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Assessment of Qualification for Treatment under the Arizona Natural and Exceptional 

Events Policy for the High Particulate (PM10) Concentration Events in the 

Phoenix and Yuma Areas on May 21, 2008 

Background

The Arizona Department of Environmental Quality (ADEQ) 

issues Dust Control Action Forecasts for the Yuma and 

Phoenix areas as part of their Natural Events Action Plans. 

On Tuesday May 20, 2008, in response to an approaching 

trough of low pressure, ADEQ air quality forecasters issued 

the Maricopa County Dust Control Action Forecast calling for 

a high risk of wind-blown dust for Wednesday May 21st, in 

Maricopa County. In anticipation of this potential wind-blown 

dust event, ADEQ also issued a High Pollution Advisory for 

Maricopa County for May 21, 2008. The approaching trough 

was forecast to impact the Yuma area as well, and ADEQ air 

quality forecasters subsequently called for a high risk of 

wind-blown dust in their Yuma and Vicinity Dust Control 

Action Forecast for Wednesday, May 21st. This potential 

regional high-wind event equated to a significant risk of 

exceeding the PM10 National Ambient Air Quality Standards 

(NAAQS) in both Yuma and Maricopa County. The forecasts/ 

advisories satisfy the requirement in 40 CFR 51.930(a)(1). 

The forecast for May 21st for both Maricopa County and 

Yuma called for sustained winds at 20-30 mph with the 

possibility of gusts greater than 40 mph capable of producing 

significant wind-blown dust. This potential wind-blown dust 

event equated to a high risk of exceeding the PM10 NAAQS in 

Maricopa County. Strong winds did occur and were observed 

in the Phoenix Metro and the Yuma areas on May 21st, 2008. 

Beginning in the morning and continuing through the evening 

hours of May 21st, strong southwesterly and westerly winds in 

Phoenix and strong west-northwesterly winds in Yuma 

generated areas of blowing dust. All appropriate State 

Implementation Plan (SIP) control measures were in place 

during the event, demonstrating per 40 CFR 50.1(j) that the 

event “is not reasonably controllable or preventable.” A 

discussion of commonly employed Best Available Control 

Measures (BACM) for dust in Maricopa and Yuma counties 

can be found in “High Wind Exceptional Events and Control 

Measures for PM10 Areas” (see “References”). 

The initialization of a wind-blown dust event is evident in the 

Phoenix visible camera images, as well as the Arizona 

Meteorological Network (AzMET), Maricopa County (MC), 

ADEQ, and National Weather Service (NWS) monitors (see 

Fig. 1). Strong winds gusting over 25 mph and as high as 35 

mph at the MC West 43rd monitor location and 37 mph at the 

NWS Luke Air Force Base were reported. The Yuma Marine 

Corps Air Stations (MCAS) also measured wind gusts up to 

37 mph along with reports of reduced visibility. This 

significant wind event brought elevated ambient 

concentrations of PM10 to the Phoenix and Yuma areas that 

exceeded the NAAQS at the West 43rd Ave. and Yuma 

Courthouse monitors. Due to the spatial variability of PM 

sources both within and outside of the Phoenix urban core, the 

PM10 NAAQS was only exceeded at the West 43rd monitors 

operated by Maricopa County, though other Phoenix area 

monitors did show elevated levels of PM10 (see Section 2 for 

more detail). The fact that ambient concentrations exceeded 

the NAAQS satisfies the criteria in 40 CFR 50.1(j) that the 

event “affects air quality.” The following are the key PM10

monitor readings for the monitors examined in this report: 

Monitor (Operator/Type) AQS ID 24-hr Avg PM10 1-hr Max PM10 Max Time Flag** 

YUMA AREA 

 Yuma Courthouse (ADEQ/TEOM) 04-027-0004* 164 504 1700 RJ 

PHOENIX METRO AREA 

 West 43rd Ave (MC/TEOM) 04-013-4009* 279 1208 0900 RJ

 Durango Complex (MC/TEOM) 04-013-9812* 110 310 0900 None 

 Greenwood (MC/TEOM) 04-013-3010* 89 219 0900 None 

 South Phoenix (MC/TEOM) 04-013-4003* 122 334 0900 None 

* EPA Air Quality System Identification Number 

** 24-hr PM10 concentration influenced by natural or exceptional event to be flagged. 

Type Abbreviations: TEOM – Tapered Element Oscillating Microbalance Monitor (Continuous monitor). 

The preliminary findings from this analysis were presented at 

stakeholders meeting on November 19, 2008, and March 19, 

2009, in Phoenix, Arizona. Following the stakeholders 

meetings, ADEQ supplemented and finalized the analysis and 

a public comment period was held from October 15, 2009 

through November 13, 2009. This finalized document and 

any comments received are being submitted to EPA to satisfy 

the requirements in 40 CFR 50.14(c)(3)(i). 
Hr T(F) PM Spd Max Dir Hr T(F) PM Spd Max Dir Hr T(F)

