Pinal County Air Quality June 6, 2007 PM 10 Exceptional Event

June 6, 2007 Strong winds associated with a front helped transport dust from areas outside of the county. Max winds reached 28 mph which caused four PCAQCD monitors to exceed the 24-hr PM 10 NAAQS. Site24-hr PM 10 Conc. (ug/m 3 ) PCH Combs Stanfield Maricopa * June 6, 2007 also flagged by ADEQ as an exceptional event.

Pinal County Started an AQI forecasting program around June 1, Typically, the “Today” AQI is a carry forward forecast from the previous day since the PM 10 TEOM data isn’t provided throughout the day. The AQI forecasting effort is rather new and we err on the conservatively high side of the forecast, therefore the 6/5/07 PM 10 exceedance didn’t verify. However The 6/6/07 AQI forecast did verify. The daily AQI forecast is on the web at

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6/6/07 “But for” Test PCH had the following 24-hr PM 10 concentrations before/after the 6/6/07 event –6/5/07 – ug/m 3 –6/7/07 – 98.7 ug/m 3 Combs –6/5/07 – ug/m 3 –6/7/07 – ug/m 3 Stanfield –6/5/07 – ug/m 3 –6/7/07 – ug/m 3 Maricopa –6/5/07 – ug/m 3 –6/7/07 – ug/m 3 NOTE: The winds may have not been As strong as other previously noted Exceedance days. However the seasonal PM 10 “background” at this time of year is significantly higher and therefore Doesn’t take much wind to exceed the PM 10 NAAQS. As a Result had it not been (i.e. “but for”) for this atypical* frontal passage (i.e. exceptional) these monitors would NOT have exceeded the PM 10 NAAQS. *Source: Only frontal passage for June No frontal Passages for June 2006 as a comparison.