State of Arizona 

Exceptional Event Documentation 

for the Event of September 6, 2012, 

for the Phoenix PM10 Nonattainment Area 

Final Report prepared for 

Arizona Department of Environmental Quality 

Phoenix, AZ 

February 2013
This PDF document contains blank pages to accommodate two-sided printing. 
State of Arizona 

Exceptional Event Documentation 

for the Event of September 6, 2012, 

for the Phoenix PM10 Nonattainment Area 

Final Report 

STI-912098-5572-FR 

Prepared by 

Daniel Alrick 

Angela Ekstrand 

Briana Gordon 

Hilary Hafner 

Clinton MacDonald 

Hilary Minor 

Ashley Russell 

Sonoma Technology, Inc. 

1455 N. McDowell Blvd., Suite D 

Petaluma, CA 94954-6503 

Ph 707.665.9900 | F 707.665.9800 

sonomatech.com 

Prepared for 

Theresa Rigney 

Air Quality Assessment Section Manager 

1110 W. Washington Street 

Phoenix, AZ 85007 

602.771.2274

February 13, 2013 

Cover image depicts widespread blowing dust associated with thunderstorm outflow causing reduced visibilities in the 

Phoenix area 1755 LST on September 6, 2012.

Exceptional Event, Phoenix, September 6, 2012 Acknowledgments 

Acknowledgments 

The authors would like to acknowledge the Arizona Department of Environmental Quality 

for helpful discussion and feedback during the preparation of this document. 

iii

Exceptional Event, Phoenix, September 6, 2012 Table of Contents 

Table of Contents 

Section Page

Acknowledgments........................................................................................................................ iii 

List of Figures ............................................................................................................................. vii

List of Tables...............................................................................................................................viii

1. Introduction..........................................................................................................................1

1.1 Report Contents .........................................................................................................1

1.2 Exceptional Event Rule Requirements.......................................................................1

1.2.1 Public Notification that the Event Was Occurring (40 CFR 

50.14(c)(1)(i)) .................................................................................................2

1.2.2 Place Informal Flag on Data in AQS (40 CFR 50.14(c)(2)(ii))........................2

1.2.3 Notify EPA of Intent to Flag Through Submission of Initial Event 

Description by July 1 of Calendar Year Following Event (40 CFR 

50.14(c)(2)(iii))................................................................................................2

1.2.4 Document that the Public Comment Process Was Followed for Event 

Documentation (40 CFR 50.14(c)(3)(iv))........................................................2

1.2.5 Submit Demonstration Supporting Exceptional Event Flag (40 CFR 

50.14(a)(1-2)).................................................................................................3

1.2.6 Documentation Requirements (40 CFR 50.14(c)(3)(iii)) ................................3

2. Conceptual Model................................................................................................................1

2.1 Geographic Setting and Monitor Locations ................................................................1

2.2 Climate.......................................................................................................................5

2.3 Event Day Summary ..................................................................................................6

3. Causal Relationship.............................................................................................................1

3.1 Discussion..................................................................................................................1

3.2 Summary....................................................................................................................5

4. Historical Norm ....................................................................................................................1

4.1 Analysis......................................................................................................................1

4.2 Summary....................................................................................................................2

5. Not Reasonably Controllable or Preventable ......................................................................1

5.1 Background................................................................................................................1

5.1.1 Control Measures...........................................................................................1

5.1.2 Additional Measures.......................................................................................3

5.1.3 PM10 Rule Effectiveness ................................................................................4

5.1.4 Compliance and Enforcement Activities.........................................................5

5.1.5 Review of Source-Permitted Inspections and Public Complaints ..................6

5.2 Forecasts and Warnings ............................................................................................7

5.3 Wind Observations.....................................................................................................7

5.4 Summary....................................................................................................................7

6. But-For Analysis ..................................................................................................................1

6.1 Discussion..................................................................................................................1

6.2 Summary....................................................................................................................1

v
Exceptional Event, Phoenix, September 6, 2012 Table of Contents 

vi

Section Page

7. Conclusions .........................................................................................................................1

7.1 Affects Air Quality.......................................................................................................1

7.2 Not Reasonably Controllable or Preventable .............................................................1

7.3 Natural Event .............................................................................................................1

7.4 Clear Causal Relationship..........................................................................................2

7.5 Historical Norm...........................................................................................................2

7.6 But For .......................................................................................................................2

Appendix A: Air Quality and Meteorological Data for Maricopa County .................................. A-1 

Appendix B: Media Coverage, Videos, and Images ............................................................... B-1 

Appendix C: ADEQ and NWS Forecast Products.................................................................... C-1 

Appendix D: Affidavit of Public Notice...................................................................................... D-1 
Exceptional Event, Phoenix, September 6, 2012 List of Figures 

List of Figures 

Figure Page

2-1. Locations of the air quality monitor that recorded an exceedance of the 24-hr PM

NAAQS on September 6, 2012, and NWS monitors described in this report....................2

10

2-2. Location of sites monitoring PM10 in Arizona on September 6, 2012................................3

2-3. Drainage system of Phoenix, Arizona. ..............................................................................4

2-4. Average monthly temperatures and precipitation for Phoenix, 1981–2010.......................5

2-5. Cross-section of a thunderstorm creating an outflow boundary and haboob....................6

3-1. Infrared satellite image from 1615 LST on September 6, 2012 (GOES-West). ................1

3-2. Hourly PM10 concentrations at Pinal County monitors on September 6, 2012.. ...............2

3-3. Hourly PM concentrations at Maricopa County monitors and visibility at KCHD on 

September 6, 2012............................................................................................................3

10

3-4. Hourly PM concentrations and wind speeds at the West Chandler monitor on 

September 6 and 7, 2012..................................................................................................3

10

3-5. Image from an ADEQ visibility camera on North Mountain looking south toward 

downtown Phoenix and the South Mountains. ..................................................................4

3-6. Maximum 5-minute PM concentrations (colored circles), 5-minute wind speed 

and direction (vectors), maximum wind gusts (red numbers), and minimum visibility 

observations (white numbers) at Maricopa and Pinal county monitors between 

1530 and 1600 LST on September 6, 2012. .....................................................................7

10

3-7. Similar to Figure 3-6, but representing observations from 1630 to 1700 LST...................8

3-8. Similar to Figure 3-6, but representing observations from 1730 to 1800 LST...................9

3-9. Similar to Figure 3-6, but representing observations from 1830 to 1900 LST.................10

4-1. 24-hr average PM10 concentrations at the West Chandler monitor (2007–2012).............1

4-2. Daily maximum hourly average PM concentrations at the West Chandler monitor 

(2007–2012)......................................................................................................................2

10

5-1. Timeline of Maricopa County fugitive dust rules and ordinances......................................5

vii
Exceptional Event, Phoenix, September 6, 2012 List of Tables 

List of Tables 

Table Page

2-1. Arizona PM10 measurements on September 6, 2012. ......................................................7

5-1. Rules and ordinances regulating PM emissions in Maricopa County. ..............................2

5-2. Pinal County rules regulating existing and new non-point sources in Pinal County..........3

5-3. Pinal County rules regulating fugitive dust in Pinal County portion of the Phoenix 

PM10 Nonattainment Area.................................................................................................3

viii
Exceptional Event, Phoenix, September 6, 2012 Introduction

1

1. Introduction 

On September 6, 2012, an air quality monitor in the Phoenix PM10 nonattainment area 

recorded a 24-hr average PM10 concentration in excess of the National Ambient Air Quality 

Standard (NAAQS) for PM10 of 150 μg/m3

. The purpose of this report is to demonstrate that this 

exceedance was due to naturally occurring windblown dust, was not reasonably controllable or 

preventable, was historically unusual, and would not have occurred “but-for” the windblown dust 

and that it therefore constitutes an Exceptional Event as defined by the U.S. Environmental 

Protection Agency’s (EPA) Exceptional Events Rule (EER). 

1.1 Report Contents 

Section 2 of this assessment contains a conceptual model of the windblown dust event 

that transpired on September 6, 2012, providing a background narrative of the exceptional event 

and an overall explanation showing that the event affected air quality. Section 2 also provides 

evidence that the event was a natural event. 

Section 3 of this assessment establishes a clear causal connection between the natural 

event on September 6, 2012, and the exceedance of the 24-hr PM10 standard at the monitoring 

station. The evidence in this section also confirms that the event in question both affected air 

quality and was the result of natural events. 

Section 4 of this assessment illustrates that the event of September 6, 2012, produced 

PM10 concentrations in excess of normal historical fluctuations. 

Section 5 of this assessment details the existing dust control measures and 

demonstrates that, despite the presence and enforcement of these controls, the event of 

September 6, 2012, was not reasonably controllable or preventable. 

Section 6 of this assessment builds upon the demonstrations made in the previous 

sections, showing a clear causal connection between the natural event and the exceedance, 

and concludes that the exceedance of the 24-hr PM10 standard on September 6, 2012, would 

not have occurred “but for” the event. 

Appendix A contains time-series graphs and data tables to supplement Section 3. 

Appendix B contains links to videos, images, and media reports to supplement Section 3. 

Appendix C contains air quality forecasts issued by the Arizona Department of Environmental 

Quality (ADEQ) and weather statements and warnings issued by the National Weather Service. 

Appendix D contains a copy of the affidavit of public notice concerning this assessment report. 

1.2 Exceptional Event Rule Requirements 

In addition to the technical requirements that are contained within the EER, procedural 

requirements must also be met in order for the EPA to concur with the flagged air quality 

monitoring data. This section of the report lists the requirements of the EER and associated 

guidance and discusses how ADEQ addressed those requirements. 
Exceptional Event, Phoenix, September 6, 2012 Introduction

2

1.2.1 Public Notification that the Event Was Occurring (40 CFR 50.14(c)(1)(i)) 

ADEQ issued Dust Control Action Forecasts and Air Quality Forecasts for Maricopa 

County advising citizens of the potential for high wind dust events on September 6, 2012. More 

information on ADEQ’s forecasts can be found in Section 5.2 of this report. The forecast 

products that were issued for September 6, 2012, are included in Appendix C. 

1.2.2 Place Informal Flag on Data in AQS (40 CFR 50.14(c)(2)(ii)) 

ADEQ and other operating air quality agencies in Arizona submit data into the EPA’s Air 

Quality System (AQS), the official repository of ambient air quality data. This data submittal to 

AQS includes particulate matter (PM) data from both filter-based and continuous monitors 

operated in Arizona. 

When ADEQ and/or another agency operating monitors in Arizona suspect that data 

may be influenced by an exceptional event, ADEQ and/or the other operating agency expedites 

analysis of the filters collected from the potentially-affected filter-based air monitoring 

instruments, quality-assures the results, and submits the data into AQS. ADEQ and/or other 

operating agencies also submit data from continuous monitors into AQS after quality assurance 

is complete. 

If ADEQ and/or other operating air quality agencies have determined that a potential 

exists that a monitor’s reading(s) have been influenced by an exceptional event, a preliminary 

flag is submitted for the measurement in AQS. The data are not official until they undergo more 

thorough quality assurance and quality control, leading to certification by May 1 of the year 

following the calendar year in which the data were collected (40 CFR 58.15(a)(2)). The 

presence of the flag on the September 6, 2012, data can be confirmed in AQS. 

1.2.3 Notify EPA of Intent to Flag Through Submission of Initial Event 

Description by July 1 of Calendar Year Following Event (40 CFR 

50.14(c)(2)(iii)) 

ADEQ submitted notice to EPA on August 29, 2012 listing all days from calendar year 

2012 that ADEQ intends to analyze under the Exceptional Events Rule. The PM10 exceedance 

that occurred on September 6, 2012, in the Phoenix PM10 nonattainment area was included on 

this list. This assessment report serves as demonstration supporting the flagging of the data. 

1.2.4 Document that the Public Comment Process Was Followed for Event 

Documentation (40 CFR 50.14(c)(3)(iv)) 

ADEQ posted this assessment report on the ADEQ webpage and placed a hard copy of 

the report in the ADEQ Records Management Center for public review. ADEQ opened a 30-day 

public comment period on January 14, 2013. A copy of the public notice certification, along with 

any comments received, will be submitted to EPA, consistent with the requirements of 40 CFR 

50.14(c)(3)(iv). See Appendix D for a copy of the affidavit of public notice. 
Exceptional Event, Phoenix, September 6, 2012 Introduction 

3

1.2.5 Submit Demonstration Supporting Exceptional Event Flag (40 CFR 

50.14(a)(1-2)) 

At the close of the public comment period, and after ADEQ has had the opportunity to 

consider any comments submitted on this document, ADEQ will submit this document, the 

comments received, and ADEQ’s responses to those comments to EPA Region 9 headquarters 

in San Francisco, California. The deadline for the submittal of this package is September 30, 

2015. 

1.2.6 Documentation Requirements (40 CFR 50.14(c)(3)(iii)) 

The EER states that in order to justify the exclusion of air quality monitoring data, 

evidence must be provided for the following elements: 

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

a. the event affected air quality, 

b. the event was not reasonably controllable or preventable, and 

c. the event was caused by human activity unlikely to recur in a particular 

location or was a natural event; 

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

consideration and the event; 

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

historical fluctuations; and 

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

Exceptional Event, Phoenix, September 6, 2012 Conceptual Model

1 

2. Conceptual Model 

This section provides a narrative background and summarizes the meteorological and 

air quality conditions in place on September 6, 2012 in the Phoenix area. Elements described in 

this section include 

 A description and map of the geographic setting of the air quality and meteorological 

monitors. 

 A description of Phoenix’s climate. 

 An overall description of meteorological and air quality conditions on the event day. 

