2007 Ozone Plan 

Appendix A 

 

Ambient Air Quality Data 
2007 Ozone Plan 

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San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Appendix A: Ambient Air Quality Data 

2007 Ozone Plan 

Appendix A-1

Appendix A: Ambient Air Quality Data 

A.1 INTRODUCTION 

This Appendix includes more ambient air quality data and analysis for 8-hour ozone. 

A.2 AMBIENT AIR QUALITY DATA 

 

Table A-1 summarizes the annual fourth-highest daily maximum 8-hour average ozone 

concentrations for currently operating monitoring sites in the SJVAB for the years 1988-

2005. The calculation of the 3 - year average of the annual fourth-highest daily 

maximum 8-hour average ozone concentration is explained in Chapter 1. Table A-2 

shows the 3 -year average of the annual fourth-highest daily maximum 8-hour average 

ozone concentration for each site within the SJVAB for the years 1990-2005. A dash (-) 

means that there is insufficient (or no) data available to determine the value. 

Attainment status is determined for each site by analyzing 2003 through 2005 ozone 

measurements1

. If any monitoring site within the SJVAB has a design value that is 

greater than 0.08 ppm, then, by rules established by EPA, the entire air basin is 

nonattainment. Table A-3 summarizes the current attainment status on a site-by-site 

basis. Bold values indicate that one of the attainment tests is over the standard. Figure 

A-1 illustrates the San Joaquin Valley air basin map with 8-hour ozone design values on 

a site-by-site basis. 

Table A-3 shows that three of the 21 air monitoring sites2 in the SJVAB currently meet 

the attainment test for eight hour ozone: Stockton, Modesto, and Madera. Turlock and 

Hanford are very close to meeting the 8-hour average ozone NAAQS attainment test. 

Eighteen (18) out of 21 sites are nonattainment for the 8-hour average ozone standard 

for the 2003-2005 time period. This is an improvement from 1999 to 2001 period where 

twenty (20) out of 21 sites were nonattainment. Figure A-1 shows the Valley-wide 

design values for 1990-2005. Figure A-2 shows 2005 design values plotted on a map. 

More air quality trend data can be found at <http://www.arb.ca.gov>. 

 

1

 40 CFR (Code of Federal Regulations) Part 50, Appendix I, Sections 2.2 and 2.3, require that attainment 

calculations be based on at least the most recent three complete years of quality reviewed data. Data for the year 

2006 has not completed the required review. 

2

 A total of 22 ozone monitoring sites are currently operated in the SJVAB, but one of these (the Tracy – Airport site) 

has not been operating long enough to yield a design value. 
San Joaquin Valley Unified Air Pollution Control District 

Appendix A: Am

Appendix A-2

Table A-1 Fourth Highest Eight Hour Average Ozone (ppm)3

Name 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 Stockton 0.090 0.077 0.083 0.082 0.083 0.078 0.085 0.090 0.080 0.071 0.086 0.085 0.076 0.076 0.073 Modesto 0.093 0.093 0.097 0.086 0.082 0.090 0.091 0.095 0.094 0.082 0.098 0.087 0.086 0.091 0.087 Turlock - - - - 0.095 0.096 0.088 0.103 0.098 0.089 0.107 0.090 0.091 0.094 0.102 Merced - - 0.097 0.102 0.096 0.097 0.107 0.102 0.074 0.112 0.105 0.103 0.096 0.105 Madera - - - - - - - - - - 0.093 0.088 0.088 0.090 0.096 Fresno-SSP 0.112 0.100 0.071 0.105 0.106 0.110 0.099 0.103 0.105 0.097 0.122 0.099 0.114 0.113 0.119 Clovis - - 0.095 0.093 0.108 0.105 0.099 0.108 0.108 0.115 0.121 0.104 0.104 0.110 0.104 Fresno-First - - 0.103 0.118 0.105 0.111 0.105 0.108 0.109 0.098 0.117 0.104 0.104 0.104 0.109 FresnoDrummond 0.107 0.098 0.103 0.103 0.097 0.100 0.090 0.089 0.104 0.092 0.113 0.102 0.099 0.097 0.110 Parlier 0.115 0.113 0.103 0.108 0.108 0.103 0.089 0.106 0.110 0.106 0.108 0.105 0.108 0.109 0.115 Ash Mountain - - - - - - - - - - - 0.105 0.105 0.104 0.107 Lower Kaweah 0.094 0.093 0.096 0.097 0.102 0.106 0.106 0.095 0.105 0.097 0.094 0.097 0.090 0.096 0.108 Visalia 0.105 0.113 0.102 0.098 0.098 0.108 0.109 0.104 0.103 0.095 0.109 0.100 0.099 0.099 0.102 Hanford - - - - - - 0.093 0.080 0.116 0.097 0.104 0.098 0.105 0.093 0.101 Arvin - 0.120 0.118 0.117 0.110 0.111 0.112 0.115 0.126 0.105 0.114 0.109 0.111 0.109 0.118 BakersfieldCalifornia - - - - - - 0.098 0.107 0.110 0.097 0.103 0.099 0.102 0.099 0.101 BakersfieldGolden - - - - - - 0.095 0.096 0.108 0.090 0.105 0.096 0.099 0.095 0.101 Edison 0.120 0.110 0.108 0.110 0.093 0.117 0.118 0.123 0.118 0.105 0.124 0.105 0.105 0.104 0.109 Maricopa 0.111 0.106 0.098 0.097 0.100 0.101 0.093 0.109 0.111 0.097 0.123 0.089 0.093 0.098 0.106 Oildale 0.111 0.101 0.098 0.101 0.100 0.101 0.097 0.101 0.106 0.088 0.109 0.092 0.103 0.097 0.102 Shafter - 0.100 0.093 0.098 0.093 0.097 0.099 0.095 0.102 0.085 0.101 0.094 0.092 0.098 0.096 