V

R Dust Spd Gust Dir Hr 1 2

1 89 87 9 21 S

W 1 91 29 4 15

W 1 84 10 14 14 S

W 1 87 51

2 87 46 9 19 S

W 2 88 39 6 18

W 2 80 10 13 13 S

W 2 47 67

3 85 40 5 11 S

W 3 87 41 4 15

W 3 79 10 15 15 S

W 3 40 71 4 81 28 2 7 W 4 85 26 2 10 SW 4 79 10 14 14 S 4 29 39

5 82 32 3 14 S 5 83 31 2 9S

W 5 75 10 7 7 S

W 5 32 49

6 82 60 4 9 S 6 84 27 2 14 S 6 75 10 10 10 S with w/o 6 60 58

7 83 54 2 9 S 7 86 27 5 13 S 7 77 10 11 11 S

W Monitor: Event Event 7 55 67

8 86 135 10 21 S

W 8 88 30 4 15 S

W 8 81 10 17 17 S

W 1-W43RD 279 66 8 135 84

9 88 518 15 29 S

W 9 90 44 6 19 S

W 9 85 10 20 20 S

W 2-YUMA C 164 76 9 519 178

10 89 1207 18 32 S

W 10 89 334 10 30

W 10 86 10 23 23 S

W 10 1208 171

11 90 600 17 30

W 11 90 159 9 23

W 11 87 10 21 30 SW > NAAQS < NAAQS 11 601 196

12 92 413 15 29

W 12 91 139 11 26

W 12 89 10 21 28 SW 12 413 192

1 94 534 15 34 S

W 1 93 205 11 32

W 1 91 10 9 34 S

W 1 535 192

2 94 836 17 35

W 2 93 300 14 34

W 2 91 10 26 37

W 2 837 160

3 94 735 19 34

W 3 93 286 16 31

W 3 91 10 20 31

W 3 735 140

4 94 254 16 30

W 4 93 280 16 32

W 4 91 10 22 29

W 4 255 161 5 92 224 16 30

W 5 92 193 14 30

W 5 89 10 17 33

W 5 225 467 wnd @3m agl / Dir corrected to true north

6 90 243 15 32

W 6 91 167 14 28

W 6 88 10 20 25

W 6 243 504 HIGHLIGHTING Col. Parameter

7 87 262 16 31

W 7 89 198 14 29

W 7 85 10 21 26 S

W 7 263 210 Max Wind T(F) Temp. (Deg. F.)

8 84 104 12 22

W 8 86 112 9 27

W 8 83 10 16 16

W 8 105 266 > 15 mph RH Rel Humidity % 9 82 76 11 20

W 9 84 83 8 22

W 9 82 10 16 16

W 9 77 175 >25 mph Rn Rain (Inches/hr)

10 80 69 8 17

W 10 82 58 5 14

W 10 81 10 18 18 N

W 10 69 168 HR - Time (End) Spd Avg Speed mph

11 78 58 10 21

W 11 81 57 7 20

W 11 78 10 9 9

W 11 58 139 A.M. Max Max Speed mph

12 77 69 8 16 SW 12 79 63 3 9 W 12 78 10 13 13

W 12 70 140 P.M. Dir Wind Dir. (from)

5/21 - 2:00AM 5/21 - 8:0

Hr T(F) RH PM Spd Max Dir Hr T(F) PM Spd Max Dir Hr T(F) PM Spd Max Dir

1 82 25 40 9 14 S

W 1 89 26 7 20 S

W 1 88 45 8 21 S

W

2 81 25 41 3 12 S

W 2 87 41 10 26 S

W 2 86 43 10 21

W

3 75 32 49 4 14

W 3 85 48 7 18 SW 3 85 46 9 19

W

4 72 36 47 1 5 E 4 83 35 4 13 SW 4 81 41 6 13 SW5 74 33 29 4 9 SW 5 80 30 4 12 SW 5 80 37 7 16 SW Yr Sea Yr Sea