2.1 Geographic Setting and Monitor Locations 

Phoenix is located in the Salt River Valley in south-central Arizona. It lies at an elevation 

of 1,090 feet above mean sea level (msl) in the northeastern part of the Sonoran Desert. Other 

than the mountains in and around the city, the topography of Phoenix is generally flat. The 

Phoenix area is surrounded by the McDowell Mountains (~4,200 ft above msl) to the northeast, 

the foothills of the Bradshaw (~7,900 ft above msl) and Mazataal (~7,900 ft above msl) ranges 

to the north, the White Tank Mountains (~4,500 ft above msl) to the west, the Sierra Estrella 

(~4,450 ft above msl) to the southwest, and the Superstition Mountains (~5,000 ft above msl) far 

to the east. Within the City are the Phoenix Mountains (~2,600 ft above msl) and South 

Mountain (~2,600 ft above msl). Current development is pushing north, west, and south into 

Pinal County. 

A fairly dense network of air quality and meteorological monitors exists throughout the 

Phoenix area, with a much less dense network of monitors throughout the rest of Arizona. 

Figure 2-1 shows the general geographic setting of Phoenix, as well as the location of the PM10

monitor that recorded an exceedance on September 6, 2012. The monitors shown in the map 

include AQS monitors, which measure air quality and meteorological data, and National 

Weather Service (NWS) monitors, which measure meteorological data only. Some of the AQS 

monitors in the Phoenix area are run by the Maricopa County Air Quality Department (MCAQD), 

while others are run by ADEQ. The PM10 exceedance on September 6, 2012, was recorded at 

the West Chandler monitor. Phoenix Sky Harbor International Airport (KPHX) and Chandler 

Municipal Airport (KCHD) were the primary NWS sites used in this demonstration package 

because of those sites’ high data quality, data completeness, proximity to the West Chandler 

monitor, and representativeness of meteorological conditions in the Phoenix area. Figure 2-2

shows the locations of PM10 monitors statewide on September 6, 2012. 

Figure 2-3 depicts the drainage systems or watersheds for the State of Arizona. Many 

of the rivers that form Arizona’s drainage system are dry for most of the year and, consequently, 

are sources of silt and fine soils that become suspended and add to regional PM10 loadings 

during high wind events. Much of this alluvial matter and fine soil is deposited in the low-lying 

areas of central and southern Arizona, with larger depositional areas focused in and around the 

confluences of dry river channels.
2 

Figure 2-1. Locations of the air quality monitor that recorded an exceedance of the 24-hr PM10 NAAQS on Septem

and NWS monitors described in this report. 
Exceptional Event, Phoenix, September 6, 2012 Conceptual Model

3 

Figure 2-2. Location of sites monitoring PM10 in Arizona on September 6, 2012. 
Exceptional Event, Phoenix, September 6, 2012 Conceptual Model

4 

Figure 2-3. Drainage system of Phoenix, Arizona. 
Exceptional Event, Phoenix, September 6, 2012 Conceptual Model

5 

2.2 Climate 

Phoenix has an arid climate, with very hot summers and temperate winters. The 

average summer high temperatures are among the hottest of any populated area in the United 

States (Figure 2-4). Temperatures reach or exceed 100°F an average of 110 days annually, 

and reach or exceed 110°F an average of 18 days annually. Phoenix receives an average of 

7.66 inches of rain per year. The bulk of this rain usually falls during the December through 

March and July through August time periods. During the December through March period, 

winter storms originating from the Pacific Ocean can produce significant rains in southwestern 

Arizona. During the mid- to late-summer time period, monsoonal moisture originating from the 

Gulf of California, Gulf of Mexico, and large thunderstorm complexes over the Sierra Madre 

Occidental Mountains in Mexico move northward into Arizona. 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0

20

40

60

80

100

120

Precipitation (inches)

Temperature (°F)

Precipitation

Max Temp

Min Temp

Mean Temp

Figure 2-4. Average monthly temperatures and precipitation for Phoenix, 1981–2010. 

The influx of moisture associated with the monsoon, combined with strong solar heating, 

can result in unstable atmospheric conditions that are favorable for the development of 

thunderstorms. Heavy precipitation associated with thunderstorms, and the eventual collapse 

or dissipation of thunderstorms, can generate what are known as downbursts. Downbursts are 

the rapid descent of rain-cooled air in a thunderstorm. Upon reaching the surface, this air 

rapidly disperses horizontally away from the storm as the outflow boundary (also called gust 

fronts), as shown in Figure 2-5. The high winds associated with outflow boundaries can 

efficiently loft dust into the air and transport the dust over long distances, resulting in dust 

storms (also called haboobs) with high PM10 concentrations and low visibilities. 
Exceptional Event, Phoenix, September 6, 2012 Conceptual Model

6 

Cross‐section schematic of a haboob caused by the cool outflow from a

thunderstorm, with the leading edge that is propagating ahead of the storm

called an outflow boundary.  The strong, gusty winds that prevail at the

boundary are defined as a gust front.  The leading edge of the cool air is called

the nose, and the upward‐protruding part of the features is referred to as the

head.  Behind the roll in the windfield at the leading edge is a turbulent wake.  

The rapidly moving cool air and the gustiness at the gust front raise dust

(shaded) high into the atmosphere.

Figure 2-5. Cross-section of a thunderstorm creating an outflow boundary and haboob. 

(Source: Desert Meteorology, Thomas T. Warner, 2004.) 

Dust storms associated with these thunderstorms typically occur in the early part of the 

monsoon season (July) before subsequent rains moisten the soil and limit potential lofting of soil 

into the air. However, depending on the amount and frequency of precipitation received during 

the monsoon season, the extremely hot temperatures can dry the surface soils very quickly; 

thus, dust storms can occur at any time during the year. Specific PM10 source regions are 

difficult to determine during thunderstorm-driven dust storms because the thunderstorm outflow 

can carry dust over long distances that encompass many possible sources of dust. Instead, we 

consider general PM10 source regions, which are typically identified based on the locations of 

the thunderstorms that are believed to have generated the dust-laden outflow winds. 

2.3 Event Day Summary 

On the afternoon and evening of September 6, 2012, strong winds generated by 

thunderstorms over south-central Arizona transported dust northward into the Phoenix area. 

The windblown dust resulted in 24-hr average PM10 concentrations in exceedance of the 

NAAQS at one air quality monitor (Table 2-1). The PM10 concentration measured at this 

monitor was in excess of normal historical fluctuations. The dust was naturally occurring and 

likely originated over undeveloped lands south of the Phoenix area, and wind gusts in excess of 

30 mph overwhelmed reasonable dust control measures. Monitors across Maricopa and Pinal 

counties recorded high PM10 concentrations during this dust storm, illustrating the widespread, 

regional nature of the event. 
Exceptional Event, Phoenix, September 6, 2012 Conceptual Model

7 

Table 2-1. Arizona PM10 measurements on September 6, 2012. The exceedance 

monitors discussed in this report are shown in bold. 

Monitor Monitor 

Type Operator AQS Monitor ID 

24-hr 

Avg 

PM10

(μg/m3) 

1-hr 

Max 

PM10

(μg/m3) 

Time of 

Max 1-hr 

PM10

(LST) 

AQS 

Qualifier 

Flag 

Apache County 

N/A TEOM WMAT 04-001-1003-81102-1 12 25 700 

Coconino County 

N/A N/A ADEQ 04-005-1237-81102-1 N/A N/A N/A 

Gila County 

Hayden Old Jail TEOM ADEQ 04-007-1001-81102-3 41 139 1100 

Maricopa County 

Senior Center Air 

Monitoring Station N/A SRP-MIC 04-013-7020-81102-1 125 N/A N/A 

Senior Center Air 

Monitoring Station N/A SRP-MIC 04-013-7020-81102-2 121 N/A N/A 

Lehi Air Monitoring 

Station N/A SRP-MIC 04-013-7022-81102-1 150 N/A N/A 

West Phoenix BAM MC 04-013-0019-81102-1 30 117 1800 

North Phoenix BAM MC 04-013-1004-81102-1 N/A N/A N/A 

Glendale TEOM MC 04-013-2001-81102-1 39 185 1700 

Central Phoenix TEOM MC 04-013-3002-81102-4 64 624 1700 

Greenwood TEOM MC 04-013-3010-81102-1 46 247 1700 

South Phoenix TEOM MC 04-013-4003-81102-1 79 870 1700 

West Chandler TEOM MC 04-013-4004-81102-1 164 3056 1700 RJ 

Tempe TEOM MC 04-013-4005-81102-1 103 1535 1700 

Higley TEOM MC 04-013-4006-81102-1 128 2189 1700 

West 43rd Ave TEOM MC 04-013-4009-81102-1 65 508 1700 

Dysart TEOM MC 04-013-4010-81102-1 50 282 1700 

Buckeye TEOM MC 04-013-4011-81102-1 46 325 1700 

Zuni Hills TEOM MC 04-013-4016-81102-1 60 631 1800 

South Scottsdale TEOM MC 04-013-3003-81102-1 101 1094 1700 

Fort 

McDowell/Yuma 

Frank 

TEOM FMIR 04-013-5100-81102-3 N/A N/A N/A 

Durango Complex TEOM MC 04-013-9812-81102-1 81 862 1700 

JLG Supersite BAM ADEQ 04-013-9997-81102-3 37 113 600 

JLG Supersite TEOM ADEQ 04-013-9997-81102-4 N/A N/A N/A 

Navajo County 

N/A TEOM WMAT 04-017-1002-81102-1 16 35 1600 

Pima County 

Ajo TEOM ADEQ 04-019-0001-81102-3 N/A N/A N/A 

Rillito TEOM ADEQ 04-019-0020-81102-3 42 300 1400 

Orange Grove FRM PCDEQ 04-019-0011-81102-2 27 N/A N/A 
Exceptional Event, Phoenix, September 6, 2012 Conceptual Model 

8 

Monitor Monitor 

Type Operator AQS Monitor ID 

24-hr 

Avg 

PM10

(μg/m3) 

1-hr 

Max 

PM10

(μg/m3) 

Time of 

Max 1-hr 

PM10

(LST) 

AQS 

Qualifier 

Flag 

Prince Road FRM PCDEQ 04-019-1009-81102-1 18 N/A N/A 

Tangerine FRM PCDEQ 04-019-1018-81102-1 22 N/A N/A 

Santa Clara FRM PCDEQ 04-019-1026-81102-1 17 N/A N/A 

Pinal County 

Casa Grande 

Downtown TEOM PCAQCD 04-021-0001-81102-3 92 978 1500 

Apache Junction 

Fire Station FRM PCAQCD 04-021-3002-81102-3 83 746 1700 

Stanfield TEOM PCAQCD 04-021-3008-81102-3 121 1649 1600 

Combs School TEOM PCAQCD 04-021-3009-81102-3 70 497 1700 

Maricopa TEOM PCAQCD 04-021-3010-81102-3 N/A N/A N/A 

Pinal County 

Housing TEOM PCAQCD 04-021-3011-81102-3 164 2964 1600 RJ 

Cowtown TEOM PCAQCD 04-021-3013-81102-3 159 2659 1600 RJ 

Bapchule FRM GRIC 04-021-7004-81102-1 613 N/A N/A RJ 

Bapchule FRM GRIC 04-021-7004-81102-2 547 N/A N/A RJ 

Santa Cruz County 

Nogales Post Office BAM ADEQ 04-023-0004-81102-3 17 38 1200 

Yuma County 

Yuma Supersite TEOM ADEQ 04-027-8011-81102-3 25 159 2000 

TEOM: Tapered Element Oscillating Microbalance monitor 

FRM: Federal Reference Method 

WMAT: White Mountain Apache Tribe of Fort Apache Reservation, AZ 

SRP-MIC: Salt River Pima-Maricopa Indian Community of Salt River Reservation, AZ 

PCDEQ: Pima County Department of Environmental Quality 

PCAQCD: Pinal County Air Quality Control District 

GRIC: Gila River Indian Community 

RJ: qualifier flag for high winds 

1

 PM10 data for 1600 and 1700 on September 6, 2012, were not available. 
Exceptional Event, Phoenix, September 6, 2012 Causal Relationship

3. Causal Relationship 

3.1 Discussion 

Meteorological and air quality observations indicate that dust carried by thunderstorm 

outflow was directly responsible for the high PM10 concentrations observed in the Phoenix area 

on September 6, 2012. On the afternoon of September 6, a large area of thunderstorms 

developed over south-central Arizona, south of the Phoenix area (Figure 3-1). As these 

thunderstorms drifted north, they generated a dust-carrying outflow boundary that propagated 

northward into the Phoenix area. As stated in Section 2.2, thunderstorms associated with the 

summer monsoon season can generate strong winds and blowing dust across Arizona. The 

likely source region for PM10 during the September 6, 2012, event was the deserts south of 

Phoenix and largely outside the Phoenix PM10 nonattainment area. This region mainly consists 

of natural, undisturbed desert. In addition, the two weeks leading up to the event were dry in 

the Phoenix area, with the last measureable rainfall at KPHX occurring on August 23. This 

combination of geography and lack of rainfall preceding the event resulted in a large fetch of 

soils that were particularly vulnerable to particulate suspension. 

Figure 3-1. Infrared satellite image from 1615 LST on September 6, 2012 (GOES-West). 

Colder temperatures (blues, purples, and white) indicate tall, convective (thunderstorm) 

clouds. Thunderstorms over south-central Arizona generated outflow boundaries that 

carried dust northward into Arizona. 

1 
Exceptional Event, Phoenix, September 6, 2012 Causal Relationship

The effects of the thunderstorm outflow and associated windblown dust were evident at 

most Pinal County monitors between 1600 and 1700 LST on September 6, with PM10

concentrations exceeding 2,500 μg/m3

 at two monitors (Figure 3-2). The thunderstorm outflow 

and associated dust continued northward and arrived in the Phoenix area between 1700 and 

1800 LST on September 6, with visibility reduced to near zero at KCHD (Figure 3-3). PM10

concentrations at the West Chandler monitor increased sharply over this time period, with 1-hr 

PM10 concentrations exceeding 3,000 μg/m3

 (Figure 3-4). Collocated wind observations at 

West Chandler showed wind gusts in excess of 30 mph coincident with the high PM10

concentrations. Several other monitors in the Phoenix area reported gusty winds at the same 

time as the high PM10 concentrations, including a wind gust of 40 mph at KCHD (Appendix A). 

