State of Arizona Exceptional Event Documentation for the 

Events of August 25th through August 28th 2011, for the 

Phoenix PM10 Nonattainment Area 

Produced by: 

Arizona Department of Environmental Quality 

Maricopa County Air Quality Department 

Maricopa Association of Governments 

Final Report 

January 23, 2013 
EXECUTIVE SUMMARY 

In 2005, Congress identified a need to account for events that result in exceedances of the National 

Ambient Air Quality Standards (NAAQS) that are exceptional in nature1 (e.g., not expected to reoccur or 

caused by acts of nature beyond man-made controls). In response, EPA promulgated the Exceptional 

Events Rule (EER) to address exceptional events in 40 CFR Parts 50 and 51 on March 22, 2007 (72 FR 

13560). On May 2, 2011, in an attempt to clarify this rule, EPA released draft guidance documents on the 

implementation of the EER to State, tribal and local air agencies for review. Based on numerous 

comments EPA received on the May 2011 draft, EPA issued a revised draft guidance document in June 

2012. The EER allows for states and tribes to “flag” air quality monitoring data as an exceptional event 

and exclude those data from use in determinations with respect to exceedances or violations of the 

NAAQS, if EPA concurs with the demonstration submitted by the flagging agency. 

Due to the arid nature of the state, Arizona is highly susceptible to windblown dust events. These events 

are often captured by various air quality monitoring equipment throughout the state, sometimes resulting 

in exceedances or violations of the PM10 NAAQS. In the past, the Arizona Department of 

Environmental Quality (ADEQ) has submitted exceptional event documentation for these events. Due in 

part to issues within the EER, obtaining concurrence on these events has been a difficult task. The ADEQ 

is now taking a new approach and focusing exceptional event documentation on events that are believed 

to be clear-cut exceptional events that are not controllable by human intervention, such as the dust events 

which frequently occurred during the monsoon season of 2011. This new approach was used for the 

exceptional event demonstration submitted in March 2012 by the ADEQ for several PM10 events which 

occurred from July 2 – July 8, 2011, in the Phoenix region. In September 2012, EPA concurred that the 

July 2–8, 2011 events were indeed exceptional. As a result, this document is designed to follow the 

format used in the July 2–8, 2011 events submission. 

This demonstration contains detailed information about the windblown dust events that affected the 

Phoenix PM10 nonattainment area during the period August 25 – August 28, 2011. During this time 

period, 25 exceedances of the PM10 NAAQS occurred within the nonattainment area. Additional 

exceedances occurred outside of the Phoenix PM10 nonattainment area during this time period and 

additional documentation may be submitted as a separate package at a later time. ADEQ contends that 

the exceedances that were measured during August 25-28, 2011, within the Phoenix PM10 nonattainment 

area were the result of natural events that were not reasonably controllable or preventable. This 

assessment report of the August 25-28, 2011 dust events was a collaborative effort involving staff from 

the Arizona Department of Environmental Quality, Maricopa Association of Governments, Maricopa 

County Air Quality Department, and Pinal County Air Quality Control District. 

 

Section I of this assessment provides a summary of the exceptional event rules and requirements and lays 

out how those rules are met within this specific assessment. 

Section II of this assessment introduces the conceptual model of the thunderstorm events that transpired 

during August 25–28, 2011, providing a background narrative of the exceptional events. 

Section III of this assessment provides data summaries and time series graphs which help illustrate that 

the events of August 25–28, 2011, produced PM10 concentrations in excess of normal historical 

fluctuations. 

 

1

 Section 319 of the Clear Air Act (CAA), as amended by section 6013 of the Safe Accountable Flexible EfficientTransportation Equity Act: A Legacy for Users (SAFE-TEA-LU of 2005, required EPA to propose the Federal Exceptional 

Events Rule (EER) no later than March 1, 2006. 

ii
Section IV of this assessment details the existing area control measures and demonstrates that despite the 

presence and enforcement of these controls, the events of August 25–28, 2011, were not reasonably 

controllable or preventable. 

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

August 25–28, 2011, and the exceedances of the 24-hour PM10 standard at the monitoring stations. The 

evidence in this section (and the previous section on historical fluctuations) also confirms that the events 

in question both affected air quality and were the result of natural events. 

Section VI of this assessment builds upon the demonstration showing a clear causal connection between 

the natural event and the exceedances and concludes there would have been no exceedances during 

August 25–28, 2011, but for the presence of the natural events. 

Section VII contains conclusions that summarize the exceptional events that occurred during the week of 

August 25–28, 2011, and relates the requirements in the EER to the information within this document. 

iii
Table of Contents 

I. EXCEPTIONAL EVENT RULE (EER) REQUIREMENTS.....................................1

Procedural Requirements ..................................................................................................................1

Public notification that event was occurring (40 CFR 50.14(c)(1(i)) ..................................................1

Place informational flag on data in AQS (40 CFR 50.14(c)(2)(ii)) .....................................................1

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))....................................................................................1

Document that the public comment process was followed for event documentation (40 CFR 

50.14(c)(3)(iv)).....................................................................................................................................2

Submit demonstration supporting exceptional event flag (40 CFR 50.14(a)(1-2))..............................2

Documentation Requirements...........................................................................................................3

II. CONCEPTUAL MODEL..............................................................................................4

Geographic Setting and Climate .......................................................................................................4

Geographic Setting of Monitors ...........................................................................................................4

Climate .................................................................................................................................................7

Monsoon Season Description and Brief Event Summaries ............................................................8

Conclusions .......................................................................................................................................10

III. HISTORICAL FLUCTUATIONS............................................................................18

Regulatory Measures and Control Programs................................................................................22

PM10 Rule Effectiveness..................................................................................................................25

Compliance and Enforcement Activities ........................................................................................26

Conclusions .......................................................................................................................................28

V. CLEAR CAUSAL RELATIONSHIP.........................................................................29

Introduction ......................................................................................................................................29

Event #1 – August 25, 2011:.............................................................................................................29

Event #2 – August 26, 2011:.............................................................................................................38

Event #3 – August 27-28, 2011: .......................................................................................................47

Visibility Cameras ............................................................................................................................63

Conclusion.........................................................................................................................................63

VI. “BUT FOR” ANALYSIS ...........................................................................................64

VII. CONCLUSIONS .......................................................................................................65

Affects Air Quality ...........................................................................................................................65

Not Reasonably Controllable or Preventable ................................................................................65

Natural Event....................................................................................................................................65

Summary ...........................................................................................................................................65

iv
 List of Figures 

Figure 2‐1. Phoenix Geographic Setting and PM10 Monitor Locations (source: EPA AQS DataMart, NASA MODIS Satellite,

Google Earth).  PM10 monitor locations are indicated by the white markers..................................................................... 5

Figure 2‐2.  Drainage System of Phoenix, Arizona. ........................................................................................................................ 6

Figure 2‐3. Phoenix Monthly Precipitation (top) and Maximum Temperature (bottom) Climatology (source: National Weather

Service) ................................................................................................................................................................................. 7

Figure 2‐4. Cross‐section of a thunderstorm creating an outflow boundary and haboob (Source: Desert Meteorology. Thomas

T. Warner. 2004.).................................................................................................................................................................. 9

Figure 2‐5. U.S. Drought Monitor analysis released during the time period of the exceedances described in this report......... 11

Figure 2‐6. Timeline of PM10 concentrations at monitors throughout the Phoenix Metro area during the period of August 25‐

28, 2011 .............................................................................................................................................................................. 12

Figure 3‐1.  Plot of daily hourly maximum PM10 concentrations (2007 – 2011) at the Central Phoenix monitoring site. ......... 18

Figure 3‐2.  Plot of 24‐hour average PM10 concentrations (2007 – 2011) at the Central Phoenix monitoring site.................... 19

Figure 3‐3.  Plot of daily hourly maximum PM10 concentrations (2007 – 2011) at the Higley monitoring site.......................... 20

Figure 3‐4.  Plot of 24‐hour average PM10 concentrations (2007 – 2011) at the Higley monitoring site. .................................. 21

Figure 4‐1.  Timeline of Maricopa County Fugitive Dust Rules and Ordinances. ......................................................................... 26

Figure 5‐1. Satellite imagery showing strong storms developing and dissipating over northern Mexico. These storms are

believed to have been responsible for the thunderstorm outflow boundary that caused PM10 exceedances throughout

Maricopa and Pinal counties on August 25. ....................................................................................................................... 30

Figure 5‐3. Phoenix nonattainment area PM10 monitor readings and Sky Harbor visibility and wind speed for August 25, 2011.

............................................................................................................................................................................................ 31

Figure 5‐2. Pinal County PM10 monitor readings and Casa Grande visibility and wind speed for August 25, 2011. .................. 32

Figure 5‐4. Satellite imagery showing strong storms developing and dissipating over southwestern Arizona. These storms are

believed to have been responsible for the thunderstorm outflow boundary that caused PM10 exceedances in the

eastern portion of the Phoenix PM10 nonattainment area and in Pinal County on August 26......................................... 38

Figure 5‐5. Phoenix nonattainment area PM10 monitor readings and Mesa Williams visibility and wind speed for August 26,

2011.................................................................................................................................................................................... 40

Figure 5‐6. Pinal County PM10 monitor readings and Casa Grande visibility and wind speed for August 26, 2011. .................. 41

Figure 5‐7. Satellite imagery showing strong storms developing and dissipating over south‐southwestern Arizona. These

storms are believed to have been responsible for the thunderstorm outflow boundary that caused PM10 exceedances

across the Phoenix PM10 nonattainment area and in Pinal County on August 27‐28....................................................... 47

Figure 5‐8.  Phoenix nonattainment area PM10 monitor readings and Sky Harbor visibility and wind speed for August 27,

2011.................................................................................................................................................................................... 49

Figure 5‐9.  Pinal County PM10 monitor readings and Casa Grande visibility and wind speed for August 27, 2011. ................. 50

Figure 5‐10.  Phoenix nonattainment area PM10 monitor readings and Mesa Williams visibility and wind speed for August 28,

2011.................................................................................................................................................................................... 51

Figure 5‐11.  Pinal County PM10 monitor readings and Casa Grande visibility and wind speed for August 28, 2011. ............... 52

v
List of Tables 

Table 2‐1.  Summary of Statewide PM10 Measurements for August 25, 2011........................................................................... 13

Table 2‐2.  Summary of Statewide Air Quality Measurements for August 26, 2011. .................................................................. 15

Table 2‐3.  Summary of Statewide Air Quality Measurements for August 27, 2011. .................................................................. 16

Table 2‐4.  Summary of Statewide Air Quality Measurements for August 28, 2011. .................................................................. 17

Table 4‐1.  Rules and Ordinances Regulating Particulate Matter Emissions in Maricopa County ............................................... 23

Table 4‐2. Pinal County Rules Regulating Existing and New Non‐point Sources in Pinal County................................................. 24

Table 4‐3. Pinal County Rules Regulating Fugitive Dust in Pinal County Portion of MC PM10 NAA............................................ 24

vi
vii

List of Appendices 

Appendix A – 5-year Historical Fluctuation Graphs for the Phoenix Nonattainment Area PM10 Sites 

Appendix B – ADEQ Forecast Products for Phoenix, Maricopa County, and Pinal County 

Appendix C – Notice of Public Comment Period 

Appendix D – National Weather Service Forecasts, Warnings, and Alerts 
I. EXCEPTIONAL EVENT RULE (EER) REQUIREMENTS 

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

be met in order for EPA to concur with the flagged air quality monitoring data. This section of the report 

lays out the requirements of the EER and associated guidance, and discusses how the Arizona Department 

of Environmental Quality (ADEQ) addressed those requirements. 

Procedural Requirements 

This section presents a review of the procedural requirements of the EER as required by 40 CFR 50.14 

(Treatment of Air Quality Monitoring Data Influenced by Exceptional Events) and explains how ADEQ 

fulfills them. The Federal EER requirements include notifying the public that an event was occurring, 

placing informational flags on data in EPA’s Air Quality System (AQS), notifying EPA of the intent to 

flag through submission of initial event description, documenting that the public comment process was 

followed, and submitting a demonstration supporting the exceptional events flag. ADEQ has addressed 

all of these procedural and documentation requirements. 

Public notification that event was occurring (40 CFR 50.14(c)(1(i)) 

ADEQ issued Dust Control Action Forecasts and Ensemble Forecasts for the Greater Phoenix area 

advising citizens of the potential for high wind / dust events every day during the period of August 25 – 

August 28, 2011. More information on ADEQ’s forecasting program can be found in Section IV. The 

forecast products that were issued during the period August 24 – 28, 2011, are included in Appendix B. 

Place informational flag on data in AQS (40 CFR 50.14(c)(2)(ii)) 

ADEQ and other operating agencies in Arizona submit data into EPA’s AQS. Data from both filter-based 

and continuous monitors operated in Arizona are submitted to AQS. 

When ADEQ and/or another agency operating monitors in Arizona suspects 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 the operating agency have determined a potential exists that the monitor reading has been 

influenced by an exceptional event, a preliminary flag is submitted for the measurement in the 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 can be confirmed in AQS. 

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 2011 that ADEQ 

intended to analyze under the Exceptional Events Rule and notifying the EPA of which PM10 data were 

flagged in AQS. Exceedances that occurred on August 25, 26, 27, and 28, 2011, within the Phoenix 

PM10 nonattainment area were included on that list. This report serves as the demonstration supporting 

the flagging of these data. 

1
On August 25, 2011, 13 monitors at 12 sites within the boundaries of the Phoenix PM10 nonattainment 

area exceeded the 24-hour PM10 standard during the high wind event that occurred very early in the 

morning. The PM10 monitors impacted were the JLG Supersite TEOM2

 and BAM3 operated by ADEQ 

and the Buckeye, Central Phoenix, Durango Complex, Dysart, Glendale, Greenwood, South Phoenix, 

West Chandler, West 43rd, West Phoenix, and Zuni Hills monitors operated by Maricopa County Air 

Quality Department (MCAQD). 

On August 26, 2011, one monitor—the Apache Junction monitor located in Pinal County and operated by 

Pinal County Air Quality Control District (PCAQCD), but within the boundaries of the Phoenix PM10 

nonattainment area—exceeded the 24-hour PM10 standard during the high wind event that occurred 

during the afternoon/evening hours. 

On August 27, 2011, nine monitors within the boundaries of the Phoenix PM10 nonattainment area 

exceeded the 24-hour PM10 standard during the high wind event that occurred late at night. The monitors 

impacted were the Buckeye, Central Phoenix, Durango Complex, Glendale, Greenwood, South Phoenix, 

West Chandler, West 43rd, and West Phoenix monitors operated by MCAQD. 

On August 28, 2011, two monitors within the boundaries of the Phoenix PM10 nonattainment area 

exceeded the 24-hour PM10 standard during the high wind event that occurred very early in the morning. 

The monitors impacted were the Higley monitor in Maricopa County and operated by MCAQD and the 

Apache Junction monitor in Pinal County, but within the Phoenix PM10 nonattainment area, and operated 

by the PCAQCD. 

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 hardcopy of the report in the 

ADEQ Records Management Center for public review. ADEQ opened a 30-day public comment period 

on December 3, 2012. A copy of the public notice certification, along with any comments received, will 

be submitted to EPA, consistent with the requirements of 40 CFR 50.14(c)(3)(iv). See Appendix D for a 

copy of the affidavit of public notice. 

Submit demonstration supporting exceptional event flag (40 CFR 50.14(a)(1-2)) 

At the close of the 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 IX headquarters in San Francisco, California. The deadline 

for the submittal of this demonstration package is September 30, 2014. 

 

2

 TEOM is an acronym for a Tapered Element Oscillating Monitoring system. 

3

 BAM is an acronym for a Beta Attenuation Monitoring System.

2
Documentation Requirements 

Section 50.14(c)(3)(iii) of the EER states that in order to justify excluding air quality monitoring data, 

evidence must be provided for the following elements: 

a. The event satisfies the criteria set forth in 40 CFR 501(j) that: 

(1) the event affected air quality, 

(2) the event was not reasonably controllable or preventable, and 

(3) the event was caused by human activity unlikely to recur in a particular location or was a 

natural event; 

b. There is a clear causal relationship between the measurement under consideration and the event; 

c. The event is associated with a measured concentration in excess of normal historical fluctuations; 

and 

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

Section II of this assessment introduces the conceptual model of the thunderstorm events that transpired 

during August 25-28, 2011, providing a background narrative of the exceptional events and an overall 

explanation that “the event affected air quality.” Further evidence that ‘the event affected air quality’ is 

provided in Section V. Sections II and V also provide evidence that the event was a natural event. 

Section IV of this assessment details the existing area control measures and demonstrates that despite the 

presence and enforcement of these controls, the events of August 25-28, 2011 were not reasonably 

controllable or preventable. 

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

August 25-28, 2011 and the exceedances of the 24-hour PM10 standard at the monitoring stations. The 

evidence in this section (and the previous section on historical fluctuations) also confirms that the events 

in question both affected air quality and were the result of natural events. 

Section III of this assessment provides data summaries and time series graphs that help illustrate that the 

events of August 25-28, 2011 produced PM10 concentrations in excess of normal historical fluctuations. 

Section VI of this assessment builds upon the demonstration showing a clear causal connection between 

the natural event and the exceedances and concludes there would have been no exceedances during 

August 25-28, 2011, but for the presence of the natural events. 

3
II. CONCEPTUAL MODEL 

Geographic Setting and Climate

 

This section describes the geographic and climatic setting of the monitors. 

Geographic Setting of Monitors 

Phoenix is located in the Salt River Valley in south-central Arizona. It lies at a mean 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 msl) to the northeast, the foothills of the Bradshaw (~7,900 ft msl) and 

Mazataal (~7,900 ft msl) ranges to the north, the White Tank Mountains (~4,500 ft msl) to the west, the 

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

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

Current development is pushing north, west, and south into Pinal County. The Phoenix metropolitan area 

contains a fairly dense network of PM10 monitors throughout the area, with a much less dense network of 

monitors located throughout the rest of the state. Figure 2-1 shows the general geographic setting of 

Phoenix, as well as the locations of PM10 monitors throughout the state. It should be noted that some of 

the monitors shown in Figure 2-1 are filter-based monitors; therefore, monitoring data from all locations 

may be available only for select days (i.e., 1-in-6 run days). 

4
Figure 2-1. Phoenix Geographic Setting and PM10 Monitor Locations (source: EPA AQS DataMart, 

NASA MODIS Satellite, Google Earth). PM10 monitor locations are indicated by the white markers.

Figure 2-2 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. 

5
Figure 2-2. Drainage System of Phoenix, Arizona. 

6
Climate 

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

temperature is among the hottest of any populated area in the United States. The temperature reaches or 

exceeds 100oF an average of 110 days during the year and highs top 110oF an average of 18 days during 

the year. Phoenix receives an average of 7.66 inches of rain per year. 

Precipitation is sparse during the first part of the summer, but the influx of monsoonal moisture, which 

generally begins in early July and lasts until mid-September, raises humidity levels and can cause heavy 

localized precipitation and flooding. Although thunderstorms are possible at any time of the year, they 

are most common during the monsoon season from July to mid-September as humid air is advected from 

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

Occidental Mountains in Mexico. This influx in moisture, combined with intense solar heating, often 

creates a very unstable environment that is ripe for thunderstorm development. These thunderstorms can 

bring strong winds and blowing dust, large hail, and heavy rain. Dust storms associated with these 

thunderstorms typically occur in the early part of the monsoon season (July/August) before soaking rains 

help keep soil particles bound to one another. However, depending on the amount of precipitation 

received during the monsoon season, extremely hot temperatures act to dry out the surface quickly, and 

dust storms can occur at any time. During the December through March period, winter storms moving 

inland from the Pacific Ocean can produce significant rains throughout Arizona. This December–March 

time period, and July–August time period are typically the wettest parts of the year. Meanwhile, a distinct 

dry season occurs during the period April through June for Phoenix and the rest of Arizona. While these 

weather patterns describe the general climatology for the Phoenix area over a long period of time, 

Phoenix and the entire state of Arizona are also prone to a high degree of variability in these weather 

patterns from year to year. 

Figure 2-3. Phoenix Monthly Precipitation (top) and Maximum Temperature (bottom) Climatology 

(source: National Weather Service)

7
Monsoon Season Description and Event Summaries

The week of August 25-28, 2011, was characterized by frequent monsoonal thunderstorm activity 

throughout Arizona. The North American Monsoon is a shift in wind patterns in the summer which 

occurs as Mexico and the southwest U.S. warm under intense solar heating. As this happens, low level 

moisture is transported primarily from the Gulf of California and eastern Pacific Ocean into the southwestern U.S. The Gulf of California, a narrow body of water surrounded by mountains, is particularly 

important for low-level moisture transport into Arizona and Sonora. Mid and upper level moisture is also 

transported into the region, mainly from the Gulf of Mexico by easterly winds aloft. This combination 

causes a distinct rainy season over large portions of western North America, which develops rather 

quickly and sometimes dramatically. Rainfall during the monsoon is not continuous and varies considerably, depending on a variety of factors. There are usually distinct “burst” periods of heavy rain during the 

monsoon, and “break” periods with little or no rain. Even during active monsoon periods, some areas can 

go without receiving any significant precipitation while other nearby areas experience heavy rains and 

flooding.

The thunderstorm activity in Arizona during the period of August 25-28 was active in and around the 

desert areas of southern Arizona and northern Mexico. These thunderstorms did not result in much 

precipitation for the Phoenix area, but many of the storms were severe in nature and caused numerous 

significant dust-carrying outflow boundaries that propagated into the Phoenix area. Downdrafts 

associated with heavy precipitation from thunderstorms or from collapsing thunderstorms can end up 

producing what are called downbursts, or sometimes more concentrated and severe microbursts, which 

are rapidly descending bursts of air that come through the thunderstorms. These downward bursts of air 

hit the ground and then disperse away from the storms as areas of outflow. These outflow boundaries 

from the thunderstorms can kick up large areas of dust, sometimes called haboobs, and transport that dust 

for long distances from the initiating thunderstorms (see Figure 2-4). 

The active monsoon period of August 25-28 led to numerous thunderstorms and thunderstorm outflows 

that produced blowing dust in many parts of Arizona, including the Phoenix Metropolitan area. A total of 

three separate windblown dust events produced 25 PM10 exceedances in the Phoenix PM10 

nonattainment area during the four day span. The events were primarily driven by outflows from large 

areas of multiple thunderstorms producing wind gusts from one prominent direction. Dates experiencing 

PM10 exceedances in Maricopa County during this time included August 25, 26, 27, and 28. Two 

exceedances in Pinal County at the Apache Junction monitoring site on August 26 and 28 were also 

included in the documentation because this monitor is located within the eastern boundary of the Phoenix 

PM10 nonattainment area. The August 25th and August 27th-28th events were large-scale and widespread 

dust events with mostly south-southeasterly and westerly winds, respectively, transporting dust into the 

region. The event occurring on August 26 was smaller in scale, but was still related to thunderstorm 

activity over southwestern Arizona producing southwesterly outflow boundary winds across Maricopa 

and Pinal Counties and leading to PM10 exceedances at two sites on the eastern side of the Phoenix 

PM10 nonattainment area. Further details on the events can be found in Section V. 

8
Figure 2-4. Cross-section of a thunderstorm creating an outflow boundary and haboob (Source: Desert 

Meteorology. Thomas T. Warner. 2004.)

The nature of these monsoonal dust events is such that specific source areas are difficult to determine, as 

outflow from thunderstorms can carry dust over vast distances encompassing many source areas. Because 

of this, it is more appropriate to speak of general source regions for these monsoonal dust storms, which 

typically are identified based upon the locations of the thunderstorms that are believed to have created the 

dust generating and carrying outflow winds. A vast majority of the PM10 impacting the Phoenix area 

from thunderstorm-driven high wind events during the period of August 25-28 originated outside of the 

Phoenix PM10 nonattainment area. The contributing source regions to the dust events were somewhat 

widespread, but the majority of the PM that was transported into Maricopa County likely came from areas 

within Pinal County to the south and southeast of Maricopa County. Other potential source contributors 

to the PM10 events were areas in northern Pima County and southeastern and southern Maricopa County. 

