State of Arizona 

Exceptional Event Documentation 

for the Event of August 14, 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.
Cover image depicts windblown dust and haze in the Phoenix area at 2235 LST on August 14, 2012, resulting from 

strong winds associated with thunderstorm outflow. This photo was taken by an ADEQ visibility camera near 

downtown Phoenix, facing northeast toward Camelback Mountain.

State of Arizona 

Exceptional Event Documentation 

for the Event of August 14, 2012, 

for the Phoenix PM10 Nonattainment Area

Final Report

STI-912097-5571-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

Exceptional Event, Phoenix, August 14, 2012 Acknowledgments

iii

Acknowledgments

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

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

Exceptional Event, Phoenix, August 14, 2012 Table of Contents

v

Table of Contents

Section Page

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

List of Tables .............................................................................. Error! Bookmark not defined.

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................................................................................................................12

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.......................................................................................... 6

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

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

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

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

6.2 Summary................................................................................................................. 1
Exceptional Event, Phoenix, August 14, 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: Historical Fluctuation Time-Series Graphs ........................................................C-1

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

Appendix E: Affidavit of Public Notice ....................................................................................E-1
Exceptional Event, Phoenix, August 14, 2012 List of Figures

vii

List of Figures

Figure Page

2-1. Locations of air quality monitors that recorded exceedances of the 24-hr PM10

NAAQS and NWS monitors primarily used in this report..................................................2

2-2. Location of sites monitoring PM10 in Arizona on August 14, 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

2-6. Thunderstorms over northwestern Mexico and southern Arizona produced outflow 

boundaries that propagated northwestward and transported dust to the Phoenix 

area on August 14, 2012. ................................................................................................7

3-1. Infrared satellite image from 1815 LST on August 14, 2012 (GOES-West)......................1

3-2. Hourly PM10 concentrations at Pinal County monitors on August 14 and 15, 2012 ..........2

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

3-4. Hourly PM10 concentrations and wind speeds at the West 43rd Avenue monitor on 

August 14 and 15, 2012 ..................................................................................................3

3-5. Hourly PM10 concentrations and wind speeds at the Durango Complex monitor on 

August 14 and 15, 2012 ..................................................................................................4

3-6. Image from an ADEQ visibility camera near downtown Phoenix facing northeast 

toward Camelback Mountain ...........................................................................................4

3-7. Maximum 5-minute PM10 concentrations, 5-minute wind speed and direction, 

maximum wind gusts, and minimum visibility observations at Maricopa and Pinal 

County monitors between 2030 and 2100 LST on August 14, 2012 ................................7

3-8. Similar to Figure 3-7, but representing observations from 2130 to 2200 LST...................9

3-9. Similar to Figure 3-7, but representing observations from 2230 to 2300 LST.................10

3-10. Similar to Figure 3-7, but representing observations from 2330 to 0000 LST.................11

4-1. 24-hr average PM10 concentrations at the West 43rd monitor (2007–2012)......................1

4-2. Daily maximum hourly average PM10 concentrations at the West 43rd monitor 

(2007-2012).....................................................................................................................2

5-1. Timeline of Maricopa County fugitive dust rules and ordinances .....................................5
Exceptional Event, Phoenix, August 14, 2012 List of Tables

viii

List of Tables

Table Page

2-1. PM10 measurements on August 14, 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
Exceptional Event, Phoenix, August 14, 2012 Introduction

1

1. Introduction

On August 14, 2012, two air quality monitors in the Phoenix PM10 nonattainment area 

recorded 24-hr average PM10 concentrations 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 

these exceedances were due to naturally occurring windblown dust, were not reasonably 

controllable or preventable, were historically unusual, and would not have occurred “but for” the 

windblown dust and that they therefore constitute 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 August 14, 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 August 14, 2012, and the exceedances of the 24-hr PM10 standard at the monitoring 

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

quality and was the result of natural events.

Section 4 of this assessment illustrates that the event of August 14, 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 August 

14, 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 exceedances, 

and concludes that the exceedances of the 24-hr PM10 standard on August 14, 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 time-series graphs to supplement Section 4. Appendix D contains air 

quality forecasts issued by the Arizona Department of Environmental Quality (ADEQ) and 

weather statements and warnings issued by the National Weather Service (NWS). Appendix E

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 
Exceptional Event, Phoenix, August 14, 2012 Introduction

2

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

guidance and discusses how ADEQ addressed those requirements.

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 August 14, 2012. More 

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

products that were issued for August 14, 2012, are included in Appendix D.

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 the potential 

exists for a monitor’s reading(s) to 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 August 14, 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 exceedances 

that occurred on August 12, 2012, in the Phoenix PM10 nonattainment area were included on 

this list. This assessment report serves as demonstration supporting the flagging of these 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 
Exceptional Event, Phoenix, August 14, 2012 Introduction

3

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

CFR 50.14(c)(3)(iv). See Appendix E for a copy of the affidavit of public notice.

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, August 14, 2012 Conceptual Model

1

2. Conceptual Model

This section provides a narrative background and summarizes the meteorological and 

air quality conditions in place on August 14, 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 locations of PM10

monitors that recorded exceedances on August 14, 2012. Monitors shown in this map include 

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

primary NWS site used in this demonstration package was the Phoenix Sky Harbor International 

Airport (KPHX) site, because of that site’s high data quality, data completeness, and 

representativeness of meteorological conditions in the Phoenix area. Figure 2-2 shows the 

locations of PM10 monitors statewide on August 14, 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 air quality monitors that recorded exceedances of the 24-hr PM10 NAAQS and NWS monitors primarily 

used in this report.
Exceptional Event, Phoenix, August 14, 2012 Conceptual Model

3

Figure 2-2. Location of sites monitoring PM10 in Arizona on August 14, 2012.
Exceptional Event, Phoenix, August 14, 2012 Conceptual Model

4

Figure 2-3. Drainage system of Phoenix, Arizona.
Exceptional Event, Phoenix, August 14, 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, August 14, 2012 Conceptual Model

6

Figure 2-5. Cross-section of a thunderstorm creating an outflow boundary and haboob1. 

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 August 14, 2012, strong winds generated by 

thunderstorms southeast of Phoenix transported dust northwestward into the Phoenix area 

(Figure 2-6). The windblown dust resulted in 24-hr average PM10 concentrations in exceedance 

of the NAAQS at two air quality monitors in Maricopa County (Table 2-1). The PM10

concentrations measured at these monitors were in excess of normal historical fluctuations. 

The dust was naturally occurring and likely originated over undeveloped lands south of 

Maricopa County, and wind gusts in excess of 30 to 40 mph overwhelmed reasonable dust 

control measures. While only two monitors in Maricopa County recorded PM10 concentrations in 

 

1

Image source: Warner T.T. (2004) Desert meteorology, Cambridge University Press, ISBN-10: 0521817986, ISBN13: 978-0521817981, February 9.

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.
Exceptional Event, Phoenix, August 14, 2012 Conceptual Model

7

exceedance of the NAAQS, monitors across Maricopa and Pinal counties recorded elevated 

PM10 concentrations during this dust storm.

Region of initial 

thunderstorm 

development

Phoenix

Pima County

Maricopa 

County Pinal 

Windblown dust County

transported 

northwestward

Figure 2-6. Thunderstorms over northwestern Mexico and southern Arizona produced 

outflow boundaries that propagated northwestward and transported dust to the Phoenix 

area on August 14, 2012.

Table 2-1. PM10 measurements on August 14, 2012. The exceedance monitors 

discussed in this report are shown in bold.

Page 1 of 3

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 15 49 1300

Coconino County

N/A N/A ADEQ 04-005-1237-81102-1 N/A N/A N/A
Exceptional Event, Phoenix, August 14, 2012 Conceptual Model

8

Table 2-1. PM10 measurements on August 14, 2012. The exceedance monitors 

discussed in this report are shown in bold.

Page 2 of 3

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

Gila County

Hayden Old Jail TEOM ADEQ 04-007-1001-81102-3 28 49 1800

Maricopa County

West Phoenix BAM MC 04-013-0019-81102-1 106 1251 2200

North Phoenix BAM MC 04-013-1004-81102-1 44 77 700

Glendale TEOM MC 04-013-2001-81102-1 62 354 2300

Central Phoenix TEOM MC 04-013-3002-81102-4 84 916 2200

Greenwood TEOM MC 04-013-3010-81102-1 113 1352 2200

South Phoenix TEOM MC 04-013-4003-81102-1 125 1624 2200

West Chandler TEOM MC 04-013-4004-81102-1 126 1535 2200

Tempe TEOM MC 04-013-4005-81102-1 90 978 2200

Higley TEOM MC 04-013-4006-81102-1 95 313 2200

West 43rd Ave TEOM MC 04-013-4009-81102-1 254 3574 2200 RJ

Dysart TEOM MC 04-013-4010-81102-1 66 651 2300

Buckeye TEOM MC 04-013-4011-81102-1 68 283 2300

Zuni Hills TEOM MC 04-013-4016-81102-1 44 372 2300

Fort 

McDowell/Yuma 

Frank

TEOM FMIR 04-013-5100-81102-3 47 N/A N/A

Durango Complex TEOM MC 04-013-9812-81102-1 179 2540 2200 RJ

JLG Supersite BAM ADEQ 04-013-9997-81102-3 79 724 2200

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 20 47 1900

Pima County

Ajo TEOM ADEQ 04-019-0001-81102-3 49 103 2200

Rillito TEOM ADEQ 04-019-0020-81102-3 97 485 1900

Orange Grove FRM PCDEQ 04-019-0011-81102-2 41 N/A N/A

South Tucson FRM PCDEQ 04-019-1001-81102-1 32 N/A N/A

Green Valley TEOM PCDEQ 04-019-1030-81102-1 25 63 1800

Geronimo TEOM PCDEQ 04-019-1113-81102-1 32 57 1800

Pinal County

Casa Grande 

Downtown TEOM PCAQCD 04-021-0001-81102-3 132 773 2100

Apache Junction 

Fire Station FRM PCAQCD 04-021-3002-81102-3 53 267 2100

Stanfield TEOM PCAQCD 04-021-3008-81102-3 282 1209 2100 RJ
Exceptional Event, Phoenix, August 14, 2012 Conceptual Model

9

Table 2-1. PM10 measurements on August 14, 2012. The exceedance monitors 

discussed in this report are shown in bold.