Visibility cameras in the Phoenix area also clearly showed a reduction in visibility and blowing 

dust as the outflow arrived (Figure 3-5). Links to these videos and other media coverage and 

images pertaining to this windblown dust event are shown in Appendix B. It is also important to 

note that before the abrupt increase in PM10 in the Phoenix area, winds were lighter, visibilities 

were greater, and PM10 concentrations were much lower, illustrating the correlation between the 

high winds and the dust. In response to the approaching thunderstorm outflow and associated 

dust and low visibilities, the NWS office in Phoenix issued a Blowing Dust Advisory and Dust 

Storm Warning for portions of western Pinal and Maricopa Counties (Appendix C). The Blowing 

Dust Advisory and Dust Storm Warning specifically mentioned the Chandler area, which is 

where the West Chandler monitor is located. 

Figure 3-2. Hourly PM10 concentrations at Pinal County monitors on September 6, 2012. 

PM10 concentrations sharply increased between 1500 and 1700 LST, indicating the 

arrival of windblown dust. 

2 
Exceptional Event, Phoenix, September 6, 2012 Causal Relationship

Figure 3-3. Hourly PM10 concentrations at Maricopa County monitors and visibility at 

KCHD on September 6, 2012. Visibility was greatly reduced at 1700 and 1800 LST on 

September 6, 2012, coinciding with the sharp increase in PM10 concentrations at 

Maricopa County monitors, indicating the arrival of windblown dust. 

Figure 3-4. Hourly PM10 concentrations and wind speeds at the West Chandler monitor 

on September 6 and 7, 2012. PM10 concentrations and wind speeds sharply increased 

at 1700 LST on September 6, 2012, indicating the arrival of windblown dust. 

3 
Exceptional Event, Phoenix, September 6, 2012 Causal Relationship

Figure 3-5. Image from an ADEQ visibility camera on North Mountain looking south 

toward downtown Phoenix and the South Mountains. Windblown dust associated with 

thunderstorm outflow reduced visibility throughout the Phoenix area, obscuring the 

downtown skyline and South Mountains. 

The progression of the thunderstorm outflow and windblown dust through the Phoenix 

area is summarized by the radar velocity and wind vector spatial plots below (Figures 3-6 

through 3-9). 

1530-1600 LST (Figure 3-6) 

Observations at area monitors generally showed light winds with a westerly component, 

high visibilities, and low PM10 concentrations across Maricopa County. At this time, 

thunderstorm outflow was just beginning to impact monitors in western Pinal County, but the 

outflow boundary itself was not yet detected on Doppler radar. 

1630-1700 LST (Figure 3-7) 

Between 1630 and 1700 LST, the outflow boundary was detectable on Doppler radar 

over northwestern Pinal County and far southern Maricopa County and was just south of the 

West Chandler monitor. Note that the outflow boundary exhibited a bowed structure, with a 

4 
Exceptional Event, Phoenix, September 6, 2012 Causal Relationship

5 

bulge northward aimed at the West Chandler monitor. In quasi-linear thunderstorm boundaries, 

bowing structures, and especially the apex of a bowing structure, are often locations of stronger 

wind speeds. Thus, the structure and motion of the outflow boundary on September 6, 2012, 

was particularly favorable for the development of strong winds specifically in the vicinity of the 

West Chandler monitor. Monitors in western Pinal County were already impacted by the outflow 

boundary and windblown dust, reporting PM10 concentrations above 2,500 μg/m3

, gusty 

southwesterly winds, and decreased visibilities. Monitors across Maricopa County had not yet 

been affected by the outflow, and thus continued to report low PM10 concentrations, generally 

light winds, and high visibilities. 

1730-1800 LST (Figure 3-8) 

The outflow boundary continued moving northward into Maricopa County, affecting 

several monitors in the Phoenix metropolitan area, but most strongly impacting the east and 

southeast side of the Phoenix area. Conditions near and south of the outflow boundary were 

characterized by gusty south-southwesterly winds, visibilities as low as 0.25 miles, and high 

PM10 concentrations. Although only the West Chandler monitor in Maricopa County recorded 

an exceedance of the NAAQS, several other monitors reported 5-minute PM10 concentrations in 

excess of 2,500 μg/m3

. PM10 concentrations and wind speeds decreased at Pinal County 

monitors as the outflow boundary moved northward out of Pinal County. 

The West Chandler monitor likely recorded the highest PM10 concentrations because of 

its location on the southeastern side of the Phoenix urban area, closer to the undeveloped lands 

of western Pinal County where much of the dust and PM10 likely originated. And, as mentioned 

above, the bowed structure of the outflow boundary favored locally stronger winds in the vicinity 

of the West Chandler monitor. Also of note were very high 24-hour average PM10

concentrations at the filter-based monitor operated by the Gila River Indian Community (see 

Table 2-1), which is in northern Pinal County very near the West Chandler monitor. Thus, the 

West Chandler monitor was likely subject to greater quantities of transported PM10 compared to 

other monitors in the nonattainment area. 

1830-1900 LST (Figure 3-9) 

As the outflow boundary continued northward, PM10 concentrations decreased at most 

Maricopa and Pinal county monitors, including at West Chandler. Winds remained gusty across 

Maricopa County but shifted to westerly, which was no longer conducive to transport of dust and 

PM10 from the south. Finally, visibilities quickly returned to at or above 10 miles as the outflow 

boundary departed to the north of the Phoenix area. 

3.2 Summary 

The information presented in this section demonstrates a clear causal relationship 

between the windblown dust and the PM10 exceedance measured in the Phoenix PM10

nonattainment area on September 6, 2012. The wind, visibility, PM10, and radar data shown in 

this section illustrate the spatial and temporal extent of the dust storm as it moved through 

Maricopa County. 
Exceptional Event, Phoenix, September 6, 2012 Causal Relationship 

6 

In addition, meteorological data tables found in Appendix A show that the sharp increase 

in PM10 concentrations coincided with the gusty winds, low visibilities, and airport observer 

reports of blowing dust. The fact that PM10 concentrations in Pinal County spiked prior to PM10

concentrations increasing in Maricopa County illustrate that a vast majority of the dust that 

impacted the nonattainment area monitors originated outside of Maricopa County and was 

transported into the Phoenix PM10 nonattainment area. While PM10 concentrations were high 

regionally during the event, the West Chandler monitor was the closest Maricopa County 

monitor to the open and desert areas of western Pinal County, resulting in an exceedance at the 

West Chandler monitor. The proximity of the West Chandler monitor to open and desert areas 

of Pinal County provides solid evidence as to why this was the only monitor within the Maricopa 

County nonattainment area that recorded an exceedance.
Radar Site

7 

Figure 3-6. Maximum 5-minute PM10 concentrations (colored circles), 5-minute wind speed and direction (vectors

wind gusts (red numbers), and minimum visibility observations (white numbers) at Maricopa and Pinal county mon1530 and 1600 LST on September 6, 2012. Where 5-minute data are unavailable (e.g., PM10 data in Pinal County

are used. Underlying colors are Doppler radar velocity data at 1534 LST, where greens indicate motion toward the oranges/reds indicate motion away from the radar. 
Radar Site

8 

Figure 3-7. Similar to Figure 3-6, but representing observations from 1630 to 1700 LST. Doppler radar data are fr
Outflow

boundary

Radar Site

9 

Figure 3-8. Similar to Figure 3-6, but representing observations from 1730 to 1800 LST. Doppler radar data are fr
10 

Radar Site

Figure 3-9. Similar to Figure 3-6, but representing observations from 1830 to 1900 LST. Doppler radar data are fr
Exceptional Event, Phoenix, September 6, 2012 Historical Norm 

4. Historical Norm 

4.1 Analysis 

PM10 concentrations measured at Phoenix-area monitors on September 6, 2012, were 

unusual and in excess of normal historical fluctuations. To establish the severity of this event, 

PM10 concentrations measured on September 6, 2012, were compared to a historical 2007 to 

2012 annual data set at the West Chandler monitor. The PM10 concentrations measured at the 

West Chandler monitor on September 6, 2012, resulted in some of the highest 24-hr averages 

(Figure 4-1) and daily maximum hourly averages (Figure 4-2) measured over the 5-year period. 

0

50

100

150

200

250

300

350

400

450

500

PM10 Concentration (μg/m3)

Date

West Chandler 5-Year Historical Fluctuation - 24 Hour Averages

September 6, 2012

Figure 4-1. 24-hr average PM10 concentrations at the West Chandler monitor (2007–

2012). The 24-hr average PM10 concentration on September 6, 2012, is shown in red 

and highlighted by the arrow. 

1 
Exceptional Event, Phoenix, September 6, 2012 Historical Norm 

2 

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

PM10 Concentration (μg/m3)

Date

West Chandler 5-Year Historical Fluctuation - Daily Maximum Hourly Averages

September 6, 2012

Figure 4-2. Daily maximum hourly average PM10 concentrations at the West Chandler 

monitor (2007–2012). The daily maximum hourly average PM10 concentration on 

September 6, 2012, is indicated by the arrow. 

4.2 Summary 

Given the recorded values and using a methodology similar to the one accepted by EPA, 

it is clear that the PM10 levels on September 6, 2012, were outside normal historical 

fluctuations. This analysis provides evidence that the event affected air quality on a historic 

scale. 
Exceptional Event, Phoenix, September 6, 2012 Not Reasonably Controllable or Preventable

1 

5. Not Reasonably Controllable or Preventable 

5.1 Background 

ADEQ and MCAQD are responsible for implementing regulatory measures to control 

emissions from agricultural sources, stationary sources, fugitive dust sources, and open burning 

within Maricopa County. Three major programs provide or contribute to air pollution control 

measures for the Greater Phoenix area. These programs include 

1. ADEQ’s Agricultural Best Management Program (Ag BMP) 

2. Maricopa County’s Inspection and Compliance Program 

3. ADEQ’s Air Quality Forecasting Program 

Specifically, ADEQ is responsible for compliance assistance and enforcement of 

Agricultural Best Management Practices developed by the Governor’s Agricultural Best 

Management Practices Committee, while MCAQD is responsible for compliance assurance for 

all other significant sources of PM10 emissions. In addition to routine inspections and 

inspections driven by complaints, inspections are often increased when (1) ADEQ forecasters 

issue a Maricopa County Dust Control Forecast of “High Risk,” (2) ADEQ forecasters issue a 

High Pollution Advisory, or (3) near-real-time monitoring data indicate unique activity via high 

PM concentrations. The forecasting program and inspection/compliance programs work 

together so that resources can be best utilized during days of greatest risk for elevated PM 

emissions. 

On July 25, 2002, EPA took initial action to finalize approval of the Best Available 

Control Measure (BACM) and the Most Stringent Measure (MSM) demonstrations in the Serious 

Area PM10 plan for the Maricopa County portion of the metropolitan Phoenix PM10

nonattainment area (67 FR 48718). These BACM and MSM demonstrations were again 

approved by EPA on July 14, 2006 (71 FR 43979). The Agricultural Best Management 

Practices General Permit rule and related definitions have been adopted into the Arizona 

Administrative Code as R18-2-610 and R18-2-611, pursuant to Arizona Revised Statutes 

§49-4571

 Updates to the Ag BMP program in December 2011 clarified BMPs. 

5.1.1 Control Measures 

Maricopa County regulations of PM10 emissions are listed in Table 5-1. 

 

1

 Updates to the Ag BMP program in December 2011 clarified BMPs for crops and added BMPs for animal 

operations. Effective 12/29/2011, R18-2-611 was renumbered to R18-2-610.01 Agricultural PM10 General Permit 

for Crop Operations and R18-2-611.01 Animal Operations PM10 General Permit was added. Definitions for Crop 

Operations were revised at R18-2-610 and new definitions for Animal Operations were added at R18-2-611. 
Exceptional Event, Phoenix, September 6, 2012 Not Reasonably Controllable or Preventable

2 

Table 5-1. Rules and ordinances regulating PM emissions in Maricopa County. 

Rule/Ordinance Number & Title Description 

Rule 300: Visible emissions Establishes standards for visible emissions and opacity. 

Rule 310: Fugitive dust from dustgenerating operations 

Establishes limits for the emissions of particulate matter into the 

ambient air from any property, operations, or activity that may serve as 

a fugitive dust source. 

Rule 310.01: Fugitive dust from nontraditional sources of fugitive dust 

Establishes limits for the emissions of particulate matter into the 

ambient air from open areas, vacant lots, unpaved parking lots, and 

unpaved roadways which are not regulated by Rule 310 and which are 

not required to have either a permit or a dust control plan. 

Rule 311: Particulate matter from 

process industries 

Establishes emission rates based on process weight applicable to any 

affected operations not subject to Rule 316. 

Rule 312: Abrasive blasting Establishes limits for particulate emissions from abrasive blasting 

operations. 

Rule 314: Open outdoor fires and 

indoor fireplaces at commercial and 

institutional establishments 

Establishes limits for the emissions of air contaminants produced from 

open burning. 

Rule 316: Nonmetallic mineral 

processing 

Establishes limits for the emissions of particulate matter into the 

ambient air from any nonmetallic mining operation or rock product 

processing plant. 

Rule 317: Hospital/medical/infectious 

waste incinerators 

Establishes limits for the emissions of air pollutants from medical 

waste incinerators. 

Rule 322: Power plant operations 

Establishes limits for the emissions of nitrogen oxides, sulfur oxides, 

carbon monoxide, and particulate matter from existing power plants 

and cogeneration plants. 

Rule 323: Fuel burning equipment 

from industrial/commercial/ 

institutional (ICI) sources 

Establishes limits for the emissions of nitrogen oxides, sulfur oxides, 

carbon monoxide and particulate matter from ICI sources. 

