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Appendix A: Air Monitoring Site Descriptions 

Annual Air Monitoring Network Plan 

 

APPENDIX A: 

Air Monitoring Site Descriptions 

 
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Annual Air Monitoring Network Plan 

 

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Appendix A: Monitoring Site Descriptions 

Sites operated by the San Joaquin Valley Air Pollution Control District (SJVAPCD) 

Bakersfield-Muni 

The Bakersfield-Golden site was shut down for relocation in December 2009. The 

replacement site, Bakersfield-Muni, is located in the Bakersfield, CA metropolitan area 

and is operated by the San Joaquin Valley Air Pollution Control District (SJVAPCD). 

The site serves as a PAMS Type 2 site, and its purpose is to measure maximum ozone 

precursor emissions. The site monitors ozone, CO, NO2, total- and speciated-VOC, and 

meteorology for the PAMS program. The speciated PAMS equipment became 

operational in June 2012. All the other PAMS equipment except for the NMHC 

equipment began operating in July 2012. The NMHC equipment was installed and 

became operational in October 2012. The site monitored PM10 and PM2.5 from July 

2012 until late February 2013. However, it soon became apparent that this site was not 

acceptable as a PM10 and PM2.5 site because site specific emissions from nearby 

sources were impacting the site, and the site was therefore not measuring ambient 

particulate concentrations. 

Clovis-Villa 

Clovis, CA is located in the central part of the San Joaquin Valley with mountains to the 

east and northeast. North-south air flow is virtually unobstructed. Pollutant emissions 

occur locally and are also transported from upwind and nearby locations into the area 

by the wind. The Clovis-Villa monitoring site is operated by SJVAPCD and is located in 

the northeastern portion of the Fresno, CA metropolitan area. It began operating in 

September 1990. This site is a PAMS Type 2 site, a site intended to measure 

maximum ozone precursor emissions. In addition to ozone, the site also monitors 

PM2.5, PM10, PM2.5, CO, NO2, total- and speciated-VOC, and meteorology for the

PAMS program. During the summer months, high temperatures and longer daylight 

hours contribute to increases in ozone during the day. In contrast, ozone 

concentrations decrease at night with the absence of sunlight and the presence of NOx 

pollutants, which scavenge the ozone. During the winter months, ozone concentrations 

tend to be lower due to shorter daylight hours and lower temperatures. Elevated PM2.5 

concentrations are possible year round, but concentrations tend to be highest during the 

winter months due to moisture content in the air, wood-burning activities, other 

anthropogenic activities, and atmospheric chemistry. PM2.5 concentrations can also 

increase during wind events, because the wind can cause PM2.5 to become suspended 

in the air. On rare occasions, this area of the San Joaquin Valley experiences wind 

events that can carry dust into the area or lift local dust particles into the air. Such 

events can cause PM10 concentrations to increase. 

Corcoran-Patterson 

Corcoran, CA is located in the central part of the San Joaquin Valley with mountains to 

the east and west. North-south air flow is virtually unobstructed. Pollutant emissions 

occur locally and are also transported from upwind locations into the area by the wind. 

The Corcoran-Patterson monitoring site is operated by SJVAPCD and is located 67 
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miles south of the Fresno, CA metropolitan area. It began operating in October 1996. 

In 2011, the site was shut down temporarily due to safety issues and repairs were made 

to the site. The site resumed operating in August 2012. The site measures 

representative concentrations of PM10 and PM2.5. This site also monitors 

meteorology. Elevated PM2.5 concentrations are possible year round, but 

concentrations tend to be highest during the winter months due to moisture content in 

the air, wood-burning activities, other anthropogenic activities, and atmospheric 

chemistry. PM2.5 concentrations can also increase during wind events because the 

wind can cause PM2.5 to become suspended in the air. On rare occasions, this area of 

the San Joaquin Valley experiences wind events that can carry dust into the area or lift 

local dust particles into the air. Such events can cause PM10 concentrations to 

increase and sometimes exceed the NAAQS. 

 

Fresno-Drummond 

Fresno, CA is located in the central part of the San Joaquin Valley with mountains to the 

east and west. North-south air flow is virtually unobstructed. Pollutants occur locally 

and are also transported from upwind locations into the area by the wind. The FresnoDrummond monitoring site is operated by SJVAPCD and is located in the Fresno, CA 

metropolitan area. It began operating in July 1984. The purpose of the site is to 

monitor representative concentrations of hourly ozone responses in an urban area. In 

addition to ozone, the site also monitors PM10, PM2.5, CO, NO2, and meteorology. 

