some of the Strathcona Industrial Association sites located within the ACAA airshed and for passive monitoring data in the WCAS and ACAA airsheds. However, these data were in formats that were difficult and time-consuming to import into our database and would have been useful in only a few of the analyses in this section. These data were not imported because of schedule and budget considerations. The omission of SIA data will impact only the trends analysis portion of the work. Similarly, the passive monitoring. data omission will primarily impact the spatial analyses, although the passive sampling data are not directly comparable to the continuous measurements.

5 McCarthy M. (2009) Initial conceptual model and network recommendations. Technical memorandum prepared for the Alberta Capital Airshed Alliance, Edmonton, Alberta, Canada, by Sonoma Technology, Inc., Petaluma, CA, STI-909049-3764, November. 6 NMHC and VOC refer to speciated hydrocarbon measurements. Precise definitions of these two terms are based on operational and analytical differences. NMHC data are often collected on a continuous basis (i.e., hourly) while speciated VOCs are often collected as 24-hr duration grab samples in canisters.

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Table 3-1. Data available for key pollutants for the ozone network assessment. An x indicates the site had that data available directly, a y indicates the data could be calculated, and a blank indicates that no data of that type were available.

Airshed Site First Date Last Date

Ozone 1-hr

NOx

1-hr NMHC

1-hr Other

ACAA Edmonton Northwest 1/1/98 12/12/05 x x ACAA Edmonton Central 1/1/98 9/30/09 x x VOCs ACAA Edmonton East 1/1/98 9/30/09 x x VOCs ACAA Edmonton South 9/21/05 9/30/09 x x ACAA Clover Bar 1/1/03 5/29/06 x ACAA Forest Heights 1/1/03 5/23/06 x ACAA Gold Bar 5/25/06 1/1/09 x ACAA Sherwood Park 1/1/03 1/1/09 x THC ACAA Beverly 1/1/03 1/1/09 THC AE Royal Park 7/1/92 5/31/97 x x VOCs FAP Fort Saskatchewan 1/1/98 10/31/09 x x VOCs FAP Lamont County 1/1/03 10/31/09 x x x FAP Elk Island 1/1/03 10/31/09 x x VOCs FAP Hwy21TownshipRoad534 7/1/07 9/30/08 x x FAP Range Road 220 1/1/03 10/31/09 x y FAP Ross Creek 1/1/03 10/31/09 x FAP Station 401 1/1/03 10/31/09 x WCAS Breton 4/1/05 10/31/09 x x WCAS Carrot Creek 5/1/98 10/31/09 x x WCAS Genesee 3/1/04 10/31/09 x x WCAS Hightower Ridge 1/1/98 10/31/09 x x VOCs WCAS Steeper 1/1/98 10/31/09 x x WCAS Tomahawk 1/1/98 10/31/09 x x WCAS Violet Grove 1/1/98 10/31/09 x x WCAS Meadows 7/1/04 10/31/09 x WCAS Powers 7/1/04 10/31/09 x WCAS Wagner 7/1/04 1/19/09 x

THC = total hydrocarbon

We performed the following analyses:

1. 1-hr, 8-hr average, and maximum ozone concentration spatial maps

2. NO titration of ozone analysis

3. Wind and NOx pollution roses for spring and summer time periods

4. An assessment of ozone episode seasonality

5. A trends analysis of ozone, NOx, and speciated VOCs

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6. NMHC/NOx ratios to determine NOx or VOC-limitation

7. Summer ozone episode wind and pollution roses

3.1 MAXIMUM OZONE CONCENTRATION SPATIAL MAPS

Spatial maps of ozone concentrations using exposure metrics during the ozone season (March through August) provide an awareness of where high ozone events occur in an airshed. Additionally, they can be used to show where ozone concentrations are highest during episode events and to explain the spatial patterns of ozone pollution. Figures 3-1 and 3-2 are spatial maps showing the number of days in which the 1-hr or 8-hr average ozone exceeded 72 or 58 ppb, respectively, at sites in the Edmonton regional airsheds. Figure 3-1 shows the number of days per year on which 1-hr average ozone concentrations above 72 ppb occurred. Only three sites had an average of more than two days per year from 2004 through 2008 when concentrations were above 72 ppb—Hightower Ridge, Genesee, and Lamont County. Hightower Ridge had an average of 3.0 days per year, while Lamont County had 2.5 and Genesee had 2.6 days. The sites in the ACAA airshed reported the fewest days above 72 ppb. Note that the Alberta Environment 1-hr ozone objective is 82 ppb, but too few observations over the time period of interest exceeded this value, so a lower threshold was used to provide better resolution. The low number of observations above 72 ppb and somewhat flat spatial variation indicate that the infrequent high 1-hr ozone peak concentrations do not appear to be local-scale events, but rather are more regional in nature.

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Figure 3-1. Average number of days per year on which the maximum daily 1-hr average ozone concentration exceeded 72 ppb from April through September 2004-2008. Table 3-1 lists data availability. Symbol sizes do not indicate area affected.

Figure 3-2 shows the number of days per year on which 8-hr average ozone concentrations were above 58 ppb. Three sites averaged at least 12 days per year from 2004 through 2008 with 8-hr average ozone concentrations above 58 ppb: Hightower Ridge, Tomahawk, and Violet Grove. In general, the WCAS airshed sites reported far more days on which ozone concentrations were above the 58 ppb action level than either the ACAA or FAP sites.

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Figure 3-2. Average number of days per year on which the maximum daily 8-hr average ozone concentration exceeded 58 ppb from April through September 2004-2008. Table 3-1 lists data availability.

We also investigated the number of days per year that an individual site reported the highest concentration across the entire region when the ozone concentration at any site exceeded 72 ppb for 1-hr average (Table 3-2) or 58 ppb for an 8-hr average (Table 3-3), respectively. We looked at the number of days for each year from 2004 through 2008 individually. Some sites did not operate through the entire time period, such as Hightower Ridge (no measurements from 2005-2007) and Edmonton Northwest (no measurements post-2005); “no data” and zero days are indicated in the tables.

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Table 3-2. Number of days on which the site had the highest ozone concentration when the peak 1-hr ozone concentration anywhere in the network was above 72 ppb.

Site 2004 2005 2006 2007 2008

Hightower 2 no data no data 0 (only 30

days of data) 4

Carrot Creek 1 0 3 2 0 Violet Grove 0 0 3 1 0 Tomahawk 0 0 1 0 3 Breton no data 0 0 2 0 Genesee 0 0 6 1 0 Edmonton Northwest 0 0 no data no data no data

Edmonton South no data 0 (only 101

days of data) 0 1 2

Edmonton Central 0 0 0 0 0 Edmonton East 1 0 0 1 0 Highway 21 Township Rd. 534

no data no data no data 0 (only 183

days of data) 0

Fort Saskatchewan 0 0 0 2 0 Lamont County 2 0 3 1 3 Elk Island 0 0 0 0 1

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Table 3-3. Number of days on which the site had the highest ozone concentration when the peak 8-hr average ozone concentration anywhere in the network was above 58 ppb.