The exact origin of the PM sources is often difficult to determine due to the holes in the spatial coverage 

of radar data and less dense monitoring networks in the general source area. 

Another important factor that led to these significant dust storms was the on-going drought across the 

region. The most recent U.S. Drought Monitor placed the area between Tucson and Phoenix in D1 

(Moderate) to D3 (Extreme) drought (see Figure 2-5). Rainfall since the end of the summer of 2010 

leading up to the August 25-28 dust events had been 52% of normal (see the Drought Information 

Statement in Appendix D). In areas to the south of Phoenix, the most common dust source region, rainfall 

during the 2011 summer monsoon season (June 15 – August 25) was only 11% of normal in the city of 

Maricopa. For additional information pertaining to the 2011 monsoon season in Arizona, a couple news 

media web links are included below. 

9
10

2011 Monsoon Season Summary and Review  http://bcove.me/krh3qk29

This video contains information about the monsoon season, the formation of dust storms in 

Arizona, and the uniqueness of the 2011 monsoon season. 

2011 Monsoon Season Review 2  http://bcove.me/tc6otk0h

This video contains information about the 2011 monsoon season, focusing on the large 

number of dust storms that occurred, and a discussion of why there were so many dust 

storms in 2011. 

The abnormally dry conditions that were in place during the early part of the monsoon season (which 

persisted throughout the duration of the monsoon season) resulted in a large fetch of soils that were 

vulnerable to particulate suspension. The repeated thunderstorm outflow boundaries that affected 

Maricopa and Pinal counties during the August 25-28 period resulted in very little rainfall throughout 

south-central Arizona, but the high winds associated with the outflows did bring an almost daily 

occurrence of moderate to extremely high levels of particulate concentrations in the ambient air. A 

timeline summarizing these events can be seen in Figure 2-6. This figure shows hourly PM10 

concentrations during the 24 hours prior to the first event, indicating very low PM10 concentrations 

across the Phoenix region prior to the arrival of the thunderstorm outflows; PM10 concentrations during 

the three events periods analyzed in this document; and the 24 hours after the events, once again showing 

that without the impacts of the thunderstorm outflows, PM10 concentrations at all sites in the Phoenix 

PM10 nonattainment area during the August 25-28, 2011 time period would have been well below the 24-

hour average PM10 exceedance threshold of 150 μg/m3

. 

Following Figure 2-6 are a series of tables detailing the PM10 24-hour average concentrations, the daily 

maximum hourly concentrations and the time at which they occurred, and the flag given to the data in 

EPA’s AQS for all PM10 monitoring sites in Arizona and for each day during the four-day event period. 

Conclusions

This Conceptual Model was created to provide a basic description of the general climate and weather 

patterns that led to the active thunderstorm period from August 25-28 and produced frequent dust storms 

and 25 PM10 exceedances in the Phoenix PM10 nonattainment area during the four-day episode. A more 

detailed analysis of each windblown dust event is included in Section V, where a demonstration of the 

clear causal connection between the uncontrollable natural events and PM10 exceedances is presented. 

 
Figure 2-5. U.S. Drought Monitor analysis released during the time period of the exceedances described in this r

11
Timeline of Windblown Dust Events for August 25, 2011 - August 28, 2

Figure 2-6. Timeline of PM10 concentrations at monitors throughout the Phoenix Metro area during the period o

12
August 25, 2011 

Table 2-1. Summary of Statewide PM10 Measurements for August 25, 2011. 

Monitor Monitor 

Type Operator AQS Monitor ID 

24-hr Avg 

PM10 

(μg/m3

) 

1-hr Max 

PM10

(μg/m3) 

Max Time

AQS 

Qualifier 

Flag 

Apache County 

 N/A TEOM WMAT 04-001-1003-81102-1 10 27 1300 

Cochise County 

 Douglas Red Cross FRM ADEQ 04-003-1005-81102-1 16 N/A N/A 

 Paul Spur Chemical 

Lime Plant FRM ADEQ 04-003-0011-81102-1 9 N/A N/A 

 Paul Spur Chemical 

Lime Plant FRM ADEQ 04-003-0011-81102-2 9 N/A N/A 

Coconino County 

 Flagstaff Middle School FRM ADEQ 04-005-1008-81102-1 11 N/A N/A 

 N/A TEOM NN 04-005-1237-81102-1 17 46 0800 

Gila County 

 Hayden Old Jail TEOM ADEQ 04-007-1001-81102-3 23 62 0000 

 Payson Well Site FRM ADEQ 04-007-0008-81102-1 7 N/A N/A 

 Payson Well Site FRM ADEQ 04-007-0008-81102-2 8 N/A N/A 

 Miami Ridgeline FEM FMMI 04-007-0009-81102-1 12 N/A N/A IT 

 Miami Golf Course FEM FMMI 04-007-8000-81102-1 16 N/A N/A IT 

 Miami Golf Course FEM FMMI 04-007-8000-81102-2 17 N/A N/A IT 

Maricopa County 

 Buckeye TEOM MC 04-013-4011-81102-1 235 943 0300 RJ 

 Central Phoenix TEOM MC 04-013-3002-81102-4 308 2822 0200 RJ 

 Durango Complex TEOM MC 04-013-9812-81102-1 436 4240 0200 RJ 

 Dysart TEOM MC 04-013-4010-81102-1 273 2057 0300 RJ 

 Fort McDowell/Yuma 

Frank TEOM FMIR 04-013-5100-8112-1 20 N/A N/A 

 Glendale TEOM MC 04-013-2001-81102-1 240 2477 0200 RJ 

 Greenwood TEOM MC 04-013-3010-81102-1 388 4104 0200 RJ 

 High School Air 

Monitoring Station FRM SRP-MIC 04-013-7024-81102-1 90 N/A N/A 

 Higley TEOM MC 04-013-4006-81102-1 131 379 0700 

 JLG Supersite BAM ADEQ 04-013-9997-81102-3 173 985 0200 RJ, EH 

 JLG Supersite TEOM ADEQ 04-013-9997-81102-4 241 2785 0200 RJ 

 Lehi Air Monitoring 

Station FRM SRP-MIC 04-013-7022-81102-1 58 N/A N/A 

 Mesa FRM MC 04-013-1003-81102-1 N/A N/A N/A 

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

 Senior Center Air 

Monitoring Station FRM SRP-MIC 04-013-7020-81102-1 56 N/A N/A 

 Senior Center Air 

Monitoring Station FRM SRP-MIC 04-013-7020-81102-2 63 N/A N/A 

 South Phoenix TEOM MC 04-013-4003-81102-1 420 3592 0200 RJ 

 South Scottsdale FRM MC 04-013-3003-81102-1 N/A N/A N/A 

 West Chandler TEOM MC 04-013-4004-81102-1 278 2116 0100 RJ 

 West Forty Third TEOM MC 04-013-4009-81102-1 369 2915 0200 RJ 

 West Phoenix TEOM MC 04-013-0019-81102-1 212 794 0300 RJ 

 Zuni Hills TEOM MC 04-013-4016-81102-1 212 1749 0300 RJ 

Mohave County 

 Bullhead City ADEQ FRM ADEQ 04-015-1003-81102-1 26 N/A N/A 

Navajo County 

 N/A TEOM WMAT 04-017-1002-81102-1 14 46 2000 

Pima County 

 Ajo TEOM ADEQ 04-019-0001-81102-3 50 157 0100 IJ 

 Corona de Tucson FRM PCDEQ 04-019-0008-81102-1 9 N/A N/A 

 Geronimo BAM PCDEQ 04-019-1113-81102-1 16 36 2000 

 Green Valley BAM PCDEQ 04-019-1030-81102-1 11 35 1600 

13
Monitor Monitor 

Type Operator AQS Monitor ID 

24-hr Avg 

PM10 

(μg/m3

) 

1-hr Max 

PM10

(μg/m3) 

Max Time

AQS 

Qualifier 

Flag 

 Orange Grove FRM PCDEQ 04-019-0011-81102-2 15 N/A N/A 

 Prince Road FRM PCDEQ 04-019-1009-81102-1 19 N/A N/A 

 Rillito TEOM ADEQ 04-019-0020-81102-3 49 438 0000 IJ 

 Santa Clara FRM PCDEQ 04-019-1026-81102-1 15 N/A N/A 

 South Tucson FRM PCDEQ 04-019-1001-81102-1 15 N/A N/A 

 Tangerine FRM PCDEQ 04-019-1018-81102-1 15 N/A N/A 

Pinal County 

 Apache Junction Fire Stn. FRM PCAQCD 04-021-3002-81102-1 23 N/A N/A 

 Apache Junction Fire Stn. TEOM PCAQCD 04-021-3002-81102-3 25 76 1000 

 Casa Grande Downtown TEOM PCAQCD 04-021-0001-81102-3 238 1774 0200 RJ 

 Coolidge FRM PCAQCD 04-021-3004-81102-1 42 N/A N/A 

 Combs School TEOM PCAQCD 04-021-3009-81102-3 60 395 0100 

 Cowtown FRM PCAQCD 04-021-3013-81102-1 828 N/A N/A RJ 

 Cowtown TEOM PCAQCD 04-021-3013-81102-3 1064 15056 0200 RJ 

 Eloy FRM PCAQCD 04-021-3014-81102-1 127 N/A N/A 

 Maricopa TEOM PCAQCD 04-021-3010-81102-3 529 3473 0200 RJ 

 Pinal Air Park N/A PCAQCD 04-021-3007-81102-1 48 N/A N/A 

 Pinal County Housing FRM PCAQCD 04-021-3011-81102-1 107 N/A N/A 

 Pinal County Housing FRM PCAQCD 04-021-3011-81102-2 131 N/A N/A 

 Pinal County Housing TEOM PCAQCD 04-021-3011-81102-3 184 993 0200 RJ 

 Stanfield TEOM PCAQCD 04-021-3008-81102-3 267 1660 0200 RJ 

 N/A FRM PCAQCD 04-021-7004-81102-1 171 N/A N/A RJ 

 N/A FRM PCAQCD 04-021-7004-81102-2 216 N/A N/A 

Santa Cruz County 

 Nogales Post Office FRM ADEQ 04-023-0004-81102-1 21 N/A N/A 

 Nogales Post Office BAM ADEQ 04-023-0004-81102-3 30 97 2100 

Yavapai County 

 Prescott Valley FRM ADEQ 04-025-2002-81102-1 9 N/A N/A 

Yuma County 

 Yuma Supersite TEOM ADEQ 04-027-8011-81102-3 23 59 1800 

Operator Abbreviations: MC – Maricopa County Air Quality Department 

 PCAQCD – Pinal County Air Quality Control District 

 ADEQ – Arizona Department of Environmental Quality 

 FMIR – Fort McDowell Indian Reservation 

 NN – Navajo Nation, AZ, NM, UT 

 PCDEQ – Pima County Department of Environmental Quality 

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

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

14
August 26, 2011 

Table 2-2. Summary of Statewide Air Quality Measurements for August 26, 2011. 

Monitor Monitor 

Type Operator AQS Monitor ID 

24-hr Avg 

PM10 

(μg/m3

) 

1-hr Max 

PM10

(μg/m3) 

Max Time

AQS 

Qualifier 

Flag 

Apache County 

 N/A TEOM WMAT 04-001-1003-81102-1 15 29 1900 

Coconino County 

 N/A TEOM NN 04-005-1237-81102-1 16 47 2000 

Gila County 

 Hayden Old Jail TEOM ADEQ 04-007-1001-81102-3 36 167 1800 IJ 

Maricopa County 

 Buckeye TEOM MC 04-013-4011-81102-1 44 262 1700 

 Central Phoenix TEOM MC 04-013-3002-81102-4 49 236 1800 

 Durango Complex TEOM MC 04-013-9812-81102-1 50 290 1700 

 Dysart TEOM MC 04-013-4010-81102-1 41 299 1700 

 Fort McDowell/Yuma 

Frank TEOM FMIR 04-013-5100-8112-1 22 N/A N/A 

 Glendale TEOM MC 04-013-2001-81102-1 43 277 1800 

 Greenwood TEOM MC 04-013-3010-81102-1 45 237 1700 

 Higley TEOM MC 04-013-4006-81102-1 150 842 1800 

 JLG Supersite BAM ADEQ 04-013-9997-81102-3 38 142 1800 

 JLG Supersite TEOM ADEQ 04-013-9997-81102-4 39 203 1800 IJ 

 South Phoenix TEOM MC 04-013-4003-81102-1 51 210 1700 

 West Chandler TEOM MC 04-013-4004-81102-1 92 689 1700 

 West Forty Third TEOM MC 04-013-4009-81102-1 47 349 1700 

 West Phoenix TEOM MC 04-013-0019-81102-1 55 253 1700 

 Zuni Hills TEOM MC 04-013-4016-81102-1 38 331 1800 

Navajo County 

 N/A TEOM WMAT 04-017-1002-81102-1 13 51 1600 

Pima County 

 Ajo TEOM ADEQ 04-019-0001-81102-3 213 1224 2200 RJ 

 Geronimo BAM PCDEQ 04-019-1113-81102-1 29 156 1700 

 Green Valley BAM PCDEQ 04-019-1030-81102-1 17 112 1900 

 Orange Grove FRM PCDEQ 04-019-0011-81102-2 31 N/A N/A 

 Rillito TEOM ADEQ 04-019-0020-81102-3 68 295 1900 IJ 

 South Tucson FRM PCDEQ 04-019-1001-81102-1 29 N/A N/A 

Pinal County 

 Apache Junction Fire Stn. TEOM PCAQCD 04-021-3002-81102-3 169 799 2000 RJ 

 Casa Grande Downtown TEOM PCAQCD 04-021-0001-81102-3 211 1947 1800 RJ 

 Combs School TEOM PCAQCD 04-021-3009-81102-3 206 1569 1400 RJ 

 Cowtown TEOM PCAQCD 04-021-3013-81102-3 248 1038 2000 RJ 

 Maricopa TEOM PCAQCD 04-021-3010-81102-3 108 1000 0000 

 Pinal County Housing TEOM PCAQCD 04-021-3011-81102-3 257 2792 1800 RJ 

 Stanfield TEOM PCAQCD 04-021-3008-81102-3 170 406 1800 RJ 

Santa Cruz County 

 Nogales Post Office BAM ADEQ 04-023-0004-81102-3 31 74 0700 

Yuma County 

 Yuma Supersite TEOM ADEQ 04-027-8011-81102-3 22 57 1900 

Operator Abbreviations: MC – Maricopa County Air Quality Department 

 PCAQCD – Pinal County Air Quality Control District 

 ADEQ – Arizona Department of Environmental Quality 

 FMIR – Fort McDowell Indian Reservation 

 PCDEQ – Pima County Department of Environmental Quality 

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

15
 

August 27, 2011 

Table 2-3. Summary of Statewide Air Quality Measurements for August 27, 2011. 

Monitor Monitor 

Type Operator AQS Monitor ID 

24-hr Avg 

PM10 

(μg/m3

) 

1-hr Max 

PM10

(μg/m3) 

Max Time

AQS 

Qualifier 

Flag 

Apache County 

 N/A TEOM WMAT 04-001-1003-81102-1 18 40 0600 

Coconino County 

 N/A TEOM NN 04-005-1237-81102-1 25 87 2000 

Gila County 

 Hayden Old Jail TEOM ADEQ 04-007-1001-81102-3 60 123 0000 

Maricopa County 

 Buckeye TEOM MC 04-013-4011-81102-1 225 3219 2100 RJ 

 Central Phoenix TEOM MC 04-013-3002-81102-4 233 1972 2300 RJ 

 Durango Complex TEOM MC 04-013-9812-81102-1 261 3169 2200 RJ 

 Dysart TEOM MC 04-013-4010-81102-1 126 1514 2200 

 Fort McDowell/Yuma 

Frank TEOM FMIR 04-013-5100-8112-1 28 N/A N/A 

 Glendale TEOM MC 04-013-2001-81102-1 219 2908 2200 RJ 

 Greenwood TEOM MC 04-013-3010-81102-1 207 2064 2200 RJ 

 Higley TEOM MC 04-013-4006-81102-1 115 712 2300 

 JLG Supersite BAM ADEQ 04-013-9997-81102-3 127 883 2300 IJ, EH 

 JLG Supersite TEOM ADEQ 04-013-9997-81102-4 132 1220 2300 IJ 

 South Phoenix TEOM MC 04-013-4003-81102-1 301 2795 2200 RJ 

 West Chandler TEOM MC 04-013-4004-81102-1 228 2407 2300 RJ 

 West Forty Third TEOM MC 04-013-4009-81102-1 292 3633 2200 RJ 

 West Phoenix TEOM MC 04-013-0019-81102-1 164 1519 2200 RJ 

 Zuni Hills TEOM MC 04-013-4016-81102-1 112 1308 2300 

Navajo County 

 N/A TEOM WMAT 04-017-1002-81102-1 15 51 1200 

Pima County 

 Ajo TEOM ADEQ 04-019-0001-81102-3 167 400 0000 RJ 

 Geronimo BAM PCDEQ 04-019-1113-81102-1 52 451 2100 

 Green Valley BAM PCDEQ 04-019-1030-81102-1 21 51 2300 

 Orange Grove FRM PCDEQ 04-019-0011-81102-2 51 N/A N/A 

 Rillito TEOM ADEQ 04-019-0020-81102-3 84 348 1500 IJ 

 South Tucson FRM PCDEQ 04-019-1001-81102-1 30 N/A N/A 

Pinal County 

 Apache Junction Fire Stn. TEOM PCAQCD 04-021-3002-81102-3 84 424 0000 

 Casa Grande Downtown TEOM PCAQCD 04-021-0001-81102-3 123 441 2000 

 Combs School TEOM PCAQCD 04-021-3009-81102-3 157 1242 1900 RJ 

 Cowtown TEOM PCAQCD 04-021-3013-81102-3 381 2192 2000 RJ 

 Maricopa TEOM PCAQCD 04-021-3010-81102-3 267 1385 2000 RJ 

 Pinal County Housing TEOM PCAQCD 04-021-3011-81102-3 187 1479 2000 RJ 

 Stanfield TEOM PCAQCD 04-021-3008-81102-3 126 531 2000 

Santa Cruz County 

 Nogales Post Office BAM ADEQ 04-023-0004-81102-3 36 67 2100 

Yuma County 

 Yuma Supersite TEOM ADEQ 04-027-8011-81102-3 48 164 1800 

Operator Abbreviations: MC – Maricopa County Air Quality Department 

 PCAQCD – Pinal County Air Quality Control District 

 ADEQ – Arizona Department of Environmental Quality 

 FMIR – Fort McDowell Indian Reservation 

 PCDEQ – Pima County Department of Environmental Quality 

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

*Power failure and/or instrumentation range limitation occurred during expected maximum 

concentration hour(s), likely resulting in an underestimate of 24-hour average 

16
 

August 28, 2011 

Table 2-4. Summary of Statewide Air Quality Measurements for August 28, 2011. 

Monitor Monitor 

Type Operator AQS Monitor ID 

24-hr Avg 

PM10 

(μg/m3

) 

1-hr Max 

PM10

(μg/m3) 

Max Time

AQS 

Qualifier 

Flag 

Apache County 

 N/A TEOM WMAT 04-001-1003-81102-1 21 83 1700 

Coconino County 

 N/A TEOM NN 04-005-1237-81102-1 20 58 1900 

Gila County 

 Hayden Old Jail TEOM ADEQ 04-007-1001-81102-3 82 223 1000 IJ 

Maricopa County 

 Buckeye TEOM MC 04-013-4011-81102-1 44 87 0000 

 Central Phoenix TEOM MC 04-013-3002-81102-4 79 192 0400 

 Durango Complex TEOM MC 04-013-9812-81102-1 61 134 0300 

 Dysart TEOM MC 04-013-4010-81102-1 55 179 0000 

 Fort McDowell/Yuma 

Frank TEOM FMIR 04-013-5100-8112-1 305 N/A N/A 

 Glendale TEOM MC 04-013-2001-81102-1 67 227 0000 

 Greenwood TEOM MC 04-013-3010-81102-1 58 132 0300 

 Higley TEOM MC 04-013-4006-81102-1 175 1716 0000 RJ 

 JLG Supersite BAM ADEQ 04-013-9997-81102-3 77 180 0300 IJ 

 JLG Supersite TEOM ADEQ 04-013-9997-81102-4 72 201 0100 IJ 

 South Phoenix TEOM MC 04-013-4003-81102-1 71 145 0000 

 West Chandler TEOM MC 04-013-4004-81102-1 123 1107 0000 

 West Forty Third TEOM MC 04-013-4009-81102-1 58 160 0000 

 West Phoenix TEOM MC 04-013-0019-81102-1 71 170 0300 

 Zuni Hills TEOM MC 04-013-4016-81102-1 62 183 0200 

Navajo County 

 N/A TEOM WMAT 04-017-1002-81102-1 13 37 2000 

Pima County 

 Ajo TEOM ADEQ 04-019-0001-81102-3 25 57 0000 VB 

 Geronimo BAM PCDEQ 04-019-1113-81102-1 85 130 1400 

 Green Valley BAM PCDEQ 04-019-1030-81102-1 70 131 1000 

 Orange Grove FRM PCDEQ 04-019-0011-81102-2 89 N/A N/A 

 Rillito TEOM ADEQ 04-019-0020-81102-3 121 207 1000 IJ 

 South Tucson FRM PCDEQ 04-019-1001-81102-1 86 N/A N/A 

Pinal County 

 Apache Junction Fire Stn. TEOM PCAQCD 04-021-3002-81102-3 283 767 0200 RJ 

 Casa Grande Downtown TEOM PCAQCD 04-021-0001-81102-3 216 625 0200 RJ 

 Combs School TEOM PCAQCD 04-021-3009-81102-3 165 801 0100 RJ 

 Cowtown TEOM PCAQCD 04-021-3013-81102-3 183 738 0200 RJ 

 Maricopa TEOM PCAQCD 04-021-3010-81102-3 119 793 0000 

 Pinal County Housing TEOM PCAQCD 04-021-3011-81102-3 177 564 0400 RJ 

 Stanfield TEOM PCAQCD 04-021-3008-81102-3 97 542 0200 

Santa Cruz County 

 Nogales Post Office BAM ADEQ 04-023-0004-81102-3 65 141 1900 

Yuma County 

 Yuma Supersite TEOM ADEQ 04-027-8011-81102-3 178 825 0600 RJ 

Operator Abbreviations: MC – Maricopa County Air Quality Department 

 PCAQCD – Pinal County Air Quality Control District 

 ADEQ – Arizona Department of Environmental Quality 

 FMIR – Fort McDowell Indian Reservation 

 PCDEQ – Pima County Department of Environmental Quality 

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

17
 

III. HISTORICAL FLUCTUATIONS 

The PM10 concentrations measured throughout Maricopa County during the period August 25-28, 2011, 

were some of the highest hourly and 24-hour averages measured over the last five years. Time series 

plots of the 24-hour PM10 concentrations for the period January 1, 2007, through December 31, 2011, 

were created for all PM10 monitors in Maricopa County. Additionally, time series plots of the daily 

maximum hourly average PM10 concentrations were created for two monitors in Maricopa County. 

These two additional plots were created to provide a deeper understanding of the magnitude of short-term 

particulate concentrations and their contribution to PM10 exceedances in the Phoenix PM10 

nonattainment area. Time series plots for two monitoring sites (Higley and Central Phoenix) are included 

within this section, while the remaining plots are available in Appendix A. The Central Phoenix monitor 

was selected because of its central location in relation to all monitors in Maricopa County and the Higley 

monitor was selected because it is representative of southeastern Maricopa County, an area of the region 

frequently impacted by dust storms caused by thunderstorm outflow events. The graphs below and in 

Appendix A show that the August 25th event was the most extreme event of the last five years for several 

sites and that the other events during the August 25-28 period were also significant compared to previous 

data. 

