Appendix A: Analysis of Ambient Air Quality DRAFT Appendix A-1

Appendix A: Analysis of Ambient Air Quality

This Progress Report evaluates the San Joaquin Valley’s (Valley) ambient PM2.5 

concentrations since the 2008 PM2.5 Plan through a variety of metrics. The District 

conducted extensive analysis of ambient air quality data to better understand the nature 

of observed improvements as well as areas within the data set that have been more 

resistant to improvement. This Appendix presents the District’s thorough analysis, 

which was summarized in Section 3 of this Progress Report. 

PM2.5 monitoring began in 1999. The Valley’s PM2.5 monitoring network is reviewed 

and described in the District’s Annual Monitoring Network Plans.1 The District uses 

ambient air quality data as maintained in EPA’s Air Quality System (AQS),2 the official 

repository for ambient air quality data. Copies of official PM2.5 data and design value 

reports are available upon request. PM2.5 data from 2010 are preliminary as of the 

time of these analyses. Data certification for 2010 will be complete in mid-2011. Where 

possible and applicable, the District includes 2010 data throughout this appendix. 

A.1 Design Values 

Design values are one metric for assessing air quality improvements. Design value 

calculations are three-year averages that follow U.S. Environmental Protection Agency 

(EPA) protocols for rounding, averaging conventions, determining sufficiency in the 

number of samples, etc. The 2008 PM2.5 Plan more fully describes this protocol. The 

results provide consistency and transparency to determine basin-wide attainment for 

both components of the federal PM2.5 NAAQS: the 24-hour PM2.5 standard of 65 

μg/m3, and the annual PM2.5 standard of 15 μg/m3. If any monitoring site within the air 

basin has either a 24-hour or annual PM2.5 design value higher than the respective 

standard, then the entire air basin is designated nonattainment. The 2008 PM2.5 Plan

demonstrated that all Valley sites will attain the 1997 PM2.5 NAAQS by 2015. 

Table A-1 shows single-year, 98th percentile averages, and these values are used to 

generate the three-year average 24-hour design values in Table A-2. This data is 

shown graphically in Figure A-1 and A-3. Bakersfield’s 24-hour design values have 

increased slightly to levels just above the 24-hour standard. As described in Section 3 

of this Progress Report, and as will be documented in this Appendix, wildfires and data 

handling contribute to Bakersfield’s resistant 24-hour design values. 

Table A-3 shows single-year average PM2.5 concentrations, and these values are used 

to generate the three-year average annual design values in Table A-4. This data is 

shown graphically in Figures A-2 and A-4. Most Valley air monitoring sites do not meet 

the annual PM2.5 standard. The 2008 PM2.5 Plan identified the annual PM2.5 

 

1

 For more details on the San Joaquin Valley air monitoring sites, refer to San Joaquin Valley Air Pollution Control 

District Ambient Air Monitoring Network Plan, June 30, 2010 

http://www.valleyair.org/aqinfo/Docs/02%20FINAL%202010%20monitoring%20network%20plan.pdf 2

 U.S. Environmental Protection Agency. Technology Transfer Network; Air Quality System: AQS Web Application. 

Retrieved from website: http://www.epa.gov/ttn/airs/airsaqs/aqsweb/
Appendix A-2 DRAFT SJVAPCD PM2.5 Progress Report

standard of 15 μg/m3 as the primary progress indicator, since this will be the more 

challenging component of the NAAQS for the Valley to attain. 

Average ambient PM2.5 concentrations vary by monitoring site within the Valley. In 

general, monitoring sites in the northern part of the Valley record the lowest ambient 

PM2.5 concentrations. The Bakersfield-Planz monitoring site was the design site in the 

2008 PM2.5 Plan, meaning it was the site with the highest PM2.5 design values based 

on 2004-2006 data. Most of the Valley’s annual PM2.5 design values have decreased 

from their 2004-2006 levels, and all of the Valley’s annual PM2.5 design values have 

decreased since PM2.5 monitoring began. Section A-2 of this Appendix presents 

several caveats to consider in interpreting design values. 