Page 3 of 3

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

Combs School TEOM PCAQCD 04-021-3009-81102-3 113 1163 2100

Maricopa TEOM PCAQCD 04-021-3010-81102-3 231 1500 2200 RJ

Pinal County 

Housing TEOM PCAQCD 04-021-3011-81102-3 135 969 2000

Cowtown TEOM PCAQCD 04-021-3013-81102-3 481 2859 2300

Santa Cruz County

Nogales Post Office BAM ADEQ 04-023-0004-81102-3 40 78 0000

Yuma County

Yuma Supersite TEOM ADEQ 04-027-8011-81102-3 81 492 2300

TEOM: Tapered Element Oscillating Microbalance monitor

BAM: Beta Attenuation Monitor

FRM: Federal Reference Method

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

MC: Maricopa County Air Quality Department

FMIR: Fort McDowell Indian Reservation

PCDEQ: Pima County Department of Environmental Quality

PCAQCD: Pinal County Air Quality Control District

RJ: qualifier flag for high winds

Exceptional Event, Phoenix, August 14, 2012 Causal Relationship

1

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 August 14, 2012. On the evening of August 14, a large area of thunderstorms developed 

over far northwestern Mexico and southeastern Arizona, south of the Phoenix area (Figure 3-1). 

Thunderstorms southeast of Maricopa County 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 blow dust across 

Arizona. The likely source region for PM10 during the August 14, 2012, event was the desert 

region south of Phoenix, most of which lies outside the Phoenix PM10 nonattainment area. This 

region largely consists of natural, undisturbed desert. In addition, the weeks leading up to the 

event were dry in the Phoenix area, with the last measureable rainfall at KPHX occurring on 

July 28 and 29. 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 1815 LST on August 14, 2012 (GOES-West). 

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

clouds. Thunderstorms over northwestern Mexico and south-central Arizona generated 

an outflow boundary that carried dust northward into Arizona.
Exceptional Event, Phoenix, August 14, 2012 Causal Relationship

2

The thunderstorm outflow and associated windblown dust were first evident at Pinal 

County monitors after 2000 LST on August 14, with a sharp increase in PM10 at several 

monitors (Figure 3-2). The thunderstorm outflow and associated dust continued northnorthwestward and arrived in the Phoenix area during the 2200 LST hour on August 14, 

accompanied by significant reductions in visibility at KPHX (Figure 3-3). PM10 concentrations at 

the two exceedance monitors in Maricopa County increased sharply over this time period, with 

1-hr PM10 concentrations exceeding 3,500 μg/m3at West 43rd Avenue (Figure 3-4) and

2,500 μg/m3at Durango Complex (Figure 3-5). Collocated wind observations at these monitors 

showed wind gusts in excess of 45 mph coincident with the high PM10 concentrations. Several 

other wind monitors in the Phoenix area reported strong winds at the same time as the high 

PM10 concentrations (Appendix A), but wind gusts were highest in the vicinity of the two 

exceedance monitors. Visibility cameras in the Phoenix area also clearly showed blowing dust 

and reduced visibility after 2200 LST as the outflow arrived (Figure 3-6). 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 the abrupt increase in PM10 corresponded with the 

arrival of high winds in the Phoenix area, whereas in the hours immediately before and after the 

event, winds were lighter and PM10 concentrations were lower. In response to the approaching 

thunderstorm outflow and associated dust and low visibilities, the NWS office in Phoenix issued 

a Blowing Dust Advisory (Appendix D).

Figure 3-2. Hourly PM10 concentrations at Pinal County monitors on August 14 and 15, 

2012. PM10 concentrations sharply increased between 2000 and 2300 LST on August 

14, 2012, coinciding with the arrival of windblown dust.
Exceptional Event, Phoenix, August 14, 2012 Causal Relationship

3

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

KPHX. Visibility was greatly reduced at 2200 and 2300 LST on August 14, 2012,

coinciding with the sharp increase in PM10 concentrations at Phoenix area monitors, 

indicating the arrival of windblown dust.

Figure 3-4. Hourly PM10 concentrations and wind speeds at the West 43rd Avenue 

monitor on August 14 and 15, 2012. PM10 concentrations and wind speeds sharply 

increased at 2200 LST on August 14, 2012, indicating the arrival of windblown dust. 
Exceptional Event, Phoenix, August 14, 2012 Causal Relationship

4

Figure 3-5. Hourly PM10 concentrations and wind speeds at the Durango Complex 

monitor on August 14 and 15, 2012. PM10 concentrations and wind speeds sharply 

increased at 2200 LST on August 14, 2012, indicating the arrival of windblown dust. 

Sustained winds of nearly 20 mph, with gusts over 45 mph, were measured.

Figure 3-6. Image from an ADEQ visibility camera near downtown Phoenix facing 

northeast toward Camelback Mountain. Windblown dust associated with thunderstorm 

outflow caused reduced visibilities throughout the Phoenix area.
Exceptional Event, Phoenix, August 14, 2012 Causal Relationship

5

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

area is summarized by the radar velocity and wind vector spatial plots shown in Figures 3-7 

through 3-10.

2030-2100 LST (Figure 3-7)

Doppler radar indicated an outflow boundary over Pinal County moving northwest toward 

the Phoenix area. Hourly PM10 concentrations at monitors in Pinal County near the outflow 

boundary had increased to over 500 g/m3. Conditions across Maricopa County and far 

northwestern Pinal County prior to the arrival of the dust-laden outflow were generally 

characterized by low PM10 concentrations, low wind speeds, and high visibilities.

2130-2200 LST (Figure 3-8)

Between 2130 and 2200 LST, the outflow boundary continued northwestward and 

passed through western Pinal County into the southernmost part of Maricopa County, where 5-

minute PM10 concentrations exceeded 1000 μg/m3at some monitors, south to southeasterly 

winds gusted to over 30 mph, and visibilities dropped to below 1 mile at some monitors. 

Monitors not yet affected by the outflow across most of Maricopa County continued to report low 

PM10 concentrations, low wind speeds, and high visibilities.

2230-2300 LST (Figure 3-9)

Doppler radar indicated that the outflow boundary became better defined as it 

progressed into Maricopa County, with a large area of strong south-to-southeasterly winds 

(bright orange/red areas) over much of the central and eastern portions of the county. 5-minute 

PM10 concentrations increased to over 2500 μg/m3at several monitors in Maricopa County and 

over 5000 g/m3at the Durango Complex and West 43rd Avenue monitors, with widespread 

gusty winds and reduced visibilities. Although only two monitors in Maricopa County (Durango 

Complex and West 43rd Avenue) recorded PM10 concentrations in exceedance of the NAAQS, it 

is apparent that nearly all monitors showed elevated PM10 concentrations as the outflow 

boundary moved through, illustrating that the outflow affected most of the metropolitan area. 

The Durango Complex and West 43rd Avenue monitors showed the highest PM10

concentrations, most likely because of locally stronger winds of over 40 mph in the vicinity of the 

monitors. Winds were also gusty across much of central and eastern Maricopa County, but they 

were not quite as strong as the winds observed near the Durango Complex and West 43rd

Avenue monitors. Doppler radar also indicated a corridor of enhanced south-southeasterly flow 

aimed directly at the Durango Complex and West 43rd Avenue monitors. The locally strong 

winds in the vicinity of the two exceedance monitors likely overwhelmed all dust control 

measures in place near those monitors. Wind directions near the two exceedance monitors 

were from the southeast, consistent with the movement of the outflow boundary. The two 

exceedance monitors were on the southern side of the Phoenix urban area, closer to the source 

region of the thunderstorm outflow and windblown dust, and thus they were subject to greater 

quantities of transported PM10 than were other monitors in the nonattainment area. 
Exceptional Event, Phoenix, August 14, 2012 Causal Relationship

6

2330-0000 LST (Figure 3-10)

As the outflow boundary continued northwestward, gusty winds continued across much 

of Maricopa County, but PM10 concentrations started to decrease at most monitors, including 

the two exceedance monitors. PM10 concentrations increased again to over 2500 g/m3at two 

Pinal County monitors because of another thunderstorm outflow affecting that area, as indicated 

by the strong outbound radar velocities over western Pinal County and strong surface winds.
7

Radar Site

Figure 3-7. Maximum 5-minute PM10 concentrations (colored circles), 5-minute wind speed and direction, maximum wind gusts, 

and minimum visibility observations at Maricopa and Pinal County monitors between 2030 and 2100 LST on August 14, 2012. 

