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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 Area on April 30, 2008 

Background

The Arizona Department of Environmental Quality (ADEQ) 

issues Dust Control Action Forecasts as part of the Natural 

Events Action Plan for the Phoenix area. On Tuesday, April 

29, 2008, in response to a tightening pressure gradient 

associated with the tail end of a trough of low pressure and 

cold frontal passage through Arizona, ADEQ air quality 

forecasters issued the Maricopa County Dust Control Action 

Forecast calling for a moderate risk of wind-blown dust and 

thus a moderate risk for unhealthy PM10 levels in the Phoenix 

area for Wednesday, April 30th. The Dust Control Action 

Forecast called for southwesterly winds of 15 to 25 mph with 

stronger gusts possible during the afternoon. In anticipation of 

the high winds and blowing dust, a PM10 Health Watch was 

issued for April 30th (See Attachments). These 

forecasts/advisories satisfy the requirement in 40 CFR 

51.930(a)(1). 

This regional high-wind event created the potential for a 

wind-blown dust event with a moderate risk of exceeding the 

PM10 National Ambient Air Quality Standards (NAAQS) in 

Maricopa County. Strong winds did occur and were observed 

throughout portions of Maricopa County and much of the 

Phoenix Metro area on April 30th, 2008. Beginning in the 

morning and continuing until the early evening hours of April 

30th, strong southwesterly winds generated blowing dust 

which moved into portions of the Phoenix Metro area. 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), 

and National Weather Service (NWS) monitors (see Fig. 1). 

Strong winds gusting to 30 mph at the NWS Phoenix Sky 

Harbor station and as high as 41 mph at the NWS Deer Valley 

station were reported between 9:00 a.m. and 6:00 p.m., while 

many other Valley monitoring locations measured wind gusts 

over 20 mph. 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 Ave. monitor 

operated by Maricopa County (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** 

PHOENIX METRO AREA 

 West 43rd Ave (MC/TEOM) 04-013-4009* 172 1065 1100 RJ

 Durango Complex (MC/TEOM) 04-013-9812* 69 220 1100 None 

 Greenwood (MC/TEOM) 04-013-3010* 63 121 1100 None 

 Higley (MC/TEOM) 04-013-4006* 63 200 0600 None 

 West Phoenix (MC/TEOM) 04-013-0019* 55 96 1100 None 

 Central Phoenix (MC/TEOM) 04-013-3002* 51 78 1200 None 

 JLG Supersite (ADEQ/TEOM) 04-013-9997* 46 91 1100 None 

 Coyote Lakes (MC/TEOM) 04-013-4014* 53 165 0600 None 

 South Phoenix (MC/TEOM) 04-013-4003* 88 218 1600 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 meetings 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)

V

R Dust Spd Gust Dir Hr T(F)