Evaluating multiple measures of air quality can provide a broader picture of overall air 

quality progress. Single-year averages (Tables A-1 and A-3) were lower in 2010 than in 

2007 for every monitoring site and for both annual and 24-hour NAAQS levels. Also, in 

2010, only two Valley monitoring sites had annual averages above 15 μg/m3, compared 

to nine monitoring sites above this level in 2008 and all sites above this level in 2000. 

As noted in ARB’s Progress Report on Implementation of PM2.5 SIPs for the South 

Coast and San Joaquin Valley Air Basins and Proposed SIP Revisions, adopted on 

April 28, 2011, between 2001 and 2010, the number of days considered unhealthy 

under the Air Quality Index (AQI) in the Valley has been cut in half (page 12 of ARB’s 

Progress Report; see also Section 3.1.1 of the District’s Progress Report). As explained 

in section A-3 of this Appendix (and Section 3 of this Progress Report), for many 

parameters, all Valley sites are showing important PM2.5 improvements. 

Notes on Tables A-1 through A-4:

 2010 data: District staff acquired 2010 data from AQS on March 8, 2011. This 

data is preliminary and has not yet been fully reviewed for quality assurance and 

control. 

 Empty cell: No data or insufficient data 

 Asterisk (*): Values do not meet completeness criteria 

 Turlock 2008: This site only operated for about six weeks in 2008. Data for this 

site and time period is available in AQS. Since this site operated for less than 

one full quarter in the calendar year, its data is not representative of an annual 

average and is therefore not included in annual analysis. However, this data is 

used for 24-hour average analysis. 

 Bakersfield-Golden 2010: This site only operated for one week in 2010. Data 

for this site and time period is available in AQS. Since this site operated for less 

than one full quarter in the calendar year, its data is not representative of an 

annual average and is therefore not included in annual analysis. However, this 

data is used for 24-hour average analysis. 
Table A-1 EPA AMP 480 Design Value Report, Single year 24-hour PM2.5 98th percentile value

SJV Monitoring Site 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 

Stockton 79.0 55.0 58.0 50.0 41.0 36.0 44.0 42.0 48.0 61.6 Modesto 100.0 71.0 69.0 69.0 47.0 45.0 55.0 52.0 57.4 53.9 Turlock 67.4 Merced 91.9 60.0 49.3 55.1 44.2 43.0 48.3 43.8 52.7 54.0 Fresno-1st 120.0 90.0 75.0 75.0 56.0 52.0 71.0 51.0 67.0 57.4 Fresno-Winery 64.8 61.5 71.9 49.7 49.4 71.2 55.0 57.4 44.5 Clovis 59.2 72.5 71.5 53.2 48.1 52.4 63.0 51.3 60.9 49.0 Corcoran 53.0 55.1 89.5 65.1 42.2 49.4 74.5 50.1 57.9 47.9 Hanford Visalia 114.0 103.0 96.0 70.0 47.0 54.0 65.0 50.0 59.7 62.1 Bakersfield-Golden 95.3 93.9 95.9 80.4 51.9 53.9 74.9 64.4 67.7 60.8 Bakersfield-California 97.4 92.7 94.9 73.0 48.3 61.5 63.2 60.5 73.0 64.5 Bakersfield-Planz 76.5 90.6 66.8 47.5 47.6 66.4 64.7 72.2 72.3 

Please see table notes on page A-2 of this appendix

Table A-2 EPA AMP 480 Design Value Report, 24-hour PM2.5 Design Values (three-year aver

compared to standard of 65 μg/m3 

SJV Monitoring Site 1999-2001 2000-2002 2001-2003 2002-2004 2003-2005 2004-2006 2005-2007 2006-2