Rule 324: Stationary internal 

combustion (IC) engines 

Establishes limits for the emissions of carbon monoxide, nitrogen 

oxides, sulfur oxides, volatile organic compounds, and particulate 

matter from stationary internal combustion engines, including 

stationary IC engines used in cogeneration. 

Rule 325: Brick and structural clay 

products (BSCP) manufacturing 

Establishes limits for particulate matter emissions from the use of 

tunnel kilns for curing in the BSCP manufacturing processes. 

Ordinance P-25: Leaf blower 

restriction 

Establishes restrictions for leaf blowers in incorporated and 

unincorporated sections of Area A in Maricopa County. 

Ordinance P-26: Residential wood 

burning restriction Establishes restrictions for residential wood burning. 

Ordinance P-27: Vehicle parking 

and use on unstabilized vacant lots 

Establishes restrictions for vehicle parking and use on unstabilized 

vacant lots in unincorporated sections of Area A in Maricopa County. 

Ordinance P-28: Off-road vehicle 

use in unincorporated areas of 

Maricopa County 

Establishes restrictions for operating vehicles on unpaved property in 

unincorporated areas of Maricopa County. 
Exceptional Event, Phoenix, September 6, 2012 Not Reasonably Controllable or Preventable

3 

Rule/Ordinance Number & Title Description 

Arizona Administrative Code R18-

2-611 & 610: Agricultural PM10

general permit 

Establishes a requirement for commercial farmers to implement best 

management practices and maintain a record demonstrating 

compliance. 

5.1.2 Additional Measures 

In addition to the rules and regulations listed in Table 5-1, other PM10-reducing control 

measures (e.g., paving unpaved roads, PM10-certified street sweepers, controlling unpaved 

parking lots, etc.) have been committed to and implemented by local jurisdictions throughout the 

PM10 nonattainment area and incorporated into the Arizona state implementation plan (SIP) 

through PM10 plans such as the Revised Maricopa Association of Governments’ (MAG) 1999 

Serious Area Particulate Plan for PM10 for the Maricopa County Nonattainment Area. The Pinal 

County Air Quality Control District (PCAQCD) also implements regulatory control measures on 

emissions from existing and new non-point sources within Pinal County (see Table 5-2). 

Additionally, the PCAQCD implements specific nonattainment rules for that part of the Phoenix 

PM10 nonattainment area that resides in Pinal County (see Table 5-3). 

Table 5-2. Pinal County rules regulating existing and new non-point sources in Pinal County. 

Article Number & Title Description 

Article 2: Fugitive dust Provides a mechanism to reasonably regulate operations which 

periodically may cause fugitive dust emissions into the atmosphere. 

Article 3: Construction sites – 

fugitive dust 

Improves the control of excessive fugitive dust emissions that have 

been traditionally associated with construction, earthwork, and land 

development, and thereby minimize nuisance impacts. 

Table 5-3. Pinal County rules regulating fugitive dust in Pinal County portion of the 

Phoenix PM10 Nonattainment Area. 

Article Number & Title Description 

Article 4: Nonattainment area rules; 

dustproofing for commercial parking, 

drives, and yards 

Establishes rules to avoid violations of the prevailing PM10 standard 

and additionally minimize nuisance impacts by improving control of 

excessive fugitive dust emissions from unpaved parking lots. 

Article 5: Nonattainment area rules; 

stabilization for residential parking 

and drives 

Establishes rules for stabilizing residential properties. 

Article 6: Restrictions on vehicle 

parking and use on vacant lots Establishes rules for unpaved or unstable vacant lots. 

Article 7: Construction sites in 

nonattainment areas – fugitive dust 

Establishes rules to avoid violations of the prevailing PM10 standard 

and additionally minimize nuisance impacts by improving control of 

excessive fugitive dust emissions from activities associated with 

construction, earthwork, or land development. 
Exceptional Event, Phoenix, September 6, 2012 Not Reasonably Controllable or Preventable

4 

Article Number & Title Description 

Article 8: Nonattainment area rules, 

requirement for stabilization of 

disturbed areas at vacant lots 

Establishes rules for stabilizing disturbed areas at vacant lots. 

5.1.3 PM10 Rule Effectiveness 

MCAQD analyzed the effectiveness of its fugitive dust rules (Rules 310, 310.01, and 

316) in terms of permit compliance rates. This rule effectiveness (RE) study was designed to 

assess how many sources regulated by MCAQD during the subject time period received no 

PM10 emissions-related violations. As a basis for comparison, the percentage of permitted 

sources in compliance during calendar year 2007 was 76% for sources subject to Rule 310, 

85% for Rule 310.01 sources, and 40% for Rule 316 sources. In early 2008, Rules 310, 310.01, 

and 316 were strengthened, and new ordinances (covering additional source categories such as 

leaf blowers, vacant lots, and off-road vehicles) were adopted. These enhancements resulted 

from MCAQD’s obligations under such agreements as the 2005 Revised PM10 State 

Implementation Plan for the Salt River Area and the Maricopa Association of Governments 2007 

Five Percent Plan for PM10 for the Maricopa County Nonattainment Area to reduce PM10

emissions throughout the county. Three major areas that contributed to increased compliance 

were an increase in departmental staffing (especially inspectors), a robust training program, and 

regulatory changes that broadened and strengthened control measures under Rules 310, 

310.01, and 316. 

Source compliance rates were re-assessed for FY 2009 (July 2008–June 2009), a 

period that allowed time for the new and revised regulations to take effect. The results showed 

significant increases in compliance compared with the earlier period: to 90% (from 76%) for 

Rule 310 sources, 95% compliance (from 85%) for Rule 310.01 sources, and 65% (from 40%) 

for Rule 316 sources. These improvements continued into calendar year 2010 with compliance 

rates of 94% for Rule 310 sources, 96% for Rule 310.01 sources, and 73% for Rule 316 

sources. The timeline below (Figure 5-1) illustrates the improvements in RE over the last 

several years; it also points out significant revisions to previous rules, as well as newly adopted 

rules and ordinances. 
Exceptional Event, Phoenix, September 6, 2012 Not Reasonably Controllable or Preventable

5 

March 2008

September 2006

Figure 5-1. Timeline of Maricopa County fugitive dust rules and ordinances. 

5.1.4 Compliance and Enforcement Activities 

MCAQD is prepared to proactively respond to high wind events and protect human 

health and well-being. MCAQD’s approach consists of two primary components: proactive 

inspections conducted routinely, as well as surveillance inspections conducted during and after 

significant air quality events. MCAQD routinely inspects dust control-permitted sites and 

increases the frequency of inspections for permits covering areas of 10 acres or more. Rule 

316 sources are also regularly inspected multiple times every year. Maricopa County responds 

to the majority of complaints within 24 hours. 

Maricopa County monitors the ADEQ Five-Day Dust Control Forecast to identify the 

potential for elevated PM10 pollution levels due to high winds or stagnant conditions. When a 

High Pollution Advisory (HPA) is issued for Maricopa County, MCAQD conducts increased 

surveillance before, during, and after the forecast event(s). MCAQD also conducts event 

surveillance and post-event activities during exceedance days that had not been forecast (i.e., 

those instances in which an HPA had not been issued). 

Pre-event surveillance consists of surveying high-risk areas for any dust-generating 

activities, educating sources of the impending HPA event, and issuing violations for failure to 

comply with local, state, or federal regulations. During the event, MCAQD inspectors survey 

high-risk areas to confirm that control measures are in place, document any violations, and 

contact other regulatory agencies if necessary. Post-event activities include continued surveys 

of high-risk areas, re-inspecting sources that had incurred violations within two business days, 

and an internal MCAQD debriefing of event activities. 

During 2011 and 2012, a total of 17 MCAQD air monitoring sites were upgraded with 

new equipment that allows the monitoring sites to automatically report measured readings at 

5-minute intervals. Previously, only hourly readings were available. The real-time data 

reporting system includes a mechanism to alert MCAQD field staff when PM concentrations are 

elevated. The system allows MCAQD responders to review concentrations at the monitors and 
Exceptional Event, Phoenix, September 6, 2012 Not Reasonably Controllable or Preventable

6 

to consult the National Weather Service website to check for weather event activity. This 

capability allows the MCAQD responder to identify regional events and monitor specific issues. 

If necessary, the MCAQD responders can inform nearby stakeholders and local governments of 

the elevated PM10 concentrations. 

5.1.5 Review of Source-Permitted Inspections and Public Complaints 

ADEQ’s Arizona Unified Repository for Information Tracking of the Environment 

(AZURITE) database was queried to compile a list of inspections for the permitted sources in 

the Maricopa area around the time of the September 6, 2012, PM10 exceedances. An 

evaluation of all inspection reports, air quality complaints, compliance reports, and other 

documentation did not indicate any evidence of unusual anthropogenic-based PM10 emissions. 

During the period of September 3 through 9, 2012, MCAQD inspectors conducted a total of 144 

inspections of permitted facilities, of which 102 were at fugitive dust sources. Additionally, 

MCAQD conducted 69 inspections on vacant lots and unpaved parking lots. During this 7-day 

period, a total of 24 citations for violations were issued countywide for PM10 and non-PM10

related violations. One violation was issued for PM10 emissions within a 4-mile radius of an 

exceeding monitor (West Chandler). 

On September 4, 2012, a violation was issued to an earthmoving operation of 0.15 acres 

for not obtaining a dust control permit. A dust control permit was issued to this site on 

September 19, 2012. No unstable area was discovered during the inspection on September 4, 

2012, or the subsequent inspections performed on September 10, 2012, and October 15, 2012. 

The site was located approximately 3.4 miles west of the West Chandler monitor. Since winds 

during the thunderstorm outflow and high PM10 event were from the south, it is highly unlikely 

that this violation impacted PM10 concentrations at the West Chandler monitor on September 6, 

2012. 

MCAQD was prepared for any complaints received due to the high wind event. During 

the 7 day period from September 3, 2012 through September 9, 2012, MCAQD received 18 

complaints, of which 11 were windblown dust-related. Each complaint was assigned to and 

investigated by a MCAQD inspector. A review of all pertinent records from this period indicates 

that MCAQD inspectors observed no PM10 violations of local, state, or federal regulations within 

a 4-mile radius of the exceeding monitor. 

In addition to MCAQD’s efforts in pre-event surveillance and proactive inspections, 

ADEQ’s Ag BMP inspector also monitors the ADEQ Five-Day Dust Control Forecast and the 

MCAQD air monitoring sites that include real-time data. The ADEQ Ag BMP inspector uses 

specific knowledge of seasonal activities and associations with the local growers and dairymen 

to communicate the importance of limiting dust-generating activities, especially during high wind 

events. Additional outreach is conducted with facility representatives prior to forecast high wind 

alert days. Should the PM10 readings at a MCAQD air monitoring site show a notable increase, 

the ADEQ Ag BMP inspector is dispatched to contact the owners and operators of agricultural 

fields in the area to discern whether their activities are causing negative impacts. The Ag BMP 

inspector is prepared to respond to most agriculture complaints within 24 hours. 
Exceptional Event, Phoenix, September 6, 2012 Not Reasonably Controllable or Preventable

7 

Based on a review of the inspection reports and site visit documentation, there is no 

evidence to suggest that agricultural activities produced unusual PM10 emissions. On 

September 6, 2012, the ADEQ Ag BMP inspector received one complaint and conducted 

outreach in response to a dust complaint at an agricultural composting location in the area of 

Lindsey Road and Ocotillo Road. 

5.2 Forecasts and Warnings 

Dust forecasts and statements were released prior to the event by both ADEQ and the 

NWS office in Phoenix (Appendix C). On September 5, 2012, a Maricopa County Dust Control 

Forecast for September 6, 2012, was issued by ADEQ, indicating a moderate risk level for 

unhealthy PM10. The Dust Control Forecast also indicated a potential for gusty winds near 

thunderstorm outflow. 

The NWS office in Phoenix issued several Blowing Dust Advisories, Dust Storm 

Warnings, and Severe Thunderstorm Warnings between 1600 and 1800 LST for portions of 

Pinal and Maricopa counties, coincident with the period of gusty outflow winds and high PM10

concentrations in the Phoenix area. These advisories warned residents of the potential for 

gusty winds to 40 mph and visibilities reduced below 1⁄4 mile due to blowing dust generated by 

thunderstorm outflow moving northward from Pinal County into Maricopa County. 

5.3 Wind Observations 

Wind data during the event (Figure 3-2 and Appendix A) showed widespread wind gusts 

of over 30 mph coincident with the high PM10 concentrations, including a wind gust of 40 mph at 

KCHD (near the West Chandler PM10 monitor). 

5.4 Summary 

The thunderstorm outflow event of September 6, 2012, produced strong winds that 

transported dust and PM10 into the Phoenix PM10 nonattainment area. The source region of the 

outflows that caused the exceedances was largely located in areas outside the Phoenix PM10

nonattainment area, primarily the deserts south of Maricopa County. The Phoenix area is 

designated as a serious nonattainment area for PM10 and is required to have BACM for all 

significant sources of PM10. BACM on significant anthropogenic sources were in place and 

enforced during the events, and pro-active tracking and response to the events by regulatory 

agencies and local governments confirmed the uncontrollable nature of the dust emissions; 

therefore, these pre-existing prior-approved required controls are adequate for meeting the 

requirements of an exceptional event and should be considered “reasonable” for these 

purposes. 

Despite the deployment of comprehensive control measures and sophisticated response 

programs, high wind conditions associated with the thunderstorm outflow transported high 

concentrations of PM10 into, and also overwhelmed controls within, the Phoenix PM10

nonattainment area. Widespread wind gusts over 30 mph were strong enough to overwhelm 

available efforts to limit PM10 concentrations during the event. The fact that these were natural 
Exceptional Event, Phoenix, September 6, 2012 Not Reasonably Controllable or Preventable 

8 

events involving strong winds that transported PM10 emissions into and across Maricopa 

County, with a majority of the PM10 emissions recorded by Maricopa County area monitors 

coming from sources outside of the Phoenix PM10 nonattainment area, provides strong 

evidence that the exceedance of September 6, 2012, recorded within the Phoenix PM10

nonattainment area was not reasonably controllable or preventable. 

