Appendix B

Weight-of-Evidence Analysis San Joaquin Valley Air Basin: Ozone

### (This page intentionally left blank.)May 30, 2007 Appendix B 1 Appendix B

Weight-of-Evidence Analysis San Joaquin Valley Air Basin: Ozone

Introduction

Under federal law, the San Joaquin Valley Air Basin (San Joaquin Valley, SJV, Valley, or Basin) is currently classified as a Seri ous nonattainment area for the

federal 8-hour ozone standard. This classification requires attainment by June 15, 2013. Given the magnitude of emissions re ductions needed to reach attainment, including reductions relying on new or the improvement of existing control technologies, it is not likely the Valley w ill meet the 2013 attainment date. In such cases, the federal Clean Air Act allows, an d U.S. EPA recommends, bumping-up to an appropriate higher classification with a later attainment date. Based on analyses, an Extreme classification, with an attainment date of June 15, 2024, is the Valley’s most realistic optio n. The following sections describe the air quality, emissions, and supplement al analyses, as well as the photochemical modeling that support the overall con clusion that the San Joaquin Valley can attain the federal 8-hour ozone standard by the 2024 deadline.

U.S. EPA Attainment Demonstration Requirements

The attainment demonstration portion of a State Imp lementation Plan or SIP consists of the analyses used to determine whether a proposed control strategy provides the reductions necessary to meet the feder al standard by the attainment year. This attainment demonstration includes photo chemical modeling which predicts that projected controls will result in a h igh site 8-hour design value for

the SJV that is below the level of the federal stan dard by 2024. While reclassifying as Extreme extends the attainment dat e, the Valley should nevertheless realize substantial progress over the next decade. Air quality modeling predicts that all sites in the Basin will reach attainment prior to 2024, with the exception of several sites with the most s evere air quality problems. However, with the implementation of proposed emissi ons control measures, ozone air quality in these areas is projected to me et the standard by the 2024

deadline.

Because of the uncertainties inherent in photochemi cal modeling, U.S. EPA allows states to supplement the modeling results wi th a “weight of evidence” (WOE) demonstration. The WOE assessment provides a set of analyses that complement the SIP-required modeling. These analys es can include consideration of measured air quality, emissions, a nd meteorological data, evaluation of other air quality indicators, as well as additional air quality modeling, if appropriate. Because all analysis met hods have inherent strengths and weaknesses, examining an air quality problem in a variety of ways helps to

offset the limitations and uncertainties inherent t o air quality modeling. ThisMay 30, 2007 Appendix B 2

approach also provides a better understanding of th e overall problem, as well as insight about the level and mix of emissions contro ls needed for attainment.

The scope of the WOE analysis is different for each nonattainment area, with the level of appropriate detail dependent upon the comp lexity of the air quality problem, how far into the future the attainment dea dline is, and the amount of data and modeling available. This document summari zes the analyses that comprise the WOE assessment for the San Joaquin Val ley nonattainment area.

Historical Context

Over the years, ozone has posed a persistent proble m in the San Joaquin Valley. Looking at ozone air quality from an historical per spective is challenging because of the lack of long-term sites in this area. Betwe en 1975 and 1990, monitoring began at a number of sites, but was discontinued af ter several years. Furthermore, these transient monitors did not inclu de sites in the worst areas of the central and southern portions of the Basin. Fo r these reasons, 1990 was chosen as the start year for long-term trends in th e SJV. 1990 is the first year for which Arvin, consistently one of the highest sites in the Valley, has complete data during the May through October ozone season. In ad dition, data are available for a number of other typically high concentration site s, including Clovis, Edison, Parlier, and several Fresno area sites.

Over the long-term, emissions control programs have improved ozone air quality in the SJV, but not to the same degree as seen in o ther areas of California. Both the climate and geography of the Valley present sig nificant challenges to progress in the SJV. Figure B-1 shows the 1990 to 2005 basinwide trends for several air quality indicators. Because the trend lines for both federal 8-hour exceedance days and maximum concentrations reflect values for individual years, they show a fair amount of variability, with only a small amount of progress over the 15-year period. Overall, the decrease in the number of exceedance days was more substantial than the decrease in maxi mum concentrations. In contrast to these two indicators, the other two ind icators shown on the graph, the design value and the mean of the maximum concentrat ions on the Top 30 days,

are less variable because these indicators are more robust. While these two indicators show even less change over the 15-year p eriod, the 2005 values are

lower than the 1990 values.

Although not shown in Figure B-1, perhaps the great est indicator of ozone air quality improvement in the SJV is the reduction in population-weighted exposure. This indicator shows a 50 percent reduction in expo sure to concentrations above

the level of the federal 8-hour standard between 19 90 and 2005. Despite the gains in improving population-weighted exposure, th e overall rate of progress for other indicators in the SJV has been slow, and this area will face tremendous challenges in reaching attainment.May 30, 2007 Appendix B 3

Figure B-1: San Joaquin Valley Air Basin Ozone Sta tistics 1990 to 2005

San Joaquin Valley Air Basin Ozone Statistics

0.00 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16

1 9 9 0

1 9 9 1

1 9 9 2

1 9 9 3

1 9 9 4

1 9 9 5

1 9 9 6

1 9 9 7

1 9 9 8

1 9 9 9

2 0 0 0

2 0 0 1

2 0 0 2

2 0 0 3

2 0 0 4

2 0 0 5

YearOzone (ppm)