6 73 36 33 7 11 S

W 6 81 33 4 12 S

W 6 80 51 6 15 S 5 8 8 8 5/21 - 9:30AM 5/21 - 1:30PM 

7 73 38 42 4 11 S

W 7 82 45 4 11 S

W 7 81 50 4 12 S 9 9 12 9

8 80 31 53 10 23

W 8 84 55 2 15

W 8 85 56 8 18 S

W 11 11 14 14

9 83 25 82 16 26 S

W 9 87 80 1 99 SE 9 89 131 11 27 S

W 15 13 16 16

10 85 26 200 19 32 S

W 10 97 141 4 32 S

W 10 88 309 16 32

W 19 19 19 19

11 88 24 91 18 29 S

W 11 86 109 13 30 S

W 11 88 171 16 31

W 29 28 23 22

12 91 20 175 15 30

W 12 88 91 13 35

W 12 91 115 14 29

W 44 46 31 29

1 91 15 519 18 33

W 1 90 113 12 33

W 1 92 131 14 31

W 65 63 42 40

2 92 14 390 20 34

W 2 91 152 14 34

W 2 92 246 17 32

W 91 82 57 51

3 92 13 197 17 34

W 3 91 160 13 32

W 3 93 231 17 35

W 121 107 77 76

4 91 13 235 16 35

W 4 90 159 14 33

W 4 92 162 17 31

W 139 125 96 109 5/21 - 9:30AM 5/21 - 1:30PM 

5 90 13 215 16 30

W 5 90 134 13 31

W 5 91 133 15 29

W 157 134 127 182

6 88 13 143 16 29

W 6 88 129 11 28

W 6 89 136 15 30

W 192 194 186 210

7 85 15 99 14 24

W 7 87 112 13 27

W 7 87 122 16 29

W 227 220 211 212

8 81 16 64 12 19

W 8 84 93 11 25

W 8 83 106 13 25

W 313 313 349 349

9 77 20 77 9 14

W 9 82 71 10 22

W 9 81 92 11 20

W

10 74 23 46 9 14

W 10 80 62 7 16

W 10 80 65 9 18

W

11 73 22 42 8 15

W 11 80 47 8 19

W 11 78 64 9 18

W

12 73 21 47 10 17

W 12 78 31 4 13

W 12 76 56 5 12

W

5/21 - 9:30AM 5/21 - 1:30PM 

Hr T(F) RH Spd Max Dir Hr T(F) RH Spd Max Dir Hr T(F) VR Dust Spd Gust Dir Hr T(F) RH Rn Spd Max Dir

1 71 35 2 5 SE 1 81 16 9 19

W 1 82 10 0 0 N 1 78 19 - 7 18

W

2 68 41 1 4

W 2 74 25 4 13 S 2 81 10 7 7

W 2 73 28 - 4 13 S

W

3 64 52 2 7 SE 3 71 28 5 13 S 3 77 10 6 6 S 3 68 34 - 3 8 S

W

4 63 51 3 6 S 4 72 28 7 12 S

W 4 77 10 3 3 S

W 4 68 37 - 5 8 S

W

5 65 47 0 4

W 5 65 43 4 9 S

W 5 74 10 5 5 S

W 5 62 54 - 2 6 S

W 5/21 - 9:30AM 5/21 - 1:30PM 

6 65 43 3 9 S

W 6 69 37 6 9

W 6 75 10 9 9

W 6 64 53 - 4 6 S

W

7 68 40 3 9 S 7 69 38 5 11 S

W 7 76 10 5 5

W 7 67 47 - 4 13 S

W

8 76 34 6 15

W 8 77 31 13 24

W 8 81 10 13 13

W 8 77 32 - 11 21 N

W

9 79 31 7 17

W 9 78 32 15 25 N

W 9 83 10 14 23 N

W 9 78 32 - 13 20 N

W

10 80 30 8 20

W 10 79 31 15 25 N

W 10 85 10 16 24 N

W 10 80 31 - 13 20 N

W

11 82 28 8 23

W 11 81 30 16 25

W 11 87 10 16 16 N

W 11 82 30 - 15 23 N

W

12 84 26 11 26

W 12 83 26 16 27

W 12 89 9 18 26

W 12 83 27 - 15 24 NW

1 85 24 10 25

W 1 85 22 14 22

W 1 92 9 14 25 N

W 1 86 23 - 13 23 N

W

2 87 21 10 24

W 2 87 19 13 23

W 2 93 10 16 25

W 2 87 20 - 12 19 N

W

3 89 16 9 22

W 3 88 16 14 25 N

W 3 95 10 17 24 N

W 3 89 17 - 13 22 N

W 5/21 - 9:30AM 5/21 - 1:30PM 

4 89 16 12 31

W 4 89 15 15 27

W 4 95 10 20 30

W 4 89 16 - 14 22 N

W

5 87 20 17 33

W 5 86 20 20 35

W 5 91 4 BLDU 29 37

W 5 86 21 - 20 31

W

6 83 23 13 29

W 6 83 23 20 36

W 6 87 4 BLDU 26 33

W 6 82 24 - 20 31

W

7 80 26 18 31

W 7 81 25 17 32

W 7 83 9 21 29

W 7 81 26 - 17 23

W No image available

8 76 30 15 27

W 8 78 28 20 28

W 8 80 9 21 28

W 8 77 30 - 16 26 N

W

9 73 34 13 24

W 9 75 32 14 25

W 9 77 10 18 28

W 9 74 34 - 13 21

W

10 71 36 11 24

W 10 73 33 16 25

W 10 76 10 18 26

W 10 73 34 - 14 21 N

W

11 69 36 12 21

W 11 73 31 21 32 N

W 11 75 10 16 28

W 11 72 32 - 15 24 N

W

12 68 37 9 19

W 12 72 30 20 33 NW 12 74 10 15 15

W 12 72 31 - 16 25 NW

MC - WEST PHOENIX

MC - WEST PHOENIX

16477 (112.14Wx33.48N) 16375 (112.12Wx33.43N)

MC - DURANGO COMPLE

X

MC - DURANGO COMPLEX

19040 (114.63Wx32.61N)

ADEQ - YUMA MESA

ADEQ - YUMA MESA

NWS-Yuma MCAS

16659 (112.14Wx33.41N)

MC - WEST FORTY THIR

MC - WEST FORTY THIR

21525 (112.62Wx33.37N)

MC - BUCKEYE

MC - BUCKEYE

16377 (112.08Wx33.40N)

MC - SOUTH PHOENIX

MC - SOUTH PHOENIX 

Hourly PM10 Conc. (μg/m3

)

1-W43RD

WINDS 

& PM10 

DATA

AZMET Monitoring Locations F

Ke

Eve

2

164

Mon 2

25%

02-YumaValley

SUM

Between gusts in from the between NWS sitea.m., winsouthweup to 33 

GOES-West Satellite

See http://ag.arizona.edu/azmet/

NWS-Luke AFB Pink=Event Contrib. Conclusion: As shown above, the PM10 concentration would have been below the

NAAQS "BUT FOR" the event contribution (hours highlighted in pink).