Exceptional Event, Phoenix, September 6, 2012 But-For Analysis

1 

6. But-For Analysis 

6.1 Discussion 

Section 50.14(c)(3)(iv)(D) in 40 CFR Part 50 requires that an exceptional event 

demonstration satisfy the condition that “[t]here would have been no exceedance or violation but 

for the event.” The prior sections of this submittal have provided detailed information that, in 

regard to the PM10 exceedance at the West Chandler monitor on September 6, 2012, 

 the exceedance was not reasonably controllable or preventable, and 

 there was a clear causal relationship between PM10 transported strong winds originating 

in desert areas outside the Phoenix PM10 nonattainment area and the measured PM10

exceedance at the West Chandler monitor. 

The weight of evidence in these sections demonstrates that, but for the existence of dust 

emissions generated by strong winds and the associated transport of PM10, there would have 

been no exceedance of the NAAQS for 24-hr average PM10. 

As shown in Section 3, maps and time-series plots of PM10 and wind speeds establish a 

clear causal relationship between windblown dust due to thunderstorm outflow and elevated 

PM10 concentrations at Phoenix-area monitors. Multiple independent measurements of wind 

speed, wind direction, and visibility point to the presence of gusty winds generated by 

thunderstorm outflow as the mechanism for transport of PM10 into the Phoenix nonattainment 

area. In addition, PM10 concentrations were well below the NAAQS on days immediately before 

and after the windblown dust event. The source region for the PM10 is clearly identified as 

desert areas south of the Phoenix PM10 nonattainment area. The weight of evidence presented 

in this submittal provides no alternative that could tie the exceedance of September 6, 2012, to 

any causal source except PM10 transported by strong winds, confirming that there would have 

been no exceedance but for the presence of this uncontrollable natural event. 

As detailed in Section 5, all reasonable control measures were in place and/or 

implemented on a continual basis. Air quality-related inspection and compliance data revealed 

one violation with 4 miles of the exceedance monitor; however, the meteorological conditions on 

September 6, 2012, indicate that the source of this violation does not explain and could not 

have resulted in the very high PM10 concentrations observed. Local regulatory agencies, 

industry, and the general public were alerted to the possibility of dust storms due to strong 

winds via daily forecasts and media reports. 

6.2 Summary 

The weight of evidence presented in this submittal provides no alternative that could tie 

the exceedance of September 6, 2012, to any causal source other than PM10 transported by 

gusty winds due to thunderstorm outflow, confirming that there would have been no exceedance 

but for the presence of this uncontrollable natural event. 

Exceptional Event, Phoenix, September 6, 2012 Conclusions

1

7. Conclusions 

The PM10 exceedance that occurred on September 6, 2012, satisfy the criteria of the 

EER, which states that in order to justify the exclusion of air quality monitoring data, evidence 

must be provided for the following elements: 

 The event satisfies the criteria set forth in 40 CFR 50.1 (j) that 

a. the event affected air quality, 

b. the event was not reasonably controllable or preventable, and 

c. the event was caused by human activity unlikely to recur in a particular location or 

was a natural event; 

 There is a clear causal relationship between the measurement(s) under consideration 

and the event; 

 The event is associated with a measured concentration(s) in excess of normal historical 

fluctuations; and 

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

7.1 Affects Air Quality 

As stated in the preamble to the EER, the event in question is considered to have 

affected air quality if it can be shown that there is a clear causal relationship between the 

monitored exceedance and the event, and that the event is associated with a measured 

concentration in excess of normal historical fluctuations. Given the information presented in 

Sections 2, 3, 4, and 5, we can reasonably conclude that the event in question affected air 

quality. 

7.2 Not Reasonably Controllable or Preventable 

Section 50.1(j) of 40 CFR Part 50 requires that an event must be “not reasonably 

controllable or preventable” in order to be defined as an exceptional event. This requirement is 

met by demonstrating that despite reasonable control measures in place within Maricopa 

County, high winds overwhelmed all reasonably available controls (Section 5). The PM10

exceedance discussed in this report was caused by naturally occurring gusty winds associated 

with thunderstorm outflow that transported dust into the Phoenix area from areas largely outside 

the Phoenix PM10 nonattainment area. These facts provide strong evidence that the PM10

exceedance on September 6, 2012, was not reasonably controllable or preventable. 

7.3 Natural Event 

As discussed above, the PM10 exceedance at the West Chandler monitor on September 

6, 2012, was shown to be caused by transport of PM10 into the Phoenix area from gusty winds 

associated with thunderstorm outflow. The event therefore qualifies as a natural event. 
Exceptional Event, Phoenix, September 6, 2012 Conclusions 

2

7.4 Clear Causal Relationship 

The following points demonstrate that the high PM10 concentrations were caused by 

windblown dust: 

 Time-series graphs of PM10 concentrations show that the timing of high PM10 at Phoenix 

area monitors was consistent with gusty winds and low visibilities at Phoenix-area 

meteorological stations (Section 3). 

 High PM10 concentrations and gusty winds were reported at several monitors throughout 

the Phoenix metropolitan area (Sections 3 and 5). 

 PM10 concentrations were well below the NAAQS on days immediately before and after 

the windblown dust event (Section 3). 

 Dry conditions preceding the event resulted in soils that were particularly susceptible to 

particulate suspension by high winds (Section 3). 

 Wind directions, thunderstorm-generated outflow boundary propagation, and 

concentration patterns showing elevated levels of PM10 in Pinal County prior to levels 

increasing in Maricopa County illustrate that a vast majority of the dust that impacted the 

nonattainment area monitors originated outside of Maricopa County and was transported 

to the nonattainment area. The particular wind magnitudes and wind direction, and the 

proximity of the exceeding monitor to open and desert areas of Pinal County, provide 

solid evidence as to why only one monitor within the Maricopa County nonattainment 

area recorded an exceedance (Section 3). 

 Visibility cameras clearly illustrate the arrival of dust and significant reductions in visibility 

in the Phoenix area coinciding with the sharp increases in PM10 concentrations. 

7.5 Historical Norm 

The 24-hr average PM10 values measured at Phoenix area monitors were historically 

unusual compared to a multi-year data set (Section 4). 

7.6 But For 

On the basis of the weight of evidence described above and in Section 6, the 

exceedance of the federal 24-hr PM10 standard on September 6, 2012, in the Phoenix PM10

nonattainment area would not have occurred but for the high winds and transport of dust from 

areas largely outside the Phoenix PM10 nonattainment area. 
Exceptional Event, Phoenix, September 6, 2012 Appendix A 

Appendix A: 

Air Quality and Meteorological Data for Maricopa County 

This section contains tables of meteorological data from National Weather Service sites 

in the Phoenix area for September 6, 2012. Reduced visibilities, gusty winds, and blowing dust 

or dust storms were reported coincident with the arrival of thunderstorm outflow and high PM10

concentrations. 

1
2 

U.S. Department of Commerce National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL CLIMATOLOGICAL DATA 

(final) 

HOURLY OBSERVATIONS TABLE 

CHANDLER MUNICIPAL AIRPORT (53128) 

CHANDLER, AZ 

(09/2012) 

Elevation: 1243 ft. above sea level Latitude: 33.268 Longitude: -111.812 Data Version: VER2

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

Temp Date Time (LST) Station Type Sky Conditions Visibility (SM) Weather Type

(F) (C) (F) (C) (F) (C)

Rel

Humd

%

Wind 

Speed 

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hrChg

(mb)

P

(

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 

06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06

0547 0647 0749 0850 0947 1047 1147 1247 1350 1450 1547 1650 1727 1747 1850 1947 2047

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

FEW200 FEW200 FEW200 FEW250 FEW250 FEW060 FEW200 FEW060 FEW200 FEW070 SCT200 FEW070 SCT200 SCT070 BKN200 SCT070 BKN200 VV001 BKN070 BKN070 OVC200 SCT070 OVC200 BKN070 BKN200 BKN150

15.00 35.00 35.00 35.00 35.00 35.00 30.00 30.00 30.00 30.00 30.00 0.25s 1.00 4.00 15.00 15.00 15.00

BLDUs BLDU BLDU 

81818488909393979910099958686868484

27.027.029.031.032.034.034.036.037.038.037.035.030.030.030.029.029.0

7373747575767475757573747274747474

23.023.023.524.123.724.223.524.123.823.622.923.222.423.123.123.523.5

7070707068686666646361646668687070

21.021.021.021.020.020.019.019.018.017.016.018.019.020.020.021.021.0

69 69 63 55 48 44 41 36 32 30 29 36 51 55 55 63 63

7 3 3 5 6 3 5 9 9 11 9 23 23 23 17 6 17

040 110 030 VR VR 240 270 190 270 290 270 210 210 220 200 150 170

18 40 37 

28.56 28.59 28.60 28.61 28.62 28.61 28.59 28.56 28.53 28.48 28.49 28.51 28.53 28.52 28.54 28.56 28.61

M M M M M M M M M M M M M M M M M

Figure A-1. Quality-controlled local climatological data hourly observations table for Chandler Municipal Airport, Chandler, Ariz(09/06/2012). Note in the Weather Type column that BLDU (blowing dust) was reported. For a more detailed explanation of th

shown in the table above, please see http://www.nws.noaa.gov/oso/oso1/oso12/document/guide.shtml. Data dynamically gene

http://cdo.ncdc.noaa.gov/qclcd/QCLCD.
3 

U.S. Department of Commerce National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL CLIMATOLOGICAL DATA 

(final) 

HOURLY OBSERVATIONS TABLE 

GLENDALE MUNICIPAL AIRPORT (53126) 

GLENDALE, AZ 

(09/2012) 

Elevation: 1066 ft. above sea level Latitude: 33.527 Longitude: -112.295 Data Version: VER2

Dry 

Bulb 

Temp

Wet 

Bulb

Temp

Dew

Point

Temp Date Time (LST) Station Type Sky Conditions Visibility (SM) Weather Type

(F) (C) (F) (C) (F) (C)

Rel

Humd 

%

Wind 

Speed 

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb)

P

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 

06 06 06 06 06 06 06 06 06 06 06 06 06 06 06

0547 0647 0747 0847 0947 1047 1147 1247 1347 1447 1547 1647 1735 1747 1847

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

FEW120 FEW250 FEW250 FEW250 FEW250 FEW250 FEW100 FEW250 FEW100 FEW250 FEW100 SCT250 FEW080 SCT250 SCT080 BKN200 SCT080 BKN200 SCT080 SCT200 OVC250 SCT080 BKN200 OVC250 SCT080 BKN180 OVC250

20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00 3.00 4.00 10.00

BLDU BLDU

848488909091959799100102100979188

29.029.031.032.032.033.035.036.037.038.039.038.036.033.031.0

747373747575767776767675757575

23.522.822.823.123.723.924.524.724.424.524.223.924.123.924.1

706866666868686866666464666870

21.020.019.019.020.020.020.020.019.019.018.018.019.020.021.0

63 59 48 45 48 47 41 39 34 33 29 31 36 47 55

6 3 9 8 8 7 9 5 8 11 11 14 24 25 22

190170200210180200220140200190190190190180230

18 20 37 32 31

28.74 28.77 28.78 28.79 28.80 28.79 28.78 28.76 28.71 28.69 28.66 28.68 28.68 28.69 28.74

M M M M M M M M M M M M M M M

Figure A-2. Quality-controlled local climatological data hourly observations table for Glendale Municipal Airport, Glendale, Ariz

Note in the Weather Type column that BLDU (blowing dust) was reported. Dynamically generated via http://cdo.ncdc.noaa.gov
4 

U.S. Department of Commerce National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL CLIMATOLOGICAL DATA 

(final) 

HOURLY OBSERVATIONS TABLE 

PHOENIX GOODYEAR AIRPORT (03186) 

GOODYEAR, AZ 

(09/2012) 

Elevation: 968 ft. above sea level Latitude: 33.416 Longitude: -112.383 Data Version: VER2

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

Temp Date Time (LST) Station Type Sky Conditions Visibility (SM) Weather Type

(F) (C) (F) (C) (F) (C)

Rel 

Humd 

%

Wind 

Speed 

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hrChg

(mb)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 

06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06

0547 0647 0747 0847 0947 1047 1147 1247 1355 1455 1555 1647 1720 1755 1855 1947 2047

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

FEW150 FEW250 FEW250 FEW250 FEW250 SCT250 FEW050 FEW250 FEW050 FEW050 FEW070 SCT250 SCT070 SCT250 SCT070 SCT180 BKN250 SCT070 SCT180 BKN250 SCT070 SCT150 OVC200 SCT070 SCT150 OVC200 SCT070 BKN180 OVC250 SCT070 BKN180 OVC250 BKN070 BKN150 OVC200

10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 3.00 10.00 10.00 10.00 10.00

BLDU -RA

8282868891919595991001001009190888684

28.028.030.031.033.033.035.035.037.038.038.038.033.032.031.030.029.0

7474747475767776767676767576757576

23.223.223.123.423.924.525.124.524.424.524.524.523.924.424.123.824.5

7070686868707068666666666870707073

21.021.020.020.020.021.021.020.019.019.019.019.020.021.021.021.023.0

67 67 55 52 47 50 44 41 34 33 33 33 47 52 55 59 70

7 6 7 8 9 8 9 6 7 11 14 17 25 17 21 17 21

240 230 230 250 230 260 290 240 260 240 230 230 220 190 230 210 220

34 29 29 23

28.86 28.88 28.90 28.91 28.92 28.91 28.89 28.87 28.83 28.79 28.77 28.79 28.78 28.79 28.84 28.83 28.88