A dash (-) indicates that there is insufficient data available to determine the value. 

3 A total of 22 ozone monitoring sites are currently operated in the SJVAB, but one of these (the Tracy – Airport site) has not been opera

design value. 
San Joaquin Valley Unified Air Pollution Control District 

Appendix A: Am

Appendix A-3

Table A-2 3-year Average of the Annual Fourth-Highest Daily Maximum 

8-hour Average Ozone Concentrations (ppm) 

Name 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 20Stockton 0.083 0.080 0.082 0.081 0.082 0.084 0.085 0.080 0.079 0.080 0.082 0.079 0.075 0.0Modesto 0.094 0.092 0.088 0.086 0.087 0.092 0.093 0.090 0.091 0.089 0.090 0.088 0.088 0.0Turlock - - - - 0.093 0.095 0.096 0.096 0.098 0.095 0.096 0.091 0.095 0.0Merced - - - 0.098 0.098 0.100 0.102 0.094 0.096 0.097 0.106 0.101 0.101 0.1Madera - - - - - - - - - - 0.089 0.088 0.091 0.0Clovis - - 0.098 0.102 0.104 0.104 0.105 0.111 0.115 0.113 0.109 0.106 0.106 0.1Fresno- Drummond 0.102 0.101 0.101 0.100 0.095 0.093 0.094 0.095 0.103 0.102 0.104 0.099 0.102 0.1Fresno- First - - 0.108 0.111 0.107 0.108 0.107 0.105 0.108 0.106 0.108 0.104 0.105 0.1Fresno- SSP 0.094 0.092 0.094 0.107 0.105 0.104 0.102 0.101 0.108 0.106 0.111 0.108 0.115 0.1Parlier 0.110 0.108 0.106 0.106 0.100 0.099 0.101 0.107 0.108 0.106 0.107 0.107 0.110 0.1Ash Mtn. - - - - - - - - - - - 0.104 0.105 0.1Lower Kaweah 0.094 0.095 0.098 0.101 0.104 0.102 0.102 0.099 0.098 0.096 0.093 0.094 0.098 0.1Visalia 0.106 0.104 0.099 0.101 0.105 0.107 0.105 0.100 0.102 0.101 0.102 0.099 0.100 0.0Hanford - - - - - - 0.096 0.097 0.105 0.099 0.102 0.098 0.099 0.0Arvin - 0.118 0.115 0.112 0.111 0.112 0.117 0.115 0.115 0.109 0.111 0.109 0.112 0.1BakersfieldCalifornia - - - - - - 0.105 0.104 0.103 0.099 0.101 0.100 0.100 0.1Bakersfield- Golden - - - - - - 0.099 0.098 0.101 0.097 0.100 0.096 0.098 0.0Edison 0.112 0.109 0.103 0.106 0.109 0.119 0.119 0.115 0.115 0.111 0.111 0.104 0.106 0.1Maricopa 0.105 0.100 0.098 0.099 0.098 0.101 0.104 0.105 0.110 0.103 0.102 0.094 0.099 0.0Oildale 0.103 0.100 0.099 0.100 0.099 0.099 0.101 0.098 0.101 0.096 0.101 0.097 0.100 0.0Shafter - 0.097 0.094 0.096 0.096 0.097 0.098 0.094 0.096 0.093 0.095 0.094 0.095 0.0

