EVALUATION OF REGIONAL OZONE MONITORING NETWORK AND ANALYSIS OF DATA TO DETERMINE TRENDS

Transcription

1 EVALUATION OF REGIONAL OZONE MONITORING NETWORK AND ANALYSIS OF DATA TO DETERMINE TRENDS Draft Report STI DR2 By: Michael C. McCarthy Joshua P. Shiffrin Theresa E. O Brien Hilary R. Hafner Sonoma Technology, Inc N. McDowell Blvd., Suite D Petaluma, CA Prepared for: Capital Airshed Partnership P.O. Box 4379 Edmonton AB T6E 4T5 February 24, 21

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3 TABLE OF CONTENTS Section Page LIST OF FIGURES...v LIST OF TABLES... vi 1. INTRODUCTION GENERIC OZONE CONCEPTUAL MODEL PRELIMINARY ANALYSIS RESULTS Maximum Ozone Concentration Spatial Maps Analysis of Ozone Titration by NO Wind and Pollution Roses Seasonality in Ozone Episodes Ozone, NO x, and VOC Trends Analysis Ratios of NMHC to NO x Ozone Episode Meteorology and Pollution Analysis SUMMARY OF RESULTS DRAFT FINAL RECOMMENDATIONS APPENDIX A: Additional Plots and Tables of Ozone and NO x... A-1 iii

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5 LIST OF FIGURES Figure Page 2-1. Typical ozone isopleths used in U.S. EPA s Empirical Kinetics Modeling Approach Average number of days per year on which the maximum daily 1-hr average ozone concentration exceeded 72 ppb from April through September Average number of days per year on which the maximum daily 8-hr average ozone concentration exceeded 58 ppb from April through September Relative proportion of 1-hr ozone concentrations above or below 25 ppb for all days from 24 through Example wind rose April through June 6 a.m. to 6 p.m. wind roses for the years 24 to 28 in the Edmonton region July through September 6 a.m. to 6 p.m. wind roses for the years 24 to 28 in the Edmonton region April through June daytime (6 a.m. to 6 p.m.) NO x pollution roses (ppb) for the years 24 to 28 in the Edmonton region July through September daytime (6 a.m. to 6 p.m.) NO x pollution roses (ppb) for the years 24 to 28 in the Edmonton region Ozone episode occurrence frequency (days with 8-hr ozone maximum concentration >58 ppb) by month at Edmonton region monitoring sites 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 Notched box whisker plot of April through September morning (5-8) NO x concentrations (ppb) at Edmonton Central for Notched box whisker plot of summer, 24-hr average, every 6 th day ethylene concentrations (ppbc) at Edmonton Central for Ratio of NMHC/NO x in units of ppbc/ppb at the Lamont County site from 23 through 28 for summer days between 5 a.m. and 8 a.m. LST v

6 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 24 through 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 24 through NO x 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 24 through NO x 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 24 through LIST OF TABLES Table Page 3-1. Data available for key pollutants for the ozone network assessment 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 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 Qualitative summary of annual trends in ozone, NO x, and hydrocarbon data vi

7 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 Society (ACAS), 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 preliminary findings from our analyses and lay out options for the remaining analysis to be performed. Section 4 provides a refined 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). 1-1

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9 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 1 km of the atmosphere (i.e., the troposphere), ozone is a pollutant and harmful to human health. In the atmosphere 1 km to 5 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 ± 1 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 part 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. 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 (NO 2 ) is present in sunlight, it is photolyzed to create NO and O. The radical oxygen atom reacts with oxygen, O 2, to create ozone, O 3. Once formed, O 3 can react with NO to reform O 2 and NO 2. The net reaction from this cycle is an equilibrium of O 3, NO, and NO 2 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 NO x (NO + NO 2 ) 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 possible 4. VOCs are emitted from mobile sources, refineries, chemical plants, dry cleaning, and many other stationary sources that use or produce hydrocarbons. Nitrogen oxides (NO 2 Reid, N., A Review of Background Ozone in the Troposphere, 27 or Monks, 2 3 See Seinfeld and Pandis, Atmospheric Chemistry and Physics, 2 nd Ed. 1998, Chapter 5 for a complete description. 4 especially Session 5 The Basins: Challenges and Solutions Wyoming Jonah/Pinedale series of presentations. 2-1

10 and NO 2 ) come from combustion sources, including power plants, mobile sources, and fires. Titration (i.e., lowering of ozone concentrations) occurs when fresh nitrogen oxide (NO) emissions react with ozone to form NO 2 and oxygen. Ozone titration by NO is typical in the urban core of cities and downwind of large industrial combustion sources, where fresh NO emissions 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 NO x -limited. The ratio of VOCs to NO x 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 NO x. At low VOC/NO x ratios (e.g., < 4 or 5 ppbc/ppb), ozone formation is slow and inefficient (i.e., VOClimited or VOC-sensitive chemistry). Decreasing NO x levels under VOC-sensitive conditions may increase ozone formation. At high VOC/NO x ratios (e.g., > 15 ppbc/ppb), ozone formation is limited by the availability of NOx rather than of VOCs (i.e., NO x -limited or NO x -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 NO x -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,