Figure 3-1. Plot of daily hourly maximum PM10 concentrations (2007 – 2011) at the Central Phoenix 

monitoring site. 

18
The plot above shows the daily maximum hourly averages from the Central Phoenix PM10 monitor. The 

plot shows that the August 25th hourly average of 2822 μg/m3

 and August 27th hourly average of 

1972 μg/m3 were among the highest hourly PM10 concentrations recorded in the last five years. The plot 

also shows that the maximum hourly averages were comparable to those observed during the July 3 and 5, 

2011 haboob events recently concurred upon by the EPA. The hourly average concentrations from these 

two events were surpassed by additional dust storms that occurred a week earlier in August and in 

September, another indication of the uniqueness of the 2011 monsoon season. It is also clear that the 

most significant hourly average PM10 concentrations at the Central Phoenix monitor typically occur 

during the July through September time frame, a period during which the monsoon season is most active 

and the Phoenix region is frequently impacted by haboob events. The plot below shows the daily 24-hour 

averages from the Central Phoenix PM10 monitor and indicates that the August 25th event produced the 

highest 24-hour average PM10 concentration measured in the last five years and the August 27th event 

was the fifth-highest during the same time period. These events experienced concentrations similar to 

haboob events that occurred on July 19, 2007, and in the first week of July 2011. 

Figure 3-2. Plot of 24-hour average PM10 concentrations (2007 – 2011) at the Central Phoenix 

monitoring site. 

The two plots below provide a historical look at the daily maximum hourly averages and daily 24-hour 

averaged PM10 concentrations from the Higley monitor. The plots also show that the maximum hourly 

concentration and exceedance measured at the Higley monitor on August 28th were amongst the 12 

19
highest PM10 concentrations measured over the last five years. As was the case for the Central Phoenix, 

the most significant hourly average PM10 concentrations at the Higley monitor typically occur during the 

July through September time frame, a period during which the monsoon season is most active and the 

Phoenix region is frequently impacted by haboob events. 

Figure 3-3. Plot of daily hourly maximum PM10 concentrations (2007 – 2011) at the Higley monitoring 

site. 

20
Figure 3-4. Plot of 24-hour average PM10 concentrations (2007 – 2011) at the Higley monitoring site. 

The plots within this section provide a historical perspective of PM10 concentrations since 2007. These 

plots, along with those in Appendix A, show that the haboob events which occurred during the 

August 25th-28th period resulted in some of the highest PM10 concentrations seen in the last five years. In 

the case of the Central Phoenix, Greenwood, West 43rd, South Phoenix, Durango, Glendale, and Dysart 

monitoring sites, the highest 24-hour averaged PM10 concentrations measured in the last five years 

occurred on August 25. While the August 25th event contained the greatest PM10 concentrations, the 

other events in the August 25th-28th period were generally among the top 12 events in the last five years. 

This equates to PM10 concentrations in the 99.3th percentile when compared to historic data. While the 

PM10 concentrations that were measured during the August 25th-28th period were extreme in many cases, 

the plots also show that similar events are not uncommon during the monsoon season. As documented in 

several published journals and academic text books, haboobs generated from thunderstorm outflow 

boundaries are phenomena that Arizonans deal with every year, some years more so than others, namely 

in 2007 and 2011. 

21
IV. NOT REASONABLY CONTROLLABLE OR PREVENTABLE

Section 50.1(j) of Title 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 and the Phoenix PM10 

nonattainment area, high wind conditions overwhelmed all reasonably available controls. The events 

occurring from August 25-28 were directly related to strong and gusty winds generated by thunderstorm 

outflow boundaries. The strong winds overwhelmed all reasonably available controls, and were also 

responsible for transporting PM into the Phoenix PM10 nonattainment area from areas outside of the 

nonattainment area. As explained in the conceptual model, downdrafts from collapsing thunderstorms 

produce outflow boundaries that contain gusty, turbulent wakes that raise dust from the desert surfaces 

that can be as wide as 100 miles in severe cases. As shown in Section V, the source region for all of the 

dominant thunderstorm outflows and associated transported dust during the period of August 25-28, 2011, 

generally came from areas outside of the Phoenix PM10 nonattainment area—primarily from the deserts 

of Pinal, Pima, and southern Maricopa counties. While it is likely that some dust was generated within 

the PM10 nonattainment area as gusts from the thunderstorm outflows passed through the area, the 

amount of dust generated locally was easily overwhelmed by, and largely unnoticeable as compared to, 

the dust transported in from the source regions of the thunderstorm outflows. Strict controls on local 

sources of fugitive dust were in place and enforced during all of the events of August 25-28, 2011, but 

were not capable of controlling transported dust and PM10 raised by the gusty and turbulent thunderstorm 

outflows on these dates. 

The following sections describe the BACM- and MSM-level PM10 control measures in place during the 

period of August 25-28, 2011, and the robustness of the programs designed to enforce these measures. 

Pro-active response and analysis of each event as it is occurring verify the uncontrollable nature of each 

event, while inspections of local sources performed before, during, and after the events of August 25-28, 

2011, confirmed that no unusual anthropogenic PM10-producing activities occurred in Maricopa County, 

the Phoenix PM10 nonattainment area, or the local areas surrounding the exceeding monitors. 

Regulatory Measures and Control Programs

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: 

1) ADEQ’s Agricultural Best Management Program (AgBMP) 

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 High Risk for the Maricopa County Dust Control Forecast, 

(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 that are of greatest risk for 

elevated PM emissions. 

22
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 approved 

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

§ 49-4574. Maricopa County regulations of PM10 emissions are listed in Table 4-1. 

Table 4-1. Rules and Ordinances Regulating Particulate Matter 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 

Dust-Generating 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 

Non-Traditional 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 

 

4

 Updates to the AgBMP program in December, 2011, clarified BMPs for crop 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. 

23
Rule/Ordinance Number & Title Description 

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 brick and structural clay product 

(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 

Woodburning Restriction 

Establishes restrictions for residential woodburning 

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 

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 

In addition to the rules and regulations listed in the above table, other PM10 reducing control measures 

(e.g., paving of 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 SIP through PM10 plans such as the Revised 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 4-2). Additionally, the PCAQCD 

implements specific nonattainment rules for that part of the Phoenix PM10 nonattainment area that resides 

in Pinal County (see Table 4-3). 

Table 4-2. Pinal County Rules Regulating Existing and New Non-point Sources in Pinal County 

Article Number & Title Description 

Chapter 4, Article 2: Fugitive 

Dust 

Provides a mechanism to reasonably regulate operations which 

periodically may cause fugitive dust emissions into the 

atmosphere 

Chapter 4, 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 4-3. Pinal County Rules Regulating Fugitive Dust in Pinal County Portion of MC PM10 NAA 

Article Number & Title Description 

Chapter 4, 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 

Chapter 4, Article 5: 

Nonattainment Area Rules; 

Stabilization for Residential 

Parking and Drives 

Establishes rules for stabilizing residential properties 

24
Article Number & Title Description 

Chapter 4, Article 6: Restrictions 

on Vehicle Parking and Use on 

Vacant Lots

Establishes rules for unpaved or unstabilized vacant lots (valid 

in Pinal County portion of Area A) 

Chapter 4, 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 

Chapter 4, Article 8: 

Nonattainment Area Rules, 

Requirement for Stabilization of 

Disturbed Areas at Vacant Lots

Establishes rules for stabilizing disturbed areas at vacant lots 

 

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 department’s obligations under such agreements as the 2005 

Revised PM10 State Implementation Plan for the Salt River Area and the Maricopa Association of 

Governments (MAG) 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, to 95% compliance (from 

85%) for Rule 310.01 sources, and to 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, and 73% for Rule 316 sources. The timeline below illustrates the improvements in RE over the 

last several years, and also points out significant revisions to previous rules, as well as newly adopted 

rules and ordinances. 

25
01/27/2010

Rules 310 & 310.01

Revised

01/12/2011

Ordinances

P‐27 & P‐28 Revised

06/01/2005

06/08/2005

Rule 316 Revised

04/07/2004

Rule 310 Revised

02/17/2005

Rule 310.01 Revised

03/26/2008

Rules 310 & 310.01

Revised

March 2008

September 2006

02/20/2008

Ordinances P‐25, P‐27

& P‐28  Adopted

03/12/2008

Rule 316 Revised

Figure 4-1. Timeline of Maricopa County Fugitive Dust Rules and Ordinances. 

Compliance and Enforcement Activities

MCAQD is proactively prepared to respond to high wind events and to protect human health and wellbeing. MCAQD’s approach consists of two primary components: routine proactive inspections, as well 

as surveillance inspections, conducted both during and after significant events. MCAQD proactively 

inspects dust control-permitted sites, and increases the frequency for larger sites of 10 acres or more. 

Rule 316 sources are also proactively inspected multiple times every year. Maricopa County also 

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 additional surveillance before, during, 

and after the forecast event(s). MCAQD also conducts event surveillance and post-event activities on 

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. Postevent activities include continued surveys of high-risk areas, re-inspection of sources that had received 

violations within two business days, and an internal MCAQD debriefing of event activities. 

Recently, a total of 12 MCAQD air monitoring sites have been updated with new equipment that allows 

the monitoring sites to report automatically monitored readings at five-minute intervals, where previously 

only hourly data were available. The real-time monitoring data programming includes threshold triggers 

that cause the system to send alerts to MCAQD staff that the PM concentrations are elevated. The system 

allows MCAQD responders to review concentrations at the monitor and to consult the National Weather 

Service website to check for weather event activity. This capability allows the 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. 

26
For August 25th and 28th, Maricopa County Dust Control Forecasts were issued indicating a moderate 

risk level for unhealthy PM10. On August 26th, a Maricopa County Dust Control Forecast was issued 

indicating a high risk level for unhealthy PM10. The Dust Control Forecasts also indicated a potential for 

blowing dust. For the events from August 25-28, 2011, included in this analysis, MCAQD responders 

evaluated each situation when concentrations were elevated. During most of the alerts MCAQD observed 

weather system activity and noted that many monitors were simultaneously impacted by the high winds. 

In instances where strong winds were not present, or only a single monitor was affected, MCAQD issued 

broadcast alerts to nearby stakeholders and local governments, and also deployed MCAQD inspectors to 

investigate possible causes of the elevated readings. 

An evaluation of inspection reports and compliance records indicate no evidence of unusual 

anthropogenic-based PM10 emissions. During the time period of August 22 through August 31, 2011, 

MCAQD inspectors conducted a total of 197 inspections on permitted facilities, of which 142 were at 

fugitive dust sources. Additionally, MCAQD conducted 114 inspections on vacant lots and unpaved 

parking lots. 

During this 10-day period, a total of 21 violations were issued county-wide for PM10- and non-PM10-

related violations. Only two violations were issued for PM10 emissions at a single source within 4 miles 

of the exceeding West Chandler monitor. On August 25, 2011, two violations were issued to an 

earthmoving site: for failure to stabilize surface areas using one of the standards in Rule 310, Section 

304.3, and for failure to implement control measures on unpaved staging areas, unpaved parking areas and 

unpaved storage areas. The total unstabilized area was small and measured 0.21 acres. The site operators 

stabilized the area after the inspector notified the general contractor of the violations. 

 MCAQD was prepared for any complaints received due to the high wind events. MCAQD received 57 

complaints, of which 33 were windblown dust-related between August 22 and August 31. Each 

complaint was assigned to and investigated by a MCAQD inspector. A review of all records during this 

period reveals that MCAQD inspectors observed one violation of local, state, or federal regulations for 

control of PM10 within 4 miles of an exceeding monitor during their investigations. On August 31, 2011, 

MCAQD received a dust complaint concerning an earthmoving source within 4 miles of the Central 

Phoenix Monitor. On September 1, 2011, an inspector investigated the compliant and issued a violation 

for failure to maintain complete records. The source only kept records of the amount of water applied but 

did not maintain subcontractor registration numbers or maintenance of trackout control devices. The 

Central Phoenix Monitor previously exceeded on August 27, 2011. 

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

Agricultural Best Management Practice Program (Ag BMP) inspector 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 highwind events. Additional outreach is conducted with facility representatives prior to forecasted high-wind 

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

ADEQ Ag BMP inspector is dispatched to contact the owners and operators of agriculture fields in the 

area to discern if 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. From August 22 through August 26, 2011, 

the ADEQ Ag BMP inspector received five complaints, performed site visits at three agricultural 

27
operations, and conducted outreach via telephone with several facility representatives. The agriculture 

fields visited were undergoing normal agricultural practice. 

Conclusions

The thunderstorm outflow events of August 25-28, 2011 produced strong gusts and turbulent wakes 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 of Pinal, Pima, and southern 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-approved control measures on significant anthropogenic sources were in place and enforced 

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

governments confirmed the uncontrollable nature of the dust emissions; therefore, these pre-existing/prior 

approved required controls are adequate for meeting the requirements of an exceptional event and should 

be considered “reasonable” for these purposes. 

Despite the deployment of comprehensive control measures and sophisticated response programs and a 

few localized, low-impact violations of the dust control rules, high wind conditions associated with 

thunderstorms and thunderstorm outflows brought high concentrations of PM10 emissions into, and also 

overwhelmed controls within, the Phoenix PM10 nonattainment area. Numerous strong thunderstorm 

outflows with sustained winds typically ranging from 20-30 mph, and even greater nearest the source 

regions, were enough to overwhelm all available efforts to limit PM10 concentrations from the events. 

The fact that these were natural events involving strong thunderstorm outflow winds that transported 

PM10 emissions into 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 events and exceedances of August 25-28, 2011, recorded within the Phoenix 

PM10 nonattainment area, were not reasonably controllable or preventable. 

28
V. CLEAR CAUSAL RELATIONSHIP 

Introduction

A demonstration of the clear causal connection between uncontrollable natural events or uncontrollable 

emissions associated with thunderstorm outflows and PM10 exceedance days during the time period of 

August 25–28, 2011 is presented in the following time series graphs, infrared satellite imagery, and 

National Weather Service (NWS) data tables for selected, representative airports. These various pieces of 

information contain data on sustained wind speed, wind speed gusts, PM10 concentrations, visibility, 

weather observations, and thunderstorm development areas and provide the causal connection between 

the uncontrollable emissions associated with thunderstorm outflows and elevated PM10 concentrations. 

Additional NWS text products issued during the August 25-28 period containing forecasts and warnings 

of blowing dust due to thunderstorms outflows are included for reference in Appendix D. A summary of 

each event day is provided below. 

Event #1 – August 25, 2011:

On August 24, the day prior to the first event, the Phoenix region experienced typical summertime 

weather conditions (Phoenix Sky Harbor International Airport: maximum temperature of 111°F, relative 

humidity of 10-30%, winds at 5-12 miles per hour (mph) mainly out of the west, visibility at 10 miles all 

day) and PM10 concentrations (24-hour averages in the 30-70 μg/m3

 range). Between 8 p.m. Mountain 

Standard Time (MST) and 11 p.m. MST, severe thunderstorms developed over the southeastern Arizona 

and northern Mexico (as shown in Figure 5-1) and by 1 a.m. on August 25, outflows from the 

thunderstorms entrained dust from desert areas of Pinal County and generated a “haboob” that progressed 

northwestward into Maricopa County, transporting large amounts of PM10. As shown in Figure 5-2, the 

“haboob” had the following impacts in the Phoenix area: southeasterly winds increased to 18-26 mph, 

with gusts up to 34 mph; visibility dropped from 10 miles to 2 miles; weather conditions were reported as 

“haze”; and hourly PM10 concentrations increased from about 30-50 μg/m3

 to 2000+ μg/m3 at five sites 

and over 4000 μg/m3

 at the Greenwood site in central Phoenix. Once the winds subsided, visibility 

remained below 10 miles and PM10 concentrations remained high for several hours, resulting in 24-hour 

average concentrations between 200–450 μg/m3 at more than 10 monitoring sites on August 25. In total, 

12 monitoring sites in the region exceeded the PM10 NAAQS and, as was mentioned in the Historical 

Fluctuation section, 7 sites out of the 16 PM10 monitoring in the Phoenix nonattainment area saw their 

highest 24-hour average PM10 concentration measured in the past five years. Without the existence of 

the emissions generated by these thunderstorm outflows, there would not have been any exceedances of 

the 24-hour PM10 standard in the Phoenix PM10 nonattainment area. 

29
 12:00 p.m. 2:00 p.m. 4:00 p.m. 6:00 p.m. 

1900z Aug 24 2100z Aug 24 2300z Aug 24 0100z Aug 25 

 8:00 p.m. 10:00 p.m. 12:00 a.m. 3:00 a.m. 

0300z Aug 25 0500z Aug 25 0700z Aug 25 1000z Aug 25 

Figure 5-1. Satellite imagery showing strong storms developing and dissipating over northern Mexico. 

These storms are believed to have been responsible for the thunderstorm outflow boundary that caused 

PM10 exceedances throughout Maricopa and Pinal counties on August 25. 

Figure 5-2 depicts the first dust event that occurred in Maricopa County impacting the Phoenix area 

during the August 25-28 period. Hourly averaged PM10 concentrations at monitors throughout Maricopa 

County are shown along with visibility readings (blue diamonds) and wind speeds reported at the Phoenix 

Sky Harbor Airport. Sky Harbor measurements were used due to its central location amongst a number of 

the monitors that experienced exceedances on August 25. As can be seen in the graph, visibility was 

reduced down to two miles at the Sky Harbor Airport during the windblown dust event and this visibility 

reduction coincided with increased wind speeds in the 20-30 mph range and PM10 concentrations across 

Phoenix. 

As shown in Figure 5-3, several monitoring sites in the upwind, dust source region of Pinal County 

measured 24-hour average PM10 exceedances with the peak site, Cowtown, having a 24-hour average of 

1,064 μg/m3

 and an astonishing maximum 1-hour average during the 2 a.m. hour of 15,056 μg/m3. Only 

monitoring sites in Maricopa and Pinal counties exceeded the NAAQS due to thunderstorm outflows on 

this day, but the broad range of sites and the extreme hourly- and daily-averaged PM10 concentrations 

reflect the magnitude of the “haboob.” Additionally, the NWS airport meteorological data tables after 

Figure 5-3 show that the strongest winds associated with the haboob were out of the southeast. These 

winds combined with the high PM10 concentrations in Pinal County indicate that PM10 was already 

entrained in the atmosphere outside of the Phoenix PM10 nonattainment area and then transported into the 

region by the strong winds. 

30
Figure 5-3. Phoenix nonattainment area PM10 monitor readings and Sky Harbor visibility and wind 

speed for August 25, 2011.

31
Figure 5-2. Pinal County PM10 monitor readings and Casa Grande visibility and wind speed for August 

25, 2011.

32
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 

(08/2011) 

Elevation: 1107 ft. above sea level Latitude: 33.427 Longitude: -112.003 Data Version: VER3

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point

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

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

Rel 

Humd 

%

Wind 

Speed (MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Ne

3-h

Ch

(m

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

25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25

0051 0149 0151 0159 0208 0216 0223 0251 0351 0451 0551 0651 0751 0851 0951 1051 1151 1251 1351 1451 1551 1651 1751 1851 1951 2051 2151 2251 2351

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

SCT170 SCT210 SCT250 SCT017 SCT170 SCT210 SCT015 SCT170 SCT210 BKN015 BKN170 BKN210 BKN015 BKN170 BKN210 BKN015 BKN170 BKN210 SCT170 SCT210 FEW170 SCT210 FEW170 SCT210 SCT200 BKN250 SCT200 BKN250 SCT170 BKN220 SCT170 BKN220 SCT170 BKN200 SCT170 BKN200 FEW095 SCT170 BKN210 FEW120 SCT170 BKN210 FEW120 SCT170 SCT210 FEW120 SCT170 SCT210 FEW120 SCT170 SCT210 FEW120 SCT170 SCT210 FEW120 SCT170 SCT210 FEW120 SCT170 SCT210 FEW120 SCT170 SCT210 FEW120 SCT170 SCT210 SCT150 SCT200 BKN250 BKN210 BKN160 BKN210 FEW120 BKN160 BKN210

10.00 2.50 2.00 1.75 2.50 7.00 7.00 7.00 6.00 7.00 7.00 7.00 8.00 9.00 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

HZ HZ HZ HZ HZ 

101999999999797959393929394971001001051081091131101101101081071031029999

38.337.037.237.037.036.036.035.033.933.933.333.934.436.137.837.840.642.242.845.043.343.343.342.241.739.438.937.237.2

7069707070707070707069707070717171717272717171696971717070

21.220.720.921.121.121.121.121.020.920.920.820.921.121.321.521.821.621.622.022.421.521.721.720.420.721.721.421.120.9

5352535454555556575757575756555652505150484949444654535453

11.711.011.712.012.013.013.013.313.913.913.913.913.913.312.813.311.110.010.610.08.99.49.46.77.812.211.712.211.7

20 21 21 22 22 24 24 27 30 30 31 30 29 25 22 23 17 14 15 12 13 13 13 12 13 20 19 22 21

10 24 26 16 18 21 15 10 6 0 3 5 5 3 6 0 3 3 7 11 3 5 7 5 5 15 14 15 16

140150160160120130130140140000230220220VR 160000VR VR 080190VR VR 300200110060080050060

22 33 33 32 24 28 28 21 

28.60 28.62 28.62 28.63 28.63 28.63 28.63 28.63 28.62 28.62 28.61 28.64 28.66 28.66 28.66 28.66 28.65 28.62 28.60 28.56 28.52 28.51 28.51 28.53 28.55 28.58 28.60 28.60 28.61

3 8 3 0 7 6 3 1

018002013004024028013017

33
U.S. Department of Commerce 

National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL CLIMATOLOGICAL DATA 

(final) 

HOURLY OBSERVATIONS TABLE 

WILLIAMS GATEWAY AIRPORT (23104) 

PHOENIX, AZ 

(08/2011) 

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

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

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

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

Rel

Humd

%

Wind 

Speed (MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb)

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

25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 

0015 0035 0055 0115 0135 0155 0215 0235 0255 0315 0335 0355 0415 0435 0455 0515 0535 0553 0647 0747 0850 0946 1049 1147 1248 1348 1450 1554 1750 1847 1947 1955 2015 2035 

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 VV007 CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR SCT150 BKN200 SCT140 BKN200 BKN140 BKN200 BKN140 BKN200 BKN140 BKN200 BKN140 BKN200 SCT120 SCT200 FEW120 SCT120 FEW120 SCT200 FEW120 SCT200 FEW120 SCT200 FEW120 SCT200 FEW120 SCT200 SCT CLR CLR CLR 

10.00 10.00 7.00 10.00 1.75 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 20.00 15.00 15.00 15.00 15.00 15.00 35.00 35.00 35.00 35.00 35.00 35.00 20.00 20.00 10.00 10.00 10.00 

HZ 

999999979797979397919193939391909193919397102

102106109109109111109109106104104104

37.037.037.036.036.036.036.034.036.033.033.034.034.034.033.032.033.034.033.034.036.039.039.041.043.043.043.044.043.043.041.040.040.040.0

707070707070727072696971707169696971707171737272737371727070M717172

21.121.121.121.021.021.022.120.922.120.620.621.420.921.420.620.420.621.421.121.521.522.822.322.422.622.621.722.420.920.9M 21.421.422.1

54545455555559575957575957595757575959595759575554545052464654525255

12.012.012.013.013.013.015.014.015.014.014.015.014.015.014.014.014.015.015.015.014.015.014.013.012.012.010.011.08.0 8.0 12.011.011.013.0

