San Joaquin Valley Unified Air Pollution Control District March 11, 2016

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I. Background

Attainment of the 1997 PM10 Standard 

The San Joaquin Valley (Valley) attained the 24-hour 1997 PM10 National Air Quality 

Standard (NAAQS) of 150 micrograms per cubic meter μg/m3for particulate matter that 

is 10 microns or less in diameter (PM10). Attainment was based on detailed technical 

information and monitoring data showing that all Valley PM10 monitors attained the 

PM10 NAAQS for the period of 2003 through 2005. The San Joaquin Valley Unified Air 

Pollution Control District (District) subsequently adopted the 2007 PM10 Maintenance 

Plan satisfying all federal Clean Air Act (CAA) requirements for redesignation of the 

Valley to attainment. EPA proposed approval of the District 2007 PM10 Plan and 

redesignation of the Valley to attainment in April 2008 and issued final approval 

effective December 12, 2008.

District’s 2007 PM10 Plan Contingency Plan 

The Clean Air Act, Section (§) 175(d), requires maintenance plans to contain 

contingency provisions to assure prompt correction of any post-redesignation events. 

The District’s 2007 PM10 Maintenance Plan identified the action level of 155 μg/m3and 

several steps to address PM10 events above the action level: 

1. Examination of Event - First, the District will examine the event and determine if it 

needs to be classified as a natural or exceptional event in accordance with EPA’s 

final rulemaking (72 FR 13560). If the data qualify for flagging under this rule, the 

District would proceed with preparing and submitting the necessary 

documentation for a natural/exceptional event, and would not consider the 

monitored level as a trigger for the maintenance plan contingency plan. 

2. Determination of Causes and Needed Reductions - If the event does not qualify 

as a natural or exceptional event, the District would then analyze the event to 

determine its possible causes. It would examine emission reductions from 

adopted rules or rule commitments in adopted and approved plans to see if 

emission reductions not used in demonstrating maintenance would cover the 

event. 

3. Identification of Controls from Feasibility Studies - If reductions from Step 2 

above are insufficient, the District would proceed with identifying control 

measures from any feasibility studies (e.g., from the 2007 Ozone Plan

[SJVAPCD 2007]) completed to date that recommend future controls, and would 

prioritize development of the measures most relevant to reducing PM10 levels.
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II. Examination of Events 

In recent years, the Valley has experienced events in which the measured levels at 

Valley PM10 monitors exceeded the 155 μg/m3action level. Upon evaluation, the 

District determined that all of these events were caused by either high wind or extreme 

drought-related exceptional events.

Exceptional Event Evaluation Methodology 

To consider whether an event qualifies as an exceptional event, the District closely 

examines a number of aspects of the event to determine if the criteria are satisfied 

pursuant to 40 CFR Part 50.14:

1. The event satisfies the criteria set forth in 40 CFR 50.1(j);

2. There is a clear causal relationship between the measurement under 

consideration and the event that is claimed to have affected the air quality in the 

area;

3. The event is associated with a measured concentration in excess of normal 

historical fluctuations, including background; and

4. There would have been no exceedance or violation but for the event.

Through extensive meteorological and data analysis, the District determines whether 

there is a clear causal connection between the event and the concentrations recorded, 

and whether the recorded value is outside of expected normal fluctuations. By 

demonstrating that the District’s control measures were in place at the time of the event, 

the exceptional event analysis is able to show that the PM10 concentration would not 

have violated the federal standard “but for” the exceptional event that occurred.

Events Caused by High Wind

Below, Table 1 displays the recent events that have been impacted by high wind. 

Table 1 Summary of Recent Events Caused by High Wind

Date Site PM10 Concentration 

(μg/m3)

10/3/2013 Corcoran 224

1/23/2014

Bakersfield-California 260

Oildale 334

6/2/2014 Bakersfield-California 172

6/10/2014 Oildale 310

6/11/2014 Bakersfield-California 177

10/14/2014

Corcoran 180

Oildale 336

Bakersfield-California 419

12/11/2014 Corcoran 202
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As an example of the strong correlation between high winds speeds and elevated PM10 

concentrations, the following Figure 1 shows the hourly wind speeds during a high wind 

event on October 3, 2013. The wind data and hourly PM10 concentrations recorded on 

October 3 indicate that Corcoran and Hanford were initially impacted by geologic 

material that was entrained by strong local winds in the Lemoore and Tranquility areas, 

and then strengthened in western Merced County (Los Banos and Panoche). The 

winds entrained and transported the material across the western San Joaquin Valley to 

Kings County where it was deposited in Corcoran and Hanford. 