Figure A-3. Quality-controlled local climatological data hourly observations table for Phoenix Goodyear Airport, Goodyear, Ariz(09/06/2012). Note in the Weather Type column that BLDU (blowing dust) was reported. Dynamically generated via http://cdo.ncdc.noaa.gov/qclcd/QCLCD.
5 

U.S. Department of Commerce National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL CLIMATOLOGICAL DATA (final) 

HOURLY OBSERVATIONS TABLE 

LUKE AFB AIRPORT (23111) 

GLENDALE, AZ (09/2012) 

Elevation: 1085 ft. above sea level Latitude: 33.55 Longitude: -112.366 Data Version: VER2

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

Temp Date Time (LST) Station Type Sky Conditions Visibility (SM) Weather Type

(F) (C) (F) (C) (F) (C)

Rel

Humd 

%

Wind 

Speed 

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hrChg

(mb)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 

06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06

0055 0155 0255 0355 0455 0555 0655 0755 0831 0855 0955 1055 1155 1255 1355 1455 1555 1655 1729 1730 1742 1751 1755 1818 1855 1955 2055 2155 2255 2355

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR FEW090 FEW004 SCT090 FEW003 SCT090 FEW003 SCT090 FEW003 BKN080 FEW003CB SCT080CB SCT085CB CLR SCT170 FEW150 CLR FEW150 CLR

10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 5.00 4.00 5.00 3.00 6.00 6.00 10.00 10.00 10.00 10.00 10.00 10.00

HZ HZ HZ BLDU VCTS DU TS DU 

8786858584848487888991939596100101102100999793919188908685838383

30.430.029.729.429.028.728.730.731.031.532.733.834.935.837.538.439.037.937.036.034.033.032.931.032.029.929.328.528.428.3

767675757474737474757576777777767676777776767675757475757473

24.324.123.623.623.123.122.823.323.423.623.924.524.824.924.824.424.224.225.024.724.224.524.224.123.723.423.623.723.323.0

717170706969686868686869696967656465686868706970686970717069

21.421.621.321.020.820.419.920.020.019.820.220.520.520.419.318.117.618.620.020.020.021.020.721.020.220.720.921.521.120.8

59 61 61 61 61 61 59 53 52 50 47 46 43 42 34 31 29 32 37 39 44 50 49 55 48 57 61 67 65 63

17 14 13 10 9 9 5 11 11 10 10 6 5 6 13 14 13 21 31 31 24 25 25 26 17 20 21 14 11 7

210 200 200 190 200 200 200 200 200 220 170 VR VR VR 230 210 250 200 210 210 210 210 210 220 240 200 220 210 180 210

25 34 34 38 33 32 

28.68 28.69 28.69 28.70 28.71 28.71 28.74 28.75 28.75 28.76 28.76 28.76 28.74 28.71 28.68 28.64 28.63 28.63 28.64 28.64 28.64 28.65 28.66 28.69 28.70 28.70 28.74 28.74 28.75 28.75

3 3 3 0 8 5 0 1

002004017003028015020021

222222222222222222222M 22222222
6 

Figure A-4. Quality-controlled local climatological data hourly observations table for Luke Air Force Base Airport, Glendale, Ari(09/06/2012). Note in the Weather Type column that HZ (haze), BLDU (blowing dust), and DU (widespread dust) were reported

generated via http://cdo.ncdc.noaa.gov/qclcd/QCLCD.

U.S. Department of Commerce National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL CLIMATOLOGICAL DATA 

(final) 

HOURLY OBSERVATIONS TABLE 

FALCON FIELD AIRPORT (03185) 

MESA, AZ 

(09/2012) 

Elevation: 1380 ft. above sea level Latitude: 33.466 Longitude: -111.733 Data Version: VER2

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

Temp Date Time (LST) Station Type Sky Conditions Visibility (SM) Weather Type

(F) (C) (F) (C) (F) (C)

Rel

Humd 

%

Wind 

Speed 

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hrChg

(mb)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 

06 06 06 06 06 06 06 06 06 06 06 06 06

0548 0647 0755 0847 0947 1055 1147 1247 1448 1549 1647 1732 1750

0 0 0 0 0 0 0 0 0 0 0 0 0

FEW200 FEW200 FEW200 FEW200 FEW150 FEW200 FEW150TCU SCT200 FEW150TCU SCT200 FEW080 SCT160 FEW080TCU BKN200 SCT080TCU BKN200 FEW000s SCT080 BKN150

30.00 30.00 30.00 30.00 35.00 35.00 35.00 35.00 35.00 35.00 30.00 0.25s 2.00

BLDUs BLDU

828486888891919510099M 9386

28.029.030.031.031.033.033.035.038.037.0M 34.030.0

73737473737474757574M7272

22.522.823.122.822.823.223.223.823.923.5M 22.022.4

68686866666666666463616166

20.020.020.019.019.019.019.019.018.017.016.016.019.0

63 59 55 48 48 44 44 39 31 31 M 34 51

6 5 7 0 9 9 8 8 10 11 8 21 17

050 VR 050 000 300 300 230 270 250 250 230 190 220

25 25

28.41 28.44 28.45 28.46 28.46 28.45 28.44 28.41 28.34 28.34 28.34 28.35 28.37

M M M M M M M M M M M M M

Figure A-5. Quality-controlled local climatological data hourly observations table for Falcon Field Airport, Mesa, Arizona (09/06

the Weather Type column that BLDU (blowing dust) was reported. Dynamically generated via http://cdo.ncdc.noaa.gov/qclcd/Q
7 

U.S. Department of Commerce National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL CLIMATOLOGICAL DATA 

(may be updated) 

HOURLY OBSERVATIONS TABLE 

PHOENIX SKY HARBOR INTL AIRPORT (23183)

PHOENIX, AZ (09/2012) 

Elevation: 1107 ft. above sea level Latitude: 33.427 Longitude: -112.003 Data Version: VER2

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

Temp Date Time (LST) Station Type Sky Conditions Visibility (SM) Weather Type

(F) (C) (F) (C) (F) (C)

Rel 

Humd 

%

Wind 

Speed 

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hrChg

(mb)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 

06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06

0051 0151 0251 0351 0451 0551 0651 0751 0851 0951 1051 1151 1251 1351 1451 1551 1651 1733 1738 1747 1751 1757 1824 1851 1951 2051 2151 2251 2351

11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11

SCT250 SCT250 FEW250 FEW250 FEW250 FEW250 FEW250 FEW250 FEW250 FEW055 SCT250 FEW055 SCT250 FEW065 FEW075 SCT250 FEW075 SCT250 FEW075 SCT250 SCT070 BKN250 FEW070 SCT200 BKN250 FEW011 SCT080 BKN200 SCT014 SCT080 BKN200 BKN014 BKN080 OVC250 BKN014 BKN080 OVC250 BKN019 BKN080 OVC250 SCT025 SCT080 BKN200 SCT025 SCT080 BKN200 FEW080 BKN200 BKN250 FEW080 SCT200 BKN250 FEW055 SCT110 OVC160 FEW055 SCT110 OVC160 FEW110 OVC180

10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 1.75 0.75 1.50 2.00 4.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00

BLDU BLDU BLDU 

908988888786868790939396979910010199939393929391938888868585

32.231.731.131.130.630.030.030.632.233.933.935.636.137.237.838.337.234.034.034.033.334.033.033.931.131.130.029.429.4

7475747474737373747676757475757574737474747474757474757474

23.423.623.423.423.322.822.822.623.124.224.224.023.523.823.623.823.222.923.523.523.423.523.223.823.123.123.823.323.3

6768686868676766666868666464636362646666666666676767706969

19.420.020.020.020.019.419.418.918.920.020.018.917.817.817.217.216.718.019.019.018.919.019.019.419.419.421.120.620.6

47 50 52 52 53 53 53 50 45 44 44 37 34 32 30 29 30 38 41 41 42 41 44 43 50 50 59 59 59

9 6 8 6 6 6 6 0 3 7 5 6 10 10 5 11 15 18 16 14 16 24 13 16 16 5 8 9 6

270 290 300 300 280 260 230 000 VR 230 310 300 280 320 270 300 220 200 200 200 210 220 250 280 260 190 110 140 110

17 20 17 25 25 24 23 29 24 

28.66 28.68 28.68 28.68 28.69 28.69 28.72 28.73 28.74 28.74 28.73 28.71 28.69 28.66 28.62 28.62 28.63 28.63 28.63 28.63 28.63 28.63 28.64 28.66 28.68 28.73 28.73 28.73 28.73

3 2 3 0 8 5 3 0

005003017002026010017018
8 

Figure A-6. Quality-controlled local climatological data hourly observations table for Phoenix Sky Harbor International Airport, 

(09/06/2012). Note in the Weather Type column that BLDU (blowing dust) was reported. Dynamically generated via http://cdo.ncdc.noaa.gov/qclcd/QCLCD.

U.S. Department of Commerce National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL CLIMATOLOGICAL DATA 

(final) 

HOURLY OBSERVATIONS TABLE 

SCOTTSDALE AIRPORT (03192) 

SCOTTSDALE, AZ (09/2012) 

Elevation: 1473 ft. above sea level Latitude: 33.622 Longitude: -111.910 Data Version: VER2

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

Temp Date Time (LST) Station Type Sky Conditions Visibility (SM) Weather Type

(F) (C) (F) (C) (F) (C)

Rel 

Humd 

%

Wind 

Speed 

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hrChg

(mb)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 

06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06

0053 0153 0253 0353 0453 0553 0653 0753 0853 0953 1053 1153 1253 1353 1453 1553 1653 1753 1812 1820 1825 1851 1853 1953 2053 2153 2253 2353

12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12

CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR FEW003 SCT090 FEW005 SCT030 BKN090 FEW005 BKN028 BKN090 SCT020 SCT018 CLR CLR CLR CLR CLR

10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 2.50 1.50 3.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00

HZ HZ HZ 

87868585848483868788919595979999989793939391918787868583

30.630.029.429.428.928.928.330.030.631.132.835.035.036.137.237.236.736.134.034.034.033.032.830.630.630.029.428.3

73747474737273727374747574757475757473747474747373727373

22.923.123.323.322.822.422.622.422.623.123.223.823.523.823.523.723.623.222.923.523.523.223.222.922.922.422.623.0

67686969686768666667666665656364646364666666666767666769

19.420.020.620.620.019.420.018.918.919.418.918.918.318.317.217.817.817.218.019.019.019.018.919.419.418.919.420.6

52 55 59 59 59 57 61 51 50 50 44 39 37 35 31 32 33 33 38 41 41 44 44 52 52 51 55 63

3 0 6 0 0 3 0 3 3 5 6 8 0 8 9 7 7 14 6 15 11 16 17 6 5 6 0 6

VR 000 270 000 000 310 000 280 290 230 290 250 000 250 280 230 220 210 200 230 230 260 260 240 250 220 000 140

20 18 23 23 24 29 

28.29 28.29 28.29 28.29 28.30 28.31 28.33 28.35 28.36 28.36 28.35 28.33 28.30 28.27 28.24 28.23 28.24 28.25 28.25 28.26 28.26 28.28 28.28 28.31 28.34 28.35 28.35 28.35

3 3 3 0 8 5 3 0

006002016002027012024013
9 

Figure A-7. Quality-controlled local climatological data hourly observations table for Scottsdale Airport, Scottsdale, Arizona (09in the Weather Type column that HZ (haze) was reported. Dynamically generated via http://cdo.ncdc.noaa.gov/qclcd/QCLCD.

U.S. Department of Commerce National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL CLIMATOLOGICAL DATA 

(final) 

HOURLY OBSERVATIONS TABLE 

WILLIAMS GATEWAY AIRPORT (23104) 

PHOENIX, AZ 

(09/2012) 

Elevation: 1382 ft. above sea level Latitude: 33.3 Longitude: -111.666 Data Version: VER2

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

Temp Date Time (LST) Station Type Sky Conditions Visibility (SM) Weather Type

(F) (C) (F) (C) (F) (C)

Rel

Humd

%

Wind 

Speed 

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hrChg

(mb)

P

(

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 

06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 

0015 0035 0055 0115 0135 0155 0215 0235 0255 0315 0335 0355 0415 0435 0455 0515 0547 0647 0747 0847 0947 1147 1247 1347 1447 1547 1647 

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 

CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR FEW120 FEW200 FEW200 SCT200 FEW060 SCT200 FEW080 SCT100 FEW080 SCT100 FEW080 SCT100 FEW080 SCT100 FEW080 SCT100 FEW080 BKN200 

10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 30.00 35.00 45.00 30.00 30.00 30.00 30.00 30.00 30.00 10.00 30.00 

MMMMMMMMMMMMMMMM8282848890939597999999

M M M M M M M M M M M M M M M M 28.0

28.029.031.032.034.035.036.037.037.037.0

MMMMMMMMMMMMMMMM7474747576767677757574

M M M M M M M M M M M M M M M M 23.123.123.524.124.424.124.424.723.823.823.5

MMMMMMMMMMMMMMMM7070707070686868646463

M M M M M M M M M M M M M M M M 21.021.021.021.021.020.020.020.018.018.017.0

M M M M M M M M M M M M M M M M 67 67 63 55 52 44 41 39 32 32 31 

0 0 0 0 6 7 6 5 5 5 5 5 6 7 6 7 7 8 7 5 5 7 9 5 11 11 9 

000 000 000 000 120 120 110 110 090 070 090 

080 090 090 090 100 100 110 120 080 100 260 260 250 310 300 240 

28.43 28.43 28.43 28.44 28.44 28.44 28.44 28.44 28.44 28.44 28.44 28.44 28.44 28.44 28.44 28.44 28.45 28.48 28.48 28.49 28.50 28.48 28.45 28.42 28.38 28.38 28.38 

M M M M M M M M M M M M M M M M M M M M M M M M M M M 
10 

06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06 06

1700 1725 1747 1847 1947 1955 2015 2035 2055 2115 2135 2155 2215 2235 2255 2315 2335 2355

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

VV001 BKN080 BKN080 OVC150 BKN080 OVC120 BKN060 BKN100 OVC CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR

0.50s 1.50 5.00 10.00 20.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00

DSs BLDU BLDU 

9088888886MMMMMMMMMMMMM

32.031.031.031.030.0M M M M M M M M M M M M M

75747374MMMMMMMMMMMMMM

23.723.422.823.4M M M M M M M M M M M M M M

6868666868MMMMMMMMMMMMM

20.020.019.020.020.0M M M M M M M M M M M M M

48 52 48 52 M M M M M M M M M M M M M M

17 17 11 11 6 9 13 14 9 7 8 9 9 8 7 6 8 8

210 210 240 200 150 140 140 140 140 130 140 130 140 130 130 120 130 130

30 23 23 

28.40 28.42 28.41 28.42 M 28.48 28.49 28.49 28.49 28.49 28.49 28.50 28.50 28.49 28.49 28.48 28.49 28.50

M M M M M M M M M M M M M M M M M M

Figure A-8. Quality-controlled local climatological data hourly observations table for Williams Gateway Airport, Phoenix, Arizon

Note in the Weather Type column that BLDU (blowing dust) and DS (dust storm) were reported. Dynamically generated via http://cdo.ncdc.noaa.gov/qclcd/QCLCD.
Exceptional Event, Phoenix, September 6, 2012 Appendix B 

1 

Appendix B: Media Coverage, Videos, and Images 

Video Links

ADEQ visibility cameras in the Phoenix area: 

 South Mountain: www.phoenixvis.net/videos/mpeg4/SOMT_09062012.mp4

 Estrella Mountains: www.phoenixvis.net/videos/mpeg4/ESMO_09062012.mp4

 Camelback Mountains: www.phoenixvis.net/videos/mpeg4/CAME_09062012.mp4

 Superstition Mountains: www.phoenixvis.net/videos/mpeg4/SUPM_09062012.mp4

Local citizens often create videos during storms, documenting their observations. Here 

are links to two such videos. 