A dash (-) indicates that there is insufficient data available to determine the value. 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Appendix A: Ambient Air Quality Data 

2007 Ozone Plan 

Appendix A-4

Table A-3 Current Ozone Air Quality Design Values and Attainment Status 

 for the San Joaquin Valley Air Basin 

County Site 

8 hour Ozone 

Design Values (ppm)* 

Meets Attainment

Test 

San Joaquin Stockton 0.07 yes 

Stanislaus Modesto 0.08 yes 

Stanislaus Turlock 0.09 no 

Merced Merced 0.10 no 

Madera Madera 0.08 yes 

Fresno Clovis 0.09 no 

Fresno Fresno - Drummond 0.09 no 

Fresno Fresno - Sierra Sky Park 0.10 no 

Fresno Fresno - 1st 0.10 no 

Fresno Parlier 0.10 no 

Kings Hanford 0.09 no 

Tulare Ash Mountain 0.11 no 

Tulare Lower Kaweah 0.10 no 

Tulare Visalia 0.09 no 

Kern Arvin 0.11 no 

Kern Bakersfield - Golden 0.09 no 

Kern Bakersfield - California 0.10 no 

Kern Edison 0.10 no 

Kern Maricopa 0.09 no 

Kern Oildale 0.10 no 

Kern Shafter 0.09 No 

SJVAB All Sites 0.11 No 

* Bold indicates that the site does not meet the attainment test. 

 

Figure A-1 Valley-wide 3-year average of the annual fourth-highest daily 

maximum 8-hour average ozone concentrations 

0.070

0.080

0.090

0.100

0.110

0.120

0.130

1990199119921993199419951996199719981999200020012002200320042005

Year

PPM
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Appendix A: Ambient Air Quality Data 

2007 Ozone Plan 

Appendix A-5

Figure A-2 8-Hour Ozone Design Value (2005) 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Appendix A: Ambient Air Quality Data 

2007 Ozone Plan 

Appendix A-6

A.3 TREND AND SPATIAL VARIATIONS 

A.3.1 Local Trends 

While the Valley-wide design values remain essentially consistent, some sites are 

improving. Despite the reduction of emissions in the San Joaquin Valley, one site’s 

design value is increasing. All other SJVAB sites are showing either an improving or 

unchanged trend. Figure A-3 is an example of an improving trend. Seven of the 19 air 

monitoring sites in the SJVAB are showing an improving air quality trend: Stockton, 

Fresno-1st, Visalia, Hanford, Bakersfield – California, Bakersfield - Golden and Edison. 

Figure A-4 shows the trend of the only SJVAB site, Fresno Sierra Sky Park, where the 

8-hour ozone air quality is getting worse despite emission reductions. Figure A-5 is an 

example of one of the eleven of the 19 monitoring sites, in the SJVAB with an 

unchanged trend. Modesto, Turlock, Merced, Clovis, Fresno-Drummond, Parlier, Lower 

Kaweah, Arvin, Maricopa, Oildale and Shafter are showing no improvement in 8-hour 

ozone air quality. 

 

Figure A-3 Visalia (one of seven improving sites in the SJVAB) 

8-hour ozone 3-year average of the annual fourth-highest daily maximum 8-hour 

average ozone concentrations, 1990-2005 

0.070

0.080

0.090

0.100

0.110

0.120

0.130

1990199119921993199419951996199719981999200020012002200320042005

Year

PPM
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Appendix A: Ambient Air Quality Data 

2007 Ozone Plan 

Appendix A-7

Figure A-4 Fresno – Sierra Sky Park (the only site where 8-hour ozone air quality 

is getting worse) 3-year average of the annual fourth-highest daily maximum 8-

hour average ozone concentrations, 1990-2005 

0.070

0.080

0.090

0.100

0.110

0.120

0.130

1990199119921993199419951996199719981999200020012002200320042005

Year

PPM

Figure A-5 Fresno – Drummond (one of the eleven sites with no clear trend) 3-

year average of the annual fourth-highest daily maximum 8-hour average ozone 

concentrations, 1990-2005 

 

0.070

0.080

0.090

0.100

0.110

0.120

0.130

1990199119921993199419951996199719981999200020012002200320042005

Year

PPM
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Appendix A: Ambient Air Quality Data 