Site 2004 2005 2006 2007 2008

Hightower 14 no data no data 30 days of data 12

Carrot Creek 3 2 7 4 0

Violet Grove 1 12 9 2 1

Tomahawk 3 6 3 3 15

Breton no data 2 3 4 0

Genesee 7 1 10 6 0

Edmonton Northwest 0 0 no data no data no data

Edmonton South no data 0 (only

101 days of data)

1 2 1

Edmonton Central 0 0 0 0 0

Edmonton East 2 0 0 1 0 Highway 21 Township Rd. 534

no data no data no data 0 (only 183

days of data) 0

Fort Saskatchewan 0 0 0 1 6

Lamont County 2 0 8 1 7

Elk Island 0 3 0 1 0

The 1-hr average ozone concentrations were rarely above 72 ppb. When ozone concentrations were above 72 ppb, the highest concentrations were most likely to occur at one of the WCAS sites such as Hightower Ridge, Carrot Creek, and Genesee, or at Lamont County. The likelihood that the highest concentration would be recorded at the FAP sites of Elk Island and Fort Saskatchewan was much lower. This finding is relatively consistent with Figure 3-1 in the locations exhibiting the most-frequent high ozone concentrations.

The 8-hr average ozone concentrations were somewhat likely to exceed 58 ppb at many of the WCAS sites. When the 8-hr average ozone concentrations were above 58 ppb, the highest concentrations were most frequently at Hightower Ridge but were also likely at Tomahawk, Genesee, or Violet Grove. Among the eastern sites, Lamont County reported the highest frequency of 8-hr average concentrations exceeding 58 ppb. Once again, the likelihood that the highest concentrations would be seen at the FAP sites of Elk Island or Fort Saskatchewan was much lower. This finding is relatively consistent with Figure 3-2 in the locations exhibiting the most-frequent high ozone concentrations.

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3.2 ANALYSIS OF OZONE TITRATION BY NO

High concentrations of NO can reduce ozone concentrations at a monitoring site. NOx can be a source or a sink of ozone, depending on its relative availability. In urban core areas where precursor emissions are highest, ozone concentrations are often reduced through titration by NO. As air is transported away from areas of NO emissions, concentrations of ozone increase. Identifying sites where ozone titration by NO is frequent can indicate whether a monitoring site is appropriately located to meet monitoring objectives. If a site is intended to be a maximum ozone monitoring site, it should be placed away from areas of local NOx emissions.

In Figure 3-3, we display the fraction of daily maximum 1-hr ozone concentrations at each site in the region that are above or below 25 ppb for all days from 2004 through 2008. If ozone at the site is titrated by NO, the site will report a large fraction of ozone concentrations below the natural background level. We selected 25-ppb ozone as a conservative indication of titration because this level is 10 ppb below typical background concentrations. All sites reported at least 33% of ozone measurements below 25 ppb, with the notable exception of Hightower Ridge, which reported only 6%. All the sites in the ACAA airshed and the Fort Saskatchewan site reported at least 50% of their ozone measurements below 25 ppb. To put this set of numbers in perspective, Los Angeles, California, (where mobile sources dominate the emission inventory) has the worst ozone problem in the U.S.7 and only 3 of 15 ozone monitors report more than 10% of measurements below 25 ppb. A second and possibly more applicable comparison is Houston, Texas, which is heavily influenced by a large petrochemical industry. Half of that city’s monitors reported ozone concentrations below 25 ppb 10% of the time, but none of those monitors reported more than 25% below 25 ppb. The fraction of time ozone levels are below 25 ppb suggests that ozone titration by NO is significant at most of the region’s ozone monitoring sites.

7 http://www.epa.gov/air/oaqps/greenbk/gnc.html - Los Angeles is categorized as Severe 17 nonattainment, which is the most severe of any air district in the United States.

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Figure 3-3. Relative proportion of 1-hr ozone concentrations above or below 25 ppb for all days from 2004 through 2008.

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3.3 WIND AND POLLUTION ROSES

Wind roses are used to examine wind direction and speed. Pollution roses illustrate pollutant concentrations as a function of wind direction. For a primary pollutant like NOx, pollution roses can point in the direction of major sources. For secondary pollutants like ozone, pollution roses may indicate transport patterns or upwind source regions that are conducive to ozone formation. Wind and pollution rose analyses are used to identify meteorologically relevant transport regimes and source areas. Additionally, they are used to identify monitoring locations upwind of emissions source areas likely to be most useful for characterizing transport and maximum ozone concentrations. Figure 3-4 provides an example wind rose.

Figures 3-5 and 3-6 show daytime wind roses for spring (April, May, and June) and summer (July, August, and September) monitoring data from 2004 through 2008. Wind roses at each site point to the directions from which the wind originates. The length of the bar indicates the frequency the wind originates from that direction. The four colors indicate wind speeds, with light blue and black indicating relatively high winds, and purple and teal indicating more stagnant conditions.

In Figure 3-5, most of the monitoring sites show a predominant wind direction originating from the northwest quadrant. Some sites, such as Hightower Ridge and Carrot Creek, show a more-westerly component, while Tomahawk, Genesee, and Edmonton sites experience more northwesterly winds. Overall, most wind speeds are greater than 3 m/s, which are relatively high. Figure 3-6 shows a similar overall pattern and directionality relatively consistent across the two periods, but the wind speeds are considerably lower in the summer months than in the spring. In our generic ozone conceptual model, we anticipate that stagnant air with low wind speeds will be more conducive to ozone formation than high wind speeds and will therefore predict higher ozone concentrations in the summer.

Figures 3-7 and 3-8 show daytime NOx pollution roses for the spring and summer months from 2004 through 2008. Wind roses at each site point to the directions from which the wind originates. The length of the bar indicates the frequency at which the wind originates from that direction. The colors indicate the concentration of a pollutant associated with winds from that direction. Pollution roses can sometimes be used to identify the predominant direction from which emissions sources are located relative to the monitoring site. High concentrations originating predominantly from a single direction associated with a specific emissions source can provide useful evidence of emission source impacts.