 Haboob - Dust Storm Rolling over South Mountain - Phoenix, AZ 9/6/12: 

http://www.youtube.com/watch?v=2GVWgfygaAg

 September 6, 2012 - Dust Storm Time Lapse: 

http://www.youtube.com/watch?v=Zb9OOhA9vOQ (This video is from a YouTube 

channel based in Phoenix, Arizona)

Articles and Image Links 

http://www.azcentral.com/news/articles/2011/11/04/20111104arizona-drivers-warned-blowingdust-abrk04-ON.html?nclick_check=1

Dust storm, rain hit Phoenix area 

by Domenico Nicosia and Marissa Scott - Sept. 6, 2012 07:21 PM 

The Arizona Republic-12 News Breaking News Team 

Slow moving thunderstorms northwest of Peoria dropped 2 inches of rain in a one-hour period 

Thursday evening after a dust storm swept across the Phoenix metropolitan area. 

Storms moving north between Surprise and Sun City got between 0.5 and 0.75 inches of rain, 

said Charlotte Dewey, a meteorologist from the National Weather Service. 

Various areas throughout the Valley are receiving gusts of wind at approximately 25 mph 

following the dissipating dust storm, she said. 

Scattered showers helped clear visibility from the approximately 2,500-foot dust wall that 

passed through the area, meteorologists said. 

Rain probability of up to 60 percent could bring scattered showers and thunderstorms before 11 

p.m. 
Exceptional Event, Phoenix, September 6, 2012 Appendix B 

2 

The wall that traveled over highways during rush-hour traffic approached the downtown Phoenix 

area, at speeds of up to 30 mph and lowered visibility in some areas to one-quarter of a mile. 

Phoenix Sky Harbor International Airport expected delays of up to 20 minutes around 5:15 p.m. 

that lasted for about an hour, said Deborah Ostreicher, deputy aviations director at the airport. 

The opaque cloud diffused slightly and slowed as it headed away from the desert area and 

through the downtown buildings. 

Motorists who find themselves in the dust are advised to pull to the side of the road and turn off 

vehicle lights. The wall of dust was reported near Interstate 10 and Ray Road at 5:10 p.m. 

The National Weather Service issued a blowing-dust advisory until 7 p.m. Thursday. 

The storm may bring showers and thunderstorms to the Phoenix metropolitan area and may 

cause localized flash floods in the evening, said Valerie Meyers, a meteorologist for the National 

Weather Service. 

The National Weather Service earlier had issued a hazardous-weather outlook for 

thunderstorms in the Phoenix area on Thursday night. 

There is a 50 to 60 percent chance of rain in the greater Phoenix area, with possible local 

flooding and "ponding" of water in parking lots, Meyers said. 

Thunderstorm chances continue through Saturday night and Sunday at 30 percent. There is a 

10 percent chance of scattered storms on Friday, she said. 

Meyers added that this will be a "wet" weekend with storm chances increasing by the day. 

Temperatures in the Phoenix metro area will be the same throughout the weekend. The high on 

Thursday will be 101, with temperatures remaining in the lower 100s with a high of 102 on 

Friday, 103 on Saturday and 103 on Sunday. 

http://www.myfoxphoenix.com/story/19478870/2012/09/06/dust-storm-envelopes-maricopa (go 

to link for news video) 

Rain comes to wash away dust storm's remnants 

Sep 06, 2012 5:15 PM 

PHOENIX - It's another day of active weather -- dust storms over the valley and later, rain. 

A long line of dust, 2,500 feet tall, crept into the valley from the south Thursday night, right in the 

middle of rush hour, reducing visibility for drivers. It wrapped east to west from Phoenix to 

Scottsdale as it moved north. 

Planes approaching Sky Harbor were seen changing direction to avoid the wall of dust. Some 

planes were prevented from takeoff as the storm rolled in. 
Exceptional Event, Phoenix, September 6, 2012 Appendix B 

3 

The National Weather Service issued a dust storm warning on Thursday. It expired at 7 p.m. 

Wind speeds reached 25 to 35 miles per hour, with gusts up to 40 miles per hour. Visibility was 

under a quarter-mile at times, according to NWS. 

About 9:30 p.m., rain started falling in downtown Phoenix to wash away what was left by the 

dust storm. 

Heavy rain also fell in Tucson. Officials made six swift-water rescues. Most of those involved 

motorists who were briefly trapped by floodwaters on desert-area roads. 

The monsoon season officially ends Sept. 30. 

Driving tips from NWS: 

 Drivers need to be ready for a sudden drop in visibility. 

 If you encounter blowing dust or sand on the road or see it approaching, pull off and put your 

 vehicle in park. 

 Turn the lights off and keep your foot off the brake pedal. 
Exceptional Event, Phoenix, September 6, 2012 Appendix B 

4 

Photos from AZ Central

http://www.azcentral.com/photo/23288

A dust storm moves over the ASU campus in Tempe on Sept. 6, 2012. 

PHOTO BY: Cheryl Evans/The Republic. 

A dust storm moves through the Phoenix area on Sept. 6, 2012. 

PHOTO BY: Pat Shannahan/The Arizona Republic. 
Exceptional Event, Phoenix, September 6, 2012 Appendix B 

5 

A dust storm moves Thursday from the southeast towards the northwest as it climbs above South 

Mountain, with the tower at Sky Harbor International Airport in the foreground. 

PHOTO BY: Tom Tingle/The Republic. 

South Parking Lot of South Mountain Community College taken at 5:30 on 9.6.2012. 

PHOTO BY: Kathleen Hawkins. 
Exceptional Event, Phoenix, September 6, 2012 Appendix B 

6 

A dust storm moves through the Phoenix area on Sept. 6, 2012. 

PHOTO BY: Cathie Wilkerson. 

Fully Engulfed in Dust! Taken 9.6.2012. 

PHOTO BY: Kathleen Hawkins. 
Exceptional Event, Phoenix, September 6, 2012 Appendix B 

7 

A dust storm moves through the metro Phoenix area on Sept. 6, 2012. 

PHOTO BY: 12 News. 

A dust storm moves through the Phoenix area on Sept. 6, 2012. 

PHOTO BY: Kelli Andrews. 

Exceptional Event, Phoenix, September 6, 2012 Appendix C 

1 

RISK LEVEL

Appendix C: ADEQ and NWS Forecast Products 

MARICOPA COUNTY DUST CONTROL FORECAST

ISSUED Wednesday, September 5, 2012

Three-day weather outlook:

NOTE: DURING THE ACTIVE SUMMER MONSOON PERIODS, STRONG OUTFLOW WINDS FROM EVEN 

DISTANT THUNDERSTORMS CAN GENERATE PERIODS OF DENSE BLOWING DUST

Showers and thunderstorms will continue to dance around the perimeter of the Phoenix metro area through Friday. We 

could see an upswing in moisture over the weekend with a good shot at some wetting rains by Monday. Until then, dust 

remains a possibility. Thus, the risk of exceeding the 24-hr PM10 health standard in Phoenix is forecast to be 

Moderate through Saturday, dropping to Low by Sunday.

R I S K F A C T O R S

WINDS STAGNATION UNHEALTHY PM-10

Day 1: Thu. 9/6/2012

Mostly light winds are 

expected except 

gusty near + thunderstorm out flow

(20% chance of 

showers). 

No significant 

stagnation is 

expected. 

= MODERATE

Day 2: Fri. 9/7/2012

Mostly light winds are 

expected except 

gusty near 

thunderstorm out flow 

(20% chance of 

showers).

No significant 

+ stagnation is 

expected. 

= MODERATE

Day 3: Sat. 9/8/2012

Mostly light winds are 

expected except 

gusty near 

thunderstorm out flow 

(20-30% chance of 

showers).

No significant 

+ stagnation is 

expected. 

= MODERATE

EXTENDED OUTLOOK

Day 4: Sun. 9/9/2012

Mostly light winds are 

expected except 

gusty near 

thunderstorm out flow 

(30-40% chance of 

showers). 

No significant 

+ stagnation is 

expected. 

= LOW
Exceptional Event, Phoenix, September 6, 2012 Appendix C 

2 

Day 5: Mon. 9/10/2012

Mostly light winds are 

expected except 

gusty near 

thunderstorm out flow 

(40% chance of 

showers). 

No significant 

+ stagnation is 

expected. 

= LOW

The Maricopa County Dust Control Action Forecast is issued to assist in the planning of work 

activities to help reduce dust pollution. A recorded message of this forecast can be accessed at 

602-771-2368. To review the complete air quality forecast for the Phoenix metropolitan area, 

as well as the health impacts and reduction methods for different air pollutants, call 602-771-

2367 for recorded forecast information or click on ADEQ's Air Quality Forecast at 

http://www.azdeq.gov/environ/air/ozone/ensemble.pdf.

JRP 04/28/2011
Exceptional Event, Phoenix, September 6, 2012 Appendix C 

3 

VERY UNHEALTHY (201-300) 

UNHEALTHY (151-200)

UNHEALTHY FOR SENSITIVE GROUPS (101-150)

MODERATE (51-100)

GOOD (0-50)

For more information visit:

http://www.airnow.gov/index.cfm?action=aqibasics.aqi

*LINK TO 2012 AIR POLLUTION EXCEEDANCE GRAPH*

AIR QUALITY FORECAST FOR Thursday, September 6, 2012, 2012

This report is updated by 1:00 p.m. Sunday thru Friday and is valid 

for areas within and bordering Maricopa County in Arizona

FORECAST 

DATE

NOTICES 

(*SEE BELOW 

FOR DETAILS)

AIR POLLUTANT

YESTERDAY

Tue 09/04/2012

Dust

Highest AQI Reading/Site 

(*Preliminary data only*)

TODAY

Wed 09/05/2012

Dust

TOMORROW

Thu 09/06/2012

Dust

EXTENDED

Fri 09/07/2012

Dust

O3* 48

Queen Valley

51

Moderate

77

Moderate

84

Moderate

CO* 7

West Phoenix

7

Good

7

Good

6

Good

PM-10* 56

West 43rd

72

Moderate

70

Moderate

75

Moderate

PM-2.5* 44

West Phoenix

48

Good

52

Moderate

56

Moderate

* O3 = Ozone CO = Carbon Monoxide PM-10 = Particles 10 microns & smaller PM-2.5 = Particles smaller than 2.5 microns 

*“Ozone Health Watch” means that the highest concentration of OZONE may approach the federal health standard.

“PM-10 or PM-2.5 Health Watch” means that the highest concentration of PM-10 or PM-2.5 may approach the federal health standard. 

“High Pollution Advisory” means that the highest concentration of OZONE, PM-10, or PM-2.5 may exceed the federal health standard. 

“DUST” means that short periods of high PM-10 concentrations caused by outflow from thunderstorms are possible.
Exceptional Event, Phoenix, September 6, 2012 Appendix C 

4 

Health Statements

Wednesday, 09/05/2012 Unusually sensitive people should consider reducing prolonged or heavy 

exertion outdoors.

Thursday, 09/06/2012 Unusually sensitive people should consider reducing prolonged or heavy 

exertion outdoors.

SYNOPSIS AND DISCUSSION

Some impressive lightning was seen around the Valley Tuesday night, particularly to the 

south. Though no rain made it into the forecast area, the collapsing storms did send some dust 

north. Five south Valley PM10 monitors snuck into the Moderate range as a result. With each 

passing day, the local soil continues to dry out. This will make it easier for the top soil to become 

airborne with outflow from nearby storms. Models suggest an upswing in thunderstorm activity 

heading into the weekend. We're keeping the forecasted PM10 concentrations in the middle part 

of the Moderate range as a result. 

Ozone concentrations remained in the Good range of the Air Quality Index (AQI) on Tuesday. 

NOAA's Air Quality model predicts higher concentrations in the east part of the Valley the next 

few days. This is feasible as high pressure remains overhead. For now, we are keeping the 

forecasted ozone levels below Health Watch criteria, but that may change if this latest upswing 

proves to be significant. 