Figure 1 Hourly Wind Speeds at the Panoche and Los Banos CIMIS Stations, 

Lemoore NAS, and Hanford Municipal Airport and PM10 Concentrations at 

Corcoran and Hanford

*The 24-Hour Average PM10 NAAQS is defined as 150 μg/m3 rounded to the nearest 10 μg/m3.

The high wind events outlined in Table 1 qualify as exceptional events in accordance 

with EPA’s final rulemaking. The District will be submitting exceptional event 

documentation for these events to EPA. 

Events Caused by Exceptional Drought Conditions

The following Table 2 summarizes the PM10 events caused by extreme drought-related 

exceptional events. 

0

5

10

15

20

25

30

35

0

100

200

300

400

500

600

0:001:002:003:004:005:006:007:008:009:00

10:0011:0012:0013:0014:0015:0016:0017:0018:0019:0020:0021:0022:0023:00

Wind Speed (mph)

PM10 STP (μg/m3)

October 3, 2013

Corcoran PM10 STP μg/m3 Hanford PM10 LC μg/m3

Panoche CIMIS Wind Speed (mph) Los Banos CIMIS Wind Speed (mph)

Lemoore NAS Wind Speed (mph) Hanford Municipal Airport Wind Speed (mph)

Wind Entrainment Threshold

Federal 24-Hour Standard*
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Table 2 Summary of Events Caused by Exceptional Drought Conditions

Date Site Concentration (μg/m3)

11/14/2013 Corcoran 162.5

12/17/2013 Corcoran 164.4

12/18/2013

Hanford 177

Corcoran 183.5

Visalia-Church 155

1/21/2014 Bakersfield-California 158.5

1/22/2014 Corcoran 156

The events caused by exceptional drought conditions all occurred within a three month 

period during the winter of 2013-2014. During this period, a persistent and strong high 

pressure ridge over the eastern Pacific Ocean and the western United States effectively 

blocked weather disturbances from entering California. The historic strength and 

longevity of this high pressure siege resulted in a shocking lack of rainfall throughout the 

Valley, and California as a whole, during the months of November, December, and 

January. Many cities in California, including those in the San Joaquin Valley, shattered 

record low rainfall totals during the calendar year 2013, including some records that 

have stood for over 100 years.

The extreme weather conditions discussed above that led to extreme drought in the 

Valley also caused long periods of high pressure and stagnation that prevented 

pollutant dispersion throughout the winter of 2013-2014, resulting in PM2.5 and PM10 to 

become concentrated at extremely high levels throughout the region, as shown in 

Figure 2 below. Additionally, the dry conditions from lack of precipitation resulted in the 

release of more suspended particulate matter into the atmosphere. These conditions led 

to exceptionally high PM2.5 and PM10 concentrations in the San Joaquin Valley.
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Figure 2 Average Atmospheric Stability per Winter Season (Nov to Feb)

The District considers the exceptional drought conditions that caused the PM10 events 

outlined in Table 2 to be exceptional events. Therefore, the District will be submitting 

exceptional event documentation for these events to EPA. 

III. Determination of Causes and Needed Reductions

The District considers the exceptional drought conditions that caused the PM10 events 

outlined in Table 2 to be “exceptional events”. The EPA has also indicated that the 

prolonged duration and extreme stability conditions of the drought experienced in 

California may be considered as “exceptional events”. However, since the District has 

not received a definitive response from EPA regarding this matter, the District has 

proceeded with the appropriate analysis and demonstration below that the contingency 

requirements have been satisfied.