The NOx pollution roses give some indication of the predominant direction of NOx sources impacting the monitoring sites. Of note, higher NOx concentrations at the Hightower Ridge site are associated with winds from the southeast; higher NOx concentrations at the Power site are associated with winds from the south; higher NOx concentrations at the Wagner and Genesee sites are associated with winds from the northwest wind sector; higher NOx concentrations at the Edmonton NW, S, and E sites are associated with all wind directions; and higher NOx concentrations at the Fort Saskatchewan and Hwy 21 Township Rd. sites are associated with southerly winds. The findings for the Edmonton sites are consistent with the mixture of mobile source and industrial NOx emissions present throughout the urban core. Comparing these NOx pollution roses with a NOx emissions inventory map would provide additional evidence of the sources most likely to be causing high concentrations at each site.

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0

45

90

135225

270

315

5% 10% 15%

Windspeed Bins (m/s)

>0 ‐ 1

>1 ‐ 2

>2 ‐ 3

>3

Figure 3-4. Example wind rose. A wind rose provides a summary of wind patterns for a specific time period at a surface meteorological site. The size of the triangle emanating from the center of the wind rose indicates the percentage of time winds are from a specific direction (position on axes), and the wind speed time percentages are indicated with color bins along the length of the triangle.

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Figure 3-5. April through June 6 a.m. to 6 p.m. wind roses for the years 2004 to 2008 in the Edmonton region.

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Figure 3-6. July through September 6 a.m. to 6 p.m. wind roses for the years 2004 to 2008 in the Edmonton region.

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Figure 3-7. April through June daytime (6 a.m. to 6 p.m.) NOx pollution roses (ppb) for the years 2004 to 2008 in the Edmonton region.

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Figure 3-8. July through September daytime (6 a.m. to 6 p.m.) NOx pollution roses (ppb) for the years 2004 to 2008 in the Edmonton region.

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3.4 SEASONALITY IN OZONE EPISODES

Ozone season and spatial patterns can help indicate the likely cause of high ozone occurrences. Anthropogenic ozone typically occurs during the warmest months of the year, although this condition is not a requirement because wintertime anthropogenic ozone episodes have been documented in oil and gas extraction areas in Southwest Wyoming. Additionally, springtime ozone episodes in the Alps in Europe have been associated with stratospheric intrusions of ozone, not anthropogenic intrusions.

Figure 3-9 illustrates the percentage of days on which a site reported 8-hr average ozone concentrations above 58 ppb by month from 2004 through 2008. A clear bimodal distribution of seasonal patterns is seen in this figure. In springtime, many high ozone concentrations occur in April and May at Hightower Ridge, dropping to a few occurrences during the summer. All WCAS sites (in orange) show a peak number of occurrences in April and May, although none of the sites stand out as much as Hightower Ridge. The ACAA and FAP sites also experience ozone episodes in these months, but the frequency of occurrence is much lower than at the WCAS sites.

In contrast, a July peak also occurs in ozone episodes at ACAA sites, with no corresponding occurrence of ozone episodes at Hightower Ridge. This summer “peak” happens at low frequencies at all the sites.

The two distinct modes of ozone episodes suggest different mechanisms by which ozone episodes occur. In the springtime mode, the predominance of ozone episodes at Hightower Ridge and west of Edmonton, which oppose the prevailing wind direction, suggests ozone episodes are not a result of emissions from the Edmonton urban area or its nearby industrial sources. In fact, 8 of the 11 sites shown in Figure 3-9 experience a higher frequency of 8-hr average ozone concentrations exceeding 58 ppb during the spring than during the summer. It is possible that these episodes are stratospheric intrusions or high background ozone. However, the focus of this assessment is not on the springtime mode because the provincial ozone assessment has found that generally, most springtime episodes are non-anthropogenic. Therefore, the monitoring network assessment is focused on characterizing ozone during the summertime mode (personal communication with K. Friesen).

The summertime ozone mode exhibits different spatial characteristics than the springtime mode. The low ozone episode frequency at Hightower Ridge in the summer relative to the episode occurrences in the central parts of the region suggests local or regional Edmonton area emissions are more important during the summer episodes. This time period is examined further in meteorological and pollution analysis of these summertime episodes in Section 3.6.

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VioletGrv

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Breton

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Figure 3-9. Ozone episode occurrence frequency (days with 8-hr ozone maximum concentration >58 ppb) by month at Edmonton region monitoring sites. Orange sites are in the WCAS airshed, blue in the ACAA airshed, and green in the FAP airshed.

3.5 OZONE, NOX, AND VOC TRENDS ANALYSIS

Trend analysis of ozone, NOx, and VOC was performed with available monitoring data at each site. Trends in ozone for the ozone season were identified for both the 1-hr and 8-hr maximum metrics (i.e., 4th highest maximum concentration and daily maximum values). These metrics are relevant for ozone and demonstrate the likelihood of future CWS exceedances. Trends in VOCs and NOx were identified by using notched box whisker plots to show the distribution of concentrations of these pollutants with a focus on the summer for 24-hr average VOCs and summer mornings for the hourly NOx data. Morning ozone season concentrations of precursors are better indicators of emissions and their long-term trends than concentrations later in the day that may be diluted by increased mixing (i.e., higher mixing heights and higher wind speeds). A qualitative summary of findings is provided in Table 3-4.

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Table 3-4. Qualitative summary of annual trends in ozone, NOx, and hydrocarbon data. Up arrow and green highlighting indicate upward trend, down arrow and yellow highlighting indicate downward trend, “NT” indicates no significant trend in the median concentration, “N/A” indicates data were either insufficient resolution to investigate (10 ppb increments) or not processed (lower priority data sets), and “X” indicates insufficient data were available for a trend analysis (less than 5 years).

Airshed Site First Date

Last Date

Ozone April-Sept.

NOx May-Aug.,

morning

NMHC &VOCs

ACAA Edmonton Northwest 1/1/98 12/12/05 NT ↓ ACAA Edmonton Central 1/1/98 9/30/09 NT ↓ ↓ most

species, total VOC

ACAA Edmonton East 1/1/98 9/30/09 NT NT NT ACAA Edmonton South 9/21/05 9/30/09 ↑ 8-hr max;