22 22 22 24 24 24 28 30 28 32 32 32 30 32 32 33 32 32 34 32 26 24 23 19 16 16 14 14 12 12 M 18 18 20 

9 9 21 20 25 15 10 7 5 3 0 0 5 6 6 7 5 6 7 6 3 7 5 0 7 7 5 9 9 7 13 3 6 7 

140 140 130 120 120 130 140 120 120 160 000 000 280 310 320 320 310 290 210 210 240 270 290 000 VR 130 170 240 270 270 060 060 130 160 

24 33 23 

28.36 28.37 28.38 28.39 28.40 28.40 28.39 28.38 28.37 28.37 28.37 28.37 28.36 28.36 28.36 28.36 28.36 28.36 28.40 28.41 28.42 28.43 28.42 28.39 28.37 

28.34 28.31 28.28 28.27 28.29 M 28.32 28.33 28.34 

34
25 

25 25 25 25 25 25 25 25 25

2055 2115 2135 2155 2215 2235 2255 2315 2335 2355

0 0 0 0 0 0 0 0 0 0

CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR

10.00 7.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00

100100100102100100100100100100

38.038.038.039.038.038.038.038.038.038.0

70707071696970707070

21.221.221.321.620.820.321.321.321.321.3

54545454525054545454

12.012.012.012.011.010.012.012.012.012.0

21 21 21 20 20 19 21 21 21 21

6 0 6 6 6 13 16 15 14 14

170 000 040 040 360 030 030 050 040 040

16 23 21 18

28.35 28.35 28.36 28.36 28.36 28.36 28.36 28.36 28.36 28.37

35
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 

(08/2011) 

Elevation: 1462 ft. above sea level Latitude: 32.95 Longitude: -111.766 Data Version: VER2

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point

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

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

Rel 

Humd 

%

Wind 

Speed 

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Ne

3-

Ch

(m

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

25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 

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 

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 FEW065 SCT080 BKN110 FEW015 FEW065 SCT080 SCT015 SCT020 FEW013 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 5.00 2.50 5.00 4.00 3.00 4.00 5.00 7.00 6.00 7.00 7.00 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 

TS 99

9797919191919191909090888888889090909086889091939597999999100

37.036.036.033.033.033.033.033.033.032.032.032.031.031.031.031.032.032.032.032.030.031.032.033.034.035.036.037.037.037.038.0

69706969696968686868686867676768696968696968696969697070717172

20.621.020.820.620.620.620.020.020.019.919.919.919.519.519.520.120.420.419.920.420.320.120.420.620.420.721.021.321.821.822.0

52555457575755555555555555555557575755575957575755555555575757

11.013.012.014.014.014.013.013.013.013.013.013.013.013.013.014.014.014.013.014.015.014.014.014.013.013.0

13.013.014.014.014.0

21 24 24 32 32 32 30 30 30 31 31 31 33 33 33 35 33 33 31 33 40 35 33 32 28 26 24 23 25 25 24 

8 0 26s 22 17 13 0 9 5 0 0 0 0 0 0 0 0 5 3 7 0 0 5 7 10 10 13 17 16 14 9 

080000110120150150000130180000000000000000000000000040080120000000030030080060080070060070080

23 34 29 23 22 18 18 

28.29 28.30 28.32 28.31 28.30 28.30 28.30 28.29 28.28 28.27 28.27 28.27 28.27 28.27 28.27 28.27 28.28 28.28 28.29 28.30 28.30 28.31 28.31 28.32 28.32 28.32 28.33 28.33 28.33 28.33 28.34 

2 7 2 

017014020

36
37

25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25 25

1035 1055 1115 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 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 BKN004 SCT004 BKN120 FEW070 SCT100 FEW043 FEW100 CLR CLR CLR FEW032 FEW045 SCT065 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 1.00 9.00 5.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00

VCTS VCTS TS TS 

100100102102102104104106108106106106108108106106106106106106106106106106104104102102991009999999797979997959191

38.038.039.039.039.040.040.041.042.041.041.041.042.042.041.041.041.041.041.041.041.041.041.041.040.040.039.039.037.038.037.037.037.036.036.036.037.036.035.033.033.0

7272727171737272727272727272727171717171717171717171696970707070727473717170707170

22.022.022.321.821.822.622.122.422.422.122.122.122.422.422.121.721.721.721.721.721.721.721.721.721.421.420.620.621.321.221.121.322.323.222.621.521.821.021.221.721.1

5757575555575555545454545454545252525252525252525252505055545455596361575755576159

14.014.014.013.013.014.013.013.012.012.012.012.012.012.012.011.011.011.011.011.011.011.011.011.011.011.010.010.013.012.012.013.015.017.016.014.014.013.014.016.015.0

24 24 23 21 21 21 20 19 17 18 18 18 17 17 18 17 17 17 17 17 17 17 17 17 18 18 17 17 23 21 22 23 27 33 30 26 25 24 28 37 34

13 8 11 6 6 3 7 0 6 0 7 10 9 10 8 9 7 7 7 7 0 5 0 0 0 0 0 6 21 20 26 13 7 5 3 10 16 10 8 5 0

090090080100060160140000190000240210190210230230220230240240000200000000000000000080090050110030020090360010070080110230000

17 16 30 31 26 20 23 

28.33 28.32 28.32 28.31 28.30 28.29 28.29 28.28 28.28 28.27 28.27 28.25 28.25 28.24 28.23 28.22 28.21 28.20 28.20 28.20 28.20 28.20 28.20 28.20 28.21 28.21 28.22 28.23 28.24 28.24 28.25 28.24 28.24 28.25 28.25 28.25 28.25 28.27 28.27 28.28 28.28

4 7 7 2 2 

000020024014010
Event #2 – August 26, 2011:

A single exceedance at the Apache Junction monitor in Pinal County, but located within the eastern 

boundary of the Phoenix PM10 nonattainment area, occurred on August 26, 2011, and was caused by 

emissions generated from thunderstorm outflows originating in the southwestern deserts of the state (see 

Figure 5-4). The exceedance was limited to the eastern-most Apache Junction monitor due to the 

presence of moderate westerly winds in most of Maricopa County, but strong southwesterly winds in 

Pinal County. Without the dust generated by the thunderstorm outflows, there would not have been an 

exceedance of the 24-hour PM10 standard in the Phoenix PM10 nonattainment area. 

 1:00 p.m. 2:00 p.m. 4:00 p.m. 6:00 p.m. 

1900z Aug 26 2100z Aug 26 2300z Aug 26 0100z Aug 27 

 8:00 p.m. 10:00 p.m. 12:00 a.m. 3:00 a.m. 

0300z Aug 27 0500z Aug 27 0700z Aug 27 1000z Aug 27 

Figure 5-4. Satellite imagery showing strong storms developing and dissipating over southwestern 

Arizona. These storms are believed to have been responsible for the thunderstorm outflow boundary that 

caused PM10 exceedances in the eastern portion of the Phoenix PM10 nonattainment area and in Pinal 

County on August 26. 

Thunderstorms developed over southwestern Arizona during the mid-afternoon hours and, by the early 

evening hours, winds out of the west-southwest reached sustained speeds up to 30 mph at the Phoenix 

Mesa Williams Airport (also called the Williams Gateway Airport) in southeastern Maricopa County, 

visibility rapidly decreased from 35 miles to 2 miles, and PM10 concentrations simultaneously increased 

from around 50 μg/m3

 to over 500 μg/m3 at multiple monitoring sites (see Figure 5-5) as dust was 

transported into the region. The Mesa Williams data were used for this event due to the proximity of that 

station to the monitors that were most impacted by the dust event. Considering the amount of deposition 

of dust from the event on August 25th, very loose soils were also easily re-entrained back into the 

atmosphere, contributing to the rise in PM10 concentrations. The thunderstorm outflow winds produced 

broad areas of windblown dust that impacted most of the Phoenix PM10 nonattainment area monitoring 

sites (Figure 5-5 shows peak 1-hour concentrations on the 26th ranging from 200 μg/m3

 to 850 μg/m3), but 

due to the short duration of the strong winds in the Phoenix area and the southwesterly direction of the 

winds allowing the Estrella Mountain and South Mountain ranges to limit some of the PM10 transport, 

none of the Maricopa County monitoring sites exceeded the standard. It should be noted, though, that the 

38
Higley monitor in far southeastern Maricopa County did record a 24-hour average PM10 concentration of 

150 μg/m3

, which was one microgram shy of an exceedance. However, to the south in Pinal County, 

where the winds were not obstructed by terrain, hourly PM10 concentrations exceeded 1,500 μg/m3 at 

three sites (see Figure 5-6) and six of the seven PM10 monitoring sites in the county exceeded the PM10 

standard. Because of the southwesterly wind flow direction, PM10 was transported through Pinal County 

and southeastern Maricopa County and toward the Apache Junction monitor. The peak PM10 

concentrations at this monitoring site occurred a couple hours later than most of the other sites and 

because the winds weakened by the time they reached the Apache Junction area, the dust remained over 

the Apache Junction monitoring site for several hours, causing it to measure the only 24-hour average 

exceedance within the Phoenix PM10 nonattainment area on this day. 

A visualization of this dust event was created using Phoenix visibility camera images and can be found at: 

www.phoenixvis.net/videos/mpeg4/SOMT_08262011.mp4

The video clearly shows the dust blowing across the Phoenix region, but the dust cloud was not as dense 

as it was in videos of the windblown dust events in early July 2011. Videos showing other views across 

the Valley on this date are also available (see Visibility Cameras section). 

39
Figure 5-5. Phoenix nonattainment area PM10 monitor readings and Mesa Williams visibility and wind 

speed for August 26, 2011.

40
Figure 5-6. Pinal County PM10 monitor readings and Casa Grande visibility and wind speed for August 

26, 2011.

41
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 

(08/2011) 

Elevation: 1107 ft. above sea level Latitude: 33.427 Longitude: -112.003 Data Version: VER3

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point

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

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

Rel 

Humd 

%

Wind

Speed(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

N

3

C

(m

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

26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26

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

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

FEW120 SCT160 BKN210 FEW120 SCT160 BKN210 CLR FEW250 SCT150 BKN250 FEW100 SCT150 SCT250 FEW150 SCT180 SCT210 FEW150 SCT180 SCT210 FEW150 SCT180 SCT210 FEW150 SCT180 SCT210 FEW120TCU SCT150 SCT210 FEW120 SCT150 SCT210 FEW120 SCT180 SCT210 FEW120 SCT180 SCT250 FEW120 SCT180 SCT250 SCT120 SCT180 BKN250 SCT120 SCT180 BKN250 SCT120 SCT180 BKN250 SCT120 SCT180 BKN250 SCT120 SCT180 SCT250 FEW120 SCT180 SCT250 FEW120 SCT180 SCT250 FEW120 SCT250 FEW120 SCT250

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

98979594949494961011051081091111151131131131101051051021009996

36.736.135.034.434.434.434.435.638.340.642.242.843.946.145.045.045.043.340.640.638.937.837.235.6

707069696969707071717272737372727272727273737272

21.020.820.720.620.320.620.821.221.721.822.322.222.722.822.222.222.022.322.322.322.622.622.422.2

545455555455565655535352535149494852555558595960

12.212.212.812.812.212.813.313.312.811.711.711.111.710.69.49.48.911.112.812.814.415.015.015.6

23 24 26 27 26 27 28 26 22 18 16 15 15 12 12 12 12 15 19 19 23 26 27 30

9 6 6 6 10 11 11 8 10 8 7 8 7 7 8 11 8 11 11 7 7 3 3 9

080130130080080070080080100100150080VR VR 150190180200250270100160160150

18 

28.62 28.61 28.61 28.60 28.61 28.63 28.65 28.66 28.66 28.68 28.66 28.65 28.63 28.60 28.57 28.56 28.56 28.57 28.59 28.61 28.65 28.65 28.66 28.66

0 3 1 0 8 5 3 1

0000010002010101

42
U.S. Department of Commerce 

National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL CLIMATOLOGICAL DATA 

(final) 

HOURLY OBSERVATIONS TABLE 

WILLIAMS GATEWAY AIRPORT (23104) 

PHOENIX, AZ 

(08/2011) 

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

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

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

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

Rel

Humd

%

Wind 

Speed 

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-h

Chg

(mb

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

26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 

0015 0035 0055 0115 0135 0155 0215 0235 0255 0315 0335 0355 0415 0435 0455 0515 0535 0547 0647 0747 0947 1048 1147 1247 1347 1447 1547 1647 1747 1757 1835 1847 1931 1947 

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 FEW150 SCT200 FEW120 FEW200 FEW200 FEW120 SCT200 FEW120 SCT200 FEW120 SCT200 SCT120 SCT200 SCT120TCU BKN200 SCT120TCU BKN200 SCT120TCU BKN200 SCT120 BKN250 SCT120 BKN200 SCT120 BKN200 SCT120 BKN200 SCT120 BKN200 SCT120 BKN200 BKN 

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 20.00 45.00 45.00 45.00 45.00 45.00 45.00 45.00s 35.00 35.00 35.00 20.00 2.00 5.00 5.00 5.00 5.00 

BLDU BLDU BLDUs BLDU BLDU 

9999999997979797979191909090888886889097106109109111117109115115111109102102102102

37.037.037.037.036.036.036.036.036.033.033.032.032.032.031.031.030.031.032.036.041.043.043.044.047.043.046.046.044.043.039.039.039.039.0

707070706969696969686968686869696969697373737373757374737272727375M

21.121.121.121.120.820.820.820.820.820.120.619.919.919.920.620.620.320.620.422.622.922.622.622.923.722.623.422.622.022.122.322.823.9M 

54545454545454545455575555555959595957615754545454545450505257596361

12.012.012.012.012.012.012.012.012.013.014.013.013.013.015.015.015.015.014.016.014.012.012.012.012.012.012.010.010.011.014.015.017.016.0

22 22 22 22 24 24 24 24 24 30 32 31 31 31 38 38 40 38 33 30 20 16 16 15 13 16 14 12 13 15 23 24 28 M 

15 14 10 8 5 5 0 0 0 3 5 0 0 0 0 0 0 5 5 3 6 11 16 8 15 11 7 7 5 30s 9s 11 21 9 

040 030 030 030 360 050 000 000 000 260 270 000 000 000 000 000 000 090 110 120 VR 150 180 190 190 160 180 170 120 220 210 240 130 170 

28.36 28.36 28.36 28.37 28.37 28.36 28.36 28.36 28.36 28.36 28.36 28.36 28.36 28.36 28.37 28.38 28.38 28.39 28.40 28.41 28.43 28.42 28.41 28.39 28.36 28.34 28.32 28.32 28.32 28.34 28.35 28.36 28.38 M 

43
26 

26 26 26 26 26 26 26 26 26 26 26 26

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

CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR

7.00 7.00 5.00 5.00 5.00 5.00 5.00 5.00 5.00 7.00 10.00 10.00 10.00

HZ HZ HZ HZ HZ HZ HZ 

100100100100999999979797979793

38.038.038.038.037.037.037.036.036.036.036.036.034.0

74737474727272727272717371

23.122.523.123.122.422.422.422.122.122.121.522.621.5

61596161595959595959576159

16.015.016.016.015.015.015.015.015.015.014.016.015.0

28 26 28 28 27 27 27 28 28 28 26 30 32

10 9 0 3 0 3 0 5 5 8 5 5 0

160 110 000 060 000 030 000 120 130 180 160 160 000

28.39 28.40 28.40 28.41 28.41 28.41 28.42 28.42 28.42 28.43 28.42 28.43 28.43

44
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 

(08/2011) 

Elevation: 1462 ft. above sea level Latitude: 32.95 Longitude: -111.766 Data Version: VER2

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

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

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

Rel

Humd

%

Wind 

Speed 

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb)

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

26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 

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 

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 

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 

90889090868688888486868486848484848484848688889090919193959799

32.031.032.032.030.030.031.031.029.030.030.029.030.029.029.029.029.029.029.029.030.031.031.032.032.033.033.034.035.036.037.0

70707069707068676768686768676767676767696970697071717172727473

21.021.221.020.420.920.920.119.519.419.719.719.419.719.419.419.419.419.419.420.520.321.220.621.021.521.721.722.022.323.222.9

59615957616157555757575757575757575757615961595961616161616361

15.016.015.014.016.016.014.013.014.014.014.014.014.014.014.014.014.014.014.016.015.016.015.015.016.016.0

16.016.016.017.016.0

35 40 35 33 43 43 35 33 40 37 37 40 37 40 40 40 40 40 40 46 40 40 38 35 38 37 37 34 32 33 29 

0 0 5 0 3 5 6 5 6 6 6 6 7 8 8 8 8 5 5 5 6 5 5 6 5 7 5 6 3 8 6 

000 000 290 000 330 010 010 020 350 330 350 010 360 350 350 360 350 010 130 110 110 100 080 080 110 110 120 130 110 110 090 

28.28 28.28 28.29 28.29 28.28 28.28 28.27 28.27 28.27 28.27 28.27 28.27 28.27 28.27 28.27 28.28 28.28 28.29 28.30 28.31 28.31 28.32 28.32 28.33 28.33 28.33 28.34 28.34 28.34 28.34 28.34 

2 7 2 

007003020

45
46

26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26 26

1035 1055 1115 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 0 0 0

CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR SCT005 FEW005 OVC005 BKN003 BKN007 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 9.00 10.00 10.00 10.00 10.00 8.00 10.00 10.00 1.25 2.50 0.75 1.00 10.00 10.00 4.00 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

1001001021021041061061081091081081081061021041061091081061081029999979797979797979795959393919190909088

38.038.039.039.040.041.041.042.043.042.042.042.041.039.040.041.043.042.041.042.039.037.037.036.036.036.036.036.036.036.036.035.035.034.034.033.033.032.032.032.031.0

7474747474747474747373737271727273727274737374747373737272727270707070707069717170

23.023.023.323.323.123.423.423.123.322.722.722.722.421.822.122.422.822.422.423.122.822.923.523.222.622.622.622.122.122.122.121.221.220.920.921.121.120.421.521.521.2

6161616159595957575555555555555555545557596163636161615959595957575757595957616161

16.016.016.016.015.015.015.014.014.013.013.013.013.013.013.013.013.012.013.014.015.016.017.017.016.016.016.015.015.015.015.014.014.014.014.015.015.014.016.016.016.0

28 28 26 26 23 21 21 19 18 17 17 17 19 21 20 19 17 17 19 19 24 29 31 33 30 30 30 28 28 28 28 28 28 30 30 34 34 33 38 38 40

8 7 0 6 5 5 8 5 8 9 8 9 18 14 8 10 9 0 13 21 20 18 16 13 7 6 5 14 13 5 6 5 5 6 6 6 3 3 0 3 0

100 130 000 180 090 130 130 100 180 070 080 040 090 090 080 080 070 000 240 250 230 210 210 210 240 220 130 110 100 100 310 260 220 130 160 190 210 270 000 260 000

23 25 23 

28.34 28.34 28.33 28.33 28.32 28.32 28.31 28.30 28.29 28.28 28.27 28.27 28.25 28.25 28.24 28.24 28.24 28.24 28.24 28.25 28.27 28.27 28.27 28.27 28.27 28.27 28.28 28.30 28.30 28.30 28.30 28.30 28.30 28.33 28.34 28.34 28.34 28.34 28.33 28.33 28.32

2 7 7 2 2 

003024010020014
Event #3 – August 27-28, 2011:

On August 27, 2011, weather conditions were nearly identical to those on August 24, and once again 

severe thunderstorms developed in the evening hours (see Figure 5-7) over southwestern Arizona, and 

thunderstorm outflows produced a “haboob.” This resulted in the following impacts in the Phoenix area: 

winds increased to 20-25 mph, with gusts up to 32 mph; visibility dropped from 10 miles to as low as 1 

mile; and weather conditions were reported as “blowing dust” and “haze” at multiple airports in the 

region. Due to two previous days with dust events leading up to this one, broad, ambient PM10 

concentrations were elevated from those expected this time of year, roughly 50-100 μg/m3 prior to the 

arrival of the “haboob,” but during the hours of peak wind gusts late on August 27th, hourly PM10 

concentrations exceeded 2400+ μg/m3

 at six sites and over 3600 μg/m3 at the West 43rd site in Phoenix. 

Eleven sites total in the Phoenix PM10 nonattainment area exceeded the PM10 standard on August 27 and 

August 28. Without the existence of the PM10 emissions generated by the thunderstorm outflows and the 

transport of dust from western Arizona into the Phoenix region, there would not have been any 

exceedances of the 24-hour PM10 standard in the Phoenix PM10 nonattainment area. 

 12:00 p.m. 2:00 p.m. 4:00 p.m. 6:00 p.m. 

1900z Aug 27 2100z Aug 27 2300z Aug 27 0100z Aug 28 

 8:00 p.m. 10:00 p.m. 12:00 a.m. 3:00 a.m. 

0300z Aug 28 0500z Aug 28 0700z Aug 28 1000z Aug 28 

Figure 5-7. Satellite imagery showing strong storms developing and dissipating over south-southwestern 

Arizona. These storms are believed to have been responsible for the thunderstorm outflow boundary that 

caused PM10 exceedances across the Phoenix PM10 nonattainment area and in Pinal County on 

August 27-28. 

47
Figures 5-8 and 5-10 show the hourly PM10 concentrations at monitors throughout the Phoenix PM10 

nonattainment area as well as visibility readings and sustained wind speeds reported at the Phoenix Sky 

Harbor Airport for August 27th and 28th. Most of the monitors show large PM10 concentration increases, 

along with corresponding visibility decreases at the airport, between 8:00 p.m. on the August 27 and 1:00 

a.m. on August 28 as light southeasterly winds abruptly shifted to strong westerly winds with the arrival 

of the thunderstorm outflow winds. These PM10 spikes and reductions in visibility also coincided with 

reports of blowing dust and haze at the Sky Harbor Airport. Due to the west-to-east flow of the winds, 

the transport of dust impacted the PM10 monitoring sites sequentially from Buckeye in the west, to the 

central Phoenix area, to West Chandler, and then lastly to the Higley and Apache Junction sites on the 

eastern side of the Phoenix PM10 nonattainment area. The timing of winds resulted in the majority of the 

sites experiencing peak 1-hour PM10 concentrations very late on August 27th, causing their 24-hour 

averages and PM10 exceedances to occur on the 27th. However, the dust storms did not reach the eastern 

side of the region until after midnight, causing the Higley and Apache Junction monitors to experience 

their peak 1-hour concentrations and lingering elevated PM10 concentrations for several hours on August 

28 (as shown in Figure 5-10); therefore, the exceedances for those two sites occurred on the 28th. While 

the monitoring sites in Pinal County also experienced PM10 exceedances on August 27th and 28th (see 

Figures 5-9 and 5-11), the westerly wind direction during this event meant that desert areas to the west of 

the Phoenix PM10 nonattainment area were the primary dust source region, rather than the desert areas of 

Pinal County, as was the case with the first two events during the August 25-28 period. 

48
Figure 5-8. Phoenix nonattainment area PM10 monitor readings and Sky Harbor visibility and wind 

speed for August 27, 2011. 

49
Figure 5-9. Pinal County PM10 monitor readings and Casa Grande visibility and wind speed for August 

27, 2011. 

50
Figure 5-10. Phoenix nonattainment area PM10 monitor readings and Mesa Williams visibility and wind 

speed for August 28, 2011. 

51
Figure 5-11. Pinal County PM10 monitor readings and Casa Grande visibility and wind speed for August 

28, 2011. 

