2008 PM2.5 Plan This appendix has been provided by the California Air Resources Board (ARB). For information on the District ’s Weight of Ev idence work, please refer to Section 3.2.4 (Chapter 3) , Appendix E, and Appendix F.



## Appendix H

Weight of Evidence2008 PM2.5 Plan This page intentionally blank.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-1 

## Appendix H: Weight of Evidence

1. INTRODUCTION: SAN JOAQUIN VA LLEY PM2.5 SUPPLEMENTAL ANALYSIS

The State Implementation Plan or SIP serves as a demonstration of attainment for the national ambient air quality st andards (NAAQS or federal st andards). The attainment demonstration comprises analyses used to de termine the set of control measures needed to meet the NAAQS by the attainment year. These analyses typically include air quality modeling, which gene rally guides the selection of the most effective pollutants to control and the magnitude of needed emissions reductions. The Weight of Evidence (WOE) analysis provides a set of comp lementary analyses that supplement the SIP-required modeling. These analyses can include considerati on of measured air quality, emissions, and meteor ological data, evaluation of other air quality indicators, and additional air quality modeling.

A WOE approach looks at the entirety of the information at hand to provide a more informed basis for the attainment strat egy. Because all methods have inherent strengths and weaknesses, exam ining an air quality problem in a variety of ways offsets the limitations and uncertainty that are inher ent in air quality modeling. This approach also provides a better understanding of t he overall problem and the level and mix of emissions controls needed for attainment.

The United States Environmental Prot ection Agency (U.S. EPA) recognizes the importance of a comprehensive assessm ent of air quality data and modeling and encourages this type of broad assessment for a ll attainment demonstrations. In their modeling guidance, they further note that the results of supplementary analyses may be used in a WOE determination to show that a ttainment is likely despite modeled results which may be inconclusive (U.S. EPA 2007). Under the U.S. EPA guidance, future year modeled annual average design values that fall between 14.5 and 15.5 ug/m 3 should be accompanied by a WOE demonstr ation to determine whether attainment will occur. This range in modeled design values reflec ts the uncertainty in predicting absolute PM2.5 concentrations that is inherent in ai r quality modeling, and therefore recognizes that an improved assessment of attainment can be derived from examining a broader set of analyses.

U.S. EPA recommends that three basic ty pes of analyses be included to supplement the primary modeling analysis in the WOE approach:

1) analyses of trends in ambient air quality and emissions, 2) observational models and diagnostic analyses, and 3) additional modeling.

Each analysis is weighted based on its ability to quantitatively assess the ability of the proposed control measures to yield attain ment. The scope of the WOE analysis is different for each nonattainment area. The level of detail appropriate for each area depends upon the complexity of the air quality problem, how far into the future theSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-2 attainment deadline is, and the amount of data and modeling av ailable. For example, less analysis is needed for an area that is pr ojecting attainment near-term and by a wide margin, and for which recent air quality tr ends have demonstrated significant progress, than for areas with more severe air quality challenges. The following sections present the WOE assessment for PM2. 5 in the San Joaquin Valley Air Basin for each of the areas outlined in the U.S. EPA guidance.

2. ASSESSMENT OF RECENT AIR QUALITY AND EMISSION TRENDS

a. Current Air Quality

According to U.S. EPA’s guidance, even though air quality models are regarded as the most appropriate tool to assess impacts in emission changes, it is also possible to extrapolate future trends in PM2.5 based on measured historical trends of air quality and emissions. Strength of the evidence pr oduced by emissions and air quality trends is increased if an extensive monitoring netwo rk exists and if there is good correlation between past emission reductions and current trends.

Along with the South Coast, the San Joaquin Valley Air Basin has one of the most severe PM2.5 problems in the nation and represents a considerable challenge in attaining the federal PM2.5 standards. These standards consist of both a 24-hour standard of 65 ug/m 3 , and an annual averag e standard of 15 ug/m 3 . While the majority of monitors with complete data in the S an Joaquin Valley still exceed the annual PM2.5 standard, PM2.5 air quality has shown considerable improv ement since 1999 when monitoring data for assessing compliance with the federal PM2.5 standard began. When the San Joaquin Valley was first desi gnated nonattainment for the federal PM2.5 standards, the basin exceeded both the annual and the 24-hour PM2.5 standards. However, based on 2004-2006 da ta, the San Joaquin Valley meets the federal 24-hour PM2.5 standard of 65 ug/m 3 throughout the basin. Thus attaining the annual standard is the primary challenge in th is State Implementation Plan.

The San Joaquin Valley Air Basin is a lowlan d area bordered by mountains to the east, west, and south. The mountains act as air flow barriers, with the resulting stagnant conditions favoring the accumulation of emi ssions and pollutants. To the north, the Valley borders the Sacramento Valley and Delta lowland, which allows for some level of pollutant dispersion. As a result, PM2.5 c oncentrations are higher in the southern and central portions of the Vall ey, where geography, emissions, and climate pose significant challenges to air quality progress. Chapt er 3 and Appendix E of the District Plan provide detailed information on the conceptual m odel of PM2.5 formation in the Valley.

Currently, eleven sites routinely monitor PM2.5 in the Air Basin. Table H-1 provides the 2006 annual standard design values and the annual average values for 2004, 2005, and 2006 for each monitoring site with complete data. The design value is a statistic that is used to describe the air quality status of a giv en area relative to the level of the federal standard. The annual design va lues represent the average of the mean annual PM2.5 concentrations measured during the three year period. Table H-2 provides the 24-hourSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-3 standard design value for each monitoring si te with complete data and the yearly 98 th percentile value of the 24-hour concentra tions measured in 2004, 2005, and 2006. The 24-hour design value represents t he average of the yearly 98 th percentile of the 24-hour concentrations measured during the three year period. Attainment is reached when the design value is at or below t he corresponding federal standard.

