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PUBLIC NOTICE | Exceptional Events in the Maricopa County (Greater Phoenix) O3 Nonattainment Area

ADEQ is soliciting comments on its second addendum to a previously submitted demonstration for an event that caused elevated concentrations of Ozone (O3) in the Maricopa County (Greater Phoenix) O3 Nonattainment area on June 20, 2015. ADEQ has decided to flag exceedance concentrations based on these analyses.


In 2005, Congress identified a need to account for events that result in exceedances of the National Ambient Air Quality Standards (NAAQS) that are exceptional in nature (e.g., not expected to reoccur or caused by acts of nature beyond man-made controls.) In response, EPA promulgated the Exceptional Events Rule (EER) to address exceptional events in 40 CFR Parts 50 and 51 on March 22, 2007 (72 FR 13560). 

On Nov. 20, 2015, EPA released guidance on the preparation of exceptional events demonstrations for wildfire events that may influence ozone concentrations to State, tribal and local air agencies for review. The EER allows for states and tribes to “flag” air quality monitoring data as an exceptional event. If flagged, these data can be excluded from consideration in air quality planning if EPA concurs with the demonstration submitted by the flagging agency documenting that all procedural and technical requirements have been met.

Review Document

Original Published Public Notice | View>
Second Addendum to Exceptional Event Documentation | View>
First Addendum to Exceptional Event Documentation | View>
Original Exceptional Event Documentation of Ozone (O3) Exceedances on June 20, 2015 | View >

Documents can also be reviewed in person at ADEQ’s Record Center | Learn More > 

Public Comment Period

Dates: March 25, 2019 – April 23, 2019

Comments can be submitted as follows: 
EmailSend Email >
Mail (Must be postmarked or received by April 23, 2019) :
      Air Assessment Section
      1110 W. Washington Street, 3415-A
      Phoenix, AZ 85007