Where 5-minute data are not available (e.g., PM10 concentrations in Pinal County), 1-hour data are used. Underlying are Doppler 

radar velocity data at 2032 LST, where greens indicate motion toward the radar and oranges/reds indicate motion away from the 

radar.
8

Radar Site
9

Figure 3-8. Similar to Figure 3-7, but representing observations from 2130 to 2200 LST. Doppler radar data are from 2133 LST.
10

Radar Site

Figure 3-9. Similar to Figure 3-7, but representing observations from 2230 to 2300 LST. Doppler radar data are from 2234 LST.
11

Radar Site

Figure 3-10. Similar to Figure 3-7, but representing observations from 2330 to 0000 LST. Doppler radar data are from 2330 LST.
Exceptional Event, Phoenix, August 14, 2012 Causal Relationship

12

3.2 Summary

The information presented in this section demonstrates a clear causal relationship 

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

nonattainment area on August 14, 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. 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 

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

concentrations increased in Maricopa County shows 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. The proximity of the exceedance

monitors to the open and desert areas of far southern Maricopa County and western Pinal 

County, combined with strong wind gusts over 40 mph that likely overwhelmed all available 

control measures, provides solid evidence showing why these two monitors within the Maricopa 

County nonattainment area recorded an exceedance.

Exceptional Event, Phoenix, August 14, 2012 Historical Norm

1

4. Historical Norm

4.1 Analysis

PM10 concentrations measured at Phoenix-area monitors on August 14, 2012, were 

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

PM10 concentrations measured on August 14, 2012, were compared to a historical 2007-2012

six-year annual data set at each monitor (Figure 4-1, 4-2, and Appendix C). The PM10

concentrations measured at the West 43rd monitor (Figure 4-1) on August 14, 2012, resulted in 

one of the highest 24-hr averages measured over the five-year period, as well as one of the 

highest daily maximum hourly averages measured over the same period. Similar time-series 

plots for the other monitors with exceedances of the 24-hr PM10 standard are shown in 

Appendix C.

Figure 4-1. 24-hr average PM10 concentrations at the West 43rd monitor (2007–2012). 

The 24-hr average PM10 concentration on August 14, 2012, is highlighted in red.
Exceptional Event, Phoenix, August 14, 2012 Historical Norm

2

Figure 4-2. Daily maximum hourly average PM10 concentrations at the West 43rd

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

August 14, 2012, is highlighted in red.

4.2 Summary

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

EPA, it is clear that the PM10 levels on August 14, 2012, were outside normal historical 

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

scale.
Exceptional Event, Phoenix, August 14, 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 

§49-4572. 

5.1.1 Control Measures

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

 

2 Updates to the AgBMP 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, August 14, 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, August 14, 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, August 14, 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, August 14, 2012 Not Reasonably Controllable or Preventable

5

January 2004 December 2011

01/27/2010 Rules 310 & 310.01 Revised

01/12/2011 Ordinances P-27 & P-28 Revised July 2008 - June 2009 Rule Effectiveness: Rule 310: 90% Rule 310.01: 95% Rule 316: 65%

06/01/2005 06/08/2005 Rule 316 Revised

January 2010 - December 2010 Rule Effectiveness: Rule 310: 94% Rule 310.01: 96% Rule 316: 73% January 2007 - December 2007 Rule Effectiveness: Rule 310: 76% Rule 310.01: 85% Rule 316: 40%

04/07/2004 Rule 310 Revised

02/17/2005 Rule 310.01 Revised

03/26/2008

03/26/2008 Rules 310 & 310.01 and Ordinance P-26 Revised

April 2007

03/26/2008 Rules 310 & 310.01 Revise

March 200

d

8 03/18/2008 Ordinances P-25, P-27 & P-28 Adopted

02/20/2008

03/12/2008 Rule 316 Revised September 2006 02/20/2008 Ordinances P-25, P-27 & P-28 AdopteAu

dgust 2006

03/12/2008 Rule 316 Revised 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 
Exceptional Event, Phoenix, August 14, 2012 Not Reasonably Controllable or Preventable

6

elevated. The system allows MCAQD responders to review concentrations at the monitors and 

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 and Maricopa County’s Environmental Management System were queried 

to compile a list of inspections for the permitted sources in the Maricopa area around the time of 

the August 14, 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 August 11-17, 2012, 

MCAQD inspectors conducted a total of 230 inspections of permitted facilities, of which 148 

were at fugitive dust sources. Additionally, MCAQD conducted 41 inspections on vacant lots 

and unpaved parking lots. During this seven-day period, a total of 30 violations were issued 

countywide for PM10 and non-PM10 related violations. No violations were issued for PM10

emissions within a four-mile radius of an exceedance monitor.

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

the seven-day period from August 11-17, 2012, MCAQD received 25 complaints, of which 14

were related to windblown dust. Each complaint was assigned to, and investigated by, a 

MCAQD inspector. A review of all pertinent records from this period indicates that MCAQD 

inspectors did not observe any PM10 emission violations of local, state, or federal regulations 

within a four-mile radius of an exceedance 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.

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 August 14, 

2012. The ADEQ Ag BMP inspector did not receive any complaints in the two days prior to the 

event.

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 D). On August 13, 2012, ADEQ issued a Maricopa County 
Exceptional Event, Phoenix, August 14, 2012 Not Reasonably Controllable or Preventable

7

Dust Control Forecast for August 14, 2012, indicating a moderate risk level for unhealthy PM10. 

The Dust Control Forecast also indicated a potential for westerly winds of 10-20 mph with higher 

gusts and strong winds possible during the afternoon due to outflow from thunderstorms.

At 2141 LST on August 14, 2012, the NWS office in Phoenix issued Blowing Dust 

Advisories for portions of Pinal and Maricopa counties during 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 one mile due to blowing dust.

5.3 Wind Observations

Wind data during the event (Figure 3-2, Figure 3-3, and Appendix A) showed sustained 

wind speeds of over 20 mph and wind gusts of over 40 mph coincident with the high PM10

concentrations. While gusty winds were reported throughout the region, they were particularly 

strong in the vicinity of the Durango Complex and West 43rd Avenue monitors; these strong 

winds likely overwhelmed all available control measures.

5.4 Summary

The thunderstorm outflow event of August 14, 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 proactive 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 sustained winds in excess of 20 mph with gusts over 40 mph 

were strong enough to overwhelm available efforts to limit PM10 concentrations during the event. 

The fact that these were natural 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 exceedances of August 14, 2012, recorded within the Phoenix 

PM10 nonattainment area were not reasonably controllable or preventable. 

Exceptional Event, Phoenix, August 14, 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 exceedances at Phoenix area monitors on August 14, 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

exceedances in the Phoenix PM10 nonattainment area.

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 August 14, 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 

no violations or complaints in the vicinity of an exceedance monitor within three days before and 

after the time of the event. 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. Winds were particularly strong in the vicinity of the two exceedance monitors, which 

likely overwhelmed all available control measures.

6.2 Summary

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

the exceedance of August 14, 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, August 14, 2012 Conclusions

1

7. Conclusions

The PM10 exceedances that occurred on August 14, 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 exceedances 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

exceedances discussed in this report were 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 exceedances on August 14, 2012, were not reasonably controllable or preventable.

7.3 Natural Event

As discussed above, the PM10 exceedances in the Phoenix area on August 14, 2012, 

were 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, August 14, 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. While winds were gusty throughout the region, winds were 

particularly strong (in excess of 40 mph) near the two exceedance monitors. Thus, the 

wind magnitudes and wind direction, combined with the proximity of the exceedance

monitors to open and desert areas of northwestern Pinal County, provide solid evidence 

as to why only two monitors 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 

exceedances of the federal 24-hr PM10 standard on August 14, 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, August 14, 2012 Appendix A

1

Appendix A:

Air Quality and Meteorological Data for Maricopa County

This section contains tables of meteorological data from NWS sites in the Phoenix area 

for August 14, 2012. Reduced visibilities, gusty winds, and blowing dust or dust storms were 

reported coincident with the arrival of thunderstorm outflow and high PM10 concentrations.
2

U.S. Department of Commerce

National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL

CLIMATOLOGICAL DATA (final)

HOURLY OBSERVATIONS TABLE

PHOENIX SKY HARBOR INTL AIRPORT (23183)

PHOENIX, AZ (08/2012) 

National Climatic Data Center

Federal Building

151 Patton Avenue

Asheville, North Carolina 28801

Elevation: 1107 ft. above sea level

Latitude: 33.427

Longitude: -112.003

Date Time

(LST)

Station

Type

Sky

Conditions

Visibilit

y

(SM)

Weather

Type

Dry

Bulb

Temp

Wet

Bulb

Temp

Dew

Point

Temp

Rel

Humd

%

Wind

Speed

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressur

e

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb)

Sea

Level

Pressur

e

(in. hg)

Report

Type

Precip.