As shown in Table H-1, current 2006 annual average design values (reflecting the 2004 through 2006 period) r ange from 12.9 ug/m 3 to 18.9 ug/m 3 . The San Joaquin Valley monitoring sites with the highest PM2.5 annual design values are located in the southern and central portions of the basin, including Bakersfiel d and Visalia. Monitors located in the northern portion of the Vall ey, including Stockton, Modesto, and Merced have lower annual PM2.5 design values and a ttain the annual PM2.5 standard. As shown in bold in the table, the high site fo r the region is the Bake rsfield–Planz monitor with a PM2.5 design value of 18.9 ug/m 3

.

Table H-1. PM2.5 A nnual Average Values

Annual Average (ug/m 3 ) Monitor 2004 2005 2006 2006 3-year Annual Average

Design Value (ug/m 3 )
Clovis-N Villa Avenue 15.8 16.0 16.8 16.2 Bakersfield-410 E Planz Road 17.4 19.9 19.3 18.9
Bakersfield-5558 California Avenue 19.0 17.9 18.7 18.5 Bakersfield-Golden State Highway 18.1 18.9 18.6 18.5
Corcoran-Patterson Avenue 17.3 17.6 16.7 17.2
Fresno-1st Street 16.4 16.9 16.8 16.7 Fresno-Hamilton and Winery 17.0 16.9 17.6 17.2
Merced-2334 M Street 15.3 14.1 14.8 14.7
Modesto-14th Street 13.6 13.9 14.8 14.1
Stockton-Hazelton Street 13.2 12.5 13.1 12.9
Visalia-N Church Street 17.0 18.8 18.8 18.2San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-4 Table H-2. PM2.5 98th Percentile 24-hour Values

Annual 98 th Percentile (ug/m 3 ) Monitor 2004 2005 2006 2006 3-year Average of

98 th Percentile Design Value (ug/m 3 ) Clovis-N Villa Avenue 42.4 77.0 51.3 57 Bakersfield-410 E Planz Road 78.6 66.4 50.6 65*
Bakersfield-5558 California Avenue 59.3 63.6 60.5 62 Bakersfield-Golden State Highway 53.8 74.9 64.4 64
Corcoran-Patterson Avenue 49.4 74.5 50.1 58
Fresno-1st Street 52.0 71.0 51.0 58 Fresno-Hamilton and Winery 49.4 71.2 55.0 59
Merced-2334 M Street 43.0 48.3 43.8 45
Modesto-14th Street 45.0 55.0 52.0 51
Stockton-Hazelton Street 36.0 44.0 42.0 41
Visalia-N Church Street 54.0 65.0 50.0 56

*The 24-hour standard is exceeded when the design value is over 65 ug/m 3

As previously mentioned, all monitors in the San Joaquin Valley currently attain the federal 24-hour PM2.5 standard. As s hown on Table 2, 2006 24-hour PM2.5 design values (reflecting the 2004 through 2006 period) range from 41 ug/m 3 to 65 ug/m 3

. Monitoring sites with the highest 24-hour PM 2.5 design values are located in the southern portion of the Valley, around Bakersfiel d. As shown in bold on the table, the high site for the region is Bakersfield- Planz with a 24-hour PM 2.5 design value of 65 ug/m 3

.

b. Recent PM2.5 Mass Trends

Trends observed in the San Joaquin Valley show that considerable progress has occurred in the San Joaquin Valley over the last five years due to the ongoing emissions control program. As shown in Figure H-1, 24-hour design values have decreased approximately 40 percent and, as discussed above, based on the 2004 through 2006 data, attain the federal st andard at all sites in the Basin.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-5 Figure H-1: Comparison of 2006 to 2001 PM2.5 24-hour Design Values

PM2.5 24-hour Design Value

0 20 40 60 80 100 120

Modesto-14th Street Fresno-1st Street Visalia BakersfieldGoldenConcentrations (ug/m3)

2001
2006

All San Joaquin Valley monitors with complete data also show a significant decrease in annual average design values (Fi gure H-2). In 2001, all moni toring sites in the Basin had annual design values greater than 16 ug/m 3 , with the Visalia site at approximately one and a half times the level of the standard. By 2006, design values decreased throughout the basin, and only those sites in the southern and centra l portions of the Valley are still gr eater than 16 ug/m 3 . Bakersfield–Planz is the current high site, with a design value which is 26 perc ent above the standard. The gr eatest rate of progress has occurred in the northern and central basin. From 2001 through 2006, the Modesto site design value dropped 28 per cent, from 19.7 ug/m 3 to 14.1 ug/m 3 , while the Visalia site design value dropped 26 per cent from 24.7 ug/m 3 to 18.2 ug/m 3 . As a result, all monitoring sites in the northern portion of the Valley now attain the annual PM2.5 standard of 15 ug/m 3 . In contrast, the Bakersfield-Go lden site dropped 22 percent from 23.6 ug/m 3 to 18.5 ug/m 3 and the Bakersfield-California site dropped 21 percent from 23.3 ug/m 3 to 18.5 ug/m 3 . This trend is further illustra ted in Figure H-3 which depicts maps of the spatial variations in annual av erage concentrations in 2001 as compared to 2006.

Trends in 24-hour and annual average design val ues were further evaluated using the nonparametric statistical analysis test, known as the Theil test, that U. S. EPA uses in national air quality trend analysis 1 . This method tests for whether upward or downward trends are real (significant) or a chance product of year-to-year variation (not significant). Theil test results indica te the 2001 to 2006 downward trends in 24-hour and three-year annual average PM 2.5 concentrations are statistically significant.