11 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 local area. This type of site will reap the most benefits from speciated VOC measurements. Fenceline monitors may be maximum precursor emissions sites, 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. 2-3

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13 3. PRELIMINARY 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 extent of the ozone problem and the spatial characteristics of the ozone issue, as well as to identify common patterns 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 initial sets of 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 NO x to help us assess the VOC or NO x 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 25 through 27; thus analysis of data for spatial analyses from this high concentration ozone site was limited to years 24 and 28. Also note that additional historical data were available for some of the Strathcona Industrial Association sites located within the ACAA airshed. However, these data were in formats that were difficult and time-consuming to import into our database and were therefore not used because of schedule and budget considerations. This omission of data will impact only the trends analysis portion of the work. Similarly, passive monitoring data were available only as.pdf files and were not imported into a database. This data omission will primarily impact the spatial analyses, although the passive sampling data are not directly comparable to the continuous measurements. 5 McCarthy M. (29) 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 , 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 VOCs are typically collected as grab samples in canisters. 3-1

14 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 Ozone NO x NMHC Date 1-hr 1-hr 1-hr Other ACAA Edmonton Northwest 1/1/98 12/12/5 x x ACAA Edmonton Central 1/1/98 9/3/9 x x VOCs ACAA Edmonton East 1/1/98 9/3/9 x x VOCs ACAA Edmonton South 9/21/5 9/3/9 x x ACAA Clover Bar 1/1/3 5/29/6 x ACAA Forest Heights 1/1/3 5/23/6 x ACAA Gold Bar 5/25/6 1/1/9 x ACAA Sherwood Park 1/1/3 1/1/9 x THC ACAA Beverly 1/1/3 1/1/9 THC AE Royal Park 7/1/92 5/31/97 x x VOCs FAP Fort Saskatchewan 1/1/98 1/31/9 x x VOCs FAP Lamont County 1/1/3 1/31/9 x x x FAP Elk Island 1/1/3 1/31/9 x VOCs FAP Hwy21TownshipRoad534 7/1/7 9/3/8 x x FAP Range Road 22 1/1/3 1/31/9 x y FAP Ross Creek 1/1/3 1/31/9 x FAP Station 41 1/1/3 1/31/9 x WCAS Breton 4/1/5 1/31/9 x x WCAS Carrot Creek 5/1/98 1/31/9 x x WCAS Genesee 3/1/4 1/31/9 x x WCAS Hightower Ridge 1/1/98 1/31/9 x x VOCs WCAS Steeper 1/1/98 1/31/9 x x WCAS Tomahawk 1/1/98 1/31/9 x x WCAS Violet Grove 1/1/98 1/31/9 x x WCAS Meadows 7/1/4 1/31/9 x WCAS Powers 7/1/4 1/31/9 x WCAS Wagner 7/1/4 1/19/9 x THC = total hydrocarbon As described in our work plan, we performed four preliminary analyses with some minor modifications as data availability allowed. The four analyses were 1. 1-hr, 8-hr average, and maximum ozone concentration spatial maps, 2. NMHC/NO x ratio and NO titration analysis, 3. ozone, NO x, and VOC trends over time, and 4. wind and pollution roses. 3-2

15 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 24 through 28 when concentrations were above 72 ppb Hightower Ridge, Genesee, and Lamont County. Hightower Ridge had an average of 3. 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 standard 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. 3-3

16 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 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 24 through 28 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. 3-4

17 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 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 24 through 28 individually. Some sites did not operate through the entire time period, such as Hightower Ridge (no measurements from 25-27) and Edmonton Northwest (no measurements post-25); no data and zero days are indicated in the tables. 3-5

18 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 Hightower 2 no data no data (only 3 days of data) 4 Carrot Creek Violet Grove 3 1 Tomahawk 1 3 Breton no data 2 Genesee 6 1 Edmonton Northwest no data no data no data Edmonton South no data (only 11 days of data) 1 2 Edmonton Central Edmonton East 1 1 Highway 21 Township Rd. (only 183 no data no data no data 534 days of data) Fort Saskatchewan 2 Lamont County Elk Island 1 3-6

19 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 Hightower 14 no data no data 3 days of data 12 Carrot Creek Violet Grove Tomahawk Breton no data Genesee Edmonton Northwest no data no data no data Edmonton South no data (only 11 days of data) Edmonton Central Edmonton East 2 1 Highway 21 Township (only 183 no data no data no data Rd. 534 days of data) Fort Saskatchewan 1 6 Lamont County Elk Island 3 1 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. 3-7