V

R Dust Spd Gust Dir Hr 1

1 78 36 2 13 N

W 1 83 10 0 0 N 1 76 10 11 11 S

W 1 36.6

2 77 30 1 9 E 2 76 10 0 0 N 2 74 10 8 8 S 2 30.5

3 75 32 2 6 SE 3 76 10 6 6 SE 3 72 10 7 7 S 3 32.8 4 76 35 4 9 S 4 70 10 10 10 E 4 68 10 7 7 E 4 35

5 72 51 2 13 NE 5 70 10 8 8 E 5 68 10 6 6 E 5 51.4

6 68 112 3 7 NE 6 69 10 11 11 SE 6 68 10 9 9 E with w/o 6 112

7 68 109 3 7 NE 7 70 10 8 8 E 7 70 10 7 7 E Monitor: Event Event 7 109

8 74 119 3 8 N 8 74 10 6 6 E 8 73 10 9 9 SE 1-W43RD 172 66 8 120

9 78 75 3 7 N 9 79 10 0 0 N 9 77 10 9 9 S

W 9 75.3

10 83 85 5 20 S

W 10 82 10 8 8 S

W 10 79 10 11 21 S

W 10 85

11 87 404 13 23 SW 11 86 10 16 23 SW 11 82 10 13 26 SW > NAAQS < NAAQS 11 40412 89 1065 16 33

W 12 88 10 18 30

W 12 84 10 21 34 SW 12 1065

1 90 359 15 28

W 1 89 10 20 26

W 1 86 10 23 31 S

W 1 360

2 92 222 13 27 S

W 2 91 10 18 29

W 2 87 10 15 41 S

W 2 223

3 93 208 13 30 S

W 3 91 10 14 20 S

W 3 88 10 18 30

W 3 208

4 93 365 15 27 S

W 4 92 10 17 26

W 4 89 10 18 26

W 4 366 5 92 236 15 28 SW 5 90 10 20 30

W 5 88 10 23 29

W 5 236 wnd @3m agl / Dir corrected to true north

6 89 212 13 25

W 6 88 10 17 23

W 6 85 10 15 25 SW 6 212 HIGHLIGHTING Col. Parameter

7 85 133 12 23

W 7 86 10 17 17

W 7 83 10 15 29 S

W 7 134 Max Wind T(F) Temp. (Deg. F.)

8 81 77 6 12

W 8 83 10 10 10

W 8 80 10 7 7 S

W 8 77.4 > 15 mph RH Rel Humidity % 9 79 62 6 19

W 9 82 10 9 9 W 9 77 10 3 3 S 9 62.5 >25 mph Rn Rain (Inches/hr)

10 80 46 9 21 S

W 10 77 10 6 6 S 10 77 10 11 11 S

W 10 46.8 HR - Time (End) Spd Avg Speed mph

11 77 28 7 14 S

W 11 77 10 6 6 S 11 75 10 8 8 S

W 11 28.5 A.M. Max Max Speed mph

12 74 30 3 9 SW 12 74 10 3 3 S 12 72 10 8 8 SW 12 30.6 P.M. Dir Wind Dir. (from)

4/30 - 4:00AM 4/30 - 10:00AM 

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

1 76 30 5 10

W 1 80 49 2 11 S

W 1 77 37 2 7N

W

2 78 35 5 17 S

W 2 82 36 2 10 S

W 2 75 34 1 8 NE

3 77 31 5 11 SW 3 78 35 2 7 SW 3 72 40 2 7 E4 74 34 3 10 S 4 76 37 2 10 E 4 72 37 4 10 E5 70 46 3 9 NE 5 71 57 2 7 NE 5 68 45 3 9 E Yr Sea