1 U.S. EPA , National Air Quality and Emissions Trends Report, Publication No. EPA 454/R- 03-005, Office of Air Quality and Standards, Air Quality Stra tegies and Standards Division, Research Triangle Park, North Carolina. 2003. http://www.epa.gov/air/airtrends/aqtrnd03/San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-6 Figure H-2: Trends in Annual Average PM2.5 Design Values

Figure H-3: 2001 and 2006 Annual Average Values

PM2.5 (ug/m3) San Joaquin Valley Air Basin National PM2.5 Annual Average (2001)

Stockton

Modesto

Merced

Clovis Fresno-1st

Fresno-Hamilton Visalia

Corcoran

Bakersfield-Golden Bakersfield-California

Bakersfield-Planz 

### Three Year Annual Average PM2.5 Design Values

0 5 10 15 20 25 30

2001 2002 2003 2004 2005 2006 YearConcentrations (ug/m3) Bakersfield-410 E Planz

Bakersfield-5558 California

Bakersfield-Golden

Modesto-14th Street

Stockton-Hazelton

Visalia-N Church

Fresno-1st StreetSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-7 The progress observed in both the annual and the 24-hour PM2.5 sta ndards reflects the linkage between the two standards. The annual average is comprised of individual 24- hour samples which vary throughout the y ear. In the San J oaquin Valley, PM2.5 concentrations exhibit a pronounced seasonal variation, with significantly higher monthly average concentrations during the late fall and winter (November through January). PM2.5 concentrations from Ap ril through September are generally below 15 ug/m 3 . Therefore 24-hour PM2. 5 concentrations during the fall and winter seasons strongly drive the annual average concentra tions. During the late fall and winter, stagnant air, cool temperatures, and high humidi ty can lead to a build-up of PM2.5 over a period of several days to weeks.

Analyses of the changes in the distributi on of the 24-hour c oncentrations between 2001- 2003 and 2004-2006 indicate that the decre ase in both 24-hour and annual average concentrations is the result of the downwar d shift in the distri bution of daily PM2.5 concentrations during the fall/winter period. This can be seen in the decrease in the monthly average concentrations during the fall/winter months between 2001 and 2006 at Bakersfield-California and Fresno (Figures H-4 and H-5).

Figure H-4: Changes in Seasonal Pattern at the Bakersfield-California Monitoring SiteSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-8 Figure H-5: Changes in Seasonal Pa ttern at the Fresno Monitoring Site

A comparison of the changes in the frequen cy distribution of 24-hour concentrations over the last few years provides another means of understanding progress. Data collected from 24-hour samples during 1999-2001 at the Bakersfield site indicate that 6 percent of the samples had conc entrations greater than 65 ug/m 3 (Figure H-6). In comparison, during the 2004-2006 period, the number of samples with PM2.5 concentrations greater than 65 ug/m 3 fell to 1 percent. Duri ng both periods, 45 percent of the samples had concentrations above the le vel of the annual PM2.5 standard of 15 ug/m 3

.

At the Fresno site data collected duri ng the 1999–2001 period indicate that approximately 8 percent of the samples had concentra tions greater than 65 ug/m 3 (Figure H-7), while during the 2004-2006 peri od, only 1 percent of the samples had concentrations greater than 65 ug/m 3 . In addition, during 1999-200 1, 46 percent of the samples had concentrations above the leve l of the annual PM2.5 standard of 15 ug/m 3

, while during the 2004-2006 period, the number of samples wit h concentrations greater than 15 ug/m 3 fell to 34 percent. This analysis , together with the analysis of monthly average PM2.5 trends, further illustrate that progress to date in the annual average is primarily linked to reductions in peak c oncentrations from October through March.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-9 Figure H-6: PM2.5 Concentrations at Bakersfield-California 1999-2001 versus 2004-2006

Figure H-7: PM2.5 Concentrati ons at Fresno 1999-2001 versus 2004-2006San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-10 c. Historical PM2.5 Mass Trends

The PM2.5 Federal Reference Method (FRM) network t hat is used for comparison to the federal standard was deployed in 1998 a nd 1999. However, PM2.5 data have been routinely collected in the San Joaquin Vall ey Air Basin since the late 1980s using dichotomous samplers that were operat ed for research purposes. The PM2.5 dichotomous data correlate very well with the FRM data (r=0.98), but are biased lower than the FRM by 12 percent, therefore an abs olute comparison to the FRM can not be made. However, the relative changes in the dichotomous data do provide a longer-term context for assessing progress. Figure H-8 depicts PM2.5 concent rations at four sites. At all of these sites, the 3-year av erage concentrations dec reased until 1998, then increased until 2000. At two of the three hi ghest sites, Bakersfield and Visalia, the Hyear average concentrations decreased abo ut 40 percent from 1990 to 1998 (the Bakersfield site trend has a gap from 1994 to 1996). PM2.5 concentrations at Bakersfield then increased 19 percent from 1998 to 2000. The dichotomous data record at the third high site, Fresno, started in 1992. From 1992 to 1998, PM2.5 concentrations decreased 21 percent, follow ed by a 12 percent increase from 1998 to 2000. PM2.5 concentrations at the low site , Stockton, decreased 40 percent from 1991 to 1998, followed by a 20 percent increas e from 1998 to 2000. The period between 1999 and 2001 included a number of adverse winter episodes which likely lead to higher annual averages during this period. However, overall concentrations declined 20 to 30 percent over the period from 1990 through 2001. Looking at dichotomous data and FRM data together therefore illustrates an overall long-te rm improvement in PM2.5.

Figure H-8: Trends in Three-Year Averag e PM2.5 Concentrations Measured with Dichotomous Samplers



### PM2.5 Dichot Three-Year Average Trend

0 5 10 15 20 25 30 35199019911992199319941995199619971998199920002001Concentrations (ug/m3)

Bakersfield*

Fresno-1st Street

Stockton

VisaliaSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-11 d. Chemical Composition and Emissions Trends

Current Chemical Composition

Particulate matter (PM) consists of many di fferent chemical compo nents. Investigating these different components and how they vary by site and season provides us with a better understanding of their complexity and res ponses to the emission control program. This mix of chemical components consists of both directly emitted PM such as geological material and elemental carbon (soot ), known as primary PM, as well as PM formed in the atmosphere from the reaction s of precursor gases, known as secondary PM. These precursor pollutants include nitr ogen oxides (NOx), sulf ur oxides (SOx), reactive organic gases (ROG), and ammonia. NOx, SOx, and ammonia combine to form secondary ammonium nitrate and su lfate. ROG can form secondary organic carbon, as well as participate in the pr oduction of secondary ammonium nitrate.