ADEQ - YUMA AGRI CEN

ADEQ - YUMA AGRI CEN

128530 (114.71Wx32.71N)

 5%

NWS-Luke AFB

NWS-Yuma MCAS

279

24-Hr. Avg PM10

2-YUMA CH

MONITORS:

Event Contrib. Analysis

Min

Historical Distribution

5-Yr. Dist. of Values (μg/m3

)

Conclusion: Flagged Value is exceptional

Yr - All Data (5-Yrs)

 1.0% 0.5%

10%75%

99.5%99.0%

90%

Flagged

Value

Column Index

Max

Cum. Mon 1

Sea - Data for Spring

 season only (5-Yrs)

in nature (ie greater than 95% of all data)

95%

97.5%

AZMET - YUMA

MONITORS:

 2.5%

1-WEST FORTY THIR

2-YUMA COURTHOU

Freq.

50%

(looking south)

WHITE TANK MTN

(looking west)

ESTRELLA MTN

(looking south)

CAMELBACK MTN

(looking northeast)

SUPERSTITION MTN

(looking east)

SOUTH MOUNTAIN
Assessment of May 21, 2008 event (Cont.) 

- 4 - 

Assessment under the Technical Criteria Document (TCD)

1. Properly qualify and validate the air quality measurement 

to be flagged. As this was not a filter sampling date (1-in-6 

run day), only data from the continuous analyzers were 

examined. The air quality monitoring data were reviewed by 

the agency responsible for operation of the monitor. All 

hourly PM10 readings from the West 43rd Ave. and Yuma 

Courthouse monitoring sites were valid for May 21st. Audits 

of the analyzers revealed operations were within acceptable 

tolerance. 

2. Review suspected contributing sources. On May 21, 2008, 

strong westerly to southwesterly winds were occurring in the 

Phoenix area due to a low pressure system approaching from 

the west with a cold front passing over Arizona. The high 

wind event was a regional phenomenon that affected the 

entire Phoenix Metro area as well as Yuma. However, PM 

sources are highly variable across space; therefore, the 

locations of higher PM10 concentrations in Phoenix (namely 

the Salt River channel) are likely an indication that these 

locations (or areas upwind of these locations) contain greater 

sources of PM than other locations within the Phoenix 

Metropolitan area. While no specific source allocation can be 

determined for this particular day, the 2005 ADEQ revised 

PM10 SIP for the Salt River area (attached) contains modeled 

source contributions on high wind days (see section 4.2 – 

Source Categories). Results estimate that approximately 76% 

of PM10 concentrations can be attributed to windblown dust, 

of which 21% is from agricultural fields, 15% from alluvial 

channels, and 21% from vacant lots. It is not clear whether 

similar source allocations can be assumed for this April 30, 

2008, high wind event (see attachment for likely PM sources 

within the Salt River area). PM10 concentrations also spiked at 

the Yuma Courthouse monitor between 8:00 a.m. and 9:00 

p.m., roughly coincident with the spikes recorded at the West 

43rd Ave. monitor. The plot of hourly PM10 concentrations 

and max wind data in the upper right corner of Figure 1 

confirms the nearly identical timing of the elevated PM10

concentrations and strong wind gusts recorded at the West 

43rd Ave monitor. 

3. Examine all air quality monitoring information. Data from 

all monitors in the network were reviewed. Monitors from 

the affected areas are summarized in the table in the 

Background section of this assessment. Pursuant to 40 CFR 

50.14(c)(3)(iii)(C), the “Historical Distribution” Table in 

Figure 1 has been included to demonstrate that the event is 

associated with a measured concentration in excess of normal 

historical fluctuations, including background (i.e., 

concentrations greater than the 95th percentile). Additionally, 

the winds associated with the elevated PM10 concentrations 

may be characterized as unusual as described in “Impact of 

Exceptional Events’ ‘Unusual Winds’ on PM10

Concentrations” (see “References”). 

4. Examine the meteorological conditions before and during 

the event. The NWS, MC, ADEQ and AzMET surface data 

for Arizona, along with the visible camera images in Phoenix, 

provide a good explanation as to what meteorological 

conditions were in place on May 21st. The meteorological 

data are summarized in Figure 1. The wind data are 

highlighted yellow if the max wind speed in the hour exceeds 

15 mph and orange if it exceeds 25 mph. As can be seen in 

Figure 1, wind speeds did not pick up in central and southern 

Arizona until approximately 8:00 a.m., when several stations 

reported gusty winds over 20 mph. This timing corresponds to 

the onset of elevated PM10 concentrations recorded at the 

West 43rd Ave. and Yuma Courthouse monitoring sites, both 

of which remained elevated through the afternoon and into the 

evening. 