Total

(in)

Altimeter

(in. hg)

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

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

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

0051

0151

0204

0244

0251

0351

0451

0551

0651

0751

0851

0951

1051

1151

1251

1351

1451

1551

1651

1751

1851

1951

2051

2151

2226

2242

2251

2332

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

FEW110 SCT160 BKN210

FEW110 SCT160 BKN210

FEW110CB SCT160 

BKN210

FEW110 SCT160 BKN210

FEW110 SCT160 BKN210

SCT160 BKN210

SCT160 BKN210

FEW160 BKN210

FEW160 SCT210 SCT250

SCT170 BKN210

FEW170 SCT210

FEW170 SCT210

FEW170 SCT210

FEW120 SCT170 SCT210

FEW120 SCT170 SCT250

FEW120 SCT170 SCT250

FEW120 SCT170 SCT250

FEW120 SCT170 SCT250

FEW120 SCT170 SCT250

FEW120 SCT170 SCT250

FEW120 SCT170 SCT250

FEW120 SCT170 SCT250

FEW120 SCT170 SCT250

BKN130

BKN130CB

BKN130CB

BKN130CB

BKN130CB

BKN130CB

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

10.00

10.00

10.00

10.00

10.00

10.00

2.50

5.00

10.00

10.00

10.00

TS

TS BLDU

TS BLDU

TS

-TSRA

TS

99

98

99

97

96

95

94

92

94

96

98

101

103

107

108

109

112

110

111

110

109

107

105

104

95

88

88

84

84

37.2

36.7

37.0

36.0

35.6

35.0

34.4

33.3

34.4

35.6

36.7

38.3

39.4

41.7

42.2

42.8

44.4

43.3

43.9

43.3

42.8

41.7

40.6

40.0

35.0

31.0

31.1

29.0

28.9

70

69

70

70

70

70

70

69

69

69

70

71

71

71

71

71

72

72

71

70

71

70

70

70

72

72

72

74

73

21.1

20.5

21.1

20.8

21.2

21.3

20.8

20.5

20.3

20.7

21.2

21.7

21.8

21.7

21.8

21.8

22.4

22.1

21.6

21.3

21.3

21.0

21.1

21.2

22.3

22.1

22.1

23.5

22.8

54

52

54

54

56

57

56

56

54

54

55

55

54

51

51

50

51

51

48

47

48

48

50

51

61

64

64

70

68

12.2

11.1

12.0

12.0

13.3

13.9

13.3

13.3

12.2

12.2

12.8

12.8

12.2

10.6

10.6

10.0

10.6

10.6

8.9

8.3

8.9

8.9

10.0

10.6

16.0

18.0

17.8

21.0

20.0

22

21

22

24

26

28

28

30

26

24

24

22

20

15

15

14

13

14

12

12

13

14

16

17

32

45

45

63

59

6

7

5

13

11

6

5

0

0

0

3

5

3

3

0

7

9

8

11

9

10

8

5

3

23

21

10

15

16

340

330

350

080

060

100

120

000

000

000

090

060

080

VR 

000

340

210

290

290

290

230

240

220

VR 

150

170

160

170

210

18

18

22

33

36

31

23

31

28.60

28.61

28.61

28.60

28.60

28.58

28.59

28.60

28.61

28.63

28.64

28.64

28.63

28.61

28.58

28.56

28.53

28.50

28.48

28.45

28.47

28.47

28.49

28.53

28.57

28.57

28.59

28.59

28.61

1

5

3

8

8

6

5

3

009

006

015

001

024

025

004

042

29.70

29.70

M

M

29.69

29.68

29.68

29.70

29.71

29.73

29.74

29.74

29.73

29.70

29.67

29.65

29.62

29.59

29.57

29.55

29.56

29.57

29.59

29.62

M

M

29.70

M

29.72

AA

AA

SP

SP

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

SP

SP

AA

SP

AA

T

0.05

29.77

29.78

29.78

29.77

29.77

29.75

29.76

29.77

29.78

29.80

29.81

29.81

29.80

29.78

29.75

29.73

29.70

29.67

29.65

29.62

29.64

29.64

29.66

29.70

29.74

29.74

29.76

29.76

29.78

Figure A-1. Quality controlled local climatological data hourly observations table for Phoenix Sky Harbor International Airport, Phoenix, Arizona 

(08/14/2012). Note in the Weather Type column that BLDU (blowing dust) was reported around the time of the high PM10 concentrations. For a 

more detailed explanation of the weather codes shown in the table above, please see 

http://www.nws.noaa.gov/oso/oso1/oso12/document/guide.shtml. Data dynamically generated via 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

PHOENIX DEER VALLEY ARPT (03184)

PHOENIX, AZ (08/2012) 

National Climatic Data Center

Federal Building

151 Patton Avenue

Asheville, North Carolina 28801

Elevation: 1455 ft. above sea level

Latitude: 33.688

Longitude: -112.081

Data Version: VER2

Date Time

(LST)

Station

Type

Sky

Conditions

Visibility

(SM)

Weather

Type

Dry

Bulb

Temp

Wet

Bulb

Temp

Dew

Point

Temp

Rel

Humd

%

Wind

Speed

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb)

Sea

Level

Pressure

(in. hg)

Report

Type

Precip.

Total

(in)

Altimeter

(in. hg)

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

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

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

0053

0153

0253

0353

0453

0553

0653

0753

0853

0953

1053

1153

1253

1353

1453

1553

1653

1753

1853

1953

2028

2053

2153

2238

2253

2306

2308

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

CLR

CLR

CLR

CLR

CLR

CLR

CLR

SCT043

SCT045

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

10.00

10.00

10.00

10.00

10.00

10.00

10.00

3.00

3.00

10.00

TS

TS

VCTS -RA

-RA

95

94

95

95

95

92

91

93

96

99

102

105

106

107

108

109

108

108

107

105

102

103

102

99

98

93

93

86

35.0

34.4

35.0

35.0

35.0

33.3

32.8

33.9

35.6

37.2

38.9

40.6

41.1

41.7

42.2

42.8

42.2

42.2

41.7

40.6

39.0

39.4

38.9

37.0

36.7

34.0

34.0

30.0

69

68

68

68

68

67

67

68

69

69

70

70

70

71

71

71

71

70

69

70

70

70

69

69

69

71

72

72

20.4

20.0

19.7

19.9

19.7

19.2

19.3

19.9

20.4

20.6

21.1

21.3

21.2

21.6

21.5

21.7

21.5

21.3

20.8

21.3

21.1

21.0

20.6

20.6

20.4

21.4

22.0

22.1

54

53

51

52

51

51

52

53

53

52

52

51

50

51

50

50

50

49

47

51

52

51

50

52

52

59

61

65

12.2

11.7

10.6

11.1

10.6

10.6

11.1

11.7

11.7

11.1

11.1

10.6

10.0

10.6

10.0

10.0

10.0

9.4

8.3

10.6

11.0

10.6

10.0

11.0

11.1

15.0

16.0

18.3

25

25

22

23

22

25

26

26

23

21

19

16

15

15

14

14

14

14

13

16

19

18

17

21

21

32

34

50

9

5

10

9

0

0

3

0

0

5

3

7

6

6

8

11

9

7

9

10

7

0

6

18

20

26

26

14

010

030

040

090

000

000

010

000

000

160

200

250

230

VR 

250

220

280

240

250

220

230

000

070

030

060

130

130

160

20

25

28

33

33

24

28.25

28.26

28.23

28.21

28.23

28.24

28.25

28.27

28.28

28.27

28.27

28.24

28.22

28.20

28.17

28.15

28.12

28.10

28.11

28.12

28.13

28.14

28.17

28.18

28.18

28.20

28.20

28.25

1

5

3

8

8

8

5

1

010

011

013

000

023

027

002

024

29.72

29.72

29.70

29.68

29.69

29.70

29.71

29.73

29.74

29.74

29.73

29.71

29.68

29.66

29.63

29.60

29.57

29.56

29.56

29.57

M

29.60

29.63

M

29.65

M

M

29.72

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

SP

AA

AA

SP

AA

SP

SP

AA T

29.81

29.82

29.79

29.77

29.79

29.80

29.81

29.83

29.84

29.83

29.83

29.80

29.78

29.76

29.73

29.70

29.67

29.65

29.66

29.67

29.68

29.69

29.73

29.74

29.74

29.76

29.76

29.81

Figure A-2. Quality controlled local climatological data hourly observations table for Phoenix Deer Valley Airport, Phoenix, Arizona 

(08/14/2012). Note that visibilities were reduced with gusty winds after 2200 LST, coincident with high PM10 concentrations in the Phoenix area. 

Dynamically generated via http://cdo.ncdc.noaa.gov/qclcd/QCLCD.
4

U.S. Department of Commerce

National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL CLIMATOLOGICAL DATA (final)

WILLIAMS GATEWAY AIRPORT (23104), PHOENIX, AZ (08/2012) 

National Climatic Data Center

Federal Building

151 Patton Avenue

Asheville, North Carolina 28801

Elevation: 1382 ft. above sea level

Latitude: 33.3, Longitude: -111.666

Date Time

(LST)

Station

Type

Sky

Conditions

Visibility

(SM)

Weather

Type

Dry

Bulb

Temp

Wet

Bulb

Temp

Dew

Point

Temp

Rel

Humd

%

Wind

Speed

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb)

Sea

Level

Pressure

(in. hg)

Report

Type

Precip.

