Pinal County Air Quality November 15, 2007 PM 10 Exceptional Event

November 15, 2007 Strong area of low pressure moved in from the central Baja coast in California. Strong winds associated with the system helped transport dust from areas outside the county which impacted Pinal County. Max winds reached 39 mph which caused five PCAQCD monitors to exceed the 24-hr PM 10 NAAQS. Site24-hr PM 10 Conc. (ug/m 3 ) Stanfield PCH Combs Casa Grande Maricopa 162.6

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11/15/07 “But for” Test Had it not been “but for” the high winds associated with the strong low pressure and transported dust which caused Stanfield to have several 1-hr PM 10 concentrations between 580 and 1282 ug/m 3, Stanfield would have NOT exceeded the PM hr NAAQS. –If those elevated hours were replaced with the average of the other hours not affected by the winds then the 24-hr PM 10 concentration would be 98 ug/m 3 –Using the same methodology – PCH ug/m 3 –Combs – 115 ug/m 3 –Casa Grande – 101 ug/m 3 –Maricopa – 137 ug/m 3

Additional 11/15/07 “But for” Test Stanfield had the following 24-hr PM 10 concentrations before/after the 11/15/07 event –11/14/07 – 98.5 ug/m 3 –11/16/07 – 57.9 ug/m 3 PCH –11/14/07 – 134 ug/m 3 –11/16/07 – 89.2 ug/m 3 Combs –11/14/ ug/m 3 –11/16/07 – 66.9 ug/m 3 Casa Grande –11/14/07 – ug/m 3 –11/16/07 – 69.1 ug/m 3 Maricopa –11/14/07 – ug/m 3 –11/16/07 – 83.7 ug/m 3