Stockton 64 54 50 42 40 41 45 51 Modesto 80 70 62 54 49 51 55 54 Turlock Merced 67 55 50 47 45 45 48 50 Fresno-1st 95 80 69 61 60 58 63 58 Fresno-Winery 63 66 61 57 57 59 61 52 Clovis 68 66 58 51 55 56 58 54 Corcoran 66 70 66 52 55 58 61 52 Hanford Visalia 104 90 71 57 55 56 58 57 Bakersfield-Golden 95 90 76 62 60 64 69 64 Bakersfield-California 95 87 72 61 58 62 66 66 Bakersfield-Planz 84 78 68 54 54 60 68 70 

Please see table notes on page A-2 of this appendix

Appendix A: Analysis of Ambient Air Quality DRAFT Appendix A-3
Appendix A-4 DRAFT SJVAPCD PM2.5 Progress Report

Table A-3 EPA AMP 480 Design Value Report, Single Year Annual Mean PM2.5 Concentration

SJV Monitoring Site 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 

Stockton 19.7 15.5 13.9 16.7 13.6 13.2 12.5 13.1 12.9 14.4 Modesto 24.9 18.7 15.6 18.7 14.5 13.6 13.9 14.8 15.0 16.0 Turlock Merced 22.6 16.7 14.5* 18.7 15.7 15.2 14.1 14.8 15.2 14.9Fresno-1st 27.6 24.5 19.8 21.5 17.8 16.3 16.7 16.8 18.8 17.4 Fresno-Winery 18.4 18.6 21.3 17.8 17.0 16.9 17.6 16.8 16.5 Clovis 19.8 16.3 18.0 16.2 18.5* 16.4 16.3 16.4 16.4 16.2 Corcoran 14.3* 16.4 19.2 21.5 16.2 17.4 17.5 16.9 18.4 15.8 Hanford Visalia 27.6 23.9 22.5 23.2 18.2 17.0 18.8 18.8 20.4 19.8 Bakersfield-Golden 26.2 22.6 21.8 24.1 19.6 18.2 19.1 18.6 19.9 17.9 Bakersfield-California 23.8 22.5 21.2 22.7 17.1 18.9 18.0 18.7 22.0 21.9 Bakersfield-Planz 20.3 20.8 23.5 17.8 17.4 19.8 19.3 21.8 23.5 

Please see table notes on page A-2 of this appendix 

Table A-4 EPA AMP 480 Design Value Report, Annual PM2.5 Design Values (three-year aver

compared to standard of 15 μg/m3 

Monitoring Site 1999-2001 2000-2002 2001-2003 2002-2004 2003-2005 2004-2006 2005-2007 2006-2

Stockton 16.4 15.3 14.7 14.5 13.1 12.9 12.8 13.5 Modesto 19.7 17.7 16.2 15.6 14.0 14.1 14.6 15.3 Turlock Merced 17.9 16.6 16.3 16.5 15.0 14.7 14.7 15.0 Fresno-1st 24.0 21.9 19.7 18.6 16.9 16.6 17.4 17.7 Fresno-Winery 18.5 19.4 19.2 18.7 17.2 17.2 17.1 17.0 Clovis 18.0 16.8 17.6 17.0 17.1 16.4 16.4 16.3 Corcoran 19.0 19.0 18.4 17.0 17.2 17.6 17.0 Hanford Visalia 24.7 23.2 21.3 19.5 18.0 18.2 19.3 19.7 Bakersfield-Golden 23.6 22.8 21.8 20.6 19.0 18.6 19.2 18.8 Bakersfield-California 22.5 22.1 20.3 19.6 18.0 18.5 19.6 20.9 Bakersfield-Planz 21.5 20.7 19.6 18.4 18.9 20.3 21.5 

Please see table notes on page A-2 of this appendix
Figure A-1 24-hour PM2.5 Design Values from 2001 (1999-2001 average) to 2010 (2008-2010 

average) 

Bakersfield-Planz

0

20

40

60

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120

1999-

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24-Hr PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 65 

Bakersfield-California

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1999-

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2010

24-Hr PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 65 

2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Bakersfield-Golden

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120

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24-Hr PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 65 

Visalia

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24-Hr PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 65 μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality assurance and 

Corcoran

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24-Hr PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 65 μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality

Fresno-Winery

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24-Hr PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 65 

Fresno-First

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120

1999-

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24-Hr PM2.5 Design Values (μg/m3)

PM2.5 NAAQS of 65 

2010 data is preliminary and has not yet been fully reviewed for quality 

Clovis

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120

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2008-

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24-Hr PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 65 μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality assurance 

Appendix A: Analysis of Ambient Air Quality DRAFT Appendix A-5
Figure A-1 (continued) 24-hour PM2.5 Design Values from 2001 (1999-2001 average) to 2010 (2008-

2010 average) 

Merced

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120

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24-Hr PM2.5 Design Values (μg/m3)

PM2.5 NAAQS of 65 μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality assurance 

Modesto

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24-Hr PM2.5 Design Values (μg/m3)

PM2.5 NAAQS of 65 μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality 

Stockton

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24-Hr PM2.5 Design Values (μg/m3)

PM2.5 NAAQS of 65 μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality 

Appendix A-6 DRAFT SJVAPCD PM2.5 Progress Report
Figure A-2 Annual PM2.5 Design Values from 2001 (1999-2001 average) to 2010 (2008-2010 

average)

Bakersfield-Planz

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26

1999-

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PM2.5 NAAQS of 15.0 

Bakersfield-California

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Annual PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 15.0 μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality assurance and 

Bakersfield-Golden

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Annual PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 15.0 μg/m3

Visalia

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Annual PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 15.0 μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Corcoran

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Annual PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 15.0 μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Fresno-Winery

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PM2.5 NAAQS of 15.0 μg/m3

Fresno-First

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Annual PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 15.0 μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Clovis

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Annual PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 15.0 μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality assurance and 

Appendix A: Analysis of Ambient Air Quality DRAFT Appendix A-7
Figure A-2, (continued) Annual PM2.5 Design Values from 2001 (1999-2001 

average) to 2010 (2008-2010 average) 

Merced

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26

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Annual PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 15.0 μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Modesto

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Annual PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 15.0 μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality assurance and 

Stockton

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Annual PM2.5 Design Value (μg/m3)

PM2.5 NAAQS of 15.0 

μg/m3

2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Appendix A-8 DRAFT SJVAPCD PM2.5 Progress Report
Figure A-3 PM2.5 24-hour Design Value Comparison, 2002 (2000-2002 Average) and 

2010 (2008-2010 Average) 

Figure A-4 Annual PM2.5 Design Value Comparison, 2002 (2000-2002 Average) and 

2010 (2008-2010 Average) 

Appendix A: Analysis of Ambient Air Quality DRAFT Appendix A-9
Figure A-5 Bakersfield Annual Design Values Within Standard Deviation 

y = 0.5866x - 1157.2

R2

 = 0.7053

0

5

10

15

20

25

30

2003 2004 2005 2006 2007 2008 2009 2010

Annual Mean PM2.5 Concentration - μg/m3 

Standard Error Bars

Trend 

Line

A.2 Factors Affecting Design Values 

Some recent design values do not reflect the expected PM2.5 progress, but official 

design values alone do not necessarily provide for the best or most complete 

understanding of air quality trends. Analysis shows that a few unusual issues 

overwhelmed the Valley’s significant emissions reductions to increase certain design 

values. The purpose of this analysis is not to excuse the Valley from additional work to 

improve air quality, but to better inform the District on what types of additional work will 

be most effective. 

A.2.1 Monitor types 

The District and ARB presently use three types of PM2.5 monitors in the Valley: 

 Filter-based Federal Reference Method (FRM), defined as the standard 

for data collection; 

 Real-time Beta-attenuation method (BAM) monitors designated as federal 

equivalent method (FEM) (hereafter BAM/FEM); and 

 Ordinary BAMs, not designated FEM (hereafter referred to as BAM) 

Only FRM and BAM/FEM monitors produce data that is suitable for comparison with the 

NAAQS. Real-time monitors (BAM/FEM and BAM) produce hourly measurements that 

the District uses every day to produce daily air quality forecasting, wood burning 

prohibitions, public health notifications, and Real-time Air Advisory Network (RAAN) 

notifications for schools. 