6 67 60 2 8 NE 6 69 72 2 5 E 6 66 53 4 9E 5 8 4/30 - 6:00AM 4/30 - 10:00AM 

7 70 83 3 9 NE 7 70 135 2 5 E 7 69 58 5 12 E 9 98 77 89 2 7 N 8 76 82 2 7 N 8 75 65 4 7 NE 11 11

9 81 75 2 7 N 9 80 73 3 9N

W 9 82 52 2 9 NE 15 13

10 85 51 4 18 S

W 10 83 52 2 12

W 10 85 42 4 12

W 19 19

11 86 83 11 23 S

W 11 86 115 7 23

W 11 85 62 11 27 S

W 29 28

12 86 219 15 30

W 12 87 163 9 26

W 12 86 17 34

W 44 46

1 86 112 15 30

W 1 89 117 9 25

W 1 87 77 16 32

W 65 63

2 89 67 12 29

W 2 90 138 9 27

W 2 89 57 14 29

W 91 82

3 92 51 12 33

W 3 91 61 9 27

W 3 90 41 13 27

W 121 107

4 93 108 14 29

W 4 92 139 9 24

W 4 91 53 15 31

W 139 125 4/30 - 6:00AM 4/30 - 10:00AM 

5 92 69 13 31

W 5 92 218 10 27

W 5 91 73 15 35

W 157 134

6 89 85 14 27

W 6 90 114 8 22

W 6 89 59 14 27

W 192 194

7 85 82 12 28

W 7 87 94 8 20

W 7 85 70 14 27

W 227 220

8 81 62 8 15

W 8 84 73 3 10

W 8 81 47 9 20

W 313 313

9 77 56 4 10

W 9 80 92 1 4S

W 9 78 48 6 11

W

10 77 51 5 16 SW 10 80 74 2 9 W 10 78 53 7 16

W

11 75 38 5 10

W 11 78 40 2 7S

W 11 78 38 10 19

W

12 73 32 3 8 W 12 75 44 1 6 W 12 75 33 3 13

W

4/30 - 6:00AM 4/30 - 10:00AM 

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

1 71 16 1 7

W 1 76 11 4 11 S 1 79 10 2 11 S 1 72 35 4 9S

2 68 20 0 3 SE 2 75 11 4 11 S 2 76 12 3 6 S 2 70 40 2 9 SE3 66 20 3 6 NE 3 74 12 5 12 S 3 73 14 4 8 E 3 64 40 4 9E4 66 18 4 9 SE 4 71 14 5 13 S 4 71 15 5 8 E 4 62 37 6 10 E5 66 21 3 9 SE 5 69 19 3 9 SE 5 68 17 6 10 SE 5 61 39 5 9E 4/30 - 6:00AM 4/30 - 10:00AM 6 63 24 2 6 E 6 66 21 3 11 E 6 67 19 4 9 SE 6 59 75 5 10 SE7 65 25 2 8 E 7 69 23 5 13 S 7 68 23 6 11 SE 7 63 199 5 12 SE8 71 26 2 8 SE 8 72 23 7 15 S 8 72 24 7 15 S 8 74 58 8 17 S9 76 26 5 10 S 9 76 21 6 14 S 9 76 21 7 15 S 9 77 101 11 21 S

10 84 21 2 11 S

W 10 80 12 9 19 S

W 10 80 15 6 16 S

W 10 81 65 10 24 S

W

11 88 17 4 22 S

W 11 83 8 12 27 S

W 11 84 11 7 21 S

W 11 84 66 11 26 S

W

12 89 12 12 27

W 12 85 9 11 23 SW 12 87 8 13 26

W 12 87 61 9 22

W

1 90 11 13 30

W 1 87 8 11 27

W 1 87 8 14 30

W 1 88 47 11 27 S

W

2 92 11 12 26

W 2 88 8 11 26

W 2 88 8 13 26

W 2 90 49 10 27

W

3 93 13 13 26

W 3 90 10 11 27 S

W 3 90 10 11 26

W 3 92 34 8 23

W 4/30 - 6:00AM 4/30 - 10:00AM 

4 93 13 11 25

W 4 91 9 13 29 S

W 4 91 10 14 30

W 4 92 46 9 23 S

W

5 92 12 13 29

W 5 90 6 15 28 S

W 5 90 9 13 27

W 5 91 70 13 28 S

W

6 90 9 12 27

W 6 88 5 13 26 S

W 6 89 6 13 28

W 6 89 54 12 26

W

7 85 10 11 23

W 7 86 6 12 29 S

W 7 86 6 12 23

W 7 86 53 9 25

W

8 81 11 8 17

W 8 84 7 7 17

W 8 83 8 8 15

W 8 82 44 6 15

W

9 77 12 2 7 N

W 9 80 8 5 11 S

W 9 80 9 5 11

W 9 78 69 5 13 S

10 74 14 2 6

W 10 77 13 9 22 S

W 10 79 12 4 14 S

W 10 76 111 9 23 S

11 73 18 3 12 S

W 11 75 16 12 26 S 11 77 15 11 23 S 11 74 66 10 20 S

W

12 72 21 4 10 S 12 72 19 9 19 S 12 73 19 8 20 SW 12 72 47 11 20 SW

MC - SOUTH SCOTTSDAL

16478 (111.88Wx33.30N)

MC - WEST CHANDLER

MC - WEST CHANDLER

16398 (111.92Wx33.48N)

MC - SOUTH SCOTTSDAL

16380 (111.87Wx33.41N)

MC - MESA

16659 (112.14Wx33.41N)

MC - WEST FORTY THIR

MC - WEST FORTY THIR MC - DURANGO COMPLEX 16375 (112.12Wx33.43N) MC - DURANGO COMPLE

X

NWS-Deer Valley Airport F

Ke

Eve

3

WIND & 

PM10 

DATA

SUM

BeginninValley Aigusts fro41 mph. dust alofvisibility statute mwide werbetween gusts be