NT 1-hr max, 4th

high

X

ACAA Clover Bar 1/1/03 5/29/06 X ACAA Forest Heights 1/1/03 5/23/06 X ACAA Gold Bar 5/25/06 1/1/09 X ACAA Sherwood Park 1/1/03 1/1/09 X NT ACAA Beverly 1/1/03 1/1/09 NT AE Royal Park 7/1/92 5/31/97 N/A N/A FAP Fort Saskatchewan 1/1/98 10/31/09 NT NT FAP Lamont County 1/1/03 10/31/09 NT NT ↓ FAP Elk Island 1/1/03 10/31/09 NT X X FAP Hwy21TownshipRoad534 7/1/07 9/30/08 X X FAP Range Road 220 1/1/03 10/31/09 N/A NT FAP Ross Creek 1/1/03 10/31/09 X FAP Station 401 1/1/03 10/31/09 N/A WCAS Breton 4/1/05 10/31/09 NT NT WCAS Carrot Creek 5/1/98 10/31/09 NT NT WCAS Genesee 3/1/04 10/31/09 NT NT WCAS Hightower Ridge 1/1/98 10/31/09 NT ↑ WCAS Steeper 1/1/98 10/31/09 NT NT WCAS Tomahawk 1/1/98 10/31/09 NT NT WCAS Violet Grove 1/1/98 10/31/09 NT ↑ WCAS Meadows 7/1/04 10/31/09 ↑ WCAS Powers 7/1/04 10/31/09 NT WCAS Wagner 7/1/04 1/19/09 NT

3-19

For ozone, we investigated three metrics using notched box whisker plots8: daily maximum 1-hr, daily maximum 8-hr, and 4th highest 8-hr maximum concentrations. We looked qualitatively for differences in central tendencies such as the median, interquartile range, and outliers. Most sites showed no discernible trend. Edmonton South 8-hr average concentrations showed a slight upward trend, but this trend was not observed in the other metrics. Figure 3-10 shows the daily maximum 1-hr ozone concentration trend plots. Similar plots for maximum daily 8-hr average ozone concentration trends are shown in the Appendix.

The concentration plots in Figure 3-10 are also useful for inspecting the relative concentration differences among sites. By grouping all data from April through September, we include high ozone concentrations from both potential stratospheric intrusion (April and May) and anthropogenic events. In future investigations of these data, it may be important to separate these months. The following observations were made:

All the plots include the number of hours of ozone concentrations titrated by NO. Thus while the central tendencies are interesting, it is also important to look at the 75th percentile, upper whisker, and outliers. At most sites, the trends were similar among all metrics.

For the more-centrally located Edmonton sites, the 75th percentile 1-hr concentrations were typically below 50 ppb, which is consistent with the degree of ozone titration shown in Figure 3-3. Sites with less ozone titration tended to have higher 75th percentile concentrations. However, the peak 1-hr concentrations (typically depicted as x’s and o’s on the plots) were similar across the network. A cursory review of the 1-hr data showed the high concentration days did not necessarily coincide among sites.

The ozone concentrations at Breton in April through September 2008 were significantly lower than concentrations reported for the other four years of record. The 2008 data record seems anomalously low. No other site showed this concentration pattern and the data should be further investigated.

One very high 1-hr ozone concentration outlier at Violet Grove (nearly 200 ppb) should be investigated (in 1998).

8 The box shows the 25th, 50th (median), and 75th percentiles. The whiskers have a maximum length equal to 1.5 times the length of the box (the interquartile range, IQR). If data are outside the IQR, points are identified with asterisks representing the points that fall within three times the IQR from the end of the box and circles representing points beyond. The boxes are notched (narrowed) at the median and return to full width at the 95% lower and upper confidence interval values. These plots indicate that we are 95% confident that the median falls within the notch. Confidence intervals are a function of sample size; small sample size will increase these intervals.

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Figure 3-10. Notched box whisker plots of daily maximum 1-hr ozone concentrations (ppb) for April through September at (a) Breton, (b) Hightower Ridge, (c) Carrot Creek, (d) Edmonton Central, (e) Edmonton East, (f) Edmonton NW, (g) Edmonton South, (h) Elk Island, (i) Fort Saskatchewan, (j) Genesee, (k) Steeper, (l) Tomahawk, (m) Violet Grove, and (n) Lamont County for 1998-2009. Scales for both x and y axes vary among the plots.

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Figure 3-10 (continued). Notched box whisker plots of daily maximum 1-hr ozone concentrations (ppb) for April through September at (a) Breton, (b) Hightower Ridge, (c) Carrot Creek, (d) Edmonton Central, (e) Edmonton East, (f) Edmonton NW, (g) Edmonton South, (h) Elk Island, (i) Fort Saskatchewan, (j) Genesee, (k) Steeper, (l) Tomahawk, (m) Violet Grove, and (n) Lamont County for 1998-2009. Scales for both x- and y-axes vary among the plots.

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For NOx, we prepared notched box whisker plots of annual trends in hourly concentrations across all days, all mornings (0500, 0600, 0700, 0800), and summer mornings. The summer morning NOx concentrations showed more interannual variability than the peak ozone concentrations. Focusing on summer morning data, some sites showed no trend, some a slight decline in concentrations, and some a slight increase. This paints a very complex picture of NOx emissions and the sources near the monitors. An example NOx trend plot is shown in Figure 3-11. A complete set of plots for summer mornings is shown in the Appendix.

1995 2000 2005 2010YEAR

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x (p

pb )

Figure 3-11. Notched box whisker plot of April through September morning (0500-0800) NOx concentrations (ppb) at Edmonton Central for 1998-2005.

For VOCs, we investigated three sites with 24-hr, every 6th day, speciated data: Edmonton Central, Edmonton East, and Elk Island (the first two sites had the longest record of data). We focused on summer trends of the most abundant species. The 10 most-abundant species are essentially the same species with different order of abundance among sites and are the same abundant species as the PAMS sites in the U.S. At Edmonton Central, ethane, propane, butane, pentane, benzene, xylenes, and acetylene concentrations showed no trend for 1991–1998, a downward step change in concentration between 1998 and 1999, and no trend for 1999–2009. For overall VOC (sum of all reported concentrations), the trend was down. An example trend plot is shown in Figure 3-12. Ethylene concentrations showed a different pattern, with a downward trend from 1995–2004 and then no trend from 2005–2009. Isobutane showed no trend and toluene concentrations declined over time. Step changes are relatively dramatic and lead to questioning why there was a change in ambient concentrations (e.g., due to changes in fuel formulations or nearby source emissions).

3-23

1990 1995 2000 2005 2010YEAR

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ylen

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ppbC

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Figure 3-12. Notched box whisker plot of summer, 24-hr average, every 6th day ethylene concentrations (ppbC) at Edmonton Central for 1996–2009.

Concentrations of many of the abundant VOCs at Edmonton East were higher than at Edmonton Central, which may be expected for a site located closer to the major industrial area of Edmonton. There was a similar step change in the concentration data, but the change occurred in different years than at Edmonton Central. For example, at Edmonton East, ethane and acetylene concentrations showed a downward step change in concentration between 2001 and 2002 with no trend in concentrations before and after the change. Ethylene concentrations at Edmonton East were lower than at Edmonton Central and no change over time was observed. For other abundant species, including propane, butane, isobutane, benzene, toluene, and xylenes, and for the total VOC, no trend was observed at Edmonton East.