52
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 

(08/2011) 

Elevation: 1107 ft. above sea level Latitude: 33.427 Longitude: -112.003 Data Version: VER3

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point

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

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

Rel 

Humd 

%

Wind 

Speed 

(MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Ne

3-h

Ch

(m

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

27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27

0051 0151 0251 0351 0451 0551 0651 0751 0851 0951 1051 1151 1251 1351 1451 1551 1651 1751 1851 1951 2000 2051 2151 2233 2248 2251 2259 2318 2329 2342 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 11 11

FEW120 SCT250 FEW120 SCT250 FEW120 SCT250 FEW120 SCT250 FEW120 SCT250 FEW120 SCT250 FEW100 SCT150 SCT200 FEW110 SCT160 SCT250 FEW110 SCT160 SCT250 FEW110 SCT160 SCT250 FEW110 SCT160 SCT250 FEW110 SCT160 SCT250 FEW110 SCT160 SCT250 FEW110 SCT250 FEW110 SCT180 SCT250 FEW110 SCT180 SCT250 FEW110 SCT180 SCT250 FEW110 SCT180 SCT250 SCT110 BKN180 BKN250 SCT110 BKN180 BKN250 SCT110 BKN180 BKN250 SCT130 BKN190 BKN230 SCT130 BKN190 BKN250 SCT130 BKN190 BKN250 SCT130 BKN190 BKN250 BKN010 BKN130 BKN190 VV008 BKN009 BKN130 BKN190 BKN009 BKN130 BKN190 BKN015 BKN130 BKN190 BKN017 BKN130 BKN190

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 6.00 9.00 1.75 1.25 1.00 2.00 4.00 5.00 9.00

BLDU HZ 

949493929191919497101105105107110110110111111103102102101999793929190909090

34.434.433.933.332.832.832.834.436.138.340.640.641.743.343.343.343.943.939.438.939.038.337.236.034.033.333.032.032.032.032.2

73727271717171717172727273747373737271696969727373737273737271

22.521.922.321.921.721.421.421.621.621.922.322.322.823.023.022.822.522.321.520.520.320.822.122.722.622.522.322.522.522.221.6

62606261616060595756555556555554525153494851586163636364646361

16.715.616.716.116.115.615.615.013.913.312.812.813.312.812.812.211.110.611.79.49.010.614.416.017.017.217.018.018.017.016.1

35 32 36 36 37 35 35 31 26 22 19 19 19 16 16 16 14 14 19 17 16 19 26 30 37 38 39 42 42 41 38

7 6 8 5 0 5 7 3 6 7 3 5 3 11 8 7 5 5 16 13 8 6 6 22 23 22 23 18 18 18 16

140140120120000100100130070070VR 220290290280VR VR 020060030040130140280280290290290300300300

18 17 26 32 

28.66 28.66 28.65 28.66 28.66 28.66 28.69 28.69 28.70 28.70 28.69 28.68 28.66 28.64 28.60 28.58 28.57 28.56 28.58 28.60 28.60 28.62 28.64 28.66 28.66 28.66 28.66 28.66 28.68 28.69 28.69

7 3 3 0 8 6 3 1 

001004011000022023010020

53
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 

(08/2011) 

Elevation: 1107 ft. above sea level Latitude: 33.427 Longitude: -112.003 Data Version: VER3

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

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

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

Rel

Humd

%

Wind 

Speed (MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb)

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

28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28

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

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

SCT130 BKN190 FEW130 SCT190 FEW130 SCT250 SCT200 BKN250 SCT200 BKN250 FEW130 SCT250 FEW110 SCT250 FEW110 SCT250 FEW110 SCT250 FEW110 SCT250 FEW150 FEW150 FEW150 FEW110 SCT250 FEW110 SCT250 FEW110 SCT250 FEW110 SCT250 FEW110 SCT250 FEW110 SCT250 FEW110 SCT250 FEW250 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

9090909091918992949610110110410510610710610610410299989796

32.232.232.232.232.832.831.733.334.435.638.338.340.040.641.141.741.141.140.038.937.236.736.135.6

717171717171717172727372737474737272717171717171

21.921.921.921.921.721.421.421.922.222.222.722.422.623.023.122.822.422.221.721.621.421.721.621.7

626262626160616161605958575858565554535455575758

16.716.716.716.716.115.616.116.116.115.615.014.413.914.414.413.312.812.211.712.212.813.913.914.4

39 39 39 39 37 35 39 36 33 30 25 24 21 21 21 19 19 18 18 20 23 26 26 28

11 9 8 10 8 7 6 6 3 0 5 7 13 10 13 10 13 16 17 13 7 8 9 11

260 290 330 330 330 270 240 190 220 000 250 VR 280 310 260 270 260 270 260 270 250 260 280 270

17 17 17 21 20 

28.71 28.70 28.69 28.69 28.68 28.68 28.70 28.70 28.70 28.69 28.69 28.66 28.64 28.62 28.58 28.55 28.54 28.53 28.53 28.55 28.57 28.58 28.58 28.58

0 6 3 8 8 6 3 1

017010010006025026004009

54
U.S. Department of Commerce 

National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL CLIMATOLOGICAL DATA 

(final) 

HOURLY OBSERVATIONS TABLE 

WILLIAMS GATEWAY AIRPORT (23104) 

PHOENIX, AZ 

(08/2011) 

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

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

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

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

Rel

Humd

%

Wind 

Speed (MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb

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

27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 

0015 0035 0055 0115 0135 0155 0215 0235 0255 0315 0335 0355 0415 0435 0455 0515 0535 0547 0647 0747 0850 0947 1047 1147 1247 1347 1447 1547 1647 1747 1752 1827 1851 1947 

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 SCT150 SCT150 SCT150 SCT150 SCT150 SCT150 SCT150 SCT150 SCT150 SCT100 SCT250 SCT100 SCT250 SCT100 SCT250 SCT110 BKN250 SCT110 BKN250 SCT110CB BKN250 SCT110CB BKN250 CLR108CB 

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 20.00 35.00 30.00 30.00 20.00 20.00 20.00 20.00 20.00 20.00 20.00s 3.00 20.00s 20.00s 20.00 

BLDU BLDU TS BLDU TS 

91919191908888888888868888888888868888909799102106108108109109111M 108104106102

33.033.033.033.032.031.031.031.031.031.030.031.031.031.031.031.030.031.031.032.036.037.039.041.042.042.043.043.044.0M 42.0s40.041.039.0

7070707070707071717170707069696869707171747372747674737272M727272M

21.121.121.121.121.021.221.221.821.821.820.921.221.220.620.620.120.321.221.821.523.522.922.323.424.223.222.822.122.4M 22.422.122.4M 

59595959596161636363616161595957596163616461575961575552525254555555

15.015.015.015.015.016.016.017.017.017.016.016.016.015.015.014.015.016.017.016.018.016.014.015.016.014.013.011.011.011.012.013.013.013.0

34 34 34 34 35 40 40 43 43 43 43 40 40 38 38 35 40 40 43 38 34 29 23 21 22 19 17 15 14 M 17 20 19 M 

3 6 5 6 0 3 5 5 0 0 5 6 6 6 3 5 5 5 5 5 5 0 6 6 11 11 7 6 7 13 26 21 20 7 

080 080 080 090 000 160 130 150 000 000 080 090 070 090 100 110 100 150 120 130 150 000 240 270 240 270 270 260 310 330 040 040 050 VR 

34 29 26 

28.43 28.42 28.42 28.42 28.42 28.42 28.42 28.42 28.42 28.42 28.42 28.42 28.42 28.43 28.43 28.43 28.43 28.43 28.45 28.45 28.46 28.46 28.46 28.44 28.43 

28.40 28.36 28.34 28.32 28.31 28.33 28.34 28.36 M 

55
27 

27 27 27 27 27 27 27 27 27 27 27

1955 2015 2035 2055 2115 2135 2155 2215 2255 2315 2335 2355

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

SCT085 SCT085 CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR

10.00 10.00 7.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00

-RA TS 

100100100979997999797979797

38.038.038.036.037.036.037.036.036.036.036.036.0

707071727271717272737373

21.221.321.522.122.421.521.322.122.122.622.622.6

545455595957555959616161

12.012.013.015.015.014.013.015.015.016.016.016.0

21 21 22 28 27 26 23 28 28 30 30 30

17 10 16 10 3 3 5 10 16 8 7 11

050 140 150 160 140 220 110 240 260 270 280 310

24 18 28 16 18 13s 17

28.33 28.37 28.40 28.40 28.39 28.39 28.39 28.40 28.41 28.41 28.41 28.44

56
U.S. Department of Commerce 

National Oceanic & Atmospheric Administration QUALITY CONTROLLED LOCAL CLIMATOLOGICAL DATA 

(final) 

HOURLY OBSERVATIONS TABLE 

WILLIAMS GATEWAY AIRPORT (23104) 

PHOENIX, AZ 

(08/2011) 

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

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

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

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

Rel

Humd

%

Wind 

Speed (MPH)

Wind

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb)

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

28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 

0015 0035 0055 0115 0135 0155 0215 0235 0255 0315 0335 0355 0415 0435 0455 0515 0547 0647 0747 0847 0947 1047 1147 1247 1347 1447 1547 1647 1747 1847 1947 

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 M CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR CLR FEW100 BKN250 SCT150 SCT150 FEW150 FEW200 FEW170 CLR CLR FEW150 FEW150 FEW120 FEW120 FEW250 FEW250 FEW250 CLR 

2.00 2.50 5.00 7.00 10.00 10.00 5.00 5.00 7.00 7.00 7.00 7.00 7.00 7.00 7.00 7.00 5.00 5.00 5.00 7.00 7.00 7.00 7.00 7.00 20.00 15.00 15.00 20.00 30.00 35.00 20.00 

HZ HZ HZ HZ HZ HZ HZ HZ 

93939190909090909090909090909090909091939799102106106108108108108108102

34.034.033.032.032.032.032.032.032.032.032.032.032.032.032.032.032.032.033.034.036.037.039.041.041.042.042.042.042.042.039.0

737371717172727272717171717171717272737374747474737372737373M

22.922.921.721.521.522.122.122.122.121.521.521.521.521.521.521.522.122.422.622.923.223.523.323.422.922.722.422.722.722.7M 

64646161616363636361616161616161636464646363615957555455555557

18.018.016.016.016.017.017.017.017.016.016.016.016.016.016.016.017.018.018.018.017.017.016.015.014.013.0

12.013.013.013.014.0

38 38 37 38 38 41 41 41 41 38 38 38 38 38 38 38 41 42 41 38 33 31 26 21 20 17 17 17 17 17 M 

14 18 17 14 13 8 7 9 8 8 11 9 8 9 7 6 5 3 6 6 5 5 3 6 9 11 9 13 11 8 10 

330 330 320 320 310 320 320 340 350 360 360 330 330 330 310 310 290 VR 250 230 210 VR VR 250 270 300 300 280 300 300 280 

23 16 

28.45 28.45 28.46 28.46 28.46 28.46 28.46 28.46 28.45 28.45 28.44 28.45 28.44 28.44 28.44 28.44 28.44 28.46 28.46 28.46 28.46 28.45 28.43 28.40 28.37 28.34 28.31 28.29 28.29 28.29 M 

57
28 

28 28 28 28 28 28 28 28 28 28 28 28

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

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

1001001001001009997979797909390

38.038.038.038.038.037.036.036.036.036.032.034.032.0

71717172727072727271707171

21.521.521.522.022.021.322.122.122.121.521.021.421.5

55555557575559595957595961

13.013.013.014.014.013.015.015.015.014.015.015.016.0

22 22 22 24 24 23 28 28 28 26 35 32 38

11 8 8 9 7 6 6 0 3 0 3 0 0

300 300 300 310 280 250 250 000 040 000 140 000 000

28.31 28.32 28.32 28.33 28.33 28.33 28.33 28.34 28.34 28.34 28.34 28.34 28.34

58
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 

(08/2011) 

Elevation: 1462 ft. above sea level Latitude: 32.95 Longitude: -111.766 Data Version: VER2

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

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

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

Rel 

Humd

%

Wind 

Speed (MPH)

Wind 

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb)

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

27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 

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 

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 

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 

86 86 88 88 88 86 84 82 82 82 82 82 82 82 82 82 82 81 81 81 82 84 86 86 90 90 91 93 95 97 97 

30.030.031.031.031.030.029.028.028.028.028.028.028.028.028.028.028.027.027.027.028.029.030.030.032.032.033.034.035.036.036.0

70697070707069686868686868686868686868686869707071717172727372

20.920.321.221.221.220.920.520.220.220.220.220.220.220.220.220.220.220.020.020.020.220.520.920.921.521.521.722.022.322.622.1

61596161616161616161616161616161616161616161616161616161616159

16.015.016.016.016.016.016.016.016.016.016.016.016.016.016.016.016.016.016.016.016.016.016.016.016.016.0

16.016.016.016.015.0

43 40 40 40 40 43 46 49 49 49 49 49 49 49 49 49 49 51 51 51 49 46 43 43 38 38 37 34 32 30 28 

0 0 0 6 5 0 0 0 0 0 5 0 0 0 3 5 0 0 0 0 5 0 0 0 3 6 0 0 0 0 0 

000 000 000 110 090 000 000 000 000 000 060 000 000 000 100 080 000 000 000 000 130 000 000 000 170 130 000 000 000 000 000 

28.32 28.33 28.33 28.33 28.33 28.33 28.33 28.33 28.32 28.32 28.32 28.32 28.32 28.33 28.34 28.33 28.33 28.34 28.34 28.36 28.36 28.36 28.37 28.37 28.37 28.37 28.37 28.38 28.38 28.38 28.38 

7 2 2 

003003010

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 

59
27 

27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27

1035 1055 1115 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 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 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 2.50 10.00 10.00 8.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 5.00 6.00

VCTS VCTS VCTS VCTS VCTS 

97 97 99 10010210010210410410610610610810810810910910910910910910910810810810299 99 91 88 93 93 93 91 90 90 90 88 90 88 88

36.036.037.038.039.038.039.040.040.041.041.041.042.042.042.043.043.043.043.043.043.043.042.042.042.039.037.037.033.031.034.034.034.033.032.032.032.031.032.031.031.0

7373737474747474757474747575747575757474747373727471717173717372737272717170717171

22.622.622.923.123.323.123.323.123.623.423.423.423.623.623.123.823.823.823.323.323.322.822.722.423.121.821.821.822.621.822.622.022.622.322.121.521.521.221.521.821.8

6161616161616159615959595959575959595757575555545755575764636361636363616161616363

16.016.016.016.016.016.016.015.016.015.015.015.015.015.014.015.015.015.014.014.014.013.013.012.014.013.014.014.018.017.017.016.017.017.017.016.016.016.016.017.017.0

30 30 29 28 26 28 26 23 24 21 21 21 20 20 19 20 20 20 18 18 18 17 17 17 19 21 25 25 41 43 37 34 37 39 41 38 38 40 38 43 43

0 0 0 3 0 0 6 7 6 10 11 9 0 7 7 9 8 13 10 13 6 9 7 9 10 22 22 14 13 9 7 11 8 9 9 6 7 10 14 20 15

000 000 000 260 000 000 260 190 230 280 250 280 000 260 280 290 260 310 250 290 320 350 340 350 350 030 040 060 220 140 110 130 170 230 260 220 240 270 270 280 280

16 20 17 17 32 30 18 23 22

28.38 28.38 28.37 28.37 28.36 28.36 28.35 28.34 28.33 28.32 28.31 28.30 28.28 28.27 28.25 28.25 28.25 28.25 28.24 28.23 28.22 28.22 28.25 28.25 28.24 28.25 28.25 28.27 28.30 28.32 28.32 28.30 28.29 28.32 28.32 28.33 28.32 28.32 28.32 28.32 28.33

2 7 7 2 2 

003024030027007

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 M M M

60
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 

(08/2011) 

Elevation: 1462 ft. above sea level Latitude: 32.95 Longitude: -111.766 Data Version: VER2

Dry 

Bulb 

Temp

Wet 

Bulb 

Temp

Dew 

Point 

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

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

Rel 

Humd

%

Wind 

Speed (MPH)

Wind 

Dir

Wind

Gusts

(MPH)

Station

Pressure

(in. hg)

Press

Tend

Net

3-hr

Chg

(mb)

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

28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 

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 

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 

6.00 9.00 7.00 9.00 1.50 3.00 9.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 10.00 8.00 6.00 7.00 8.00 10.00 10.00 10.00 10.00 10.00 8.00 5.00 6.00 7.00 10.00 10.00 10.00 

88 90 90 91 88 88 86 86 86 86 84 84 84 84 82 81 81 81 81 81 81 82 82 84 86 88 90 91 91 91 93 

31.032.032.033.031.031.030.030.030.030.029.029.029.029.028.027.027.027.027.027.027.028.028.029.030.031.032.033.033.033.034.0

70696968717170707070696969697070707070696970707071727272727273

21.220.420.420.121.821.820.920.920.920.920.520.520.520.520.821.021.021.021.020.620.620.820.821.221.522.122.122.322.322.322.6

61575755636361616161616161616364646464636363636363646363636363

16.014.014.013.017.017.016.016.016.016.016.016.016.016.017.018.018.018.018.017.017.017.017.017.017.018.0

17.017.017.017.017.0

40 33 33 30 43 43 43 43 43 43 46 46 46 46 53 56 56 56 56 54 54 53 53 49 46 45 41 39 39 39 37 

16 16 13 11 11 11 10 8 9 7 6 3 0 0 3 5 5 3 0 5 3 7 7 7 7 8 7 7 3 0 5 

290 290 300 320 350 360 360 010 350 350 360 210 000 000 210 230 200 200 000 210 220 190 200 210 200 190 210 210 230 000 190 

23 21 

28.34 28.35 28.36 28.36 28.37 28.38 28.37 28.36 28.36 28.37 28.37 28.36 28.36 28.36 28.36 28.36 28.36 28.36 28.37 28.38 28.39 28.39 28.39 28.39 28.38 28.38 28.38 28.38 28.38 28.38 28.37 

2 7 2 

020007010

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 

61
62

28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28 28

1035 1055 1115 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 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 CLR CLR CLR CLR CLR CLR CLR

10.00 10.00 10.00 9.00 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 10.00 10.00 10.00 10.00

95 95 97 97 99 10010010010210410610610610610810810610610610610610410210210010099 99 97 97 97 95 95 95 93 93 91 91 90 90 88

35.035.036.036.037.038.038.038.039.040.041.041.041.041.042.042.041.041.041.041.041.040.039.039.038.038.037.037.036.036.036.035.035.035.034.034.033.033.032.032.031.0

727273737374M72M7373737272737372737373M7473727272717070707069696968686868686867

22.322.322.622.622.923.0M 22.0M 22.622.922.922.422.422.722.722.422.822.822.8M 23.122.822.322.022.021.821.321.021.021.020.720.720.720.120.119.820.019.919.919.3

6161616161615957575757575555555555575757575959575757575555555555555554545455555554

16.016.016.016.016.016.015.014.014.014.014.014.013.013.013.013.013.014.014.014.014.015.015.014.014.014.014.013.013.013.013.013.013.013.012.012.012.013.013.013.012.0

32 32 30 30 29 28 M 24 M 21 20 20 19 19 17 17 19 20 20 20 M 23 24 23 24 24 25 23 24 24 24 26 26 26 27 27 29 30 31 31 31

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

000 000 270 270 270 270 260 300 320 320 290 310 270 320 300 260 270 280 250 250 260 260 260 280 270 270 270 270 270 280 280 270 270 290 280 260 000 240 230 000 000

17 18 16 17 16 20 20 18 

28.36 28.36 28.35 28.35 28.34 28.33 M 28.31 M 28.29 28.28 28.27 28.27 28.25 28.25 28.24 28.23 28.22 28.22 28.22 M 28.21 28.21 28.21 28.21 28.22 28.22 28.23 28.23 28.24 28.24 28.25 28.25 28.25 28.25 28.25 28.25 28.25 28.25 28.25 28.25

7 7 7 2 2 

010027024003010

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 M M M
Visibility Cameras

Visibility camera images were compiled into time lapse photography videos in order to visually show the 

dust impacts on portions of Maricopa County on June 27. The animations are available online for each 

event and or each of the visibility camera sites in Maricopa County. These views can be accessed using 

the camera site codes SOMT (South Mountain), CAME (Camelback Mountains), SUPM (Superstition 

Mountains), ESMO (Estrella Mountains), and WHTM (White Tank Mountains). It should be noted that 

these time lapse photography videos may require the installation of a mp4 viewer. 

The video files can be accessed as follows: 

http://www.phoenixvis.net/videos/mpeg4/xxxx_mmddyyyy.mp4

xxxx = 4-character site code (ie. SOMT) 

mm = 2-character month (ie. 06) 

dd = 2-character day (ie. 27) 

yyyy = 4-character year (ie. 2012) 

Conclusion

The information presented within this section has adequately demonstrated a clear causal relationship 

between the emissions generated by uncontrollable natural events and the exceedances measured at the 

monitors. The satellite images, time series graphs, and meteorological data tables provided in this section 

show the temporal progression of the dust events from the development of the thunderstorms, to the 

increase in wind speeds, and to the rise in PM10 concentrations. The combination of the PM10 and wind 

data from Maricopa and Pinal counties shows the transport of particulate matter from the south through 

Pinal County and into the Phoenix PM10 nonattainment area. This information supports the conclusion 

that the events were primarily drawing from emission sources outside of Maricopa County and were being 

transported into the Phoenix area. 

63
VI. “BUT FOR” ANALYSIS 

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

satisfy 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 the exceedances during the period of August 25-28, 

2011, were not reasonably controllable or preventable and there is a clear causal relationship between 

transported PM10 from thunderstorm outflows originating in the desert areas outside of the Phoenix 

PM10 nonattainment area and the measured exceedances within the nonattainment area. The weight of 

evidence in these sections demonstrates that but for the existence of emissions generated by these 

thunderstorm outflows and associated transported PM10, there would have been no exceedances of the 

24-Hour PM10 standard. 

As detailed in Section IV, all reasonable control measures were in place and actively enforced before, 

during, and after the exceedances of August 25-28, 2011. Inspection and compliance data of local 

fugitive dust sources during this time period revealed that PM10 from anthropogenic activities was well 

controlled and constant. Local regulatory agencies, industry, and the general public were alerted to the 

possibility of dust storms due to thunderstorm activity through daily forecasts and media reports. 

Heightened, real-time surveillance of PM10 monitoring stations during the events established a clear link 

between rapidly rising PM10 concentrations and the arrival of the thunderstorm outflows. On-the-ground 

observations recorded during the events consistently identify transported or re-entrained PM10 as the 

cause of the elevated concentrations near the exceeding monitors. 

As shown in Section V, detailed, time series data establish a clear causal relationship between the arrival 

of emissions generated by thunderstorm outflows and elevated PM10 concentrations at the monitors. 

Multiple, independent measurements of wind speed, wind direction, and visibility all point to the presence 

of thunderstorm outflows as the delivery vehicle for transported PM10 into the nonattainment area. Any 

local PM10 generated during the arrival of the thunderstorm outflows are linked to the turbulent and gusty 

outflow front of the storm and pale in comparison to the amount of transported PM10 originating outside 

the nonattainment area. The source regions for the thunderstorm outflows and transported PM10 are 

clearly identified as the desert areas outside of the Phoenix PM10 nonattainment area. 

The body of evidence presented in this submittal provides no alternative that could tie the exceedances of 

August 25-28, 2011 to any other causal source but transported and re-entrained PM10 generated from 

thunderstorm outflows, confirming that there would have been no exceedances but for the presence of 

these uncontrollable natural events. 

64
VII. CONCLUSIONS 

The exceedances that occurred during August 25-28, 2011, satisfy the following criteria of 40 CFR 

50.1(j) and meet the definition of an exceptional event: 

 The event affects air quality. 

 The event is not reasonably controllable or preventable. 

 The event is unlikely to reoccur at a particular location or [is] a natural event. 

Affects Air Quality

As stated in the preamble to the Exceptional Events Rule, the event in question is considered to have 

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

exceedance and the event, and that the event is associated with a measured concentration in excess of 

normal historical fluctuations. Given the information presented in Sections 2, 3, 4, and 5, we can 

reasonably conclude that the event in question affected air quality. 