Total

(in)

Altimeter

(in. hg)

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

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

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

0015

0035

0055

0115

0135

0155

0215

0335

0355

0415

0435

0515

0547

0647

0747

0847

0947

1047

1147

1247

1347

1447

1547

1647

1747

1847

1947

1955

2015

2035

2047

2055

2115

2132

2135

2155

2215

2335

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

0

0

0

0

0

0

0

0

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

SCT120 BKN250

SCT120 BKN200

SCT120 BKN200

SCT120 BKN200

SCT150 BKN200

SCT150 BKN200

FEW150 SCT200

FEW120

FEW120

FEW120 FEW250

FEW120 FEW250

SCT120 SCT250

FEW120 SCT200

FEW120 BKN250

BKN

CLR

CLR

CLR

BKN

CLR

CLR

FEW002 BKN100

CLR

SCT001 SCT070 SCT110

CLR

CLR

10.00

10.00

10.00

10.00

10.00

10.00

10.00

7.00

10.00

10.00

10.00

10.00

20.00

30.00

30.00

30.00

30.00

30.00

30.00

30.00

30.00

30.00

30.00

30.00

30.00

20.00

20.00

10.00

10.00

10.00

20.00

10.00

10.00

0.75

4.00

3.00

3.00

10.00

DS

HZ

HZ

VCTSHZ

100

100

97

97

97

93

93

93

93

91

88

91

97

90

97

100

104

108

108

109

109

109

111

111

111

109

108

106

106

104

106

100

100

102

100

97

97

86

38.0

38.0

36.0

36.0

36.0

34.0

34.0

34.0

34.0

33.0

31.0

33.0

36.0

32.0

36.0

38.0

40.0

42.0

42.0

43.0

43.0

43.0

44.0

44.0

44.0

43.0

42.0

41.0

41.0

40.0

41.0

38.0

38.0

39.0

38.0

36.0

36.0

30.0

70

70

69

69

69

68

68

68

68

67

67

67

69

67

69

70

71

72

71

72

70

70

71

70

70

69

M

69

69

68

M

69

69

71

72

72

71

71

21.3

21.3

20.3

20.8

20.8

20.1

20.1

20.1

20.1

19.3

19.3

19.3

20.8

19.1

20.8

21.3

21.9

22.0

21.6

22.1

21.3

21.3

21.6

21.2

21.2

20.7

M

20.2

20.4

20.1

M

20.3

20.3

21.5

22.0

22.1

21.5

21.8

54

54

52

54

54

54

54

54

54

52

54

52

54

52

54

54

54

52

50

52

48

48

48

46

46

45

46

45

46

46

48

50

50

54

57

59

57

64

12.0

12.0

11.0

12.0

12.0

12.0

12.0

12.0

12.0

11.0

12.0

11.0

12.0

11.0

12.0

12.0

12.0

11.0

10.0

11.0

9.0

9.0

9.0

8.0

8.0

7.0

8.0

7.0

8.0

8.0

9.0

10.0

10.0

12.0

14.0

15.0

14.0

18.0

21

21

22

24

24

27

27

27

27

26

31

26

24

27

24

21

19

16

14

15

13

13

12

11

11

12

M

13

13

14

M

19

19

20

24

28

26

48

0

0

3

3

0

3

5

5

6

6

5

9

3

5

3

6

6

7

9

11

6

7

5

11

9

6

6

6

3

0

3

0

0

23

24

24

24

0s

000

000

240

240

000

100

090

060

060

110

110

120

110

100

170

100

100

250

200

270

220

230

260

330

290

280

260

270

260

000

280

000

000

150

150

170

180

000

33

33

32

28.37

28.37

28.37

28.36

28.36

28.36

28.36

28.36

28.35

28.34

28.34

28.34

28.35

28.36

28.38

28.39

28.40

28.38

28.36

28.34

28.32

28.29

28.26

28.23

28.22

28.23

M

28.25

28.25

28.25

M

28.26

28.27

28.31

28.31

28.34

28.34

28.40

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

M

M

M

M

M

M

M

M

M

M

M

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

29.83

29.83

29.83

29.82

29.82

29.82

29.82

29.82

29.81

29.80

29.80

29.80

29.81

29.82

29.84

29.85

29.86

29.84

29.82

29.80

29.78

29.75

29.72

29.69

29.68

29.69

29.69

29.70

29.70

29.71

29.71

29.72

29.73

29.77

29.77

29.80

29.80

29.86

Figure A-3. Quality controlled local climatological data hourly observations table for Williams Gateway Airport, Phoenix, Arizona (08/14/2012). 

Note in the Weather Type column that DS (dust) and HZ (haze) with reduced visibilities and gusty winds were reported between 2132 and 2215 

LST, coincident with high PM10 concentrations in the Phoenix area. 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 (08/2012) 

National Climatic Data Center

Federal Building

151 Patton Avenue

Asheville, North Carolina 28801

Elevation: 1085 ft. above sea level

Latitude: 33.55, Longitude: -112.366

Date Time

(LST)

Station

Type

Sky

Conditions

Visibility

(SM)

Weather

Type

Dry

Bulb

Temp

Wet

Bulb

Temp

Dew

Point

Temp

Rel

Humd

%

Wind

Speed

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb)

Sea

Level

Pressure

(in. hg)

Report

Type

Precip.

Total

(in)

Altimeter

(in. hg)

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

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

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

0034

0055

0103

0119

0137

0155

0255

0355

0455

0555

0655

0755

0855

0955

1055

1155

1255

1355

1455

1555

1655

1755

1855

1955

2055

2155

2255

2306

2323

2331

2337

2338

2347

2350

2355

2357

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

0

0

0

0

0

0

SCT150

BKN140

FEW090CB BKN140

FEW090CB BKN140

FEW007 SCT140 SCT180

CLR

CLR

BKN220

FEW150

FEW160

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

SCT170

FEW140

FEW006 BKN130

BKN130

BKN005 BKN130

BKN005

BKN005

BKN005

SCT005

SCT005

SCT005

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

10.00

10.00

10.00

10.00

10.00

10.00

10.00

10.00

10.00

0.50s

5.00

4.00

2.50

3.00

2.50

2.00

2.50

3.00

TS

-TSRA

BLDUs

HZ

HZ

HZ

HZ

HZ

HZ

VCTS HZ

VCTS HZ

97

98

99

99

97

97

96

95

92

92

90

97

100

103

105

106

108

109

110

112

111

111

109

105

101

101

101

100

95

95

93

93

91

91

91

90

36.0

36.8

37.0

37.0

36.0

36.3

35.7

35.0

33.5

33.1

32.2

35.9

37.5

39.5

40.4

41.3

42.3

42.9

43.5

44.2

44.1

43.8

42.7

40.7

38.6

38.3

38.5

38.0

35.0

35.0

34.0

34.0

33.0

33.0

32.5

32.0

71

70

70

71

70

70

70

69

69

69

69

71

72

72

72

72

73

73

73

73

72

71

72

72

71

71

70

72

73

73

73

73

73

73

73

73

21.6

21.2

21.1

21.4

20.8

20.8

20.9

20.7

20.8

20.8

20.7

21.8

22.3

22.0

22.1

22.0

22.5

22.6

22.8

22.8

22.3

21.6

22.2

22.0

21.7

21.7

21.2

22.0

22.9

22.9

22.9

22.9

22.6

22.6

22.9

22.5

57

55

54

55

54

54

55

55

57

57

58

58

58

55

54

53

54

54

54

53

51

48

52

54

55

55

53

57

63

63

64

64

64

64

65

64

14.0

12.8

12.0

13.0

12.0

12.3

12.6

12.6

13.8

14.1

14.7

14.4

14.2

13.0

12.2

11.5

12.0

12.3

12.0

11.5

10.4

8.7

11.3

12.4

13.0

12.7

11.6

14.0

17.0

17.0

18.0

18.0

18.0

18.0

18.2

18.0

26

24

22

23

24

24

25

26

31

31

34

27

25

20

18

17

17

16

16

14

14

12

15

18

22

22

20

24

35

35

38

38

41

41

42

42

14

16

13

15

20

14

10

7

6

0

7

0

5

3

0

8

10

11

0

11

9

9

10

8

8

8

8

29

24

31

25

28

34

33

32

30

030

010

360

010

350

030

040

040

310

000

350

000

050

150

000

160

220

190

000

210

250

230

230

210

230

260

010

120

120

130

130

130

140

140

140

140

24

28

39

30

43

43

43

41

41

41

41

28.62

28.62

28.61

28.62

28.61

28.61

28.61

28.61

28.61

28.63

28.64

28.66

28.66

28.66

28.65

28.63

28.60

28.58

28.55

28.52

28.50

28.47

28.48

28.49

28.51

28.54

28.57

28.57

28.59

28.60

28.60

28.60

28.62

28.62

28.63

28.63

8

3

3

8

8

6

5

3

001

002

015

003

023

027

003

025

29.67

29.67

M

29.67

29.66

29.66

29.66

29.66

29.67

29.68

29.69

29.71

29.72

29.72

29.71

29.69

29.66

29.63

29.60

29.57

29.55

29.53

29.54

29.55

29.57

29.59

29.62

29.62

29.65

29.66

29.66

29.66

29.67

29.68

29.69

29.69

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

T

T

T

T

29.77

29.77

29.76

29.77

29.76

29.76

29.76

29.76

29.76

29.78

29.79

29.81

29.81

29.81

29.80

29.78

29.75

29.73

29.70

29.67

29.65

29.62

29.63

29.64

29.66

29.69

29.72

29.72

29.74

29.75

29.75

29.75

29.77

29.77

29.78

29.78

Figure A-4. Quality controlled local climatological data hourly observations table for Luke Air Force Base, Glendale, Arizona (08/14/2012). Note 

in the Weather Type column that HZ (haze) and BLDU (blowing dust) with reduced visibilities and gusty winds were reported coincident with high 