Possible Causes

During the winter season of 2013-2014 when the high values found in Table 2 occurred, 

the Valley experienced the strongest recorded atmospheric stability over the past 15 

years. Climate conditions caused by this type of weather pattern resulted in historically 

dry and poor air quality conditions in the San Joaquin Valley and other parts of 

California. Due to the abnormally strong stability and lack of precipitation, the 

exceptional drought continued to worsen beyond this winter season and covered much 

of the western parts of the San Joaquin Valley and the western U.S. as a whole. This 

-1.5

-1

-0.5

0

0.5

1

1.5

2

2.5

3

3.5

1999-20002000-20012001-20022002-20032003-20042004-20052005-20062006-20072007-20082008-20092009-20102010-20112011-20122012-20132013-2014

T850MB Stability Parameter ( ̊C)
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stable pattern effectively trapped pollutants and caused elevated PM10 and PM2.5 

concentrations, resulting in events above the action level.

Emission Reductions Not Already Used In Maintenance Plan

Since the adoption of the 2007 PM10 Maintenance Plan, multiple rules and regulations 

have been adopted by the District and ARB to reduce PM10 emissions beyond the 

commitments in the plan. In 2015, the Valley did not experience any PM10 events 

above the action level, including during the 2014-15 winter season during which the 

Valley continued to experience drought and stagnation conditions conducive to the 

formation of PM10. In 2016, the Valley has not experienced any PM10 events as of the 

date of this report. As the discussion below demonstrates and as evidenced by the 

Valley not experiencing any PM10 events from winter of 2014-15 to date, the stringent 

control measures adopted and implemented by the District and ARB beyond those 

included in the maintenance plan achieve sufficient emissions reductions to minimize 

the potential of future PM10 events. These control measures will achieve even greater 

emissions reductions as they are fully implemented in the coming years. In addition to 

these regulatory measures, the District has implemented a robust incentive program 

that has achieved significant additional cost-effective emissions reductions. 

District Rules

The District has adopted several rules, substantially reducing PM10 emissions beyond 

the 2007 PM10 Maintenance Plan. One example is Rule 4901(Wood Burning 

Fireplaces and Wood Burning Heaters). It is the most stringent rule of its kind in the 

nation and significantly reduces particulate matter emissions during periods of 

atmospheric stagnation when those reductions are needed most. Even though already 

providing considerable particulate matter reductions, the District amended this rule in 

October 2008 to reduce particulate matter by an additional 2.4 tons per day. In 

September of 2014, the District amended it again to lower the curtailment threshold for 

non-registered wood burning devices from 30 to 20 μg/m3, which is significantly lower 

than any other rule in the nation. This amendment further reduced particulate matter 

emissions by 5.1 tons per day. More reductions will be achieved as Valley residents 

continue to replace their existing wood burning fireplaces and wood burning heaters 

with cleaner devices through the District’s Burn Cleaner incentive program.

The following is a summary of District rules amended or adopted that resulted in 

significant PM10 emission reductions beyond the plan. 
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Table 3 Summary of Rules Adopted After 2007 PM10 Maintenance Plan

District Rule

Adoption/ 

Amendment

Date(s)