GOES-West Satellite

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

MC - CENTRAL PHOENIX

MC - CENTRAL PHOENIX MC - MESA 16505 (111.72Wx33.31N)

AZMET Monitoring Locations

Min

Column Index

1-WEST 43RD AVE

Sea - Data for Spring

 season only (5-Yrs)

Yr - All Data (5-Yrs)

24-Hr. Avg PM1010%

 2.5%

MC - HIGLEY

MC - HIGLEY

50%95%

97.5%

 0.5%

WHITE TANK MTN

(looking west)

SOUTH MOUNTAIN

(looking south)

SUPERSTITION MTN

(looking east)

Pink=Event Contrib.

Conclusion: As shown above, the PM10 

concentration wouldhave been below theNAAQS "BUT FOR" the event contribution (hours highlighted in pink).

16329 (112.05Wx33.46N)

 5%

Freq.

Historical Distribution

MONITORS:

5-Yr. Dist. of Values (μg/m3

)

NWS-Phoenix Sky Harbor

NWS-Phoenix Sky Harbor

NWS-Deer Valley Airport

16377 (112.08Wx33.40N)

MC - SOUTH PHOENIX

MC - SOUTH PHOENIX 90% 75%

Event Contrib. Analysis

Hourly PM10 Conc. (μg/m3

)

1-W43RD

Cum. Mon 1

2-Mon 23-Mon 3

MONITORS:

25%Max

99.5%99.0%

Conclusion: Flagged Value is exceptional

 1.0%

Value

172

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

(looking northeast)

ESTRELLA MTN

(looking south)

CAMELBACK MTN

Flagged
Assessment of April 30, 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 a filter sampling date (1-in-6 run 

day), data from both the continuous analyzers and filter based 

monitors 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. 

monitoring site were valid for April 30, 2008. Audits of the 

analyzers revealed operations were within acceptable 

tolerance. No local sources were reported as significantly 

contributing to the air quality episode. Exceedances of the 

NAAQS were recorded by the continuous monitor located at 

the West 43rd Ave. monitoring site operated by Maricopa 

County. 

2. Review suspected contributing sources. The NWS, 

AzMET, and MC 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 April 

30th. Strong westerly to southwesterly winds occurred in the 

Phoenix area due to a low pressure system approaching from 

the west. The plot of hourly PM10 concentration and max 

wind data in the upper right corner of Figure 1 confirms the 

nearly identical timing of the elevated PM10 concentrations 

and the strong wind gusts recorded by the West 43rd Ave. 

monitor. The high wind event was a regional phenomenon 

that affected the entire Phoenix Metro area. However, PM 

sources are highly variable across space; therefore, the 

locations of higher PM10 concentrations (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. 

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 MC and NWS 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 Arizona until approximately 9:00 

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. monitoring site, 

which remained elevated through the afternoon hours until a 

time when winds, including those reported at Sky Harbor and 

Deer Valley airports, decreased to below 20 mph. 

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. 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 April 30, 2008. 

Visual evidence of reduced visibility can be seen in the 

images located in the lower right portion of Figure 1. These 

images, along with the graph of West 43rd wind gusts and 

PM10 concentrations, provide proof that the elevated PM10

concentrations in Phoenix were coincident with strong gusty 

winds and can be attributed to soil emissions. 

6. Estimation of Contribution from Source or Event. The 

primary source appears to be wind-blown dust over central 

Arizona for which there is not an effective or efficient method 

to estimate the relative contributions from specific sources. 

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 exceedance or violation but for the event (i.e., 

the contribution during the event overwhelmed the 24-hour 

average). 

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 concentration in West 43rd Ave. was attributed to a 

natural event. 