0 25 50 75 100 125 150 175 200

Maximum Concentration Design Value* Mean Top 30 Concentrations Exceedance Days

Assessment of Recent Air Quality Trends

General Basinwide Perspective

Over the years, ozone improvement in the SJV has la gged behind other areas of California, and the Valley ranks second only to the South Coast Air Basin with respect to the nation’s worst ozone air quality. M odest levels of progress have occurred in the SJV over the last ten years, with a 15 percent drop in maximum concentration, a 5 percent drop in design value, an d a 35 percent drop in exceedance days between 1995 and 2005 (refer to Fig ure B-1). However, most of this improvement has occurred since 2003. While values for 2006 were up slightly from 2005 (maximum concentration of 0.121 ppm and 86 exceedance days), they were still among the lowest values over the last 15 years. Ozone levels in the SJV are not as high as in the South C oast; however, maximum concentrations during 2006 were still more than 40 percent higher than the federal standard, with nearly three months of excee dance days each year.

While ozone levels are still unhealthy, modest impr ovements over the years have resulted in a reduction of the extent of the proble m, especially in the northern portion of the Valley. The maps in Figure B-2 are based on monitoring data and estimate the reduction in days exceeding the nation al 8-hour standard over the last decade (1995 to 2005), throughout the San Joaq uin Valley, thereby providing an estimate of the spatial extent of the ozone prob lem. Ten years ago (1993 to 1995 average map), more than half of the SJV experi enced between 21 and 50 federal 8-hour exceedance days, with the worst s ite experiencing about 90 days. Areas in the northern SJV were cleaner th an areas in the central and southern Valley. However, only a relatively small portion of the Basin averaged 10 or fewer exceedance days. * The design value for 1990 is based on 2 years of data, while the design values for all other years a re based on 3 years of data.May 30, 2007 Appendix B 4

Figure B-2: San Joaquin Valley Air Basin Change in Federal 8-Hour Exceedance Days 1995 to 2005

Today (2003 to 2005 average map), we see a substant ial expansion of areas with 10 or fewer exceedance days. Ambient concentr ations in most of San Joaquin and Stanislaus counties are now below t he level of the federal

8-hour ozone standard. Much of the rest of the Val ley experiences an average of only 6 to 20 exceedance days per year. Areas with more than 20 exceedance days are now generally limited to the eastern porti on of the central and southern

SJV. While the extent of these areas is much small er than during 1995, the areas of poor ozone air quality are also some of th e most heavily populated (Fresno and Kern counties). Even though these area s still pose a substantial challenge, the worst sites show an average reductio n in exceedance days of approximately 35 percent over the last ten years.

In summary, although there has been some progress i n the SJV over the last ten years, the rate of progress has been slow in co mparison to other areas of the State. Overall, the trend lines for various air qu ality indicators, including maximum concentration, exceedance days, design valu e, and mean of the Top 30 concentrations, are relatively flat, with so me year-to-year variability caused by meteorology (refer to Figure B-1). Most of the progress seen over the last 15 years has occurred since 2003. While there has been only a 15 percent decrease in maximum concentration since 1995, the d ecrease in the number of exceedance days has been more substantial, at close to 35 percent. In spite of the slow rate of progress, the ozone problem is now confined mostly to the central and southern portions of the Valley, as con tinued emissions reductions have been successful in shrinking the spatial exten t of the problem areas. At theMay 30, 2007 Appendix B 5

same time, the “clean” areas have expanded substant ially, and nearly all of San Joaquin and Stanislaus counties now have air qu ality that meets the federal 8-hour standard. However, although these counties are generally clean with respect to ozone, emissions from these northern SJV areas can impact ozone air quality in other portions of the Valley.

Regional Analyses

The basinwide air quality indicators for the SJV sh ow limited progress because they are dominated by the high sites, which pose th e most severe problems. However, when the Basin is subdivided into differen t regions, different patterns of progress emerge. For the following discussion, the Valley is divided into three general areas, as shown in Figure B-3: the norther n SJV, the central SJV, and the southern SJV. For convenience, these regions a re divided along county boundaries. However, they generally represent thre e distinct areas with respect to geography, meteorology, and air quality. While ozone air quality within each of the three subregions tends to be similar, the level of air quality and rates of progress from one area to another can vary substant ially.

Figure B-3: San Joaquin Valley Air Basin Subregion sMay 30, 2007 Appendix B 6

A third of the Basin population lives in the northe rn SJV. This lowland area is bordered by the Sacramento Valley and Delta lowland to the north, the central portion of the SJV to the south, and on the other t wo sides by mountains. Because of the marine influence, which extends into this area through gaps in the coastal mountains to the west, the northern SJV experiences a more temperate climate than the rest of the Basin. Thes e cooler temperatures and the predominant air flow patterns generally favor bette r ozone air quality.

In contrast to the northern SJV, most of the Valley population lives in the central and southern portions of the Basin, in and around t he Fresno and Bakersfield

urban areas. Sites in the central and southern are as exceed the federal standard by the greatest margin, and geography, emissions, a nd climate pose significant challenges to air quality progress. Similar to the northern SJV, the central and southern SJV are also low lying areas, flanked by m ountains on their west and east sides. The southern SJV represents the termin us of the Valley and is flanked by mountains on the south, as well. The su rrounding mountains in both areas act as barriers to air flow, and combined wit h recirculation patterns and stable air, trap emissions and pollutants. The hig her temperatures and more stagnant conditions in these two regions lead to a build-up of ozone and overall poorer air quality. In addition to the urban air q uality problems, emissions and pollutants from these areas are transported downwin d, making for even poorer air quality in downwind areas such as Arvin and the Sequoia National Park.