Rule 4103 Open Burning 04/15/2010

Rule 4307 Boilers, Steam Generators, and Process Heaters 

 2 to 5 MMBtu/hr

10/16/2008

05/19/2011

Rule 4308 Boilers, Steam Generators, and Process Heaters 

 0.075 to <2 MMBtu/hr

12/17/2009

11/14/2013

Rule 4311 Flares 06/18/2009

Rules 4306 & 4320 Boilers, Steam Generators, and Process Heaters 

 >5 MMBtu/hr 10/16/2008

Rule 4352 Solid Fuel Fired Boilers, Steam Generators, and Process 

 Heaters 12/15/2011

Rule 4354 Glass Melting Furnaces 

10/16/2008

09/16/2010

05/19/2011

Rule 4401 Steam-Enhanced Crude Oil Production Wells 06/16/2011

Rule 4402 Crude Oil Production Sumps 12/15/2011

Rule 4566 Organic Material Composting Operations 08/18/2011

Rule 4570 Confined Animal Facilities 06/18/2009

10/21/2010

Rule 4601 Architectural Coatings 12/17/2009

Rule 4602 Motor Vehicle Assembly Coatings 12/17/2009

Rule 4603 Surface Coating Of Metal Parts And Products, Plastic Parts 

And Products, And Pleasure Crafts

10/16/2008

09/17/2009

Rule 4605 Aerospace Assembly and Component Coatings Operations 06/16/2011

Rule 4606 Wood Products and Flat Wood Paneling Products 10/16/2008

Rule 4607 Graphic Arts and Paper, Film, Foil and Fabric Coatings 12/18/2008

Rule 4612 Motor Vehicle and Mobile Equipment Coating Operations 10/21/2010

Rule 4621 Gasoline Transfer into Stationary Storage Containers, 

Delivery Vessels, and Bulk Plants 12/19/2013

Rule 4622 Gasoline Transfer into Motor Vehicle Fuel Tanks 12/19/2013

Rule 4625 Wastewater Separators 12/15/2011

Rule 4653 Adhesives and Sealants 

09/17/2009

09/16/2010

Rule 4682 Polystyrene, Polyethylene, and Polypropylene Products 

Manufacturing 12/15/2011

Rule 4684 Polyester Resin Operations 

09/17/2009

08/18/2011
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District Rule

Adoption/ 

Amendment

Date(s)

Rule 4692 Commercial Charbroiling 09/17/2009

Rule 4695 Brandy Aging and Wine Aging Operations 09/17/2009

Rule 4702 Internal Combustion Engines 08/18/2011

11/14/2013

Rule 4901 Wood Burning Fireplaces and Wood Burning Heaters 10/16/2008

09/18/2014

Rule 4902 Residential Water Heaters 03/19/2009

Rule 4905 Natural Gas-Fired, Fan-Type Central Furnaces 01/22/2015

Rule 9410 Employer-based Trip Reduction 12/17/2009

ARB Mobile Source Control Measures

Since the adoption of the 2007 PM10 Maintenance Plan, ARB has adopted numerous

mobile source control measures. For example, in 2012, ARB adopted the On-Road 

Heavy-Duty Diesel Vehicles (In-Use) Regulation (later readopted in 2014). The 

regulation requires diesel trucks and buses that operate in California to reduce 

emissions by replacing older trucks with newer diesel vehicles, retrofitting engines, and 

installing diesel particulate filters. This rule has already achieved significant emission 

reductions, and as the compliance schedule below indicates, the requirement of this 

rule will continue to achieve additional emission reductions.
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In addition to heavy duty trucks, other higher-emitting heavy-duty vehicles with long 

service lives can remain on the road for many years. To address this legacy fleet, ARB 

adopted heavy-duty vehicle in-use control measures to significantly reduce PM and 

NOx emissions from existing diesel vehicles operating in California. These recent in-use 

control measures include:

 Drayage (Port or Rail Yard) Regulation;

 Public Agency and Utilities Regulation;

 Solid Waste Collection Vehicle Regulation;

 ATCM to Limit Diesel-Fueled Commercial Motor Vehicle Idling;

 Heavy-Duty Diesel Vehicle Inspection Program;

 Periodic Smoke Inspection Program;

 Fleet Rule for Transit Agencies;

 Lower-Emission School Bus Program; and

 Heavy-Duty Truck Idling Requirements.

In 2012, ARB also adopted California's Advanced Clean Cars program, a new 

emissions-control program for model years 2017 through 2025. Upon full 

implementation in 2025, consumer vehicles will produce 75% less emissions.

IV. Conclusion

As demonstrated in this document, the District is in compliance with the 2007 PM10 

Maintenance Plan and CAA contingency requirements for maintenance plans. For all of 

the PM10 events identified in this document, the District is in the process of preparing 

exceptional event documentation and upon completion will submit the documents to 

ARB for eventual transmission to the EPA. Additionally, for events caused by 

exceptional drought conditions, the District has demonstrated compliance with the 

contingency requirements by determining the possible causes for the events and 

explaining how the extensive emissions reductions from adopted rules and regulations
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beyond those included in the 2007 PM10 Maintenance Plan are sufficient to cover the 

events. As the District continues to develop new attainment plans to address the latest 

federal ozone and PM2.5 standards in the coming year, significant additional emissions 

reductions are expected, particularly with respect to mobile sources under ARB and 

EPA jurisdiction that make up over 85% of remaining San Joaquin Valley emissions.