Overall, no trend was apparent in ozone and mixed results (up, down, no trend) in NOx concentrations at the monitoring sites. Similarly, little trend is found at most sites with the more limited VOC data. This indicates it is unlikely that ozone concentrations will decline in the future under these conditions.

3.6 RATIOS OF NMHC TO NOX

As noted in the introduction, the relative levels of volatile organic compounds (VOCs) to NOx (NO + NO2) can be used to describe whether a given receptor is VOC-limited or NOx-limited. As shown in Figure 2-1, ozone formation is slower when the ratio of VOC/NOx is less than 5 ppbC/ppb or greater than 15 ppbC/ppb. Ratios between 5 and 15 ppbC/ppb are transitional, which is an area where controlling both VOC and NOx may be most effective. In contrast, the VOC- and NOx-limited regimes indicate that controlling either NOx or VOC is most effective, and reducing emissions of non-limiting pollutant may actually increase concentrations of ozone. Note that this analysis is receptor specific; monitors near the urban core may be

3-24

VOC-limited while downwind monitors may be NOx-limited because of differences in photochemical processing as pollution is transported away from emissions sources.

In the Edmonton region, only two monitoring sites routinely reported concentrations of the sum of VOCs alongside measurements of NOx. These measurements were of the nonmethane hydrocarbon (NMHC). While multiple sites measured speciated VOCs, the speciated measurements did not also contain a summed value across all identified and unidentified species, thus rendering these measurements unusable for a VOC/NOx ratio analysis. Future VOC measurements could be more effective for this type of analysis by including a total nonmethane organic compound (TNMOC) and unidentified VOC measurement report for each canister.

Figure 3-13 shows the trend in NMHC/NOx ratios in units of ppbC/ppb from 2003 through 2008 for summer mornings from 5 a.m. through 8 a.m. The median ratio from 2004 through 2006 is just above 5 ppbC/ppb but dips to zero in 2007 and 2008. These data are from the Lamont County monitor, which is one of the sites on the eastern periphery of the monitoring network. However, the data from this site clearly show that even a site this far from the urban core is VOC-limited. Note that there was a step change in 2007 NMHC values because more than 90% of available summertime morning concentrations were reported as zero at this site. However, more than 50% of reported observations in the data from 2008 and 2009 (not shown) indicated 0 ppbC of NMHC. This could be due to a baseline shift in the instrument response. However, if these observations are accurate, the area is clearly VOC-limited.

2002 2003 2004 2005 2006 2007 2008 2009YEAR

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NM

HC

_NO

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Figure 3-13. Ratio of NMHC/NOx in units of ppbC/ppb at the Lamont County site from 2003 through 2008 for summer days between 5 a.m. and 8 a.m. LST.

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3.7 OZONE EPISODE METEOROLOGY AND POLLUTION ANALYSIS

If ozone episode days have different meteorology than non-episode days, typical patterns in VOCs and NOx may not be representative of ozone events. The basic approach of this analysis is to compare meteorology and NOx concentrations on ozone episode days versus typical days to assess differences in concentrations and timing of peak levels. In this analysis, we chose a subset of summer ozone episode days to compare wind roses and pollution roses for NOx with the summer wind rose and pollution rose maps in Section 3.3. Two threshold levels were chosen for this analysis. The 1-hr maximum ozone concentration level chosen was 65 ppb. This level is not relevant for any regulatory objective but does provide sufficient counts of days to perform the analysis. The 8-hr maximum ozone concentration level chosen was 58 ppb, which is the trigger level chosen for other analyses in this report.

Figures 3-14 and 3-15 display wind roses for the subsets of summer daytime winds from 6 a.m. to 6 p.m. local standard time (LST) that had at least one monitor report a 1-hr ozone concentration above 65 ppb or an 8-hr ozone concentration above 58 ppb, respectively. Both figures have a striking similarity and have a substantial overlap between the days that comprise each figure. Comparing either of these figures to Figure 3-6 displays an obvious difference in wind direction and speed. Ozone episode days are comprised of days with light southerly winds for all sites closest to the Edmonton urban area. Where Figure 3-6 had the highest frequency of days with high winds from the northwest and west, the ozone episode days nearly reverse this flow with light winds from the south and southeast. This wind pattern is consistent with air that previously passed over the Edmonton region in previous days being recirculated and impacting the region on subsequent days.

Figures 3-16 and 3-17 display NOx pollution roses for the subsets of summer daytime winds from 6 a.m. to 6 p.m. LST that had at least one monitor report a 1-hr ozone concentration above 65 ppb or an 8-hr ozone concentration above 58 ppb, respectively. These figures can be compared to Figure 3-8. The same directional shift is seen as in Figures 3-14 and 3-15 because, in terms of direction, a pollution rose has a 1:1 correspondence with a wind rose. WCAS sites including Carrot Creek, Power, Wagner, Violet Grove, and Tomahawk have higher NOx concentrations. Genesee and Breton appear to have lower or similar NOx concentrations on episode days, which may be a result of less influence from nearby emissions sources when winds are from the southeast. Similarly, the Fort Saskatchewan, Range Road 220, and HWY 21 Township Rd. sites in FAP have higher episode day concentrations. Quantitative comparisons of concentrations among the high NOx sites in ACAA and FAP are not possible with these figures, although the directional changes are clear.

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Figure 3-14. Wind roses for summertime 6 a.m. to 6 p.m. days where at least one monitor reported a 1-hr ozone concentration above 65 ppb from 2004 through 2008.

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Figure 3-15. Wind roses for summertime 6 a.m. to 6 p.m. days where at least one monitor reported an 8-hr ozone concentration above 58 ppb from 2004 through 2008.

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Figure 3-16. NOx pollution roses for summertime 6 a.m. to 6 p.m. days where at least one monitor reported a 1-hr ozone concentration above 65 ppb from 2004 through 2008.

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Figure 3-17 NOx pollution roses for summertime 6 a.m. to 6 p.m. days where at least one monitor reported an 8-hr ozone concentration above 58 ppb from 2004 through 2008.

4-1

4. SUMMARY OF RESULTS

The current monitoring network has many praiseworthy features: a large number of sites are in place, most sites collect collocated ozone and NOx measurements, measurements are made year round, some sites collect speciated VOC and other hydrocarbon measurements, many sites collect surface meteorological measurements, and sites collect several years of data.

The number of days with daily peak ozone concentrations (8-hr averages above 58 ppb or 1-hr averages above 72 ppb) is highest on the periphery of the monitoring network (e.g., Hightower Ridge, Tomahawk, and Lamont County sites), as shown in Figures 3-1 and 3-2.

– Hightower Ridge records the greatest frequency of high ozone concentration days on the western side of the Edmonton metropolitan area, with many high concentration days occurring in April and May.