Appendix A-10 DRAFT SJVAPCD PM2.5 Progress Report
Appendix A: Analysis of Ambient Air Quality DRAFT Appendix A-11

The District’s Annual Monitoring Network Plans summarize the types of monitors used 

at Valley air monitoring sites. The District is considering replacing some PM2.5 FRMs 

with BAM/FEMs, due to FRM maintenance and part replacement difficulties. Historical 

data shows that FRM and FEM data are not truly equivalent in the Valley, and therefore 

monitor type may impact design values. This issue will be analyzed further in future 

Monitoring Network Plans and PM2.5 attainment plans. 

A.2.2 Effects of Exceptional Events on PM2.5 Data 

With proper documentation and EPA concurrence, data influenced by exceptional 

events can be excluded from official design value calculations.3 The Valley has 

experienced three main types of exceptional events: wildfires, high winds, and 

fireworks. Exceptional events are not reasonably preventable or controllable, so it is 

inappropriate to use data without recognition of these circumstances. The District and 

ARB limit the submittal of documentation for these events, and EPA generally reviews 

only those requests that will directly affect an area’s attainment status. Even without 

formal submittal, the District tracks these events and their impact on design values as 

part of its ongoing air quality analysis. In its effort to more accurately characterize 

ambient PM2.5 concentrations, the District evaluated the Valley’s PM2.5 data with 

careful consideration of exceptional events, including those not formally submitted to 

EPA. 

A.2.2.1 PM2.5 Exceptional Event Documentation Submitted to EPA 

The District submitted documentation for exceptional events of fireworks and wildfires 

that occurred in the summers of 2007 and 2008. If EPA approves this documentation, 

data from those events will be excluded from official design value calculations. 

On July 4th and 5th, 2007, hourly PM2.5 concentrations at Fresno-First and BakersfieldCalifornia coinciding with fireworks activity. In the summer of 2008, just months after 

adoption of the 2008 PM2.5 Plan, California experienced a record number of wildfires, 

with 5,812 fires burning 1,339,839 acres. The resulting emissions, most from outside 

the Valley, caused serious public health impacts and unprecedented levels of PM2.5 

and ozone in the Valley and throughout the state. Valley PM2.5 concentrations were 

elevated for a number of days during this period. 

These exceptional events caused the Valley’s PM2.5 design values to be higher than 

normal. Table A-7 summarizes the affects of removing this data from official design 

values. The prolonged 2008 wildfire event has a noticeable impact on design values, 

especially for monitoring sites closest to the wildfire in the northern portion of the Valley. 

The largest difference occurred at the Stockton air monitoring site, where the 24-hour 

value was 61.6 μg/m3 with the exceptional event data included, and 48.2 μg/m3 with that 

data removed. Excluding days that were impacted by smoke reduces the PM2.5 

annual average design value by 0.7 μg/m3. 

 

3

 EPA’s Treatment of Air Quality Monitoring Data Influence by Exceptional Events, Codified in 40 CFR Chapter 1 (7-

1-2010 Edition), Section 50.14. 
Table A-5 Exceptional Event Impact on 24-hour and Annual Mean PM2.5 Values 