5. Perform a qualitative attribution to emission source(s). All 

evidence indicates the elevated PM10 concentrations in the 

Phoenix area can be attributed to soil emissions that were 

transported over portions of the Phoenix Metro area in 

Maricopa County. While it is possible that local soil sources 

may have contributed to the West 43rd Ave. monitor being the 

only one to exceed the NAAQS in the Phoenix Metro area, no 

source specific emission allocation is possible based on the 

data available for analysis. The hourly concentration data do 

not show any significant source other than the wind-blown 

dust event occurring on May 21, 2008. Visual evidence of 

reduced visibility can be seen in the images located in the 

lower right portion of Figure 1. In the Yuma area, visibility 

was reduced to 4 miles and blowing dust was reported by 

trained weather spotters at the Yuma MCAS during the late 

afternoon and early evening hours. Yuma radar data also 

suggests that blowing dust was occurring in southeastern 

California and southwestern Arizona (see attachment). 

6. Estimation of Contribution from Source or Event. The 

demonstration analysis contained in this report establishes the 

linkage between the measurements to be flagged and the 

event, thus satisfying the requirement in 40 CFR 

50.14(c)(3)(iii)(B). Pursuant to 40 CFR 50.14(c)(3)(iii)(D), 

the “Event Contrib. Analysis” Table in Figure 1 has been 

included to demonstrate that there would have been no 

exceedances or violations but for the event (i.e., the 

contribution during the event overwhelmed the 24-hour 

averages). 

7. Determination that a Natural or Exceptional Event 

Contributed To an Exceedance. Based on this analysis, the 

event satisfies the requirement in 40 CFR 50.1(j) that the 

elevated concentrations at West 43rd Ave. and the Yuma 

Courthouse were attributed to a natural event. 

Conclusion

Transport of dust from soils by high winds. The region wide 

elevated PM10 event on May 21, 2008, in Yuma and Maricopa 

Counties was the result of the transport of dust and soils from 

winds that suspended natural soils and soils from areas where 

Best Available Control Measures are in place and should be 

flagged for air quality planning purposes. The “high wind” 

(RJ) flag should be applied to the monitor readings indicated 

in the table at the beginning of this report, as the monitor 

would have been below the NAAQS but for the contribution 

of the event. 
ATTACHMENTS AND REFERENCES 

FOR EXCEPTIONAL EVENTS ANALYSIS 

The following are supplemental materials helpful in understanding the exceptional 

event summarized in the main report. In addition, the reader is referred to the 

following references. 

REFERENCES

Arizona Department of Environmental Quality (ADEQ), Air Quality Exceptional and 

Natural Events Policy, Policy Number 2009.002 (April 28, 1999; revised January 10, 

2006 and June 22, 2007). 

Arizona Department of Environmental Quality (ADEQ), Technical Criteria Document 

for Determination of Natural Exceptional Events for Particulate Matter Equal to or Less 

Than Ten Microns in Aerodynamic Diameter (PM10) (May 31, 2000). 

Arizona Department of Environmental Quality (ADEQ), Technical Criteria Document 

for Determination of Natural and Exceptional Events (December 12, 2005). 

Arizona Department of Environmental Quality (ADEQ), Impact of Exceptional Events 

‘Unusual Winds’ on PM10 Concentrations (October 14, 2009). 

Arizona Department of Environmental Quality (ADEQ), High Wind Exceptional Events 

and Control Measures for PM10 Areas (October 14, 2009). 

Environmental Protection Agency (EPA), The Treatment of Data Influenced by 

Exceptional Events (Exceptional Event Rule), 73 FR 70597; 40 CFR Parts 50 and 51 

(November 21, 2008). 
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.epa.gov/airnow/aqibroch

 

NEW!!! CLICK HERE FOR UPDATED 2008 OZONE SEASON STATS NEW!!! 

AIR QUALITY FORECAST FOR WEDNESDAY, MAY 21, 2008

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 

MON 05/19/2008

OZONE HEALTH 

WATCH 

NWS EXCESSIVE 

HEAT WARNING 

Highest AQI Reading/Site 

(Preliminary data only) 

TODAY 

TUE 05/20/2008

OZONE HIGH 

POLLUTION 

ADVISORY 

NWS EXCESSIVE 

 HEAT WARNING 

TOMORROW 

WED 05/21/2008

PM-10 HIGH 

POLLUTION 

ADVISORY 

OZONE HEALTH 

WATCH 

NWS WIND 

ADVISORY 

EXTENDED 

THU 05/22/2008

PM-10 HEALTH 

WATCH 

POSSIBLE 

DUST 

O3* 

97 

TONTO NATIONAL 

MONUMENT 

124 

UNHEALTHY 

FOR SENSITIVE 

GROUPS 

93 

MODERATE 

80 

MODERATE 

CO* 14 

PHOENIX SUPERSITE 

09 

GOOD 

06 

GOOD

06 

GOOD 

PM-10* 80 

WEST FORTY THIRD 

74 

MODERATE

140 

UNHEALTHY 

FOR SENSITIVE 

GROUPS 

92 

MODERATE

PM-2.5* 44 

DURANGO 

32 

GOOD

53 

MODERATE

55 

MODERATE
Health message for Tuesday, May 20: Active children and adults, and people with 

lung disease such as asthma, should reduce prolonged or heavy outdoor exertion. 