During the summer months, high temperatures and longer daylight hours contribute to 

increases in ozone during the day. In contrast, ozone concentrations decrease at night 

with the absence of sunlight and the presence of NOx pollutants which scavenge the 

ozone. During the winter months, ozone concentrations tend to be lower due to shorter 

daylight hours and lower temperatures. During the winter months, ozone 

concentrations tend to be lower due to shorter daylight hours and lower temperatures. 

Elevated PM2.5 concentrations are possible year round, but concentrations tend to be 

highest during the winter months due to moisture content in the air, wood-burning 

activities, other anthropogenic activities, and atmospheric chemistry. PM2.5 

concentrations can also increase during wind events, because the wind can cause 

PM2.5 to become suspended in the air. On rare occasions, this area of the San 

Joaquin Valley experiences wind events that can carry dust into the area or lift local 

dust particles into the air. Such events can cause PM10 concentrations to increase. 

Fresno-Pacific 

Fresno, CA is located in the central part of the San Joaquin Valley with mountains to the 

east and west. North-south air flow is virtually unobstructed. Pollutants occur locally 

and are also transported from upwind locations into the area by the wind. The FresnoPacific monitoring site is operated by SJVAPCD and is located in the Fresno, CA 

metropolitan area. It began operating in January 2000. The purpose of the site is to 

monitor representative PM2.5 concentrations in an urban area. Elevated PM2.5 

concentrations are possible year round, but concentrations tend to be highest during the 

winter months due to moisture content in the air, wood-burning activities, other 

anthropogenic activities, and atmospheric chemistry. PM2.5 concentrations can also 

increase when wind causes PM2.5 to become suspended in the air. Occasionally, wind 
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will carry dust across the city or lift local dust particles into the air, and cause PM2.5 

concentrations to become elevated, but PM2.5 exceedances due to wind events are 

rare. 

Fresno-Sky Park 

Fresno, CA is located in the central part of the San Joaquin Valley with mountains to the 

east and west. Pollutants occur locally and are also transported from upwind locations 

into the area by the wind. The Fresno-Sky Park monitoring site is operated by 

SJVAPCD and is located in the Fresno, CA metropolitan area. It began operating in 

July 1986. The purpose of the site is to monitor representative concentrations of hourly 

ozone responses in an urban area. In addition to ozone, the site also monitors CO, 

NO2, and meteorology. During the summer months, high temperatures and longer 

daylight hours contribute to increases in ozone during the day. In contrast, ozone 

concentrations decrease at night with the absence of sunlight and the presence of NOx 

pollutants which scavenge the ozone. During the winter months, ozone concentrations 

tend to be lower due to shorter daylight hours and lower temperatures. 

Hanford-Irwin 

Hanford, CA is located in the central part of the San Joaquin Valley with mountains to 

the east and west. North-south air flow is virtually unobstructed. Pollutants occur 

locally and are also transported from upwind locations into the area by the wind. The 

Hanford-Irwin monitoring site is operated by SJVAPCD and is located 51 miles south of 

the Fresno, CA metropolitan area. The site began operating in October 1993 and was 

decommissioned in October 2007 due to plans to move it to a different part of the Irwin 

location. The purpose of the site is to monitor representative concentrations of hourly 

ozone, PM2.5, PM10, and NO2 responses from upwind and nearby urban areas. The

site also monitors meteorology. The PM2.5, PM10, and ozone monitors were 

temporarily moved to Corcoran during site reconstruction. In February 2010, the ozone 

and PM2.5 monitors were returned to Hanford and the site became operational again. 

The PM10 monitor was returned and became operational in July 2010. During the 

summer months, high temperatures and longer daylight hours contribute to increases in 

ozone during the day. In contrast, ozone concentrations decrease at night with the 

absence of sunlight and the presence of NOx pollutants which scavenge the ozone. 

During the winter months, ozone concentrations tend to be lower due to shorter daylight 

hours and lower temperatures. Elevated PM2.5 concentrations are possible year round, 

but concentrations tend to be highest during the winter months due to moisture content 

in the air, wood-burning activities, other anthropogenic activities, and atmospheric 

chemistry. PM2.5 concentrations can also increase during wind events because the 

wind can cause PM2.5 to become suspended in the air. On rare occasions, this area of 

the San Joaquin Valley experiences wind events that can carry dust into the area or lift 

local dust particles into the air. Such events can cause PM10 concentrations to 

increase and sometimes exceed the NAAQS. 