Year Site 

Annual Mean 

Before EE 

Concurrence 

Annual Mean 

with EPA EE 

Concurrence 

Difference

μg/m3

24-hour Mean 

Before EE 

Concurrence 

24-hour Mean 

with EPA EE 

Concurrence 

Difference

μg/m3

2008 Stockton 14.4 12.9 -1.5 61.6 48.2 -13.4 

Modesto 16.0 14.7 -1.3 53.3 49.5 -3.8 

Merced 14.9 13.9 -1.0 51.1 45.2 -5.9 

Clovis 16.0 14.8 -1.2 49.0 49.0 0.0 

Fresno-1st 17.4 16.1 -1.3 57.4 54.4 -3.0 

FresnoWinery 16.5 15.6 -0.9 44.5 44.5 0.0 

Visalia 21.0 19.5 -1.5 62.1 55.5 -6.6 

BAK-CA 21.9 20.0 -1.9 64.5 63.4 -1.1 

BAK-Planz 23.5 22.8 -0.7 72.3 72.3 0.0 

2007 Fresno 1st 18.8 18.4 -0.4 67.0 66.0 -1.0 

BAK-CA 22.0 21.8 -0.2 73.0 73.0 0.0 

A.2.2.2 High-Wind Events Effects on PM2.5 Data 

The District has also been evaluating the possible PM2.5 impact of high wind events, 

though the District has not submitted formal PM2.5 exceptional event document to EPA 

for these events at this time. In some most of these cases, the District submitted formal 

PM10 exceptional event documentation for these dates and monitors. Geologic 

particulates are the primary component of elevated PM10 during high wind events, but 

the geologic component of PM2.5 is still under investigation. 

The District has observed similarities in hourly increases in PM10 and PM2.5 during 

certain high wind events, though. High-wind events affected Bakerfield-Planz on 

January 4, 2008 and October 13, 2009, and corresponding PM2.5 measurements were 

unusually high at 100.3 μg/m3 and 167.7 μg/m3, respectively. Table A-8 summarizes 

the impact of the 2008 and 2009 events on Bakersfield-Planz design values. Similarly, 

the District expects to document a PM10 exceptional event affecting Bakersfield-Planz 

on April 11, 2010. PM2.5 levels were also much higher than normal in conjunction with 

this event, and excluding this single day would decrease the 2008-2010 24-hour design 

value by about 10 μg/m3 (as mentioned in Section 3.2.2 of this Progress Report). 

Appendix A-12 DRAFT SJVAPCD PM2.5 Progress Report
Appendix A: Analysis of Ambient Air Quality DRAFT Appendix A-13

Table A-6 High-Wind Event Influence on Bakersfield–Planz Design Value 

 24-hour Design Values μg/m3 Annual Design Values μg/m3

 High-Wind Event 

 Included Excluded Included Excluded 

2007* 72.2 72.2 21.8 21.8

2008 72.3 61.0 23.5 22.6

2009 65.5 65.4 22.5 21.4

Design Value 2007-2009 70 66 22.6 21.9

Difference 4 0.7 

* - No high wind events were captured in the 2007 data set. 

A.3 PM2.5 Trends 

Design values summarize a site’s large amounts of data with just two concentrations: an 

annual average, and a value representing 24-hour peaks. These parameters are 

important for attainment determinations, but design values alone will not reveal how 

public health might be impacted by PM2.5 from day-to-day or throughout the day. The 

District’s multi-faceted analysis of all available Valley PM2.5 data reveals patterns of 

seasonal variations and hourly fluctuations and, in general, demonstrates air quality 

improvements between 2005 and 2010. The District also investigated potential 

emissions source changes and PM2.5 sample speciation, where available, to consider 

potential causes for the Valley’s PM2.5 patterns. 

A.3.1 Daily PM2.5 Trends 

As mentioned in section A.2.2 of this appendix, many of the Valley’s air monitoring sites 

use real-time PM2.5 monitors, which produce hourly PM2.5 measurements. The 

District uses this data every day to produce daily air quality forecasting, wood burning 

prohibitions, public health notifications, and Real-time Air Advisory Network (RAAN) 

notifications for schools. The District compiled long-term diurnal profiles to analyze how 

PM2.5 concentrations vary throughout the day at each Valley monitoring site (Figure A6). 

The District found that PM2.5 concentrations generally peak in the early morning and 

late evening, with lower concentrations during the middle of the day. From year to year, 

this general pattern has remained consistent for most sites, but the magnitude of peaks 

have generally decreased to lower PM2.5 concentrations overall. 