– Lamont County and Elk Island are farthest east of the Edmonton CMA and record the greatest frequency of high ozone concentration days on the eastern side.

– Ozone episodes during springtime occur most frequently at the Hightower Ridge site, with a decreasing number of episodes occurring to the east. However, most sites show more daily 8-hr average concentrations above 58 ppb in the spring than in the summer. July/August high ozone concentrations occur at similar rates across the FAP, ACAA, and WCAS airsheds. These episodes suggest a different mechanism for high 8-hr average ozone days in spring and summer.

– Springtime ozone concentrations at Hightower Ridge are likely a natural phenomenon and may be a result of naturally high background concentrations, high elevation, and/or stratospheric intrusions. These different mechanisms would have different spatial characteristics that could be examined by performing additional analyses. However, this ozone monitoring network focuses only on summer episodes, which are more likely to be of anthropogenic origin.

Ozone concentrations within the Edmonton CMA are usually low for a number of reasons:

– Ozone concentrations at most monitoring sites are titrated by fresh NO emissions.

– Edmonton’s daytime temperatures are usually not very high. Although ozone can form at lower temperatures, ozone formation is faster at higher temperatures.

– Topographically, the area around Edmonton is relatively flat, although the river valleys may channel wind flows. Thus, pollutants can disperse easily and are usually not trapped near Edmonton.

4-2

Most of the ozone measured at the sites is being titrated by NO.

– Monitors downwind of major NOx sources will have low ozone concentrations.

– Monitors located in the urban core near major roadways will have low ozone concentrations.

– Monitors located downwind of large power plants will report low ozone concentrations when they are in the emissions plume.

– The time that ozone monitors record concentrations below 25 ppb (i.e., well below natural background) at Edmonton region sites was far greater than in Los Angeles or Houston.

Winds during the summer months are predominantly from the west-northwest; winds during summer ozone episodes are much more frequently from the south and southeast than during typical summer days.

– Portions of the upwind direction and most of the predominant downwind areas have poor monitoring coverage of ozone and ozone precursor concentrations for typical summer days.

– Most upwind directions and portions of the predominant downwind areas have poor monitoring coverage of ozone and ozone precursor concentrations relative to ozone episode days.

Upwind ozone being transported into Edmonton is being titrated by NO, and concentrations are often below remote background concentrations on typical days. Days during which ozone episodes occur have higher NOx concentrations than typical days without such episodes, but predominant wind direction is shifted, and background ozone concentrations on these days are not available due to lack of spatial coverage.

Peak ozone concentrations from anthropogenic sources are probably not captured by the current monitoring network because sites are not far enough downwind of the urban CMA or in the correct direction downwind of the source areas. This is true for all days and for days on which ozone episodes are typical, even though the wind patterns are different.

Although the CASA data warehouse had a significant fraction of all measurements, the analyses performed in this network assessment required a substantial amount of additional data processing to merge multiple datasets from different sources in different data formats. Additionally, some data were left out due to time and money considerations because they were available only in hard-to-manipulate formats like .pdf files. Future analyses would benefit from having all the data available in a single format from a single source.

5-1

5. FINAL RECOMMENDATIONS

Some of the monitors collecting ozone routinely titrated by NO should be relocated to sites less influenced by large NOx sources, possibly even to the recommended upwind or downwind locations, unless they are intended to monitor community exposure.

Additional upwind and downwind monitors are needed for the Edmonton CMA. At a minimum, these sites should measure ozone, NOx, and meteorological parameters. Given the predominant wind patterns in Edmonton, as shown in Figures 3-5 through 3-8 and 3-14 and 3-15, these monitors should be located west-northwest, south, southeast, and east of the Edmonton urban fringe.

– An additional upwind site that is not at high elevation and not influenced by the power plants west of the city would be useful to measure typical background ozone outside the Edmonton CMA. This site may also end up being the peak ozone site on episode days as wind flows reverse. The ideal location for this site would be northwest of Edmonton, with potential locations at Sandy Beach, Barrhead, or as far northwest as Swan Hills.

– Two or more monitors may be needed to capture the transport and formation of ozone downwind of Edmonton. One or two sites should be located south to east-southeast of the city at a distance of 20 to 50 km from the edge of the eastern/southeastern boundary of Edmonton. An additional monitor a few hundred km downwind would be useful to help constrain model boundary conditions and evaluate the extreme downwind concentrations of ozone.9 Note that these sites may end up being upwind monitors on ozone episode days. Possible downwind locations include Millet, New Sarepta, and Tofield. A far-downwind site could be located on the arc described by the Hughenden, Edgerton, or Lloydminster areas.

– Adding some measure of VOCs would be helpful at both upwind and near-downwind sites to constrain boundary conditions for models and determine whether the area is NOx or VOC limited. Total nonmethane hydrocarbon (NMHC) measurements (with 100 ppbC resolution) may work and are relatively inexpensive. Speciated VOC measurements are more useful but far more expensive. The list of speciated VOCs should reflect the source mixture expected for the Edmonton area (common alkanes such as butanes, pentanes; aromatics such as toluene, benzene, xylenes; alkenes such as 1,3-butadiene, ethylene, propylene) and potential background (e.g., ethane, propane) or biogenic markers (e.g., isoprene) and potentially include photo-oxidized species such as formaldehyde and acetaldehyde.

The area of highest ozone concentrations is probably typically located east-southeast of the city and beyond the current range of monitors. A short-term passive ozone and NOx monitoring study that attempts to map ozone gradients to the northwest, east, and southeast of the city boundaries would be useful for determining the best placement of permanent downwind maximum ozone concentration monitoring site(s). At a minimum, a maximum ozone concentration monitoring site should be at least 20 km downwind and

9 Distances from EPA PAMS site descriptions website. http://www.epa.gov/oar/oaqps/pams/general.html

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potentially 200 km downwind of the Strathcona Industrial Area and the southeastern boundary of the CMA.

Current hydrocarbon measurements are spatially and temporally insufficient to determine the spatial extent over which Edmonton ozone is VOC- or NOx-limited. Adding NMHC measurements to upwind and downwind sites would help meet this goal. Alternatively, highly time-resolved (i.e., less than 4-hr duration) canister monitoring of VOCs could be performed during ozone episodes (episodic monitoring). If canisters are used, early morning measurements are needed to resolve source mixture, while afternoon measurements are useful for identifying photochemical transformation and transport.

– An NMHC monitor at the upwind site could be compared to urban NMHC monitors to assess local/regional contribution of NMHC emissions. An NMHC monitor at downwind sites would help identify when urban area emissions are transported to the downwind site. Instrument resolution needs to be sufficient to distinguish concentrations as low as 10 ppbC.