2007 Ozone Plan 

Appendix A-8

A.3.2 Number of Days Above the Eight Hour Ozone NAAQS 

The regulatory 8-hour ozone attainment status for the SJVAB is based upon the design 

value being less than or equal to 0.08 ppm. Previous figures (A-3, A-4, and A-5) 

demonstrate examples of trends using the 3-year average of the annual fourth-highest 

daily maximum 8-hour average concentration vs. year for a particular site. Another way 

to examine the ozone air quality data is to determine the number of days where the 8-

hour ozone concentration is greater than 0.08 ppm. (Note that the number of days 

greater than 0.08 ppm is not used in determining the attainment status of the SJVAB. It 

is solely used in determining the number of days of exposure to levels above the level of 

the NAAQS for 8-hour ozone.) 

Figure 1-5 (in Chapter 1) shows the number of days over the 8-hour numerical value by 

site for 2003, 2004, and 2005; it shows that all sites of the Valley are experiencing fewer 

days over the level of the standard than a couple of years ago. Figures A-6, A-7, and A8 show the number of days over the level of the 8-hour ozone standard for the Visalia, 

Fresno – Sierra Sky Park, and Fresno – Drummond air monitoring sites, respectively. 

On each of these figures, the number of days over of ozone standard for the entire 

basin is included to emphasize that the number of days at individual sites is generally 

much lower than the total number of days for the entire basin. Table A-3 summarizes 

the number of days above the 8-hour ozone standard for each air-monitoring site in the 

SJVAB and basin-wide from 1990-2005. On a site-by-site basis, a majority of the 

SJVAB residents are not being exposed to as many days over the level of the 8-hour 

standard as the Basin-wide total shows. 

Figure A-6 Number of Days Over the Level of the 8-hour Ozone Standard: Visalia 

0

20

40

60

80

100

120

140

160

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Year

Number of Days

Visalia Basin-wide
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Appendix A: Ambient Air Quality Data 

2007 Ozone Plan 

Appendix A-9

Figure A-7 Number of Days Over the Level of the 8-hour Ozone Standard: 

Fresno – Sierra Sky Park 

0

20

40

60

80

100

120

140

160

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Year

Number of Days

Fresno-SSP Basin-wide

Figure A-8 Number of Days Over the Level of the 8-hour Ozone Standard: 

Fresno – Drummond 

0

20

40

60

80

100

120

140

160

1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005

Year

Number of Days

Fresno-Drummond Basin-wide
San Joaquin Valley Unified Air Pollution Control District 

Appendix A: Am

Appendix A-10

Table A-4 Number of Days Above the 8-Hour Ozone Standard of 0.08 ppm 

Site 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 Stockton 3 3 2 1 4 4 2 0 4 4 0 1 0 1 Modesto 7 5 2 7 9 14 15 2 13 7 4 7 6 1 Turlock - - 11 11 10 18 19 8 29 9 10 7 25 18 Merced - - 40 19 26 36 44 1 35 40 37 29 56 54 Madera - - - - - - - - 12 10 9 13 18 14 Clovis 8 18 61 29 33 44 60 69 62 49 44 56 38 30 Fresno-Drummond 29 34 30 17 6 9 34 11 41 28 24 29 43 45 Fresno-First 31 72 42 54 51 53 49 23 44 45 41 40 41 47 Fresno-SSP - 32 44 25 32 39 36 15 52 30 70 83 78 32 Parlier 39 50 44 44 8 25 59 48 54 68 66 74 83 92 Ash Mtn. - - - - - - - - - 52 40 61 80 72 Lower Kaweah 27 34 50 48 58 18 50 26 27 39 8 27 73 42 Visalia 33 23 14 50 51 40 44 17 45 33 29 25 26 31 Hanford - - - - 12 1 81 26 31 25 51 18 27 15 Arvin 82 103 87 77 77 80 106 46 64 85 73 81 87 116 Bakersfield-California - - - - 33 57 67 23 38 47 40 47 35 48 Bakersfield-Golden - - - - - 25 47 11 33 26 30 27 29 40 Edison 66 76 17 87 89 88 78 30 61 55 58 54 51 50 Maricopa 30 45 36 29 23 67 78 36 66 14 15 46 53 29 Oildale 29 48 30 24 28 37 52 5 44 28 36 35 37 49 Shafter 16 31 12 24 24 26 49 4 27 25 25 30 25 15 Basin-Wide 104 121 119 104 108 109 114 95 84 117 103 109 125 134 

A dash (-) indicates that there is insufficient data available to determine the value. 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Appendix A: Ambient Air Quality Data 

2007 Ozone Plan 

Appendix A-11

A.3.3 Difference Between Urban and Rural Ozone Response 

Previous strategies have been directed at the one-hour ozone standard. Peak values of 

the one-hour ozone standard are associated with large urban areas and nearby 

downwind areas adjacent to the large urban areas. The one-hour ozone strategy was 

implemented to reduce maximum hourly values in the large urban and down-wind areas 

and was expected to similarly reduce peak one-hour ozone in the smaller urban and 

rural areas. The one-hour ozone strategy assumes a proportional effect for benefit of 

urban reductions on rural ozone levels, but this may not be an accurate assumption for 

the eight-hour ozone. 