In the San Joaquin Valley, chem ical components are routinely measured at four sites, Bakersfield, Fresno, Visalia, and Modesto. These sites repres ent urban areas in different portions in the air basin. The chemical composition of PM2.5, seasonal variability, and trends in these components at tw o of these sites, Fresno and Bakersfield are discussed below to provide further insight into the linkage between observed progress and ongoing emission reductions.

The annual average PM2.5 chemical compositi on for Bakersfield and Fresno is shown in Figure H-9. Ammonium nitrate and organic carbon are the major constituents at both sites. However, at Bakersfield, ammoni um nitrate constitutes a higher percentage (39 percent) of PM2.5 t han organic carbon (35 percent), wh ile the reverse (37 percent ammonium nitrate and 41 percent organic carbon) occurs in Fresno. Ammonium nitrate is formed in the atmosphere from chemical reactions of NOx emitted from motor vehicles and stationary combustion source s. Stagnant, cold, and damp conditions in the winter promote the formation and accumu lation of ammonium nitrate. Burning activities, such as residential wood combusti on, cooking, and direct tailpipe emissions from mobile sources are majo r sources of organic carbon. Ammonium sulfate is also formed in the atmosphere from chemical re actions of SOx emitted from combustion sources. Ammonium sulfate constitutes about one tenth of ambient PM2. 5 at both sites. Elemental carbon resulting fr om mobile and stationary combustion sources, and geological material from roads and other dus t producing activities also contribute to PM2.5 at both sites, but to a lesser extent.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-12 Figure H-9: 2004-2006 Average Chemical Composition of PM2.5 at Bakersfield and Fresno

Figures H-10 and H-11 illustrate the seasonal variability in chemical components that make up PM2.5 for the Bakersfield and Fres no sites averaged over 2004 through 2006. As discussed previously, PM2.5 concentrations are highest during the fall and winter. These higher concentrations are driven by incr eases in ammonium nitrate and carbon. At the Bakersfield site (Figure H-10), ammo nium nitrate is highest during the fall and winter months (November through January) and lowest from April through September. Ammonium nitrate concentrations at Fresno follow the same trend. Cold and humid conditions during the fall and winter favor t he formation of ammonium nitrate in the atmosphere from chemical reactions of nitrogen oxides emi tted from mobile and stationary combustion sources. At the Fres no site (Figure H-11), organic carbon has a similar trend as that of ammonium nitrate. At the Bakersfield site, organic carbon is also highest during the fall and winter months, but at this site organic carbon levels start high in January, decrease until April and then in crease almost linearly until reaching a maximum in December. Incr eased activity in residentia l wood combustion during the fall/winter period is one cause of higher organic carbon concentrations. At both locations, elemental carbon component remain s fairly constant throughout the year, while the ammonium sulf ate component is more pr evalent from May through September, and the geological com ponents from April through October. 2004-2006 Average Composition Bakersfield

AmmNitrate 39%

AmmSulfate
13% OC
35% Geological
6% EC
5% Elements 2% 2004-2006 Average Composition Fresno

AmmNitrate 37%

AmmSulfate
11% OC
41% Geological
4% EC
5% Elements 2%San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-13 Figure H-10: Seasonal Variation in PM2. 5 Chemical Component s at Bakersfield

Figure H-11: Seasonal Variation in PM2.5 Chemical Co mponents at FresnoSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-14 Chemical Composition and Precursors Trends

As discussed previously, monitoring sites in the San Joaquin Valley have shown PM2.5 concentrations decreasing from 2001 to 2006. Trends in individual chemical components and precursor concentrations, as we ll as emissions inventory trends were evaluated to understand the main chemical components responsible for this progress and to evaluate the response to our ongoing control program. Figures H-12 and H-13 illustrate recent trends in PM2.5 concentrati ons and its individual chemical components at Fresno and Bakersfield. Improvements in PM2.5 in the San Joaquin Valley can be mostly attributed to reductions in carbonace ous aerosols and ammonium nitrate. In Fresno, carbonaceous aerosols have droppe d 37 percent, and ammonium nitrate concentrations have dropped 24 percent. T he overall improvement in PM2.5 mass observed in Fresno is therefore due in most part to reductions in carbonaceous aerosols (63 percent), with a smaller portion of the remaining PM2.5 improvement due to reductions in ammonium nitrate (24 percent). In Bakersfield, carbonaceous aerosols have dropped by 16 percent and ammonium nitrate concentrations dropped by 23 percent since 2002. Therefore 41 percent of the overall reduction in PM2.5 mass is due to reductions in carbonaceous aerosols, wh ile 59 percent is due to reductions in ammonium nitrate. Under standing the role of car bonaceous compounds in PM2.5 pollution, the San Joaquin Valley Air Poll ution Control Distric t made the Valley’s Residential Wood Combustion Rule more stri ngent in 2003, which may have contributed to the observed decrease in carbonaceous aerosols.

Figure H-12: Trends in PM2.5 Mass and Chemical Components at Fresno

* The three-year design value is not considered valid.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-15 Figure H-13: Trends in PM2.5 Mass and Chemical Co mponents at BakersfieldCalifornia

Concentrations in ambient NO x, a precursor to nitric acid and ammonium nitrate decreased steadily from 2001 through 2006. Fi gures H-14 and H-15 ill ustrate the shortterm trends in the Basin aver age NOx compared to ammonium nitrate concentrations in Fresno and Bakersfield. Ambient NOx c oncentrations in the Valley have shown a modest decrease of 15 percent. Ammonium nitrate concentrations were highest in 2002 at both sites, with a small decreas e between 2001 and 2006 at Fresno of 7 percent.