Conclusion

Transport of dust from soils by high winds. The elevated 

PM10 event on April 30, 2008, in Maricopa County was the 

result of the transport of dust and soils from high 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, APRIL 30, 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 04/28/2008

NONE 

Highest AQI Reading/Site 

(Preliminary data only) 

TODAY 

TUE 04/29/2008

NONE 

 

TOMORROW 

WED 04/30/2008

OZONE HEALTH 

WATCH 

PM-10 HEALTH 

WATCH 

EXTENDED 

THU 05/01/2008

NONE 

 

O3* 90 

NORTH PHOENIX 

84 

MODERATE 

97 

MODERATE 

87 

MODERATE 

CO* 13 

WEST INDIAN SCHOOL 

11 

GOOD

8 

GOOD 

9 

GOOD 

PM-10* 59 

BUCKEYE 

68 

MODERATE

90 

MODERATE

57 

MODERATE

PM-2.5* 65 

DURANGO 

58 

MODERATE

54 

MODERATE

51 

MODERATE
Health message for Tuesday, Apr 29: Unusually sensitive people should consider 

reducing prolonged or heavy exertion outdoors. 

 

Health message for Wednesday, Apr 30: Unusually sensitive people should 

consider reducing prolonged or heavy exertion outdoors. 

 

Synopsis and Discussion

*An Ozone Health Watch AND a PM10 Health has been issued for Wednesday, April 30, 2008* 

Ozone levels continue to hold in the mid to upper “Moderate” range with little relief. It’s only going to get 

worse before it gets better as a trough of low pressure moves through the western U.S. the next couple of 

days. The tail end of the disturbance will impact Arizona Wednesday with winds increasing to 30 mph at 

times across the deserts, even stronger in higher elevations of Arizona. Yuma is already indicating that 

another transport situation is underway with Ozone in the upper “Moderate” range on Tuesday. That 

means that today and likely tomorrow should see some high levels across the Phoenix forecast. An 

increase in winds also means we could see areas of blowing dust across the dry deserts (now 65 

consecutive days without measurable rain in Phoenix). As a result of this latest weather system and its 

potential impact on the Valley’s air quality, we are issuing both an Ozone and PM10 Health Watch for 

Wednesday. The situation will be re-evaluated tomorrow, but conditions should improve Thursday and 

Friday as the system exits the region. Check back then for the latest. Have a good day! –J.Paul 

 

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, APRIL 28, 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) 64 64 

Blue Point 50 42 

Buckeye 65 67 

Casa Grande (Pinal County) 67 74 

Cave Creek 71 87 

Central Phoenix 66 71 

Combs School (Pinal County) 62 58 

Dysart 67 74 

Falcon Field 61 54 

Fountain Hills 64 64 

Glendale 70 84 

Humboldt Mountain 66 71 

Maricopa (Pinal County) 65 67 

North Phoenix 72 90 

Phoenix Supersite NOT AVBL NOT AVBL NOT AVBL 

Pinal Air Park (Pinal County) 65 67 

Pinnacle Peak 67 74 

Queen Valley (Pinal County) 66 71 

Rio Verde 66 71 

South Phoenix 68 77 

South Scottsdale 64 64 

Tempe 67 74 

Tonto Nat’l Mon. (Gila County) 66 71 

West Chandler 65 67 

West Phoenix 71 87 

Yuma (Yuma County) 70 84 
CO (CARBON MONOXIDE) 

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

Central Phoenix 0.8 9 

Greenwood 0.9 10 

Phoenix Supersite NOT AVBL NOT AVBL NOT AVBL 

West Indian School 1.1 13 

West Phoenix 1.0 11 

PM-10 (PARTICLES)

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

Buckeye 72.3 59 

Central Phoenix 39.9 36 

Combs School (Pinal County) 87.8 67 

Coyote Lakes 46.0 42 

Durango 59.1 53 

Greenwood 58.2 53 

Higley 62.0 54 

Maricopa (Pinal County) 73.6 60 

Phoenix Supersite 38.3 35 

South Phoenix 59.2 53 

West Forty Third 63.0 55 

West Phoenix 48.5 44 

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 21.3 65 

Dysart 6.5 21 

Estrella Mountain Park 10.5 34 

Phoenix Supersite 14.6 47 

Vehicle Emissions Lab 8.0 26 

West Phoenix 12.6 41 

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} 
ADEQ AIR POLLUTION HEALTH WATCH

ISSUANCE NOTICE 

Issuance Date and Time: Tuesday, April 29, 2008 11:30 a.m. 

