1. Pinal County Air Quality July 23, 2007 PM 10 Exceptional Event

2. July 23, 2007 Strong winds associated with a monsoon cell which developed close to the Combs monitor. Max winds reached 24 mph which caused one PCAQCD monitor to exceed the 24-hr PM 10 NAAQS. Site24-hr PM 10 Conc. (ug/m 3 ) Combs 160.9

5. 9 p.m. 7/22/07 to 8 p.m. 7/23/07 local time Location of Combs monitor

6. and strong cell

7. Location of Combs monitor and strong cell

8. Location of Combs monitor and strong cell

9. Location of Combs monitor and strong cell

10. Location of Combs monitor and strong cell

11. Location of Combs monitor and strong cell

12. Location of Combs monitor and strong cell

13. Location of Combs monitor

17. 7/23/07 “But for” Test Had it not been “but for” the high winds between 5-6 p.m. associated with the cell development near Combs which caused it to have a 1-hr PM 10 concentration of 2,158 ug/m 3, Combs would have NOT exceeded the PM 10 24-hr NAAQS. –If the 2,158 ug/m 3 was replaced with the average of the other 23 hours then the 24-hr PM 10 concentration would be 70 ug/m 3

18. Additional 7/23/07 “But for” Test Combs had the following 24-hr PM 10 concentrations before/after the 7/23/07 event –7/22/07 – 23.2 ug/m 3 –7/24/07 – 49.3 ug/m 3