ARB staff completed an analysis of ozone episodes t hat occurred in both the central and southern SJV during 2004 and 2005. Bas ed on these data, high ozone concentrations occurred as multi-day episodes more than 65 percent of the time, in both regions. Furthermore, episodes w ith higher federal 8-hour concentrations typically spanned a greater number o f days, with the highest concentrations occurring in the middle of the episo de period. During 2004 and 2005, more than 75 percent of the central SJV ozone episodes showed their highest 8-hour concentration at sites located withi n the Sequoia National Park. During more than 40 percent of the episodes, exceed ances were limited only to sites located within the Sequoia National Park. Wh ile the downwind Sequoia sites tend to be the most problematic in the centra l SJV, is it interesting to note that very few central SJV episodes began prior to t he start of an episode in the southern SJV. In fact, nearly 90 percent of the ce ntral SJV episodes started on the same day or during an ozone episode in the sout hern SJV. The most problematic site in the southern SJV is Arvin, and during 2004 and 2005, about 95 percent of the southern SJV ozone episodes showe d their highest 8-hour

concentration at Arvin.

Figure B-4 shows the average number of exceedance d ays during 1995 and 2005 for each of the subregions mapped in Figure B- 3. Two sites, Sequoia National Park-Lower Kaweah and Arvin are plotted se parately, and therefore,

data for these two sites are not included in the to tals for the central and southern SJV areas. The Sequoia National Park-Lower Kaweah and Arvin sites areMay 30, 2007 Appendix B 7

located downwind of the Fresno and Bakersfield urba n areas, respectively, and tend to have poorer air quality.

The northern SJVAB continues to be far cleaner than the other areas of the SJV. Over the last decade, the number of exceedance days in this area has decreased about 70 percent. During 2005, about 80 percent of the days during the May through October ozone season were below the more stringent State 8-hour standard. However, while the number of days in this region has shown improvement, Modesto stands out as the high site in the northern SJV.

Figure B-4: San Joaquin Valley Air Basin Change in Number of Federal 8-Hour

Exceedance Days by Subregion 1995 and 2005

Number of Exceedance Days
During 1995 and 2005

0 10 20 30 40 50 60 70 80 90 100

N o r t h e r n S J V C

e n t r a l S J V

S o u t h e r n S J V

S

e q u o i a - L o w e r K a w e a h A

r v i n# of Exceedance Days 1995 2005

From north to south, the severity of the ozone prob lem in the SJV generally increases. Between 1995 and 2005, the number of ex ceedance days at sites in the central SJV (excluding the Sequoia area) decrea sed 55 percent. Although the decrease is still relatively high, the number o f days in the central SJV during 2005 was five times higher than in the northern SJV . The number of exceedance days in the southern SJV (excluding Arvin) decrease d about 65 percent during the last decade, and the number of exceedance days during 2005 was just slightly higher than the number of days in the cent ral SJV. With respect to days below the State 8-hour standard, about 40 percent o f the days during the ozone

season were below this level in both the central SJ V and the southern SJV areas during 2005. Similar to the basinwide trends, most of the progress in the central and southern SJV subregions has occurred since 2003

.

The sites downwind of the Fresno and Bakersfield ur ban areas continue to pose the most severe problems in the SJV, and improvemen ts in these areas have

been much slower than in other areas. Arvin has al ways been one of the high sites in the Basin. Between 1995 and 2005, federal exceedance days declinedMay 30, 2007 Appendix B 8

about 30 percent, which is lower than the rate seen at other sites in the southern SJV region. In contrast, sites located at higher e levations in the Sequoia National Park have shown worsening ozone air qualit y over the last several years. Between 1995 and 2005, the number of federa l exceedance days actually increased more than 75 percent at the Sequoia-Lower Kaweah site. This increase highlights the problem of transported emis sions and pollutants from the upwind urban area. The Sequoia-Lower Kaweah site w as used in this comparison because it is a long-term site with data for both 1995 and 2005. However, it should be noted that during 2005, the S equoia-Kings Canyon site had even poorer air quality. In fact, during 2005, the Kings Canyon site had the same number of exceedance days as Arvin, as well as a similar maximum

concentration.

Similar to exceedance days, concentrations have als o been decreasing at a faster rate in the urban areas than at Arvin or Seq uoia. Peak concentrations, as measured by the mean of the Top 4 daily concentrati ons, decreased only 3 percent over the last five years at Arvin and inc reased in the Sequoia area. However, the same indicator decreased at twice that rate in the Bakersfield and Fresno urban areas. Today, the 4 th highest 8-hour ozone concentration averages 0.095 ppm for sites in both urban areas, c ompared with 0.105 ppm five years ago. Similarly, the mean of the Top 30 conce ntrations for both urban areas is declining and is now close to the level of the f ederal standard. The mean of the Top 30 concentrations is 0.084 ppm for the Fres no/Merced area and 0.089 ppm for the Bakersfield region. Five years a go, both of these urban areas had mean Top 30 concentrations greater than 0.100 p pm. Although the mean of the Top 30 concentrations is not directly comparabl e to the federal standard, it is a fairly stable statistic that is less influenced b y year-to-year changes in meteorology. Therefore, it provides an indication of how concentrations on the worst days of the year are changing over time.