Huron 

Huron, CA is located in southwestern Fresno County, and is about 40 miles southwest 

of Fresno, CA, with the coastal mountain range just to the west. North-south air flow is 
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virtually unobstructed. This monitoring site was established in January 2007 in order to 

comply with Assembly Bill (AB) 841. Currently, this site monitors PM2.5 (Non-FEM, 

Lebec 

Lebec, CA is located in the southern-most portion of the San Joaquin Valley. The 

Lebec monitoring station was initiated by the Tejon Ranch in 2004, and the District 

assumed responsibility for this site as of January 2009. This site allows the District to 

better understand pollution impacts in the southern San Emigdio Mountains. The site 

measures PM2.5 and meteorological parameters. This site is used for general 

residential wood-burning declarations for the Greater Frazier Park Area. 

Madera-City 

Madera, CA is located in the northern part of the San Joaquin Valley with mountains to 

the east and west. North-south air flow is virtually unobstructed. The Madera-City 

monitoring site is located closer to the city center of Madera than the Madera-Pump 

Yard site. The Madera-City site is operated by the SJVAPCD and became operational 

in June 2010. The site monitors ozone, PM2.5, PM10, and meteorology. The purpose 

of this site is to measure downwind concentrations of the city of Madera which will 

provide needed information about the variability of air quality levels on the Valley floor of 

Madera County.

Madera-Pump Yard 

Madera, CA is located in the northern part of the San Joaquin Valley with mountains to 

the east and west. North-south air flow is virtually unobstructed. The Madera-Pump 

Yard Street monitoring site is operated by SJVAPCD and is located in Madera, CA. It 

began operating in August 1997. This site was established as a PAMS Type 1 site, 

located in an area upwind of Fresno and not to be influenced by upwind or local ozone 

precursor emissions. In addition to ozone, this site also monitors CO, total- and 

speciated-VOC, and meteorology for the PAMS program. During the summer months, 

high temperatures and longer daylight hours contribute to increases in ozone during the 

day. In contrast, ozone concentrations decrease at night with the absence of sunlight 

and the presence of NOx pollutants which scavenge the ozone. During the winter 

months, ozone concentrations tend to be lower due to shorter daylight hours and lower 

temperatures. 

Manteca 

Manteca, CA is located in the northern part of the San Joaquin Valley with mountains to 

the east and west. North-south air flow is virtually unobstructed. Pollutants are both 

local and up wind in origin. The Manteca monitoring site is located in Manteca, CA and 

operated by SJVAPCD. It became operational in November 2010. The purpose of the 

site is to monitor transport of and representative concentrations of ozone, PM2.5, and 

PM10 from upwind and nearby urban areas. The site also monitors meteorology. 

During the winter months, ozone concentrations tend to be lower due to shorter daylight 

hours and lower temperatures. Elevated PM2.5 concentrations are possible year round, 

but concentrations tend to be highest during the winter months due to moisture content 

in the air, wood-burning activities, other anthropogenic activities, and atmospheric 
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chemistry. PM2.5 and PM10 concentrations can also increase during wind events 

because the wind can cause PM to become suspended in the air. Occasionally, wind 

will carry dust across the city and also cause PM concentrations to increase, but PM2.5 

and PM10 exceedances due to wind events are rare. 

Maricopa 

Maricopa, CA is located at the southern end of the San Joaquin Valley with mountains 

to the east, west, and south. Because the mountains block or slow down air flow 

pollutants can get trapped and build up in the area. The Maricopa monitoring site is 

operated by the SJVAPCD and is located 45 miles southwest of the Bakersfield, CA 

metropolitan area. It began operating in July 1987. The purpose of the site is to 

monitor representative concentrations of hourly ozone in a rural area. The site also 

monitors meteorology. During the summer months, high temperatures and longer 

daylight hours contribute to increases in ozone during the day. In contrast, ozone 

concentrations decrease at night with the absence of sunlight and the presence of NOx 

pollutants which scavenge the ozone. During the winter months, ozone concentrations 

tend to be lower due to shorter daylight hours and lower temperatures. 