– Speciated VOC measurements at a downwind site could help constrain model photochemistry by identifying the key hydrocarbon species concentrations in the afternoon plume. These measurements may also be used to assess photochemical processing by comparing them to urban area measurements. Make sure to include total nonmethane organic compounds (TNMOC) and unidentified VOC as additional parameters in the measurement suite to make these measurements suitable for assessing VOC- or NOx-sensitivity.

At least one monitor located in an area of high precursor emissions should measure speciated hydrocarbons. While periodic (e.g., every third day) 24-hr average data are useful over the long term to assess emissions trends, higher time resolution data (e.g., daily or hourly) are needed to better understand emission sources, transport, and photochemistry. An automatic gas chromatograph (auto-GC) or GC monitor for 4 to 6 species would provide the most data for the dollar, but summa canisters can be used as well. These measurements would be useful for validating emission inventories, constraining model inputs and outputs, and performing case study analyses of hydrocarbon concentrations on episode days. The current list of target hydrocarbons in the Edmonton area is comprehensive. The key species relevant to ozone formation (based on ozone formation potential10 and relative abundance) include ethylene, propylene, xylenes, toluene, i-pentane, isoprene, and trimethylbenzenes.

Consider measuring other photochemically produced species such as formaldehyde (also important to ozone formation) and acetaldehyde at upwind, maximum precursor emission, and downwind sites. These pollutants can be very useful for identifying transport and emission patterns of photochemically active plumes.

Summer ozone episodes may be a result of recirculation of air aloft. If aloft winds blow to the east-northeast during the night, aged Edmonton area emissions could mix down into the surface layer in the morning when winds reverse. Aloft ozone formation has been seen in other areas where the titrated surface layer is decoupled from the aloft

10 Carter W.P.L. (1994) Development of ozone reactivity scales for volatile organic compounds. J. Air & Waste Manag. Assoc. 44, 881-899.

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boundary layer at night. Upper-air meteorological measurements (sodar or radar wind profilers) or tower measurements of meteorology, ozone, and NOx may be useful for identifying ozone formation and recirculation aloft.11,12 This hypothesis is consistent with (but not proved by) the reversal of surface winds seen in the ozone episodes analysis in Section 3-7.

Potential recommended follow-on analyses:

– Perform source apportionment on VOC data at the Edmonton sites to better constrain local source mixture of pollutants. Performing this analysis can also help identify differences between emission inventory speciation and ambient profiles (i.e., relative abundance of hydrocarbons).

– Perform conditional probability analyses of NOx to identify NOx sources influencing current monitor locations.

– Compare diurnal profiles during summer episode days at all sites to examine spatial differences in ozone concentrations and the degree of titration of ozone by NO.

Data management recommendation:

– All data collected from the CAP area should be reported to a single data archive in a single data format. The data format should be a “vertical” database structure rather than a cross-tabbed structure.

11 Hanna S.R., MacDonald C.P., Lilly M., Knoderer C.A., and Huang C.H. (2006) Analysis of three years of boundary layer observations over the Gulf of Mexico and its shores. Estuarine, Coastal and Shelf Science 70, 541-550. 12 Real time data available as example at http://profilerops.sonomatechdata.com/scaqmd/map.jsp

A-1

APPENDIX A

SUPPLEMENTARY PLOTS AND TABLES OF OZONE AND NOx

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30

40

50

60

70

80

OZ

ON

E 8

-HR

AV

G D

AIL

Y M

AX

(p

pb)

Figure A-1. Notched box whisker plots of daily maximum 8-hr average ozone concentrations (ppb) for April through September at (a) Breton, (b) Hightower Ridge, (c) Carrot Creek, (d) Edmonton Central, (e) Edmonton East, (f) Edmonton NW, (g) Edmonton South, (h) Elk Island, (i) Fort Saskatchewan, (j) Genesee, (k) Steeper, (l) Tomahawk, (m) Violet Grove, and (n) Lamont County for 1998-2009. Scales for both x and y axes vary among the plots.

A-4

(g)

2004 2005 2006 2007 2008 2009 2010YEAR

0

10

20

30

40

50

60

70

80O

ZO

NE

8-H

R A

VG

DA

ILY

MA

X (

pp b

)

(h)

2002 2003 2004 2005 2006 2007 2008 2009 2010YEAR

0

10

20

30

40

50

60

70

80

OZ

ON

E 8

-HR

AV

G D

AIL

Y M

AX

(pp

b)

(i)

1995 2000 2005 2010YEAR

0

10

20

30

40

50

60

70

80

OZ

ON

E 8

-HR

AV

G D

AIL

Y M

AX

(p

pb)

(j)

2003 2004 2005 2006 2007 2008 2009 2010YEAR

0102030405060708090

OZ

ON

E 8

-HR

AV

G D

AIL

Y M

AX

(p

pb)

(k)

1995 2000 2005 2010YEAR

0

10

20

30

40

50

60

70

80

OZ

ON

E 8

-HR

AV

G D

AIL

Y M

AX

(pp

b)

(l)

1995 2000 2005 2010YEAR

0102030405060708090

OZ

ON

E 8

-HR

AV

G D

AIL

Y M

AX

(p

pb)

Figure A-1 (continued). Notched box whisker plots of daily maximum 8-hr average ozone concentrations (ppb) for April through September at (a) Breton, (b) Hightower Ridge, (c) Carrot Creek, (d) Edmonton Central, (e) Edmonton East, (f) Edmonton NW, (g) Edmonton South, (h) Elk Island, (i) Fort Saskatchewan, (j) Genesee, (k) Steeper, (l) Tomahawk, (m) Violet Grove, and (n) Lamont County for 1998-2009. Scales for both x and y axes vary among the plots.

A-5

(m)

1995 2000 2005 2010YEAR

0

20

40

60

80

100

120

OZ

ON

E 8

-HR

AV

G D

AIL

Y M

AX

(pp

b)

(n)

2002 2003 2004 2005 2006 2007 2008 2009 2010YEAR

0

10

20

30

40

50

60

70

80

OZ

ON

E 8

-HR

AV

G D

AIL

Y M

AX

(pp

b)

Figure A-1 (continued). Notched box whisker plots of daily maximum 8-hr average ozone concentrations (ppb) for April through September at (a) Breton, (b) Hightower Ridge, (c) Carrot Creek, (d) Edmonton Central, (e) Edmonton East, (f) Edmonton NW, (g) Edmonton South, (h) Elk Island, (i) Fort Saskatchewan, (j) Genesee, (k) Steeper, (l) Tomahawk, (m) Violet Grove, and (n) Lamont County for 1998-2009. Scales for both x and y axes vary among the plots.