In summary, there have been changes in the patterns of exceedances on a subregional basis in the SJV over the last ten year s. Today, the numbers of exceedance days in all areas except the Sequoia reg ion are smaller than they were ten years ago. The most progress occurred in the northern SJV, and ozone

concentrations in this area are now below the level of the more stringent State 8-hour standard 80 percent of the time during the o zone season. Trends in peak ozone concentrations reflect similar subregional di fferences. Based on current air quality and past trends, the areas downwind of Bakersfield and Fresno will likely pose the most difficulty for attainment.

Meteorology and Air Quality Trends

Ozone in the ambient air is the result of several f actors, two of the most important being pollutant emissions and meteorology. The met eorological and photochemical processes leading to ozone formation are complex,May 30, 2007 Appendix B 9

involving interactions both at the surface and in t he upper air. However, they can be characterized in very general terms: strong sun light and weak dispersion generate relatively high ozone levels, while weak s unlight and strong dispersion generate relatively low ozone levels. Meteorology, or weather conditions, can vary widely, and these day-to-day conditions strong ly influence ambient ozone

concentrations.

The previous trends discussion looked at air qualit y as measured at ambient monitoring sites, without any consideration of or a djustment for meteorological variability. The following discussions characteriz e the general meteorological conditions leading to high ozone concentrations, as well as several different methods of accounting for meteorological variabilit y. These analyses are an effort to better understand the impact of meteorolo gy on air quality and thereby track improvements attributable to emissions reduct ions. Another goal of these analyses is to determine the role meteorology has p layed in the SJV, where ozone improvement has lagged behind other areas of the State. Although ozone improvements have been slower to occur in the SJV, the following analyses show that modest progress has occurred.

Characterization and Frequency of Episodic Conditi ons

In evaluating the meteorological conditions associa ted with ozone episodes, ARB staff identified three well-defined patterns as bei ng associated with the majority of episodes. Collectively, these three patterns are a ssociated with nearly 90 percent of the 8-hour exceedances. Summertime m eteorology in the Valley is dominated by a constant ebb and flow between high a tmospheric pressure over the Southwest Desert and low pressure over the Gulf of Alaska. When a high pressure ridge moves over California, stagnant cond itions can persist for several days, resulting in widespread violations of the fed eral 8-hour standard. When a low pressure trough pushes inland, the Valley floor may see considerable improvements in air quality. However, downwind tra nsport-impacted areas may experience higher concentrations.

In order to categorize the air flow patterns preval ent in the San Joaquin Valley, ARB staff performed a cluster analysis involving al l days during May through October, 1990 through 2005. Subsequently, staff co nsidered the meteorological characteristics of a subset of the clusters (2000 t hrough 2005) and the incidence of federal 8-hour ozone episodes found in each clus ter. These assessments show that nearly 90 percent of the SJV federal 8-ho ur exceedances are associated with three meteorological patterns, each distinguishable by the relative dominance of a high pressure ridge versus a low pressure trough. These patterns are generally characterized by high pressu re aloft, mostly clear skies, warm temperatures, and strong morning inversions. The differences between the patterns are seen through large-scale variation s in atmospheric pressure along the coast.May 30, 2007 Appendix B 10

Under the “high pressure ridge pattern,” a ridge of high pressure covers all of the SJV, leaving the region with clear skies and very w arm temperatures. Surface winds are terrain driven, with little or no sea bre eze moving through the Carquinez Strait. Average afternoon wind speeds ty pically range between 3 and 7 miles per hour (mph), with only a few hours above 10 mph recorded in the northern part of the Basin. Maximum surface temper atures normally reach 100 degrees in most areas, with occurrences of 105 degrees or greater during the peak summer months. The resulting stagnant con ditions promote the formation of high ozone levels throughout the Basin , with maximum concentrations found close to the major source area s. Areas typically dominated by transport, such as the higher elevations of Sequ oia National Park, will exhibit lower concentrations in comparison, as light winds keep pollution movement to a minimum. This pattern has led to the highest ozone readings in the Basin, and

was associated with about half of the 8-hour ozone exceedances recorded during May through October of 2000 to 2005.

The “approaching trough pattern” causes ozone and i ts precursors to move downwind from source locations. Under this pattern , the high pressure ridge over central California is weaker, and this increas es the sea breeze flowing through the Carquinez Strait. Average afternoon wi nd speeds range between 6 and 12 mph, with a few hours above 14 mph recorded in the northern parts of the Basin. The maximum surface temperatures reach into the upper 90s in most southern areas, with northern areas in the upper 80 s to lower 90s. High ozone levels are observed downwind of the major urban sou rce areas (for example, downwind of Stockton, Fresno, and Bakersfield). Hi gh ozone levels are also observed in the foothill areas, such as the Sequoia National Park area. During this weather pattern, the extreme northern sections of the Valley experience lower ozone concentrations, as increased wind flow pushes pollutants further south and east. During May through October of 2000 to 2005, the approaching trough pattern was associated with about 20 percent of the measured 8-hour

ozone exceedances.