While the short-term trends for ammoni um nitrate have been modest, longer-term records show concomitant decreases betwe en ambient NOx and amm onium nitrate as well as between ambient SO2 and ammonium su lfate. Figure H-16 shows trends in the basin three-year average ambient NOx c oncentrations and the corresponding ambient nitrate measurements from t he PM10 network extending back to the late 1980s. The hills and valleys in the ammonium nitrate concent rations reflect the e ffects of the varying meteorology on ammonium nitrate formation . Since 1987, ambient NOx has decreased 50 percent while ammonium nitrate decreas ed by 35 percent. Figure H-17 shows the trends from 1987 to 1996 in the basin three- year average ambient SO2 concentrations and ammonium sulfate measurements from t he PM10 network. During this period SO2 decreased by 42 percent with a concurrent decrease in PM10 sulfate of 39 percent.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-16 Figure H-14: PM2.5 Ammonium Ni trate Compared to NOx – Fresno

Figure H-15: PM2.5 Amm onium Nitrate Compared to NOx - BakersfieldSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-17 Figure H-16: Long-Term Trends in Three-Y ear Average Concentrations of PM10 Nitrate and NOx in San Joaquin Valley

Three-year Average Concentrations
of PM10 Nitrate and NO x in San Joaquin Valley

0 1 2 3 4 5 6 7 8 9 101987198819891990199119921993199419951996199719981999200020012002200320042005PM10 Nitrate (ug/m3)

0 1 2 3 4 5NOx(pphm)
NO3-

NOx

Figure H-17: Long-Term Trends in Three-Y ear Average Concentrations of PM10 Sulfate and NOx in the San Joaquin Valley

Three-year Average Concentrations of PM10 Sulfate
and SO 2 in the SJV

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.01987198819891990199119921993199419951996199719981999200020012002200320042005PM10 Sulfate (ug/m3)

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0SO2(pphm)
SO4--

SO2 SO2 monitoring discontinued
in 1997San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-18 Emission Trends

At the same time that ambient concentra tions have been declining, the emissions of pollutants that contribute to the different components of PM 2.5 have been decreasing. Figure H-18 illustrates the recent emission tr ends in the San Joaquin Valley air basin from 2001 through 2005. The greatest decre ase in emissions occurred in ROG with a decrease of 33 tpd or 8 percen t. NOx also decreased slight ly, with a decline of 28 tpd, or 4 percent. Direct PM2.5 emissions showed a decrease of 7 tpd, or 7 percent, while SOx emissions did not change.

The combined downward trends in PM2.5 co mponents, precursor concentrations, and emissions all indicate that over both in the short- and long-term the ongoing control program has had substantial benef its in improving air qualit y and that similar emission reductions in the future should provide cont inuing progress towards attaining the federal PM2.5 standards.

Figure H-18: PM2.5 and PM 2.5 Precursor Emission Tre nds in the San Joaquin Valley

Annual Emission Inventory Trends 2001-2005

0 100 200 300 400 500 600 700

2001 2002 2003 2004 2005Emissions (tpd) NOx
ROG
SOx
PM2.5San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-19 3. OBSERVATIONAL MODELS AND DIAGNOSTIC ANALYSES

Observational models take advantage of moni tored data to draw conclusions about the relative importance of different types of em issions and precursors as factors contributing to observed PM2.5 concentrations. Acco rding to U.S. EPA guidance, observational models can be used to corroborate the effects of prior control strategies, as well as identify the potential effectiveness of proposed control approaches. U.S. EPA recommends using both source apportionmen t (receptor models) and indicator species approaches. The two most widely applied receptor modeling approaches are multivariate statistical models such as positive matrix factorization (PMF) and the chemical mass balance model (CMB). Receptor models are particularly useful in identifying the source contributions to directly emitted PM. This section summarizes results from prior source apportionment studies as well as bot h PMF and CMB applied to recent data. In addition, previous work using an indicator species approach to assess the limiting precursor in secondary nitrate formation in the San Joaquin Valley is discussed.

a. Observational Models

Prior Source Apportionment Studies

The Chemical Mass Balance (CMB), and the Positive Matrix Factorization (PMF) and UNMIX (named for its function, which is to "unmix" the concentrations of chemical species measured in the ambient air to ident ify the contributing sources) multivariate receptor models have been applied to PM2.5 data collected in the San Joaquin Valley. Chow, et al. 2 used the CMB source apporti onment model to estimate the contribution of sources to PM2.5 in Fres no during high PM2.5 days occu rring from December 15, 2000 through February 3, 2001 illustrated in Figur e H-19. Secondary ammonium nitrate is the most significant source, contributi ng 32 percent to the measured PM2.5. Residential wood combustion constitutes 30 percent of PM2.5. Vehicle emissions account for 13 percent of PM2. 5, with similar contributions from gasoline (7 percent) and diesel (6 percent) fueled vehicles. C ooking accounts for 12 percent of PM2.5.

2 J .C. Chow, J. G. Watson, D. H. Lowenthal, L.-W. A. Chen, B. Zelinska, L. R. Rinehart, and K. L. Magliano: Evaluation of organic markers for chemical mass balanc e source apportionment at the Fresno Supersite, Atmospheric Chemistry and Physics Discussions, 6, 10341 – 10372, 2006San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-20 Figure H-19: Source Contribution to PM2. 5 Concentrations at Fresno Estimated Using the Chemical Mass Balance (CMB) Method

Chen, et al. 3 applied the PMF and UNMIX models to chemically speciated PM2.5 measurements from 23 sites operated in the in the San Joaqui n Valley during the 2000/2001 Central California PM Air Quality Study (CRPAQS) to estimate source contributions. Figure H-20 illustrates the resulting s ource contribution throughout the Valley, estimated for the period when high PM2.5 concentrations occurred (November through January). PMF and UNMIX source contri bution estimates are similar. Particles formed through chemical reactions in the at mosphere, including ammonium nitrate and secondary organic compounds are the major c ontributors, accounting for 48 percent (PMF) and 51 percent (UNMIX) of PM2.5. Residential wood combustion follows, with a contribution of 23 percent (PMF) and 24 percent (UNMIX). Particles directly emitted from motor vehicles account for 10 percent (PMF) and 15 percent ( UNMIX) of PM2.5. In addition, the zinc component resulting fr om the PMF analysis is thought to be related to brake and tire wear and cont ributes 9 percent to PM2.5.