 

Not Reasonably Controllable or Preventable

Section 50.1(j) of Title 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 and the Phoenix PM10 

nonattainment area, high wind conditions overwhelmed all reasonably available controls. Despite the 

deployment of comprehensive control measures and sophisticated response programs, high wind 

conditions associated with thunderstorms and thunderstorm outflows brought high concentrations of 

PM10 emissions into, and also overwhelmed controls within, the Phoenix PM10 nonattainment area. The 

events discussed in this document that caused the exceedances in this request (see Sections 2 and 5) were 

caused by thunderstorm driven outflow winds that transported dust into Maricopa County from areas 

largely outside of the Phoenix PM10 nonattainment area. The fact that these were natural events 

involving strong thunderstorm outflow winds that transported PM10 emissions into 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 events and 

exceedances of August 25-28, 2011 recorded within the nonattainment area were not reasonably 

controllable or preventable. 

Natural Event

As discussed above, the events shown to cause these exceedances were emissions of PM10 driven by high 

winds caused by thunderstorm activity and related outflow boundaries during the period of August 25-28, 

2011. The events therefore qualify as natural events. 

Summary

In summary, the exceedances of the federal 24-hour PM10 standard on August 25, August 26, August 27, 

and August 28, 2011, would not have occurred but for the monsoonal thunderstorm driven high winds and 

windblown dust transport from areas largely outside the Phoenix PM10 nonattainment area, based on the 

following weight of evidence: 

 Graphs of PM10 at various Phoenix area monitors in Section V and the tables containing 

meteorological data for representative NWS airport sites show that the timing of elevated PM10

events was consistent with decreased visibility and high winds at the NWS sites. 

65
66

 V. 

 Visibility camera imagery discussed in Section V indicates that large quantities of PM10 were 

transported into the Phoenix Metro area during the August 26th event. The timing of the dust 

storms depicted in the visibility camera imagery is consistent with the PM10 concentration 

measurements, elevated winds, and reduced visibility reported during the event. 

 Historical Fluctuation analyses and graphs in Section III and Appendix A showing five years of 

24-hour average data for each of the Phoenix PM10 nonattainment area monitors depict numerous 

atypically high PM10 concentrations during the third quarter of 2011 including the period of 

August 25-28. The sudden increase in the frequency of elevated PM10 concentrations during this 

time period was exceptional from a historical perspective. 

 Each of the exceedances of the PM10 standard recorded during the period of August 25-28 are 

tied to thunderstorm activity and thunderstorm generated outflow winds, as can be seen in data 

and analyses in Section

 Figures and tables in Section V show that the timing of thunderstorm-generated outflow boundary 

passage and increases in wind speeds at monitoring locations and National Weather Service 

stations during each of the events during this period is consistent with the timing of elevated 

PM10 concentrations recorded at the monitoring locations in the Phoenix PM10 nonattainment 

area. 

 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, all depicted in Section V, help show that a vast majority of the dust that impacted Phoenix 

PM10 nonattainment area monitors originated in Pinal County and other areas located generally 

south of the Phoenix PM10 nonattainment area. 

 Approximate PM10 emissions source flux calculations for select events are provided in Section V 

to give an idea of the magnitude of the dust storms that affected the Phoenix area and the amounts 

of PM10 that can be transported in during these types of events. 

 Section IV discusses rules that are in place in the Phoenix PM10 nonattainment area as well as 

inspections that were conducted in the area to verify compliance with those rules in order to show 

that the events are not reasonably controllable or preventable. Additionally, the visibility webcam 

time lapse photography videos referenced in Section II also help illustrate the magnitude and scale 

of these events, which supports the claim that the exceedances recorded during this period were 

not reasonably controllable or preventable. 
APPENDIX A

5-YEAR HISTORICAL FLUCTUATION GRAPHS FOR 

THE PHOENIX PM10 NONATTAINMENT AREA MONITORING SITES












APPENDIX B

ADEQ FORECAST PRODUCTS FOR PHOENIX,

MARICOPA COUNTY, AND PINAL COUNTY
MARICOPA COUNTY DUST CONTROL FORECAST 

ISSUED WEDNESDAY, AUGUST 24, 2011

Three-day weather outlook:

DURING ACTIVE SUMMER MONSOON EPISODES STRONG GUSTY WINDS AND DENSE BLOWING DUST ARE 

POSSIBLE, EVEN FROM DISTANT THUNDERSTORMS

Temperatures will decrease slightly each day through the weekend while the chances for showers and thunderstorms continue to 

hover around 10-30% during this period. Daytime winds will remain fairly light. The chance for blowing dust from distant storms 

will also continue into early next week. Thus, the risk of exceeding the 24-hr PM10 health standard in Phoenix will be 

MODERATE each day through at least Monday. 

 

RISK FACTORS

WINDS STAGNATION UNHEALTHY PM-10 

RISK LEVEL

Day 1: Thu 08/25/2011

Southwest winds 

between 5 and 10 mph 

are expected (10-20% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= MODERATE 

Day 2: Fri 08/26/2011

Southwest winds 

between 5 and 10 mph 

are expected (20-30% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= MODERATE

Day 3: Sat 08/27/2011

Southwest winds 

between 5 and 10 mph 

are expected (20-30% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= MODERATE

EXTENDED OUTLOOK 

Day 4: Sun 08/28/2011

Southwest winds 

between 5 and 10 mph 

are expected (20-30% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= MODERATE

Day 5: Mon 08/29/2011

Southwest winds 

between 5 and 10 mph 

are expected (20-30% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= MODERATE 

The Maricopa County Dust Control Action Forecast is issued to assist in the planning of work activities 

to help reduce dust pollution. A recorded message of this forecast can be accessed at 602-771-2368. To 

review the complete air quality forecast for the Phoenix metropolitan area, as well as the health impacts 

and reduction methods for different air pollutants, call 602-771-2367 for recorded forecast information or 

click on ADEQ's Air Quality Forecast at http://www.azdeq.gov/environ/air/ozone/ensemble.pdf. 

JRP 04/28/2011
MARICOPA COUNTY DUST CONTROL FORECAST 

ISSUED THURSDAY, AUGUST 25, 2011

Three-day weather outlook:

DURING ACTIVE SUMMER MONSOON EPISODES STRONG GUSTY WINDS AND DENSE BLOWING DUST ARE 

POSSIBLE, EVEN FROM DISTANT THUNDERSTORMS

A dust storm that moved through the forecast area early Thursday morning has caused several monitors to exceed the PM10 health 

standard for the day. Some of these particulates may carry over into Friday. In addition, there is a good possibility of some

additional dust from thunderstorm this evening impacting the Phoenix forecast area. Concentrations should tail off a bit Saturday 

through early next week as chances for more storms decreases. Thus, the risk of exceeding the 24-hr PM10 health standard in 

Phoenix will be HIGH on Friday, decreasing to MODERATE Saturday through next Tuesday. 

 

RISK FACTORS

WINDS STAGNATION UNHEALTHY PM-10 

RISK LEVEL

Day 1: Fri 08/26/2011

Southwest winds 

between 5 and 10 mph 

are expected (20-30% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= HIGH 

Day 2: Sat 08/27/2011

Southwest winds 

between 5 and 10 mph 

are expected (10-20% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= MODERATE

Day 3: Sun 08/28/2011

Southwest winds 

between 5 and 10 mph 

are expected (10% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= MODERATE

EXTENDED OUTLOOK 

Day 4: Mon 08/29/2011

Southwest winds 

between 5 and 10 mph 

are expected (10-20% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= MODERATE

Day 5: Tue 08/30/2011

Southwest winds 

between 5 and 10 mph 

are expected (20-30% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= MODERATE 

The Maricopa County Dust Control Action Forecast is issued to assist in the planning of work activities 

to help reduce dust pollution. A recorded message of this forecast can be accessed at 602-771-2368. To 

review the complete air quality forecast for the Phoenix metropolitan area, as well as the health impacts 

and reduction methods for different air pollutants, call 602-771-2367 for recorded forecast information or 

click on ADEQ's Air Quality Forecast at http://www.azdeq.gov/environ/air/ozone/ensemble.pdf. 

JRP 04/28/2011
MARICOPA COUNTY DUST CONTROL FORECAST 

ISSUED FRIDAY, AUGUST 26, 2011

Three-day weather outlook:

DURING ACTIVE SUMMER MONSOON EPISODES STRONG GUSTY WINDS AND DENSE BLOWING DUST ARE 

POSSIBLE, EVEN FROM DISTANT THUNDERSTORMS

Afternoon desert temperatures will be near 110°F as high pressure holds on through the weekend. By Monday and Tuesday, it 

begins to weaken. This will allow temperatures to drop to 103°F by Thursday of next week. We will also see a break in 

thunderstorm activity Monday and Tuesday with somewhat drier air being pulled into the region. The approaching trough of low 

pressure could bring with it a chance for more showers and thunderstorms as it sweeps through the region. For now, the risk of

exceeding the 24-hr PM10 health standard in Phoenix due to blowing dust will be MODERATE on Saturday and Sunday, LOW

on Monday and Tuesday, and MODERATE again on Wednesday. 

 

RISK FACTORS

WINDS STAGNATION UNHEALTHY PM-10 

RISK LEVEL

Day 1: Sat 08/27/2011

Southwest winds 

between 5 and 10 mph 

are expected (10-20% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= MODERATE 

Day 2: Sun 08/28/2011

Southwest winds 

between 5 and 10 mph 

are expected (10% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= MODERATE

Day 3: Mon 08/29/2011

Southwest winds 

between 5 and 10 mph 

are expected (10% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= LOW

EXTENDED OUTLOOK 

Day 4: Tue 08/30/2011

Southwest winds 

between 5 and 10 mph 

are expected 

(10%chance of showers 

and t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= LOW

Day 5: Wed 08/31/2011

Southwest winds 

between 5 and 10 mph 

are expected (20-30% 

chance of showers and 

t-storms). 

+ 

Rather stagnant 

conditions are likely 

early, improving late. 

= MODERATE 

The Maricopa County Dust Control Action Forecast is issued to assist in the planning of work activities 

to help reduce dust pollution. A recorded message of this forecast can be accessed at 602-771-2368. To 

review the complete air quality forecast for the Phoenix metropolitan area, as well as the health impacts 

and reduction methods for different air pollutants, call 602-771-2367 for recorded forecast information or 

click on ADEQ's Air Quality Forecast at http://www.azdeq.gov/environ/air/ozone/ensemble.pdf. 

JRP 04/28/2011
MARICOPA COUNTY DUST CONTROL FORECAST 

ISSUED SUNDAY, AUGUST 28, 2011

Five-day weather outlook:

DURING ACTIVE SUMMER MONSOON EPISODES STRONG GUSTY WINDS AND DENSE BLOWING DUST ARE 

POSSIBLE EVEN FROM DISTANT THUNDERSTORMS

Although summer monsoon activity with significant rainfall does not look likely for the Phoenix metro area proper the next few 

days, there will continue to be a heightened potential for episodes of dense blowing dust generated by outflow boundaries from 

thunderstorms east and southeast of the metro area. Low-level gradients and upslope flow will yield breezy to gusty conditions at 

times each afternoon. 

RISK FACTORS

WINDS STAGNATION

UNHEALTHY PM-10

RISK LEVEL

Day 1: Mon 08/29/2011

Westerly 10-20 mph 

during the afternoon 

except strong and gusty 

due to outflow from 

thunderstorms. 

+ 

No significant 

stagnation expected. = MODERATE 

Day 2: Tue 08/30/2011

Westerly 10-20 mph 

during the afternoon 

except strong and gusty 

due to outflow from 

thunderstorms. 

+ 

No significant 

stagnation expected. = MODERATE 

Day 3: Wed 08/31/2011

Westerly 5-15 mph 

during the afternoon 

except strong and gusty 

due to outflow from 

thunderstorms. 

+ 

No significant 

stagnation expected. = MODERATE 

EXTENDED OUTLOOK 

Day 4: Thu 09/01/2011

Westerly 5-15 mph 

during the afternoon 

except strong and gusty 

due to outflow from 

thunderstorms. 

+ 

No significant 

stagnation expected. = MODERATE 

Day 5: Fri 09/02/2011

Westerly 5-15 mph 

during the afternoon 

except strong and gusty 

due to outflow from 

thunderstorms. 

 

+ No significant 

stagnation expected. = MODERATE 

The Maricopa County Dust Control Action Forecast is issued to assist in the planning of work activities to 

help reduce dust pollution. A recorded message of this forecast can be accessed at 602-771-2368. To review 

the complete air quality forecast for the Phoenix metropolitan area, as well as the health impacts and 

reduction methods for different air pollutants, call 602-771-2367 for recorded forecast information or click on 

ADEQ's Air Quality Forecast at http://www.azdeq.gov/environ/air/ozone/ensemble.pdf.

CKR 04/28/2011
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

 

NEW!!! CLICK HERE FOR UPDATED OZONE SEASON STATS NEW!!!

AIR QUALITY FORECAST FOR THURSDAY, AUGUST 25, 2011

This report is updated by 1:00 p.m. Sunday thru Friday and is valid 

for areas within and bordering Maricopa County in Arizona 

 

* 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.

FORECAST 

DATE

NOTICES 

(*SEE BELOW 

FOR DETAILS) 

AIR POLLUTANT 

YESTERDAY 

TUE 08/23/2011

Highest AQI Reading/Site 

(Preliminary data only) 

TODAY 

WED 08/24/2011

TOMORROW 

THU 08/25/2011

DUST 

Possible 

EXTENDED 

FRI 08/26/2011

DUST 

Possible 

O3* 

80 

HUMBOLDT 

MOUNTAIN 

84 

MODERATE 

87 

MODERATE 

80 

MODERATE 

CO* 7 

GREENWOOD 

7 

GOOD 

7 

GOOD 

7 

GOOD 

PM-10* 52 

BUCKEYE 

42 

GOOD 

77 

MODERATE

65 

MODERATE

PM-2.5* 29 

ESTRELLA 

28 

GOOD

48 

GOOD

38 

GOOD
Health message for Wednesday, August 24: Unusually sensitive people should 

consider limiting prolonged exertion outdoors. 

Health message for Thursday, August 25: Unusually sensitive people should 

consider limiting prolonged exertion outdoors. 

Temperatures will peak today across the Valley with a forecasted high somewhere around 114-116°F. 

This is well above normal for this time of year. 

Questions have been asked recently about the relationship between temperature and ground-level 

ozone. The short answer is: there isn’t one. Ozone formation and peak concentrations at a given location is 

very complex. First there needs to be abundant amounts of precursors (which apparently we don’t 

currently have). Then there needs to be unimpeded, direct sunlight (which we do have). Wind speeds can 

affect a developing ozone plume by mixing the air up. Light winds (which we currently have) promote 

ozone formation. Then you must factor in the wind direction, however strong or weak that may be. 

Models call for a slight southeast-to-northwest flow today and Thursday. This means that we can expect 

the highest concentrations to be in the north-central part of the forecast area. Other factors to take into 

account are the development of nearby thunderstorms. Such storm can climb to 40-60,000 feet high. The 

updrafts can draw air from valley floors, taking with it the pollution that is accumulating. This can result in 

lower than potential ozone concentrations in the valley, such as the Phoenix metro area. 

All the factors have played a role in the recent lower-than-potential ozone concentrations in the 

Phoenix forecast area. We expect to see slightly higher concentrations today and Thursday in the north and 

northeast part of the Valley. Cloud cover Friday morning may hold ozone production down a bit, resulting 

in lower overall concentrations. 

PM10 levels climbed into the lower MODERATE range at the Buckeye and Durango monitors on 

Tuesday. There really hasn’t been much wind to cause the elevated levels. This raises a valid concern that 

the Valley soil is not as stable as we would like it to be and the threat of blowing dust from distant and even 

localized thunderstorms could send PM10 concentrations deep into the MODERATE category or even into 

UNHEALTHY FOR SENSITIVE GROUPS territory sometime in the next week. Such events are very 

difficult to accurately predict, but we’ve raised the PM10 forecast to cover the possibility on Thursday. 

Check back tomorrow for more. Until then, have a good day! -J.Paul 

 

 

MONITORING SITE MAPS

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

http://aqwww.maricopa.gov/AirMonitoring/SitePollutionMap.aspx INTERACTIVE MAPS http://www.airnow.gov/

POLLUTION MONITOR READINGS FOR TUESDAY, AUGUST 23, 2011 

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 (La Paz County) NOT AVBL NOT AVBL NOT AVBL 

Apache Junction (Pinal County) 58 49 

Blue Point 63 61 

Buckeye 47 40 

Casa Grande 49 42 

Cave Creek 68 77 

Central Phoenix 60 51 

Dysart 52 44 

Falcon Field 59 50 

Fountain Hills 63 61 

Glendale 53 45 
Humboldt Mountain 69 80 

North Phoenix 67 74 

Phoenix Supersite 63 61 

Pinal Air Park (Pinal County) 67 74 

Pinnacle Peak 52 44 

Queen Valley (Pinal County) 61 54 

Rio Verde 65 67 

South Phoenix 59 50 

South Scottsdale 63 61 

Tempe 55 47 

Tonto Nat’l Mon. (Gila County) 57 48 

West Chandler 56 47 

West Phoenix 61 54 

Yuma NOT AVBL NOT AVBL NOT AVBL 

CO (CARBON MONOXIDE)

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

Central Phoenix 0.3 3 

Greenwood 0.6 7 

West Phoenix 0.4 5 

PM-10 (PARTICLES)

SITE NAME MAX 24-HR VALUE (μg/m3) MAX AQI AQI COLOR CODE

Buckeye 57.1 52 HIGHEST LOCALLY 

Central Phoenix 45.2 41 

Combs School (Pinal County) 70.5 58 

Durango 56.0 51 

Dysart 31.7 29 

Glendale 35.8 33 

Greenwood 42.3 39 

Higley 38.1 35 

Maricopa (Pinal County) 52.1 48 

Phoenix Supersite 37.6 34 

South Phoenix 43.0 39 

West Chandler 36.1 33 

West Forty Third 47.5 43 

West Phoenix 49.7 45 

Zuni Hills 30.0 27 

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 8.3 27 

Dysart 5.0 16 

Estrella Mountain Park 8.9 29 

Glendale 8.1 26 

Phoenix Supersite 8.6 28 

North Phoenix 7.8 25 

South Phoenix 6.3 20 

Vehicle Emissions Lab NOT AVBL NOT AVBL NOT AVBL 

West Phoenix 7.9 26 
LOCAL AIR POLLUTANTS IN DETAIL 

O3 (OZONE): 

Description – This is a secondary pollutant that is formed by the reaction of other primary 

pollutants (precursors) such as VOCs (volatile organic compounds) and NOx (Nitrogen Oxides) 

in the presence of heat and sunlight. 

Sources – VOCs are emitted from motor vehicles, chemical plants, refineries, factories, and 

other industrial sources. NOx is emitted from motor vehicles, power plants, and other sources of 

combustion. 

Potential health impacts – Exposure to ozone can make people more susceptible to respiratory 

infection, result in lung inflammation, and aggravate pre-existing respiratory diseases such as 

asthma. Other effects include decrease in lung function, chest pain, and cough. 

 Unit of measurement – Parts per billion (ppb). 

 Averaging interval – Highest eight-hour period within a 24-hour period (midnight to midnight). 

Reduction tips – Curtail daytime driving, refuel cars and use gasoline-powered equipment as late 

in the day as possible. 

CO (CARBON MONOXIDE): 

Description – A colorless, odorless, poisonous gas formed when carbon in fuels is not burned 

completely. 

Sources – In cities, as much as 95 percent of all CO emissions emanate from automobile exhaust. 

Other sources include industrial processes, non-transportation fuel combustion, and natural 

sources such as wildfires. Peak concentrations occur in colder winter months. 

Potential health impacts – Reduces oxygen delivery to the body’s organs and tissues. The health 

threat is most serious for those who suffer from cardiovascular disease. 

 Unit of measurement – Parts per million (ppm). 

 Averaging interval – Highest eight-hour period within a 24-hour period (midnight to midnight) 

 Reduction tips – Keep motor vehicle tuned properly and minimize nighttime driving. 

 

PM-10 & PM-2.5 (PARTICLES): 

Description – The term “particulate matter” (PM) includes both solid particles and liquid droplets 

found in air. Many manmade and natural sources emit PM directly or emit other pollutants that 

react in the atmosphere to form PM. Particles less than 10 micrometers in diameter tend to pose 

the greatest health concern because they can be inhaled into and accumulate in the respiratory 

system. Particles less than 2.5 micrometers in diameter are referred to as “fine” particles and are 

responsible for many visibility degradations such as the “Valley Brown Cloud” (see 

http://www.phoenixvis.net/). Particles with diameters between 2.5 and 10 micrometers are referred 

to as “coarse”. 

Sources – Fine = All types of combustion (motor vehicles, power plants, wood burning, etc.) and 

some industrial processes. Coarse = crushing or grinding operations and dust from paved or 

unpaved roads. 

Potential health impacts – PM can increase susceptibility to respiratory infections and can 

aggravate existing respiratory diseases, such as asthma and chronic bronchitis. 

 Units of measurement – Micrograms per cubic meter (ug/m3) 

 Averaging interval – 24 hours (midnight to midnight). 
 Reduction tips – Stabilize loose soils, slow down on dirt roads, carpool, and use public transit. 

 {Updated 03/23/2010} 
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

 

NEW!!! CLICK HERE FOR UPDATED OZONE SEASON STATS NEW!!!

AIR QUALITY FORECAST FOR FRIDAY, AUGUST 26, 2011

This report is updated by 1:00 p.m. Sunday thru Friday and is valid 

for areas within and bordering Maricopa County in Arizona 

 

* 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.

FORECAST 

DATE

NOTICES 

(*SEE BELOW 

FOR DETAILS) 

AIR POLLUTANT 

YESTERDAY 

WED 08/24/2011

Highest AQI Reading/Site 

(Preliminary data only) 

TODAY 

THU 08/25/2011

(Ozone and PM10) 

DUST

TOMORROW 

FRI 08/26/2011

 (PM10) (Ozone) 

DUST

EXTENDED 

SAT 08/27/2011

DUST 

O3* 97 

QUEEN VALLEY 

106 

UNHEALTHY for 

SENSITIVE 

GROUPS 

93 

MODERATE 

80 

MODERATE 

CO* 7 

GREENWOOD 

7 

GOOD 

7 

GOOD 

7 

GOOD 

PM-10* 57 

BUCKEYE 

250 

VERY 

UNHEATHY

125 

UNHEALTHY for 

SENSITIVE 

GROUPS

65 

MODERATE

PM-2.5* 

32 

ESTRELLA 

MOUNTAIN PARK 

48 

GOOD

45 

GOOD

38 

GOOD
Health message for Thursday, August 25: People with respiratory disease, such as 

asthma, should avoid any outdoor activity; everyone else, especially the elderly and 

children, should limit outdoor exertion. 

Health message for Friday, August 26: People with respiratory disease, such as 

asthma, should limit outdoor exertion. 

...SAME DAY PM10 AND OZONE HIGH POLLUTION ADVISORY FOR THURSDAY, AUGUST 25, 2011... 

...THURSDAY’S PM10 HPA IS BEING EXTENDED THROUGH FRIDAY, AUGUST 26, 2011... 

...AN OZONE HEALTH WATCH IS BEING ISSUED THROUGH FRIDAY, AUGUST 26, 2011... 

An area of disturbance in the stealth of the night generated a wall of dust that pushed northwest from 

north of Tucson through Pinal County (Casa Grande), settling out in northwestern Maricopa County. 

That’s a path of more 130 miles. It took just over 4 hours for the wall of dust to move through. In its 

wake, nearly all of Pinal County’s PM10 monitors and several more of Maricopa County’s monitors 

exceeded the health standard. This occurred between 1-2am this morning. Even if every hour from now 

until midnight registered completely clean air, the 24-hr average still exceeds. Thus, we have issued a 

PM10 High Pollution Advisory for Thursday. There’s not much anyone can do to prevent something 

that has already happened, but there is plenty they can do to keep it from becoming worse as well as 

protecting their healthy by avoiding outdoor exposure today. 