Two notable exceptions to this typical pattern are sites in Fresno and Corcoran. Data 

from the Fresno 1st Street site, as shown in Figure 4-4, shows more evening 

improvement, “flattening” the evening peak. Rule 4901 wood burning prohibitions are 

most likely generating this progress in evening PM2.5 levels in Fresno. The profile of 

measurements from Corcoran, on the other hand, shows the development of a mid-day 

peak, which is higher than the evening peak in 2009. The District will continue to 

analyze this finding as more data becomes available to determine if there could be new 

source activity that may be impacting these daily patterns. 
Figure A-6 Average Annual PM2.5 Diurnal Profiles by Year by Site 

Stockton

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Hour

Annual Avg Hourly Concentration (μg/m3)

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2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Modesto

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2002 2003 2004 2005 2006 2007 2008 2009 2010

2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Turlock

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2007 2008 2009 2010

2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Fresno-First

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Annual Avg Hourly Concentration (μg/m3)

2002 2003 2004 2005 2006 2007 2008 2009 2010

2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Clovis

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2007 2008 2010

2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Corcoran

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0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Hour

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2007 2008 2009 2010

2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Appendix A-14 DRAFT SJVAPCD PM2.5 Progress Report
Figure A-6 (continued) Average Annual PM2.5 Diurnal Profiles by Year by Site

Visalia

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Annual Avg Hourly Concentration (μg/m3)

2003 2004 2005 2006 2007 2008 2009 2010

2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Ash Mountain

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2009 2010

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Bakersfield - California

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2010 data is preliminary and has not yet been fully reviewed for quality assurance and control.

Appendix A: Analysis of Ambient Air Quality DRAFT Appendix A-15
A.3.2 Seasonal PM2.5 Trends 

The Valley’s PM2.5 concentrations vary throughout the year. PM2.5 levels are typically 

highest during the winter months as a result of low-level inversion layers that trap 

pollution in the atmosphere and increased PM2.5 emissions from residential wood 

burning and other sources. However, since the 2008 PM2.5 Plan was adopted, the 

Valley has experienced some of the cleanest winters on record, as discussed in Section 

3.1.1 of this Progress Report. 

The District analyzed the Valley’s long-term seasonal PM2.5 variations based on 

quarterly averages, which are the basis for annual average design value calculations 

(Figure A-7). First quarter (January-March) and fourth quarter (October-December) 

show significant improvements, and Rule 4901 wood burning prohibitions from 

November through February are a likely driver for much of this improvement. Despite 

this improvement, the Valley’s third quarter (July-September) averages have not 

decreased. In some years, third quarter average increased. At least part of these 

increases is likely attributable to late summer wildfire smoke, particularly in 2008. While 

third quarter PM2.5 concentrations are not the year’s highest values, an increase in this 

quarter impacts annual averages, somewhat masking the improvement seen during 

other times of the year. The District will continue to analyze possible emissions sources 

that could be disproportionally impacting third quarter emissions. 

Appendix A-16 DRAFT SJVAPCD PM2.5 Progress Report
Figure A-7 PM2.5 Annual Mean by Monitor Site by Quarter 

1st Quarter

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1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

μg/m3

Stockton Modesto Merced Fresno 1st

Fresno Pacific Clovis Visalia Corcoran

BFL-Gold BFL-Ca BFL-Planz

3rd Quarter

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1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

μg/m3

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Fresno Pacific Clovis Visalia Corcoran

BFL-Gold BFL-Ca BFL-Planz 

2nd Quarter

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1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

μg/m3

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Fresno Pacific Clovis Visalia Corcoran

BFL-Gold BFL-Ca BFL-Planz

4th Quarter

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1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

μg/m3

Stockton Modesto Merced Fresno 1st

Fresno Pacific Clovis Visalia Corcoran

BFL-Gold BFL-Ca BFL-Planz

A.3.3 Annual PM2.5 Trends 

Table A-3 presents single year annual average PM2.5 concentrations. While a 3-year 

design value can mask years of very high or very low PM2.5 concentrations, single year 

annual average trends can make progress or issues more apparent. Figure A-8 shows 

that overall, despite year-to-year variations, the Valley’s annual average PM2.5 

concentrations are decreasing. In 2010, only two monitoring sites had annual averages 

above 15 μg/m3, the level of the annual NAAQS.