Finally, the “trough pattern” results in peak ozone further downwind of the major emission sources, primarily affecting the eastern a nd southernmost portions of the SJV. Under this pattern, the ridge of high pre ssure is weakened more significantly. This increases wind flow through th e Carquinez Strait, causing temperature and ozone levels to be much lower over the northern and central portions of the Valley. Surface winds are predomin antly from the west-northwest in the northern portion of the Basin. As the surfa ce winds move southward, channeled by the terrain, they veer and become a no rthwest flow. Average afternoon wind speeds range between 8 and 16 mph, w ith some stronger gusts at night. Maximum temperatures still reach near 90 degrees or slightly above in most low lying areas of Kern and Tulare counties, w ith the northern areas in the 80s. Under this weather pattern, ozone levels peak in the southern region of the Basin, downwind of major emission source areas. Th e highest ozone levels areMay 30, 2007 Appendix B 11

found at sites such as Parlier, Arvin, and Sequoia National Park, where transport is typically the dominant mechanism for ozone and p recursor movement. The trough pattern was associated with about 20 percent of the 8-hour ozone exceedances recorded during May through October, 20 00 to 2005.

High Ozone Forming Potential

As one approach to help understand the types of met eorological conditions leading to high ozone concentrations, ARB staff com pleted an analysis of ozone and meteorology using Classification and Regression Tree (CART) techniques. The CART analysis determined rules that separated d ays into 15 groups, based on the degree to which weather conditions favor ozo ne formation. The CART rules used daily data for surface air temperature, air temperature at

1500 meters 1 , wind speed/direction, atmospheric stability, and other factors in relation to daily maximum 8-hour ozone concentratio ns. From the 15 groups, a subset with high average ozone levels and containin g on average about one-third of the ozone season were considered to represent hi gh ozone forming potential (OFP).

The analysis, presented in Figure B-5, shows the nu mber of days with high OFP along with the number of days exceeding the federal 8-hour ozone standard each year (three-year moving means). The changes in exc eedance days relative to the changes in high OFP days helps distinguish chan ges due to meteorology from changes due to emissions reductions. Progress is shown when the number of exceedance days decreases in relation to the num ber of high OFP days.

The two lines generally track together, indicating that year-to-year changes in exceedance days have been largely attributable to y ear-to-year changes in weather, rather than changes in emissions. Relativ e to the high OFP line, however, the number of exceedance days has decrease d. During the 1990’s, the trend for exceedance days averaged 14 days abov e the trend for high OFP days. Since 1999, however, the trend for exceedanc e days averaged 4 days below the trend for high OFP days, indicating a “re al” decrease of about 18 days.

Furthermore, the unsmoothed trends in Figure B-6 sh ow the 68 exceedance days measured in 2005 was a new low for the Basin ( note that the 68 exceedance days reflects only those occurring durin g the May through October ozone season). Three years, 1990, 1997, and 1999, had OFP values similar to 2005, but exceedance days during these years averag ed 13 days above the OFP trend. In contrast, the 68 exceedance days measure d during 2005 were 13 fewer than the number of high OFP days. These r esults indicate that some real progress in reducing ozone is now taking place in the SJV, as increasingly adverse meteorological conditions are needed to cre ate ozone levels exceeding

the federal 8-hour standard.

1 Above sea levelMay 30, 2007 Appendix B 12

Figure B-5: San Joaquin Valley Air Basin Three-Yea r Means of Federal 8-Hour

Exceedance Days and High OFP Days 1990 to 2005

San Joaquin Valley Ozone Trends

(Federal 8-hour Exceedance Days and "High OFP" Days )*

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 200 2 2003 2004 2005

YearNumber of Days (3-year moving mean)

Fed. 8-hr Exceedance Days Days in High OFP CART Bins

* Based on a CART model relating meteorology to the basinwide daily maximum 8-hour ozone from 1990 - 1 992.

Figure B-6: San Joaquin Valley Air Basin Federal 8- Hour Exceedance Days

and High OFP Days 1990 to 2005

San Joaquin Valley Ozone Trends

(Federal 8-hour Exceedance Days and "High OFP" Days )*

0 10 20 30 40 50 60 70 80 90 100 110 120 130 140

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 200 2 2003 2004 2005

YearNumber of Days

Fed. 8-hr Exceedance Days Days in High OFP CART Bins

* Based on a CART model relating meteorology to the basinwide daily maximum 8-hour ozone from 1990 - 1 992.May 30, 2007 Appendix B 13 Meteorologically Adjusted Trends

As discussed above, meteorological parameters such as temperature, pressure, and wind speed are systematically correlated with s unlight and dispersion, and can be used in formulas that predict daily ozone le vels. As a second method to address the role of meteorology, a statistical mode l that predicts daily maximum ozone on the basis of daily meteorological data was used to adjust daily ozone observations.

First, days from the May through October ozone seas on for the years 1990 to 2005 were assigned to separate groups based on pres sure and temperature gradients, along with selected wind speeds and dire ctions. Together, three of the groups accounted for the vast majority of exceedanc e days during the ozone season in the San Joaquin Valley. For each of thes e groups, data from 1990 through 1993 were used to calibrate a within-group model to predict daily maximum 8-hour ozone from daily weather data. The limited span of years was used for calibration so that when it was applied fo r all the years (1990 through 2005), it would provide a level playing field for m eteorological effects, apart from the influence of changes in emissions.

Met-adjusted trends are presented in the following three figures. The figures are based on data for basinwide daily maximum ozone con centrations after these have been reconciled to long-term meteorological no rms regarding group frequencies and concentrations within each group. The three lines on each graph represent the mean of the Top 10, Top 20, and Top 30 met-adjusted concentrations. The trends in Figures B-8 and B-9 were smoothed using a three-year moving mean, because the process of met- adjustment does not remove all meteorological effects perfectly, and ot her factors also affect the year-to-year changes.