Eight-hour ozone is much different in pattern and frequency of occurrences than onehour ozone due to technical factors that affect how ozone levels change over a period of 

several hours in urban and rural areas. Changes in ozone levels occur more rapidly in 

urban areas than in rural areas. The difference in response to emissions changes 

creates a difficult challenge for determining an optimum approach for achieving 

attainment of the eight-hour standard. 

During the night, in urban areas, fresh emissions of ozone precursors interact with and 

remove existing ozone (referred to as scavenging). This process causes a rapid 

change in the ozone concentrations and results in very low nighttime ozone 

concentrations. When focusing on the peak hour of ozone, this removal process is not a 

dominant technical issue; however, lowering the eight-hour concentration requires more 

attention on this issue. 

Rural areas with fewer sources emitting precursor emissions do not experience the 

same ozone removal process as the urban areas. When ozone is transported directly 

to a rural area, or is created there by transported precursors, there are not enough fresh 

(scavenging) emissions to remove the ozone quickly. In the rural areas, ozone may 

remain at high levels during extended periods during the entire 24-hour day. 

 

Figure A-9 provides an example of how urban and rural ozone levels vary due to the 

differences in local emissions during a day. Hourly averaged ozone at Ash Mountain 

and Bakersfield (Golden State Highway) monitoring stations on July 2, 2005 shows how 

urban levels change rapidly and rural ozone levels are less responsive. The urban 

mechanism described above is demonstrated in the plot of ozone data at Bakersfield, 

where there are significant hourly emissions of NOx and volatile organic compounds 

(VOC). After sunrise, there is a dramatic rise in ozone because sunlight is now 

available to drive the creation of ozone from the available NOx and VOC. After the sun 

sets, chemical reactions and deposition result in a drop in ozone concentrations, which 

typically continues its downward trend until dawn. 

The Ash Mountain monitoring station, which is located at the southern entrance of 

Sequoia National Park at 1500-foot elevation, demonstrates the hourly ozone response 

in a rural area. On summer days, ozone and precursors can be transported to Ash 

Mountain from other locations. At this location, there are significantly lower hourly 
San Joaquin Valley Unified Air Pollution Control District April 30, 2007

Appendix A: Ambient Air Quality Data 

2007 Ozone Plan 

Appendix A-12

emissions of NOx as compared to urban areas such as Bakersfield or Fresno. The 

amount of available NOx at Ash Mountain to scavenge the ozone is much lower. 

Because the ozone scavenging at Ash Mountain is much less than the ozone 

scavenging in urban areas, Ash Mountain can experience elevated ozone 

concentrations for a 24-hour period during ozone episodes. Since the ozone 

concentration is already fairly high at dawn, only a relatively small amount of additional 

ozone can cause levels in the atmosphere to exceed federal standards. All areas with a 

small population and low NOx emissions that are located in regions subject to ozone 

transport can experience a similar ozone pattern. This pattern can occur at Arvin and 

the foothills of the Sierra Nevada and Tehachapi mountain ranges. This phenomenon is 

an important issue to be examined as part of the plan to reach attainment of the 8-hour 

ozone standard. 

Figure A-9 Ozone Concentrations (ppb) at Ash Mountain and 

Bakersfield - Golden on July 2, 2005 

0

10

20

30

40

50

60

70

80

90

100

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hour (PST)

Ozone (ppb)

Ash Mountain

Bakersfield - GS

Trend analysis of air quality monitoring data has not indicated what changes in the 

current strategy designed to address the one-hour standard would be effective in 

enhancing ozone reduction efforts for the eight-hour standard. District staff and ARB 

continue to evaluate air quality data and trends to identify factors that will aid in the 

determination of a successful strategy for attainment of the eight-hour ozone standard. 

Trend evaluation will be compared to results of modeling and other corroborative 

analysis to provide support for the regulatory decision-making process.