Ozone levels were in the 90s of the Air Quality Index (AQI) at several forecast area monitors on 

Thursday as well. That wall of dust that brought all of the particulates also imported some ozone as well. 

Many Valley monitors are starting 10 to 20 parts per billion (ppb) higher than 24 hours earlier. As the sun 

comes out, addition ozone will be generated, likely pushing some parts over the Valley above the health 

standard for ozone, as well. Thus, we have also issued a same-day Ozone HPA for Thursday. 

Models are suggesting that we have an increased chance for some showers/thunderstorms moving in 

tonight from the southeast. Along with this possibility comes the likelihood of more blowing dust. This 

will likely add to today’s totals for PM10. The hold over of lingering dust Friday morning could be enough 

to push some Valley monitors over the edge once more. So... we are EXTENDING today PM10 HPA 

through Friday. Cloud cover Friday morning along with a sustained southeast-to-northwest flow should 

result in slightly lower Ozone levels, but we are issuing an Ozone Health Watch for Friday with the 

target area of highest concentrations in the north-central part of the forecast area. 

Check back tomorrow for the weekend outlook. Until then, have a good day! -J.Paul 

 

 

MONITORING SITE MAPS

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

http://aqwww.maricopa.gov/AirMonitoring/SitePollutionMap.aspx INTERACTIVE MAPS http://www.airnow.gov/

POLLUTION MONITOR READINGS FOR TUESDAY, AUGUST 23, 2011 

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 (La Paz County) 56 47 

Apache Junction (Pinal County) 66 71 

Blue Point 72 90 

Buckeye 47 40 

Casa Grande 52 44 

Cave Creek 73 93 

Central Phoenix 60 51 

Dysart 54 46 

Falcon Field 64 64 
Fountain Hills 71 87 

Glendale 56 47 

Humboldt Mountain 73 93 

North Phoenix 68 77 

Phoenix Supersite 63 61 

Pinal Air Park (Pinal County) 53 45 

Pinnacle Peak 65 67 

Queen Valley (Pinal County) 74 97 

Rio Verde 70 84 

South Phoenix 58 49 

South Scottsdale 65 67 

Tempe 56 47 

Tonto Nat’l Mon. (Gila County) 65 67 

West Chandler 63 61 

West Phoenix 59 50 

Yuma NOT AVBL NOT AVBL NOT AVBL 

CO (CARBON MONOXIDE)

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

Central Phoenix 0.3 3 

Greenwood 0.6 7 

West Phoenix 0.4 5 

PM-10 (PARTICLES)

SITE NAME MAX 24-HR VALUE (μg/m3) MAX AQI AQI COLOR CODE

Buckeye 67.9 57 

Central Phoenix 40.4 37 

Combs School (Pinal County) 60.5 53 

Durango 52.0 47 

Dysart 34.7 32 

Glendale 38.5 35 

Greenwood 41.3 38 

Higley 37.7 34 

Maricopa (Pinal County) 62.8 54 

Phoenix Supersite 37.7 34 

South Phoenix 48.3 44 

West Chandler 39.6 36 

West Forty Third 47.7 43 

West Phoenix 45.1 41 

Zuni Hills 31.9 29 

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 8.3 27 

Dysart 5.5 18 

Estrella Mountain Park 9.8 32 

Glendale 9.1 30 

Phoenix Supersite 7.6 25 

North Phoenix 6.9 22 

South Phoenix 6.7 22 

Vehicle Emissions Lab NOT AVBL NOT AVBL NOT AVBL 
West Phoenix 7.6 25 

LOCAL AIR POLLUTANTS IN DETAIL 

O3 (OZONE): 

Description – This is a secondary pollutant that is formed by the reaction of other primary 

pollutants (precursors) such as VOCs (volatile organic compounds) and NOx (Nitrogen Oxides) 

in the presence of heat and sunlight. 

Sources – VOCs are emitted from motor vehicles, chemical plants, refineries, factories, and 

other industrial sources. NOx is emitted from motor vehicles, power plants, and other sources of 

combustion. 

Potential health impacts – Exposure to ozone can make people more susceptible to respiratory 

infection, result in lung inflammation, and aggravate pre-existing respiratory diseases such as 

asthma. Other effects include decrease in lung function, chest pain, and cough. 

 Unit of measurement – Parts per billion (ppb). 

 Averaging interval – Highest eight-hour period within a 24-hour period (midnight to midnight). 

Reduction tips – Curtail daytime driving, refuel cars and use gasoline-powered equipment as late 

in the day as possible. 

CO (CARBON MONOXIDE): 

Description – A colorless, odorless, poisonous gas formed when carbon in fuels is not burned 

completely. 

Sources – In cities, as much as 95 percent of all CO emissions emanate from automobile exhaust. 

Other sources include industrial processes, non-transportation fuel combustion, and natural 

sources such as wildfires. Peak concentrations occur in colder winter months. 

Potential health impacts – Reduces oxygen delivery to the body’s organs and tissues. The health 

threat is most serious for those who suffer from cardiovascular disease. 

 Unit of measurement – Parts per million (ppm). 

 Averaging interval – Highest eight-hour period within a 24-hour period (midnight to midnight) 

 Reduction tips – Keep motor vehicle tuned properly and minimize nighttime driving. 

 

PM-10 & PM-2.5 (PARTICLES): 

Description – The term “particulate matter” (PM) includes both solid particles and liquid droplets 

found in air. Many manmade and natural sources emit PM directly or emit other pollutants that 

react in the atmosphere to form PM. Particles less than 10 micrometers in diameter tend to pose 

the greatest health concern because they can be inhaled into and accumulate in the respiratory 

system. Particles less than 2.5 micrometers in diameter are referred to as “fine” particles and are 

responsible for many visibility degradations such as the “Valley Brown Cloud” (see 

http://www.phoenixvis.net/). Particles with diameters between 2.5 and 10 micrometers are referred 

to as “coarse”. 

Sources – Fine = All types of combustion (motor vehicles, power plants, wood burning, etc.) and 

some industrial processes. Coarse = crushing or grinding operations and dust from paved or 

unpaved roads. 

Potential health impacts – PM can increase susceptibility to respiratory infections and can 

aggravate existing respiratory diseases, such as asthma and chronic bronchitis. 
 Units of measurement – Micrograms per cubic meter (ug/m3) 

 Averaging interval – 24 hours (midnight to midnight). 

 Reduction tips – Stabilize loose soils, slow down on dirt roads, carpool, and use public transit. 

 {Updated 03/23/2010} 
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

 

NEW!!! CLICK HERE FOR UPDATED OZONE SEASON STATS NEW!!!

AIR QUALITY FORECAST FOR SATURDAY, AUGUST 27, 2011

This report is updated by 1:00 p.m. Sunday thru Friday and is valid 

for areas within and bordering Maricopa County in Arizona 

 

* 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.

FORECAST 

DATE

NOTICES 

(*SEE BELOW 

FOR DETAILS) 

AIR POLLUTANT 

YESTERDAY 

THU 08/25/2011

(Ozone and PM10) 

DUST 

Highest AQI Reading/Site 

(Preliminary data only) 

TODAY 

FRI 08/26/2011

 (PM10) (Ozone) 

DUST

TOMORROW 

SAT 08/27/2011

(Ozone) 

DUST

EXTENDED 

SUN 08/28/2011

O3* 122 

PHOENIX SUPERSITE 

93 

MODERATE 

93 

MODERATE 

77 

MODERATE 

CO* 5 

GREENWOOD 

7 

GOOD 

7 

GOOD 

7 

GOOD 

PM-10* 316 

DURANGO

125 

UNHEALTHY for 

SENSITIVE 

GROUPS

65 

MODERATE

56 

MODERATE

PM-2.5* 111 

DURANGO 

45 

GOOD

38 

GOOD

35 

GOOD
Health message for Friday, August 26: People with respiratory disease, such as 

asthma, should limit outdoor exertion. 

Health message for Saturday, August 27: Unusually Sensitive People should 

consider limiting prolonged exertion outdoors. 

...A PM10 HIGH POLLUTION ADVISORY REMAINS IN EFFECT FOR FRIDAY, AUGUST 26, 2011... 

FRIDAY’S OZONE HEALTH WATCH HAS BEEN EXTENDED THROUGH SATURDAY, AUGUST 27, 2011 

The results are in for yesterday’s air quality levels, and their pretty eye opening. That early morning 

dust storm caused all but one site to exceed the 24-hr PM10 health standard. Not only that, but Durango’s 

monitor registered levels in the code BROWN category, which is HAZARDOUS. That’s incredible. 

Durango’s PM2.5 monitor was the only one to exceed that standard as well, but several others got close, 

reaching the upper MODERATE range. Ozone levels exceeded at six monitors with Phoenix Supersite 

(17th avenue and Campbell) reaching 122 on the Air Quality Index (AQI). Overall, it was not a good day 

to be outside in the Phoenix metro area (not to mention the 113°F heat!) 

Many ozone monitors are at or below where they were yesterday. A few are slightly higher. The good 

news is that the rate of increase has slowed. We have an Ozone Health Watch in place for today with the 

highest concentrations expected to be in the north and northwest part of the Valley, around Cave Creek, 

Glendale, North Phoenix, and Dysart. Tomorrow’s pattern and levels will be similar to today, so we are 

extending that Health Watch through Saturday. With high pressure breaking down Sunday through next 

week, we will see a shift in winds out of the southwest. This will not only drop our thunderstorm chances, 

but also help decrease local ozone levels. 

The dust has cleared out nicely as mostly monitors are now showing PM10 concentrations in the 

GOOD range. We still have the PM10 HPA in place for today, but that will be allowed to expire at 

midnight with no further extension. 

The latest WRF-RUC model suggests thunderstorms will develop over the Valley tonight around 8pm. 

If it does happen, that would be a good thing as rain will clear the air and stabilize the soil. It’s only when 

the storm originate outside of the Valley the concern of significant dust is raised. 

Check back on Sunday for the weekend wrap up and a look ahead at next week’s weather and air 

quality. Until then, have a good day! -J.Paul 

 

 

MONITORING SITE MAPS

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

http://aqwww.maricopa.gov/AirMonitoring/SitePollutionMap.aspx INTERACTIVE MAPS http://www.airnow.gov/

POLLUTION MONITOR READINGS FOR THURSDAY, AUGUST 24, 2011 

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 (La Paz County) NOT AVBL NOT AVBL NOT AVBL 

Apache Junction (Pinal County) 64 64 

Blue Point 75 100 

Buckeye 64 64 

Casa Grande 64 64 

Cave Creek 82 116 

Central Phoenix 71 87 

Dysart 74 97 

Falcon Field 68 77 

Fountain Hills 77 104 

Glendale 82 116 
Humboldt Mountain 73 93 

North Phoenix 82 116 

Phoenix Supersite 84 122 

Pinal Air Park (Pinal County) 68 77 

Pinnacle Peak 73 93 

Queen Valley (Pinal County) 69 80 

Rio Verde 72 90 

South Phoenix 74 97 

South Scottsdale 71 87 

Tempe 62 58 

Tonto Nat’l Mon. (Gila County) NOT AVBL NOT AVBL NOT AVBL 

West Chandler 67 74 

West Phoenix 80 111 

Yuma 53 45 

CO (CARBON MONOXIDE)

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

Central Phoenix 0.2 2 

Greenwood 0.4 5 

West Phoenix 0.3 3 

PM-10 (PARTICLES)

SITE NAME MAX 24-HR VALUE (μg/m3) MAX AQI AQI COLOR CODE

Buckeye 235.9 141 

Central Phoenix 308.7 178 

Combs School (Pinal County) 60.1 53 

Durango 437.5 316 

Dysart 273.7 160 

Glendale 241.2 144 

Greenwood 388.6 250 

Higley 131.4 89 

Maricopa (Pinal County) 529.3 425 

Phoenix Supersite 242.2 144 

South Phoenix 421.5 296 

West Chandler 278.6 163 

West Forty Third 370.3 223 

West Phoenix 212.6 130 

Zuni Hills 212.8 130 

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 39.4 111 

Dysart 17.9 57 

Estrella Mountain Park 22.5 68 

Glendale 24.1 72 

Phoenix Supersite 33.0 94 

North Phoenix 9.6 31 

South Phoenix 23.7 71 

Vehicle Emissions Lab NOT AVBL NOT AVBL NOT AVBL 

West Phoenix 31.6 91 
LOCAL AIR POLLUTANTS IN DETAIL 

O3 (OZONE): 

Description – This is a secondary pollutant that is formed by the reaction of other primary 

pollutants (precursors) such as VOCs (volatile organic compounds) and NOx (Nitrogen Oxides) 

in the presence of heat and sunlight. 

Sources – VOCs are emitted from motor vehicles, chemical plants, refineries, factories, and 

other industrial sources. NOx is emitted from motor vehicles, power plants, and other sources of 

combustion. 

Potential health impacts – Exposure to ozone can make people more susceptible to respiratory 

infection, result in lung inflammation, and aggravate pre-existing respiratory diseases such as 

asthma. Other effects include decrease in lung function, chest pain, and cough. 

 Unit of measurement – Parts per billion (ppb). 

 Averaging interval – Highest eight-hour period within a 24-hour period (midnight to midnight). 

Reduction tips – Curtail daytime driving, refuel cars and use gasoline-powered equipment as late 

in the day as possible. 

CO (CARBON MONOXIDE): 

Description – A colorless, odorless, poisonous gas formed when carbon in fuels is not burned 

completely. 

Sources – In cities, as much as 95 percent of all CO emissions emanate from automobile exhaust. 

Other sources include industrial processes, non-transportation fuel combustion, and natural 

sources such as wildfires. Peak concentrations occur in colder winter months. 

Potential health impacts – Reduces oxygen delivery to the body’s organs and tissues. The health 

threat is most serious for those who suffer from cardiovascular disease. 

 Unit of measurement – Parts per million (ppm). 

 Averaging interval – Highest eight-hour period within a 24-hour period (midnight to midnight) 

 Reduction tips – Keep motor vehicle tuned properly and minimize nighttime driving. 

 

PM-10 & PM-2.5 (PARTICLES): 

Description – The term “particulate matter” (PM) includes both solid particles and liquid droplets 

found in air. Many manmade and natural sources emit PM directly or emit other pollutants that 

react in the atmosphere to form PM. Particles less than 10 micrometers in diameter tend to pose 

the greatest health concern because they can be inhaled into and accumulate in the respiratory 

system. Particles less than 2.5 micrometers in diameter are referred to as “fine” particles and are 

responsible for many visibility degradations such as the “Valley Brown Cloud” (see 

http://www.phoenixvis.net/). Particles with diameters between 2.5 and 10 micrometers are referred 

to as “coarse”. 

Sources – Fine = All types of combustion (motor vehicles, power plants, wood burning, etc.) and 

some industrial processes. Coarse = crushing or grinding operations and dust from paved or 

unpaved roads. 

Potential health impacts – PM can increase susceptibility to respiratory infections and can 

aggravate existing respiratory diseases, such as asthma and chronic bronchitis. 

 Units of measurement – Micrograms per cubic meter (ug/m3) 

 Averaging interval – 24 hours (midnight to midnight). 
 Reduction tips – Stabilize loose soils, slow down on dirt roads, carpool, and use public transit. 

 {Updated 03/23/2010} 
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

 

NEW!!! CLICK HERE FOR UPDATED OZONE SEASON STATS NEW!!! 

AIR QUALITY FORECAST FOR MONDAY, AUGUST 29, 2011

This report is updated by 1:00 p.m. Sunday thru Friday and is valid 

for areas within and bordering Maricopa County in Arizona

 

* 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.

FORECAST 

DATE

NOTICES 

(*SEE BELOW 

FOR DETAILS) 

AIR POLLUTANT 

YESTERDAY 

SAT 08/27/2011

OZONE HEALTH 

WATCH 

DUST 

NWS EXCESSIVE 

 HEAT WARNING 

Highest AQI Reading/Site 

(Preliminary data only) 

TODAY 

SUN 08/28/2011

PM-10 HEALTH 

 WATCH 

DUST 

NWS EXCESSIVE 

HEAT WARNING 

TOMORROW 

MON 08/29/2011

DUST 

NWS EXCESSIVE 

HEAT WARNING 

EXTENDED 

TUE 08/30/2011

DUST 

 

O3* 90 

CAVE CREEK 

77 

MODERATE 

80 

MODERATE 

80 

MODERATE 

CO* 05 

GREENWOOD 

07 

GOOD 

06 

GOOD

06 

GOOD 

PM-10* 174 

SOUTH PHOENIX 

95 

MODERATE

75 

MODERATE

75 

MODERATE 

PM-2.5* 119 

DURANGO 

35 

GOOD

50 

GOOD

44 

GOOD
Health message for Sunday August 28: Unusually sensitive people should consider reducing 

prolonged or heavy exertion outdoors. 

Health message for Monday August 29: Unusually sensitive people should consider reducing 

prolonged or heavy exertion outdoors. 

 

Synopsis and Discussion

OZONE: Hot daytime temperatures and minimal cloud cover will promote above average ozone production the next 

few days. However, a low-level westerly wind regime will help to keep ozone accumulation at below average levels 

thru Tuesday. As a result, expect highest local ozone levels in the mid to upper-moderate range of the Air Quality 

Index to occur over the east Valley thru this forecast period. 

PARTICLES: A PM-10 HEALTH WATCH HAS BEEN ISSUED FOR THE REMAINDER OF TODAY 

Due to lingering suspended dust from last evening’s wind event, at 9:00 a.m. this morning hourly PM-10 

concentrations around the Valley ranged from 40ug/m3 at Buckeye to 148ug/m3 at Central Phoenix. This has 

prompted the issuance of a PM-10 Health Watch for the remainder of today. Although summer monsoon activity with 

significant rainfall does not look likely for the Phoenix metro area proper the next few days, there will continue to be a 

heightened potential for similar episodes of dense blowing dust generated by outflow boundaries from thunderstorms 

east and southeast of the metro area. Low-level gradients and upslope flow will yield breezy to gusty conditions at 

times each afternoon. 

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://www.airnow.gov/ 

POLLUTION MONITOR READINGS FOR SATURDAY, AUGUST 27, 2011 

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 (La Paz County) 62 58 

Apache Junction (Pinal County) 62 58 

Blue Point 64 64 

Buckeye 58 49 

Casa Grande (Pinal County) 58 49 

Cave Creek 72 90 

Central Phoenix 65 67 

Dysart 61 54 

Falcon Field 64 64 

Fountain Hills 69 80 

Glendale 67 74 

Humboldt Mountain 65 67 

North Phoenix 71 87 

Phoenix Supersite 71 87 

Pinal Air Park (Pinal County) 56 47 

Pinnacle Peak 64 64 

Queen Valley (Pinal County) 67 74 

Rio Verde 64 64 

South Phoenix 64 64 

South Scottsdale 65 67 

Tempe 58 49 

Tonto Nat’l Mon. (Gila County) 61 54 

West Chandler 61 54 

West Phoenix 68 77 

Yuma (Yuma County) NOT AVBL NOT AVBL NOT AVBL 
CO (CARBON MONOXIDE) 

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

Central Phoenix 0.2 02 

Greenwood 0.4 05 

Phoenix Supersite NOT AVBL NOT AVBL NOT AVBL 

West Phoenix 0.3 03 

PM-10 (PARTICLES)

 SITE NAME MAX 24-HR VALUE (ug/m3) MAX AQI AQI COLOR CODE 

Buckeye 226 136 

Central Phoenix 234 140 

Combs School(Pinal County NOT AVBL NOT AVBL NOT AVBL 

Durango 261 154 

Dysart 126 86 

Glendale 220 130 

Greenwood 208 127 

Higley 115 81 

Maricopa (Pinal County) NOT AVBL NOT AVBL NOT AVBL 

Phoenix Supersite 132 89 

South Phoenix 301 174 

West Chandler 229 138 

West Forty Third 292 169 

West Phoenix 164 105 

Zuni Hills 112 79 

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 (ug/m3) MAX AQI AQI COLOR CODE 

Durango 43.0 119 

Dysart 11.7 38 

Estrella Mountain Park 21.5 66 

Glendale 42.7 119 

Phoenix Supersite 21.9 67 

South Phoenix 30.6 88 

Vehicle Emissions Lab 18.9 59 

West Phoenix 24.6 73 

 
LOCAL AIR POLLUTANTS IN DETAIL 

O3 (OZONE): 

Description – This is a secondary pollutant that is formed by the reaction of other primary 

pollutants (precursors) such as VOCs (volatile organic compounds) and NOx (Nitrogen Oxides) 

in the presence of heat and sunlight. 

Sources – VOCs are emitted from motor vehicles, chemical plants, refineries, factories, and 

other industrial sources. NOx is emitted from motor vehicles, power plants, and other sources of 

combustion. 

Potential health impacts – Exposure to ozone can make people more susceptible to respiratory 

infection, result in lung inflammation, and aggravate pre-existing respiratory diseases such as 

asthma. Other effects include decrease in lung function, chest pain, and cough. 

 Unit of measurement – Parts per billion (ppb). 

 Averaging interval – Highest eight-hour period within a 24-hour period (midnight to midnight). 

Reduction tips – Curtail daytime driving, refuel cars and use gasoline-powered equipment as late 

in the day as possible. 

CO (CARBON MONOXIDE): 

Description – A colorless, odorless, poisonous gas formed when carbon in fuels is not burned 

completely. 

Sources – In cities, as much as 95 percent of all CO emissions emanate from automobile exhaust. 

Other sources include industrial processes, non-transportation fuel combustion, and natural 

sources such as wildfires. Peak concentrations occur in colder winter months. 

Potential health impacts – Reduces oxygen delivery to the body’s organs and tissues. The health 

threat is most serious for those who suffer from cardiovascular disease. 

 Unit of measurement – Parts per million (ppm). 

 Averaging interval – Highest eight-hour period within a 24-hour period (midnight to midnight) 

 Reduction tips – Keep motor vehicle tuned properly and minimize nighttime driving. 

 

PM-10 & PM-2.5 (PARTICLES): 

Description – The term “particulate matter” (PM) includes both solid particles and liquid droplets 

found in air. Many manmade and natural sources emit PM directly or emit other pollutants that 

react in the atmosphere to form PM. Particles less than 10 micrometers in diameter tend to pose 

the greatest health concern because they can be inhaled into and accumulate in the respiratory 

system. Particles less than 2.5 micrometers in diameter are referred to as “fine” particles and are 

responsible for many visibility degradations such as the “Valley Brown Cloud” (see 

http://www.phoenixvis.net/). Particles with diameters between 2.5 and 10 micrometers are referred 

to as “coarse”. 

Sources – Fine = All types of combustion (motor vehicles, power plants, wood burning, etc.) and 

some industrial processes. Coarse = crushing or grinding operations and dust from paved or 

unpaved roads. 

Potential health impacts – PM can increase susceptibility to respiratory infections and can 

aggravate existing respiratory diseases, such as asthma and chronic bronchitis. 

 Units of measurement – Micrograms per cubic meter (ug/m3) 

 Averaging interval – 24 hours (midnight to midnight). 

 Reduction tips – Stabilize loose soils, slow down on dirt roads, carpool, and use public transit. 