Figures B-7 and B-9 show that ozone declined approx imately five percent from 1990 to 2005. An upswing in the trend from 2001 to 2004 may be attributable to meteorological effects for which the process of met -adjustment is incomplete. Following the upswing, the met-adjusted values for 2005 reached a new low for all three indicators, indicating that modest improv ement (5 percent) in ozone occurred in the San Joaquin Valley in the 2000s, co mpared to the 1990s. It is also noteworthy that this progress has been similar for all three indicators: mean of the Top10, Top20, and Top30 ozone concentrations . This shows that the Top 30 (top 16 percent 2 ) summer ozone concentrations have responded very similarly to emissions reductions in the SJV since 1990.

2 The May – October ozone season has 184 days, of wh ich 30 is 16%.May 30, 2007 Appendix B 14

Figure B-7: San Joaquin Valley Air Basin Ozone Tren ds 1990 to 2005 Adjusted for Meteorology

San Joaquin Valley Air Basin -- Basinwide Ozone Tre nds

(Annual Means for Top 10, Top 20, and Top 30 Met-Adjusted Daily Max 8-Hour Obs.)*

0.095 0.100 0.105 0.110 0.115 0.120 0.125 0.130

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 200 2 2003 2004 2005

YearMean Ozone (ppm)

Mean of Top 10 Mean of Top 20 Mean of Top 30

* Relationship between ozone and meteorology was ca librated using data from 1990-1992.

Figure B-8: San Joaquin Valley Air Basin Three-Year Mean Ozone Trends 1990 to 2005 Adjusted for Meteorology

San Joaquin Valley Air Basin -- Basinwide Ozone Tre nds

(Annual Means for Top 10, Top 20, and Top 30 Met-Adjusted Daily M ax 8-Hour Obs.)*

0.095 0.100 0.105 0.110 0.115 0.120 0.125 0.130

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 200 2 2003 2004 2005

YearMoving Avg. (3-year) Ozone (ppm)

Mean of Top 10 Mean of Top 20 Mean of Top 30

*Relationship between ozone and meteorology was cal ibrated using data from 1990-1992.May 30, 2007 Appendix B 15

Figure B-9: San Joaquin Valley Air Basin Ozone Tren ds 1990 to 2005 Adjusted for Meteorology and Expressed as a Percentage of the Base Year

San Joaquin Valley Air Basin -- Basinwide Ozone Tre nds

(Annual Means for Top 10, Top 20, and Top 30 Met-Ad justed Daily Max 8-Hour Obs.)*

85% 90% 95% 100% 105% 110%

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 200 2 2003 2004 2005

YearMoving 3-Year Mean Ozone (% 1990-1992)

Mean of Top 10 Mean of Top 20 Mean of Top 30

*Relationship between ozone and meteorology was cal ibrated using data from 1990-1992.

The above analyses use different methods to account for the variable impacts of meteorology on ozone air quality. Results of these analyses confirm that progress has occurred in the San Joaquin Valley Air Basin, especially during the last several years. Although adjusting ozone air q uality for meteorology does not change the overall flatness of the trend in the SJV throughout most of the analysis period, it does show some measure of real progress during the most
recent years.

Emissions and Precursor Trends

Oxides of nitrogen (NOx) and reactive organic gases (ROG) are precursors to

ozone. Emissions controls have reduced the amounts of these precursors throughout the Basin, resulting in the modest impro vement in ozone air quality observed in the SJV. The following sections descri be the NOx and ROG emissions trends in the SJV since 1994, as well as the amounts of these precursors measured in the ambient air.

Emissions Trends

Emissions controls have substantially reduced the a mounts of both ROG and NOx emitted by various sources throughout the San J oaquin Valley. Figure B-10 shows the estimated basinwide trend in these precur sor emissions from 1994 to

2005. The totals reflect estimates for the summer season in tons per day and include emissions from natural biogenic sources.May 30, 2007 Appendix B 16

Figure B-10: San Joaquin Valley Air Basin Estimate d NOx and ROG Emissions

1994 to 2005

San Joaquin Valley Air Basin NOx & ROG Emissions Summer SIP Inventory with Biogenics - Ver 1.06

0 100 200 300 400 500 600 700 800 900 1000 1100

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

YearTons/Day

San Joaquin Valley Air Basin ROG San Joaquin Valley Air Basin NOx

Since 1994, there has been a fairly steady decrease , basinwide, in both ROG

and NOx emissions. While the relative amounts of t he two precursors have remained fairly constant over the 12-year period, t he overall reduction in ROG emissions (about 15 percent) has been slightly smal ler than the overall reduction in NOx emissions (about 20 percent). However, it i s important to note that a substantial portion of the ROG emissions (from 45 a nd 50 percent of the total ROG between 1994 and 2005) comes from biogenic sour ces. Because the biogenic portion is constant over time, it masks th e reductions attributable to emissions control programs. When looking only at t he anthropogenic portion of the ROG inventory, ROG emissions impacted by contro l programs decreased nearly 25 percent between 1994 and 2005.