Merced-Coffee 

Merced, CA is located in the northern part of the San Joaquin Valley with mountains to 

the east and west. North-south air flow is virtually unobstructed. Pollutants are both 

local and up wind in origin. The Merced-Coffee monitoring site is operated by SJVAPCD 

and is located in the Merced, CA. It began operating in October 1991. The purpose of 

the site is to monitor representative concentrations of hourly ozone responses from 

upwind urban areas. The site also monitors PM2.5, NO2, and meteorology. During the 

summer months, high temperatures and longer daylight hours contribute to increases in 

ozone during the day. In contrast, ozone concentrations decrease at night with the 

absence of sunlight and the presence of NOx pollutants which scavenge the ozone. 

During the winter months, ozone concentrations tend to be lower due to shorter daylight 

hours and lower temperatures. 

Merced-M Street

Merced, CA is located in the northern part of the San Joaquin Valley with mountains to 

the east and west. North-south air flow is virtually unobstructed. Pollutants are both 

local and up wind in origin. The Merced-M Street monitoring site is operated by 

SJVAPCD and is located in Merced, CA. It began operating in April 1999. The purpose 

of the site is to monitor representative concentrations of PM2.5 and PM10 responses 

from upwind urban areas. Elevated PM2.5 concentrations are possible year round, but 

concentrations tend to be highest during the winter months due to moisture content in 

the air, wood-burning activities, other anthropogenic activities, and atmospheric 

chemistry. PM2.5 and PM10 concentrations can also increase during wind events 

because the wind can cause PM to become suspended in the air. Occasionally, wind 

will carry dust across the city and also cause PM concentrations to increase, but PM2.5 

and PM10 exceedances due to wind events are rare. 

 
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Parlier 

Parlier, CA is located in the central part of the San Joaquin Valley with mountains to the 

east and west. North-south air flow is virtually unobstructed. Pollutants are both local 

and up wind in origin. The Parlier monitoring site is operated by SJVAPCD and is 

located 20 miles southeast of the Fresno, CA metropolitan area. It began operating in 

March 1983. The purpose of the site, as a PAMS Type 3 site, is to monitor maximum 

ozone concentrations and ozone responses from upwind urban areas. The site also 

monitors NO2, total- and speciated-VOC, and meteorology for the PAMS program. 

During the summer months, high temperatures and longer daylight hours contribute to 

increases in ozone during the day. In contrast, ozone concentrations decrease at night 

with the absence of sunlight and the presence of NOx pollutants which scavenge the 

ozone. During the winter months, ozone concentrations tend to be lower due to shorter 

daylight hours and lower temperatures. 

Porterville 

Porterville, CA is located in the southeastern part of the San Joaquin Valley near the 

foothills of the Sierra Nevada Mountains to the east. It is approximately 25 miles 

southeast of Visalia, CA, and so transport of pollutants from Visalia towards Porterville 

is possible. The Porterville air monitoring site became operational in March 2010 and is 

operated by the SJVAPCD. The purpose of this site is to monitor ozone, PM2.5, and 

meteorology, and represent air quality levels present near the foothills of the 

southeastern portion of the Valley. 

Stockton-Wagner/Holt 

Stockton, CA is located in the northern part of the San Joaquin Valley with mountains to 

the east and west. North-south air flow is virtually unobstructed. Pollutants occur 

locally, but the wind can transport pollutants into the area from upwind locations or 

through the Sacramento Delta from the Bay Area. The Stockton-Wagner/Holt 

monitoring site is operated by SJVAPCD and is located in the Stockton, CA 

metropolitan area. It began operating in October 1996. The purpose of the site is to 

monitor representative concentrations of PM10 in an urban area. Occasionally, wind 

will carry dust across the city and cause PM10 concentrations to increase, but PM10 

exceedances are rare. 

Tracy-Airport 

Tracy, CA is located in the northern part of the San Joaquin Valley with mountains to 

the east and west. North-south air flow is virtually unobstructed. Pollutants occur 

locally, but the wind can transport pollutants into the area from upwind locations or 

through the Sacramento Delta from the Bay Area. The Tracy-Airport monitoring site is 

operated by SJVAPCD and is located in Tracy, CA. It began operating in January 2005. 

The purpose of the site is to monitor transport of ozone, PM2.5, and PM10 from upwind 

and nearby urban areas. The site also monitors NO2 and meteorology. During the 

summer months, high temperatures and longer daylight hours contribute to increases in 

ozone during the day. In contrast, ozone concentrations decrease at night with the 

absence of sunlight and the presence of NOx pollutants which scavenge the ozone. 