Health message for Wednesday, May 21: Active children and adults, and people 

with lung disease such as asthma, should reduce prolonged or heavy exertion. 

Synopsis and Discussion

AN OZONE HIGH POLLUTION ADVISORY REMAINS IN EFFECT TODAY MAY 20

A PM-10 HIGH POLLUTION ADVISORY AND AN OZONE HEALTH WATCH HAVE BEEN ISSUED FOR 

WEDNESDAY MAY 21

Local ozone levels approached unhealthy levels at several east Valley locations on Monday, and as of 

10:00 a.m. this morning hourly concentrations were running 10-15 parts per billion higher than 24 hours 

ago at most monitoring sites; therefore, today’s High Pollution Advisory will continue thru the early 

evening hours. All eyes now turn to the significant wind/blowing dust/unhealthy PM-10 (coarse particle) 

event that is looking inevitable for Wednesday. A transition from record heat to below average 

temperatures will begin on Wednesday as a surface cold front moves over the state ahead of an intense 

upper level trough. A sharp temperature contrast will be reflected in tight pressure and contour gradients 

that will be capable of producing sustained winds over 30 mph and wind gusts in excess of 40 mph over a 

wide area, much of it open desert. The likelihood that widespread blowing dust will be generated by 

afternoon has prompted the issuance of a PM-10 High Pollution Advisory. Under sunny skies and with 

continuing additional ozone transport from California, local ozone levels could also be a concern. -Reith 

 

MONITORING SITE MAPS: STATIC MAP - http://www.azdeq.gov/environ/air/monitoring/images/map.jpg

 INTERACTIVE MAPS - http://aqwww.maricopa.gov/AirMonitoring/SitePollutionMap.aspx

 http://www.airnow.gov/ 

POLLUTION MONITOR READINGS FOR MONDAY, MAY 19, 2008 

O3 (OZONE) 

For facts on new 8-hr ozone standard go to: http://www.epa.gov/air/ozonepollution/pdfs/2008_03_aqi_changes.pdf

For maps go to: http://www.airnow.gov/index.cfm?action=airnow.currentconditions

 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) 68 77 

Blue Point 66 71 

Buckeye 54 46 

Casa Grande (Pinal County) 64 64 

Cave Creek 66 71 

Central Phoenix 62 58 

Combs School (Pinal County) 57 48 

Dysart 54 46 

Falcon Field 67 74 

Fountain Hills 67 74 

Glendale 54 46 

Humboldt Mountain 64 64 

Maricopa (Pinal County) 55 47 

North Phoenix 61 54 

Phoenix Supersite 63 61 

Pinal Air Park (Pinal County) 60 51 

Pinnacle Peak 63 61 

Queen Valley (Pinal County) 72 90 

Rio Verde 70 84 

South Phoenix 66 71 

South Scottsdale 62 58 

Tempe 64 64 

Tonto Nat’l Mon. (Gila County) 74 97 

West Chandler 61 54 

West Phoenix 64 64 

Yuma (Yuma County) 57 48 
CO (CARBON MONOXIDE) 

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

Central Phoenix 0.9 10 

Greenwood 1.1 13 

Phoenix Supersite 1.2 14 

West Indian School 1.0 11 

West Phoenix 0.6 07 

PM-10 (PARTICLES)

 SITE NAME MAX 24-HR VALUE (ug/m3) MAX AQI AQI COLOR CODE 

Buckeye 47 44 

Central Phoenix 41 38 

Combs School(Pinal County) 59 53 

Coyote Lakes 37 34 

Durango 54 50 

Greenwood 47 44 

Higley 46 43 

Maricopa (Pinal County) 74 60 

Phoenix Supersite 33 31 

South Phoenix 50 46 

West Forty Third 113 80 

West Phoenix 42 39 

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 13.6 44 

Dysart 4.3 14 

Estrella Mountain Park 6.4 21 

Phoenix Supersite 13.0 42 

Vehicle Emissions Lab 6.2 20 

West Phoenix 10.7 35 
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 08/14/2007} 
MARICOPA COUNTY 

DUST CONTROL ACTION FORECAST

ISSUED TUESDAY, MAY 20, 2008

Three-day weather outlook:

 

tttttttttttttttttttt 

R I S K F A C T O R S

In the wake of the heat wave on Monday and Tuesday the approach of an intense late-season trough in the mid-latitude storm 

track will make for very windy conditions region-wide beginning on Wednesday. On that day a surface cold front will move 

over Arizona ahead of the trough; both the duration and speed of the winds have the potential to produce widespread blowing 

dust over the desert areas with a HIGH risk of unhealthy PM-10 levels in the Phoenix area; High Pollution Advisory will be 

issued as a result. On Thursday and Friday somewhat less gradient wind may be enhanced by thunderstorm downdrafts so the 

risk level will remain elevated both days. 

 

 WINDS STAGNATION RISK LEVEL

Day #1: Wed 05/21/2008

+ =

 

 

Southwest to westerly 

15-30 mph with gusts 

near 40 mph possible.

Rather stagnant during 

the morning hours 

with improvement by 

afternoon. 