20 3.2 ANALYSIS OF OZONE TITRATION BY NO High concentrations of NO can reduce ozone concentrations at a monitoring site. NO x 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 fresh NO x emissions, concentrations of ozone increase. Reductions of NO x can thus reduce the ozone titration by NO in urban core areas and actually result in higher ozone concentrations at the previously titrated monitors. Sites upwind of the urban area may be near major NO x sources and can be titrated or not, depending on transport patterns. 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 NO x 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 and below 25 ppb for all days from 24 through 28. 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 1 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 5% 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 1% 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 1% of the time, but none of those monitors reported more than 25% below 25 ppb. The findings for Edmonton suggest that ozone titration by NO is significant at most of the region s ozone monitoring sites Los Angeles is categorized as Severe 17 nonattainment, which is the most severe of any air district in the United States. 3-8

21 3-9 Figure 3-3. Relative proportion of 1-hr ozone concentrations above or below 25 ppb for all days from 24 through 28.

22 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 NO x, 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 24 through 28. 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 NO x pollution roses for the spring and summer months from 24 through 28. 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 NO x pollution roses give some indication of the predominant direction of NO x sources impacting the monitoring sites. Of note, higher NO x concentrations at the Hightower Ridge site are associated with winds from the southeast; higher NO x concentrations at the Power site are associated with winds from the south; higher NO x concentrations at the Wagner and Genesee sites are associated with winds from the northwest wind sector; higher NO x concentrations at the Edmonton NW, S, and E sites are associated with all wind directions; and higher NO x 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 NO x emissions present throughout the urban core. Comparing these NO x pollution roses with a NO x emissions inventory map would provide additional evidence of the sources most likely to be causing high concentrations at each site. 3-1

23 Windspeed Bins (m/s) > 1 >1 2 >2 3 > % 1% 15% 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. 3-11

24 3-12 Figure 3-5. April through June 6 a.m. to 6 p.m. wind roses for the years 24 to 28 in the Edmonton region.

25 3-13 Figure 3-6. July through September 6 a.m. to 6 p.m. wind roses for the years 24 to 28 in the Edmonton region.

26 3-14 Figure 3-7. April through June daytime (6 a.m. to 6 p.m.) NO x pollution roses (ppb) for the years 24 to 28 in the Edmonton region.

27 3-15 Figure 3-8. July through September daytime (6 a.m. to 6 p.m.) NO x pollution roses (ppb) for the years 24 to 28 in the Edmonton region.

28 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 24 through 28. 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 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 regulations assume that all 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

29 percent of days above 58 ppb Hightower > 5% Hightower CarrotCrk VioletGrv Tomahawk Breton Genesee EdmontonS EdmontonC EdmontonE FortSask ElkIsl Lamont month 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, NO X, AND VOC TRENDS ANALYSIS Trend analysis of ozone, NO x, 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., 4 th 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 NO x 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 NO x 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

30 Table 3-4. Qualitative summary of annual trends in ozone, NO x, 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 (1 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. NO x May- Aug., morning NMHC &VOCs ACAA Edmonton Northwest 1/1/98 12/12/5 NT ACAA Edmonton Central 1/1/98 9/3/9 NT most species, total VOC ACAA Edmonton East 1/1/98 9/3/9 NT NT NT ACAA Edmonton South 9/21/5 9/3/9 8-hr max; NT 1-hr max, 4 th high ACAA Clover Bar 1/1/3 5/29/6 X ACAA Forest Heights 1/1/3 5/23/6 X ACAA Gold Bar 5/25/6 1/1/9 X ACAA Sherwood Park 1/1/3 1/1/9 X NT ACAA Beverly 1/1/3 1/1/9 NT AE Royal Park 7/1/92 5/31/97 N/A N/A FAP Fort Saskatchewan 1/1/98 1/31/9 NT NT FAP Lamont County 1/1/3 1/31/9 NT NT FAP Elk Island 1/1/3 1/31/9 NT X X FAP Hwy21TownshipRoad534 7/1/7 9/3/8 X X FAP Range Road 22 1/1/3 1/31/9 N/A NT FAP Ross Creek 1/1/3 1/31/9 X FAP Station 41 1/1/3 1/31/9 N/A WCAS Breton 4/1/5 1/31/9 NT NT WCAS Carrot Creek 5/1/98 1/31/9 NT NT WCAS Genesee 3/1/4 1/31/9 NT NT WCAS Hightower Ridge 1/1/98 1/31/9 NT WCAS Steeper 1/1/98 1/31/9 NT NT WCAS Tomahawk 1/1/98 1/31/9 NT NT WCAS Violet Grove 1/1/98 1/31/9 NT WCAS Meadows 7/1/4 1/31/9 WCAS Powers 7/1/4 1/31/9 NT WCAS Wagner 7/1/4 1/19/9 NT X 3-18