During the winter months, ozone concentrations tend to be lower due to shorter daylight 
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hours and lower temperatures. Elevated PM2.5 concentrations are possible year round, 

but concentrations tend to be highest during the winter months due to moisture content 

in the air, wood-burning activities, other anthropogenic activities, and atmospheric 

chemistry. PM2.5 and PM10 concentrations can also increase during wind events 

because the wind can cause PM to become suspended in the air. Occasionally, wind 

will carry dust across the city and also cause PM concentrations to increase, but PM2.5 

and PM10 exceedances due to wind events are rare. 

Tranquillity 

Tranquillity, CA is located in western Fresno County, and is about 25 miles west of 

Fresno, CA, with the coastal mountain range just to the west. North-south air flow is 

virtually unobstructed. This monitoring site was established in November 2009 and is 

operated by the SVAPCD. The purpose of this site is to monitor ozone, PM2.5, and 

meteorology. The site also represents background and rural pollutant concentrations on 

the west side of the San Joaquin Valley for research purposes. 

Turlock 

Turlock, CA is located in the northern part of the San Joaquin Valley with mountains to 

the east and west. North-south air flow is virtually unobstructed. Pollutants occur 

locally, but the wind can transport pollutants into the area from upwind locations or 

through the Sacramento Delta from the Bay Area. The Turlock monitoring site is 

operated by SJVAPCD and is located in the Turlock, CA. It began operating in April 

1992. The purpose of the site is to monitor representative concentrations of hourly 

ozone, PM2.5, and PM10 from upwind urban areas. The site also monitors CO, NO2, 

and meteorology. During the summer months, high temperatures and longer daylight 

hours contribute to increases in ozone during the day. In contrast, ozone 

concentrations decrease at night with the absence of sunlight and the presence of NOx 

pollutants which scavenge the ozone. During the winter months, ozone concentrations 

tend to be lower due to shorter daylight hours and lower temperatures. Elevated PM2.5 

concentrations are possible year round, but concentrations tend to be highest during the 

winter months due to moisture content in the air, wood-burning activities, other 

anthropogenic activities, and atmospheric chemistry. PM2.5 and PM10 concentrations 

can also increase during wind events because the wind can cause PM to become 

suspended in the air. Occasionally, wind will carry dust across the city and also cause 

PM concentrations to increase, but PM2.5 and PM10 exceedances due to wind events 

are rare. 

Visalia-Airport 

Visalia, CA is located where the central and southern parts of the San Joaquin Valley 

meet. The Sierra Nevada mountain range is approximately 20 miles east of Visalia. 

North-south air flow is virtually unobstructed. The Visalia-Airport monitoring site is 

operated by SJVAPCD and serves as a wind profiler monitoring surface wind speed and 

wind direction. It also monitors air temperature, and relative humidity at the surface. It 

began reporting official meteorological data in January 2001. Meteorological 

parameters have a direct influence on how and where pollutants are transported and 

how much pollutant concentrations increase or decrease. 
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Sites Operated by the California Air Resources Board (CARB) 

Arvin-Di Giorgio 

Arvin, CA is located at the southern end of the San Joaquin Valley with mountains to the 

east, west, and south. Because the mountains block or slow down air flow pollutants 

can get trapped and build up in the area. Pollutants occur locally and are also 

transported from upwind locations into the area by the wind. 

The Arvin-Bear Mountain Boulevard ozone monitoring site was established by the Air 

Resources Board (ARB) in 1989 and has periodically been the Valley’s ozone design 

site. Due to circumstances beyond ARB’s control, ARB was unable to renew the lease 

at this location, and monitoring had to be discontinued at the end of the 2010 ozone 

season. The loss of this monitoring site has implications for determining the ozone 

attainment status of the region. The ARB is actively working with the United States 

Environmental Protection Agency on an appropriate solution to address this situation. 