 

 HIGH 

 

Day #2: Thu 05/22/2008 + = 

Southwest to westerly 

15-25 mph with 

stronger gusts near 

thunderstorms. 

Little if any stagnation 

expected. 

 

 MODERATE 

 

 

Day #3: Fri 05/23/2008 + = 

Southerly 15-25 mph 

by afternoon with 

higher gusts near 

thunderstorms. 

Little if any 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. To review the complete air quality forecast for the Phoenix metropolitan area 

and the health effects of air pollution, please see ADEQ's Air Quality Forecast at 

http://www.azdeq.gov/environ/air/ozone/ensemble.pdf, or call 602-771-2367 for recorded forecast 

information. 
 YUMA AND VICINITY 

DUST CONTROL ACTION FORECAST

ISSUED TUESDAY, MAY 20, 2008

Three-day weather outlook:

tttttttttttttttttttt 

 

 

In the wake of the heat wave on Monday and Tuesday the approach of an intense late-season trough in the mid-latitude storm 

track will make for very windy conditions region-wide beginning on Wednesday. On that day a surface cold front will move 

over Arizona ahead of the trough; both the duration and speed of the winds have the potential to produce widespread blowing 

dust over the desert areas with a HIGH risk of unhealthy PM-10 levels in the Yuma area. Equally strong down-river winds are 

possible on Thursday, enhanced by the possibility of thunderstorm downdrafts. 

 WINDS WIND-BLOWN DUST RISK 

Day #1: Wed 05/21/2008 

 

West to northwesterly 

20-30 mph with gusts 

over 40 mph possible 

by afternoon. 

 

 HIGH 

 

 

 

 

Day #2: Thu 05/22/2008 

Northwest to northerly 

20-30 mph with gusts 

approaching 40 mph. 

 

 

 HIGH 

 

Day #3: Fri 05/23/2008 

Southerly 15-25 mph 

with gusts to 30 mph 

except stronger near 

thunderstorms. MODERATE 

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 (brown cloud). 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, minimize travel on dirt roads, utilize tarps on haul trucks, limit use of leaf-blowers, 

and on high-wind days reduce outdoor activities. 

 CKR 05/09/2005
05/21/2008 - ADDITIONAL GRAPHS

West 43rd - PM 10 vs. Wind Speed

0

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PM Concentration (μg/m^3)

0510152025303540

Wind Speed (mph)

PM10Max Wind

Durango - PM 10 vs. Wind 

0

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5/21/2008

PM Concentration (μg/m^3)

PM10Max Wind

South Phoenix - PM 10 vs. Wind Speed

0

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PM Concentration (μg/m^3)

0510152025303540

Wind Speed (mph)

PM10Max Wind

Yuma Courthouse - PM 10 vs. 

0

200400600800

100012001400

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1:00

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PM Concentration (μg/m^3)

PM10Max Wind Yuma MesaMax Wind Yuma Ag.
Phoenix Area PM10 and Meteorological Monitors 

Source: US EPA, ADEQ, & Google Earth 
Yuma Area PM10 and Meteorological Monitors 

Source: US EPA, ADEQ, & Google Earth 
May 21st 2008 Radar and Satellite Data 

Radar data obtained from the National Oceanic and Atmospheric Administration’s 

National Climatic Data Center in conjunction with MODIS satellite photography 

obtained from NASA’s Rapid Response System allows for a visual reassessment of the 

event. These data were downloaded as KMZ files and displayed using Google Earth 

software. The overlay of the products clearly shows that much of the suspended dust 

originated in southeastern California and was transported to the east. It can be seen that 

large sources of dust appear to come from the Imperial Sand Dunes of southern 

California (also known as the Algodones Dunes) and other similar dunes or open desert 

areas to the southwest of the Salton Sea. Another common source of blowing dust 

appears to be an area of open desert to the south / southeast of Yuma. While some of the 

radar images are obscured by noise, the dust sources are still clearly visible. 

Figure 1 - Radar data and MODIS satellite imagery show a major source of blowing dust located to 

the southwest of the Salton Sea. 

 
Figure 2 – Right around the time of highest PM10 concentrations and lowest visibilities in the Yuma 

area, radar data show what are likely high concentrations of blowing dust to the west / northwest of 

Yuma. These returns (shown as purple colors) are likely indicative of blowing dust originating from 

the Imperial Sand Dunes. 
The MODIS satellite data are from the Terra satellite with 250 meter resolution an

bands 7, 2, and 1 to accentuate vegetation. Lighter tan areas are indicative of open de

while darker b

d use 

sert 

rown areas indicate areas of higher elevation or differing soil type 

ompared to that of the open desert). The suspected PM sources are outlined in the 

image below. 

(c

Figure 3 - Image courtesy of MODIS Rapid Response Project at NASA/GSFC displayed using 

Google Earth software. 
26

CHAPTER 4: OVERVIEW OF PM10 CONTROL MEASURES 

4.1 INTRODUCTION 

Chapter 1.2.2 of this SIP ("Regulatory History of the Metropolitan Maricopa PM10 Nonattainment 

Area") notes that on July 25, 2002, EPA approved the Maricopa Serious PM10 Nonattainment Area, 

and granted Arizona's request, in accordance with CAA § 188(e), to extend the CAA deadline for 

attainment of the annual and 24-hour PM10 standards from December 31, 2001, to December 31, 

2006 (67 FR 48718). 

