Pinal County Air QualityOctober 27, 2008

PM10 Exceptional/Natural Event

October 27, 2008• Winds associated with abnormally tight pressure

gradient caused by high pressure and a back door cold front to the east. The tight pressure gradient caused significant areas of blowing dust. The Maximum winds reached 28 mph and three PCAQCD monitors exceeded the 24-hr PM10 NAAQS.

PM10 24-hr

Site AQS Site# Conc. (ug/m3)– Stanfield 04-021-3008(3) 212.6– Stanfield 04-021-3008(1) 201.0– Maricopa 04-021-3010(3) 159.4

Strong high pressure &“back door” cold front

Result in a strongpressure gradient

October 27, 2008PM10 Exceedance

Wind Event

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

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Stanfield PM10 Maricopa PM10 Maricopa AZMET

Stanfield 24-hr Avg. 212.6 ug/m3

Maricopa 24-hr Avg. 159.4 ug/m3

NOTE: Stanfield had 2 invalid hours at 1 and 2 pm.

27-Oct-08Stanfield PM10

1 HOUR AVG 24 HOUR AVG DATE TIME Hourly WS (mph) Max WS (mph) WD47.3 84.6 10/27/2008 1:00:05 AM 3.8 7.4 16032.5 85.1 10/27/2008 2:00:05 AM 2 3.8 10662.3 86.2 10/27/2008 3:00:05 AM 1.3 3.8 6

161.2 90.3 10/27/2008 4:00:05 AM 1.3 4.5 34826 89.4 10/27/2008 5:00:05 AM 2.5 5.4 290

52.3 88.8 10/27/2008 6:00:05 AM 2 5.4 241128.9 90.0 10/27/2008 7:00:05 AM 1.3 4.3 215256.3 94.8 10/27/2008 8:00:05 AM 5.6 15.4 82335.1 106.2 10/27/2008 9:00:05 AM 13 20.6 84478.9 122.5 10/27/2008 10:00:05 AM 16.1 24.4 85

1526.9 181.8 10/27/2008 11:00:05 AM 18.3 26.6 81635.3 205.6 10/27/2008 12:00:05 PM 16.3 27.7 82

211.6 10/27/2008 1:00:05 PM 17 26.2 79218.5 10/27/2008 2:00:05 PM 16.8 25.3 74

271.4 228.8 10/27/2008 3:00:05 PM 15.4 23.3 72151.9 234.3 10/27/2008 4:00:05 PM 13.6 21.7 71

92 235.8 10/27/2008 5:00:05 PM 13 21 7278.4 230.7 10/27/2008 6:00:05 PM 8.7 15.4 6269.8 222.8 10/27/2008 7:00:05 PM 7.2 11.6 6145.1 217.0 10/27/2008 8:00:05 PM 7.4 10.3 6841.2 212.5 10/27/2008 9:00:05 PM 9.6 13.6 7055.1 210.5 10/27/2008 10:00:05 PM 9.8 15.2 8060.7 211.2 10/27/2008 11:00:05 PM 9.2 16.1 8269.1 212.6 10/28/2008 12:00:05 AM 8.9 13 78

Maricopa AZMET

27-Oct-08Maricopa PM10

1 HOUR AVG 24 HOUR AVG DATE TIME Hourly WS (mph) Max WS (mph) WD239.9 86.1 10/27/2008 1:00:05 AM 3.8 7.4 160143.5 87.2 10/27/2008 2:00:05 AM 2 3.8 106

70.3 86.4 10/27/2008 3:00:05 AM 1.3 3.8 673.8 86.6 10/27/2008 4:00:05 AM 1.3 4.5 34898.7 88.0 10/27/2008 5:00:05 AM 2.5 5.4 29091.8 89.2 10/27/2008 6:00:05 AM 2 5.4 241

129.8 91.2 10/27/2008 7:00:05 AM 1.3 4.3 215160.4 93.1 10/27/2008 8:00:05 AM 5.6 15.4 82326.2 102.1 10/27/2008 9:00:05 AM 13 20.6 84852.9 132.4 10/27/2008 10:00:05 AM 16.1 24.4 85496.5 150.1 10/27/2008 11:00:05 AM 18.3 26.6 81293.2 160.4 10/27/2008 12:00:05 PM 16.3 27.7 82

176 166.1 10/27/2008 1:00:05 PM 17 26.2 79141.9 171.2 10/27/2008 2:00:05 PM 16.8 25.3 74

84.8 173.7 10/27/2008 3:00:05 PM 15.4 23.3 7276.6 175.4 10/27/2008 4:00:05 PM 13.6 21.7 7168.6 175.9 10/27/2008 5:00:05 PM 13 21 7260.4 174.7 10/27/2008 6:00:05 PM 8.7 15.4 6256.2 174.8 10/27/2008 7:00:05 PM 7.2 11.6 6145.1 174.9 10/27/2008 8:00:05 PM 7.4 10.3 6836.1 171.6 10/27/2008 9:00:05 PM 9.6 13.6 7030.8 166.8 10/27/2008 10:00:05 PM 9.8 15.2 8033.2 164.0 10/27/2008 11:00:05 PM 9.2 16.1 8238.7 159.4 10/28/2008 12:00:05 AM 8.9 13 78

Maricopa AZMET

Casa Grande Airport NWS Observations

Sustained wind speed/gust & Visibility

10/27/08 “But for” Test• Stanfield (TEOM) had the following 24-hr

PM10 concentrations before/after the 10/27/08 exceptional/natural event– 10/26/08 – 86.2 ug/m3

– 10/28/08 – 87.8 ug/m3

• Maricopa (TEOM) had the following 24-hr PM10 concentrations before/after the 10/27/08 exceptional/natural event– 10/26/08 – 84.0 ug/m3

– 10/28/08 – 72.6 ug/m3