The Di Giorgio site is located 18 miles southeast of the Bakersfield, CA metropolitan 

area. The purpose of the site, as a PAMS Type 3 site, is to monitor maximum ozone 

concentrations and transport from upwind urban areas. The site also monitors NO2, 

NMOC, NMHC, and meteorology and CARB plans to install methane/CO2 and trace CO 

analyzers for special purpose monitoring. In addition, a NOy monitor will be added to 

the Arvin-Di Giorgio air monitoring site to comply with the latest regulation for PAMS 

Type 3 sites. During the summer months, high temperatures and longer daylight hours 

contribute to increases in ozone during the day. In contrast, ozone concentrations 

decrease at night with the absence of sunlight and the presence of NOx pollutants 

which scavenge the ozone. During the winter months, ozone concentrations decrease 

due to shorter daylight hours and lower temperatures. Pollutants occur locally and are 

also transported into the area by wind. 

Bakersfield-Planz

Bakersfield, CA is located at the southern end of the San Joaquin Valley with mountains 

to the east, west, and south. Because the mountains block or slow down air flow 

pollutants can get trapped and build up in the area. Pollutants occur locally, and are 

transported from upwind locations into the area by the wind. The Bakersfield-Planz 

monitoring site is operated by CARB and is located 6 miles north of the Bakersfield, CA 

metropolitan area. It began operating in September 2000. The purpose of the site is to 

monitor representative concentrations of PM2.5 from upwind and nearby urban areas. 

Elevated PM2.5 concentrations are possible year round, but concentrations tend to be 

highest during the winter months due to moisture content in the air, wood-burning 

activities, other anthropogenic activities, and atmospheric chemistry. PM2.5 

concentrations can also increase during wind events because the wind can cause 

PM2.5 to become suspended in the air. 

 
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Bakersfield-California 

Bakersfield, CA is located at the southern end of the San Joaquin Valley with mountains 

to the east, west, and south. Because the mountains block or slow down air flow 

pollutants can get trapped and build up in the area. Pollutants occur locally, and are 

transported from upwind locations into the area by the wind. The Bakersfield-California 

monitoring site is operated by CARB and is located in the Bakersfield, CA metropolitan 

area. It began operating in March 1994. The purpose of the site is to monitor 

representative concentrations of hourly and daily ozone, PM10, and PM2.5 in an urban 

area. After the shutdown of the Bakersfield-Golden site, the District requested CARB’s 

permission to temporarily operate a real time PM10 monitor at the Bakersfield-California 

site (06-029-0014). The temporary PM10 monitor was used for daily AQI forecasting 

purposes. This temporary monitor was later moved to the Bakersfield-Muni site, 

however the monitor is no longer operating at Bakersfield-Muni (see Appendix C for 

details). The Bakersfield-California site also monitors NO2 and meteorology. During the 

summer months, high temperatures and longer daylight hours contribute to increases in 

ozone during the day. In contrast, ozone concentrations decrease at night with the 

absence of sunlight and the presence of NOx pollutants which scavenge the ozone. 

Elevated PM2.5 concentrations are possible year round, but concentrations tend to be 

highest during the winter months due to moisture content in the air, wood-burning 

activities, other anthropogenic activities, and atmospheric chemistry. PM2.5 

concentrations can also increase during wind events because the wind can cause 

PM2.5 to become suspended in the air. 

Edison 

Edison, CA is located at the southern end of the San Joaquin Valley with mountains to 

the east, west, and south. Because the mountains block or slow down air flow 

pollutants can get trapped and build up in the area. Pollutants occur locally, and are 

transported from upwind locations into the area by the wind. The Edison monitoring site 

is operated by CARB and is located 9 miles east of the Bakersfield, CA metropolitan 

area. It began operating in January 1980. The purpose of the site is to monitor 

representative concentrations of hourly ozone from upwind and nearby urban areas. 

The site also monitors NO2 and meteorology. During the summer months, high 

temperatures and longer daylight hours contribute to increases in ozone during the day. 

In contrast, ozone concentrations decrease at night with the absence of sunlight and the 

presence of NOx pollutants which scavenge the ozone. During the winter months, 

ozone concentrations decrease due to shorter daylight hours and lower temperatures. 

Fresno-Garland 

Fresno, CA is located in the central part of the San Joaquin Valley with mountains to the 

east and west. North-south air flow is virtually unobstructed. Pollutants occur locally, 

and are transported from upwind locations into the area by the wind. In December 

2011, CARB moved the Fresno-First monitoring site to Garland Avenue which is two 

blocks north of the Fresno-First site. The new site is now referred to as Fresno-Garland 

and became operational on December 31, 2011. The Fresno-Garland monitoring site is 

a National Core (NCore) site operated by CARB and is located in the Fresno, CA 

metropolitan area. The purpose of the site is to monitor representative concentrations 
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of hourly ozone, PM2.5, and PM10 in an urban area. The site also monitors CO, NO2, 

SO2, NMOC, NMHC, toxics, and meteorology. During the summer months, high 

temperatures and longer daylight hours contribute to increases in ozone during the day. 