Check back tomorrow for the latest. Until then, have a good day! -J.Paul

MONITORING SITE MAPS

STATIC MAP http://www.azdeq.gov/environ/air/monitoring/images/map.jpg

http://aqwww.maricopa.gov/AirMonitoring/SitePollutionMap.aspx

INTERACTIVE MAPS http://156.42.96.39/alert/Google/air.html

http://www.airnow.gov/

POLLUTION MONITOR READINGS FOR Tuesday, September 4, 2012

O3 (OZONE)

Info on current 8-hour ozone standard: http://www.epa.gov/air/ozonepollution/pdfs/2008_03_aqi_changes.pdf

For archived AQI maps go to: http://www.airnow.gov/index.cfm?action=airnow.maps

SITE NAME MAX 8-HR VALUE (PPB) MAX AQI AQI COLOR CODE

Alamo Lake 43 36

Apache Junction 49 42

Blue Point 56 47

Buckeye 43 36

Casa Grande 46 39

Cave Creek 47 40

Central Phoenix 50 42

Dysart 42 36

Falcon Field 53 45

Fountain Hills 50 42

Glendale 43 36

Humboldt Mountain NOT AVBL NOT AVBL NOT AVBL 

Phoenix Supersite 46 39

North Phoenix 51 43

Pinal Air Park 50 42

Pinnacle Peak 56 47

Queen Valley 57 48

Rio Verde NOT AVBL NOT AVBL NOT AVBL 

South Phoenix 50 42
Exceptional Event, Phoenix, September 6, 2012 Appendix C 

5 

South Scottsdale 53 45

Tempe 50 42

Tonto Nat’l Mon. 47 40

West Chandler 50 42

West Phoenix 49 42

Yuma 38 32

CO (CARBON MONOXIDE)

SITE NAME MAX 8-HR VALUE (PPM) MAX AQI AQI COLOR CODE

Central Phoenix 0.2 2

Greenwood 0.4 5

West Phoenix 0.6 7

PM-10 (PARTICLES)

SITE NAME MAX 24-HR VALUE (μg/m3) MAX AQI AQI COLOR CODE

Apache Junction 22.2 21

Buckeye 63.0 55

Central Phoenix NOT AVBL NOT AVBL NOT AVBL 

Combs School (Pinal County) 45.8 42

Durango 63.8 55

Dysart 41.2 38

Glendale 46.8 43

Greenwood 61.4 54

Higley 41.7 38

Maricopa (Pinal County) NOT AVBL NOT AVBL NOT AVBL 

North Phoenix 49.2 45

Phoenix Supersite 51.9 47

South Phoenix 35.0 32

Tempe 37.4 34

West Chandler 31.9 29

West Forty Third 65.3 56

West Phoenix 55.9 51

Zuni Hills 41.8 38

PM-2.5 (PARTICLES)

(Some data derived from light-scattering equipment)

For maps go to: http://www.airnow.gov/

SITE NAME MAX 24-HR VALUE (μg/m3) MAX AQI AQI COLOR CODE

Durango 10.3 33

Dysart 8.5 28

Estrella Mountain Park 9.5 31

Glendale 8.5 28

Phoenix Supersite 7.7 25

North Phoenix 8.8 29

South Phoenix 7.5 24

Tempe NOT AVBL NOT AVBL NOT AVBL 

Vehicle Emissions Lab 6.9 22

West Phoenix 13.4 44
Exceptional Event, Phoenix, September 6, 2012 Appendix C 

Statements, Advisories, and Warnings issued by the National Weather Service office in 

Phoenix, AZ pertaining to this dust storm event: 

URGENT - WEATHER MESSAGE 

NATIONAL WEATHER SERVICE PHOENIX AZ 

416 PM MST THU SEP 6 2012 

AZZ028-070100- 

/O.NEW.KPSR.DS.W.0016.120906T2316Z-120907T0100Z/ 

NORTHWEST AND NORTH CENTRAL PINAL COUNTYINCLUDING THE CITIES OF...APACHE JUNCTION...CASA GRANDE... 

FLORENCE 

416 PM MST THU SEP 6 2012 

...DUST STORM WARNING IN EFFECT UNTIL 6 PM MST THIS EVENING... 

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A DUST STORM 

WARNING...WHICH IS IN EFFECT UNTIL 6 PM MST THIS EVENING. 

POWERFUL THUNDERSTORMS SOUTH AND SOUTHWEST OF CASA GRANDE HAVE 

GENERATED STRONG NORTHWARD MOVING WIND GUSTS THAT HAVE KICKED UP 

DUST WITH VISIBILITIES BELOW 1/4 MILE AT TIMES. 

* AFFECTED AREA...PORTIONS OF PINAL COUNTY NEAR THE CITIES OF CASA 

 GRANDE...MARICOPA...STANFIELD...COOLIDGE...SACATON...AND NEARBY 

 PORTIONS OF INTERSTATE 10 BETWEEN CASA GRANDE AND PHOENIX. 

* TIMING...DUST STORM WARNING THROUGH 6 PM. 

* WINDS...20 TO 30 MPH WITH GUSTS TO 40 MPH. 

* VISIBILITY...LESS THAN 1/4 MILE AT TIMES. 

* IMPACTS...DANGEROUSLY LOW VISIBILITIES IN DENSE BLOWING DUST. 

PRECAUTIONARY/PREPAREDNESS ACTIONS... 

BE READY FOR A SUDDEN DROP IN VISIBILITY TO NEAR ZERO. IF YOU 

ENCOUNTER BLOWING DUST OR BLOWING SAND ON THE ROADWAY OR SEE IT 

APPROACHING...PULL OFF THE ROAD AS FAR AS POSSIBLE AND PUT YOUR 

VEHICLE IN PARK. TURN THE LIGHTS ALL THE WAY OFF AND KEEP YOUR 

FOOT OFF THE BRAKE PEDAL. 

REMEMBER...PULL ASIDE...STAY ALIVE. 

6 
Exceptional Event, Phoenix, September 6, 2012 Appendix C 

BULLETIN - EAS ACTIVATION REQUESTED 

SEVERE THUNDERSTORM WARNING 

NATIONAL WEATHER SERVICE PHOENIX AZ 

419 PM MST THU SEP 6 2012 

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A 

* SEVERE THUNDERSTORM WARNING FOR... 

 WEST CENTRAL PINAL COUNTY IN SOUTH CENTRAL ARIZONA... 

 INCLUDING THE AREAS NEAR STANFIELD...WEST CASA GRANDE... 

 NORTHWARD TO THE TOWN OF MARICOPA. 

* UNTIL 500 PM MST 

* AT 412 PM MST...NATIONAL WEATHER SERVICE METEOROLOGISTS DETECTED 

 SEVERE THUNDERSTORMS CAPABLE OF PRODUCING DAMAGING WINDS IN 

 EXCESS OF 60 MPH. THIS STORM WAS LOCATED 15 MILES SOUTH OF 

 MARICOPA...OR 19 MILES WEST OF CASA GRANDE. THIS STORM WAS 

 NEARLY STATIONARY. 

* THE SEVERE THUNDERSTORM WILL OTHERWISE REMAIN OVER MAINLY RURAL 

 AREAS OF THE INDICATED COUNTY. 

PRELIMINARY LOCAL STORM REPORT 

NATIONAL WEATHER SERVICE PHOENIX AZ 

429 PM MST THU SEP 06 2012 

..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON... 

..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE.... 

 ..REMARKS.. 

0410 PM DUST STORM CASA GRANDE 32.89N 111.74W 

09/06/2012 PINAL AZ AMATEUR RADIO 

 0.25 MILE VISIBILITY IN BLOWING DUST 

PRELIMINARY LOCAL STORM REPORT 

NATIONAL WEATHER SERVICE PHOENIX AZ 

431 PM MST THU SEP 06 2012 

..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON... 

..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE.... 

 ..REMARKS.. 

0415 PM DUST STORM 1 WSW COOLIDGE 32.98N 111.54W 

09/06/2012 PINAL AZ TRAINED SPOTTER 

 VISIBILITY LESS THAN 0.25 MILE IN BLOWING DUST 

7 
Exceptional Event, Phoenix, September 6, 2012 Appendix C 

SHORT TERM FORECAST 

NATIONAL WEATHER SERVICE PHOENIX AZ 

437 PM MST THU SEP 6 2012 

AZZ023-070145- 

GREATER PHOENIX AREAINCLUDING THE CITIES OF...BUCKEYE...CAREFREE...CAVE CREEK... 

CHANDLER...FOUNTAIN HILLS...GILBERT...GLENDALE...MESA...PEORIA... 

PHOENIX...SCOTTSDALE...SUN CITY...AND TEMPE 

437 PM MST THU SEP 6 2012 

.NOW... 

GUSTY SOUTH WINDS 25 TO 35 MPH WITH GUSTS 40 MPH...GENERATED FROM 

POWERFUL THUNDERSTORMS NEAR CASA GRANDE...WILL MOVE THROUGH THE 

AHWATUKEE...CHANDLER...TEMPE...AND PHOENIX AREAS BETWEEN 5 PM AND 7 

PM. A DUST STORM WITH VISIBILITIES UNDER 2 MILES AT TIMES WILL ALSO 

MOVE THROUGH THE AREA. 

GREATER PHOENIX AREAINCLUDING THE CITIES OF...MESA...PHOENIX 

441 PM MST THU SEP 6 2012 

...BLOWING DUST ADVISORY IN FOR PHOENIX EFFECT UNTIL 7 PM MST THIS 

EVENING... 

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A BLOWING DUST 

ADVISORY FOR THE GREATER PHOENIX AREA...WHICH IS IN EFFECT UNTIL 7 PM 

MST THIS EVENING. 

* AFFECTED AREA...FIRST AHWATUKEE...CHANDLER...TEMPE...MESA... THE 

 SPREADING INTO DOWNTOWN PHOENIX NORTHWARD. 

* TIMING...BETWEEN 455 PM AND 7 PM. 

* WINDS...SOUTH WINDS 25 TO 35 MPH WITH GUSTS TO 40 MPH. 

* VISIBILITY...UNDER 1 MILE AT TIMES. 

* IMPACTS...DANGEROUSLY LOW VISIBILITIES FOR MOTORISTS. 

PRECAUTIONARY/PREPAREDNESS ACTIONS... 

BE READY FOR A SUDDEN DROP IN VISIBILITY. IF YOU ENCOUNTER 

BLOWING DUST OR BLOWING SAND ON THE ROADWAY OR SEE IT 

APPROACHING...PULL OFF THE ROAD AS FAR AS POSSIBLE AND PUT YOUR 

VEHICLE IN PARK. TURN THE LIGHTS ALL THE WAY OFF AND KEEP YOUR 

FOOT OFF THE BRAKE PEDAL. 

REMEMBER...PULL ASIDE...STAY ALIVE. 

8 
Exceptional Event, Phoenix, September 6, 2012 Appendix C 

URGENT - WEATHER MESSAGE 

NATIONAL WEATHER SERVICE PHOENIX AZ 

452 PM MST THU SEP 6 2012 

AZZ023-070200- 

/O.UPG.KPSR.DU.Y.0048.000000T0000Z-120907T0200Z/ 

/O.EXB.KPSR.DS.W.0016.000000T0000Z-120907T0200Z/ 

GREATER PHOENIX AREAINCLUDING THE CITIES OF...MESA...PHOENIX 

452 PM MST THU SEP 6 2012 

...DUST STORM WARNING IN EFFECT UNTIL 7 PM MST THIS EVENING... 

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A DUST STORM 

WARNING...WHICH IS IN EFFECT UNTIL 7 PM MST THIS EVENING. THE 

BLOWING DUST ADVISORY ISSUED EARLIER IS NO LONGER IN EFFECT. 

* AFFECTED AREA...FIRST AHWATUKEE...CHANDLER...TEMPE...MESA...THEN 

 SPREADING NORTHWARD INTO PHOENIX. 

* TIMING...THROUGH 7 PM. 

* WINDS...SOUTH WINDS 25 TO 35 MPH WITH GUSTS TO 40 MPH. 

* VISIBILITY...UNDER 1/4 MILE AT TIMES. 

* IMPACTS...DANGEROUSLY LOW VISIBILITIES FOR MOTORISTS. 

PRECAUTIONARY/PREPAREDNESS ACTIONS... 

BE READY FOR A SUDDEN DROP IN VISIBILITY TO NEAR ZERO. IF YOU 

ENCOUNTER BLOWING DUST OR BLOWING SAND ON THE ROADWAY OR SEE IT 

APPROACHING...PULL OFF THE ROAD AS FAR AS POSSIBLE AND PUT YOUR 

VEHICLE IN PARK. TURN THE LIGHTS ALL THE WAY OFF AND KEEP YOUR 

FOOT OFF THE BRAKE PEDAL. 

REMEMBER...PULL ASIDE...STAY ALIVE. 

PRELIMINARY LOCAL STORM REPORT 

NATIONAL WEATHER SERVICE PHOENIX AZ 

527 PM MST THU SEP 06 2012 

..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON... 

..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE.... 

 ..REMARKS.. 

0524 PM DUST STORM 3 E MESA RIVERVIEW MALL 33.43N 111.82W 

09/06/2012 MARICOPA AZ TRAINED SPOTTER 

 VSBY LESS THAN 0.25 MI. 

9 
Exceptional Event, Phoenix, September 6, 2012 Appendix C 

10 

PRELIMINARY LOCAL STORM REPORT 

NATIONAL WEATHER SERVICE PHOENIX AZ 

555 PM MST THU SEP 06 2012 

..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON... 

..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE.... 

 ..REMARKS.. 

0543 PM DUST STORM 4 SW WITTMANN 33.74N 112.58W 

09/06/2012 MARICOPA AZ TRAINED SPOTTER 

 LESS THAN 0.25 MI. VSBY 
Exceptional Event, Phoenix, September 6, 2012 Appendix D 

Appendix D: 

Affidavit of Public Notice 

1