Valid for Date(s): Wednesday, April 30, 2007 

Pollutant: Course Particulates (PM-10) 

Message: Elevated particulate levels combined with 

breezy to windy conditions Wednesday may 

lead to concentrations approaching the 

health standard. 

Detailed air quality forecast information is available on:

• The internet at www.azdeq.gov

• A telephone recording at 602-771-2367 

 

Duty Forecaster: Christopher Reith 602-771-2360 

 Joe Paul 602-771-2363 

 

 CKR 01/18/2005 
MARICOPA COUNTY 

DUST CONTROL ACTION FORECAST 

ISSUED TUESDAY, APRIL 29, 2008

Three-day weather outlook:

A trough of low pressure will move through the western U.S. the next several days with the tail end of the disturbance impacting 

Arizona Wednesday afternoon. Winds will increase out of southwest and west to around 30 mph at times across the deserts, 

lasting into early hours of Thursday before decreasing. Cooler air will filter in behind the system which means afternoon desert 

temperatures will only be in the upper 80s on Thursday. Winds will be much lighter Thursday afternoon through Friday. The 

risk of exceeding the 24-hr PM10 health standard in Phoenix will be “Moderate” on Wednesday, dropping back to “Low” by 

Thursday. 

R I S K F A C T O R S

 WINDS STAGNATION RISK LEVEL

 

Day #1: Wed 04/30/2008 + = 

 

Southwest winds 15 to 

25 mph with stronger 

gusts possible at times 

are expected during 

the afternoon hours.

Little to no stagnation 

is expected. 

 

 

MODERATE 

 

 

Day #2: Thu 05/01/2008 + = 

Slightly stagnant 

conditions are 

expected early with 

improvement by the 

afternoon. 

West winds 10 to 15 

mph are expected 

during the afternoon 

hours. LOW 

 

Day #3: Fri 05/02/2008 

 + = 

Somewhat stagnant 

conditions are 

expected early with 

improvement by the 

afternoon. 

West winds 5 to 10 

mph are likely much of 

the day.

LOW 

To review the complete air quality forecast for the Phoenix metropolitan area visit www.azdeq.gov or call 

602-771-2367 for recorded forecast information. 

 
04/30/2008 - ADDITIONAL GRAPHS

West 43rd - PM 10 vs. Wind Speed

0

200400600800

10001200

0:00

1:00

2:00

3:00

4:00

5:00

6:00

7:00

8:00

9:00

10:00

11:00

12:00

13:00

14:00

15:00

16:00

17:00

18:00

19:00

20:00

21:00

22:00

23:00

4/30/2008

PM Concentration (μg/m^3)

05101520253035

Wind Speed (mph)

PM10Max Wind

South Phoenix - PM 10 vs. W

0

200400600800

10001200

0:00

1:00

2:00

3:00

4:00

5:00

6:00

7:00

8:00

9:00

10:00

11:00

12:00

13:00

14:00

4/30/2008

PM Concentration (μg/m^3)

PM10Max Wind

Durango - PM 10 vs. Wind Speed

0

200400600800

10001200

0:00

1:00

2:00

3:00

4:00

5:00

6:00

7:00

8:00

9:00

10:00

11:00

12:00

13:00

14:00

15:00

16:00

17:00

18:00

19:00

20:00

21:00

22:00

23:00

4/30/2008

PM Concentration (μg/m^3)

05101520253035

Wind Speed (mph)

PM10Max Wind

Greenwood - PM 10 vs. Win

0

200400600800

10001200

0:00

1:00

2:00

3:00

4:00

5:00

6:00

7:00

8:00

9:00

10:00

11:00

12:00

13:00

14:00

4/30/2008

PM Concentration (μg/m^3)

PM10Max Wind
Phoenix Area PM10 and Meteorological Monitors 

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

Source: US EPA, ADEQ, & Google Earth 
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%