 {Updated 03/23/2010} 
 

 

 

 

 

 

FORECAST 

GOOD (0-50) MODERATE (51-100) UNHEALTHY FOR 

SENSITIVE GROUPS 

(101-150) 

UNHEALTHY 

(151-200)

VERY UNHEALTHY 

(201-300) HAZARDOUS (301-500) 

AIR QUALITY FORECAST FOR 

THURSDAY, AUGUST 25, 2011 

This forecast is updated by 1:00 p.m. Monday through Friday and as needed 

(AQI Forecast on Twitter – see tables below for location specific Twitters) 

Valid for areas within Pinal County Arizona 

Highest AQI value/Site 

in Pinal County 

Highest AQI forecasted value 

(see tables below for forecasts by monitoring location) 

YESTERDAY 

TUE 8/23/11 

TODAY 

WED 8/24/11 

TOMORROW

THU 8/25/11 

EXTENDED 

FRI 8/26/11 

EXTENDED 

SAT 8/27/11 

OZONE 49 

APACHE JUNCTION 

70 

MODERATE 

55 

MODERATE 

52 

MODERATE 

55 

MODERATE 

PM-10* 58** 

SAN TAN VALLEY 

67** 

MODERATE 

85** 

MODERATE 

80** 

MODERATE 

60** 

MODERATE 

HEALTH 

WATCH/ 

ADVISORY

NONE NONE DUST DUST NONE

*PM-10 = Particles 10 microns and smaller 

**Excludes Cowtown monitor. See following page for Cowtown forecast. 

“Ozone Health Watch” means that the highest concentration of OZONE may approach the federal health standard. 

“PM-10 Health Watch” means that the highest concentration of PM-10 may approach the federal health standard.

“High Pollution Advisory” (HPA) means that the highest concentration of OZONE or PM-10 may exceed the 

federal health standard. 

“DUST” means that short periods of high PM-10 concentrations caused by outflow from thunderstorms are possible. 

Health message for Thursday, August 25, 2011: Active children, adults and people with 

lung disease, such as asthma, should consider reducing prolonged or heavy exertion 

outdoors. 
Discussion

Updated Wednesday, August 24, 2011 at 11:35 a.m. 

The strong high pressure aloft will continue to bring record or near-record 

temperatures to the region the next several days. Yesterday’s high temperature in Casa 

Grande was 111 degrees! 

 A few minor weather disturbances will pass through during the ThursdaySaturday timeframe. No local rain is expected however storm development (and 

associated strong outflow winds) to the south and east of Pinal County may create areas 

of blowing dust that may make their way into the county. Therefore the PM10 forecast has 

been increased into the middle and upper range of the moderate AQI category for 

Thursday and Friday. 

 The ozone levels should reach the good to low moderate range of the AQI scale 

the next few days. 

 Everyone is encouraged to limit outdoor activities during the heat of the day and 

drink plenty of water. Check back tomorrow for an updated air quality forecast. 

Forecaster – S. DiBiase 

COWTOWN 

(Twitter: Cowtown_AQI)

YESTERDAY 

TUE 8/23/11 

TODAY’S 

AQI FORECAST

WED 8/24/11 

TOMORROW 

AQI FORECAST

THU 8/25/11 

EXTENDED 

AQI FORECAST 

FRI 8/26/11 

EXTENDED 

AQI FORECAST

SAT 8/27/11 

PM-10* 99 105 110 115 105 

MONITORING NETWORK MAP YESTERDAY’S AQI LEVELS

AIR QUALITY FORECAST BY LOCATION FOR 

PM-10 (PARTICLES) 

SITE NAME TODAY’S 

AQI 

FORECAST 

WED 8/24/11 

TOMORROW

AQI 

FORECAST 

THU 8/25/11 

EXTENDED 

AQI 

FORECAST 

FRI 8/26/11 

EXTENDED 

AQI 

FORECAST 

SAT 8/27/11 

Casa Grande (Twitter: CG_AQI) 50 55 55 45 

Eleven Mile Corner 

(Twitter: PC_Housing_AQI) 50 75 70 48 

Maricopa (Twitter: 

MaricopaCity_AQ) 52 60 60 50 

San Tan Valley 

(Twitter: Santan_AQI) 52 65 60 50 

Stanfield 

(Twitter: Stanfield_AQI) 67 85 80 60 
OZONE* 

SITE NAME TODAY’S 

AQI FORECAST 

WED 8/24/11 

TOMORROW 

AQI FORECAST 

THU 8/25/11 

EXTENDED 

AQI FORECAST 

FRI 8/26/11 

EXTENDED 

AQI FORECAST 

SAT 8/27/11 

Apache Junction 

(Twitter: AJ_AQI) 70 55 50 50 

Casa Grande 

(Twitter: CG_AQI) 50 49 50 50 

Pinal Air Park 

(Twitter:

PC_Airpark_AQI)

50 50 52 55 

AIR POLLUTANTS IN DETAIL 

PM-10 & PM-2.5 (PARTICLES):

Description – The term “particulate matter” (PM) includes both solid particles and 

liquid droplets found in air. Many manmade and natural sources emit PM directly or 

emit other pollutants that react in the atmosphere to form PM. Particles less than 10 

micrometers in diameter tend to pose the greatest health concern because they can be 

inhaled into and accumulate in the respiratory system. Particles less than 2.5 

micrometers in diameter are referred to as “fine” particles and are responsible for 

many visibility degradations such as the “Valley Brown Cloud” (see 

http://www.phoenixvis.net/). Particles with diameters between 2.5 and 10 

micrometers are referred to as “coarse”. 

Sources – Fine = All types of combustion (motor vehicles, power plants, wood 

burning, etc.) and some industrial processes. Coarse = crushing or grinding operations 

and dust from paved or unpaved roads. 

Potential health impacts – PM can increase susceptibility to respiratory infections 

and can aggravate existing respiratory diseases, such as asthma and chronic 

bronchitis. 

Units of measurement – Micrograms per cubic meter (ug/m3) 

Averaging interval – 24 hours (midnight to midnight). 

Reduction tips – Stabilize loose soils, slow down on dirt roads and carpool. 

O3 OZONE:

Description – This is a secondary pollutant that is formed by the reaction of other 

primary pollutants (precursors) such as VOCs (volatile organic compounds) and NOx 

(Nitrogen Oxides) in the presence of heat and sunlight. The ozone “season” generally 

occurs during the spring and summer months (April-October) when high temperatures 

and extended daylight hours create the conditions most conducive to ozone formation. 

Sources – VOCs are emitted from motor vehicles, chemical plants, refineries, 

factories, and other industrial sources. NOx is emitted from motor vehicles, power 

plants, and other sources of combustion. 

Potential health impacts – Exposure to ozone can make people more susceptible to 

respiratory infection, result in lung inflammation, and aggravate pre-existing 

respiratory diseases such as asthma. Other effects include decrease in lung function, 

chest pain, and cough. 
Unit of measurement – Parts per billion (ppb). 

Averaging interval – Highest eight-hour period within a 24-hour period (midnight to 

midnight). 

Reduction tips – Curtail daytime driving, refuel cars and use gasoline-powered 

equipment as late in the day as possible.
 

 

 

 

 

 

FORECAST 

GOOD (0-50) MODERATE (51-100) UNHEALTHY FOR 

SENSITIVE GROUPS 

(101-150) 

UNHEALTHY 

(151-200)

VERY UNHEALTHY 

(201-300) HAZARDOUS (301-500) 

AIR QUALITY FORECAST FOR 

FRIDAY, AUGUST 26, 2011 

This forecast is updated by 1:00 p.m. Monday through Friday and as needed 

(AQI Forecast on Twitter – see tables below for location specific Twitters) 

Valid for areas within Pinal County Arizona 

Highest AQI value/Site 

in Pinal County 

Highest AQI forecasted value 

(see tables below for forecasts by monitoring location) 

YESTERDAY 

WED 8/24/11 

TODAY 

THU 8/25/11 

TOMORROW

FRI 8/26/11 

EXTENDED 

SAT 8/27/11 

EXTENDED 

SUN 8/28/11 

OZONE 71 

APACHE JUNCTION 

55 

MODERATE 

53 

MODERATE 

52 

MODERATE 

53 

MODERATE 

PM-10* 78** 

STANFIELD 

165** 

UNHEALTHY 

75** 

MODERATE 

60** 

MODERATE 

60** 

MODERATE 

HEALTH 

WATCH/ 

ADVISORY

NONE

HIGH 

POLLUTION 

ADVISORY 

DUST NONE NONE

*PM-10 = Particles 10 microns and smaller 

**Excludes Cowtown monitor. See following page for Cowtown forecast. 

“Ozone Health Watch” means that the highest concentration of OZONE may approach the federal health standard. 

“PM-10 Health Watch” means that the highest concentration of PM-10 may approach the federal health standard.

“High Pollution Advisory” (HPA) means that the highest concentration of OZONE or PM-10 may exceed the 

federal health standard. 

“DUST” means that short periods of high PM-10 concentrations caused by outflow from thunderstorms are possible. 

Health message for Friday, August 26, 2011: Active children, adults and people with lung 

disease, such as asthma, should consider reducing prolonged or heavy exertion outdoors. 
Discussion

Updated Thursday, August 25, 2011 at 11:30 a.m. 

*** PM10 HIGH POLLUTION ADVISORY (HPA) IN EFFECT 

THURSDAY AUGUST 25, 2011 *** 

Blowing dust from thunderstorm outflows during the early morning hours 

Thursday resulted in several of Pinal County monitors recording high PM10 readings. 

Several sites already exceed the 24 hour National Ambient Air Quality Standard in the 

western half of Pinal County. Therefore, a PM10 High Pollution Advisory (HPA) is in 

effect for the remainder of today. Thunderstorm activity is possible again this afternoon 

and evening adding onto the already elevated particulate matter concentrations. 

For Friday the chance for thunderstorms remain in the forecast but with slightly 

lower chances. The PM10 HPA will not be extended into Friday. Wind blown dust is still 

a possibility during the afternoon and evening hours. Strong high pressure will remain in 

place and continue to bring near-record high temperatures. Ozone is expected to remain 

in the Good to Moderate range of the AQI scale. 

Anyone with respiratory and/or heart ailments should limit outdoor activities 

today in order to reduce health impacts due to the high levels of PM10. Forecaster – M. 

Sundblom 

COWTOWN 

(Twitter: Cowtown_AQI)

YESTERDAY 

WED 8/24/11 

TODAY 

AQI FORECAST

THU 8/25/11 

TOMORROW 

AQI FORECAST

FRI 8/26/11 

EXTENDED 

AQI FORECAST 

SAT 8/27/11 

EXTENDED 

AQI FORECAST

SUN 8/28/11 

PM-10* 142 375 115 105 105 

MONITORING NETWORK MAP YESTERDAY’S AQI LEVELS

AIR QUALITY FORECAST BY LOCATION FOR 

PM-10 (PARTICLES) 

SITE NAME TODAY’S 

AQI 

FORECAST 

THU 8/25/11 

TOMORROW

AQI 

FORECAST 

FRI 8/26/11 

EXTENDED 

AQI 

FORECAST 

SAT 8/27/11 

EXTENDED 

AQI 

FORECAST 

SUN 8/28/11 

Casa Grande (Twitter: CG_AQI) 120 52 45 45 

Eleven Mile Corner 

(Twitter: PC_Housing_AQI) 110 54 48 48 

Maricopa (Twitter: 

MaricopaCity_AQ) 165 57 50 50 

San Tan Valley 

(Twitter: Santan_AQI) 65 54 50 50 

Stanfield 

(Twitter: Stanfield_AQI) 110 75 60 60 
OZONE* 

SITE NAME TODAY’S 

AQI FORECAST 

THU 8/25/11 

TOMORROW 

AQI FORECAST 

FRI 8/26/11 

EXTENDED 

AQI FORECAST 

SAT 8/27/11 

EXTENDED 

AQI FORECAST 

SUN 8/28/11 

Apache Junction 

(Twitter: AJ_AQI) 55 53 52 53 

Casa Grande 

(Twitter: CG_AQI) 49 47 50 50 

Pinal Air Park 

(Twitter:

PC_Airpark_AQI)

50 45 45 50 

AIR POLLUTANTS IN DETAIL 

PM-10 & PM-2.5 (PARTICLES):

Description – The term “particulate matter” (PM) includes both solid particles and 

liquid droplets found in air. Many manmade and natural sources emit PM directly or 

emit other pollutants that react in the atmosphere to form PM. Particles less than 10 

micrometers in diameter tend to pose the greatest health concern because they can be 

inhaled into and accumulate in the respiratory system. Particles less than 2.5 

micrometers in diameter are referred to as “fine” particles and are responsible for 

many visibility degradations such as the “Valley Brown Cloud” (see 

http://www.phoenixvis.net/). Particles with diameters between 2.5 and 10 

micrometers are referred to as “coarse”. 

Sources – Fine = All types of combustion (motor vehicles, power plants, wood 

burning, etc.) and some industrial processes. Coarse = crushing or grinding operations 

and dust from paved or unpaved roads. 

Potential health impacts – PM can increase susceptibility to respiratory infections 

and can aggravate existing respiratory diseases, such as asthma and chronic 

bronchitis. 

Units of measurement – Micrograms per cubic meter (ug/m3) 

Averaging interval – 24 hours (midnight to midnight). 

Reduction tips – Stabilize loose soils, slow down on dirt roads and carpool. 

O3 OZONE:

Description – This is a secondary pollutant that is formed by the reaction of other 

primary pollutants (precursors) such as VOCs (volatile organic compounds) and NOx 

(Nitrogen Oxides) in the presence of heat and sunlight. The ozone “season” generally 

occurs during the spring and summer months (April-October) when high temperatures 

and extended daylight hours create the conditions most conducive to ozone formation. 

Sources – VOCs are emitted from motor vehicles, chemical plants, refineries, 

factories, and other industrial sources. NOx is emitted from motor vehicles, power 

plants, and other sources of combustion. 
Potential health impacts – Exposure to ozone can make people more susceptible to 

respiratory infection, result in lung inflammation, and aggravate pre-existing 

respiratory diseases such as asthma. Other effects include decrease in lung function, 

chest pain, and cough. 

Unit of measurement – Parts per billion (ppb). 

Averaging interval – Highest eight-hour period within a 24-hour period (midnight to 

midnight). 

Reduction tips – Curtail daytime driving, refuel cars and use gasoline-powered 

equipment as late in the day as possible.
 

 

 

 

 

 

FORECAST 

GOOD (0-50) MODERATE (51-100) UNHEALTHY FOR 

SENSITIVE GROUPS 

(101-150) 

UNHEALTHY 

(151-200)

VERY UNHEALTHY 

(201-300) HAZARDOUS (301-500) 

AIR QUALITY FORECAST FOR 

SATURDAY, AUGUST 27 THROUGH 

MONDAY, AUGUST 29, 2011 

This forecast is updated by 1:00 p.m. Monday through Friday and as needed 

(AQI Forecast on Twitter – see tables below for location specific Twitters) 

Valid for areas within Pinal County Arizona 

Highest AQI value/Site 

in Pinal County 

Highest AQI forecasted value 

(see tables below for forecasts by monitoring location) 

YESTERDAY 

THU 8/25/11 

TODAY 

FRI 8/26/11 

TOMORROW

SAT 8/27/11 

EXTENDED 

SUN 8/28/11 

EXTENDED 

MON 8/29/11 

OZONE 77 

PINAL AIR PARK 

53 

MODERATE 

52 

MODERATE 

53 

MODERATE

55 

MODERATE 

PM-10* 425** 

MARICOPA 

155** 

UNHEALTHY 

70** 

MODERATE 

60** 

MODERATE

65** 

MODERATE 

HEALTH 

WATCH/ 

ADVISORY

PM10 HPA 

DUST 

PM10 HPA 

DUST NONE NONE NONE

*PM-10 = Particles 10 microns and smaller 

**Excludes Cowtown monitor. See following page for Cowtown forecast. 

“Ozone Health Watch” means that the highest concentration of OZONE may approach the federal health standard. 

“PM-10 Health Watch” means that the highest concentration of PM-10 may approach the federal health standard.

“High Pollution Advisory” (HPA) means that the highest concentration of OZONE or PM-10 may exceed the 

federal health standard. 

“DUST” means that short periods of high PM-10 concentrations caused by outflow from thunderstorms are possible. 

Health message for Saturday, August 27 through Monday, August 29, 2011: Active 

children, adults and people with lung disease, such as asthma, should consider reducing 

prolonged or heavy exertion outdoors. 
Discussion

Updated Friday, August 26, 2011 at 11:15 a.m. 

*** PM10 High Pollution Advisory (HPA) in effect 

for the remainder of Friday August 26, 2011 *** 

Blowing dust from thunderstorm outflows in Pima County during the 

overnight/early morning hours Thursday and again on Thursday evening resulted in 

several of Pinal County monitors exceeding the PM10 health standard. Both the Cowtown 

and Maricopa monitors reached the Hazardous level on the AQI scale. 

Unfortunately today will also be an active day weather-wise, especially to our 

south and east. More storm outflows and blowing dust are likely today; therefore a same 

day PM10 High Pollution Advisory (HPA) is being issued for the remainder of Friday. 

 Anyone with respiratory and/or heart ailments should limit outdoor activities 

today in order to reduce health impacts due to the high levels of PM10. 

Saturday and Sunday will feature lower chances at storm development and 

blowing dust. The PM10 levels will range from upper good to mid moderate range of the 

AQI scale with slightly lower levels of ozone expected. Forecaster – S. DiBiase 

COWTOWN 

(Twitter: Cowtown_AQI)

YESTERDAY 

THU 8/25/11 

TODAY 

AQI FORECAST

FRI 8/26/11 

TOMORROW 

AQI FORECAST

SAT 8/27/11 

EXTENDED 

AQI FORECAST 

SUN 8/28/11 

EXTENDED 

AQI FORECAST

MON 8/29/11 

PM-10* 889 155 105 115 105 

MONITORING NETWORK MAP YESTERDAY’S AQI LEVELS

AIR QUALITY FORECAST BY LOCATION FOR 

PM-10 (PARTICLES) 

SITE NAME TODAY 

AQI 

FORECAST 

FRI 8/26/11 

TOMORROW 

AQI 

FORECAST 

SAT 8/27/11 

EXTENDED 

AQI 

FORECAST 

SUN 8/28/11 

EXTENDED 

AQI 

FORECAST 

MON 8/29/11 

Casa Grande (Twitter: CG_AQI) 110 55 50 52 

Eleven Mile Corner 

(Twitter: PC_Housing_AQI) 110 55 48 50 

Maricopa (Twitter: 

MaricopaCity_AQ) 150 55 50 50 

San Tan Valley 

(Twitter: Santan_AQI) 100 55 50 55 

Stanfield 

(Twitter: Stanfield_AQI) 155 70 60 65 
OZONE* 

SITE NAME TODAY 

AQI FORECAST 

FRI 8/26/11 

TOMORROW 

AQI FORECAST 

SAT 8/27/11 

EXTENDED 

AQI FORECAST 

SUN 8/28/11 

EXTENDED 

AQI FORECAST 

MON 8/29/11 

Apache Junction 

(Twitter: AJ_AQI) 53 52 53 55 

Casa Grande 

(Twitter: CG_AQI) 47 52 50 50 

Pinal Air Park 

(Twitter:

PC_Airpark_AQI)

45 52 50 49 

AIR POLLUTANTS IN DETAIL 

PM-10 & PM-2.5 (PARTICLES):

Description – The term “particulate matter” (PM) includes both solid particles and 

liquid droplets found in air. Many manmade and natural sources emit PM directly or 

emit other pollutants that react in the atmosphere to form PM. Particles less than 10 

micrometers in diameter tend to pose the greatest health concern because they can be 

inhaled into and accumulate in the respiratory system. Particles less than 2.5 

micrometers in diameter are referred to as “fine” particles and are responsible for 

many visibility degradations such as the “Valley Brown Cloud” (see 

http://www.phoenixvis.net/). Particles with diameters between 2.5 and 10 

micrometers are referred to as “coarse”. 

Sources – Fine = All types of combustion (motor vehicles, power plants, wood 

burning, etc.) and some industrial processes. Coarse = crushing or grinding operations 

and dust from paved or unpaved roads. 

Potential health impacts – PM can increase susceptibility to respiratory infections 

and can aggravate existing respiratory diseases, such as asthma and chronic 

bronchitis. 

Units of measurement – Micrograms per cubic meter (ug/m3) 

Averaging interval – 24 hours (midnight to midnight). 

Reduction tips – Stabilize loose soils, slow down on dirt roads and carpool. 

O3 OZONE:

Description – This is a secondary pollutant that is formed by the reaction of other 

primary pollutants (precursors) such as VOCs (volatile organic compounds) and NOx 

(Nitrogen Oxides) in the presence of heat and sunlight. The ozone “season” generally 

occurs during the spring and summer months (April-October) when high temperatures 

and extended daylight hours create the conditions most conducive to ozone formation. 

Sources – VOCs are emitted from motor vehicles, chemical plants, refineries, 

factories, and other industrial sources. NOx is emitted from motor vehicles, power 

plants, and other sources of combustion. 

Potential health impacts – Exposure to ozone can make people more susceptible to 

respiratory infection, result in lung inflammation, and aggravate pre-existing 

respiratory diseases such as asthma. Other effects include decrease in lung function, 

chest pain, and cough. 
Unit of measurement – Parts per billion (ppb). 

Averaging interval – Highest eight-hour period within a 24-hour period (midnight to 

midnight). 

Reduction tips – Curtail daytime driving, refuel cars and use gasoline-powered 

equipment as late in the day as possible.
APPENDIX C

NOTICE OF PUBLIC COMMENT PERIOD
Request for Public Comments on Exceptional Events in the Greater Phoenix Area

In 2005, Congress identified a need to account for events that result in exceedances of the 

National Ambient Air Quality Standards (NAAQS) that are exceptional in nature (e.g., not 

expected to reoccur or caused by acts of nature beyond man-made controls.) In response, EPA 

promulgated the Exceptional Events Rule (EER) to address exceptional events in 40 CFR Parts 

50 and 51 on March 22, 2007 (72 FR 13560). On May 2, 2011, EPA released draft guidance 

documents on the implementation of the EER to State, tribal and local air agencies for review. 

The EER allows for states and tribes to “flag” air quality monitoring data as an exceptional 

event. If flagged, these data can be excluded from consideration in air quality planning if EPA 

concurs with the demonstration submitted by the flagging agency documenting that all 

procedural and technical requirements have been met. 

Pursuant to 40 CFR 50.14(c)(3)(i), the Arizona Department of Environmental Quality (ADEQ) is 

soliciting comments on its final demonstrations of events that have caused elevated 

concentrations of PM10 in the Greater Phoenix area on February 19; July 18; August 3; August 

18; August 25 through 28; September 2; October 4; November 4, 2011; January 21 – 22 and 

February 27, 2012. ADEQ has decided to flag these episodes based on these analyses. Copies of 

the demonstrations are available for review beginning Monday, December 3, 2012, on the ADEQ 

website at www.azdeq.gov/environ/air/plan/. Interested parties can submit written comments 

throughout the comment period which will end at 5:00 p.m. on Tuesday, January 1, 2013. Any 

comments received will be responded to and forwarded to EPA with the final demonstrations. 

Written comments should be addressed, faxed, or e-mailed to: 

Andra Juniel, Air Assessment Section, Arizona Department of Environmental Quality, 1110 W. 

Washington Street, 3415-A, Phoenix, AZ 85007, PHONE: (602) 771-4417; FAX: (602) 771-

2366, E-mail: juniel.andra@azdeq.gov. 

In addition to being available on-line, copies of the analyses are available for review, Monday 

through Friday, 8:30 a.m. to 4:30 p.m., at the ADEQ Records Center, 1110 W. Washington St., 

Phoenix, AZ, 85007, Attn: David Olivo, (602) 771-4380, email: olivo.david@azdeq.gov. 

Persons with a disability may request reasonable accommodations by contacting Linda Morrison 

at (602) 771-4793 or 1-800-234-5677 ext. 771-4793. This document is available in alternative 

formats by contacting ADEQ TDD phone number at (602) 771-4829. 
APPENDIX D

NATIONAL WEATHER SERVICE FORECASTS, 

WARNINGS, AND ALERTS