PM10 concentrations in the Phoenix area. 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

(08/2012) 

National Climatic Data Center

Federal Building

151 Patton Avenue

Asheville, North Carolina 28801

Elevation: 1473 ft. above sea level

Latitude: 33.622

Longitude: -111.910

Data Version: VER2

Date Time

(LST)

Station

Type

Sky

Conditions

Visibility

(SM)

Weather

Type

Dry

Bulb

Temp

Wet

Bulb

Temp

Dew

Point

Temp

Rel

Humd

%

Wind

Speed

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb)

Sea

Level

Pressure

(in. hg)

Report

Type

Precip.

Total

(in)

Altimeter

(in. hg)

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

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

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

0053

0153

0253

0353

0453

0553

0653

0753

0853

0953

1053

1153

1253

1353

1453

1553

1653

1753

1853

1953

2053

2153

2237

2243

2253

2315

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

CLR

CLR

FEW065 SCT080 SCT100

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

SCT029

BKN027

BKN027

SCT027

FEW075 BKN100

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

10.00

10.00

10.00

10.00

2.50

3.00

4.00

8.00

10.00

-RA

VCTS HZ

VCTS HZ

VCTS HZ

96

96

90

94

92

91

92

94

97

100

103

105

106

108

111

109

109

109

107

105

103

102

95

93

94

91

88

35.6

35.6

32.2

34.4

33.3

32.8

33.3

34.4

36.1

37.8

39.4

40.6

41.1

42.2

43.9

42.8

42.8

42.8

41.7

40.6

39.4

38.9

35.0

34.0

34.4

33.0

31.1

70

69

74

70

70

70

69

70

69

70

70

70

70

71

72

71

70

71

71

70

69

69

71

71

71

72

71

20.9

20.6

23.4

21.3

21.3

20.8

20.5

20.8

20.5

21.0

21.0

21.3

21.2

21.5

22.0

21.7

21.3

21.7

21.4

21.1

20.5

20.4

21.7

21.4

21.9

22.3

21.5

55

54

67

58

59

58

56

56

53

53

51

51

50

50

50

50

48

50

50

50

49

49

59

59

60

63

62

12.8

12.2

19.4

14.4

15.0

14.4

13.3

13.3

11.7

11.7

10.6

10.6

10.0

10.0

10.0

10.0

8.9

10.0

10.0

10.0

9.4

9.4

15.0

15.0

15.6

17.0

16.7

25

24

47

30

33

33

30

28

23

21

18

16

15

14

13

14

13

14

15

16

16

17

30

32

32

39

42

7

6

13

3

0

0

0

0

0

3

3

6

6

5

3

7

7

7

7

7

6

11

14

5

15

9

11

010

030

050

070

000

000

000

000

000

VR 

180

200

VR 

250

VR 

230

260

250

220

240

080

060

170

VR 

190

130

130

17

29

29

22

20

22

28.24

28.23

28.25

28.20

28.21

28.22

28.23

28.26

28.27

28.26

28.25

28.23

28.20

28.18

28.16

28.12

28.10

28.08

28.08

28.10

28.13

28.15

28.21

28.22

28.23

28.24

28.24

0

8

3

8

8

6

5

3

000

009

017

002

023

026

001

044

29.73

29.72

29.74

29.69

29.70

29.71

29.72

29.75

29.76

29.75

29.74

29.72

29.70

29.67

29.65

29.62

29.59

29.57

29.57

29.59

29.62

29.64

M

M

29.73

M

29.73

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

SP

SP

AA

SP

AA

T

T

T

29.83

29.82

29.84

29.79

29.80

29.81

29.82

29.85

29.86

29.85

29.84

29.82

29.79

29.77

29.75

29.71

29.69

29.67

29.67

29.69

29.72

29.74

29.80

29.81

29.82

29.83

29.83

Figure A-5. Quality controlled local climatological data hourly observations table for Scottsdale Airport, Scottsdale, Arizona (08/14/2012). Note 

in the Weather Type column that HZ (haze) with reduced visibilities and gusty winds were reported coincident with high PM10 concentrations in 

the Phoenix area. 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

CASA GRANDE MUNICIPAL ARPT (03914)

CASA GRANDE, AZ

(08/2012) 

National Climatic Data Center

Federal Building

151 Patton Avenue

Asheville, North Carolina 28801

Elevation: 1462 ft. above sea level

Latitude: 32.95

Longitude: -111.766

Data Version: VER2

Date Time

(LST)

Station

Type

Sky

Conditions

Visibility

(SM)

Weather

Type

Dry

Bulb

Temp

Wet

Bulb

Temp

Dew

Point

Temp

Rel

Humd

%

Wind

Speed

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb)

Sea

Level

Pressure

(in. hg)

Report

Type

Precip.

Total

(in)

Altimeter

(in. hg)