In contrast, ozone concentrations decrease at night with the absence of sunlight and the 

presence of NOx pollutants which scavenge the ozone. During the winter months, 

ozone concentrations tend to be lower due to shorter daylight hours and lower 

temperatures. Elevated PM2.5 concentrations are possible year round, but 

concentrations tend to be highest during the winter months due to moisture content in 

the air, wood-burning activities, other anthropogenic activities, and atmospheric 

chemistry. PM2.5 concentrations can also increase during wind events because the 

wind can cause PM2.5 to become suspended in the air. On rare occasions, this area of 

the San Joaquin Valley experiences wind events that can carry dust into the area or lift 

local dust particles into the air. Such events can cause PM10 concentrations to 

increase. 

Modesto-14th Street 

Modesto, CA is located in the northern part of the San Joaquin Valley with mountains to 

the east and west. North-south air flow is virtually unobstructed. Pollutants occur 

locally, but the wind can transport pollutants into the area from upwind locations or 

through the Sacramento Delta from the Bay Area. The Modesto-14th Street monitoring 

site is operated by CARB and is located in the Modesto, CA metropolitan area. It began 

operating in January 1981. The purpose of the site is to monitor representative 

concentrations of hourly ozone, PM2.5, and PM10 in local and upwind urban areas. 

The site also monitors CO and meteorology. During the summer months, high 

temperatures and longer daylight hours contribute to increases in ozone during the day. 

In contrast, ozone concentrations decrease at night with the absence of sunlight and the 

presence of NOx pollutants which scavenge the ozone. During the winter months, 

ozone concentrations tend to be lower due to shorter daylight hours and lower 

temperatures. Elevated PM2.5 concentrations are possible year round, but 

concentrations tend to be highest during the winter months due to moisture content in 

the air, wood-burning activities, other anthropogenic activities, and atmospheric 

chemistry. PM2.5 concentrations can also increase during wind events because the 

wind can cause PM2.5 to become suspended in the air. Occasionally, wind will carry 

dust across the city and cause PM10 concentrations to increase, but PM10 

exceedances are rare. 

Oildale 

Oildale, CA is located at the southern end of the San Joaquin Valley with mountains to 

the east, west, and south. Because the mountains block or slow down air flow 

pollutants can get trapped and build up in the area. Most pollutants occur locally, 

however, a small amount are also transported from upwind locations into the area by 

the wind. The Oildale monitoring site is operated by CARB and is located 6 miles north 

of Bakersfield, CA within the metropolitan area. It began operating in January 1980. 

The purpose of the site is to monitor representative concentrations of hourly ozone 

concentrations, and PM10 every 6 days in an urban area. The site also monitors 

meteorology. During the summer months, high temperatures and longer daylight hours 
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contribute to increases in ozone during the day. In contrast, ozone concentrations 

decrease at night with the absence of sunlight and the presence of NOx pollutants 

which scavenge the ozone. Not only does the metropolitan area generate its own 

pollution, it is also the recipient of pollutants that get transported by wind. On rare 

occasions, this area of the San Joaquin Valley experiences wind events that can carry 

dust into the area or lift local dust particles into the air. Such events can cause PM10 

concentrations to increase. 

Shafter 

Shafter, CA is located at the southern end of the San Joaquin Valley with mountains to 

the east and west, and 58 miles to the south. Because the mountains to the south are 

further away, southward air flow is less obstructed through Shafter so pollutant build-up 

is less pronounced compared to Bakersfield and the towns further south. Pollutants 

occur locally and wind can transport pollutants into and through Shafter from nearby 

and upwind areas. The Shafter monitoring site is a shared site operated by CARB and 

the SJVAPCD and is located 18 miles northwest of the Bakersfield, CA metropolitan 

area. It began operating in January 1989. This site was established as a PAMS Type 1 

site, located in an area upwind of Bakersfield and not to be influenced by upwind or 

local ozone precursor emissions. In addition to ozone, the site also monitors NO2, totaland speciated-VOC and meteorology for the PAMS program. During the summer 

months, high temperatures and longer daylight hours contribute to increases in ozone 

during the day. In contrast, ozone concentrations decrease at night with the absence of 

sunlight and the presence of NOx pollutants which scavenge the ozone. Being located 

upwind of Bakersfield, the Shafter site tends to have lower ozone concentrations than 

does the metropolitan area to the south. 