Because the attainment deadline for this plan revision is also December 31, 2006, and the 

measures must be applied to all similar sources throughout the Phoenix Nonattainment Area (see 

67 FR 44369, July 2, 2002), the control strategies must meet the "Most Stringent Measures" test, as 

well as the “Best Available Control Measures/Technology” test. In its July 25, 2002, approval of the 

Maricopa County Plan, EPA defined “most stringent measures” (MSMs) as the most stringent 

measures included in any state implementation plan, or being implemented in any state, that are 

economically and technologically feasible for the nonattainment area in question. “Best Available 

Control Measures” (BACM) must be applied in serious nonattainment areas, also taking into 

account the economic and technological feasibility of each measure. 

This chapter details the proposed BACM and MSM that were evaluated for each significant source 

category. 

4.2 SOURCE CATEGORIES 

The Salt River Study Area 2002 base year emissions inventory is described in Chapter 3.0 and the 

TSD’s Chapter 4.0. The 2002 emissions source category contributions to ambient PM10 are 

depicted in Table 4.2.1. The average concentrations are derived from the modeled concentrations 

outlined in the TSD, Chapter 6. 

Assumptions used to calculate trackout emissions appear in Appendix K “Methodology for 

Weighting Trackout Emissions” and Appendix P “Mapping Weighted Trackout Emissions into 

Predicted Concentrations” of the October 2004 TSD. Calculation methodology for street sweeping 

emissions reductions appears in Appendix L “Street Sweeping Reductions” of the October 2004 

TSD. 

Table 4.2.1 2002 Salt River Study Area Source Category Contributions to Ambient PM10

Concentrations 

Average Low Wind 

Day Contribution 

Average High Wind 

Day Contribution 

Highest 

Contribution(μg/m3) Source Category Percentage 

Contribution 

Percentage 

Contribution 

Low Wind 

Day 

High Wind 

Day 

Industrial Sources 25.9% 8.3% 60.2 31.8 

 Point Emissions 2.7% 1.1% 5.3 3.0 

 Area Emissions 23.2% 7.2% 54.9 28.8 

Construction 5.8% 0.9% 6.0 4.4 

Area Sources 4.2% 0.7% 8.0 3.1 

 Unpaved Parking Lots 1.7% 0.2% 0.8 1.4 

 Unpaved Shoulders 2.5% 0.4% 7.2 1.7 
27

Table 4.2.1 2002 Salt River Study Area Source Category Contributions to Ambient PM10

Concentrations 

Average Low Wind 

Day Contribution 

Average High Wind 

Day Contribution 

Highest 

Contribution(μg/m3) Source Category Percentage 

Contribution 

Percentage 

Contribution 

Low Wind 

Day 

High Wind 

Day 

Roads & Trackout 63.7% 13.5% 73.6 42.7 

 Freeway 0.4% 0.2% 0.7 0.4 

 Primary Roads 43.6% 9.3% 44.8 33.3 

 Secondary Roads 7.5% 1.5% 6.9 1.5 

 Trackout 12.1% 2.5% 21.2 7.5 

Agricultural Tillage 0.4% NA 0.2 NA 

Windblown Dust NA 76.7% NA 290.1 

 Agricultural Fields NA 21.3% NA 84.9 

 Alluvial Channels NA 14.9% NA 79.5 

 Construction NA 3.5% NA 14.0 

 Industrial NA 7.3% NA 33.6 

 Disturbed Areas NA 5.2% NA 25.9 

 Stockpiles NA 3.6% NA 12.6 

 Vacant Lots NA 20.9% NA 39.6 

Note: Bold concentrations exceed the 5 μg/m3 threshold for significant sources.

In Table 4.2.2, the modeled contributions for each of the source categories are given for the 2006 

attainment case. These percentages are similar to the 2002 case, but with several significant 

differences. For example, the windblown contribution decreases from 77% to 59% from 2002 to 

2006. 

Table 4.2.2 Salt River Study Area Source Category Contributions to Ambient PM10 

Concentrations for the 2006 Attainment Case 

Average Low Wind Day 

Contribution 

Average High Wind Day 

Contribution 

Source Category 

Percentage Contribution Percentage Contribution 

Industrial Sources 29.7% 12.1% 

 Point Source Emissions 4.4% 3.1% 

 Area Emissions 25.2% 8.9% 

Construction 5.2% 1.8% 

Area Sources 7.1% 2.1% 

 Unpaved Parking Lots 0.5% 0.6% 

 Unpaved Shoulders 6.6% 1.5% 

Roads & Trackout 58.0% 24.7% 

 Freeway 0.9% 0.4% 

 Primary Roads 48.3% 21.6% 

 Secondary Roads 6.8% 1.9% 

 Trackout 2.0% 0.7% 

Agricultural Tillage 0.1% NA 

Windblown Dust NA 59.4% 

 Agricultural Fields NA 8.9% 

 Alluvial Channels NA 15.4% 

 Construction NA 4.2% 

 Industrial NA 6.7% 

 Disturbed Areas NA 10.1% 

 Stockpiles NA 5.9% 

 Vacant Lots NA 8.4%