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

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

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

0015

0035

0055

0115

0135

0155

0215

0235

0255

0315

0335

0355

0415

0435

0455

0515

0535

0555

0615

0635

0655

0715

0735

0755

0815

0835

0855

0915

0935

0955

1015

1035

1055

1115

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

0

0

0

0

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

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

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

93

93

93

91

91

91

91

91

90

91

91

91

91

90

90

88

88

86

84

84

84

86

88

90

91

93

93

97

99

100

100

100

102

102

34.0

34.0

34.0

33.0

33.0

33.0

33.0

33.0

32.0

33.0

33.0

33.0

33.0

32.0

32.0

31.0

31.0

30.0

29.0

29.0

29.0

30.0

31.0

32.0

33.0

34.0

34.0

36.0

37.0

38.0

38.0

38.0

39.0

39.0

68

68

68

68

68

68

68

68

67

67

67

67

67

66

66

66

66

65

65

65

65

66

67

67

68

68

68

69

70

71

71

71

71

71

20.1

20.1

20.1

19.8

19.8

19.8

19.8

19.8

19.6

19.3

19.3

19.3

19.3

19.1

19.1

18.8

18.8

18.4

18.0

18.0

18.6

18.9

19.5

19.6

19.8

20.1

20.1

20.8

21.1

21.5

21.5

21.5

21.5

21.8

54

54

54

54

54

54

54

54

54

52

52

52

52

52

52

52

52

52

52

52

54

54

55

54

54

54

54

54

54

55

55

55

54

55

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

11.0

11.0

11.0

11.0

11.0

11.0

11.0

11.0

11.0

11.0

11.0

12.0

12.0

13.0

12.0

12.0

12.0

12.0

12.0

12.0

13.0

13.0

13.0

12.0

13.0

27

27

27

29

29

29

29

29

29

26

26

26

26

27

27

29

29

31

33

33

36

33

33

29

29

27

27

24

22

22

22

22

20

21

8

6

7

7

5

7

9

8

7

8

10

8

9

8

8

7

3

7

5

6

0

3

3

0

7

9

5

9

7

8

8

13

9

3

040

040

350

010

350

360

360

010

360

040

040

020

040

040

060

070

060

260

250

230

000

170

160

000

080

110

140

120

140

140

150

210

180

220

28.28

28.28

28.28

28.27

28.27

28.27

28.27

28.27

28.27

28.27

28.25

28.27

28.27

28.25

28.25

28.25

28.27

28.27

28.27

28.28

28.28

28.29

28.30

28.30

28.30

28.30

28.30

28.30

28.30

28.30

28.30

28.30

28.29

28.29

2

7

2

7

007

007

017

003

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

M

M

M

M

M

M

M

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

29.83

29.83

29.83

29.82

29.82

29.82

29.82

29.81

29.81

29.81

29.80

29.81

29.81

29.80

29.80

29.80

29.81

29.82

29.82

29.83

29.83

29.84

29.85

29.85

29.85

29.85

29.85

29.85

29.85

29.85

29.85

29.85

29.84

29.84
14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

14

1135

1155

1215

1235

1255

1315

1335

1355

1415

1435

1455

1515

1535

1555

1615

1635

1655

1715

1735

1755

1815

1835

1855

1915

1935

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

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

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

CLR

SCT050 BKN070 BKN120

FEW030 BKN047 OVC120

SCT029 BKN048 OVC065

SCT021 BKN031 OVC110

FEW021 SCT040 BKN060

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

10.00

10.00

10.00

10.00

10.00

10.00

10.00

10.00

10.00

10.00

10.00

1.75

7.00

10.00

10.00

10.00

9.00

10.00

8.00

10.00

VCTS

TS

TS

TS

TS

TS

104

104

106

106

108

108

108

108

108

108

108

108

109

109

109

109

109

109

108

108

108

106

106

106

104

102

102

102

100

93

91

91

91

91

86

77

73

75

40.0

40.0

41.0

41.0

42.0

42.0

42.0

42.0

42.0

42.0

42.0

42.0

43.0

43.0

43.0

43.0

43.0

43.0

42.0

42.0

42.0

41.0

41.0

41.0

40.0

39.0

39.0

39.0

38.0

34.0

33.0

33.0

33.0

33.0

30.0

25.0

23.0

24.0

71

71

72

72

72

72

72

72

72

72

72

72

72

72

73

73

73

73

72

72

72

72

72

72

71

71

71

71

70

70

69

69

69

69

71

70

68

68

21.8

21.8

22.1

22.1

22.4

22.4

22.4

22.4

22.4

22.0

22.0

22.0

22.1

22.1

22.6

22.6

22.5

22.5

22.4

22.4

22.4

22.1

22.1

22.1

21.8

21.5

21.8

21.5

21.2

20.9

20.6

20.6

20.6

20.6

21.5

20.9

20.2

19.9

54

54

54

54

54

54

54

54

54

52

52

52

52

52

54

54

54

54

54

54

54

54

54

54

54

54

55

54

54

57

57

57

57

57

63

66

66

64

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

11.0

11.0

11.0

11.0

11.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

12.0

13.0

12.0

12.0

14.0

14.0

14.0

14.0

14.0

17.0

19.0

19.0

18.0

19

19

18

18

17

17

17

17

17

16

16

16

15

15

16

16

16

16

17

17

17

18

18

18

19

20

21

20

21

30

32

32

32

32

46

69

79

69

8

0

0

6

10

11

10

13

3

9

9

9

7

6

11

10

16

14

15

14

14

10

11

9

6

6

6

6

5

31s

29

23

18

24

28

21

17

18

230

000

000

260

270

260

300

220

330

320

300

290

320

240

270

260

260

260

250

250

250

260

260

260

250

280

250

250

210

150

160

160

140

130

130

140

240

220

16

20

20

21

20

22

20

18

40

36

29

30

32

28

24

24

28.28

28.27

28.27

28.25

28.25

28.25

28.25

28.24

28.23

28.22

28.21

28.20

28.19

28.18

28.18

28.17

28.15

28.15

28.14

28.14

28.15

28.15

28.16

28.16

28.16

28.16

28.17

28.18

28.20

28.23

28.24

28.25

28.28

28.27

28.28

28.32

28.30

28.31

7

7

2

2

020

030

003

044

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

M

M

M

M

M

M

M

M

M

M

M

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

AA

0.03

0.03

0.03

0.25

0.25

0.25

29.83

29.82

29.81

29.80

29.80

29.79

29.79

29.78

29.77

29.76

29.75

29.74

29.73

29.72

29.72

29.71

29.69

29.69

29.68

29.68

29.69

29.69

29.70

29.70

29.70

29.70

29.71

29.72

29.74

29.77

29.78

29.80

29.83

29.82

29.83

29.87

29.85

29.86

Figure A-6. Quality controlled local climatological data hourly observations table for Casa Grande Municipal Airport, Casa Grande, Arizona 

(08/14/2012). Note that reduced visibilities and gusty winds were reported coincident with high PM10 concentrations after 2100 LST in the Casa 

Grande area. Dynamically generated via http://cdo.ncdc.noaa.gov/qclcd/QCLCD.
Exceptional Event, Phoenix, August 14, 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_08142012.mp4

Estrella Mountains: www.phoenixvis.net/videos/mpeg4/ESMO_08142012.mp4

Camelback Mountains: www.phoenixvis.net/videos/mpeg4/CAME_08142012.mp4

Superstition Mountains: www.phoenixvis.net/videos/mpeg4/SUPM_08142012.mp4

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

some links to these videos.

Arizona Monsoon - August 14th, 2012

http://www.youtube.com/watch?v=Za4IL9iW65k

Arizona Thunder Storm 8/14/2012

http://www.youtube.com/watch?v=FFUe2A-rAtk
Exceptional Event, Phoenix, August 14, 2012 Appendix B

2

Articles and Image Links

http://www.azfamily.com/news/Photos-Overnight-storm-brings-rain-morning-haze-and-airportdelays-166277196.html (see video at link)

Photos: Overnight storm brings rain, morning haze and airport delays

By Mike Gertzman

Posted on August 15, 2012 at 10:00 AM

Azfamily.com

PHOENIX -- Monsoon storms rolled through the Valley overnight. The storms brought rain, 

thunder and plenty of lightning.

Parts of the Valley, from central Phoenix to Ahwatukee, got heavy rain. Enough rain fell in some 

areas to cause street flooding. More than 1.5 inches of rain fell in Maricopa, Ariz. The north side 

of the Valley, including Scottsdale and all the way to the northwest side of town, barely got any 

rain.

A power outage around 7th and Glendale Avenues was likely caused by the storm. That 

neighborhood was dark and the traffic lights were not working. More than 1,000 SRP customers 

were left without electricity. Utility crews went to work on the problem right away and the power

was quickly restored.

The most severe weather was seen in the town of Maricopa, Ariz. where lightning hit a house at 

about 3:00 a.m. and caused a fire.

Lightning sparks house fire in Maricopa

The streets were dry by morning, but the sunrise revealed a very hazy sky. Tower cameras and 

ADOT traffic cameras that normally show miles of visibility were only offering very limited views 

on Wednesday morning.

Visibility was so poor that there were flight delays at Sky Harbor Airport. Airport officials reported

delays of 10 to 20 minutes.

The air was so thick that it appeared to be filled with smoke, fog or smog. But 3TV meteorologist 

April Warnecke explained that it was actually dust suspended in the air because it was hanging 

on to all the moisture particles that came with the overnight rain.

Also, the Valley cooled off overnight creating an inversion that trapped all of that particulate 

pollution near the ground.

Temperatures around the Valley dropped into the 80's for the first time in several days. The 

National Weather Service has canceled the Excessive Heat Warning a day before it was set to 

expire.
Exceptional Event, Phoenix, August 14, 2012 Appendix B

3

With more moisture coming into the Valley this week, we could some much more monsoon 

storm activity over the next few days.

The forecast high for Wednesday is 106 degrees -- the first day in the past 10 days that the high 

will be below 110 degrees.

http://www.azfamily.com/news/Photos-Overnight-storm-brings-rain-morning-haze-and-airportdelays-166277196.html?gallery=y&img=0&c=y#/news/Photos-Overnight-storm-brings-rainmorning-haze-and-airport-delays-166277196.html?gallery=y&img=0&c=y

Selected pictures (more at link above):
Exceptional Event, Phoenix, August 14, 2012 Appendix C

1

Appendix C: Historical Fluctuation Time-Series Graphs

Figure C-1. 24-hr average PM10 concentrations at the Durango monitor (2007-2012). 

The 24-hr average PM10 concentration on August 14, 2012, is shown in red.
Exceptional Event, Phoenix, August 14, 2012 Appendix C

2

Figure C-2. Daily maximum hourly average PM10 concentrations at the Durango monitor 

(2007-2012). The maximum hourly average PM10 concentration on August 14, 2012, is 

shown in red.
Exceptional Event, Phoenix, August 14, 2012 Appendix D

D-1

Appendix D:

ADEQ and NWS Forecast Products
Exceptional Event, Phoenix, August 14, 2012 Appendix D

D-2

JRP 04/28/2011
Exceptional Event, Phoenix, August 14, 2012 Appendix D

D-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 Tuesday, August 14, 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

Sun 08/12/2012

Highest AQI Reading/Site

(*Preliminary data only*)

TODAY

Mon 08/13/2012

Ozone Health

Watch

Dust

TOMORROW

Tue 08/14/2012

Dust

EXTENDED

Wed 08/15/2012

Dust

O3* 101

North Phoenix

97

Moderate

71

Moderate

64

Moderate

CO* 7

West Phoenix

6

Good

6

Good

6

Good

PM-10* 59

Dysart

65

Moderate

65

Moderate

75

Moderate

PM-2.5* 44

West Phoenix

42

Good

44

Good

47

Good

* 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, August 14, 2012 Appendix D

D-4

Moderate

Moderate

Moderate

Moderate

Moderate

Moderate

Moderate

Moderate

Moderate

Moderate

Moderate

Moderate

Moderate

USG

Moderate

Health Statements

Monday, 08/13/2012 Unusually sensitive people should consider reducing prolonged or heavy 

exertion outdoors.

Tuesday, 08/14/2012 Unusually sensitive people should consider reducing prolonged or heavy 

exertion outdoors.

SYNOPSIS AND DISCUSSION

AN OZONE HEALTH WATCH REMAINS IN EFFECT UNTIL LATE THIS EVENING 

OZONE: Although another exceedance occurred on Sunday, the local ozone concentration

trend has started downward and this should continue for the next few days at least. The biggest 

factor causing this decrease will be the daytime surface winds which – due to the combination of

gradient and upslope flow – should become westerly for the foreseeable future with gusts over 20

mph possible by Tuesday. This situation helps to disperse the local ozone plume and lessens the 

potential for high concentrations over a large area. Still have to get thru today, however, and an 

Ozone Health Watch remains in effect.