Appendix A: Analysis of Ambient Air Quality DRAFT Appendix A-17
Figure A-8 Annual Average PM2.5 Concentrations Decreasing 

Annual Average PM2.5 Concentrations

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2007

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Year

PM2.5 Concentration (μg/m3)

Stockton Modesto Merced

Fresno-1st Fresno-Winery Clovis

Corcoran Visalia Bakersfield-Golden

Bakersfield-California Bakersfield-Planz

A.3.4 Days Over the 24-hour PM2.5 Standards 

The number of days over the level of the PM2.5 NAAQS is another indicator of PM2.5 

progress, though it would not be used for attainment determinations. Figure A-9 shows 

a basin-wide count of the number of days above the level of both the 1997 and 2006 24-

hour average PM2.5 NAAQS (65 μg/m3 and 35 μg/m3, respectively). These counts 

have been normalized to account for the varying sampling schedules of the Valley’s 1-

in-6-day, 1-in-3-day, and daily PM2.5 monitors. Since the calculation form of the 24-

hour NAAQS is a 98th percentile standard, per monitoring site, an area could attain the 

NAAQS even where the basin-wide exceedance day count shows a few days over the 

level of the NAAQS. 

Figure 9 shows that 2009 and 2010 had fewer exceedance days than 2007 and 2008. 

Also, 2010 had the lowest number of days over the level of the 2006 NAAQS since 

monitoring began. 

Appendix A-18 DRAFT SJVAPCD PM2.5 Progress Report
Figure A-9 Days over the level of the 24-hour NAAQS 

Progress towards 24-hour PM2.5 standards: 

Days over the level of the NAAQS

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2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010

Year

Number of days, Basin-wide total

Days over 35 μg/m3 (2006 NAAQS)

Days over 65 μg/m3 (1997 NAAQS)

A.3.5 Ongoing Analysis of PM2.5 Sources and Species 

Bakersfield-Planz is the Valley’s design site, meaning it has the Valley’s highest PM2.5 

design values. As discussed in Section 3 and this Appendix, some of Planz’s PM2.5 

data analysis is influenced by exceptional events. Additionally, in some of the District’s 

analyses, Planz patterns differ from patterns seen at other monitoring sites, even those 

seen at another Bakersfield site within five miles. While all three Bakersfield monitoring 

sites show higher annual average concentrations than other Valley monitoring sites, the 

Bakersfield-Planz site consistently measures the highest concentrations. 

To investigate potential causes of the PM2.5 differences seen at Planz, the District 

evaluated emissions inventory data from collected from permitted sources within a 5-

mile radius of monitoring site. However, this analysis couldn’t capture non-permitted 

emissions activity (such as mobile sources), and the results were inconclusive. 

The District and ARB also conducts speciation analysis to determine the types of 

particulates contributing to the Valley’s PM2.5 concentrations. Accredited laboratories 

speciate many of the Valley’s collected PM2.5 filters to quantify the amounts of up to 75 

different chemical elements appearing on the filters. Though this analysis identifies 

Appendix A: Analysis of Ambient Air Quality DRAFT Appendix A-19
Appendix A-20 DRAFT SJVAPCD PM2.5 Progress Report

individual atoms rather than complex molecules, these elemental trends can point to 

potential emissions sources warranting further investigation. The speciation analysis 

identifies the Valley’s prominent PM2.5 chemical constituents, including ammonium 

ions, nitrates, silicon, organic carbon, and elemental carbon. Through the California 

Regional Particulate Air Quality Study (CRPAQS, described in section 1.2 of this 

Progress Report) and the District’s own research efforts, additional speciation analysis 

is ongoing in preparation for the 2012 PM2.5 Attainment Plan for the 2006 PM2.5 

NAAQS (mentioned in Section 4 of this Progress Report).