Stockton-Hazelton 

Stockton, CA is located in the northern part of the San Joaquin Valley with mountains to 

the east and west. North-south air flow is virtually unobstructed. Pollutants occur 

locally, but the wind can transport pollutants into the area from upwind locations or 

through the Sacramento Delta from the Bay Area. The Stockton-Hazelton monitoring 

site is operated by CARB and is located in the Stockton, CA metropolitan area. It began 

operating in June 1976. The purpose of the site is to monitor representative 

concentrations of ozone, PM2.5, and PM10 in an urban area. The site also monitors 

CO, NO2, toxics, and meteorology. During the summer months, high temperatures and 

longer daylight hours contribute to increases in ozone during the day. In contrast, 

ozone concentrations decrease at night with the absence of sunlight and the presence 

of NOx pollutants which scavenge the ozone. During the winter months, ozone 

concentrations tend to be lower due to shorter daylight hours and lower temperatures. 

Elevated PM2.5 concentrations are possible year round, but concentrations tend to be 

highest during the winter months due to moisture content in the air, wood-burning 

activities, other anthropogenic activities, and atmospheric chemistry. PM2.5 

concentrations can also increase during wind events because the wind can cause 

PM2.5 to become suspended in the air. On rare occasions, wind will carry dust across 

the city and cause PM10 concentrations to increase, but PM10 exceedances are rare. 
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Visalia-Church 

Visalia, CA is located where the central and southern parts of the San Joaquin Valley 

meet. The Sierra Nevada mountain range is approximately 20 miles east of Visalia. 

North-south air flow is virtually unobstructed. Pollutants occur locally, and can be 

transported from upwind locations into the area by the wind. The Visalia-Church 

monitoring site is operated by CARB. It began operating in July 1979. The purpose of 

the site is to monitor representative concentrations of hourly ozone, PM2.5, and PM10 

from upwind and nearby urban areas. The site also monitors NO2 and meteorology. 

During the summer months, high temperatures and longer daylight hours contribute to 

increases in ozone during the day. In contrast, ozone concentrations decrease at night 

with the absence of sunlight and the presence of NOx pollutants which scavenge the 

ozone. During the winter months, ozone concentrations tend to be lower due to shorter 

daylight hours and lower temperatures. Elevated PM2.5 concentrations are possible 

year round, but concentrations tend to be highest during the winter months due to 

moisture content in the air, wood-burning activities, other anthropogenic activities, and 

atmospheric chemistry. PM2.5 concentrations can also increase during wind events 

because the wind can cause PM2.5 to become suspended in the air. On rare 

occasions, wind will carry dust across the city and cause PM10 concentrations to 

increase, but PM10 exceedances are rare. 

Sequoia and Kings National Park and Forest Monitoring Sites 

Sequoia-Ash Mountain 

The Ash Mountain monitoring station is operated by Sequoia National Forest and is 

located at the southern entrance of Sequoia National Park at a 1,500-foot elevation. It 

originally began operating in 1985, though the site has been relocated several times 

over the years. The site demonstrates the hourly ozone concentrations in the foothills. 

The site also monitors PM2.5 and meteorology. On summer days, ozone and 

precursors can be transported to Ash Mountain from other locations. At this location, 

there are significantly lower hourly emissions of NOx as compared to urban areas such 

as Bakersfield, or Fresno, CA. 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.

Sequoia-Lower Kaweah 

The Lower Kaweah monitoring station is operated by Sequoia National Forest and is 

located at the southern entrance of Sequoia National Park at a 6,200-foot elevation. It 

began operating in April 1987. The site demonstrates the hourly ozone concentrations 

in a rural area. The site also monitors meteorology. On summer days, ozone and 

precursors can be transported to Ash Mountain from other locations. At this location, 

there are significantly lower hourly emissions of NOx as compared to urban areas such 

as Bakersfield, or Fresno, CA. The amount of available NOx at Lower Kaweah to 

scavenge the ozone is much lower. Because the ozone scavenging at Lower Kaweah 
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is much less than the ozone scavenging in urban areas, Lower Kaweah 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.