Figures B-11 and B-12 show the estimated emissions trends for the three SJV subregions. In all three areas, both ROG and NOx e missions are decreasing. Similar to the basinwide trend, NOx emissions are d ecreasing at a faster rate than ROG in both the central and southern areas, bu t not in the northern SJV. Another interesting observation is that similar to the basinwide trend, ROG emissions are at a higher level than NOx emissions only in the central SJV. In the other two areas, NOx emissions are higher. Ove rall, the greatest reductions in NOx emissions (with respect to both percentages and tons per day) occurred

in the southern SJV. This area has also seen subst antial reductions in the number of 8-hour exceedance days in both the upwind and downwind portions of the region.May 30, 2007 Appendix B 17

Figure B-11: Northern and Central SJV ROG and NOx Emissions 1994 to 2005

San Joaquin Valley Air Basin NOx & ROG Emissions Northern & Central SJV - Summer SIP Inventory w/ Bi ogenics - Ver 1.06

0 50 100 150 200 250 300 350 400 450 500 550 600

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

YearTons/Day

Central SJV ROG Central SJV NOx Northern SJV NOx Northern SJV ROG

Figure B-12: Southern SJV ROG and NOx Emissions 199 4 to 2005

San Joaquin Valley Air Basin NOx & ROG Emissions Southern SJV - Summer SIP Inventory with Biogenics - Ver 1.06

0 50 100 150 200 250 300 350 400 450 500

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

YearTons/Day

Southern SJV NOx Southern SJV ROG

Precursor Trends

In addition to the reduction in overall emissions a s estimated by the emissions inventory, measured data show a reduction in the am ounts of ROG and NOx in the ambient air. Ambient monitoring data from the Photochemical Assessment Monitoring Stations (PAMS) network are plotted in F igure B-13 and show reductions in both precursors. Since 1994, ROG, as measured by the PAMS network in the SJV, shows an overall reduction of a bout 75 percent. Coupled

with the reduction in ROG is a similar reduction in the reactivity of the hydrocarbon mix (about 70 percent between 1994 and 2005). During this same timeframe, ambient NOx concentrations decreased app roximately 50 percent, with the greatest decrease occurring between 1994 a nd 1995. Between 1995 and 2005, ambient NOx concentrations were flatter, with only a modest overallMay 30, 2007 Appendix B 18

reduction. The overall trends from the ambient mon itoring network are generally

consistent with the trends in estimated emissions i n that they both show both precursors decreasing.

Figure B-13: San Joaquin Valley Air Basin Summer M orning Average ROG,

Reactivity, and NOx at PAMS Stations

San Joaquin Valley Air Basin July-August Average at PAMS Stations (5-7 am/6-8 am)* for PAMS ROG, PAMS Reactivity, and NOx

0 50 100 150 200 250 300

1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Yearppb(C)

0 10 20 30 40 50 60NOx ppb(N)

PAMS NMOC PAMS Reactivity NOx

* 3-hour ROG/PAMS samples were from either 5-7 am o r 6-8 am. The same 55 compounds were used for 1994 -2005 (carbonyls were not included). Several samples with very high mixing ratios (orders of magnitude higher than the rest) for one or more com pounds were identified/excluded .

Based on the PAMS ambient data, the reductions in p recursor and reactivity levels in the Valley suggest there should have been improvements in peak ozone levels. However, SJV ozone levels have changed ver y little, except during the last three years. This implies that there are othe r factors at work that affect the production of ozone. Perhaps emissions in the SJV remain in the Valley for longer periods of time, providing additional opport unities for lower reactivity precursors to contribute to peak ozone levels. In addition, because ambient ROG levels have changed faster than NOx levels, the ratio of ROG to NOx has

decreased from 5.0 in 1994 to 2.8 in 2005. This ch ange in the precursor ratio has likely changed the responsiveness of the Valley to predominately ROG emissions reductions. As a result, NOx emissions r eductions may become more important for future emission control strategies. The greater decrease in estimated NOx emissions, coupled with the substanti al drop in exceedance days in the southern SJV, appear to support this conclus ion. Finally, meteorology is an important factor. Changes in temperature and ve rtical mixing are known to impact ozone levels. Therefore, accounting for met eorology is one way to provide a better understanding of the available dat a (refer to previous section on Meteorology and Air Quality Trends).May 30, 2007 Appendix B 19

Modeling Results

The ozone modeling domain for the SJV was based on the domain defined for the year 2000 Central California Ozone Study (CCOS) and includes not only the Central Valley, but the San Francisco Bay area, as well. The domain comprises a grid measuring 185 by 185 cells with a horizontal resolution of four kilometers. The required meteorological fields were generated u sing the MM5 prognostic meteorological model, and the required emissions in ventories were developed by ARB staff. The ozone air quality modeling utilized the Comprehensive Air Quality Model with Extensions (CAMx) air quality model, wit h initial and boundary

conditions based on estimates of clean-air concentr ations.

ARB staff completed ozone modeling for two episode periods – one during July 1999 and the other during July/August 2000. D uring these episodes, 8-hour ozone concentrations exceeding the federal standard occurred throughout the region. Analysis of the model outputs included the estimation of 1-hour and

8-hour ozone concentrations for each ozone monitori ng site within the domain, as well as statistical measures comparing observed and simulated ozone concentrations. These analyses were used to evalua te model performance by subregion within the domain.

As required by U.S. EPA, a relative reduction facto r (RRF) approach was used in projecting future year design values. The RRF refl ects the ratio between the future year model prediction (in this case the end of 2023) and the reference year model prediction. A reference year design value is then multiplied by the RRF to project a future year design value.