3 L.-W. A. Chen, J. G. Watson, J. C. Chow, and K. L. Magl iano: Quantifying PM2.5 Sour ce Contributions for the San Joaquin Valley with Multivariate Recept or Models, submitted for publication, 2006. PM2.5 Source Contribution (CMB) in Percent Fresno - 2000/2001 Winter Average

Wood Burning

30% Ammonium Nitrate

32%

Ammonium Sulfate

2% Cooking
12% Vehicle Exhaust (Gasoline)
7% Unknown
11% Vehicle Exhaust (Diesel)

6%San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-21 Figure H-20: Source Contribution to PM2. 5 in the San Joaquin Valley Estimated Using the Positive Matrix Factoriz ation (PMF) and the UNMIX Models

Recent Studies

To evaluate the major PM2.5 sources and thei r contributions in the San Joaquin Valley using recent data, two differ ent source apportionment techni ques were applied to data collected in 2003 through 2006. The Chemical Mass Balance model (CMB) uses measured source profiles and chemical spec iation data in combination to determine source contributions. A f undamental underlying assumption is that the source profiles used as input are appropriate and representativ e for the region. In contrast, PMF does not require the input of sour ce profiles, but rather eval uates the covariance of the chemical species to determine a set of factors, which are typi cally interpreted as source types. Source contributions are then calcul ated for each of the fa ctors. Because the factors reflect species which vary in time in a similar manner, the factors may reflect the impacts of primary source s, as well the secondary species that have condensed on these primary particles. Since each te chnique has strengths and weaknesses, combined the two source apportionment techniques provide complementary results.

Positive Matrix Factorization

The PMF2 model was applied to chemically speciated PM2.5 data collected at the Fresno-First St. and Bakersfield-California Ave. Speciation Trends Network (STN) monitoring sites from July 2003 through December 2006. The average source contribution estimates illustrated in Figure H-21 show ammonium nitrate is the major contributor to PM2.5 at both sites (41 percent at Fresno and 45 percent at Bakersfield). Biomass smoke contributes similar percentages at both sites (8 percent at Fresno, 7 percent at Bakersfield) as does the total aged aerosol (10 percent at Fresno, 11 percent at Bakersfield). The main differ ences in source contribution between the two sites include particles directly emitted from motor vehicles, which at Fresno account for 23 percent of PM2.5, the 2 nd major component, while at Bakersfield account for 13 percent. Ammonium sulfate accounts for 10 percent of PM2.5 at Fresno and Source Contibution (PMF) in Percent San Joaquin Valley - 2000/2001 Winter Average

Motor Vehicle
10% Residential

Wood Combustion
23% Zinc
9% Cooking
3% Fugitive Dust
5% Ag-Dairy
2%

Ammonium Nitrate and Secondary

Organic

48% Source Contribution (UNMIX) in Percent San Joaquin Valley - 2000/2001 Winter Average

Motor Vehicle
15% Ag-Dairy
2% Fugitive Dust
3%

Residential

Wood Combustion
24% Ammonium Nitrate and Secondary

Organic

51% Cooking

5%San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-22 14 percent at Bakersfield. Airborne soil is a minor contributor to PM2.5 at Fresno (3 percent), with a 9 percent c ontribution at Bakersfield.

Figure H-21. Average Source Contri butions Estimated Using PMF2 (2003-2006)

Chemical Mass Balance Modeling

Annual average source contributions at Bake rsfield-5558 California Avenue (BAC) and Fresno-1st Street (FSF) were also estima ted by applying the Chemical Mass Balance (CMB 8.2) model to indivi dual PM2.5 sample concentra tions collected between January 1, 2004 and December 31, 2006 and using source profiles for PM2.5 developed during previous studies. Source contribution es timates were calculated based on the 2004- 2006 annual average of the individual sample s. Figure H-22 shows the calculated contributions to ambient fine particulate ma tter made by sources included in the model. Ammonium nitrate was the most significant source contributing 44% and 39% of the PM2.5 mass at Bakersfield and Fresno, res pectively. Ammonium sulfate accounted for 12% at Bakersfield and 10% at Fresno. T he motor vehicle exhaust (diesel and gasoline combined) contribution was 9% at both si tes. Vegetative burning, which included residential wood combustion and agricultural and prescribed burning, contributed 9% and 14%, respectively, of the PM2.5 mass. T he sea salt contribution was negligible at both sites. The ‘Other O C’, which represents contribut ions from secondary organic carbon, other unidentified prim ary sources, and the possibl e positive sampling artifacts of organic carbon, accounted for 20% to 23% of the PM2.5 mass. July 2003 - Dec. 2006 Average Source Contribution in Fresno-1st Street

Airborne

soil 3% Secondary nitrate 41% Aged aerosol with sea

salt2 5%

Motor vehicle

23% Industrial 5%

Biomass smoke

8% Aged aerosol with sea

salt1 5%

Secondary Sulfate

10% July 2003 - Dec. 2006 Average Source Contribution in Bakersfield-California Ave.

Secondary

nitrate 45% Airborne

soil 9% Industrial 1% Aged aerosol with sea

salt2 7%

Motor vehicle

13% Aged aerosol with sea

salt1 4%

Biomass smoke

7%

Secondary Sulfate

14%San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-23 Figure H- 22. CMB Model Calcul ated 2004-2005 Average PM2.5 Source Contributions.

