Pinal County Air Quality August 30, 2007 PM 10 Exceptional Event

August 30, 2007 Strong winds associated with monsoon activity that developed over eastern portions of the county and moved westward on August 30th. Max winds reached 48 mph which caused two PCAQCD monitors to exceed the 24-hr PM 10 NAAQS. Site24-hr PM 10 Conc. (ug/m 3 ) Combs Maricopa 158.5

4 p.m. local time Cells developed to the east of the county during the evening of 8/30/07 which provided the wind that caused the elevated PM 10 in Pinal County

5 p.m. local time Cells developed to the east of the county during the evening of 8/30/07 which provided the wind that caused the elevated PM 10 in Pinal County

6 p.m. local time Cells developed to the east of the county during the evening of 8/30/07 which provided the wind that caused the elevated PM 10 in Pinal County

7 p.m. local time Cells developed to the east of the county during the evening of 8/30/07 which provided the wind that caused the elevated PM 10 in Pinal County

8/30/07 “But for” Test Had it not been “but for” the high winds between 7-9 p.m. associated with the cell development in the county that caused Combs to have a 1-hr PM 10 concentration of 3,641 ug/m 3, Combs would have NOT exceeded the PM hr NAAQS. –If the 3,641 ug/m 3 was replaced with the average of the other 23 hours then the 24-hr PM 10 concentration would be 123 ug/m 3 –Maricopa – 134 ug/m 3

Additional 8/30/07 “But for” Test Combs had the following 24-hr PM 10 concentrations before/after the 8/30/07 event –8/29/07 – ug/m 3 –8/31/07 – 65.0 ug/m 3 Maricopa – 8/29/07 – 97.7 ug/m 3 – 8/31/07 – 46.1 ug/m 3