A-6

(a)

2004 2005 2006 2007 2008 2009 2010YEAR

0102030405060708090

100

NO

x (p

pb)

(b)

1995 2000 2005 2010YEAR

0102030405060708090

100

NO

x (p

pb)

(c)

1995 2000 2005 2010YEAR

0

10

20

30

40

50

60

70

NO

x (p

pb)

(d)

1995 2000 2005 2010YEAR

0

100

200

300

400

500

NO

x (p

pb)

(e)

1995 2000 2005 201YEAR

0

100

200

300

400

500

NO

x (p

pb)

(f)

1997 1998 1999 2000 20012002 2003 2004 2005 2006YEAR

0

100

200

300

400

500N

Ox

(pp

b )

Figure A-2. Notched box whisker plots of April through September morning (0500-0800) 1-hr NOx concentrations (ppb) at (a) Breton, (b) Hightower Ridge, (c) Carrot Creek, (d) Edmonton Central, (e) Edmonton East, (f) Edmonton NW, (g) Edmonton South, (h) Elk Island, (i) Fort Saskatchewan, (j) Genesee, (k) Steeper, (l) Tomahawk, (m) Violet Grove, (n) Lamont County, (o) Meadows, (p) Powers, and (q) Wagner for 1998-2009. Other sites with only three or four years of data were omitted from this figure. Scales for both x and y axes vary among the plots.

A-7

(g)

2004 2005 2006 2007 2008 2009 2010YEAR

0

50

100

150

200

NO

x (p

pb)

(h)

2005 2006 2007 2008 2009 2010YEAR

0

10

20

30

NO

x (p

pb)

(i)

1995 2000 2005 2010YEAR

0

100

200

300

NO

x (p

pb)

(j)

2003 2004 2005 2006 2007 2008 2009 201YEAR

0

10

20

30

40

NO

x (p

pb)

(k)

1995 2000 2005 2010YEAR

0

10

20

30

40

NO

x (p

pb)

(l)

1995 2000 2005 201YEAR

0

10

20

30

40

50N

Ox

(ppb

)

Figure A-2 (continued). Notched box whisker plots of April through September morning (0500-0800) 1-hr NOx concentrations (ppb) at (a) Breton, (b) Hightower Ridge, (c) Carrot Creek, (d) Edmonton Central, (e) Edmonton East, (f) Edmonton NW, (g) Edmonton South, (h) Elk Island, (i) Fort Saskatchewan, (j) Genesee, (k) Steeper, (l) Tomahawk, (m) Violet Grove, (n) Lamont County, (o) Meadows, (p) Powers, and (q) Wagner for 1998-2009. Other sites with only three or four years of data were omitted from this figure. Scales for both x and y axes vary among the plots.

A-8

(m)

1995 2000 2005 2010YEAR

0

10

20

30

40

50

NO

x (p

pb)

(n)

2002 2003 2004 2005 2006 2007 2008 2009 2010YEAR

0

10

20

30

40

50

NO

x ( p

pb)

(o)

2003 2004 2005 2006 2007 2008 2009 2010YEAR

0

50

100

150

NO

x (p

pb)

(p)

2003 2004 2005 2006 2007 2008 2009 2010YEAR

0

10

20

30

NO

x (p

p b)

(q)

2003 2004 2005 2006 2007 2008 2009YEAR

0

10

20

30

40

50

NO

x (p

pb)

Figure A-2 (continued). Notched box whisker plots of April through September morning (0500-0800) 1-hr NOx concentrations (ppb) at (a) Breton, (b) Hightower Ridge, (c) Carrot Creek, (d) Edmonton Central, (e) Edmonton East, (f) Edmonton NW, (g) Edmonton South, (h) Elk Island, (i) Fort Saskatchewan, (j) Genesee, (k) Steeper, (l) Tomahawk, (m) Violet Grove, (n) Lamont County, (o) Meadows, (p) Powers, and (q) Wagner for 1998-2009. Other sites with only three or four years of data were omitted from this figure. Scales for both x and y axes vary among the plots.

A-9

Table A-1. Counts of days per year at all sites with 1-hr maximum ozone concentrations exceeding 82 ppb.

Site 2004 2005 2006 2007 2008

Hightower 0 No data No data 0 (30 days of data) 2



Tomahawk 0 0 0 0 1

Breton No data 0 0 2 0

Genesee 0 0 1 0 0


Edmonton East 1 0 0 0 0

Edmonton South No data

0 (101 days of data)

1 1 1

Fort Saskatchewan 0 0 1 0 0

Lamont County 1 0 2 0 0

Elk Island 0 0 1 0 0

Table A-2. Counts of days per year at sites with 8-hr maximum ozone concentrations exceeding 65 ppb.

Site 2004 2005 2006 2007 2008

Hightower 4 No data No data 0 (30 days of data) 25



Tomahawk 0 0 4 0 11

Breton No data 0 3 4 0

Genesee 1 0 7 4 0

Edmonton Northwest 1 0 No data No data No data


Edmonton South No data 0 (101 days of data) 0 2 3

Edmonton East 2 0 0 3 1

Fort Saskatchewan 1 1 0 1

Lamont County 3 4 0 4

Elk Island 1 2 0 1

A-10

(a)

0 10 20 30 40 50NOX

0

10

20

30

40

O3

(b)

0 50 100 150 200NOX

0

10

20

30

40

O3

(c)

0 10 20 30NOX

0

10

20

30

40

O3

(d)

0 50 100 150NOX

0

10

20

30

40

O3

Figure A-3. Bar chart comparisons of average ozone concentrations (ppb) below 35 ppb with NOx concentrations (ppb) in 1 ppb bins for summer 2004-2008 at (a) Carrot Creek, (b) Edmonton Central, (c) Breton, and (d) Fort Saskatchewan monitors.

This appendix figure was added to illustrate the significance of NO titration as a factor at sites well outside the Edmonton urbanized area. Figure A-3 shows the average ozone concentration as a function of NOx concentrations at four sites; NOx concentrations at (a) Carrot Creek and (c) Breton are relatively low, while NOx concentrations at (b) Edmonton Central and (d) Fort Saskatchewan are relatively high. This analysis was performed only for ozone concentrations at or below natural background concentrations, restricting all ozone concentrations to those below 35 ppb, regardless of NOx concentration. The inverse relationship between O3 average concentrations and NOx average concentrations is clear. Higher NOx concentrations are reducing average ozone concentrations at these sites. This relationship is clear even at the lowest levels of NOx measured. It is common for urban areas to act as net sinks of ozone.13

13 See Seinfeld and Pandis, Atmospheric Chemistry and Physics, 2nd Ed. 1998, page 94.

evaluation of regional ozone monitoring network …

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