While the specific contributions vary to some extent, taken t ogether these sources apportionment studies highlight the impor tance of secondary ammonium nitrate contributions to both the 24-hour and annual average concentrations. In addition, biomass burning and mobile sources were found to be significant contributors to primary PM2.5.

Diagnostic Analyses

Indicator Species Approach

As discussed in prior sections, trends in a mmonium nitrate concentrations have tracked well with concurrent reductions in NOx, suggesting that NOx control is an effective approach for ensuring further reductions in a mmonium nitrate. An indicator species approach provides an additional method to in vestigate which chemical precursor a secondary species such as ammonium nitrat e is most responsive to control of. Ammonium nitrate is formed in the atmo sphere through the reactions of precursor nitrogen oxides (NOx), reactive organic gases (ROG), and ammonia (NH3). The amount of each precursor in the atmosphere relative to each other determines how much ammonium nitrate is formed. The c hemistry is complex, but essentially the precursor in shortest supply will limit how much ammonium nitrate is produced. Reducing emissions of this limiting precur sor provides the best opportunity to cut ammonium nitrate levels. In simple te rms, photochemical reactions of NOx and ROG form nitric acid (HNO3). Nitric acid then reacts with ammonia (NH3) to form ammonium BAC Modeled 2004-2006 Avg

Ammonium
Nitrate
45%

Ammonium

Sulfate

12% Sea Salt

0% Biomass Burning

9% Other OC

20% Airborne Soil
4% Tire/Brake
1%

Motor
Vehicle

9% FSF Modeled 2004-2006 Avg

Ammonium
Nitrate
39%

Ammonium

Sulfate

10% Sea Salt

0% Biomass Burning

14% Other OC

23% Airborne Soil
4%

Motor
Vehicle

9% Tire/Brake
1%San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-24 nitrate. Lurmann, et al. 4 compared ammonia and nitric acid ambient concentrations measured in the San Joaquin Valley duri ng the winter of 2000/2001, as part of CRPAQS. Figures H- 23 and H- 24 show the concentrations of nitric acid and ammonia measured at the rural Angiola site and at th e urban Fresno site. At both sites ammonia concentrations are generally at least an order of magnitude higher t han the nitric acid concentrations. These ammonia-rich condi tions throughout the Valley indicate that, during the winter, nitric acid is the limiting precur sor.

Figure H-23: Comparison of Ammonia and Nitric Acid Concentrations Measured at Angiola during the Winter of 2000/2001 as Pa rt of CRPAQS

4 F. W. Lurmann, S. G. Brown, M. C. McCarthy, and P. T. Roberts: Processes Influencing Secondary Aerosol Formation in the San Joaquin Valley during Winter, Jour nal of Air and Waste Managem ent Association, 56, 1679- 1693, 2006. Comparison of Ammonia and Nitric Acid Concentrations Angiola - Winter 2000/2001

-10

0 10 20 30 40 50 60

-2 0 2 4 6 8 10 12 14 16 18 HNO3 Concentration (ug-N/m3)NH3 Concentration (ug-N/m3)

1:1 LineSan Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-25 Figure H-24: Comparison of Ammonia and Nitric Acid Concentrations Measured at Fresno during the Winter of 2000/2001 as Part of CRPAQS

Comparison of Ammonia and Nitric Acid Concentrations Fresno - Winter 2000/2001

-4 0 4 8 12 16 20

-2 0 2 4 6 8 HNO3 Concentration (ug-N/m 3 )NH3 Concentration (ug-N/m3)

1:1 Line

4. AIR QUALITY MODELING

a. Rollback Modeling

In addition to the evaluation of air qualit y trends and the observational and diagnostic analyses, a rollback modeling analysis was c onducted by the District to estimate the impacts of future emission reductions on result ing air quality. An extensive discussion of the rollback methodology and the result s are provided in Chapter 3 and associated spreadsheets of the District Plan. The rollback modeling showed that Fresno and Corcoran would attain the annual PM2.5 standard with baseli ne emission reductions in 2014. With the addition of the ARB and District proposed control strategy, both Visalia and Bakersfield-Planz would attain in 2014 as well.

b. Grid-Based Modeling

As stipulated in the EPA Modeling Guidance, a grid-based photochemical model is necessary to perform the modeled attainment test for PM 2.5 (EPA, 2007). Such models offer the best availabl e representation of important atmospheric processes and are an essential tool in analyzing the im pacts of proposed emissions controls on pollutant concentrations. The EPA recomme nds guidelines for choosing a model for use in the attainment test. For example, the model sour ce code should be free or low cost, modeling elements should have underg one rigorous scientific peer-review, and it should have been shown to perform well in the past for similar applications.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-26 The Community Multiscale Air Qualit y Modeling System (CMAQ) has been selected for use in the PM 2.5 modeled attainment demonst ration for the San Joaquin Valley Air Pollution Control District. CMAQ is a state- of-the-science “one-atmosphere” system that treats major atmospheric and land processes (e.g., advection, diffusion, gas phase chemistry, gas-particle mass transfer, nucleation, coagulation, wet and dry deposition, aqueous phase chemistry, etc.) a nd a range of species (e.g., anthropogenic and biogenic, primary and seco ndary, gaseous and particulat e) in a comprehensive framework (EPA, 1999; CMAS, 2007).

CMAQ was run for the year 2000 to provi de the basis for the model performance evaluation. It was during 2000 t hat the California Regional PM 10 /PM 2.5 Air Quality Study (CRPAQS) took place. The study resulted in a wealth of data with which to evaluate model performance. As it is necessary to execute simulations for a model reference year and a future year to perform the re commended modeled attainment demonstration, 2005 and 2014 were also simulated. Simulations for all years were driven by the meteorological inputs for 2000, while emissions varied from year to year.