Results of the modeling analyses indicate that NOx reductions will be relatively more effective than ROG reductions in reducing ozon e concentrations in the San Joaquin Valley. Therefore, the attainment stra tegy relies on a 75 percent reduction in NOx, in combination with a 25 percent reduction in ROG, to bring the

worst-case sites into attainment.

Because ozone concentrations vary throughout the Va lley, the modeling

indicates different overall reductions are needed i n different areas to reach attainment. However, as emissions controls are imp lemented, ozone

concentrations will decrease in all areas of the Va lley. San Joaquin Valley Unified Air Pollution Control District ( District) staff estimate that by 2015, over 50 percent of the Valley’s population will live in areas that meet the federal 8-hour ozone standard. By 2020, the portion of the population living in clean areas will increase to 90 percent. Although ozone concentrations will drop measurably throughout the entire Valley over time, downwind areas such as Arvin will require the greatest level of emissions reductions to meet the standard. Some of these reductions rely on technological adva ncements and are expected after 2020, but no later than 2023. These reductio ns are expected to bring the last remaining nonattainment areas into compliance with the federal 8-hour

ozone standard.May 30, 2007 Appendix B 20

Summary

The Weight of Evidence (WOE) package comprises a se t of complementary analyses that supplement the SIP-required modeling, thereby providing additional support for the attainment demonstration . Currently, the San Joaquin Valley is classified as a Serious nonattainment are a with an attainment date of June 15, 2013. Because of the magnitude of emissions reductions re quired, the District is requesting reclassification as Extreme, with a required attainment date of June 15, 2024. The Extreme classification allow s the attainment demonstration to rely on emissions reductions from measures that anticipate the development of new technologies or improvement of e xisting technologies.

These measures are often referred to as “black box” measures and go beyond

the short-term measures that are based on known and demonstrated technologies.

U.S. EPA guidance allows the use of a Weight of Evi dence (WOE) analysis to supplement photochemical modeling in demonstrating attainment. The ARB staff’s modeling results indicate substantial NOx a nd ROG emissions reductions will be needed to bring the Valley into attainment. However, with reclassification as an Extreme nonattainment area, the SJV will be a ble to reach attainment by the 2024 deadline with a 75 percent reduction in NO x emissions, in combination with a 25 percent reduction in ROG emissions. Base d on these reductions, even

the worst-case sites will attain the federal 8-hour ozone standard. Based on modeling, as well as supporting analyses completed as part of this WOE evaluation, attainment by 2024 is anticipated becau se of the following factors:

 Over the last decade, the number of basinwide exce edance days decreased 35 percent. The maximum concentrati on and design value show more modest reductions, with decr eases of 15 and 5 percent, respectively. Because these are basinwide numbers, they reflect the “worst case” sites. On a subregional basis, the amount of improvement during the last te n years is greater. While values for 2006 were up slightly fr om 2005, they are still among the lowest values over the last 15 years.

 During the mid-1990s, the ozone problem was widesp read throughout the San Joaquin Valley. Today, the spat ial extent of the relatively clean areas has expanded substantial ly. The greatest amounts of improvement have occurred in th e northern SJV, and ambient concentrations in most of San Joaquin and Stanislaus counties now meet the fe deral standard. Over the last decade, the number of exce edance days in the northern SJV decreased 70 percent, and during 2005, about 80 percent of the days during the ozone season were below the more stringent State 8-hour ozone st andard.May 30, 2007 Appendix B 21  The ozone problem is now confined primarily to the central and southern portions of the Valley. Sites located dow nwind of the Fresno and Bakersfield urban areas continue to pose the most severe problems. While the number of exceedance da ys has declined substantially at most sites in the central and southern SJV (55 to 65 percent between 1995 and 2005), excee dance days have declined more slowly at Arvin, while incr easing at sites located at higher elevations in the Sequoia N ational Park.

 Estimated ROG and NOx emissions trends, as well as measured data from the PAMS monitoring network in t he San Joaquin Valley indicate reductions in both prec ursors since

1994. These reductions have resulted in modest ozo ne improvements over the last decade.

 Analyses suggest that recent ozone improvements ar e linked to

emissions reductions. The decline in the number of exceedance days relative to the number of days with a high potential for ozone formation indicates that the mo dest improvements in ozone over the last few years were related to

emissions reductions rather than favorable meteorol ogical conditions. Results of these analyses also indicat e that increasingly adverse meteorological conditions are now needed to create ozone levels exceeding the federal 8-hour standard.

 Emissions estimates indicate a continuing decline in ROG and NOx emissions as the State and District pursue the aggressive dual pollutant strategy outlined in the SIP. Based on the magnitude of emissions reductions needed for ozone attainment, as well as the readiness of NOx control technologies, a NOx-heavy strategy is proposed and will provide the most efficient path to attainment (75 percent N Ox reduction, coupled with 25 percent ROG reduction).

 Photochemical modeling shows all sites in the San Joaquin Valley Air Basin will attain the federal 8-hour ozo ne standard by the end of 2023, as required for Extreme nonattainm ent areas. Many areas will reach attainment before this date. The District estimates that by 2015, 50 percent of the Basin pop ulation will live in areas attaining the standard, and by 2020, the number will increase to 90 percent.

Taken together, all of these factors indicate that all sites in the San Joaquin Valley can expect to attain the federal 8-hour ozon e standard by June 15, 2024, the required attainment date for an Extreme ozone n onattainment area.