31 For ozone, we investigated three metrics using notched box whisker plots 8 : daily maximum 1-hr, daily maximum 8-hr, and 4 th 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 3-1 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 3-1 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 significant number of hours of ozone concentrations titrated by NO. Thus while the central tendencies are interesting, it is also important to look at the 75 th percentile, upper whisker, and outliers. At most sites, the trends were similar among all metrics. For the more-centrally located Edmonton sites, the 75 th percentile 1-hr concentrations were typically below 5 ppb, which is consistent with the degree of ozone titration shown in Figure 3-3. Sites with less ozone titration tended to have higher 75 th 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 28 were significantly lower than concentrations reported for the other four years of record. The 28 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 2 ppb) should be investigated (in 1998). 8 The box shows the 25 th, 5 th (median), and 75 th 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. 3-19

32 (a) OZONE 1-HR DAILY MAX (ppb) (b) OZONE 1-HR DAILY MAX (ppb) (c) OZONE 1-HR DAILY MAX (ppb) (d) OZONE 1-HR DAILY MAX (ppb) (e) OZONE 1-HR DAILY MAX (ppb) (f) OZONE 1-HR DAILY MAX (ppb) (g) OZONE 1-HR DAILY MAX (ppb) (h) OZONE 1-HR DAILY MAX (ppb) Figure 3-1. 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 Scales for both x and y axes vary among the plots. 3-2

33 (i) OZONE 1-HR DAILY MAX (ppb) (j) OZONE 1-HR DAILY MAX (ppb) (k) OZONE 1-HR DAILY MAX (ppb) (l) OZONE 1-HR DAILY MAX (ppb) (m) OZONE 1-HR DAILY MAX (ppb) (n) OZONE 1-HR DAILY MAX (ppb) Figure 3-1 (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 Scales for both x- and y-axes vary among the plots. 3-21

34 For NO x, we prepared notched box whisker plots of annual trends in hourly concentrations across all days, all mornings (5, 6, 7, 8), and summer mornings. The summer morning NO x 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 NO x emissions and the sources near the monitors. An example NO x trend plot is shown in Figure A complete set of plots for summer mornings is shown in the Appendix. 5 4 NOx (ppb) Figure Notched box whisker plot of April through September morning (5-8) NO x concentrations (ppb) at Edmonton Central for For VOCs, we investigated three sites with 24-hr, every 6 th 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 1 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 , a downward step change in concentration between 1998 and 1999, and no trend for For overall VOC (sum of all reported concentrations), the trend was down. An example trend plot is shown in Figure Ethylene concentrations showed a different pattern, with a downward trend from and then no trend from I-butane showed no trend and toluene concentrations declined over time. Step changes are relatively dramatic and lead to questioning whether there was a real change in ambient concentrations due to changes in fuel formulations or nearby source emissions, or whether the concentration change was a result of laboratory analytical differences between the two time periods. 3-22

35 2 ethylene (ppbc) Figure Notched box whisker plot of summer, 24-hr average, every 6 th day ethylene concentrations (ppbc) at Edmonton Central for 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 21 and 22 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, i-butane, 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 NO x 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 NO X As noted in the introduction, the relative levels of volatile organic compounds (VOCs) to NO x (NO + NO 2 ) can be used to describe whether a given receptor is VOC-limited or NO x - limited. As shown in Figure 2-1, ozone formation is slower when the ratio of VOC/NO x 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 NO x may be most effective. In contrast, the VOC- and NO x -limited regimes indicate that controlling either NO x 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 NO x

36 limited while downwind monitors may be VOC-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 NO x. 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/NO x 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/NO x ratios in units of ppbc/ppb from 23 through 28 for summer mornings from 5 a.m. through 8 a.m. The median ratio from 24 through 26 is just above 5 ppbc/ppb but dips to zero in 27 and 28. 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 27 NMHC values because more than 9% of available summertime morning concentrations were reported as zero at this site. However, more than 5% of reported observations in the data from 28 and 29 (not shown) indicated 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. 5 4 NMHC_NOX Figure Ratio of NMHC/NO x in units of ppbc/ppb at the Lamont County site from 23 through 28 for summer days between 5 a.m. and 8 a.m. LST. 3-24

37 3.7 OZONE EPISODE METEOROLOGY AND POLLUTION ANALYSIS If ozone episode days have significantly 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 NO x 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 standard 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. 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 significant 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 NO x 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 NO x concentrations. Genesee and Breton appear to have lower or similar NO x 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 22, and HWY 21 Township Rd. sites in FAP have higher episode day concentrations. Quantitative comparisons of concentrations among the high NO x sites in ACAA and FAP are not possible with these figures, although the directional changes are clear. 3-25