PARTICLES: Although a low-grade summer monsoon period is forecast for the next few 

days, moisture will remain sufficient for a chance for showers and thunderstorms in proximity to 

the Phoenix metro area until a more significant return of moisture by Wednesday. As a result, the 

possibility for periods of dense blowing and transported dust generated by strong thunderstorm 

outflow boundary winds have resulted in a forecast for elevated PM-10 (coarse particle) 

concentrations – with potential for locally much higher readings depending on winds and volume

of dust. Otherwise, particle pollution levels will be low.

Check back tomorrow for the latest. Until then, have a good day! -C.Reith

MONITORING SITE MAPS

STATIC MAP http://www.azdeq.gov/environ/air/monitoring/images/map.jpg

INTERACTIVE MAPS

http://aqwww.maricopa.gov/AirMonitoring/SitePollutionMap.aspx

http://156.42.96.39/alert/Google/air.html

http://www.airnow.gov/

POLLUTION MONITOR READINGS FOR Sunday, August 12, 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 60 51

Apache Junction 61 54

Blue Point 63 61

Buckeye 62 58

Casa Grande 62 58

Cave Creek 62 58

Central Phoenix 68 77

Dysart 69 80

Falcon Field 61 54

Fountain Hills 60 51

Glendale 62 58

Humboldt Mountain 63 61

Phoenix Supersite 69 80

North Phoenix 76 101

Pinal Air Park 62 58
Exceptional Event, Phoenix, August 14, 2012 Appendix D

D-5

Moderate

Moderate

Good

Moderate

Moderate

Moderate

Moderate

Moderate

Moderate

Moderate

Good

Good

Good

Good

Moderate

Good

Good

Good

Moderate

Moderate

Good

Good

Good

Good

Good

Good

Good

Good

Good

Good

Moderate

Good

Good

Good

Good

Good

Good

Good

Good

Good

Good

Pinnacle Peak 70 84

Queen Valley 62 58

Rio Verde 59 50

South Phoenix 70 84

South Scottsdale 73 93

Tempe 64 64

Tonto Nat’l Mon. 61 54

West Chandler 62 58

West Phoenix 71 87

Yuma 63 61

CO (CARBON MONOXIDE)

SITE NAME MAX 8-HR VALUE (PPM) MAX AQI AQI COLOR CODE

Central Phoenix 0.3 3

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 41.9 39

Buckeye 61.9 54

Central Phoenix 48.7 44

Combs School (Pinal County) 49.3 46

Durango 40.7 37

Dysart 71.7 59

Glendale 65.7 56

Greenwood 44.5 41

Higley 45.5 41

Maricopa (Pinal County) 44.7 41

North Phoenix 53.3 49

Phoenix Supersite 50.3 46

South Phoenix 48.6 44

Tempe 45.1 41

West Chandler 45.4 41

West Forty Third 37.7 34

West Phoenix 48.3 44

Zuni Hills 71.2 59

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 10.2 33

Dysart 10.0 32

Estrella Mountain Park 6.7 22

Glendale 11.3 37

Phoenix Supersite 7.8 25

North Phoenix 11.5 37

South Phoenix 7.2 23

Tempe 9.0 29

Vehicle Emissions Lab 6.0 19

West Phoenix 13.5 44
Exceptional Event, Phoenix, August 14, 2012 Appendix D

6

Statements, Advisories, and Warnings issued by the National Weather Service office in 

Phoenix, AZ pertaining to this dust storm event:

SHORT TERM FORECAST

NATIONAL WEATHER SERVICE PHOENIX AZ

823 PM MST TUE AUG 14 2012

AZZ028-150500-

NORTHWEST AND NORTH CENTRAL PINAL COUNTYINCLUDING THE CITIES OF...APACHE JUNCTION...CASA GRANDE...COOLIDGE...

AND FLORENCE

823 PM MST TUE AUG 14 2012

.NOW...

GUSTY SOUTHEAST WINDS 20 TO 30 MPH WILL OVERSPREAD MUCH OF NORTHWEST

PINAL COUNTY THROUGH 10 PM. SOME BLOWING DUST WILL BE POSSIBLE.

LOCATIONS LIKELY TO EXPERIENCE GUSTY WINDS AND SOME BLOWING DUST

INCLUDE COOLIDGE...FLORENCE...AND CASA GRANDE. THERE WILL BE A SLIGHT

CHANCE FOR A THUNDERSTORM THIS EVENING.

SHORT TERM FORECAST

NATIONAL WEATHER SERVICE PHOENIX AZ

918 PM MST TUE AUG 14 2012

AZZ023-150700-

GREATER PHOENIX AREAINCLUDING THE CITIES OF...BUCKEYE...CAREFREE...CAVE CREEK...

CHANDLER...FOUNTAIN HILLS...GILBERT...GLENDALE...MESA...PEORIA...

PHOENIX...SCOTTSDALE...SUN CITY...AND TEMPE

918 PM MST TUE AUG 14 2012

.NOW...

SOUTHEAST WINDS 20 TO 30 MPH...WITH GUSTS TO 35 MPH...WILL OVERSPREAD

THE GREATER PHOENIX METROPOLITAN AREA THROUGH 11 PM. SOME BLOWING

DUST WILL LIKELY ACCOMPANY THE ONSET OF THE GUSTY WINDS...ESPECIALLY

OVER THE SOUTHEAST VALLEY BETWEEN 915 PM AND 945 PM...WHERE VISIBILITY

COULD BRIEFLY DROP BELOW 2 MILES. AN ISOLATED THUNDERSTORM WILL BE

POSSIBLE THROUGH MIDNIGHT.

$$

AZZ027-150700-

SOUTHWEST MARICOPA COUNTYINCLUDING THE CITY OF...GILA BEND

918 PM MST TUE AUG 14 2012

.NOW...

SOUTHEAST WINDS 15 TO 30 MPH...WITH GUSTS TO 35 MPH...WILL

OVERSPREAD MUCH OF SOUTHWEST MARICOPA COUNTY THROUGH 11 PM. SOME

BLOWING DUST WILL LIKELY ACCOMPANY THE ONSET OF THE GUSTY

WINDS...WITH VISIBILITY BRIEFLY DROPPING BELOW 2 MILES. AN ISOLATED

THUNDERSTORM WILL BE POSSIBLE THROUGH MIDNIGHT.
Exceptional Event, Phoenix, August 14, 2012 Appendix D

7

AZZ022-150700-

NORTHWEST MARICOPA COUNTYINCLUDING THE CITIES OF...BUCKEYE...LAKE PLEASANT...MORRISTOWN...

NEW RIVER...TONOPAH...AND WICKENBURG

918 PM MST TUE AUG 14 2012

.NOW...

SOUTHEAST WIND 15 TO 25 MPH...WITH GUSTS TO 30 MPH...WILL OVERSPREAD

NORTHWEST MARICOPA COUNTY BETWEEN 10 PM AND MIDNIGHT. SOME BLOWING

DUST WILL LIKELY ACCOMPANY THE ONSET OF GUSTY WINDS...WITH VISIBILITY

BRIEFLY DROPPING BELOW 2 MILES. AN ISOLATED THUNDERSTORM WILL BE

POSSIBLE THROUGH MIDNIGHT.

URGENT - WEATHER MESSAGE

NATIONAL WEATHER SERVICE PHOENIX AZ

941 PM MST TUE AUG 14 2012

AZZ023-150600-

/O.NEW.KPSR.DU.Y.0034.120815T0441Z-120815T0600Z/

/O.CON.KPSR.EH.W.0011.000000T0000Z-120816T0300Z/

GREATER PHOENIX AREAINCLUDING THE CITIES OF...BUCKEYE...MESA...PHOENIX

941 PM MST TUE AUG 14 2012

...BLOWING DUST ADVISORY IN EFFECT UNTIL 11 PM MST THIS

EVENING...

...EXCESSIVE HEAT WARNING REMAINS IN EFFECT UNTIL 8 PM MST

WEDNESDAY...

THE NATIONAL WEATHER SERVICE IN PHOENIX HAS ISSUED A BLOWING DUST

ADVISORY...WHICH IS IN EFFECT UNTIL 11 PM MST THIS EVENING. AN

EXCESSIVE HEAT WARNING REMAINS IN EFFECT UNTIL 8 PM MST

WEDNESDAY. 

* AFFECTED AREA...PHOENIX METROPOLITAN AREA...ESPECIALLY THE

 SOUTHEAST VALLEY.

* TIMING...UNTIL 11 PM. 

* WINDS...SOUTHEAST 20 TO 30 MPH...WITH GUSTS TO NEAR 40 MPH. 

* VISIBILITY...BELOW 1 MILE AT TIMES MAINLY SOUTHEAST VALLEY

* IMPACTS...SUDDENLY REDUCED VISIBILITIES ON ROADWAYS WILL CREATE

 DANGEROUS DRIVING CONDITIONS. MULTI-CAR PILEUPS ARE MORE LIKELY

 DURING BLOWING DUST EVENTS. 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

BE READY FOR A SUDDEN DROP IN VISIBILITY. IF YOU ENCOUNTER BLOWING

DUST 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.
Exceptional Event, Phoenix, August 14, 2012 Appendix E

1

Appendix E:

Affidavit of Public Notice