Regional air quality modeling only represents a portion of the attainment test. In order to perform the EPA-recommended Specia ted Modeled Attainment Test, or SMAT, the relative response between the modeled reference and future years must be considered in conjunction with observations. This approach minimizes the uncertainties in predicting future year attain ment that result from potenti al model bias in predicting absolute species concentrations.

Federal Reference Method (FRM) PM 2.5 mass measurements provide the basis for nonattainment designations. For this re ason it is recommended that the FRM data also be used to project future air quality and progress towards attainment of the healthbased National Ambient Air Q uality Standard (NAAQS) for PM 2.5 . However, given the complex physicochemical nature of PM 2.5 , it is necessary to consider individual species as well. While the FRM measurements give the mass of the bulk sample, a method for apportioning this bulk mass to individual PM 2.5 components is a first step towards determining the best targets for emissions cont rols in order to reach NAAQS levels in a timely manner. Given that (1) attainment status is currently dependent upon FRM measurements and (2) concent rations of individual PM 2.5 species need to be considered in order to understand the nature of and efficient ways to ameliorate the PM 2.5 problem in a given region, a method has been developed to speciate bulk FRM PM 2.5 mass with known FRM limitations in mind. This method is referred to as the measured S ulfate, A djusted N itrate, D erived W ater, I nferred C arbonaceous material and estimated aerosol acidity ( H +) approach or “SANDWICH”. SA NDWICH is based on speciated measurements from other (o ften co-located) samplers, such as those from the Speciated Trends Network (STN), and the k nown sampling environme nt of the FRM. The approach serves to provide mass clos ure, reconciliation between speciated and bulk mass concentration measurements, and the basis for a connection between observations, modeled PM 2.5 concentrations, and the air quality standard.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-27 The SMAT procedure was applied to FRM m onitors operating in the San Joaquin Valley with minimal deviations from U. S. EPA’s recommended procedure. The 2005 design value was used as a basis from which to project forwar d to estimated future year design values for the year 2014. Speciation data for four STN (speciation) sites was used to speciate the FRM mass for all FRM si tes. For those sites not collocated with STN monitors, “surrogate” speciation si tes were determined based on analysis of CRPAQS data to determine which sites had similar speciation profiles. The composition was assumed to be the same at all three Bakersfield sites (BAC, BGS, and BEP). Similarly, the percent composition at the two Fresno sites (FSF and FSH) was assumed to be the same. In addition, Sto ckton (SOH), Clovis (CLO ), Corcoran (COP), and Modesto (MRM), were assumed to have t he same speciation as one of the four speciation sites based on CRPAQS data analysis.

Quarterly average species concentrations were calculated at each STN site using the SANDWICH procedure. Modeled concentrations for the reference year (2005) and future year (2014) for each component were extrac ted for the FRM sites as a nine-cell average. The relative response factors were calculated for each component for each quarter. These calculations were performed using all modeled days, as we assumed that the selected FRM measur ements provided a stable quarterly average value.

These quarterly species percentages were then multiplied against the base year design value for 2006 (the average FRM PM 2.5 concentrations for 2004, 2005, and 2006). The quarterly observed species concentrations were then multiplied by the RRFs and summed and averaged to get a future year PM 2.5 design value at each FRM site. See Table H-3 for the pr edicted baseline and controlled 2014 PM 2.5 design values. For the “controlled” 2014 emissions sensit ivity scenario described above, future annual PM 2.5 concentrations at all FRM sites are below the annual PM 2.5 NAAQS of 15.0 μ g/m 3

, and, therefore, the San Joaqui n Valley has passed the s peciated modeled attainment test for the annual PM 2.5 NAAQS.

A similar procedure to the attain ment demonstration for the annual PM 2.5 standard was followed for the 24-hour PM 2.5 standard attainment demonstration. The exception was that only t he top 25% of the measur ed and modeled days for each quarter were used instead of all available da ys. The top 25% of the days are expected to be more representative of the 24-hour design value than would all available days for a given quarter.

Table H-4 shows the pr edicted 2014, 24-hour PM 2.5 design values for the top five 2006 design value sites for the co ntrolled emissions case. As shown, all sites in the SJV attained the 24-hour standard in 2006, and fu rther emissions controls do not cause any monitors to become non-attainment in 2014.San Joaquin Valley Unified Air Polluti on Control District April 30, 2008

Appendix H: Weight of Evidence 2008 PM2.5 Plan H-28 Table H-3. Reference and future year annual design values for SJV FRM sites

Site Code Speciation 2006 DV 2014 Baseline DV 2014 "Controlled" DV Bakersfield - 5558 California BAC BAC 18.51 15.40 13.84

Bakersfield - 410 E Planz Road BEP BAC 18.86 15.83 14.30

Bakersfield - Golden State BGS BAC 18.64 16.32 14.68

Clovis - N Villa Avenue CLO FSF 16.39 14.83 13.40

Corcoran - Patterson Avenue COP VCS 17.24 14.61 13.12

Fresno - 1st Street FSF FSF 16.68 14.77 13.32
Fresno - Hamilton and Winery FSH FSF 17.16 15.06 13.59

Merced - 2334 M Street MRM M14 14.69 13.07 11.96
Modesto - 14th Street M14 M14 14.10 12.40 11.33
Stockton - Hazelton Street SOH M14 12.93 11.92 11.01
Visalia - N. Church Street VCS VCS 18.20 15.88 14.29

Table H-4. Reference and future year 24-hour design values for SJV FRM sites

Site Code Speciation 2006 DV 2014 "Controlled" DV Bakersfield - 5558 California BAC BAC 62.4 42.9

Bakersfield - 410 E Planz Road BEP BAC 65.2 41.9

Bakersfield - Golden State BGS BAC 64.4 44.6
Fresno - 1st Street FSF FSF 58.0 42.2
Fresno - Hamilton and Winery FSH FSF 58.5 40.3