Exceptional Events

 Exceptional Event Information

Ambient air quality can be affected by many circumstances. Depending on the parameter measured at a site, the values can be affected by sources (mobile and stationary), activities (human and natural), and weather, occurring either nearby or some distance from that particular location. Many activities can be controlled, altered, or regulated in some manner in order to improve air quality. Other activities affecting air quality are outside the scope of regulation.

A mechanism is set up through EPA for reviewing the data affected by either uncontrollable or non-preventable activities. Data which are in exceedance of a National Ambient Air Quality Standard (NAAQS) are analyzed to determine if they are affected by events which meet this "exceptional event" criteria. If Pinal County Air Quality determines that data may have been affected by an "exceptional event", the data and circumstances are investigated. The county may then flag the data in the Air Quality System (AQS) as being affected by an "exceptional event". The information is submitted to EPA annually for concurrence. If EPA does concur with the county's determination, the data flag is then finalized. The documentation is made available for review to the public throughout the year within the Exceptional Event's page. Comments are accepted during the Public Comment period (30 days) that will be posted within the Public Notice page of the Exceptional Events.

An "exceptional event" is defined by EPA as an event that:

1. Affects air quality
2. Is not reasonably controllable or preventable
3. Is an event caused by human activity that is unlikely to recur at a particular location or a  natural event; and
4. Is determined by EPA through the process established in the regulations, 40 CFR Part 50.14.

Some examples of natural events causing an exceptional event include:

1. High winds
2. Volcanic eruptions
3. Certain fires
4. Seismic activity

Some examples of exceptional events caused by human activity include:

1. Prescribed fires
2. Fireworks
3. Clean up after a major natural disaster

If you have any questions, please e-mail scott.dibiase@pinalcountyaz.gov or call (520) 866-6929.


 Past Years Exceptional Events

2013 Exceptional Events
{Pending EPA Approval}
2012 Exceptional Events
{Pending EPA Approval}
2011 Exceptional Events
{Pending EPA Approval}
2010 Exceptional Events
{Pending EPA Approval}
2009 Exceptional Events
{Pending EPA Approval}
2008 Exceptional Events
{Pending EPA Approval}
2007 Exceptional Events
{Pending EPA Approval}

 Summary Information [Draft Subject to Change]

 Additional Information

To view or download a copy of EPA's Exceptional Event ruling, click here.

 Exceptional Events 2014

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1/24/14Use SHIFT+ENTER to open the menu (new window).
Stanfield200.2 ug/m3PM10Backdoor Cold Front (Max. wind speed 36 mph)